 |
| Titel |
Climatology of the relationship of cusp-related density anomaly with zonal wind and large-scale FAC based on CHAMP observations: IMF By and solar cycle dependence |
| VerfasserIn |
Guram Kervalishvili, Hermann Lühr |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087156
|
| Publikation (Nr.) |
 EGU/EGU2014-1176.pdf |
|
|
|
|
|
| Zusammenfassung |
| We present climatology of the relationship of cusp-related density enhancement with the
neutral zonal wind velocity, large-scale field-aligned current (FAC), small-scale FAC,
and electron temperature using the superposed epoch analysis (SEA) method. The
dependence of these variables on the interplanetary magnetic field (IMF) By component
orientation and solar cycle are of particular interest. In addition, the obtained results of
relative density enhancement (Ïrel), zonal wind, electron temperature and FAC are
subdivided into three local seasons of 130 days each: local winter (1 January ±65 days),
combined equinoxes (1 April ±32 days and 1 October ±32 days), and local summer (1
July ±65 days). Our investigation is based on CHAMP satellite observations and
NASA/GSFC’s OMNI online data set for solar maximum (Mar/2002-2007) and minimum
(Mar/2004-2009) conditions in the Northern Hemisphere. The SEA technique uses the
time and location of the thermospheric mass density anomaly peaks as reference
parameters. The relative amplitude of cusp-related density enhancement does on
average not depend on the IMF By orientation, solar cycle phase, and local season.
Also, it is apparent that the IMF By amplitude does not have a big influence on the
relative amplitude of the density anomaly. Conversely, there exists a good correlation
between Ïrel and the negative amplitude of IMF Bz prevailing about half an hour
earlier.
In the cusp region, both large-scale FAC distribution and thermospheric zonal wind
velocity exhibit a clear dependence on the IMF By orientation. In the case of positive
(negative) IMF By there is a systematic imbalance between downward (upward) and upward
(downward) FACs peaks equatorward and poleward of the reference point, respectively. The
zonal wind velocity is directed towards west i.e. towards dawn in a geomagnetic
latitude-magnetic local time (MLat-MLT) frame. This is true for all local seasons and solar
conditions.
The thermospheric density enhancements appear half way between Region 1 (R1) and
Region 0 (R0) field-aligned currents, in closer proximity to the upward FAC region. In our
case R0 currents are systematically weaker than R1 ones. Also, around the cusp region we
find no sign of Region 2 field-aligned currents. We can conclude that there is a close spatial
relationship between FACs and cusp-related density enhancements, but we cannot offer any
simple functional relation between field-aligned current strength and density anomaly
amplitude. There seem to be other quantities (e.g. precipitating electrons) controlling this
relation.
All the conclusions drawn above are true for the Northern Hemisphere. There may be
differences in the Southern Hemisphere. |
|
|
|
|
|
|