A Study on the Ionosphere and Thermosphere Interaction Based on NCAR-TIEGCM: Dependence of the Interplanetary Magnetic Field (IMF) on the Momentum Forcing in the High-Latitude Lower Thermosphere

Details A Study on the Ionosphere and Thermosphere Interaction Based on NCAR-TIEGCM: Dependence of the Interplanetary Magnetic Field (IMF) on the Momentum Forcing in the High-Latitude Lower Thermosphere A Study on the Ionosphere and Thermosphere Interaction Based on NCAR-TIEGCM: Dependence of the Interplanetary Magnetic Field (IMF) on the Momentum Forcing in the High-Latitude Lower Thermosphere

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005jass...22..147k&link_type=abstract

Journal of Astronomy and Space Sciences. Vol. 22, no. 2, 147-174

Astronomy and Astrophysics

Astronomy

Momentum Forcing, High-Latitude Lower Thermosphere, Imf

Scientific paper

To understand the physical processes that control the high-latitude lower thermospheric dynamics, we quantify the forces that are mainly responsible for maintaining the high-latitude lower thermospheric wind system with the aid of the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM). Momentum forcing is statistically analyzed in magnetic coordinates, and its behavior with respect to the magnitude and orientation of the interplanetary magnetic field (IMF) is further examined. By subtracting the values with zero IMF from those with non-zero IMF, we obtained the difference winds and forces in the high-latitude lower thermosphere(<180 km). They show a simple structure over the polar cap and auroral regions for positive(B_y > 0.8 |bar{B}_z|) or negative(B_y < - 0.8 |bar{B}_z|) IMF-bar{B}_y conditions, with maximum values appearing around -80° magnetic latitude. Difference winds and difference forces for negatie and positive bar{B}_y have an opposite sign and similar strength each other. For positive(B_z > 0.3125 |bar{B}_y|) or negative(B_z < - 0.3125 |bar{B}_y|) IMF-bar{B}_z conditions the difference winds and difference forces are noted to subauroral latitudes. Difference winds and difference forces for negative bar{B}_z have an opposite sign to positive bar{B}_z condition. Those for negative bar{B}_z are stronger than those for positive indicating that negative bar{B}_z has a stronger effect on the winds and momentum forces than does positive bar{B}_z At higher altitudes(>125 km) the primary forces that determine the variations of the neutral winds are the pressure gradient, Coriolis and rotational Pedersen ion drag forces; however, at various locations and times significant contributions can be made by the horizontal advection force. On the other hand, at lower altitudes(108-125 km) the pressure gradient, Coriolis and non-rotational Hall ion drag forces determine the variations of the neutral winds. At lower altitudes(<108 km) it tends to generate a geostrophic motion with the balance between the pressure gradient and Coriolis forces. The northward component of IMF bar{B}_y-dependent average momentum forces act more significantly on the neutral motion except for the ion drag. At lower altitudes(108-125 km) for negative IMF-bar{B}_y condition the ion drag force tends to generate a warm clockwise circulation with downward vertical motion associated with the adiabatic compress heating in the polar cap region. For positive IMF-bar{B}_y condition it tends to generate a cold anticlockwise circulation with upward vertical motion associated with the adiabatic expansion cooling in the polar cap region. For negative IMF-bar{B}_z the ion drag force tends to generate a cold anticlockwise circulation with upward vertical motion in the dawn sector. For positive IMF-bar{B}_z it tends to generate a warm clockwise circulation with downward vertical motion in the dawn sector.

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