Comparison of models and measurements at Millstone Hill during the January 24–26, 1993, minor storm interval

Results from four first-principle models are compared with Millstone Hill incoherent scatter radar and Fabry-Perot interferometer measurements taken during January 24–26, 1993, a period which included a minor geomagnetic storm. The models used in this study are the thermosphere ionosphere electrodynamics general circulation model (TIEGCM) with and without forcings from the assimilative mapping of ionospheric electrodynamics (AMIE) technique, the coupled thermosphere ionosphere model (CTIM), and the field line interhemispheric plasma (FLIP) model. The present study is the first time the AMIE inputs have been used in the TIEGCM model. TIEGCM and CTIM both underestimate the neutral temperature because of an underestimation of the Joule heating rate. An increase in the high latitude Joule heating would modify the thermospheric circulation. This could result in increases in N2 and O2 density above Millstone Hill, which would decrease the AMIE TIEGCM peak electron density (NmF2) to agree better with the observations, but would result in poorer agreement between CTIM and the data. The FLIP model NmF2 is a little low compared to the data, perhaps because of an inadequacy of the mass spectrometer incoherent scatter (MSIS) 86 model composition or the H+ flux in the model. Good agreement is obtained between atomic oxygen density [O] given by MSIS and [O] obtained from the radar data using a heat balance equation, provided an O+–O collision frequency factor of 1.3 is used. While the TIEGCM underestimates the electron and ion temperatures, the FLIP model reproduces major features of the data, apart from a large nighttime enhancement in Te. During the minor storm interval the observed neutral winds show alternating equatorward surges and abatements apparently due to passage of traveling atmospheric disturbances (TADs) seen in the model results. These are associated with a late evening increase observed in NmF2 accompanied by a large increase in F2 peak height (hmF2). These perturbations in NmF2 and hmF2 are not reproduced by the TIEGCM or CTIM. The NmF2 increase may be due to a decrease in O+ recombination rate caused by the higher hmF2, combined with compressional effects of a TAD and an enhanced downward flux of O+ ions.