Possible Link between Solar Proton Events and Weather via Atmospheric Electric Currents

1. IAGA/SCOSTEP 2017 Workshop, 13-16 November 2017, Prague, Czech Republic Possible link between solar proton events and weather via atmospheric electric currents Peter Tonev Space Research and Technology Institute, SCS Bulgarian Academy of Sciences e-mail: ptonev@bas.bg

2. Global electrical circuit (GEC) GEC is considered as mediator in transmission of solar influences on climate in short time-scale In GEC el. currents are generated from thunderstorms to ionosphere; in fair-weather regions the return (downward) current of density Jz flows back from ioonosphere to surface. Jz is considered as key characteristic assoc to meteorological responses by changes in cloud cover, temperature, pressure, or dynamics. The electric current Jz (~2 pA/m2) flowing through clouds, creates space charge in conductivity gradients at cloud boundaries, which can affect microphysical interactions between droplets, and ice-forming nuclei and condensation nuclei (Tinsley, 2007). Short-term inputs to GEC due to solar activity: (1) Forbush decreases of GCR flux; (2) SEP events; (3) Changes in relativistic electron precipitation; (4) Changes in trans-polar ionospheric convection potential. Different effects have been revealed which concern short-term sun-weather link: of Burns; Mansurov; Wilcox, Kniveton, Roldugin; Misumi; Schuurmans, Veretenenko; Roberts, Pudovkin, Egorova

3. Role of current Jz in formation of clouds Fig. 1. Atmospheric conductivity s: model profile. In clouds conductivity is 3-10 times lower (the dashed line).When current Jz flows through cloud boundary of large conductivity gradient, electric charge is accumulated which facilitates formation of cloud condensation nuclei (CCN). CCN formation possibly increases non-linearly with Jz increase, so that larger short-term variations of Jz can has larger effect on cloud formation. The column resistance is R=  dz/s(z) over all altitudes z, Separately, RTfor troposphere is >> RS for stratosphere. Fig. 2. A possible mechanism of ion-induced nucleation of ultrafine condensation nuclei (UCN): condensable vapours, may eventually grow into cloud condensation nuclei (CCN). The presence of charge induced due to current Jz facilitates (accelerates) this process (from Carslaw et al. 2002).

4. Sun – Weather & Climate relationships via the current Jz Tinsley, Rep. Prog. Phys. 71 (2008) 066801. Processes connecting thunder-storms, solar activity and galactic cosmic ray flux with the global atmospheric electric circuit, cloud and aerosol microphysics, and weather and climate. In particular, solar proton events (SPE) hypothetically can affect meteorological responses via hypothesized chains of cloud microphysical and macroscopic processes.

5. Effects of solar proton events on weather found in studies For example, Veretenenko and Thejl (2004), etc. The squared vorticity [s-2] in North Atlantic (50-70oN, 0-40oW), associated with SPE events. Dashed line is the mean level. A series of results show that the solar proton events (SPE) can lead to changes in loweratmosphere characteristics by intensification of regeneration of well-developedcold cyclones together with changes in tropospheric pressure and temperature in troposphere at high-latitudes in North Atlantic. Moderately strong SPE with energies of particles large enough for penetration into the stratosphere (Е > 90 MeV) are accompanied by decrease of pressure above North Atlantic. It has been concluded that the intensification of cyclones associated to SPE can be due to changing of cloudiness which can be controlled by GEC and the atmospheric electric current Jz. The question arises: Is current Jz effectively affected by SPE, and, if so, how ?

