SEASONAL CHANGES IN DAY-TO-DAY VARIABILITY OF UPPER AIR WINDS NEAR THE 100 KM LEVEL OF THE ATMOSPHERE,
RAND CORP SANTA MONICA CALIF
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The day-to-day differences in ionospheric F-region critical frequencies near noon are studied as a measure of corresponding differences in the wind-generated ionospheric electric field at the magnetic equator. These changes in F-region critical frequencies reflect corresponding changes in height of the F-region, caused by the electric field of the daily variation. It is shown that the daily variation, though proportional to both the electric field and the electric conductivity, is probably a good indicator of day-to-day changes in wind speeds in the E-region. The data do not support the view that the ionizing solar radiation fluctuates much from one day to the next. The day-to-day changes in wind speed indicated for the E-region in middle latitudes are found to be largest in northern winter, and least in northern summer, and are discussed in relation to evidences of variability dependent on season noted from meteorology for tropospheric winds. Changes in wind speed with sunspot cycle are also discussed.