Development Characteristics and Dynamic Structure of Tropical Intraseasonal Convection Anomalies

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Abstract
The development and dynamical structure of intraseasonal low-frequency convection anomalies in the equatorial region are investigated using 10 years (1975–85) of outgoing longwave radiation (OLR) and 7 years (1979–85) of 200 and 850 mb wind data. The composite OLR anomalies for 36 cases show a four-stage development process: initiation over equatorial Africa, rapid intensification when passing through the Indian Ocean, mature evolution characterized by a weakening in the maritime continent and redevelopment over the western Pacific, and dissipation near the date line in moderate events or emanation from the equator toward North America and southeastern Pacific in strong events. A noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases. Equatorial upper- (lower-) level easterly (westerly) anomalies and associated twin anomalous anticyclonic (cyclonic) circulation an... Abstract The development and dynamical structure of intraseasonal low-frequency convection anomalies in the equatorial region are investigated using 10 years (1975–85) of outgoing longwave radiation (OLR) and 7 years (1979–85) of 200 and 850 mb wind data. The composite OLR anomalies for 36 cases show a four-stage development process: initiation over equatorial Africa, rapid intensification when passing through the Indian Ocean, mature evolution characterized by a weakening in the maritime continent and redevelopment over the western Pacific, and dissipation near the date line in moderate events or emanation from the equator toward North America and southeastern Pacific in strong events. A noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases. Equatorial upper- (lower-) level easterly (westerly) anomalies and associated twin anomalous anticyclonic (cyclonic) circulation an...

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