Influence of the solar wind high-speed streams on the thermospheric neutral density during the declining phase of solar cycle 23

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Influence of the solar wind high-speed streams on the thermospheric neutral density during the declining phase of solar cycle 23

Verbanac, Giuliana / Bandić, Mario / Krauss, Sandro

Abstract Thermospheric neutral density derived from the GRACE A satellite and normalized at altitude of 490 km ( $ρ$ ) are used to investigate the $ρ$ behavior during the period of recurrent geomagnetic activity (25 January - 5 May, 2005) caused by solar wind high-speed streams (HSSs). The north and south hemispheric $ρ$ values divided in three latitudinal bins are analyzed separately at dayside and nightside. The variations, not caused by solar/geomagnetic activity, are investigated accounting for the relationship between solar flux index, illumination, latitude and DOY for particular magnetic local times (MLTs). Analysis has shown that: $ρ$ increases/decreases from high to low latitudes at dayside/nightside; $ρ$ increases from high to low latitudes at dayside caused by solar EUV radiation is most prominent around MLT = 14 and decrease rapidly with departure from this MLT; the difference between north and south hemispheric $ρ$ values are not the same prior and after the equinox; quiet time $ρ$ differs among latitudinal bins; $ρ$ contains a clear imprint of solar/geomagnetic activity. The cross-correlation analysis reveals a high degree of correlation between $ρ$ and different employed $ρ$ indicators. Time lags based on all $ρ$ indicators suggest that $ρ$ disturbance: occurs about 4 h earlier at high than at lower latitudes and propagates presumably without losses toward equatorial region both at dayside and nightside; propagates faster between polar and mid latitudes at dayside and between mid and low latitudes at nightside. This study provides the most probable characteristics of the $ρ$ variations during the periods in which magnetospheric-thermospheric system is affected primarily by HSSs.