Steep Electron Density Gradients in the Midlatitude Nighttime Ionosphere: Current Understanding and Future Directions

Details Steep Electron Density Gradients in the Midlatitude Nighttime Ionosphere: Current Understanding and Future Directions Steep Electron Density Gradients in the Midlatitude Nighttime Ionosphere: Current Understanding and Future Directions

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsa11b..03m&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SA11B-03

Physics

2400 Ionosphere, 2439 Ionospheric Irregularities, 2443 Midlatitude Ionosphere, 2494 Instruments And Techniques

Scientific paper

The midlatitude nighttime ionosphere is generally considered to be a fairly quiet system. Indeed, when compared to the highly active low- and high-latitudes, this seems to be a valid description. However, observations in the 1990s, notably those conducted as part of the multi-instrument Combined Ionospheric Campaigns (CICs) carried out periodically from 1997 to 1999, have shown that disturbances can indeed occur in this region. For example, a relatively common feature seen in allsky images taken at 630.0 nm are bands of depleted intensity aligned from the northwest to southeast that propagate to the southwest (in the northern hemisphere). The general characteristics of these bands are now fairly well documented, as is the basic understanding of their underlying physics. The effects of these medium-scale traveling ionospheric disturbances, or electrobouyancy waves, is to produce gradients in the electron density and F-layer height. During quiet magnetic periods, these gradients are fairly small, of the order of a few TEC units. However, these structures seem to be amplified by high geomagnetic activity at which times the gradients can be of the order of 10 to 20 TEC units over distances as small as several 10s of kilometers. Although much was learned about these structures during the CICs of the late 1990s, there are still several unexplained features that warrant further investigation, notably their genesis region, Kp dependence, and effects (if any) on trans-ionospheric radio signals. We suggest the need for a new set of campaigns in the Caribbean to address these questions, modeled on the CICs but extending their spatial coverage and including additional instrumentation not available during the initial campaigns. It is only through such a comprehensive, multi-technique investigation that we will make further headway on understanding these phenomena.

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