92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Tuesday, 24 January 2012: 9:15 AM
Electrodynamic, Plasma Density, and Neutral Density Response to Recent Sudden Stratospheric Warmings
Room 252/253 (New Orleans Convention Center )
Tim Fuller-Rowell, CIRES/Univ. of Colorado, Boulder, CO; and R. A. Akmaev, F. Wu, H. Wang, T. W. Fang, M. Fedrizzi, R. Viereck, and M. Iredell

The plasma density and electrodynamic response to the January 2009 sudden stratospheric warming (SSW) has been well documented and extensively modeled. The changes in the local time variation of plasma density and total electron content has be attributed to changes in electrodynamics, which in turn can be associated with changes in the tidal wind fields propagation from the lower atmosphere into the lower thermosphere dynamo region. Much of the change in electrodynamics during the SSW has been attributed to an increase in the terdiurnal migrating tide at the expense of the semidiurnal. The migrating tide should not introduce longitude dependence in the electrodynamic response. However, by modeling the system, the interaction of the winds with the global wave number one number associated with the offset of the geomagnetic pole, does change the phase of the electrodynamic response, and is consistent with observations in the American and Asian sectors.

The CHAMP accelerometer satellite observations during the 2009 SSW appeared to show a neutral density decrease, indicating an upper thermospheric cooling. Modeling the period indicated that the main cooling signature could be attributed to changes in geomagnetic activity, rather than as a result of the SSW itself. On the contrary, whole atmosphere modeling indicated a slight warming in response to the SSW. However, this warming was relatively small and would have been difficult to discern in the local-time sampling of the satellite, and due to a much larger contribution to the variability from geomagnetic sources. At this stage, therefore, it is not possible to ascertain if a cooling or warming occurred in the upper thermosphere in response to the stratospheric warming.

In January 2010, a weaker warming occurred, which enables the physical interpretation of the whole atmosphere, electrodynamic, plasma density, and neutral density response to be tested. The 2010 event was quite different from the 2009 warming. In 2009, the stratosphere polar vortex split, with a large increase in zonal wave number two. In 2010, however, the conditions were more indicative of a displaced vortex, with predominantly an increase in zonal wave number one. In spite of these differences, modeling of the event in 2010 still showed a significant change in the amplitude of the migrating tidal modes in the lower thermosphere. Comparing the two events provides an ideal opportunity to test and validate whole atmosphere models, and enable the physical processes involved in the dynamic, electrodynamics, and plasma and neutral density response to be unraveled.

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