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High Latitude Cusp Signature Observations for Southward IMF B sub Z

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Final rept. 15 May 89-14 May 92,

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High latitude coherent and incoherent radar systems have given much new information about the physical processes at auroral latitudes. This report presents observational features of the Cusp, situated close to magnetic noon at 70-75 degrees inv. latitude, when the Interplanetary Magnetic Field of the Solar Wind is southward and staying southward for more than half a day. For this condition, the observations of the convectional flow pattern comply with the two-cell model of the global convectional flow at auroral and polar cap latitudes. During moderate disturbed magnetic conditions, the temporal extent of the Cusp can be defined by an increased F-region electron density, while the E- region density decreases or stays constant for mostly northward convectional flow in the magnetic noon sector. The temporal extent of this condition is observed to be up to two hours. When the Cusp is overhead of the radars in Sondre Stromfjord, Greenland, the ionograms show enhanced spread-F condition, a phenomenon associated to electron density enhancements in a turbulent plasma, which flows into the polar cap. Ionogram oblique F-region traces are observed in conjunction with drifting patches. Patches drift through the Cusp region, but they are also observed before and after the defined Cusp and seem not to be confined by the latter. Spectral analysis of F-region electron density variations in the noon sector has been performed. Periods down to the Pc5 range are observed more frequently in the northward convectional flow regime near noon than in the adjacent time sectors. The same analysis of the magnetic pulsations from the Greenland Magnetometer Chain give periods of 10 minutes in the whole dawn sector until the time, when the Cusp is observed by the radars. This dawn side phenomana are often observed for IMF B sub Z southward in the magnetometer chain data.

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  • Atmospheric Physics

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