Space- and Ground-Based Observations of Solar Cycle and Local Time Dependence of Equatorial Plasma Bubble Activity

Recent in situ observations from the C/NOFS satellite during the current solar minimum period have suggested an unusually high occurrence rate of equatorial electron density irregularities, particularly in the pre-sunrise local time sector. Conventional understanding of equatorial plasma bubbles suggests that they should form within an hour of sunset, with depleted regions occurring less frequently and later in local time during solar minimum periods. The GUVI (Global Ultraviolet Imager) instrument has made optical observations of plasma bubbles in the nightside equatorial ionosphere at all local times during 2002—2007. The SSUSI (Special Sensor Ultraviolet Spectrographic Imager) instrument on-board the DMSP F16 satellite has global observations of the ionosphere at 8 PM local time during 2004—2009. The CNFI (Cornell Narrow Field Imager) at Haleakala, Hawaii and the 50-MHz radar at Christmas Island also have observations of plasma bubbles throughout the night during 2002—2009. Climatological statistics of plasma bubble occurrence from these four instruments are presented jointly, including the effects of solar cycle and local time variations on plasma bubble occurrence. Leading theories of equatorial plasma depletion formation will be invoked to explain the observed phenomena.