THE JUNE-1991 THERMOSPHERIC STORM OBSERVED IN THE SOUTHERN-HEMISPHERE

Neutral upper thermospheric wind and temperature measurements obtained at South Pole, Antarctica (90 degrees S, 75 degrees invariant latitud e (INV)), and Mt John, New Zealand (44 degrees S, 171 degrees E, 52 de grees INV) during the storm period June 11-13 1991 are presented. Wind s peaking at about 800 m/s and typical temperatures reaching up to 200 0 K were found in the polar cap. Peak winds above Mount John reached 3 00 m/s in response to the strong high-latitude forcing which had sprea d equatorward to midlatitudes. The temperature predictions of the MSIS 86 model were in broad agreement with the observations but were overe stimates by several hundred degrees near 0800 UT on June 12 and undere stimates by a similar amount near 0800 UT on June 13. The observed mer idional winds at South Pole were less uniform and a few hours differen t in phase than indicated by the vector spherical harmonic (VSH) model predictions. Although the wind magnitudes were similar to VSH at most times, there was a 12 hour difference in the phase in the zonal compo nent. For the Mount John observations the VSH model predictions exagge rated the equatorward penetration of the polar thermospheric circulati on relative to the observations. Predicted zonal winds exceeded observ ations at almost all times. The observed wind pattern at Mount John di ffered from normal midlatitude quiescent behavior according to the usu al pattern but not in simple proportionality with the variations of ge omagnetic activity, expressed as Ap or Kp. It is suggested that the si gn of the interplanetary magnetic field Y component is an important fa ctor which determines how momentum is coupled between high and middle latitudes during storms and that it will be needed in the specificatio ns for models such as VSH.