Interactive ionosphere modeling: A comparison between TIGCM and ionosonde data

Abstract

Results from a time dependent geomagnetic storm simulation of the coupled thermosphere and ionosphere using the new interactive thermosphere‐ionosphere general circulation model (TIGCM) (Roble et al., 1988) of the National Center for Atmospheric Research are compared with F2‐ layer data obtained from a latitudinal chain of East Asian ionosonde stations situated close to the −165° magnetic meridian and separated by about 5° in magnetic latitude. This is among the first extended comparisons (10 days) between the TIGCM modeled ionosphere and data, where the effects of neutral dynamics on the ionosphere are studied using a global, fully interactive thermosphere‐ionosphere model. The ionosonde stations provide latitudinal coverage that extends from 15° to 50° magnetic north. Hourly values from both the simulation results and ionosonde data for hmF2, ƒoF2, and meridional neutral winds, for the period March 19–28, 1979, are fitted in latitude using Legendre polynomials, and variations from quiet‐time values are displayed in latitude‐UT coordinates. Color graphics for both the simulation and data are used to illustrate the equatorward penetration of ionospheric disturbances and their dependence on Kp, storm time, and local time. Observed effects are interpreted in terms of plausible electric field, neutral wind, and neutral composition changes during the storm period and where possible are related to TIGCM predictions. It is shown that the TIGCM ionosphere responds very well to varying geomagnetic conditions. The agreement between data and model for critical frequency ƒoF2, is very good at 45° magnetic north, but the agreement decreases equatorward. The agreement for critical height hmF2, however, is good through the whole region of comparison. A test of the general procedure used to derive winds from ionosonde data is also presented. Winds derived from the model's ionosphere hmF2 compare well with winds computed by the TIGCM. This agreement shows the strong coupling between meridional neutral winds and critical height at mid‐latitudes and gives some validity to the methods of computing disturbance winds from variations in F2 layer height.