Noctilucent Clouds, Polar Mesospheric Summer Echoes, and Dusty Plasmas

1. Noctilucent Clouds, Polar Mesospheric Summer Echoes, and Dusty Plasmas R. B. Sheldon (1), H. D. Voss (2), P. A. Webb (3), W. D. Pesnell (3),R. A. Goldberg (3), J. Gumbel (4), M. P. Assis (2) 1) NSSTC, 2) Taylor University 3) NASA/GSFC, 4) Stockholm University November 3, 2006

2. NLC gallery Noctilucent clouds �night-shining� are seen at high latitudes after sunset, near or slightly after summer solstice. This photographs are taken in Norway, Finland, and Germany, though they have been observed at Salt Lake City (41 deg N).Noctilucent clouds �night-shining� are seen at high latitudes after sunset, near or slightly after summer solstice. This photographs are taken in Norway, Finland, and Germany, though they have been observed at Salt Lake City (41 deg N).

3. NLC viewing geometry The viewing geometry of these clouds is right after sunset on clear nights, when the very high clouds (80km or 50 miles up) are still sunlit. They cannot be seen in the daytime.The viewing geometry of these clouds is right after sunset on clear nights, when the very high clouds (80km or 50 miles up) are still sunlit. They cannot be seen in the daytime.

4. This picture from the International Space Station, shows that from space we can see noctilucent clouds even in the daytime.This picture from the International Space Station, shows that from space we can see noctilucent clouds even in the daytime.

5. The righthand plot is a plot of the temperature from ground to 500 km. The bottom 300 km are enlarged in the lefthand plot. The coldest spot in the atmosphere is the mesopause at 80 km, and this is the altitude for NLC and PMSE. The upper left plot shows the observational bias, with days around summer solstice on the x-axis, and geographic latitude on the y-axis. The black band is the pole.The righthand plot is a plot of the temperature from ground to 500 km. The bottom 300 km are enlarged in the lefthand plot. The coldest spot in the atmosphere is the mesopause at 80 km, and this is the altitude for NLC and PMSE. The upper left plot shows the observational bias, with days around summer solstice on the x-axis, and geographic latitude on the y-axis. The black band is the pole.

6. Radar, Lidar observations This is what radar and lidar measure. Right-hand plot shows a lidar return from a noctilucent cloud layer. Left-hand side shows a radar return from a PMSE. They are different days, or else you would see that the PMSE is above the NLC.This is what radar and lidar measure. Right-hand plot shows a lidar return from a noctilucent cloud layer. Left-hand side shows a radar return from a PMSE. They are different days, or else you would see that the PMSE is above the NLC.

7. Observations & Open Questions NLC are >20nm ice grains forming at the mesopause ~140K. Reported since 1885. Peak occurrence after summer solstices. Explained by mesosphere weather PMSE first observed in 1979 at Poker Flat, are related to <10nm charged ice grains usually in a layer 2 km above NLC, that reflect radar (50MHz-2GHz or 2'-100' wavelengths). Strongest at midnight, weakest at dusk. PMSE: How do they reflect? Why do they form? What relation to NLC? The cause and origin of NLC is pretty well known, but PMSE are not understood nearly as well. Open questions are how does a fine ice-crystal cloud reflect radar, when radar goes right through clouds and snow? How do PMSE form? How are they related to NLC?The cause and origin of NLC is pretty well known, but PMSE are not understood nearly as well. Open questions are how does a fine ice-crystal cloud reflect radar, when radar goes right through clouds and snow? How do PMSE form? How are they related to NLC?

8. How can aerosols reflect radar? Charged aerosols? large plasma density? If they are positive, then electron density rises Draine & Sutin 87 argued for nm dust to become positive (because of large E-fields) Havnes flies retarding grids, Gumbel flies alternating plates, Rapp, Horanyi, et al fly magnets to exclude electrons and trap positive ions/aerosols PMSE�s have negative dust, NLC�s maybe positive? Charged aerosols? large plasma gradients? Langmuir probes see �bite-outs� Havnes argues for dust vortices to make �holes� Multiple Langmuir probes never agree on �bite-outs� Reflections are coherent �Bragg�, not incoherent turbulence The most immediate question is how can ice clouds reflect radar. Two solutions have been proposed: a) PMSE are positively charged dust which increases the electron density b) PMSE cause dust turbulence that leads to plasma turbulence that causes scatter Both solutions raise more questions than they solve. This has been the reason for several rocket campaigns. The most immediate question is how can ice clouds reflect radar. Two solutions have been proposed: a) PMSE are positively charged dust which increases the electron density b) PMSE cause dust turbulence that leads to plasma turbulence that causes scatter Both solutions raise more questions than they solve. This has been the reason for several rocket campaigns.

9. The DROPPS rocket campaign consisted of 2 rockets with ground support (radars mostly) launched out of Andoya in 1999. This graphic shows the DROPPS rocket with the instrumentation labelled. Around the rocket are the large and small dust grains. On the left and right sides are the signals observed by the Particle Impact Detector (PID) as a function of altitude. The inset shows the location of the PID detector at the nose of the rocket. The rocket shock is a significant effect on the data, and is shown schematically in gray.The DROPPS rocket campaign consisted of 2 rockets with ground support (radars mostly) launched out of Andoya in 1999. This graphic shows the DROPPS rocket with the instrumentation labelled. Around the rocket are the large and small dust grains. On the left and right sides are the signals observed by the Particle Impact Detector (PID) as a function of altitude. The inset shows the location of the PID detector at the nose of the rocket. The rocket shock is a significant effect on the data, and is shown schematically in gray.

10. The Elevation and Attitude of the DROPPS1 rocket is shown in these slides. Even thought the rocket was launched due North from Andoya at Midnight, it was headed straight for the Sun, which was 51 degrees lower in elevation but identical in azimuth.The Elevation and Attitude of the DROPPS1 rocket is shown in these slides. Even thought the rocket was launched due North from Andoya at Midnight, it was headed straight for the Sun, which was 51 degrees lower in elevation but identical in azimuth.

11. PID Charge/Mass Telescopes and PAT These are schematics of the PID and PAT instruments. PID was the Taylor university �particle impact telescope� which had two, nearly identical telescopes consisting of 3 grids. The main difference was the larger volume in the CHARGE PID, due to the Gaussian cylinder detectors, which caused the CHARGE telescope to outgas for a longer time than the MASS telescope. The other main difference were the type of detector in the bottom of each, with CHARGE having a polyvinylidene impact detector (sensitive to ice crystals r>100nm), and MASS having a cooled solid state �x-ray� detector with a window that admitted x-rays and E>40keV electrons. The PAT sensor consisted of 10 plates of alternating voltage that did not contact the rocket sheath (since the plates are 0.5 cm apart, and the rocket sheath > 1cm away), so they didn't act as Langmuir probes, but they were sensitive to charged aerosols (and maybe heavy ions) that could penetrate the rocket sheath. Both PID and PAT were exposed to solar UV.These are schematics of the PID and PAT instruments. PID was the Taylor university �particle impact telescope� which had two, nearly identical telescopes consisting of 3 grids. The main difference was the larger volume in the CHARGE PID, due to the Gaussian cylinder detectors, which caused the CHARGE telescope to outgas for a longer time than the MASS telescope. The other main difference were the type of detector in the bottom of each, with CHARGE having a polyvinylidene impact detector (sensitive to ice crystals r>100nm), and MASS having a cooled solid state �x-ray� detector with a window that admitted x-rays and E>40keV electrons. The PAT sensor consisted of 10 plates of alternating voltage that did not contact the rocket sheath (since the plates are 0.5 cm apart, and the rocket sheath > 1cm away), so they didn't act as Langmuir probes, but they were sensitive to charged aerosols (and maybe heavy ions) that could penetrate the rocket sheath. Both PID and PAT were exposed to solar UV.

