Solar wind plasma entry into the magnetosphere under northward IMF conditions

Abstract

[1] This study examines how solar wind plasma enters the magnetosphere under northward interplanetary magnetic field (IMF) conditions, using the Open Geospace General Circulation Model (OpenGGCM) for various solar wind, IMF, and geomagnetic dipole conditions. We trace flow paths of individual fluid elements from the solar wind and study the variation of the topology of the magnetic field line along those flow paths. We find that there is an entry window through which the solar wind plasma can enter the magnetosphere as a result of double high-latitude reconnection under northward IMF conditions. We investigate how the entry window depends on solar wind, IMF, and geomagnetic dipole parameters, and we estimate the solar wind plasma entry rate for various conditions. We find that the effective entry rate under northward IMF conditions is of the order of 10 26 to 10 27 particles per second. We also estimate the conditions for which solar wind plasma entry is most efficient. The newly created flux tubes with closedfield topology are subsequently convected to the nightside and consequently cause magnetosheath plasma to be captured and enter the magnetosphere. Some captured dayside plasma takes about 90 min to convect along the magnetopause to a near tail flank region of the central plasma sheet, thus forming a cold dense plasma sheet. Double highlatitude reconnection can also release the captured plasma. Thus a balance of inflow and outflow of the captured plasma is eventually established under prolonged northward IMF conditions. We find that high-latitude reconnection is common under northward IMF conditions in our simulations. It occurs for IMF with any clock angle within [À90°, 90°], measured in front of the bow shock, and for any geomagnetic dipole tilt angle within [À30°, 30°]. An IMF field line with a zero x component usually first reconnects with a geomagnetic field line at the northern high-latitude boundary when the geomagnetic dipole tilts positive toward the Sun, and vice versa for negative dipole tilt. Our simulations also show that ionosphere conductance affects the convection of the newly closed field lines. Consequently, ionosphere conductance can change the solar wind plasma effective entry rate and can cause asymmetric effective entry rate with respect to positive and negative IMF clock angles.

Solar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times

“…If these particles enter within 1 min (observed periodicity of pulsed reconnection at the high-latitude magnetopause 43 ), the entry rate can be estimated to be of the order of between 10 24 and 10 27 particles per second for different events. The upper value is comparable to estimations of entry rates during active times 7,44 , and also consistent with recent global MHD simulation results 22 of 10 26 -10 27 particles per second during northward IMF. If reconnection is continuous 45 instead of pulsed, the entry process will be continuous and then the entry rate can be even larger.…”

“…The entry region locations at the high latitude that are predicted by the simulations (the yellow or green regions of Fig. 2(6) of Li et al 22 ) are very well consistent with our observations. Moreover, the density is higher at the near-Earth locations (Fig.…”

“…Although previous studies have demonstrated that enhanced amounts of plasma enter to form a relatively thick, lowlatitude boundary layer 2,12,13 and a denser plasma sheet 13,14 when the IMF is northward even during quiet times, the dominant mechanism of solar wind entry into the magnetosphere (and entry location on the magnetopause) under these conditions is less clear and still controversial. It is still not very clearly understood whether the entering plasma is a result of the highlatitude MR 12,[15][16][17][18][19][20][21][22] , impulsive penetration 23,24 , or from the low latitudes through instabilities 25,26 or gradient drift 27 .…”

“…Previous observations have shown that the magnetospheric lobe 6,7 , which occupies the majority of the magnetotail volume in the high latitudes, typically forms a reservoir of magnetic energy 28 , consisting of tenuous, low energy ions of internal, ionospheric origin 7,29 . Although observations 30 and numerical simulations [20][21][22] have inferred that plasmas from outer regions, for example, compressed solar wind in the magnetosheath, may enter the highlatitude lobe regions, direct observations of these plasmas inside are rare, partly because high-latitude lobes tailward of the mid-altitude cusps have seldom been explored in situ, restricting our ability to gain an understanding of this region. The four-satellite Cluster mission, however, uniquely has both sufficient polar orbital coverage ( Fig.…”

X lines in the magnetotail for southward and northward IMF conditions

“…The energy stored for the triggering of the X lines and the substorm in the tail under northward IMF is just the remnant energy in the period of preexiting southward IMF [Li et al, 2008;Du et al, 2011;Miyashita et al, 2011]. Due to the weaker convection electric field for northward than southward IMF [Maezawa, 1976;Usadi et al, 1993;Borovsky et al, 1998;Petrukovich et al, 2003;Wang et al, 2006], it is prone to conjecture that not enough energy and/or magnetic flux can be deposited in the tail to form a thin current sheet and generate an X line under northward IMF condition [Min et al, 1985;Ma et al, 1995;Pritchett and Coroniti, 1994;Petrukovich et al, 2011].…”