6. Effects of SPE and GLE on atmosphere: Profiles of ionization rate Fig.2 Ionization rate profiles (Usoskin, 2011). Dashed line is for GCR, 1-day event duration. Red solid line shows ionization due to SPE 23 February 1956. Blue solid line shows ionization due to the 3-4 August 1972 SPE Fig.1. Ionization rate profiles for two GLE events: in August 1972 (blue lines); and SPE69 on 20th January 2005 obtained by Usoskin (solid curves) and by Jackman (dashed curves). Ionization by SEP flux dominates over GCR usually only above the troposphere; below ~20 km ionization is by GCR, except for the strongest GLE in 1956 (Fig.2). The strong ionization by SEP causes modifications in atmospheric conductivity, and thus, variations of electric current Jz. Columnar resistance changes slightly, since its tropospheric part is dominant.

7. Evolution in time of SPE’s in January 2005 (Seppala et al., J. geophys. res., 113, A11311, 2008 (it is important for determining changes in GEC) Figure 2. Calculated proton ionization rates at stratospheric (40 km, solid line) and mesospheric (60 km, dashed line) altitudes for 15–24 January. (to be used in theory of growing aerosol particles during SPE) Fig 1. (a) GOES integrated proton fluxes at two threshold energies (>10 MeV and >100 MeV) for 14–24 January 2005. The dashed lines indicate the hard spectrum SPE of 20 January (red) and the preceding regular spectrum SPE of 17 January (blue). (b) Differential proton spectrums of the hard spectrum event (red dash-dot line) and the regular spectrum event (blue solid line). The average GOES quiet time proton spectrum is presented for contrast (black dashed line). Penetration of protons by energies Energy, MeV Altitudes, km 60-90 35-50 100 30 300 15

8. Modifications in conductivity and column resistance in polar regions for the SPE69 at 20.01.2005 (strongest GLE for last decades ) Kokorowski et al.(2012). J. Geophys. Res., 117, A05319, doi:10.1029/2011JA017363 Fig. Comparisons of modeled conductivity profiles at 20 January 2005 at polar latitudes (34 E, 70 S). Two profile sets are for 06:00 UT (before the SEP event onset; solid) and 09:00 UT (after onset; dashed). • Increase of conductivity in atmospheric regions during SPE • - In the high troposphere: usually up to few tens of percent • - In stratosphere: up to two orders of magnitude or more • - Total resistance: by up to several percent (GLE-1956 is an exception). • resistances; change. The stratospheric columnar resistance RPS decreases by more than an order of magn. however, the total resistance RP drops only by up to several percent (~5%). • Only the most powerful GLE in 1956 caused much large change of RP.

9. Effects of SPE on atmospheric electric characteristics Jz, el.field Ez I. Case of high latitudes, at surface (Kasatkina et al., Atmos. Chem. Phys. Discuss., 9, 21941-58, 2009 Fig. 2. (a) Vertical atmospheric electric field (Ez) at Apatity (geomag. latitude 63.8) during GLE on 18 April 2001 combined with CME; (c) 1-min flux values of electrons with E > 2 MeV (1), protons with E > 1 MeV (2), protons with E >10 MeV (3), and protons with E >100 MeV. Fig. 3. The same as for Fig. 2 but for the 4 November 2001 GLE Large increase of Ez (several times( with large variations in hour timescale during first phase of SPE. Decrease of Ez with large variations and sporadic reverses of sign during second phase

10. Measurements at surface at low latitudes during SPE (Tacza et al., 32nd URSI GASS, Montreal, 19-26 August 2017) Time, hours from event Left Figure: Atmospheric electric field (AEF) (lower panels) measured at CASLEO (31.798°S, 69.295°W) at 2552 m altitude, during GLE on May 17, 2012 (the upper panel). Right Figure: Relative deviations from mean atmospheric electric field for 8 events - In the first phase (~3 hours) of SPE (when is its peak) AEF decreases well below typical values. - In the slow-down phase (~5 hours) AEF increases to larger values than typical ones. Time, UT