12. Particle Trap (PAT) instrument This is the output from PAT sensor in the altitude range between 80 and 90 kilomters that covered the NLC and the PMSE as marked in the slide. The oscillations are due to the rocket spin, and show that the UV was important in the signal. Two PAT sensors were flown, one coated with graphite, one with gold, this is the graphite-coated sensor. The plates were alternately positive 3.9 Volts (red) or negative 3.9 V (blue). Presumeably, blue plates would emit photoelectrons, and red plates would absorb them. Negative aerosols would preferentially show up on red plates, positive on blue. The NLC shows an excess in the blue plates, whereas the PMSE shows an excess in the red. We'll address these excessses after we address the spin modulation.This is the output from PAT sensor in the altitude range between 80 and 90 kilomters that covered the NLC and the PMSE as marked in the slide. The oscillations are due to the rocket spin, and show that the UV was important in the signal. Two PAT sensors were flown, one coated with graphite, one with gold, this is the graphite-coated sensor. The plates were alternately positive 3.9 Volts (red) or negative 3.9 V (blue). Presumeably, blue plates would emit photoelectrons, and red plates would absorb them. Negative aerosols would preferentially show up on red plates, positive on blue. The NLC shows an excess in the blue plates, whereas the PMSE shows an excess in the red. We'll address these excessses after we address the spin modulation.

13. We constructed a 3-D model of the PAT sensor, and defined the rocket spin angle, sun angle and illumination of the sensor. The key thing to note is that as the son sweeps across the horizontal plates (the picture on the cover of GRL was wrong), it goes from illuminating the top of the plates to the bottom of the plates and back to the top. After a great deal of vector math described on the next page ...We constructed a 3-D model of the PAT sensor, and defined the rocket spin angle, sun angle and illumination of the sensor. The key thing to note is that as the son sweeps across the horizontal plates (the picture on the cover of GRL was wrong), it goes from illuminating the top of the plates to the bottom of the plates and back to the top. After a great deal of vector math described on the next page ...

14. Sun-illumination Model The location of the PAT sensor is identified in inertial coordinates with the Euler matrix listed (a rotation around z-axis by (wt) followed by a rotation about y-axis by theta.) Then the plates in the PAT sensor have normal vectors (o,m,n). whose location can be specified in inertial space (defined by rocket pointing along z) . The nutation of the rocket has not been taken into account in this model. The angles between the plates and the sun sensor can be calculated, and the shadowing estimated, giving an illumination model... The location of the PAT sensor is identified in inertial coordinates with the Euler matrix listed (a rotation around z-axis by (wt) followed by a rotation about y-axis by theta.) Then the plates in the PAT sensor have normal vectors (o,m,n). whose location can be specified in inertial space (defined by rocket pointing along z) . The nutation of the rocket has not been taken into account in this model. The angles between the plates and the sun sensor can be calculated, and the shadowing estimated, giving an illumination model...

15. That produced these curves. Note the nice reproduction of the triple peaks, due to the path that the sun makes over the plates. Because of limited digitization accuracy, the PAT sensor has to be heavily smoothed to generate decent curves, and we have used a 19point boxcar filter in this plot that has perhaps rounded out the peaks a little too much. Note how symmetric the negative plate is above the PMSE, and remains nearly symmetric in the PMSE, but shows a marked asymmetry in the NLC. The positive plate shows a constant asymmetry preferring dawn, which is weakest during the PMSE. We take these asymmetries to be \ a) the sun model is illuminating both plates symmetrically b) the positive plate asymmetry is due to dawn-dusk asymmetry in collection efficiency which we attribute to photo-enhanced ion density reducing the mobility of the negative carriers. The remaining asymmetries (in the NLC on the negative plates) or the symmetry of the positive plates in the PMSE (which must be due to an asymmetric collection that neutralized the normal asymmetry), we take to be a consequence of aerosol impact preferentially on the dusk side of the rotation phase angle. That produced these curves. Note the nice reproduction of the triple peaks, due to the path that the sun makes over the plates. Because of limited digitization accuracy, the PAT sensor has to be heavily smoothed to generate decent curves, and we have used a 19point boxcar filter in this plot that has perhaps rounded out the peaks a little too much. Note how symmetric the negative plate is above the PMSE, and remains nearly symmetric in the PMSE, but shows a marked asymmetry in the NLC. The positive plate shows a constant asymmetry preferring dawn, which is weakest during the PMSE. We take these asymmetries to be \ a) the sun model is illuminating both plates symmetrically b) the positive plate asymmetry is due to dawn-dusk asymmetry in collection efficiency which we attribute to photo-enhanced ion density reducing the mobility of the negative carriers. The remaining asymmetries (in the NLC on the negative plates) or the symmetry of the positive plates in the PMSE (which must be due to an asymmetric collection that neutralized the normal asymmetry), we take to be a consequence of aerosol impact preferentially on the dusk side of the rotation phase angle.

16. Spin averaged PAT upleg profiles By summing over the spin frequency, we produce these spin-averaged currents on the two PAT detectors (gold and graphite) and the two different biased plates. Now we can see clearly that gold and graphite have slightly different currents, and that the currents grow larger (in both directions) with increasing altitude. The smooth curves can be fit rather well with a simple exponential, which confirms our conclusion from the spin-modulation that these are UV currents, since the UV penetration is exponential at this altitude. Once we explain the exponential fits, we can return to the two anomalies, the increased positive current (on all plates) seen in the NLC, and the increased negative current (seen on all plates) in the PMSE. Note, however, that the PMSE is a constant additive current to the four plates, whereas the NLC brings both gold and graphite plates up to the same current, it adds more to the gold than it adds to the graphite plates.By summing over the spin frequency, we produce these spin-averaged currents on the two PAT detectors (gold and graphite) and the two different biased plates. Now we can see clearly that gold and graphite have slightly different currents, and that the currents grow larger (in both directions) with increasing altitude. The smooth curves can be fit rather well with a simple exponential, which confirms our conclusion from the spin-modulation that these are UV currents, since the UV penetration is exponential at this altitude. Once we explain the exponential fits, we can return to the two anomalies, the increased positive current (on all plates) seen in the NLC, and the increased negative current (seen on all plates) in the PMSE. Note, however, that the PMSE is a constant additive current to the four plates, whereas the NLC brings both gold and graphite plates up to the same current, it adds more to the gold than it adds to the graphite plates.

17. Positively Charged Aerosols?? Since earlier versions of PAT and PID on earlier rocket flights had tentatively associated positive currents with positive aerosols, we address this possibity in our data. The only place that might have seen positive aerosols is in the NLC, which we had colored blue in the previous plot.Since earlier versions of PAT and PID on earlier rocket flights had tentatively associated positive currents with positive aerosols, we address this possibity in our data. The only place that might have seen positive aerosols is in the NLC, which we had colored blue in the previous plot.

