Correlations of ionospheric electric fields and energetic particle precipitation

Abstract

Direct measurements of the thermal ionospheric ion distribution function made from two sounding rockets launched into the expansive phase of an auroral substorm are discussed. Ion flows perpendicular (convective) and parallel to the geomagnetic field lines are derived from these observations at altitudes from 200 to 840 km. Equivalent convective electric fields were observed to vary between a few tens of millivolts per meter to over 150 mV/m and are shown to be highly correlated with energetic electron precipitation. High‐velocity (up to 2 km/s) parallel ion flows were observed at various times and also found to be correlated with auroral electron precipitation. A correlation analysis of perpendicular (or equivalent electric fields E⊥) and parallel ion flow velocities with energetic electron intensities I at various energies is presented. The form of the E⊥ versus the logarithm of I relationship is shown to be approximately linear over most of the observed E⊥ range. Ionospheric ‘line‐tying’ models are presented and compared with the measured E⊥ versus I relationship. The model is found to be most consistent with observations when magnetospheric forces are assumed to be independent of the instantaneous values of E⊥ and I rather than viscouslike. No evidence was found to suggest that decoupling of magnetospheric and ionospheric convection through parallel electric fields produced the observed anticorrelation of E⊥ and I.

Plasma Flow in the North‐South Aligned Discrete Aurora Equatorward of the Cusp

“…For the plasma flow depression coincident with the auroral arc, a similar tendency has been previously identified in observations made premidnight (e.g., Evans et al, 1977;Wescott et al, 1969), near midnight (e.g., Maynard et al, 1973;Potter, 1970;Whalen et al, 1975), and postmidnight (e.g., Hosokawa et al, 2010;Juusola et al, 2016). The present study has shown that this tendency can also occur in the noon sector.…”

Relative contribution of ionospheric conductivity and electric field to ionospheric current

“…Figure 9 shows the distributions of the Pedersen (left panels) or Hall (right panels) current density in both altitude and MLT according to current intensity levels. A variation of the current density in altitude is caused by the altitude variation of the conductivity, since the magnetic and electric fields can be assumed constant at a height down to about 90 km [ Whalen et al , 1975]. The distributions of the Pedersen current density are not changed so significantly with the current intensity levels.…”

“…The perpendicular electric field E is thus expressed as where v is the ion velocity measured in the F region, and the magnetic field B is derived from the International Geomagnetic Reference Field (IGRF1995) model [ Barton , 1997]. Since the magnetic field‐aligned electric field is much smaller than the perpendicular electric field, the magnetic field lines are assumed to be equipotential down to around 90 km in height [ Whalen et al , 1975].…”

Auroral vector electric field and particle comparisons, 1, Premidnight convection topology

“…All of these large parallel fields have been directed downward. Whalen et al [1975] measured ion velocities in both directions along the magnetic field in a negative bay (at different times during a flight) of 2 km/s, from which they deduced by using collision frequencies derived from Coulomb interactions a parallel field of 0.1 mV/m. The measurements reported here set an upper limit of +4 mV/m on the dc parallel electric field during the flight.…”