The 3-D Moisture Structure of Quasi-Biweekly Mode Revealed by AIRS

摘要

Using the humidity profiles from Atmospheric Infrared Sounder (AIRS) data set, rainfall from TRMM GPI and winds from QSCAT as well as SST from Aqua/AMSR_E, We analyze the structure of summer quasi biweekly mode (QBM) over western Pacific region in 2003-2004. We find that the signal of 10-20d oscillation in western Pacific originates from Philippine Sea, which propagates northwestward to south of China. The AIRS data reveal much larger tropospheric moisture perturbations than those depicted in ECMWF analysis. It also reveals that the boundary-layer moisture leads the mid-troposphere moisture during the QBM propagation. The positive SST anomaly may play an important role to moistening the boundary-layer, which preconditions the QBM propagation. Therefore, the 10-20d SST anomaly could positively feed back to the atmosphere through moistening the boundary layer, destabilizing the troposphere, and contributing to the northwestward propagation of the QBM in western North Pacific. On the other hand, the salient feature that the boundary-layer moisture anomaly leads mid-troposphere moisture does not exist in ECMWF analysis.