1 / 105

THE NEUTRAL ATMOSPHERE Temperature and density structure Hydrogen escape Thermospheric

THE NEUTRAL ATMOSPHERE Temperature and density structure Hydrogen escape Thermospheric variations and satellite drag Mean wind structure Standard atmospheres (Numerical simulation models to be discussed after the ionosphere) • Neutral chemistry. Tropo

emilia
Download Presentation

THE NEUTRAL ATMOSPHERE Temperature and density structure Hydrogen escape Thermospheric

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. THE NEUTRAL ATMOSPHERE • Temperature and density structure • Hydrogen escape • Thermospheric • variations and • satellite drag • Mean wind structure • Standard • atmospheres • (Numerical simulation models to be • discussed after the ionosphere) • Neutral chemistry ASEN 5335 Aerospace Environment -- Upper Atmospheres

  2. Tropo (Greek: tropos); “change” Lots of weather Strato (Latin: stratum); Layered Meso (Greek: messos); Middle Thermo (Greek: thermes); Heat Exo (greek: exo); outside ASEN 5335 Aerospace Environment -- Upper Atmospheres

  3. Noctilucent Clouds • Clouds at extremely high altitude, about 85 km, that literally (as the name suggests) shine at night. They form in the cold, summer polar mesopause and are believed to be ice crystals. Because of their high altitude, in a very dry part of the atmosphere, noctilucent clouds are rather an enigma and are being studied by a number of people around the world. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  4. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  5. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  6. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  7. Temperature Decrease or Water Vapor Increase ? Number of nights per year, N, on which noctilucent clouds were reported from north-west Europe, with the effect of solar activity removed (Gadsden, 1990) Evidence for decreases in mesospheric temperature (Aikin et al., 1991). (a) NOAA TIROS data and (b) Haute Provence lidar data. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  8. Tropo (Greek: tropos); “change” Lots of weather Strato (Latin: stratum); Layered Meso (Greek: messos); Middle Thermo (Greek: thermes); Heat Exo (greek: exo); outside ASEN 5335 Aerospace Environment -- Upper Atmospheres

  9. HEAT SOURCES AND SINKS Thermosphere - Sources • absorption of EUV (200-1000 Å; photo-ionization of O, N2, O2) and UV (1200-2000 Å; photo-dissociation of O2) radiation; photo-ionization and photo-dissociation lead to chemical reactions and collisions that liberate heat. • dissipation of upward propagating gravity waves (weather systems; flow over topography) and tides (periodic heating). • joule heating of electric currents (mostly auroral / polar regions) • particle precipitation (mostly auroral / polar regions) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  10. Absorption of Solar Radiation vs. Height and Species ASEN 5335 Aerospace Environment -- Upper Atmospheres

  11. Thermosphere - Sinks Thermal conduction (molecular and turbulent) removes heat from thermosphere to mesosphere (here collision frequencies are high enough that polyatomic molecules CO2, O3, H2O can radiate energy away in infrared). Let = heat flux due to conduction = As a first approximation, heat input is balanced by loss due to conduction: ASEN 5335 Aerospace Environment -- Upper Atmospheres

  12. Therefore must always be sufficiently large to conduct away heat deposited at higher levels. Therefore • above 200 km since • also is maximum around 120 - 150 km ASEN 5335 Aerospace Environment -- Upper Atmospheres

  13. Tropo (Greek: tropos); “change” Lots of weather Strato (Latin: stratum); Layered Meso (Greek: messos); Middle Thermo (Greek: thermes); Heat Exo (greek: exo); outside ASEN 5335 Aerospace Environment -- Upper Atmospheres

  14. Mesosphere - Sources some UV absorption by O3 in lower region heat carried downward from thermosphere (minor contribution) Mesosphere - Sinks infrared radiation by CO2, O3, H2O, OH Stratosphere - Sources strong absorption of UV (2,000 - 3000 Å) by O3 (produces maximum in temperature at stratopause) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  15. Troposphere - Sources absorption by planetary surface of infrared and visible radiation, and conduction to atmosphere atmospheric absorption of terrestrial and solar IR. latent heat release by water Troposphere - Sinks (and Sources) infrared radiation by surface, atmosphere (absorption) evaporation of water thermal convection important in transporting heat between different levels ASEN 5335 Aerospace Environment -- Upper Atmospheres

  16. Aerospace EnvironmentASEN-5335 • Instructor: Prof. Xinlin Li (pronounce: Shinlyn Lee) • Contact info: e-mail: lix@lasp.colorado.edu (preferred) phone: 2-3514, or 5-0523, fax: 2-6444, website: http://lasp.colorado.edu/~lix • Instructor’s office hours: 9-11 am at ECOT 534 • TA’s office hours: 3:15-5:15 pm Wed at ECAE 166. E-mail: Christopher.Hood@colorado.edu • READ classnotes and Chapter 6 • HW6 due today • Quiz-7 on 4/29 • HW7 due 5/1 ASEN 5335 Aerospace Environment -- Upper Atmospheres

