Multiscale Variability of the Atmospheric Mixed Layer over the Western Pacific Warm Pool

Sounding data from Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) have provided a first opportunity to document the variability of the atmospheric mixed layer over the western Pacific warm pool on timescales ranging from diurnal to intraseasonal. Six-hourly sounding data from four sites-the atoll Kapingamarangi and R/Vs Moana Wave, Shiyan 3, and Xiangyanghong 5-are used to determine the mixed layer depth and its thermodynamic properties. Almost three-quarters of the soundings at these four sites exhibited well-mixed structures: nearly constant profiles of potential temperature and specific humidity capped by a 150-m-deep entrainment zone. The majority of the remaining soundings were modified by precipitation and their associated downdrafts. It is estimated that approximately 40%-50% of the total soundings in COARE were influenced by precipitation downdrafts.