Analysis of the seasonal variations of equatorial plasma bubble occurrence observed from Haleakala, Hawaii

Over 300 nights of airglow and GPS scintillation data collected between January 2002 and August 2003 (a period near solar maximum) from the Haleakala Volcano, Hawaii are analyzed to obtain the seasonal trends for the occurrence of equatorial plasma bubbles in the Pacific sector (203° E). A maximum probability for bubble development is seen in the data in April (45%) and September (83%). A broad maximum of occurrence is seen in the data from June to October (62%). Many of the bubbles observed from June through August occur later in the evening, and, as seen in the optical data, tend to be "fossilized." This suggests that the active growth region during these months is to the west of the observing location. These seasonal trends are consistent with previous data sets obtained both from other groundbased and satellite studies of the occurrence of equatorial bubbles in the Pacific sector. However, our data suggests a much greater probability of bubble occurrence than is seen in other data sets, with bubbles observed on over 40% of the nights studied.