Abstract: From several years of Atmosphere Explorer data we show that large‐scale plasma density depletions (horizontal scale greater than 1000 km) in the nocturnal F region occur mainly during the first half of the night. The geomagnetic latitude of these depletions depends on season: at solstice periods the occurrence is mainly in the summer hemisphere and at equinoxes mainly on the geomagnetic equator. Large‐scale depletions occur most often at longitudes characterized by a large magnetic declination. We interpret the large‐scale plasma depletio...
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Topics: 
Atmospheric sciences
Climatology