18. Dusty Plasma Lab, Abbas et. al. 2006 The support for positively biassed aerosols is somewhat spotty. Rapp (1999) and others had argued that the workfunctions of aerosols in the presence of an electron-dominated plasma led to more attachment by electrons than photoemission by UV. Thus aerosols would charge negative, unless they had ridiculously low work functions for photoemission, similar to Na or K. Then the aerosol community came across the astrophysics work of Draine and Sutin 87, which is a typical astrophysics semi-empirical model for charging of dust grains. Their model extrapolated from 1 micron down to nm sizes, and suggested that small grains could charge positive because of the larger electric field. This result is seemingly at odds with the atomic & molecular physics of bulk materials and atom clusters, yet gained a lot of adherents in the astrophysics community, who used it to explain high solar winds of O type stars. In 2004, the lab here at NSSTC investigated the charge of sub-micron dust grains and found that the linear relation used by Draine and Sutin does not hold for small grains, but photoemission drops off rapidly as the grain gets small.. This brings the experiment in agreement with theory from both AMO and bulk studies, Abbas et al, Ap J 2006. (Note, they did not investigate ice grains because funding for a cyrogenic facility has been curtailed, so they worked with SiO2 and C. But since the workfunction of ice is supposedly higher than these two, one would expect ice to be even less likely to charge positive.) Therefore there is no laboratory nor theoretical support for positively charged aerosols. The support for positively biassed aerosols is somewhat spotty. Rapp (1999) and others had argued that the workfunctions of aerosols in the presence of an electron-dominated plasma led to more attachment by electrons than photoemission by UV. Thus aerosols would charge negative, unless they had ridiculously low work functions for photoemission, similar to Na or K. Then the aerosol community came across the astrophysics work of Draine and Sutin 87, which is a typical astrophysics semi-empirical model for charging of dust grains. Their model extrapolated from 1 micron down to nm sizes, and suggested that small grains could charge positive because of the larger electric field. This result is seemingly at odds with the atomic & molecular physics of bulk materials and atom clusters, yet gained a lot of adherents in the astrophysics community, who used it to explain high solar winds of O type stars. In 2004, the lab here at NSSTC investigated the charge of sub-micron dust grains and found that the linear relation used by Draine and Sutin does not hold for small grains, but photoemission drops off rapidly as the grain gets small.. This brings the experiment in agreement with theory from both AMO and bulk studies, Abbas et al, Ap J 2006. (Note, they did not investigate ice grains because funding for a cyrogenic facility has been curtailed, so they worked with SiO2 and C. But since the workfunction of ice is supposedly higher than these two, one would expect ice to be even less likely to charge positive.) Therefore there is no laboratory nor theoretical support for positively charged aerosols.

19. PhotoCurrents to Rocket Sheath Then if this is not an effect of charged aerosols, it must be positive current generated on the surface. This means we must model the photoemission currents of the system. We start with the spin-averaged, dry, photocurrents. Our model is that the net photo current, when both the negative and positive plates are summed together, is a function of the potential difference between the illuminated PAT surface and the rocket photosheath. It also depends on the area and the intensity of sunlight and some efficiency factors. That is formula (1). We know the work function for gold and graphite aquadag, so if we form the ratio of the two PAT sensors, the area and sunlight intensity cancel out, and we are left with just the rocket sheath potential. Solving for the rocket sheath potential, we have equation 3. However, we know the rocket voltage from the electric field experiment of Holzworth. A plot of the rocket bias is given in the bottom of this slide. Taking several readings from this (very small) graph, we can add (or actually, subtract) the rocket bias from the rocket sheath potential, which should give us the work function for the aluminum skin of the rocket. which should be a constant . Then if this is not an effect of charged aerosols, it must be positive current generated on the surface. This means we must model the photoemission currents of the system. We start with the spin-averaged, dry, photocurrents. Our model is that the net photo current, when both the negative and positive plates are summed together, is a function of the potential difference between the illuminated PAT surface and the rocket photosheath. It also depends on the area and the intensity of sunlight and some efficiency factors. That is formula (1). We know the work function for gold and graphite aquadag, so if we form the ratio of the two PAT sensors, the area and sunlight intensity cancel out, and we are left with just the rocket sheath potential. Solving for the rocket sheath potential, we have equation 3. However, we know the rocket voltage from the electric field experiment of Holzworth. A plot of the rocket bias is given in the bottom of this slide. Taking several readings from this (very small) graph, we can add (or actually, subtract) the rocket bias from the rocket sheath potential, which should give us the work function for the aluminum skin of the rocket. which should be a constant .

20. Calculated Work Functions This table shows that the sum of the rocket bias and rocket sheath potential does indeed come to a constant, close to 5.04 Volts. Because there are no adjustable parameters in this model (check it out!) this is a confirmation that the spin-averaged currents are indeed photocurrents to the rocket sheath, and that the model we have developed is indeed accurate to ~1%. Truly remarkable. However, in the NLC and the PMSE, we used interpolated values for the current, as if the disturbances were not there. That is, we fit an exponential with height to the photocurrents outside the NLC/PMSE, and used this fit to interpolate the undisturbed currents in the NLC/PMSE. These have been marked with an asterisk. This table shows that the sum of the rocket bias and rocket sheath potential does indeed come to a constant, close to 5.04 Volts. Because there are no adjustable parameters in this model (check it out!) this is a confirmation that the spin-averaged currents are indeed photocurrents to the rocket sheath, and that the model we have developed is indeed accurate to ~1%. Truly remarkable. However, in the NLC and the PMSE, we used interpolated values for the current, as if the disturbances were not there. That is, we fit an exponential with height to the photocurrents outside the NLC/PMSE, and used this fit to interpolate the undisturbed currents in the NLC/PMSE. These have been marked with an asterisk.

21. Particle Trap (PAT) instrument So re refresh your memory with this plot of spin-modulated and spin-averaged PAT currents. Note the positive excess in the NLC is on both plates, but more on the negative plates, and more on the gold, whereas the negative excess in the PMSE is on both plates, more on the negative plates, but equally on both gold and graphite. We interpret this as real negative dust collected in the PMSE on both sets of plates, but more obvious on the positive plates because of their attraction of the dust. Whereas no real positive dust occurs in the NLC, but enhanced photocurrents that changed the workfunction of the gold and graphite to be the same. Alternatively, the impact of the NCL ice grains could be transferring postive charge to the PAT sensor, what we refer to as impact ionization or triboelectric effect.. In order to evaluate these various charging mechanisms, we turn to the literature So re refresh your memory with this plot of spin-modulated and spin-averaged PAT currents. Note the positive excess in the NLC is on both plates, but more on the negative plates, and more on the gold, whereas the negative excess in the PMSE is on both plates, more on the negative plates, but equally on both gold and graphite. We interpret this as real negative dust collected in the PMSE on both sets of plates, but more obvious on the positive plates because of their attraction of the dust. Whereas no real positive dust occurs in the NLC, but enhanced photocurrents that changed the workfunction of the gold and graphite to be the same. Alternatively, the impact of the NCL ice grains could be transferring postive charge to the PAT sensor, what we refer to as impact ionization or triboelectric effect.. In order to evaluate these various charging mechanisms, we turn to the literature

22. Water Cluster Ion Charging Vostrikov 87 developed an apparatus where water is evaporated, ionized and expanded through three nozzles followed by skimmers, such that charged water molecular ions were introduced into a vacuum system at high velocity. These molecular cluster ions were impacted onto various metal surfaces, and the resulting ions collected and analyzed as a function of voltage. The current produced as a function of voltage generates these langmuir probe-like profiles, from which the charge and mass of the fragments can be analyzed. Vostrikov found positive ions to be preferentially generated on gold surfaces, with a peak near 70 degrees from normal. This work was relevant to the rocket data, and so Andersson 97 extended the work to graphite surfaces. Once again it was primarily positive ions generated, until Andersson heated the graphite surface to 1320K, when the production of negative ions overtook the positive ions. Our heuristic analysis is that the impacting water cluster ions produce hot electrons that preferentially condense on the cold surface, leaving behind positive ions. However when the surface is hot enough that the opposite process occurs, then the electrons preferentially condense on the water, generating negative ions. Andersson model this with a photoemission effect with a hot, Boltzmann distribution (see equation 1 & 2) Now in the NLC, we record positive current, which is equivalent to negative ions leaving the surface. Yet the PAT surfaces were closer to ambient temperature of 200K, where positive ions (negative current) should have been produced. We argue that the presence of UV light effectively provides the hot electrons needed to tunnel from the surface to the escaping water ions. Vostrikov 87 developed an apparatus where water is evaporated, ionized and expanded through three nozzles followed by skimmers, such that charged water molecular ions were introduced into a vacuum system at high velocity. These molecular cluster ions were impacted onto various metal surfaces, and the resulting ions collected and analyzed as a function of voltage. The current produced as a function of voltage generates these langmuir probe-like profiles, from which the charge and mass of the fragments can be analyzed. Vostrikov found positive ions to be preferentially generated on gold surfaces, with a peak near 70 degrees from normal. This work was relevant to the rocket data, and so Andersson 97 extended the work to graphite surfaces. Once again it was primarily positive ions generated, until Andersson heated the graphite surface to 1320K, when the production of negative ions overtook the positive ions. Our heuristic analysis is that the impacting water cluster ions produce hot electrons that preferentially condense on the cold surface, leaving behind positive ions. However when the surface is hot enough that the opposite process occurs, then the electrons preferentially condense on the water, generating negative ions. Andersson model this with a photoemission effect with a hot, Boltzmann distribution (see equation 1 & 2) Now in the NLC, we record positive current, which is equivalent to negative ions leaving the surface. Yet the PAT surfaces were closer to ambient temperature of 200K, where positive ions (negative current) should have been produced. We argue that the presence of UV light effectively provides the hot electrons needed to tunnel from the surface to the escaping water ions.

