Dayside Mid-Latitude F-Region Enhancements During Small or Moderate Geomagnetic Disturbances

Details Dayside Mid-Latitude F-Region Enhancements During Small or Moderate Geomagnetic Disturbances Dayside Mid-Latitude F-Region Enhancements During Small or Moderate Geomagnetic Disturbances

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa33a1437d&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SA33A-1437

Physics

Geophysics

[1739] History Of Geophysics / Solar/Planetary Relationships, [2435] Ionosphere / Ionospheric Disturbances, [2441] Ionosphere / Ionospheric Storms, [2443] Ionosphere / Midlatitude Ionosphere

Scientific paper

We have used the SPIDR internet resource to collect F-region peak density data from 217 ionosonde stations, between the years of 1957 (IGY) and 2008. The stations are located around the globe, with a distribution that is far from uniform; there is especially a concentration in Europe, with quite a few in Russia, as well as North America. In our recent work at Utah State University and University of Texas Dallas [Heelis et al 2009; Sojka et al 2009], we carried out modeling studies showing how an electric field of magnetospheric origin, if expanded to mid- or low-latitudes during a storm period, can be responsible for large increases in the dayside TEC. Such an electric field may be of small magnitude, just 1 mV/m at 50 deg magnetic latitude, and still have a large effect. The enhancements created in this way can result in very steep density gradients, as much as 1 TECu per km, in the dayside ionosphere. In the present study, with a wealth of ionosonde data at our disposal, we focus on periods of small or moderate disturbance, for two reasons. First is the fact that, contrary to what is often assumed, a small disturbance is often sufficient to create large enhancements; the data does not reveal a strong correlation between the magnitude of the positive storm effect and the storm intensity as indicated by the drop in the Dst index. Second, during large-scale storms or super-storms, the data often presents a seemingly haphazard distribution of effects, stemming from the fact that many large storms do not have a clear-cut profile of onset and recovery. Our intention is to take a broad view of small-to-moderate storm periods in general, with particular attention being paid to the longitudinal distribution of positive storm effects. We find that for mild disturbances having a clear onset time and recovery phase, there is often a marked geographical coherence in the distribution of storm effects. As an example, a small storm that occurred on 15 Jan 1972, in which Dst dropped to -70 nT and Kp rose to a value of 5, resulted in significant F-region enhancements throughout North America, but not elsewhere (see figure). In the case of this rather mild storm, the F-region density enhancements in North America were as large as a factor of 2.

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