资源环境科技发展态势分析平台

Bimodally distributed column water vapor (CWV) indicates a well-defined moist regime in the Tropics, above a margin value near 48 kg m(-2) in current climate (about 80% of column saturation). Maps reveal this margin as a meandering, sinuous synoptic contour bounding broad plateaus of the moist regime. Within these plateaus, convective storms of distinctly smaller convective and mesoscales occur sporadically. Satellite data composites across the poleward most margin reveal its sharpness, despite the crude averaging: precipitation doubles within 100 km, marked by both enhancement and deepening of cloudiness. Transported patches and filaments of the moist regime cause consequential precipitation events within and beyond the Tropics. Distinguishing synoptic flows that cross the margin from flows that move the margin is made possible by a novel satellite-based Lagrangian CWV tendency estimate. Climate models do not reliably reproduce the observed bimodal distribution, so studying the moist mode's maintenance processes and the margin-zone air mass transformations, guided by the Lagrangian tendency product, might importantly constrain model moist process treatments.

Plain Language Summary Satellite snapshots indicate that tropical column-integrated water vapor (CWV) in the atmosphere has broad, almost-uniform moist regions, with sharp edges or margins that meander and move. This structure comprises a bimodal frequency distribution, an important qualitative distinction that justifies the term "regime." Deep convective storms and rainfall are largely confined inside the moist regime, where they are quite sporadic. In some places, the margin of the moist regime is observed to be moved by the wind, but in other places the wind flows across the margin, with air columns undergoing a rapid moistening as they cross the narrow marginal zone. The continued maintenance of this quasi-uniform vapor regime (despite spotty, intense losses in rain events), and of the sharpness of its margins, implies that convective and dynamical processes act in very concerted ways. We show that this concerted process coupling is nontrivial, since current climate models variously lack or exaggerate the bimodality of the CWV frequency distribution. A new data set for identifying regions of cross-margin flows (air column transformations) is offered.