The Vertical Structure of Tropical Cyclone Rainbands as seen by the TRMM Precipitation Radar

Ten years of three-dimensional Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR) echoes reveal the typical vertical structure of rainband precipitation features seen in tropical cyclones. Statistical analyses based on annular regions spaced evenly from the center of the cyclone indicate different vertical precipitation structures for the organized rainbands closest to the storm center and the disorganized rainbands further afield.

The rainband echoes in the inner regions are intense but less deep and highly uniform at all levels, mostly containing stratiform precipitation with a limited amount of vertically-constrained convection. The distant disorganized rainbands are weaker, sparse, highly convective and less vertically constrained. When the results are stratified by storm intensity, the vertical constraint on inner region rainband convection of intense storms becomes more distinctive, but the outer region rainband convection is not affected.

The PR data are normalized by the amount of radar echo in each sample and examined quadrant-by-quadrant relative to the direction of the environmental shear. The changes in these normalized statistics indicate the rainband convection initiates in the upshear-right quadrant of the distant rainbands, matures in the downshear right quadrant as it travels inwards, and dissipates in the downshear-left quadrant of the inner rainbands. The non-normalized statistics indicate that the associated rainfall asymmetry places most of the rainfall in the downshear-left quadrant of the rainbands, both from precipitation particles travelling downwind along the rainbands as well as particles travelling outward from the inner regions of the storm.

These results indicate that environmental wind shear is mostly responsible for the changes in convective structure around tropical cyclone rainbands as well as the placement of rainfall around the storm. Variations in storm intensity primarily impacts the depth of inner rainband convection.