The effect of mid-latitude electron precipitation on the geoelectric field

A simple model is outlined to describe electron precipitation from the population of charged particles trapped in the Earth's magnetic field; almost all of the precipitation is shown to occur in the region of the South Atlantic Anomaly (SAA). When the effect of a dawn-to-dusk electric field across the magnetosphere is included in the model, a diurnal modulation of the precipitated electron flux is predicted. Experimental evidence which supports the diurnal modulation model is described; the measurements which are discussed are principally those from University of Houston rocket payloads flown in the region dominated by the SAA. The resulting diurnal variation in atmospheric conductivity in the SAA is shown to be such that it could account for part of the daily UT variation in the geoelectric field. The observed seasonal variation in the pattern of geoelectric field modulation is also shown to be consistent with the proposed source of the daily variation. The difficulty of altering global conductivity by intense ionization of the mesosphere is discussed and the point is made that further in situ investigation of the Antarctic mesosphere is needed.     

Relativistic electron precipitation and resonance with ion cyclotron waves

It is shown that only highly relativistic electrons can resonate with ion-cyclotron waves when finite temperatures are considered. The application to dayside relativistic electron precipitation events is discussed.     

Morning sector electron precipitation events observed by incoherent scatter radar

Two auroral zone electron precipitation events in the morning sector have been studied in detail using the UHF incoherent scatter radar in northern Scandinavia. The electron density profiles are interpreted in terms of the incoming spectrum of energetic electrons, and it is shown that the spectrum is most energetic at the maximum of the event and softens subsequently. The observations cannot be explained by simple gradient-curvature drift of trapped electrons. It is shown, further, that events appearing to be fresh substorms in magnetometer and riometer data may be no more than intensifications of continuing activity. During a pulsation event the incoming electron spectrum was modulated in energy as well as in intensity. The height and thickness of the resulting radio-absorption layers are derived.     

On the effect of electron precipitation on the fair-weather electric field

In this short paper we have estimated the influence of the diurnal modulation of the electron precipitation at low and middle latitudes of the South Atlantic Magnetic Anomaly (SAMA) on the fair-weather electric field. We have used simple exponential atmospheric conductivity models, together with the ion production rates determined from balloon and rocket measurements in the SAMA. An upper limit to this influence was also calculated and compared with the normal diurnal variation of the fair-weather electric field due to the diurnal variation of the global thunderstorm activity.     

Broad-band auroral VLF hiss and inverted-V electron precipitation in the polar magnetosphere

A polar map of the occurrence rate of broad-band auroral VLF hiss in the topside ionosphere was made by a criterion of simultaneous intensity increases more than 5 dB above the quiet level at 5, 8, 16 and 20 kHz bands, using narrow-band intensity data processed from VLF electric field (50 Hz–30 kHz) tapes of 347 ISIS passes received at Syowa Station, Antarctica, between June 1976 and January 1983.The low-latitude contour of occurrence rate of 0.3 is approximately symmetric with respect to the 10–22 MLT (geomagnetic local time) meridian. It lies at 74° around 10 MLT, and extends down to 67° around 22 MLT. The high-latitude contour of 0.3 lies at invariant latitude of about 82° for all geomagnetic local times. The polar occurrence map of broad-band auroral VLF hiss is qualitatively similar to that of inverted-V electron precipitation observed by Atmospheric Explorer.(AE-D) (Huffman and Lin, 1981, American Geophys. Union, Geophysics Monograph, No. 25, p. 80), especially concerning the low-latitude boundary and axial symmetry of the 10–22 h MLT meridian.The frequency range of the broad-band auroral VLF hiss is discussed in terms of whistler Aode Cerenkov radiation by inverted-V electrons (1–30 keV) precipitated from the boundary plasma sheet. High-frequency components, above 12 kHz of whistler mode Cerenkov radiation from inverted-V electrons with energy below 40 keV, may be generated at altitudes below 3200 km along geomagnetic field lines at invariant latitudes between 70 and 77°. Low-frequency components below 2 kHz may be generated over a wide region at altitudes below 6400 km along the same field lines. Thus, the frequency range of the downgoing broad-band auroral hiss seems to be explained by the whistler mode Cerenkov radiation generated from inverted-V electrons at geocentric distances below about 2 R_E (Earth's radius) along polar geomagnetic field lines of invariant latitude from 70 to 77°, since the whistler mode condition for all frequencies above 1 kHz of the downgoing hiss is not satisfied at geocentric distance of 3 r_e on the same field lines.     

