Auroral and thermospheric response to the 9 day periodic variations in the dayside reconnection rate in 2005

Abstract

[1] In this paper we seek the means to forecast changes in thermospheric composition. In particular, we focus on a period where there was a strong 9 day periodicity in the high-latitude drivers, as this provides the best opportunity to explore our ability to determine the signature of the drivers that change the thermosphere. Using measurements from ACE and TIMED/GUVI in 2005, we establish a link among the dayside magnetic merging rate (MMR), auroral hemispheric power (HP), thermospheric neutral density, and temperature as all of them showed a clear 9 day variation. The magnitude of the 9 day variation in the thermospheric temperature increased from the equator (∣latitude∣ < 30) to the midlatitude (30 < ∣latitude∣ < 45) and reached its peak values at high latitudes (45 < ∣latitude∣ < 90). These observations confirm that changes in thermospheric composition are created locally at high latitude (i.e., in the auroral zone). These composition changes then expanded to lower latitudes due to the global thermosphere circulation. The correlation among the drivers (MMR and HP) and the thermospheric density/temperature provides an opportunity to establish a forecast relationship between solar wind and IMF measurements and thermospheric conditions. The 9 day periodic variation in HP and the thermosphere also leads to periodic variations in ionosphere electron density/conductance and field-aligned currents. All these changes strongly impact satellite drag, satellite surface charging, and radio frequency propagation.