The influence of IMF By on the nature of the nightside high-latitude ionospheric flow during intervals of positive IMF Bz

Abstract

Abstract. This paper further addresses the issue of nightside flow bursts which occur during intervals of northward but strongly B Y -influenced IMF. Recent discussions of such bursts concerned intervals during which the IMF B Y component was negative. The present study concerns an interval of B Y -positive IMF which occurred on 20 March 2002 (01:00-12:00 UT). During the interval B Y increased steadily from ∼2 to 12 nT, whilst the B Z component decreased steadily from ∼10 to 0 nT. There was thus a ∼6-h sub-interval during which the IMF clock angle remained between 30 • and 60 • , such that moderate dayside reconnection and open flux production was maintained. It is found that flow bursts of a similar size and speed to those observed under B Y negative (∼1000 m s −1 , spanning 2-3 h of MLT in the midnight sector) also occur when B Y is positive. However, the direction of east-west flow is reversed, indicating that they are driven by processes in the magnetosphere which are directly related to the orientation of the IMF. It is suggested that they are caused by a reconfiguration of an asymmetric tail resulting from prolonged dayside reconnection with a B Y -dominated IMF. This is consistent with previous suggestions that they are associated with convective transport following reconnection in the more distant tail. Analysis of ground magnetic data, auroral images and geosynchronous particle data also show associated features, but indicate that the flow bursts are not directly associated with substorms.

Multi-instrumentation observations of a transpolar arc in the northern hemisphere

“…There are two cells which are not symmetrical and slightly biased toward dawn, as a consequence of the IMF By>0, (e.g., Russell, 1972;Cowley, 1981;Reiff and Burch, 1985;Cowley and Lockwood, 1992;Huang et al, 2000;Milan et al, 2000;Chisham et al, 2004). The bright spot in the premidnight sectors is associated with relatively strong eastward flows, similar to these reported by Senior et al (2002), Grocott et al (2003Grocott et al ( , 2004, and Walker et al (1998). Such flows are usually observed during episodes of magnetotail reconnection happening during extended intervals of northward IMF but with no evidence of substorm activity.…”

“…5b). Events termed TRINNIs are an important component of the magnetic flux transfer process within the magnetosphere (Grocott et al, 2003(Grocott et al, , 2004 and these are indicative of magnetic flux closure in the nightside. Data from the LANL geosynchronous satellites confirms the absence of any substorm activity in the interval of interest.…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…More recently, Grocott et al (2003Grocott et al ( , 2004cGrocott et al ( , 2005 have used SuperDARN to study nightside convection when the IMF was consistently northward, but dominated by a significant B y component. No classic substorm features were observed during these intervals, yet there was evidence in the ionosphere for flux closure occurring in the magnetotail at rates of *30-50 kWb/s Milan et al 2005a, b).…”

Space- and ground-based investigations of solar wind–magnetosphere–ionosphere coupling

“…It now appears that there are also intervals of tail reconnection that are not associated with the classic signatures of substorms (e.g. breakup aurora, magnetogram bays), which often occur during periods of northward IMF (Grocott et al, 2003(Grocott et al, , 2004Milan et al, 2005b). When the IMF is directed northwards dayside reconnection no longer occurs between closed terrestrial field lines and the IMF, but with lobe field lines -field lines that are already open (e.g.…”