An attempt to derive electron energy spectra for auroral daytime precipitation events

A set of quiet daytime electron density profiles is established on the basis of EISCAT measurements. This set is used as a background correction in the CARD program [Brekke A., Hall C. and Hansen T.L. (1989) Ann. Geophysicae7, 269] in order to derive the energy spectra of precipitating electrons at daytime.For disturbed daytime events on 25–26 June 1985, we find that the particle precipitation typically consists of small fluxes (10⁵ el/cm² sster keV) of high energetic particles (20–30 keV). The Hall: Pedersen conductance ratios for such events are found to be meaningless as an indicator of the energy of the particles, in contrast to nighttime precipitation.     

Energetic electron precipitation at the South Atlantic Magnetic Anomaly: a review

This paper reviews the status of knowledge concerning energetic electron precipitation at the South Atlantic Magnetic Anomaly (SAMA). The main purpose is to place recent results in the context of the long-standing problems about energetic electron precipitation at the SAMA region. A synopsis of results achieved in the last two decades, in relation to the various physical mechanisms responsible for precipitating energetic electrons, are also presented. The major uncertainties in the understanding of the energetic electron precipitation at the SAMA include: (1) temporal and spatial precipitation changes from magnetically quiet to disturbed periods; (2) the role of wave-induced precipitation processes.     

Spread-F and ionization anomaly belt

The present investigation attempts to bring out the dynamics of the F-region at magnetic equatorial and low latitudes in the American zone. Data are examined for two sets of nights, one with strong range-type spread at Huancayo another with complete absence of spread-F. A prominent bulge of the F-region was observed within and below a latitude 10°N in the evening hours of the spread-F nights. Contours of electron distribution during post-sunset hours at the equatorial latitude, Huancayo (Dip 2°N); low latitude, Talara (dip 13°N); and a location near the anomaly crest location, Panama (dip 38°N), indicated a much steeper gradient in electron density at fixed heights on spread-F nights compared to a rather low gradient on the nonspread-F nights. Enhanced concentration of electrons at the anomaly crest location Panama, and a lower density at the equatorial location Huancayo, were observed on spread-F present nights. This is attributed to the phenomena of an evening plasma fountain in operation at equatorial latitudes on spread-F nights.     

The effect of electric field-induced vertical convection on the precipitation E-layer

The effects of perpendicular electric fields on the high-latitude nocturnal precipitation E-layer are studied in terms of model calculations. The deformations of the electron density profiles caused by vertical plasma movements are described assuming various incident electron energies and flux densities, as well as different field intensities and directions. Manifestations of the profile variations in vertical sounding observations and changes in the conductivity profiles are examined. The results show that field-induced vertical convection is important in plasma densities even higher than 10¹¹ m⁻³. Erroneous results may be obtained if the effect of the electric field is neglected when determining the incident electron spectrum from a measured ionospheric density profile.     

The relationship between electron temperature and electron density under quiet conditions in the auroral zone

A theoretical model is described which predicts electron temperature in the day-time F-region above EISCAT on geomagnetically quiet days, given the observed values of electron concentration, ion temperature and heat conduction, the daily average of solar radiation at 10.7cm and the MSIS-86 model of the neutral atmosphere. The values predicted by the model agree very closely with the observed temperatures, both for average conditions and for individual days. On two occasions the onset of a geomagnetic disturbance after a period of quiet conditions was accompanied by a growing divergence between the predicted and observed values, which corresponds to an additional source of electron heating such as would be provided by low energy particle precipitation.     

