Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
The presenter is listed in italics. All poster presentations are the property of their respective authors. Please contact the authors for permission to use images, information, or ideas.

Thermal expansion effects on F-region height changes during geomagnetic storms

M. Fedrizzi¹ (Mariangel.Fedrizzi@noaa.gov), T. J. Fuller-Rowell¹, M. Codrescu², H. Khalsa²), N. Maruyama¹

The increased high-latitude energy input during geomagnetic storms, mainly resulting from Joule heating, causes the atmosphere to heat and expand at thermospheric heights. As a consequence, a global wind surge is generated and propagates from both polar regions to low latitudes and into the opposite hemisphere. Those winds are driven by the pressure inequalities due to temperature differences between high-latitudes and equatorial regions. Divergence in horizontal winds drive vertical upward winds across pressure surfaces, the so-called “divergence velocity”. Conversely, convergent horizontal winds are associated with a downward “divergence wind”. The circulation is closed by a return flow in the lower thermosphere. At the same time, the expansion and contraction of a fixed pressure level atmospheric parcel cause vertical winds, the so-called “barometric velocity”. Barometric winds are related to the thermal expansion of the atmosphere, while vertical divergence winds are associated with the conservation of mass relative to fixed pressure levels. The F2-layer height can change during a geomagnetic storm both from the change in horizontal winds pushing plasma parallel to the inclined magnetic field, and due to vertical winds from the thermal expansion of the neutral atmosphere. In this study, numerical experiments are conducted using a global, three-dimensional, time-dependent, non-linear coupled model of the thermosphere, ionosphere, plasmasphere, and electrodynamics (CTIPe) to quantify the impact of the thermospheric winds and thermal expansion on changes in F2 peak height. The results demonstrate that height changes in the neutral atmosphere from thermal expansion are clearly reflected in the changes of hmF2. Model results are compared to mid-latitude ionosonde observations during the March 31, 2001 magnetic storm, showing good agreement. The analysis of the contribution of thermospheric winds and thermal expansion at two mid-latitude locations during that storm event reveal that both processes contribute significantly to the F-region height changes. The relative importance of those physical mechanisms depends on the local time at storm commencement, the spatial distribution of the energy input over the polar regions, and the storm development and recovery duration.

1. University of Colorado/CIRES - NOAA/SEC, Boulder, CO
2. NOAA/SEC, Boulder, CO