23. Water Work Function Assuming the rocket work function = 5.04V Gold 5.3 ?wet 4.92 eV Carbon 4.9?wet 4.87 eV This schematic shows a model of the process. The UV light heats the electrons in the metal (Au in our diagram) which then tunnel onto the water molecule near the surface. The subsequent evaporation of the water molecule generates a negative water ion that is then attracted to the positive plate above. Both UV and water ions must be present for this enhanced photoemission to occur. We test this NLC hypothesis by fitting a spin-averaged light intensity curve to the gold and graphite plates. We then use the 5.04 V work function for the Al rocket skin (arguing that most of the rocket stays dry even in the NLC), then we go back to equation 1 on the slide 3 previous, where we plug in the observed current and solve for the work function of the modified surface. Gold goes from 5.3eV to 4.92 eV, whereas graphite decreases from 4.9 to 4.87. Both workfunctions come very close to each other, demonstrating that the effect does act the way we inferred. Once again note that there are no adjustable parameters in this model. This schematic shows a model of the process. The UV light heats the electrons in the metal (Au in our diagram) which then tunnel onto the water molecule near the surface. The subsequent evaporation of the water molecule generates a negative water ion that is then attracted to the positive plate above. Both UV and water ions must be present for this enhanced photoemission to occur. We test this NLC hypothesis by fitting a spin-averaged light intensity curve to the gold and graphite plates. We then use the 5.04 V work function for the Al rocket skin (arguing that most of the rocket stays dry even in the NLC), then we go back to equation 1 on the slide 3 previous, where we plug in the observed current and solve for the work function of the modified surface. Gold goes from 5.3eV to 4.92 eV, whereas graphite decreases from 4.9 to 4.87. Both workfunctions come very close to each other, demonstrating that the effect does act the way we inferred. Once again note that there are no adjustable parameters in this model.

24. Electron Density Bite-outs?? Having dispensed with the positive aerosol argument for PMSE generation, the next question is the relation of electron density, Ne, �bite-outs� in the data. Are they generating such large gradients that radar is reflected?Having dispensed with the positive aerosol argument for PMSE generation, the next question is the relation of electron density, Ne, �bite-outs� in the data. Are they generating such large gradients that radar is reflected?

25. DEMETERLangmuir Probes In order to understand the biteouts, we have to understand the instruments that take these measurements. They are simple metal probes whose I-V profiles are used to infer the plasma density. Pictures of similar (not DROPPS) probes were taken from another instrument, the DEMETER satellite. Langmuir probes come in two flavors: spheres and cylinders, because the geometry affects the current collection, and other geometries are too complicated to model. In addition, the surface of the probes must be clean, having a constant and understandable work function, and not generate much photoemission so as to not contaminate the current collection of electrons.In order to understand the biteouts, we have to understand the instruments that take these measurements. They are simple metal probes whose I-V profiles are used to infer the plasma density. Pictures of similar (not DROPPS) probes were taken from another instrument, the DEMETER satellite. Langmuir probes come in two flavors: spheres and cylinders, because the geometry affects the current collection, and other geometries are too complicated to model. In addition, the surface of the probes must be clean, having a constant and understandable work function, and not generate much photoemission so as to not contaminate the current collection of electrons.

26. DROPPSLangmuir Probes These are the upleg and downleg profiles from Croskey's 2001 GRL paper, showing the biteouts on the upleg and downleg. The lower right panel is an enlarged region of the biteouts, with the range of the PMSE and NLC listed to the left. Note the factor 20 change in electron density over a few tens of meters. The electrons being highly mobile, can't stand this gradient, so there must be something else not observed that is responsible for this effect. These are the upleg and downleg profiles from Croskey's 2001 GRL paper, showing the biteouts on the upleg and downleg. The lower right panel is an enlarged region of the biteouts, with the range of the PMSE and NLC listed to the left. Note the factor 20 change in electron density over a few tens of meters. The electrons being highly mobile, can't stand this gradient, so there must be something else not observed that is responsible for this effect.

27. Upleg and Downleg for Charge Telescope grids 1, 2 & 3 This is the profiles from the CGRID instrument on DROPPS, and the very first panel, CGRID1 is a +6V biased grid that acts as an unconventional Langmuir probe (since it isn't round or cylindrical). It still responds to Ne and indeed shows two biteouts. The upleg is depressed from 65-86 km, which we attribute to outgassing from the rather large enclosed volume in the Charge telescope. So it just catches the tail end of a biteout at 86km. The downleg is clearer, with a distinct biteout at 85km, though not as deep as a factor 20 seen in Croskey. One problem: they don't occur at the same places. Now one can argue that unconventional Langmuir probes have non-linear effects in their I-V curves, but here we are talking about a factor 20 change in density, which should occur in the very same place on both instruments. What gives?This is the profiles from the CGRID instrument on DROPPS, and the very first panel, CGRID1 is a +6V biased grid that acts as an unconventional Langmuir probe (since it isn't round or cylindrical). It still responds to Ne and indeed shows two biteouts. The upleg is depressed from 65-86 km, which we attribute to outgassing from the rather large enclosed volume in the Charge telescope. So it just catches the tail end of a biteout at 86km. The downleg is clearer, with a distinct biteout at 85km, though not as deep as a factor 20 seen in Croskey. One problem: they don't occur at the same places. Now one can argue that unconventional Langmuir probes have non-linear effects in their I-V curves, but here we are talking about a factor 20 change in density, which should occur in the very same place on both instruments. What gives?

28. Big Bite-out, where's the PMSE? The second rocket flight was no better. Once again biteouts don't agree between the two instruments. But Croskey sees even larger biteouts, yet NO PMSE WAS OBSERVED in the radar. If these gradients are reflecting radar, why is DROPPS 2 seeing gradients and radar isn't?? And if these gradients aren't reflecting radar, why not? Shouldn't radar see something? The second rocket flight was no better. Once again biteouts don't agree between the two instruments. But Croskey sees even larger biteouts, yet NO PMSE WAS OBSERVED in the radar. If these gradients are reflecting radar, why is DROPPS 2 seeing gradients and radar isn't?? And if these gradients aren't reflecting radar, why not? Shouldn't radar see something?

