Multi-day Periodicities in Thermosphere Density during the Declining Phase of Solar Cycle 23

Jiuhou Lei, Jeffrey P. Thayer, Jeffrey M. Forbes, Eric K. Sutton, and R. Steven Nerem

Department of Aerospace Engineering Sciences University of Colorado

Outline

1. CHAMP Density in 2005

2. Solar Activity Dependence of Multi-day Periodicities

3. Preliminary Comparison between Data and TIEGCM

CHAMP density in 2005

27 days/3

Lei, J., J. P. Thayer, J. M. Forbes, E. K. Sutton, and R. S. Nerem (2008), Rotating solar coronal holes and periodic modulation of the upper atmosphere, Geophys. Res. Lett., 35, L10109, doi:10.1029/2008GL033875.

Thermospheric density response to solar wind: 2005-2007

ascend

descend

Thermospheric density response to solar wind: 2002-2004

ascend

descend

Solar Activity Dependence

Latter part of the declining phase

Correlation between density oscillations and Kp

Percent of the band-pass filter density residuals to 11-day running mean. The band-pass filter was centered at the period of 9 days.

Correlation from 2002 to 2007

1. The neutral densities show the presence of several prominent

periods around 9, 7, and 5 days from 2004-2007, with the most

pronounced periodicities of 9 and 7 days observed in 2005, and

2006, respectively.

2. The periodicity of neutral density highly correlates with that of

geomagnetic activity and solar wind parameters during the latter

part of the declining phase. This solar activity dependence of the

periodicities is explained by the corresponding variations of high-

speed solar wind and the associated geomagnetic activity.

Lei, J., et al. (2008b), Global thermospheric density variations caused by high-speed solar wind streams

during the declining phase of solar cycle 23, J. Geophys. Res., doi:10.1029/2008JA013433, in press.

Summary I

Preliminary Comparison for Mass Density

Preliminary Comparison for O/N2

Lei, J., et al. (2008), Ionosphere Response to Solar Wind High-Speed Streams, Geophys. Res. Lett., doi:10.1029/2008GL035208

Ionospheric response

9- and 7-day periodic oscillations are also present in the global mean Total Electron Content (TEC) from 1 January 2005 to 31 December 2006. Spectral analysis indicates that the pronounced periodicities of 9 and 7 days observed in TEC are associated with variations in solar wind high-speed streams and geomagnetic activity.

Summary II