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Variations in lower thermosphere dynamics at midlatitudes during intense geomagnetic storms

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

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  1. Variations in lower thermosphere dynamics at midlatitudes during intense geomagnetic storms L. Goncharenko, J. Salah, J. Foster, C. Huang Haystack Observatory, MIT, Westford, MA

  2. ISR wind measurements ion drift; measured electric field; measured collision frequency; based on NRLMSISE00 Instrument: Millstone Hill ISR, 42.6oN, 288.5oE

  3. Average wind • Zonal and meridional components • Altitudes 100-130 km • Semidiurnal tide dominates • Wind magnitude < 100 m/s

  4. Storm periods 25 Sep 1998 Kp = 8+ 15 July 2000 Kp = 9 31 Mar 2001 Kp = 9-

  5. 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

  6. September 25, 1998 neutral motion Ion motion Zonal merid

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. DMSP ion drift

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