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Narrow precipitation spikes of energetic electrons observed in the inner zone drift loss cone during the 1968–1970 period by instrumentation on the OV1‐14 and OV1‐19 satellites are shown to have characteristics which are consistent with pitch angle scattering produced through a resonant interaction with ground‐based VLF transmissions. Analysis of the pitch angle distributions indicates that for virtually all of the events the electrons last interacted with the atmosphere in the vicinity of 55°–62° east longitude. The L dependency of the spikes as a function of energy is consistent with scattering by a monochromatic wave. The presumption is that the Russian station UMS, located at 44°E and operating at a frequency of 16.2 kHz during this period, was responsible for these precipitation events.

The precipitation of energetic electrons which are commonly observed in the drift loss cone east of 60° east longitude between L ∼1.6 and L ∼1.8 can be accounted for by a Doppler‐shifted cyclotron resonance between the electrons and nonducted whistler mode waves from high‐power, ground‐based VLF transmitters. A ray‐tracing analysis using a diffusive‐equilibrium model shows that 17.1‐kHz waves starting with vertical wave normals between 23° and 31° magnetic latitude cross the magnetic equator between L ∼1.6 and f L ∼1.8 with wave normals of approximately 63°. A relativistic cyclotron‐resonance analysis for the same model plasmasphere using the ray‐tracing results gives an energy versus L shell dependence for the precipitated electrons which is in excellent agreement with the observed dependence. The primary VLF transmitter is most probably the UMS transmitter located near Gorki, USSR. It transmits on 17.1 kHz. VLF records covering this frequency band were available for only three of the time periods when electrons were observed. In two cases UMS was transmitting at the time required to account for the observations. In the third case a higher frequency is required to fit the data. At the time, the NWC transmitter at North West Cape, Australia was operating at 22.3 kHz. These data are consistent with a model in which weak pitch angle scattering by whistler mode waves from NWC does not completely fill the drift loss cone at the longitude of NWC.

Spectra of locally precipitating 36-to 317-keV electrons obtained by instrumentation on the S3-2 satellite are used to calculate energy deposition profiles as a function of latitude, longitude, and altitude. In the 70-to 90-km altitude, mid-latitude ionization due to these precipitating energetic electrons can be comparable to that due to direct solar H Lyman a. At night, the electrons produce ionization more than an order of magnitude greater than that expected from scattered H Lyman a. Maximum precipitation rates inthe region of the South Atlantic Anomaly are of the order of 10 -2 erg/cm 2 s with a spectrum of the form j(E) = 1.34 x 105 E -2'27 (keV). Southern hemisphere precipitation dominates that in the north for 1.1 < L < 6 except for regions of low local surface field in the northern hemisphere. Above L -6, local time effects dominate; i.e., longitudinal effects due to the asymmetric magnetic field which are strong features below L = 6 disappear and are replaced by highlatitude precipitation events which are local time features. INTRODUCTION The study of atmospheric ionization sources has been a topic of considerable interest for a number of years (see, for example, Rosenberg and Lanzerotti [1979] and references therein). Middle-atmospheric ionization due to energetic particle or electromagnetic wave penetration affects the propagation of VLF communications signals [Potemra and Zmuda, 1970], and Crutzen et al. [1975], Thorne [1977], and Reagan et al. [1978] have suggested that minor neutral species concentrations might be significantly affected by variations in the middle atmospheric energy input. Other effects of magnetospheric and extraterrestrial penetrating radiation, including possible influences on weather-related phenomena [e.g., Roberts and Olson, 1973a, b; Markson, 1978] and atmospheric aerosol formation [Mohnen and Kiang, 1978], have been discussed. Galactic cosmic rays, solar X rays and H Lyman a emissions, energetic solar protons, auroral electrons, and energetic precipitating radiation belt electrons and their associated bremsstrahlung X rays have been identified as significant middle-atmosphere ionization sources (see reviews by Potemra and Zmuda [1970], Potemra [1973, 1974], and Reagan [1977]). For each of these ionization sources, attempts have been made to estimate the long-term 'average' ionization as a function of altitude and latitude, as well as the variations expected during strong 'events.' In this paper we concentrate on evaluating the long-term contribution of precipitating magnetospheric electrons to middle-atmosphere ionization in the high-, middle-, and low-latitude regions. The extremely large data set acquired by the S3-2 spacecraft (over 107 samples per channel) has allowed us to examine the latitude and geographic longitude dependence of electron precipitation. For example, we can compare precipitating electron fluxes and their atmospheric effects in regions of anomalously low surface magnetic field (such as the South Atlantic Anomaly (SAA)) to longitudinally averaged values...