UNIVERSITY OF ILLINOIS AERONOMY REPORT NO. 78 ENERGETIC PARTICLES AND IONIZATION IN THE NIGHTTIME MIDDLE AND LOW LATITUDE IONOSPHERE by I H. D. Voss L. G. Smith I November 1, 1977 L Library of Congress ISSN 0568-0581 INASA-CR-156943) ENERGETIC PARTICLES AND N78-29665 IONIZATION IN THE NIGHTTIMIE ?IIDDLE AND LOW LATITUDE IONOSPHERE (Illinois Univ.) 323 p HC A14/MF A01 CSCL 04A Unclas G Z46 27857 Aeronomy Laboratory Supported by Department of Electrical Engineering National Aeronautics and Space Administration University of Illinois Grant NGR 14-005-181 Urbana, Illinois CITATION POLICY The material contained in this report is preliminary information cir­ culated rapidly in the interest of prompt interchange of scientific information and may be later revised on publication in accepted aeronomic journals It would therefore be appreciated if persons wishing to cite work contained herein would first contact the authors to ascertain if the relevant material is part of a paper pub­ lished or in process UILU-ENG 77 2502 AERONOMY REPORT NO. 78 ENERGETIC PARTICLES AND IONIZATION IN THE NIGHTTIME MIDDLE AND LOW LATITUDE IONOSPHERE by H. D. Voss L G. Smith November 1, 1977 Supported by Aeronomy Laboratory National Aeronautics and Department of Electrical Engineering Space Administration University of Illinois Grant NGR 14-005-181 Urbana, Illinois ABSTRACT Seven Nike Apache rockets, each equipped with an energetic particle spectrometer (12 < E < 80 keV) and electron-density experiments, have been launched from Wallops Island, Virginia and Chalca, Peru, under varying geomagnetic conditions near midnight. At Wallops Island the energetic particle flux (E < 40 keV) is found to be strongly dependent on Kp The pitch-angle distribution is asymmetrical about a peak at 900 signifying a predominantly quasi-trapped flux and exolaining the linear increase of count rate with altitude in the altitude region 120 to 200 km. The height-averaged ionization rates derived from the electron-density profiles are consistent with the rates calculated from the observed total particle flux for magnetic index Kp > 3 In the region 90 to 110 km it is found that the nighttime ionization is primarily a result of Ly-S radiation from the geocorona and interplanetary hydrogen for even very disturbed conditions. Below 90 km during rather disturbed conditions energetic electrons can be a significant ionization source. Two energetic particle precipitation zones have been identified at midlatitudes The Wallops Island precipitation zone is centered at L = 2.6 and the Arecibo precipitation zone is centered at L = 1 4 A precipitation null exists at L = 1 8 which is the situation for White Sands The locations of maximum precipitation in the South Atlantic Magnetic Anomaly are found to be associated directly with the precipitation zones at L = 1 4 and L = 2.6 At the equator the first rocket-borne detection of low altitude kilovolt protons is observed with count rates steadily increasing from 170 km altitude The flux depends strongly on magnetic activity and is believed to be associated with a double charge exchange mechanism of neutral hydrogen with the ring current Furthermore, it is found that at iv kilovolt energies the theoretical calculations used to compute multiple scattering for electrons are largely in error. An experimental apparatus was developed to measure the scattering of a beam of electrons in air These results were then used to obtain profiles of mirror­ height spreading as a function of altitude V TABLE OF CONTENTS ABSTRACT . TABLE OF CONTENTS . .... V LIST OF TABLES ..... ... x LIST OF FIGURES ....... Xi I INTRODUCTION.... ... I 1.1 General Introduetton ................. ...... 1 1.2 Objecttves of this Study ................ .... 3 2. IONIZATION SOURCES IN THE NIGHTTIME E REGION......... 7 2.1 Electron Density in the Nighttime Midlatitude Ionosphere . 7 2.2 Evidence for an Ionization Source .... ....... ...... 12 2 2.1. Recombinatton ................ ......... 12 2.2.2 Transport .......... ........ .. ...... 19 2 3 Ionization Rates for the Nighttime E Region ............ 20 2.3,1 Ionization rates calculated from the conttnuity equation for the steady-state no-transport case . 20 2 3.2 Iontzation rates calculated from the intermediate layer ........... ......... .......... 21 2.3 3 Wind shear theory as an explanation of the intermedtate Layer ...... ........ ....... 28 2.4 Sianiftcance of Ultravtolet Iontzatton ?,n the Ntghttime Ionosphere ................. ............ ... 33 2.4.1 Introduction.............. ......... ... 35 2.4.2 Hydrogen Ly-a emissson ....... ...... ........ 35 2.4 3 Hydrogen Ly-S emission ...... ......... 37 2.4.4 Helium I emssion ......... ......... ... .... 39 2 4.5 Helum II emission . ............ ... .. 39 vi 2.4.6 Ionization rates and electron densities produced by ultraviolet radiation at night. 40 3 EXPERIMENTAL TECHNIQUE. 43 3 1 Design and Calibrationof a Rocket-borne Energetic Electron Spectrometer 43 3 1 1 Choice of detector . 43 3 1 2 Electronic circuits. 46 3 1.3 Calibration 49 3 2 Determinationof the Rocket Attitude from the Magn tometer Signal . .. 