29. Langmuir Probe Theory Back to Langmuir probe theory. IN the left panel, the current collected by a probe is plotted as a function of voltage. Taking the absolute value of the current (reflecting about the yellow line) and then taking the logarithm, generates the right-hand plot, which enables us to talk about the region near zero voltage. Now probes can operate in a sweep mode, where they make these I-V curves and then analyze them, or they can operate in a fixed voltage mode. But in a fixed voltage mode, such as that used by Croskey 01 on DROPPS, one must have a good understanding of the I-V curve characteristics or else it is hard to determine Ne. Generally this is accomplished by running the voltage high enough that the probe is in the electron saturation region to the far right of the graph. The slope is minimal, and therefore slight changes to the rocket potential aren't going to change the current (and hence, the Ne calculation) by much more than 10%. However, if the probe is sitting in the steep slope region, then even the slightest change to rocket potential will generate huge errors in density estimation. Croskey 01, uses the E-field outer booms to adjust the Langmuir probe. But does he use the aft (contaminated) or the stern (uncontaminated) E-field (Holzworth 01)? He never says. Now, lets go back to the PAT analysis, and ask, what happens when the probe encounters water-enhanced photoemission? This means electrons are leaving the probe, making a positive current. But the probe is trying to collect negative current, so this effect moves the probe I-V curve to the left, right into the steep gradient region, and reduces the collected current. This is all completely consistent with the biteouts observed in the NLC. It has the right sign and the right magnitude.Back to Langmuir probe theory. IN the left panel, the current collected by a probe is plotted as a function of voltage. Taking the absolute value of the current (reflecting about the yellow line) and then taking the logarithm, generates the right-hand plot, which enables us to talk about the region near zero voltage. Now probes can operate in a sweep mode, where they make these I-V curves and then analyze them, or they can operate in a fixed voltage mode. But in a fixed voltage mode, such as that used by Croskey 01 on DROPPS, one must have a good understanding of the I-V curve characteristics or else it is hard to determine Ne. Generally this is accomplished by running the voltage high enough that the probe is in the electron saturation region to the far right of the graph. The slope is minimal, and therefore slight changes to the rocket potential aren't going to change the current (and hence, the Ne calculation) by much more than 10%. However, if the probe is sitting in the steep slope region, then even the slightest change to rocket potential will generate huge errors in density estimation. Croskey 01, uses the E-field outer booms to adjust the Langmuir probe. But does he use the aft (contaminated) or the stern (uncontaminated) E-field (Holzworth 01)? He never says. Now, lets go back to the PAT analysis, and ask, what happens when the probe encounters water-enhanced photoemission? This means electrons are leaving the probe, making a positive current. But the probe is trying to collect negative current, so this effect moves the probe I-V curve to the left, right into the steep gradient region, and reduces the collected current. This is all completely consistent with the biteouts observed in the NLC. It has the right sign and the right magnitude.

30. PID Upleg profile As confirmation of this NLC generated problem on the Langmuir probes, note where the biteouts are observed with respect to the NLC/PMSE ice grains. On the upleg, CGRID sees the biteout ABOVE the PMSE dust signature recorded on CGRID3. There are NO charged aerosols above the PMSE, so what is causing this �bite-out�?As confirmation of this NLC generated problem on the Langmuir probes, note where the biteouts are observed with respect to the NLC/PMSE ice grains. On the upleg, CGRID sees the biteout ABOVE the PMSE dust signature recorded on CGRID3. There are NO charged aerosols above the PMSE, so what is causing this �bite-out�?

31. PID Downleg profile On the downleg, CGRID sees the biteout BELOW the PMSE dust signature on CGRID3. This suggests that the PMSE occurrence is temporally and causally connected to the existence of biteouts. Likewise Mitchell et al 2001, shows that the aft Langmuir probe saw a biteout after the blunt probe indicated an increase in negative ion current, almost identically with CGRID data. This doesn't appear to be the enhanced photoemission that is causing the biteouts, since, we didn't see enhanced photoemission in the PAT sensor for the PMSE, only for the NLC. So what else could be causing this? Another possibility is not that the currents to the Langmuir probes have been changed, but the mobility of the electrons has suddenly changed. In other words, big heavy ions are keeping the electrons from moving to the probes. Mitchell 01, shows the positive ion-collecting Gerdiens are in-phase with the negative aerosol collecting blunt probes. Large heavy positive ions seem to increase in the vicinity of negative aerosols. Could it be water vapor? Very suggestive is Croskey (01) analysis of the Gerdien sensors on positive ions. Normally, as the voltage is swept, the current saturates, meaning that all the positive ions are collected from the airstream. But above 83 km, the current never saturates, indicating that the ions are too immobile, or too big to get collected. This is consistent with large numbers of postive water ions (hydrated protons) whose mass can exceed the 2200amu upper threshold of the Gerdiens. This is also consistent with the blunt probes (Mitchell 01), which see no change in the current collected (mobility not required!) as they descend through the PMSE. But it is expected that the ice cloud is stratified, with larger ice at the bottom. Then the current could stay the same, but the water content could be increasing. This would load the shock, making the transition from Mach 3 to rocket frame steeper and steeper. It should be a positive-feedback response, until a very steep gradient develops, scavenges all the mobile electrons, and the aft probe responds with a rapid decrease in current. On the downleg, CGRID sees the biteout BELOW the PMSE dust signature on CGRID3. This suggests that the PMSE occurrence is temporally and causally connected to the existence of biteouts. Likewise Mitchell et al 2001, shows that the aft Langmuir probe saw a biteout after the blunt probe indicated an increase in negative ion current, almost identically with CGRID data. This doesn't appear to be the enhanced photoemission that is causing the biteouts, since, we didn't see enhanced photoemission in the PAT sensor for the PMSE, only for the NLC. So what else could be causing this? Another possibility is not that the currents to the Langmuir probes have been changed, but the mobility of the electrons has suddenly changed. In other words, big heavy ions are keeping the electrons from moving to the probes. Mitchell 01, shows the positive ion-collecting Gerdiens are in-phase with the negative aerosol collecting blunt probes. Large heavy positive ions seem to increase in the vicinity of negative aerosols. Could it be water vapor? Very suggestive is Croskey (01) analysis of the Gerdien sensors on positive ions. Normally, as the voltage is swept, the current saturates, meaning that all the positive ions are collected from the airstream. But above 83 km, the current never saturates, indicating that the ions are too immobile, or too big to get collected. This is consistent with large numbers of postive water ions (hydrated protons) whose mass can exceed the 2200amu upper threshold of the Gerdiens. This is also consistent with the blunt probes (Mitchell 01), which see no change in the current collected (mobility not required!) as they descend through the PMSE. But it is expected that the ice cloud is stratified, with larger ice at the bottom. Then the current could stay the same, but the water content could be increasing. This would load the shock, making the transition from Mach 3 to rocket frame steeper and steeper. It should be a positive-feedback response, until a very steep gradient develops, scavenges all the mobile electrons, and the aft probe responds with a rapid decrease in current.

32. PID TelescopesShockLangmuir Plasma ProbeX10 DensityCushioned Deceleration HeatingSublimationClean Time (~200ms )  Back to CGRID hydrodynamics. From Gumbel and Smiley simulations of the telescope gas dynamics, we know that the temperature in the telescope is upwards of 600K, far above the vaporization point for water. Likewise the density is increased, and the heat load to small grains crossing the shock front will evaporate them. This has been studied in greater detail by Phillip Webb, reaching the same conclusions. Thus the PMSE loads a great deal of water vapor into the CGRID telescope as the nanometer ice grains evaporate in the rocket shock. This additional mass load feeds back into the shock, causing an even greater shock transition, and greater sequestering of electrons by water ions, leading to a rapid decrease in current in CGRID1. The key point here is that the water ice creates a positive feedback on the shock, making the transition extra sharp. But it should have a time-lag.Back to CGRID hydrodynamics. From Gumbel and Smiley simulations of the telescope gas dynamics, we know that the temperature in the telescope is upwards of 600K, far above the vaporization point for water. Likewise the density is increased, and the heat load to small grains crossing the shock front will evaporate them. This has been studied in greater detail by Phillip Webb, reaching the same conclusions. Thus the PMSE loads a great deal of water vapor into the CGRID telescope as the nanometer ice grains evaporate in the rocket shock. This additional mass load feeds back into the shock, causing an even greater shock transition, and greater sequestering of electrons by water ions, leading to a rapid decrease in current in CGRID1. The key point here is that the water ice creates a positive feedback on the shock, making the transition extra sharp. But it should have a time-lag.

