Introductionto the Ionoshpereand Geomagnetism
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N6517513 INTRODUCTION TO THE IONOSHPERE AND GEOMAGNETISM OCT 1964 SEL-64-111 INTRODUCTION TO THE IONOSPHERE AND GEOMAGNETISM by H. Rishbeth and O. K. Garriott October 1964 Reproduction in whole or in part is permitted for any purpose of the United States Government. Technical Report No. 8 Prepared under National Aeronautics and Space Administration Grant NsG 30-60 Radioscience Laboratory Stanford Electronics Laboratories Stanford University Stanford, California CONTENTS -=_:_!-_¸ Paze I. THE NEUTRAL ATMOSPHERE .................. 1 I. Atmospheric Nomenclature ............... 1 2. Evolution of the Earth's Atmosphere ......... 5 3. Structure of the Atmosphere ............. 7 4. Dissociation and Diffusive Separation ........ 12 5. Thermal Balance ................... 16 6. The Exosphere .................... 2O __J, 7. Experimental Techniques ............... 21 II. MEASUREMENT OF IONOSPHERIC PARAMETERS .......... 27 I. Introduction ..................... 27 2. Determination of Electron Density by Sounding .... 27 3, Propagation Methods ................. 36 4. Direct Measurements ................. 44 z, 5. Incoherent Scatter .................. 46 III. PROCESSES IN THE IONOSPHERE ............... 50 I. The Balance of Ionization .............. 50 2. Chapman's Theory ................... 53 3. Production and Loss ................. 63 4. The D, E and F1 Photochemical Regime ....... 69 5. Plasma Diffusion ................... 81 6. Solving the Continuity Equation ........... 88 IV. MORPHOLOGY OF THE IONOSPHERE 94 1. D Region .................... 94 2. E and F1 Regions 98 3. F2 Region Problems ................ I01 4. F: Region Rates _ ..... 108 5. Eclipse Effects : _ 110 6. Ionospheric Irregularities .............. 116 7. Sporadic E ..................... 122 Precedingpageblank " SEL-64-111 Page 8. Artificial Disturbances ............... 125 V. RELEVANT ASPECTS OF GEOMAGNETISM ............. 127 i. Introduction ..................... 127 2. The Geomagnetic Field ................ 129 3. Regular Variations ................. 133 4. Storm Variations .................. 137 VI. DYNAMO THEORY ...................... 140 i. Atmospheric Oscillations ............... 140 2. Conductivities .................. 144 3. Motions in the Ionosphere and Magnetosphere ..... 151 4. Observational Data .................. 155 VII. STORMS AND THEIR IONOSPHERIC EFFECTS ........... 160 I. Synopsis of Storm Effects .............. 160 2. Storm Effects in the Lower Ionosphere ........ 165 3. Storm Effects in the F Region ........... 168 4. Theories of Geomagnetic Storms ............ 173 VIII. REFERENCES ........................ 178 TABLES Number I Production and loss processes ............. 70 II Photochemical reactions ................. 79 III Rounded values of F2 layer parameters ......... 112 IV Finch and Leaton coefficients ............. 133 V Some orders of magnitude of quantities in dynamo theory 156 VI Storm phenomena ..................... 162 SEL-64-111 iv - ILLUSTRATIONS Figure Pag___..ee 1 Regions of the atmosphere, showing conventional names descriptive of levels, physical regimes, and character- istic constituents .................... 1 2 U.S. Standard Atmosphere ................. 4 3 Theoretical models of Harris and Priester ........ 12 4 Ratios of the concentrations of the major neutral con- stituents of the upper atmosphere ............ 14 5 An idealized ionogram, showing virtual height vs frequency 30 6 Observed amplitude ratios of partially reflected extra- ordinary and ordinary waves; the deduced electron density profile ......................... 38 7 Illustrating the measurement of N and v by the ratio- wave interaction technique ................ 39 8 Electron temperature profiles obtained on five rocket flights from Wallops Island, Va, and Fort Churchill, Canada .......................... 46 9 Normalized Chapman production function q(z,X)/qo = exp (1 - z - e -z sec X) ................. 58 10 Normalized Chapman production function vs reduced height, parametric in zenith angle ................ 59 ll Geometry used in the calculation of Ch (No) ....... 60 12 Sec Xo and Ch (Xo) vs _o' parametric in (R/H) .... 62 13 Extreme-ultraviolet (EUV) flux vs wavelength, based on the data of Watanabe and Hinteregger ............. 64 14 The altitude of unit optical depth vs wavelength ..... 65 15 Illustrating the wavelength and zenith angle dependences of the prodUctiOn profiles for 0 +, N_ and O_ ....... 66 16 Electron density profiles for the "transition region," assuming a Chapman production function q(z) with peak at z = 0 and a recombination coefficient U, independent of height ........................ 76 17 Relative ion concentration vs altitude for three rocket flights ............. - ............ 