49 3 3 The Flux Related to the Detector Count Rate . 58 3.3 1 General considerations 58 3 3 2 Detector count rate 64 3 3 3 Shadowing by the payload . 68 4 DIRECT OBSERVATIONS OF ENERGETIC ELECTRONS. 71 4 1 New Rocket Measurements at Mdlatitudes 71 4.1 1 Nike Apache 14.439; 1 November 1972 72 4.1 2 Nke Apache 14.520, 18 April 1974 78 4 1 3 Nike Apaches 14 521 and 14.522, 29 June 1974 . 88 4 2 New Rocket Measurements at the Geomagnetic Equator 91 4.3 Satellite Observations. 98 4.4 Other Rocket Measurements . 107 4 5 Summary of Observations . 111 4 5 1 Geographic variations and precipitation zones III 4 5 2 Variation of count rate with altitude 113 4.5 3 Magnetic activity and particle precipitation 115 S INDIRECT EVIDENCE OF ENERGETIC ELECTRON PRECIPITATION 120 VII 5 1 Midlatitude 391.4 nm Enisston ... 120 5 2 Ionization Rate Variations with Kp ... .125 5.3 VLF Doppler Shifts and Field Intensity Variations . 125 5.4 The CriticalFrequency, fxEn, of the nighttime Intermediate Layer . I . 126 5.5 Kp Variations and electron Temperature . 127 5.6 Bremsstrahlung X-rays as a Global Precipitation Snapshot . 129 6 PARTICLE INJECTION AND DIFFUSION . .. 131 6 1 The Magnetosphere. .... .. 131 6.2 Radiation Belts. 135 6 3 ParticlePrecipitationExcited by Wave-particle Interactions .. .... 136 6.4 PlasmasphericHiss Exciting the Wallops Island and Arecibo PrecipitationZones. 140 6 5 Longitude Variations of ParticlePrecipitationand the Cause of the South Atlantic Magnetic Anomaly Precipitation 144 7. MODELING THE PARTICLE SOURCE FUNCTION. ...... 152 7.1 The Variation of Count Rate with Altitude. 152 7.2 The Pitch-angle Distribution . 160 7.2.1 Observation of pitch-angle distributions.. 161 7 2 2 Change of pitch angle with altttude for a dipole field 164 7.3 Computer Simulation of the Count-rate Profile. 167 7 4 Equatorial Proton Precipitation. 172 7.5 Comparison Between Near Simultaneous Satellite and Rocket Measurements ...... .. 176 7.6 Global Precipitation Patterns at Night . 183 Vill 7.7 The Relatvve Importance of Bnergetic Electrons and Protons. 188 8 INTERACTION OF ENERGETIC ELECTRONS WITH THE ATMOSPHERE . 191 8.1 Electron Scattering Cross Sections .... 192 8 1 1 Easttc collisions ... ....... 192 8.1.2 Inelastvc colitatons . ........ 196 8.1.3 Comb-tned elastic and inelasttc scattering. .. ... 198 8 2 Energy Loss by Particle Prec-pitation, Ioniatvon, Excitaton and eating 199 8.2.1 Introductton . 199 8.2 2 Electron energy loss rate &n air . 200 8 3 Bastc Multiple Scattertng Formulas. 204 8 4 Pkpernmental Study of Electron Scattertng tn Air. 207 8 4.1 Ezpermental arrangement ... 208 8 4.2 Elpermental results of electron scattering.. 211 8 4.3 Observattons of electron energy loss sn air. .. 216 8.5 Scattering influence on the Pitch-angle Distribution. 216 9 CALCULATION OF IONIZATION RATES FOR ENERGETIC PARTICLES . 225 9 1 Atmospheric Ionization by Electrons 225 9 1 1 Etlp-rical methods. 225 9.1 2 Monte Carlo simulation . 226 9 1 3 Boltzmann equation methods . 229 9.2 Ionization Rate for a Quast-trapped Distribution of &2ergeticElectrons . ........ 231 9 2.1 Energy consi-dersatsons . 231 9 2 2 Pitch-angle dstrtbutzon . 234 9 3 Energy Loss and lonbzat-ion by Quas-z-trapped Fergetc Electrons 235 1x 9.3.1 Approximate calculation .... ....... ...... 235 9 3.2 Calculationof ionizatton rate for indivtdual electrons ................ ........... 237 9.4 Numerical Studies of Ionization by Quas--trapped Energettc Electrons ....... .......... ..... 243 9.5 Average Ionization Rates Computed from Rocket-borne Particle Measurements ........ ......... ..... 256 9 5.1 Ionization rates obtatned from the incident energy flux ............... ............ 256 9 5 2 Detailed calculations of energy flux . 259 9.5.3 Calculationsof tonization rates.. ........ 262 9.5.4 Comparison with ionization rates due to UV.... .. 265 10. CONCLUSION . .......... .. 269 10 1 Summary ................ ............... .. 269 10.2 Conclustons .............. .............. ..271 10.3 Suggestions for Future Work .......... ....... ..273 REFERENCES..... .. ......... 275 x LIST OF TABLES Table Page 2 1 Recombination Rate Calculations 15 4 1 Nighttime Middle and Low Latitude Rocket Experiments 108 4 2 Magnetic Index Comparisons 117 9 1 Average Ionization Rates (120-200 km). 266 X1 LIST OF FIGURES Figure Page I I Profile 1 is representative of the daytime electron density (105 cm-3). Towards night this electron density rapidly decays to a lower nighttime equilibrium level of about 103 cm- (Profile 2). The nighttime density-profile shows much variability and structure ............ ... 2 2.1 Three electron-density profiles representative of Kp values of 3+ (Profile 1), 5+ (Profile 2) and 8 (Profile 3) . 8 2.2 Electron-density profiles from the probes on rockets launched from Wallops Island on 22 February 1976 [Smith, 1970]. The profiles are each displaced by one decade. The electron­ density scales for the first and last profiles are given. The part of the profiles below 90 km should be regarded as indicating the structure, rather than as absolute values .