Moisture bursts over the tropical Pacific Ocean

The frequency and location of moisture bursts are examined. A moisture burst is described and defined, and this definition is applied to IR imagery for four six-month cool seasons (November-April) in the eastern North Pacific. It is observed that about ten moisture bursts/month occur during the cool seasons; the bursts last about 2-4 days and no more than 10 days; and they are distributed uniformly across the Pacific to the west of 110 deg W. The relation between the moisture bursts and the El Nino event of 1982-1983, and moisture bursts in the general circulation are analyzed. The analyses reveal that few bursts occur in the region associated with the El Nino event, and the moisture bursts resemble transient intensification of the mean meridional circulation in regions with a weak Hadley cell. Two modes for the behavior of the Hadley cell in the Pacific are proposed.