11. Experimental results for Ez and Jz at surface at middle latitudes (Reading, UK, 51.45°N, 0.97°W) during SPE on April 11 2013 (Nicol and Harrison, Phys. Rev. Lett., 112, 225001, 2014). Fig.1 Proton flux data from GOES-13 around April 11, 2013 (year day 101), for proton energies >10 (black line), >30 (brown), and >60 MeV (gray). Vertical lines mark observed surface atmospheric electrical fluctuations. No GLE has been detected. Geomagnetic conditions were quiet. Fig.2. Ionization rate profiles measured over Reading, UK: the mean of 3 undisturbed profiles (in black); during SPE on 11th April 2013, 1319 UT (orange); on 12th April 2013, 0931 UT (purple). Fig.3. Electric current Jz (in grey) and potential gradient (in black) at the surface measured in Reading, UK, during SPE on April 11, 2013, by fair-weather conditions and quiet geomagnetic conditions. Jz exhibits reversal of direction and large negative values Quite untypical results; hardly can be explained by local factors.

12. Variance of current Jz at surface, at low latitudes during SPE and CME Elhalel et al., J. Space Weather Space Clim. 4 (2014) A26: Fig.1. Effect of SPE October 24-25 2011 together with CME impact on Jz variance. Upper panel: Jz fluctuations measured in Mitzpe-Ramon, Israel (31 N, 35 E). Lower panel: ACE SW proton density (blue curve). Conclusions: During SPE the el. current Jz and field Ez at surface can vary significantly; large changes (or only large variance) occur; unexplained reversal of sign can take place. At high latitudes: Common Increase and large variations in tens of minutes-hour time-scale during first phase of SPE; Common decrease with smaller variations in second part. At middle-low latitudes. A decrease during first phase of SPE; an increase in the second.

13. Electric characteristics in polar stratosphere (31-33 km) during SPE69 (20th January 2005, GLE), Kokorowski et al., J. Geophys. Res. 33, L20105 (2006, 2012) Vertical electric field Ez at height 31-33 km, by coordinates between (70.9 S, 10.9 W) and (71.4 S, 21.5 W). GOES 11 proton energy channels 11-17 for <1, 5, 10, 30, 50, 60, 100 MeV. Increase of >100 MeV channel by four orders in minutes (Kokorowski et al., 2012). Peculiarities of AEF Ez - At arrival of SPE Ez~0, then gradually increases - - With first jump of protons of energies 1-5 MeV Ez jumps to ~0; - With the second (larger) jump of protons of 1-5 MeV Ez reverses to upward and remains positive for many hours.

14. Model study of the response of current Jz and el.fields Ez to SPE Step I. Estimations of Jz variations averaged in time (for steady-state conditions) Ionosphere ‘RPS ~200 W << RPT RSrc3~105W RLS~5 W << RLT 103A El. current generator (thunderstorms) RLT ~195 W RSrc2 RPT ~7.6 kW RSrc1~104W Total RL= RLT+ RLS ~200 W Total RP= RPT+ RPS ~7.8 kW Polar latitudes REGION OF THUNDERSTORMS Non-polar latitudes FAIR WEATHER REGION Fig. Equivalent electric circuit (EEC) used to represent GEC. Resistances: RSrc for the common electric source (thunderstorms & electrified clouds over the globe); at low& middle lats RL= RLT+ RLS with tropospheric RLT and stratospheric RLS terms; at polar latitudes RP=RPT+ RPS where R=  dz/s(z) over a height interval depends on conductivity profiles(z). The effect of strong SPE will be a decrease of RP by up to 5% at polar latitudes, and smaller at lower latitudes due to geomagnetic cut-off rigidity. - For 5% decrease of RP only this leads to increase of the ionospheric potential VI by much less than 1%, and such will be also the relative increase of Jz at non-polar latitudes. - At polar latitudes the current Jz becomes smaller by up to ~5%. Similar (time averaged) estimations of Jz response to SPE have been proposed, e.g. by Farell and Desh (2002),Tinsley (2007): do not predict observed large variations.