78 18 Idealized distributions of electrons (e) and of O+, He + and H+ ions, computed by solving Eqs. (III-59), (III-60) 87 19 Equilibrium electron density distribution N(z) for the F2 layer ........................ 91 - v - SEL-64-111 Figure Page 20 Concentrations of positive ions, negative ions and electrons vs altitude for a very quiet sun ........ 96 21 Average diurnal variation for the I0 International Quiet Days in each month at Slough ............... 103 22 N(t) curves, showing the average diurnal variation of electron density at fixed altitudes for magnetically quiet days during one month at Slough .......... 104 23 Loss coefficient at 300 km, _(300), as a function of temperature and 10.7 cm solar flux density for noon and midnight ......................... Iii 24 Illustrating the variation of production rate on a control day and the production rate and maximum E region elec- tron density on the day of a hypothetical total eclipse 113 25 The Sq variation in AX, _Y and AZ at various latitudes ........................ 134 26 The overhead current system corresponding to the external part of Sq for sunspot minimum, equinoctial conditions 136 27 Block diagram of the dynamo theory, showing its mechanical and its electrodynamic aspects .............. 141 28 Amplitude and phase angle of the semidiurnal pressure variation, as a function of height ............ 143 29 Idealized trajectories for electrons and ions subject to an electric field in the plane of the diagram and a magnetic field directly out of the plane ......... 145 30 Mobilities for a single charged species, as a function of reduced height z .................... 147 31 Conductivities per ion pair (JO' ffl' if2' _3 ) plotted on a logarithmic scale relative to the value Ne/B, as a function of reduced height z for an idealized isothermal model atmosphere ..................... 149 32 Dst variations of NmF2 in each of eight latitude zones for strong and weak magnetic storms which exhibit sudden commencements ...................... 170 33 Streamlines of the magnetospheric convection in the earth's equatorial plane 176 SEL-64-111 - vi - I. THE NEUTRAL ATMOSPHERE I. Atmospheric NomenclatUre The scientific study of the upper atmosphere has'become known as ii_ _ aeronomy. As generally happens in the study of a complex natural system, nomenclature has been developed to describe the different parts of the atmosphere (Chapman, 1950). The description may be based on chemical composition or on temperature or on the dominant physical processes. For each of these alternatives there exists a series of words terminating in "-sphere," each using some property to characterize the atmosphere within a certain range of altitude. The upper boundary of any "-sphere" may be denoted by a similar word ending in "-pause"; thus, the "tropopause" is the upper bound of the troposphere. Sometimes these levels can be defined to within a few kilometers, but in other cases, the "-pause" nomenclature is inappropriate because the divisions can only be specified within tens or hundreds of kilometers. Figure 1 contains all the "-sphere" terms that occur in this review. I0000 6370 EARTH RADIUS 3OO0 ] PROTONOSPHER£ 1000 MAGNETOSPHERE / EXOSPHERE ) HELIOS_ _" E 5O0 _/ F 200NOSPHERE x v THERMOSPHERE seporot,on auroras FI_,. _oo furbopause meteors "" E'_ mesopouse 5 30 MESOSPHERE mixing OZONOSPHERE ST RATOSPHERE I0 ropopause TROPOSPHERE l | .l I _ l t 500 IOOO 15OO I0 5 0 TEMPERATURE E_CTRON DENSITY 32027 T('K) N(lOII _3 ) FIG. I. REGIONS OF THE ATMOSPHERE, SHOWING CONVENTIONAL NAMES DESCRIPTIVE OF LEVELS, PHYSICAL REGIMES, AND CHARACTERISTIC CON- STITUENTS. The temperature profile is taken from the U.S. Standard Atmosphere and the electron density profile represents average daytime conditions for middle latitudes, high solar activity. - 1 - SEL-64-111 The lowest layer is the troposphere, in which the composition is uniform and the temperature generally decreases upward. The emission and absorption of infrared radiation by molecules such as water vapor, carbon dioxide and ozone provides the most efficient transfer of heat between different levels in this region. If we solve simplified equations for radiative transfer, we find that the equilibrium temperature in the lower atmosphere decreases approximately linearly with the partial pressure of these constituents. At low heights, this would lead to a "lapse rate" (negative temperature gradient) exceeding the "dry adiabatic lapse rate," which is about i0 °K/km. Such a situation is unstable and the lapse rate is maintained by turbulence and water vapor condensation at a somewhat smaller value, about 7 °K/km, throughout the troposphere. Under certain conditions, particularly at night, "inversions" may be set up in which the temperature gradient near the ground is positive. Until the turn of the century, it