The Diurnal Cycle of West Pacific Deep Convection and Its Relation to the Spatial and Temporal Variation of Tropical MCSs

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Abstract
Infrared (IR) and visible satellite data from the Japanese Geostationary Meteorological Satellite (GMS-4) with 5-km spatial and 1-h temporal resolution were used to examine the diurnal cycle of deep convection over a sector of the tropical west Pacific warm pool bounded by 0°–20°N, 140°E–180°. Data were analyzed for 45 days of summer from 22 June to 5 August 1994 and for 65 days of winter between 28 November 1994 and 31 January 1995. Deep convective clouds were identified in IR imagery using brightness temperature (TBB) threshold techniques. Based on previous studies, a −65°C cloud-top TBB threshold was chosen to isolate pixels containing active, deep convection. Spectral analysis of time series constructed from hourly cold cloud (⩽−65°C) pixel counts revealed a powerful diurnal cycle of deep convection significant at the 95% confidence level during summer and winter. Composited hourly statistics of fractional areal cloud cover documented a 0500–0600 local standard time (LST) maximum with a 1500–... Abstract Infrared (IR) and visible satellite data from the Japanese Geostationary Meteorological Satellite (GMS-4) with 5-km spatial and 1-h temporal resolution were used to examine the diurnal cycle of deep convection over a sector of the tropical west Pacific warm pool bounded by 0°–20°N, 140°E–180°. Data were analyzed for 45 days of summer from 22 June to 5 August 1994 and for 65 days of winter between 28 November 1994 and 31 January 1995. Deep convective clouds were identified in IR imagery using brightness temperature (TBB) threshold techniques. Based on previous studies, a −65°C cloud-top TBB threshold was chosen to isolate pixels containing active, deep convection. Spectral analysis of time series constructed from hourly cold cloud (⩽−65°C) pixel counts revealed a powerful diurnal cycle of deep convection significant at the 95% confidence level during summer and winter. Composited hourly statistics of fractional areal cloud cover documented a 0500–0600 local standard time (LST) maximum with a 1500–...

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