15. Step II. Estimations of short (minute) time-scale variations of Jz When rapid changes in R (e.g. during SPE), the re-distribution of electrical charges in GEC becomes important. R is considered as impedance resistance. The general equation to solve is: Layer i+1 Layer i where J is current density, e0 is the dielectric constant. The resistances RT and RS in EEC are represented as series of impedances (Fig.1). The capacitors are included to account for displacement currents caused due to conductivity gradient. We estimate Jz change at 6 km altitude at SPE beginning. Estimations of changes of Jz (= 1.7 pA m-2 initially) due to changes of resistances RPS (= 200 W) initially) and RPT (= 7.6 kW initially) by different times needed to reach the max resisitence modification Fig.1.Each column resistance in EEC is represented by a series of impedances, each into a thin layer, to take account for dynamics of electric charges Time to reach DRPTmax, s 200 500 1200 DJz / Jzmax, % 6.2 5.2 4.8 Conclusion: Thus predicted Jz variations are too small to explain measured large variations.

16. Step III. Variations of Jz when aerosol layer is present in polar stratosphere There is discrepancy between experimental data and modeling, The small relative change of polar column resistance RC, even during the strongest SPE determine small modifications of Jz. The observed larger effect can be explained if the highly variable stratospheric resistance becomes comparable to tropospheric resistance: this is the case when a well-developed aerosol layer is created in the stratosphere. Such aerosol layer in upper stratosphere was predicted by Tinsley and Zhou (2006). Fig.1. Profile of concentration of ultra-fine (<~10 nm) aerosol particles at high latitudes (the case is for Antarctic, December), according to model by Tinsley and Zhou (2006) (in contrast to aerosol layers at 15 and 21 km uniformly distributed over the globe). Particles are associated with strongest volcanic eruptions, but the layer is well-expressed also during low volcanic activity (dashed line). Solid line is for high volcanic activity Fig.2. Ion density profiles by the same conditions for solar min (solid lines) and max (dot-dashed lines) for high volcanic activity; and for solar min (dotted) and solar max (dashed lines) at low volcanic activity. Ions are severely reduced in the layer since they rapidly attach to aerosol particles.

17. Mechanism of increase of Jz variations due to the presence of aerosol layer Fig.1. Profiles of conductivity by the same conditions. Conductivity decreases because of the low mobility of aerosol particles. Column resistance in the upper stratosphere becomes comparable to (or even larger than) that of troposphere. Large variations of stratospheric conductivity during SPE now cause large variations of the total column resistance. RPS RPT and has large rapid variations during SPE RS3~105W RML-S~5 W El.current generator (thunderstorms) RML-T ~195 W RPT RS2 RP= RPT+ RPS varies strongly Total RL= RLT+RLS~200 W RS1~104W Polar latitudes Non-polar latitudes F A I R W E A T H E R R E G I O N Thunderstorms By large rapid changes in RP during SPE big currents are generated in GEC together with large variations of the ionospheric electric potential VI = 250-300 kV. Changes in resistance RPS now amplify effect of SPE on vriations of the el. current Jz.

18. Model estimations of Jz variations by presence of aerosol layer We estimate response of conductivity s(z) and column resistance RPS to beginning of CME The beginning of SPE69 on 20.01.2005 caused fast (in minutes) and big (several orders of magnitude) increase of ionization rate q, and increase of conductivity s. For the aerosol layer in polar stratosphere centered at 40 km (Tinsley and Zhou, 2006) the ion-aerosol balance equation is: (1) q is ionization rate, a - ion-ion recombination rate, bi is an effective coefficient of attachment to aerosol particles and water droplets of type i, with concentration Si. The conductivity s is: s= n e (m1 + m2) m1, m2:mobilities of positive and negative ions. During arrival of SPE: conductivity s increases and column resistance RPS decreases. Time dependence of RPS is important for short-time Jz variations We study the situation at the arrival of SPE using Eq.(1). Fig. Profiles of effective ion attachment rate coeff ibiSi(solid & dotted lines: for max& minvolcanic activity), and for the ion-ion recombination parametera.n(dot-dashedand dashed for max & min volcanic activity) Antarctica, December,.