  17. > 700 keV ions and > 500 keV electrons ASEN 5335 Aerospace Environment -- Upper Atmospheres

  18. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  19. > 20 MeV Ions (most protons) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  20. > 20 MeV Ions (most protons) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  21. > 20 MeV Ions (most protons) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  22. > 20 MeV Ions (most protons) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  23. > 20 MeV Ions (most protons) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  24. > 20 MeV Ions (most protons) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  25. SEE HAZARD REGISTER & ANOMALIES FOG anomalies (white stars) and SEE register values (color scale) Detected EDAC Errors Latitude Latitude Longitude Longitude FOG - Fiber Optic Gyroscope EDAC - Error Detection And Correction Spacecraft altitude region in graphs is 1450-1710 km. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  26. 500 km alt. Earth’s Surface SAA Inner Radiation Zone and South Atlantic Anomaly • Region of enhanced Single Event Effects caused by the intense and very energetic proton (EP ≥ 10 MeV) fluxes in the inner radiation belt. • Possible problem region for satellites in low altitude orbit or in elliptical orbits that traverse low altitudes. • In the South Atlantic region the energetic protons come closest to earth because of asymmetries in the magnetic field. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  27. Magnetospheric Substorm • Major contributor of space-weather effects inside the magnetosphere cavity. • Heats plasma at large anti-sun distances and “drives” it inward toward the Earth. • Generates auroral displays in the high latitude regions. • Causes surface charging of satellites in the pre-midnight to local morning local time regions. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  28. Injection of Particles During a Substorm (The Aerospace Corp.) ASEN 5335 Aerospace Environment -- Upper Atmospheres

  29. Basic Radiation Physics • As an example of the interaction between radiation and matter, an energetic electron passing through air will leave a trail of ionized particles. • If the electron is moving too slowly, it lacks the energy necessary to create ionizations. • If the electron moves too fast, it “passes through” without effectively interaction with the ambient atoms and molecules. • Consequently, radiation damage to materials is dependent not only on the nature of the radiation, but on the energy of the radiation and the nature of the material itself (see figure on next page). • The official SI unit of radiation is the Gray, 1 Gray=radiation which deposits 1 J/Kg of materials. • You may be more familiar with Rad or Roentgen: 1 Rad=radiation which deposits 0.01 J/Kg of materials. 1 Roentgen=amount of x-rays or gamma radiation that produces a given amount of ionization in air. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  30. Two major factors in the determination of radiation damages: (1) total dose over the life of a material, (2) dose rate, the rate at which energy is deposited. • Different materials have different susceptibilities to damage: ASEN 5335 Aerospace Environment -- Upper Atmospheres

  31. Relative Biological Equivalent (RBE) factors • In biological applications, the terms REM and RBE are used. • RBE (Relative Biological Effectiveness) is the number of rads of x-ray or gamma radiation that produces the same biological damages as 1 Rad of the radiation being used. • REM (Roentgen Equivalent in Man) is the product of the dose in Rad and the RBE factor. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  32. PARTICLE ENERGIES OF CONCERN ASEN 5335 Aerospace Environment -- Upper Atmospheres

  33. Biological Risks • Primary biological risk from space radiation exposure is cancer • When radiation is absorbed in biological material, the energy is deposited along the tracks of radiation. • Heavy ions produce much denser pattern of ionization more biological effects per unit of absorbed radiation dose. • Secondary concerns such as cataracts are beginning to receive more administrative attention ASEN 5335 Aerospace Environment -- Upper Atmospheres

  34. Another example of satellite fragmentation in elliptical orbit  Nearly same apogee height; therefore, fragmentation occurred near apogee fragmentation height = 2088 km mostly retrograde impulse + 1976-126A ASEN 5335 Aerospace Environment -- Upper Atmospheres

  35. Greenhouse Effect atmosphere transparent to visible, but opaque to infrared H2O, CO2 289 k (288 k 10yr ago), otherwise, 253 k. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  36. Sources of Carbon Dioxide • CO2 build up due to fossil fuel consumption. Currently the average concentration is about 365 ppmv and is increasing at a rate of about 0.4% (3 giga-tons) per year. • On the other hand, without the greenhouse effect, the average temperature of the Earth would be 253 K but now the average temperature is 289 K (288 K 10 years ago). • Fossil-fuel combustion is the principal global source of carbon dioxide (~60-70%), with deforestation estimated to be the second major source (~30-40%). The production of cement, which involves crushing and baking calcium carbonate, contributes the rest. • USA (16%), EU (<16%), The nations of eastern Europe (19%). ASEN 5335 Aerospace Environment -- Upper Atmospheres

