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Variations in lower thermosphere dynamics at midlatitudes during intense geomagnetic storms. L. Goncharenko, J. Salah, J. Foster, C. Huang Haystack Observatory, MIT, Westford, MA. ISR wind measurements. ion drift; measured. electric field; measured. collision frequency; based on NRLMSISE00.
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Variations in lower thermosphere dynamics at midlatitudes during intense geomagnetic storms L. Goncharenko, J. Salah, J. Foster, C. Huang Haystack Observatory, MIT, Westford, MA
ISR wind measurements ion drift; measured electric field; measured collision frequency; based on NRLMSISE00 Instrument: Millstone Hill ISR, 42.6oN, 288.5oE
Average wind • Zonal and meridional components • Altitudes 100-130 km • Semidiurnal tide dominates • Wind magnitude < 100 m/s
Storm periods 25 Sep 1998 Kp = 8+ 15 July 2000 Kp = 9 31 Mar 2001 Kp = 9-
Electric field measurements • Ey – northward electric field (westward ion flow) • Ex – eastward electric field • Quiet time – Ey, Ex < 3 mV/m • Storm time: • 25 Sep 1998 – Ey ~ 25 mV/m • 15 Jul 2000 – Ey ~ 100 mV/m • 31 Mar 2001 – Ey ~40 mV/m • Agrees with ion velocities from DMSP overflights • Agrees with convection pattern flow
September 25, 1998 neutral motion Ion motion Zonal merid
September 25, 1998 • Ion drag effects: • Zonal component: • eastward disturbance wind • 50-200 m/s • penetrates down to 100 km • Meridional component: • southward disturbance wind • ~50 m/s • around 120 km altitude Storm time – at 13.3 UT (8.3LT) Quiet time – average for 4 days
July 15, 2000 • Strong westward ion drift, ~1000 m/s • Westward wind up to 700-800 m/s at 130 km • Northward ion drift (due to Pedersen effect) • Southward neutral wind > 300 m/s
March 31, 2001 • Eastward ion drift in the morning, westward in the afternoon • Zonal neutral wind follows zonal ion drift • Southward drift in the morning, northward in the afternoon • Region of northward wind at 12-17 UT; equatorward wind after 18 UT
March 31, 2001 - Ti • Storm-time ion heating up to 300-500 K • Results from Joule heating • Confirms large differences between ion drift and neutral wind Storm time – Mar 31, 2001 Quiet time – average for 4 days, Apr 1-4, 2001
Summary • Case study of three major storms • Electric fields up to 100 mV/m • E-region ion drift in the two-cell convection pattern, up to 1000 m/s • Ion drag is a primary mechanism for zonal wind disturbances • Meridional component shows a complex response: • Southward flow as response to ion drag • Northward wind as a return flow • Equatorward wind due to pressure gradients