Climatological characteristics of fronts in the western North Pacific based on surface weather charts

Abstract

Composite front climatology in the western North Pacific is determined using a newly developed 1.0° gridded data set. Here we propose a research strategy for determining the spatiotemporal distribution of fronts using weather chart images published by the Japan Meteorological Agency, one of the major data providers in the region. A preliminarily investigation of the internal data characteristics for the period of 2000–2010 is undertaken, and the final 4 years of data are used for an analysis of front climatology to avoid the effect of any spurious trends. This enables in-depth analyses to be conducted, which have not previously been possible in the region, including the composites of cross-sectional patterns for the thermal fields and precipitation near fronts, front length seasonality, and the significance of the thermal gradient near the fronts, in addition to determining the frontal frequency and spatial distribution of frontal precipitation. Pixel-wise analysis reveals that 56% of the local precipitation maximum is located on the warm side of a cold front caused by less tilted upward motion on the warm side, with the intrusion of the upper level cold dry air into the warm side. This new data set also enables a further analysis of the occluded fronts, which are not correctly distinguished in the existing objective detection method.