Analysis of Surface Wind Diurnal Cycles in Tropical Regions using Mooring Observations and the CCMP Product

Diurnal cycles in ocean surface winds and their convergence were analyzed using available tropical mooring observations from the TAO, PIRATA, and RAMA programs and a gridded surface wind product, the Cross-Calibrated Mutli-Platform Ocean Surface Wind Velocity (CCMP), which is a blended product using available satellite surface wind observations and ERA-40 reanalysis as the background. The objectives of our study are to assess the variability of surface winds in diurnal frequency bands, to understand multiscale interactions in the tropical regions, and to prepare for the application of wind observations from future satellite missions, especially the Cyclone Global Navigation Satellite System (CYGNSS) mission. With an eight-microsatellite constellation, the CYGNSS mission is designed to measure the surface wind field with a mean revisit time of 4 hours between 35N and 35S and through all levels of precipitation events.

Our analysis period is from 2002 to 2011, during which there were at least six satellites such as F13, F14, TMI, F15, QuickScat, and AMSRE providing wind observation inputs to the CCMP. The Root Mean Square Difference (RMSD) between 4 times daily CCMP wind and tropical mooring observations is around 1-2 m/s (30% of the total wind speed), and CAMP-to-mooring correlations are high , indicating the fidelity of CCMP products. Discrepancies between CCMP wind and mooring observations tend to be larger during precipitating periods. Regions of large diurnal cycle in wind is the land-sea interface and regions between subtropical highs and trade winds. The ITCZ and SPCZ regions show up more clearly in the diurnal cycle of surface wind convergence. The relation between diurnal cycle and intraseasonal variability will also be presented.