19. Estimation of variations of columnar resistance during initial phase of a SPE By assumption that ionization rate increases linearly with time: q(t) = q0 + Gq t at altitudes of the aerosol layer at 30-50 km q0 = 2 cm-3s-1 is the undisturbed ionization rate before SPE; G0 is time gradient of q. Column resistances RPL of the layer 35-45 and RP (total) at polar latitudes as functions of time during increase of ionization rate q. Curves 1, 2, 3, and 4 correspond to different time needed by ionization rate q to reach its maximum: 200, 500, 1200, and 2400 s, resp. Colored curves are for the layer 35-45 km; black curves are for the total column resistance. Model param-s are from Tinsley and Zhou (2006). Conclusion: Tolal columnar resistance at polar latitudes can drop more than twice depending on many conditions. The same change of ionization rate q leads to much larger change in RP when q is small

20. Variations of Jz during initial phase of a strong SPE: preliminary estimations At time-scales of tens of minutes – hours (steady-state conditions): Jz can increase up to twice or even more during arrival of SPE At lesser timescale (1 min), the maximum changes are: Time to reach DRPTmax, s 200 500 1200 2400 DJz / Jzmax, % 31.1 18.3 7.2 6.2 These are preliminary estimations, but it is that Jz can vary significantly at the beginning of SPE. When layer of ultra-fine aerosols exists in the upper stratosphere many of the peculiarities of the experimental results can b explained. Do layers of ultra-fine aerosol particles really exist above lower stratosphere? Fig.1. Vertical electric field measured in a noctilucent cloud at ~81 km altitude (Holzworth and Goldberg, 2004). Estima-ted conductivity is reduced by several orders of magnitude. Authors assume that ion attachment to aerosol occurs

21. Layers of ultra-fine aerosol particles which grow during SEP event (Mironova et al. (2008, 2012, 2015) Fig.2. Growing of aerosol after SPE on 20.01.2005 (Mironova et al., 2012). They assume that at initial phase of growing, the aerosol particles size can be belowthe satellite-based instruments detection threshold, in order to explain the revealed decrease of the mean size of growing particles Stages of growing of aerosol particles If can be assumed that growing of ultra-fine aerosol particles take part during SPE (or, possibly, precipitating relativistic electrons) in layers in stratosphere and above (which remain sub-detectable in observation), it could possibly explain the strong variations of current Jz during SPE.

22. CONCLUSIONS • The problem is considered whether GEC can be a mediator between SPE and weather-climate changes so that to explain the relationships between SPE and weather demonstrated in series of works. The agent considered here is the ionosphere-to-surface electric current Jz and its short-term variations, according to the theory proposed by Tinsley. • Large and untypical short-term variations of the current Jz have been observed during SPE which can possibly play role to facilitate formation of clouds and cyclone invigoration. The mechanism of these large variations are still to be explained better. • We show by modeling that significant variations of the current Jz can take place during SPE when a well-expressed aerosol layer of ultra-fine particles exists in upper polar stratosphere. Such layer was theoretically predicted by as predicted by Tinsley and Zhou (2006). • At timescale of significant changes in the proton flux (several minutes to hours) the current Jz can change by tens of percent or more at high latitudes and much less at the other lat-s, in agreement with experimental results. • At smaller timescales transient variations of the current Jz increase with altitude, and thus are more effective for cloud formation at upper heights. Larger transient Jz variation occur by larger column resistance in aerosol layer in periods of its faster decrease, such as at SPE arrival. • This preliminary study shows that GEC can be an effective mediator of sun-weather links if layers of ultra fine aerosol particles are present in stratosphere or above.

23. T H A N K Y O U