HR: 08:55h
AN: SA41A-04    [Abstracts]
TI: The Effect of IMF By on Thermospheric Composition at High and Middle Latitudes
AU: * Immel, T J
EM: immel@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California Berkeley, 7 Gauss Way, Berkeley, CA 94720 United States
AU: Crowley, G
SA41A-04 AF: Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228 United States
AU: Hackert, C L
SA41A-04 AF: Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228 United States
AU: Craven, J D
SA41A-04 AF: Geophysical Institute and Physics Department, University of Alaska Fairbanks, 900 Yukon Dr., Fairbanks, AK 99775 United States
AU: Roble, R G
SA41A-04 AF: National Center for Atmospheric Research, 1850 Table Mesa Dr , Boulder, CO 80305 United States
AB: The strength and orientation of the interplanetary magnetic field (IMF) has a strong effect on the high latitude plasma convection pattern, thereby influencing the speed and direction of thermospheric winds. The possibility of similar IMF control over the compositional response of the thermosphere during geomagnetic disturbances has not been fully investigated. This study finds that the y-component of the IMF (IMF By) exerts significant control over the development and subsequent transport of composition disturbances during periods of heightened geomagnetic activity. This is accomplished using global-scale far-ultraviolet images from the first 3 weeks of the Dynamics Explorer 1 mission, and thermospheric modeling using the NCAR-TIMEGCM for this period. The images reveal changes in the relative thermospheric column abundance of O vs. N₂ (σO/N₂). These changes are reproduced by the model, incorporating variable IMF strength and orientation as inputs. It is found that simple reversal of IMF By leads to subsequent changes in σO/N₂ at middle latitudes by as much as 30%. Multiple occurrences of strong IMF By influence at middle latitudes are found in the study period, suggesting that they are common in nature. The study confirms an earlier hypothesis that IMF-By effects on middle-latitude thermospheric composition are important, however it suggests that the effect of By is opposite of that suggested in the earlier report. The study also provides a powerful illustration of the value of global-scale imaging in validating 3-D global simulations.
DE: 0310 Airglow and aurora
DE: 0355 Thermosphere: composition and chemistry
DE: 0358 Thermosphere: energy deposition (3369)
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005