The shift of the auroral electron precipitation boundaries in the dawn‐dusk sector in association with geomagnetic activity and interplanetary magnetic field

Abstract

On the basis of the auroral precipitating electron data along the dawn‐dusk meridian from a Defense Meteorological Satellite Program satellite (DMSP‐F2), we show that the electron precipitation region extends poleward, often to the geomagnetic latitudes ≳85° from the average oval location, during quiet periods (namely, during periods of a large positive Bz component). This result may be interpreted as an indication that only a small amount of geomagnetic flux interconnects with the northward IMF, resulting in a contracted “open” region (the polar cap). The control of the location of the poleward boundary by the north–south component of the IMF is also statistically examined. The rate of latitudinal movement is about 0.4° to 0.8° per 1 nT for positive IMF Bz values and about 0.7° to 1.1° per 1 nT for negative IMF Bz values. The shift of the equatorward boundary is not obvious, however, for positive IMF Bz values. As geomagnetic activity increases, both the poleward and equatorward boundaries shift toward lower latitudes. The equatorward shift of the poleward boundary is greater than that of the equatorward boundary, resulting in a thinner electron precipitation region during disturbed periods than during quiet periods.

Polar cap ion beams during periods of northward IMF: Cluster statistical results

“…On the other hand, during periods of northward IMF the lobe region shrinks (e.g. Makita et al, 1983). However, there is observational evidence that most of the time -and whatever is the IMF orientation -there exists a lobe region only populated by cold plasma undetected by particle detectors (e.g.…”

Estimating the location of the open-closed magnetic field line boundary from auroral images

“…The location of the OCB can be best estimated from measurements of particle precipitation boundaries (PPB) made by satellites in low-altitude orbits (e.g., Vampola, 1971;Makita et al, 1983;Makita and Meng, 1984;Newell et al, 1991;Mishin et al, 1992;Newell et al, 1996;Sotirelis and Newell, 2000). However, whilst these PPBs are considered to provide the best proxy of the OCB, they typically provide only infrequent, point measurements of this boundary.…”

Features of Particle Precipitation in the Cusp Region as Observed by DMSP Satellite.

“…oval determined by ion precipitation accordingly to the criteria of TROSHICHEV and NIsHIDA (1991). The dashed lines indicate the transition boundary determined by electron precipitation (MAKITA et al,1983). As Fig.…”

“…The cusp is localized near the noon with a 2-3 hours length in MLT and =1 ° width in latitude, whereas the cleft may be extended to the dawn-dusk meridian and further. Until recently the main attention was paid to electron characteristics in the studies about the auroral oval position, the structure and the intensity of a precipitation (KAMIDE et x1.,1976;ZANETTI et x1.,1981;MENG,1982MAKITA et al,1983MAKITA et al, ,1985MAKITA et al, ,1988CANDIDI et al, 1983;MAKITA and MENG, 1984;CANDIDI andMENG, 1984,1988;HARDY, 1984;HARDY et al, 1985;CARBARY andMENG,1986a, b,1988;GUSSENHOVEN et al,1987), and only a few papers were devoted to the features of the proton and ion precipitation in the dayside oval and the polar cap (HILL and REIFF,1977;REIFF et al, 1979;POTEMRA et al,1978;SAUVAUD et al,1980). Some progress in the study of auroral ion features is due to a successful realization of Defense Meteorological Satellite Program.…”