33. Chamber Clean Out Time �t ~ x^2 / D� where x= 8cm length of telescope (or back plate to CGRID2)������������� and D = diffusion constant.�D ~ 1/3 <v> L� where <v> is average thermal speed and L is mean free path�L ~ 1 / (n s)� where the density (from Smiley) is 4e21/m^3��������������� and s= cross section for water molecules or clusters.�Guessing for s = pi (r^), where r= (cube root of density) = 0.3 nm���������� (and of course, water cluster ions might be bigger)�� s = 3e-19 m2Giving�� L = 8e-4 mThen <v> = sqrt(3kT/m) where m = 30 AMU, T = 500K (from Smiley)������� giving 642 m/sFinally, D = 0.18and the diffusion time = x^2/D = 0.08^2/0.18 = 36ms Using a diffusion transport time for heated water vapor (using the temperature from Gumbel's simulation) from the back of the CGRID telescope to the front, we find that evaporating ice grains on the back detector would take about 40ms to transport the water vapor to the front grid, assuming a stagnant flow of course. At 1 km/s, this corresponds to 40 meters of altitude. Examination of the downleg plot, shows about 50-100meters separates the PMSE peak from the biteout, which is suggestive that water vapor may be responsible for the delayed onset of a biteout after encountering a PMSE layer. This is also consistent with the Holzworth 01 results, that suggest the mobility must be greatly reduced if the rocket sheath can produce such large potential variations. On the downleg, the Gerdiens show a positive Using a diffusion transport time for heated water vapor (using the temperature from Gumbel's simulation) from the back of the CGRID telescope to the front, we find that evaporating ice grains on the back detector would take about 40ms to transport the water vapor to the front grid, assuming a stagnant flow of course. At 1 km/s, this corresponds to 40 meters of altitude. Examination of the downleg plot, shows about 50-100meters separates the PMSE peak from the biteout, which is suggestive that water vapor may be responsible for the delayed onset of a biteout after encountering a PMSE layer. This is also consistent with the Holzworth 01 results, that suggest the mobility must be greatly reduced if the rocket sheath can produce such large potential variations. On the downleg, the Gerdiens show a positive

34. Mitchell et al (2001) analysis From Mitchell 01, we have the delays between the blunt probes &aft probe for the downleg biteout as follows: UPLEG DOWNLEG +blunt saw PMSE at 89.86-94.17s 257.21-258.40s -blunt saw PMSE at 91.91-93.62s 257.74-257.98s aft saw PMSE at 91.87(base)-93.35 257.94-258.13s At a velocity of 1 km/s, the 200ms delay between the probes is about 200 meters, or 10 times the length of the rocket. The downleg 530ms delay between + & - blunt probe is consistent with CGRID if we take the upper edge of the PMSE, rather than the peak of the PMSE, since the +blunt probe didn't show much of a peak. We can't do this for upleg, mostly because we lack CGRID1 data. Using Gumbels model for rocket sheath, we have 300K at 1e20/m3 giving the following diffusion �times� for selected distances: CGRID 0.08 m --> 36 ms, Blunt probe 2.5 cm --> 1 ms; Aftprobe to rocket shock~1.5m --> 1.6seconds. Thusthe 0.5-2s delays in the aft probe response are ballpark right, but details don't match too well, suggesting other processes are responsible for the delay. The enhanced spin modulation in the upleg suggests that water modulated photo-emission is playing a part in this �biteout�, less so in the downleg.From Mitchell 01, we have the delays between the blunt probes &aft probe for the downleg biteout as follows: UPLEG DOWNLEG +blunt saw PMSE at 89.86-94.17s 257.21-258.40s -blunt saw PMSE at 91.91-93.62s 257.74-257.98s aft saw PMSE at 91.87(base)-93.35 257.94-258.13s At a velocity of 1 km/s, the 200ms delay between the probes is about 200 meters, or 10 times the length of the rocket. The downleg 530ms delay between + & - blunt probe is consistent with CGRID if we take the upper edge of the PMSE, rather than the peak of the PMSE, since the +blunt probe didn't show much of a peak. We can't do this for upleg, mostly because we lack CGRID1 data. Using Gumbels model for rocket sheath, we have 300K at 1e20/m3 giving the following diffusion �times� for selected distances: CGRID 0.08 m --> 36 ms, Blunt probe 2.5 cm --> 1 ms; Aftprobe to rocket shock~1.5m --> 1.6seconds. Thusthe 0.5-2s delays in the aft probe response are ballpark right, but details don't match too well, suggesting other processes are responsible for the delay. The enhanced spin modulation in the upleg suggests that water modulated photo-emission is playing a part in this �biteout�, less so in the downleg.

35. Charged Dust Collection Having addressed the anomalous biteout and positive charge behavior, we can finally address what the Charge telescope was designed to measure, charged dust.Having addressed the anomalous biteout and positive charge behavior, we can finally address what the Charge telescope was designed to measure, charged dust.

36. Dust Trajectories in Charge Telescope SIMION The three grids of the telescope are simulated in this SIMION 3D program, with the black lines tracing out the trajectories of particles of specific mass/charge ratios. The first positive grid will attract negative dust, but the 2nd negative grid will repel the dust. Simulations show that only dust with a mass/charge ratio of 1100 amu/e or greater can penetrate the 2nd grid. Phillip Webb's simulations include both this effect and the ablation of ice grains, so the lower limit is a bit higher, since ice grains will have lost some material already by the time they encounter the 2nd grid.The three grids of the telescope are simulated in this SIMION 3D program, with the black lines tracing out the trajectories of particles of specific mass/charge ratios. The first positive grid will attract negative dust, but the 2nd negative grid will repel the dust. Simulations show that only dust with a mass/charge ratio of 1100 amu/e or greater can penetrate the 2nd grid. Phillip Webb's simulations include both this effect and the ablation of ice grains, so the lower limit is a bit higher, since ice grains will have lost some material already by the time they encounter the 2nd grid.

37. Particle size range for PAT and PID Then looking at these numbers for the Mass telescope, the Charge telescope, the PAT sensors and the PVDF impact sensors, we can identify which detectors are sensitive to which mass/charge particles. In our observations, only CGRID3 measured dust, as well as PAT. This means the dust did not sublimate completely in the shock, and must be somewhat larger than 1 nm diameter. Likewise the lack of PVDF signature says the dust was smaller than 80nm or so, which is consistent with the lack of a photometer detection. Details of the signature on grids 2 and 3 suggest that the size range is between 4-10 nm, as discussed in Phillip Webb's paper.Then looking at these numbers for the Mass telescope, the Charge telescope, the PAT sensors and the PVDF impact sensors, we can identify which detectors are sensitive to which mass/charge particles. In our observations, only CGRID3 measured dust, as well as PAT. This means the dust did not sublimate completely in the shock, and must be somewhat larger than 1 nm diameter. Likewise the lack of PVDF signature says the dust was smaller than 80nm or so, which is consistent with the lack of a photometer detection. Details of the signature on grids 2 and 3 suggest that the size range is between 4-10 nm, as discussed in Phillip Webb's paper.