  37. Long-Term CO2 Measurements • The long-term trend in carbon dioxide concentrations, as determined by measurements of the composition of air in glacial ice bubbles, is illustrated. This record can be extended back for tens of thousands of years. However, the comparison of atmospheric CO2 levels before and after the Industrial Revolution (beginning in the late 18th century; the steam engine was invented by James Watt in Scotland in 1751) is instructive. • The seasonal rise and fall of carbon dioxide are in perfect rhythm with life’s basic activity, photosynthesis. In the summer, when the air is warm and sunlight is plentiful, vegetation takes up large amounts of carbon dioxide through excess photosynthesis. Recent variations in carbon dioxide, monthly values in ppmv. Seasonal variation associated with photosynthesis/respiration is several ppmv. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  38. Very Long-term CO2 and T • The maximum variation in CO2 concentration ranges from about 170 to 280 ppmv, or a change of about 110 ppmv. This is only slightly greater than the change in CO2 concentration that has occurred during the past century (about 80 ppmv) and is much smaller than the change that will have occurred by the time the CO2 concentration doubles to about 600 ppmv in the twenty-first century (according to some projections). • The variations in CO2 may not lead the variations in temperature; rather, they may follow the temperature changes. This can be seen only at a finer time resolution. • Potential impacts of greenhouse warming: surface temperature, a rise in sea level (12 cm/1000yr, rate doubled in the past 50 yr). ASEN 5335 Aerospace Environment -- Upper Atmospheres

  39. HYDROSTATIC EQUILIBRIUM If ….. n = # molecules per unit volume m = mass of each particle nm dh = total mass contained in a cylinder of air (of unit cross-sectional area) Then, the force due to gravity on the cylindrical mass = nmg dh and the difference in pressure between the lower and upper faces of the cylinder balances the above force in an equilibrium situation: P + dP dP P nmgdh ASEN 5335 Aerospace Environment -- Upper Atmospheres

  40. Assuming the ideal gas law holds, Then the previous expression may be written: where H is called the scale height and ASEN 5335 Aerospace Environment -- Upper Atmospheres

  41. This is the so-calledhydrostatic laworbarometric law. Integrating, where and z is referred to as the"reduced height"and the subscript zero refers to a reference height at h=0. Similarly, For an isothermal atmosphere, then, TYPOS ASEN 5335 Aerospace Environment -- Upper Atmospheres

  42. Strictly speaking, since m varies from constituent to constituent (i.e., H, He, O, O2, N2, ....), the above relations apply to individual constituents, i.e., where Pi is the partial pressure and Thus, each individual constituent has the tendency to distribute vertically according to its own individual scale height. The process which makes this possible is molecular diffusion (see following figure). ASEN 5335 Aerospace Environment -- Upper Atmospheres

  43. For average dayside conditions ASEN 5335 Aerospace Environment -- Upper Atmospheres

  44. Variation of the density in an atmosphere with constant temperature (750 K). ASEN 5335 Aerospace Environment -- Upper Atmospheres

  45. Vertical distribution of density and temperature for high solar activity (F10.7 = 250) at noon (1) and midnight (2), and for low solar activity (F10.7 = 75) at noon (3) and midnight (4) according to the COSPAR International Reference Atmosphere (CIRA) 1965. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  46. Now, the efficiency of molecular diffusion increases according to the mean free path of atmospheric particles, and hence inversely with atmospheric density. At sufficiently low altitudes in the atmosphere, molecular diffusion is not able to compete with the various mixing processes in the atmosphere (turbulent diffusion, wave and general dynamical transport, etc.). The atmosphere, in fact, remains well-mixed below about 100 km. This regime is called the homosphere and is characterized by a constant mean molecular weight as a function of height: A mean scale height is thus defined: 78.1% N2 20.9% O2 .9% Ar .03% CO2 .002% Ne .0005% He Variable H2O ASEN 5335 Aerospace Environment -- Upper Atmospheres

  47. and all constituents possess the same scale height and number density (and pressure) distributions with height: • It is not until about 100 km (the exact height is species dependent, due to the dependence of molecular diffusion velocity on mean molecular weight) that molecular diffusion begins to take over, and each species separates according to its individual scale height. • This separation occurs at the homopause, sometimes called the turbopause. Above the homopause is the heterosphere; homosphere below. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  48. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  49. What is the meaning of temperature at high altitude? Can we measure it with a thermometer ? For an ideal gas consisting of perfectly elastic spheres in random thermal motion, and under equilibrium conditions, the number of molecules dN out of a total N having a speed between c and (c+dc) is given by the Maxwell-Boltzmann distribution: The above provides a definition of kinetic temperature valid whenever a gas is in thermal equilibrium. ASEN 5335 Aerospace Environment -- Upper Atmospheres

  50. In practice, at very high altitudes in the earth's atmosphere, the gas temperature can only be determined from a measurement of the particle velocities since any heat sensing instrument would radiate away any energy it received faster than collisions could raise it to the gas temperature. Above a certain level the mean free path of the particles exceeds the atmospheric scale height: The region where is called the exosphere, and the level where is called the exobase. Sometimes the level where is called the barosphere. In the exosphere particles are in ballistic orbits around the earth. Above the exobase there exists a substantial fraction of the particles with velocities greater than the escape velocity (~ 11 km/sec): ASEN 5335 Aerospace Environment -- Upper Atmospheres

More Related