Tuesday, 24 January 2012
Relating Ocean Surface Wind and Rain
Hall E (New Orleans Convention Center )
The fifteen years of continuous measurements of TRMM satellite provide us the first statistically reliable observation of two meteorological phenomena: the diurnal variation of rain and the rain patterns of tropical cyclones. Rain should be closely related to surface wind convergence at short time scales through convection over tropical oceans. The monitoring of the ocean surface wind/stress was also advanced by the suite of spacebased scatterometers: six-month tandem mission when two identical scatterometers were flown with different local crossing times, on QuikSCAT and Midori-2, and also by tandem missions among QuikSCAT, European Advanced Scatterometer (ASCAT), and OSCAT on India's Oceansat-2. We have compared the maps of the amplitudes and phase of the diurnal cycle of wind convergence from scatterometers and surface rain from TRMM. In the Bay of Bengal, the cycles of rain and wind convergence were found to be in phase. In the Pacific ITCZ, wind convergence peaks about 3 to 4 hours ahead of rain, while it is a few hours behind the rain offshore near Columbia. These phase lags are being investigated. We have also related rain and wind under tropical cyclones through composite of synoptic maps; they are best provided by the wide-swath spacebased instruments, like a scatterometer or TRMM microwave imager. Using over 8000 scans of scatterometer measurements of tropical cyclones in nine years over global oceans, we revealed the azimuthal asymmetry in radial velocity, tangential velocity, relative angular momentum input, and frictional drag. Wind asymmetry affects wind convergence asymmetry. Convergence causes the uplifting and rain. We are examining the relation between wind convergence and rain asymmetry with respect to hurricane intensification.