Driving the high-latitude ionosphere with variable time resolution ``K-like'' geomagnetic indices

Details Driving the high-latitude ionosphere with variable time resolution ``K-like'' geomagnetic indices Driving the high-latitude ionosphere with variable time resolution ``K-like'' geomagnetic indices

Jun 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000jastp..62..773d&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 62, Issue 9, p. 773-786.

Physics

1

Scientific paper

The 3-h Kp index is widely used as a measure of geomagnetic activity for ionospheric studies. Specifically, it is the planetary index used to determine the geomagnetic dependence of statistical auroral patterns and the convection electric field for certain models. Its quasi anti-logarithm, the Ap index, is similarly used in statistical models of the neutral atmosphere and neutral wind. Physics-based ionospheric models, such as the Utah State University (USU) Time-Dependent Ionospheric Model (TDIM), use these statistical models as magnetospheric and thermospheric inputs. However, the 3-h time interval between index computations is now considered a shortfall with regard to specifying and forecasting phenomena known to have faster time constants, e.g., auroral electrojet variations during a substorm. Therefore, these indices have been targeted for high-time resolution development; we have developed such indices in Della-Rose et al. (1999). We now use our 15-minute station ``K-like'' index to determine the effect of introducing high-time resolution magnetic fluctuations into the TDIM inputs. This study represented the high-latitude ionosphere by a grid of 1484 locations, and was carried out for a geomagnetic storm period during solar maximum and ``simulated'' winter solstice conditions. We found that, for fixed Interplanetary Magnetic Field (IMF) By/Bz ratio, driving the TDIM with our 15-minute ``K-like'' index altered the average high-latitude NmF2 value by as much as 8% (vs. the average NmF2 obtained using a 3-h index to drive the TDIM). More significantly, the standard deviation of the NmF2 variations was up to 35%. Under some conditions, the average NmF2 was changed by up to 30% with a standard deviation of over 60%. However, the effect of selecting different convection patterns that represented three southward IMF Bz orientations led to larger effects. The high-latitude average NmF2 changed by 10% or less, but the spread in the distribution always ranged from standard deviations of 29 to 68%. These results indicate that there is a substantial need to consider both short-term magnetic fluctuations and inclusion of real-time IMF data in the inputs to ionospheric models.

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