38. PID and PAT compared Here we plot MGRID2 in the first panel, with the spikes caused by sweeping the voltage of the MGRID1, overplotted with the PAT1 spin-averaged data, scaled by a factor of 100. Both show the NLC effect, both show the exponential growth of UV light. The second panel shows CGRID2, and it barely sees the NLC. Earlier we had attributed this to the outgassing of CGRID on the upleg that suppressed the current until above the NLC. Nevertheless, at greately reduced scale, one can make out the principle peaks in CGRID2 that match MGRID2. (MGRID2 had much less volume and surface area than CGRID, so outgassing appears to be minimal) IN the third panel, we plot CGRID3, the negative charge density. Note how it lines up with the PAT sensor. Dividing the current by the volume swept out by the CGRID telescope, and assuming one electron charge per ice crystal, gives a maximum dust density of 10,000/cc in the peak. Here we plot MGRID2 in the first panel, with the spikes caused by sweeping the voltage of the MGRID1, overplotted with the PAT1 spin-averaged data, scaled by a factor of 100. Both show the NLC effect, both show the exponential growth of UV light. The second panel shows CGRID2, and it barely sees the NLC. Earlier we had attributed this to the outgassing of CGRID on the upleg that suppressed the current until above the NLC. Nevertheless, at greately reduced scale, one can make out the principle peaks in CGRID2 that match MGRID2. (MGRID2 had much less volume and surface area than CGRID, so outgassing appears to be minimal) IN the third panel, we plot CGRID3, the negative charge density. Note how it lines up with the PAT sensor. Dividing the current by the volume swept out by the CGRID telescope, and assuming one electron charge per ice crystal, gives a maximum dust density of 10,000/cc in the peak.

39. This identification of the PMSE with negatively charged dust can be compared with several other vertical profiles of the DROPPS 1 rocket. In the first panel we have the MGRID2 data, in the 2nd panel the photometer. IN the third panel the CGRID3 data, and in the fourth panel the radar reflection profiles. Note how the NLC corresponds to photometer profiles, whereas the radar is much closer to the negative particulate profile measured by CGRID3. Thus our model is that the NLC are made of uncharged, visible ice grains, and above these large ice grains is a dense, subvisible charged ice crystals that make up the PMSE and the radar return. What then is the relation between NLC and PMSE?This identification of the PMSE with negatively charged dust can be compared with several other vertical profiles of the DROPPS 1 rocket. In the first panel we have the MGRID2 data, in the 2nd panel the photometer. IN the third panel the CGRID3 data, and in the fourth panel the radar reflection profiles. Note how the NLC corresponds to photometer profiles, whereas the radar is much closer to the negative particulate profile measured by CGRID3. Thus our model is that the NLC are made of uncharged, visible ice grains, and above these large ice grains is a dense, subvisible charged ice crystals that make up the PMSE and the radar return. What then is the relation between NLC and PMSE?

40. Energetic electron precipitation (E>40keV) Serendipitously, we also flew a cooled solid state detector on the rocket, intended to measure the impact of charged particles, but instead, we left the thin window covering the active region in place. This meant only X-rays and E>40keV electrons could penetrate the detector. On the upleg, we saw a broad peak at 100km , consistent with a Chapman layer of approximately 40keV electrons. Now electrons coming down the field line are being repelled by the increasing magnetic field strength. This means they have a peak at 90 deg pitchangle. Since we are observing close to 0 deg pitchangle, we are observing only the isotropic, scattered population. The electrons become isotropic at the location where they scatter most intensely, which is the Chapman layer. Hence the broad peak at 100 km is consistent with this interpretation. The sharp peak at 110 km occurred when the on board DROPPS attitude control realigned the rocket, and for a brief moment, the rocket was looking in the 90 deg pitchangle direction. These are anisotropic electrons, not in the Chapman layer, mirroring above the loss cone. Assis has plotted these counts versus magnetic pitchangle and observes the same peaked at 90, empty downward loss cone, distribution.Serendipitously, we also flew a cooled solid state detector on the rocket, intended to measure the impact of charged particles, but instead, we left the thin window covering the active region in place. This meant only X-rays and E>40keV electrons could penetrate the detector. On the upleg, we saw a broad peak at 100km , consistent with a Chapman layer of approximately 40keV electrons. Now electrons coming down the field line are being repelled by the increasing magnetic field strength. This means they have a peak at 90 deg pitchangle. Since we are observing close to 0 deg pitchangle, we are observing only the isotropic, scattered population. The electrons become isotropic at the location where they scatter most intensely, which is the Chapman layer. Hence the broad peak at 100 km is consistent with this interpretation. The sharp peak at 110 km occurred when the on board DROPPS attitude control realigned the rocket, and for a brief moment, the rocket was looking in the 90 deg pitchangle direction. These are anisotropic electrons, not in the Chapman layer, mirroring above the loss cone. Assis has plotted these counts versus magnetic pitchangle and observes the same peaked at 90, empty downward loss cone, distribution.

41. Ionospheric Chapman layer But back to Chapman layers. Since the density of the atmosphere is exponentially decreasing with height, then an monoenergetic beam of electrons that loses energy, dE/dx, at an increasing rate with loss of energy, produces a profile first described by Sidney Chapman, that has a sharp lower boundary, and a long upper tail==> figure 1. Several monoenergetic beams are shown in the right hand panel, with the peaking altitude. It should be clear that the 100 km peak is 40keVor greater. So what happens to the beam when it stops? It deposits its energ in ~10eV atmospheric electrons. These electrons are about 10x hotter than the usual photo-generated ionospheric electrons of ~1 eV. And these supra-thermal electrons are concentrated in a layer.But back to Chapman layers. Since the density of the atmosphere is exponentially decreasing with height, then an monoenergetic beam of electrons that loses energy, dE/dx, at an increasing rate with loss of energy, produces a profile first described by Sidney Chapman, that has a sharp lower boundary, and a long upper tail==> figure 1. Several monoenergetic beams are shown in the right hand panel, with the peaking altitude. It should be clear that the 100 km peak is 40keVor greater. So what happens to the beam when it stops? It deposits its energ in ~10eV atmospheric electrons. These electrons are about 10x hotter than the usual photo-generated ionospheric electrons of ~1 eV. And these supra-thermal electrons are concentrated in a layer.

42. Ice charging Model Ice grains are in equilibrium with UV and Ne. <q> ~ -1 Now ice charging models usually assume that there exists an equilibrium between electron attachment onto the surface of an ice grain, and UV photo-detachment from the surface. These models find that for UV intensities and electron densities, the average charge state of an ice grain is less than 1 charge per grain. However, in the presence of a supra-thermal electron population, something else happens. Now ice charging models usually assume that there exists an equilibrium between electron attachment onto the surface of an ice grain, and UV photo-detachment from the surface. These models find that for UV intensities and electron densities, the average charge state of an ice grain is less than 1 charge per grain. However, in the presence of a supra-thermal electron population, something else happens.

