The dynamics and relationships of precipitation, temperature and convection boundaries in the dayside auroral ionosphere

Abstract

Abstract.A continuous band of high ion temperature, which persisted for about 8 h and zigzagged north-south across more than five degrees in latitude in the dayside (07:00-15:00 MLT) auroral ionosphere, was observed by the EIS-CAT VHF radar on 23 November 1999. Latitudinal gradients in the temperature of the F-region electron and ion gases (T e and T i , respectively) have been compared with concurrent observations of particle precipitation and field-perpendicular convection by DMSP satellites, in order to reveal a physical explanation for the persistent band of high T i , and to test the potential role of T i and T e gradients as possible markers for the open-closed field line boundary. The north/south movement of the equatorward T i boundary was found to be consistent with the contraction/expansion of the polar cap due to an unbalanced dayside and nightside reconnection. Sporadic intensifications in T i , recurring on ∼10-min time scales, indicate that frictional heating was modulated by time-varying reconnection, and the band of high T i was located on open flux. However, the equatorward T i boundary was not found to be a close proxy of the open-closed boundary. The closest definable proxy of the open-closed boundary is the magnetosheath electron edge observed by DMSP. Although T e appears to be sensitive to magnetosheath electron fluxes, it is not found to be a suitable parameter for routine tracking of the open-closed boundary, as it involves case dependent analysis of the thermal balance. Finally, we have documented a region of newly-opened sunward convecting flux. This region is situated between the convection reversal boundary and the magnetosheath electron edge defining the openclosed boundary. This is consistent with a delay of several minutes between the arrival of the first (super-Alfvénic) magnetosheath electrons and the response in the ionospheric convection, conveyed to the ionosphere by the interior Alfvén wave. It represents a candidate footprint of the low-latitude boundary mixing layer on sunward convecting open flux.

Motion of the dayside polar cap boundary during substorm cycles: II. Generation of poleward-moving events and polar cap patches by pulses in the magnetopause reconnection rate

“…The second was by F12 which crossed the OCB at 12:24 MLT and 9:01 UT (when the EISCAT beam 1 was near 11:46MLT) and is shown in Fig. 5 of Moen et al (2004). Both these passes showed small stepped cusp ion signatures which, given the association with poleward-moving events, are consistent with rapid magnetopause reconnection rate pulses, as predicted by Cowley et al (1991b) and Lockwood and Smith (1992).…”

“…1, 2 and 4, except at the lowest latitudes early in the interval, where it is eastward. This region of sunward flow is that discussed by Moen et al (2004) and the equatorward edge of the patches shown in Fig. 1a is the green line drawn in Fig.…”

“…The patches between the deeper minima last for of order 10 min, giving patch sizes L p of order 1700 km in the direction of motion), whereas the patches between the more shallow minima last for of order 2 min giving L p ≈340 km. Davies et al (2002) and Moen et al (2004) have noted that the ion temperatures at the time of many of these events showed transient enhancements, implying that the polewardmoving density structures were connected to transient flow and reconnection bursts. Figure 2 confirms that there is some association between the patches and reconnection rate pulses.…”

“…Davies et al (2002) have shown that some of these patches are linked to poleward-moving events seen by the HF CUTLASS SuperDARN radar at Hankasalmi. A full description of the interplanetary conditions, seen by the Wind and ACE satellites, has been given in Paper I and by Moen et al (2004). The response in the polar cap detected by the EISCAT VHF radar, the auroral electrojet magnetometers and by various DMSP satellites, is also presented in Paper I, along with an analysis of the local reconnection rate around EISCAT beam 1.…”

“…6 of Paper I and Fig. 5 of Moen et al, 2004). If the polar cap patches (high N e -low T e ) were remnants of precipitation, in no case did either of the EISCAT beams intersect the source precipitation region (which would be identified by elevated N e and T e ).…”