Large Enhancements in the O/N2 Ratio in the Evening Sector of the Winter Hemisphere During Geomagnetic Storms - NASA Technical Reports Server (NTRS)
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Large Enhancements in the O/N2 Ratio in the Evening Sector of the Winter Hemisphere During Geomagnetic StormsIn this paper, we have looked for enhancements of the O/N2 ratio in data measured by the Dynamics Explorer 2 (DE 2) satellite in the middle latitudes of the winter hemisphere, based on a prediction that was made by the National Center for Atmospheric Research thermosphere/tonosphere general circulation model (NCAR-TIGCM) that such increases occur. The NCAR-TIGCM predicts that these enhancements should be seen throughout the low latitude region and in many middle latitude locations, but that the enhancements in O/N2 are particularly strong in the middle-latitude, evening-to-midnight sector of the winter hemisphere. When this prediction was used to look for these effects in DE 2 NACS (neutral atmosphere composition spectrometer) data, large enhancements in the O/N2 ratio (approx. 50 to 90%) were seen. These enhancements were observed during the main phase of a storm that occurred on November 24, 1982, and were seen in the same region of the winter hemisphere predicted by the NCAR-TIGCM. They are partially the result of the depletion of N2 and, as electron loss is dependent on dissociative recombination at F(sub 2) altitudes, they have implications for electron densities in this area. Parcel trajectories, which have been followed through the NCAR-TIGCM history file for this event, show that large O/N2 enhancements occur in this limited region in the winter hemisphere for two reasons. First, these parcels of air are decelerated by the antisunward edge of the ion convection pattern; individual parcels converge and subsidence occurs. Thus molecular-nitrogen-poor air is brought from higher to lower heights. Because neutral parcels that are found a little poleward of the equatorial edge of the eveningside convection pattern are swept inward toward the center of the auroral oval, the enhancements occur only in a very limited range of latitudes. Second, nitrogen-poor air is transported from regions close to the magnetic pole in the winter hemisphere. During geomagnetic storms, enhanced meridional winds are driven by the increased pressure-gradient force that is associated with intensified Joule heating in the auroral oval. These pressure-driven winds decrease rapidly on the dayside beyond the auroral oval where the parcels originate, limiting the region into which the parcels can be transported. Thus these two processes drive values of O/N2 in a limited region of the winter hemisphere, and reinforce only in the evening sector, causing large changes in this region.
Document ID
19970023975
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1029/94JA03235
Authors
Burns, A. G. (Michigan Univ. Ann Arbor, MI United States)
Killeen, T. L. (Michigan Univ. Ann Arbor, MI United States)
Carignan, G. R. (Michigan Univ. Ann Arbor, MI United States)
Roble, R. G. (National Center for Atmospheric Research Boulder, CO United States)
Date Acquired
September 6, 2013
Publication Date
August 1, 1995
Publication Information
Publication: Journal of Geophysical Research
Publisher: American Geophysical Union
Volume: 100
Issue: A8
ISSN: 0148-0227
Subject Category
Geophysics
Report/Patent Number
NAS 1.26:204887
Paper-94JA03235
NASA-CR-204887
Report Number: NAS 1.26:204887
Report Number: Paper-94JA03235
Report Number: NASA-CR-204887
ISSN: 0148-0227
Accession Number
97N24187
Funding Number(s)
CONTRACT_GRANT: NAG5-465
CONTRACT_GRANT: NSF ATM-94-00877
CONTRACT_GRANT: NSF ATM-89-18476
CONTRACT_GRANT: NAGw-3457
Distribution Limits
Public
Copyright
Public Use Permitted.

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