鄂尔多斯博物馆馆藏北魏鎏金带饰的保护

鄂尔多斯博物馆馆藏的北魏时期鎏金铜带饰,体现了鲜卑族高超的铸造及鎏金工艺,是研究北魏时期冶金技术及工艺技术的珍贵实物资料.     

Emergence of the American manufacturing belt: an interpretation

This study proposes that the American manufacturing belt emerged during the antebellum years as a replicated set of regional industrial systems. A broad-based set of demands spurred the growth of regional manufactures, including the pivotal producer durables sector. Eastern regions industrialized first, and they were followed by frontier regions in the Midwest. The relative importance of regional market manufactures declined over time and multiregional/national market manufactures increased. Regional industrial systems became increasingly specialized; the result was higher levels of interregional trade in industrial specialties. The decline of regional market manufactures eroded the bases for the emergence of regional industrial systems by the 1860s. The westward spread of the manufacturing belt ended, and internal differentiation and structural change within the belt were characteristics of late nineteenth century industrialization. The South failed to join the manufacturing belt during the antebellum years because regional demands for manufactures were insufficient to support important regional industrial systems. It lacked the bases to participate significantly in late nineteenth century industrialization.     

Solar-induced variation of proton precipitation near the equator

This paper reports the solar condition dependences of the quasi-trapped component (low energy) of the proton population of energy 0.65–35 MeV which peaks in the equatorial zone centered on the minimum magnetic field equator in the altitude range 170–850 km. The proton populations compared pertain to AZUR observation in 1969–1970, S81-1 mission observation in 1982 and EXOS-C observation during 1984–1986. In the equatorial zone, the dependence of the flux normalization constant, which represents the absolute proton population, upon factors like L (1.1–1.3), B (0.29–0.32 gauss), latitude ( ± 20°), longitude (0–360°) and anisotropy index q (~6–12) of the pitch angle distribution function is not so significant in the given range of these factors as it is upon the solar epoch. It is found that the absolute proton flux in 1982 was, at least, forty times that in 1984–1986 and, almost, three times that in 1969–1970, possibly, due to, varying solar conditions in those epochs.     

The effects of ionospheric horizontal electron density gradients on whistler mode signals

Whistler mode group delays observed at Faraday, Antarctica (65° S, 64° W) and Dunedin, New Zealand (46° S, 171° E) show sudden increases of the order of hundreds of milliseconds within 15 minutes. These events (‘discontinuities’) are observed during sunrise or sunset at the duct entry regions, close to the receiver's conjugate point. The sudden increase in group delay can be explained as a tilting of the up-going wave towards the sun by horizontal electron density gradients associated with the passage of the dawn/dusk terminator. The waves become trapped into higher L-shell ducts. The majority of the events are seen during June-August and can be understood in terms of the orientation of the terminator with respect to the field aligned ducts. The position of the source VLF transmitter relative to the duct entry region is found to be important in determining the contribution of ionospheric electron density gradients to the L-shell distribution of the whistler mode signals.     

K-shell X-ray fluxes at satellite altitude from proton precipitation

A sample calculation is presented of K-shell X-ray emission resulting from energetic proton precipitation into the upper atmosphere. It is found that intense fluxes of K-shell X-rays at low satellite altitudes (450 nautical miles) can result from observed fluxes of precipitating protons.     

The electron content of the ionosphere and the Southern boundary of diffuse Aurora

Measurements of latitudinal dependence of ionospheric electron content over Europe exhibit strong enhancements around 60° geomagnetic latitude, occuring during some winter nights. One of these events — on December 4th, 1977 — could be related to the precipitation of soft electrons (<400 eV) at the equatorward boundary of a bright diffuse Aurora.