43. Range and Secondary e- in Ice From Olivero et al. JGR 1972, we find that the dE/dx for electrons in water drops rapidly below 30eV, since the electrons no longer can create a 35eV ion pair, which is the primary drag on an electron. Then taking the incident energy E, and dividing by dE/dx, give an approximate range for the electron (assuming a power law fit to dE/dx with an exponent of 1). This estimate is plotted as the upper, blue curve in the first graph. Between 5eV and 40eV, a power-law exponent n=5 is a better fit, and this gives the lower, green curve. Attempting an instantaneous power-law fit gives the intermediate pink curve, which is probably best between 10-70eV. Using this fit, the range has a minimum of r~10 nm at 30eV to r>100nm below 15 eV or above 80 eV. This means that the PMSE ice grains of roughly 2-10nm become invisible to electrons of 15eV or lower, that incoming electrons below 15 keV do not leave any charge on the ice grain. From Stolarski and Green JGR 1967, in the right-hand plot, we find that the production of 30 eV electrons by a primary beam of 10 keV electrons is only about 1.5 per incident electron, whereas a 30keV beam produces about 5, and a 40 keV about 10. Therefore there is a threshold of roughly 30keV primary beams which suddenly interact with 10nm ice. They simultaneously penetrate to about 90km deep in the atmosphere, but the efficiency or multiplication of the penetrating electrons doesn't really pick up until 40-50keV electrons, which penetrate to 80-85 km. That is, only for precipitating electrons of E>30keV do the precipitating electrons stop inside the ice grain and charge it up. And only for E>30keV do precipitating electrons overlap the mesopause boundary where ice grains are forming. The range minimum at 8-10nm also suggest that once ice grains grow to this diameter, their probability of becoming charged grows very large, which may affect the ability of the ice grain to accrete additional water ions. Thus this minima may cause the ice grains to become all identically sized and charged. From Olivero et al. JGR 1972, we find that the dE/dx for electrons in water drops rapidly below 30eV, since the electrons no longer can create a 35eV ion pair, which is the primary drag on an electron. Then taking the incident energy E, and dividing by dE/dx, give an approximate range for the electron (assuming a power law fit to dE/dx with an exponent of 1). This estimate is plotted as the upper, blue curve in the first graph. Between 5eV and 40eV, a power-law exponent n=5 is a better fit, and this gives the lower, green curve. Attempting an instantaneous power-law fit gives the intermediate pink curve, which is probably best between 10-70eV. Using this fit, the range has a minimum of r~10 nm at 30eV to r>100nm below 15 eV or above 80 eV. This means that the PMSE ice grains of roughly 2-10nm become invisible to electrons of 15eV or lower, that incoming electrons below 15 keV do not leave any charge on the ice grain. From Stolarski and Green JGR 1967, in the right-hand plot, we find that the production of 30 eV electrons by a primary beam of 10 keV electrons is only about 1.5 per incident electron, whereas a 30keV beam produces about 5, and a 40 keV about 10. Therefore there is a threshold of roughly 30keV primary beams which suddenly interact with 10nm ice. They simultaneously penetrate to about 90km deep in the atmosphere, but the efficiency or multiplication of the penetrating electrons doesn't really pick up until 40-50keV electrons, which penetrate to 80-85 km. That is, only for precipitating electrons of E>30keV do the precipitating electrons stop inside the ice grain and charge it up. And only for E>30keV do precipitating electrons overlap the mesopause boundary where ice grains are forming. The range minimum at 8-10nm also suggest that once ice grains grow to this diameter, their probability of becoming charged grows very large, which may affect the ability of the ice grain to accrete additional water ions. Thus this minima may cause the ice grains to become all identically sized and charged.

44. But 40 keV electrons should be generating X-rays when they impact on the atmosphere. The POLAR/PIXIE instrument was able to image the x-rays from various conditions. This was the picture, with some integration going on, for a large storm in 1998. Note how the peak electron precipitation moves from post-midnight around toward noon. Also note how the minima is almost always at dusk. This matches the occurrence statistics for PMSE.But 40 keV electrons should be generating X-rays when they impact on the atmosphere. The POLAR/PIXIE instrument was able to image the x-rays from various conditions. This was the picture, with some integration going on, for a large storm in 1998. Note how the peak electron precipitation moves from post-midnight around toward noon. Also note how the minima is almost always at dusk. This matches the occurrence statistics for PMSE.

45. PIXIE Xray vs Kp,Dst(1996-98) Here we look at 2 years of X-ray data binned by Kp, a magnetic activity index. Note again how post-noon is the weakest location for precipitating electrons. Binning by Dst is even more obvious. During storms, energetic electron precipitation occurs as ring current strengthens and moves inward. Here we look at 2 years of X-ray data binned by Kp, a magnetic activity index. Note again how post-noon is the weakest location for precipitating electrons. Binning by Dst is even more obvious. During storms, energetic electron precipitation occurs as ring current strengthens and moves inward.

46. Precipitating Electron effects The dusk side is depleted in electrons The energy of the electrons changes the Chapman-layer altitude. Double peaked energy spetra would produce double layers in atmosphere. Electron energy is a function of MLT & magnetosphere activity. This then would explain many of the details of the observed PMSE activity. The double PMSE layers form from double peaked electron precipitation. Dropps 1 saw PMSE since it had auroral activity, Dropps 2 did not, being exceptionally quiet that night. (Goldberg 01) The change in altitude of the PMSE corresponds to the MLT dependence on the electron cloud that is precipitating from a storm or plasmasheet. The NLC would always form, but charging and subsequent PMSE appearance would depend on details of the precipitating electrons. Note that occasionally PMSE are observed but not NLC. We attribute this to lack of sensitivity (and/or coverage) for NLC observations, and should satellite data be available, AIM for example, there will always be an NLC during a PMSE event. The PMSE reflects radar because its high charge state negative dust creates a dusty plasma, and dust acoustic waves would then be anti-correlated with electron density. This anti-correlation has been noted by Havnes in several places.This then would explain many of the details of the observed PMSE activity. The double PMSE layers form from double peaked electron precipitation. Dropps 1 saw PMSE since it had auroral activity, Dropps 2 did not, being exceptionally quiet that night. (Goldberg 01) The change in altitude of the PMSE corresponds to the MLT dependence on the electron cloud that is precipitating from a storm or plasmasheet. The NLC would always form, but charging and subsequent PMSE appearance would depend on details of the precipitating electrons. Note that occasionally PMSE are observed but not NLC. We attribute this to lack of sensitivity (and/or coverage) for NLC observations, and should satellite data be available, AIM for example, there will always be an NLC during a PMSE event. The PMSE reflects radar because its high charge state negative dust creates a dusty plasma, and dust acoustic waves would then be anti-correlated with electron density. This anti-correlation has been noted by Havnes in several places.

47. Dust Acoustic Waves These are two images of dust acoustic waves, the left from Ed Thomas Jr experiment at Auburn University, the right from U of Iowa experiment. The waves have a wavelength of cm, and the speed of the waves is cm/s in the laboratory. However, at 80 km altitude, the neutral density is less, and the dust grains are about 1000 times smaller, which gives them a mass 10^6 smaller. Therefore we expect the frequency to scale as the root(mass) and the resulting wavelength will be larger. In the UIowa experiment, the dust waves are in nitrogen at 80mTorr, with wavelength about 0.6cm, travelling 8cm/sec and a frequency of 15Hz. Using Barkan 1995, Phys.Plasmas, we calculate that the replacement of 5micron kaolin with 5nm ice would speed up the waves to 2.5 m/s. The frequency would remain about the same, since the ionosphere has roughly the same pressure as used in the lab experiment, which gives a wavelength of 150cm. This corresponds to a 200MHz radar, which is in the middle of the 5MHz-1.2GHz range of radars that have observed PMSE. Hall & Rottger GRL 01, show Doppler data estimating 2m/s upward PMSE motion at 500MHz, which is consistent with gravity wave energy propagation through DAW.These are two images of dust acoustic waves, the left from Ed Thomas Jr experiment at Auburn University, the right from U of Iowa experiment. The waves have a wavelength of cm, and the speed of the waves is cm/s in the laboratory. However, at 80 km altitude, the neutral density is less, and the dust grains are about 1000 times smaller, which gives them a mass 10^6 smaller. Therefore we expect the frequency to scale as the root(mass) and the resulting wavelength will be larger. In the UIowa experiment, the dust waves are in nitrogen at 80mTorr, with wavelength about 0.6cm, travelling 8cm/sec and a frequency of 15Hz. Using Barkan 1995, Phys.Plasmas, we calculate that the replacement of 5micron kaolin with 5nm ice would speed up the waves to 2.5 m/s. The frequency would remain about the same, since the ionosphere has roughly the same pressure as used in the lab experiment, which gives a wavelength of 150cm. This corresponds to a 200MHz radar, which is in the middle of the 5MHz-1.2GHz range of radars that have observed PMSE. Hall & Rottger GRL 01, show Doppler data estimating 2m/s upward PMSE motion at 500MHz, which is consistent with gravity wave energy propagation through DAW.

48. Conclusions There is no evidence for positive charged aerosols. Water work function explains +current. Electron density bite-outs are likely instrumental PMSE's are subvisible <10nm ice that has a high charge state. The charge state may be a direct result of >10 keV electron precipitation Dust Acoustic Waves may be responsible for the Bragg-reflected radar returns