A climatological study of mesoscale convective complexes (MCCs) during 1983–1985 over the western Pacific region (WPR), using full-disc, enhanced infrared satellite imagery from the Japanese Geostationary Meteorological Satellite is presented.

The results indicate that MCCs are common in the WPR and display many of the same characteristics as those found in the Americas. The systems are nocturnal and tend to form over or in the immediate vicinity of land. Cold-cloud shields in the Americas last for about 10 h while WPR shields last about 11 h. The cold-cloud-shield size distribution is similar to that of the Americas, with most systems exhibiting areas between 2 × 105 and 3 × 105 km2. Seasonal distributions of WPR systems are also similar to that in the Americas. Specifically, the frequency of midlatitude systems peaks in late spring and early summer while low-latitude MCCs are distributed uniformly throughout the warm season.

As with western systems, WPR MCCs occur in preferred zones. Climatologically, low-level jets of high-θe, air and upper-level diffluence are present in these zones. Tracks of WPR MCCs show that, like American systems, they typically move to the right (left in the Southern Hemisphere) of the climatological mean 700–500-mb flow. The deviation from the mean flow is in the direction of the source region of higher-θe air. A few MCCs that moved over water formed tropical storms. Likewise, a few tropical systems moved over land and formed MCCs.

It is concluded that the strong similarity of the properties and environment of WPR MCCs to that in the Americas indicates that they are essentially the same phenomenon. Their high frequency in the Americas and the WPR makes them potentially important contributors to the global hydrologic cycle.

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