Spatial variability of air-sea fluxes in the western equatorial Pacific ocean (120E-180E, 20S-20N) during COARE IOP are described using data from different sources. Heat and momentum fluxes are calculated using surface meteorology from ECMWF special run. Shortwave radiation is from the data of International Satellite Cloud Climatology Project. Longwave radiation is from ECMWF model. Rainfall is from SSM/I product.
In the record-length-mean (averaged from November 15, 1992 to February 15, 1993) fields, variability of net heat flux is mainly in the north-south direction with the ocean losing (gaining) heat north (south) of 5N. This is due to northward gradients in the distribution of mean latent heat and in the mean net shortwave radiation. The distribution of the mean latent heat is consistent with meteorological conditions typical of this period of the year when the northeasterly trade winds progressed toward the equator from north and the southeasterly trade winds retreated southward. The distribution of mean shortwave radiation is due to the seasonal cycle of the solar elevation. The variability over a special event can have different spatial structure than the record-length-mean. For example, during the December westerly wind burst, the development and subsequent evolution of two tropical storms caused much increased latent heat loss and much reduced shortwave radiation in the affected regions. During the period corresponding to the January low wind period observed at the WHOI mooring, there was a widespread gain of net heat flux south of 5N associated with quiet and clear sky conditoins, while in the northeastern region, there was a large heat loss due to enhanced northeasterly trade wind.
Over the record period, SST decreased in the region north of 10S and increased south of it, indicating that warm pool was migrating southward corresponding to the seasonal cycle. Local heat budget analysis at several locations suggests that SST changes are largely due to local flux forcing. However, the mismatch between the pattern of changes in SST and the pattern of surface heat flux implies that other processes must have cooled the upper ocean. This is a result consistent with climatologies that warm pool is a region where net heat flux is positive into the ocean but SST remains nearly constant.
A heat balance scheme similar to that maintains the cold tongue in the eastern tropical Pacific ocean is proposed for the annual mean. In this scheme, colder water from the top of thermocline was entrained into the upper layer to absorb the surface heat. Then, it leaves warm pool to other regions where it is cooled and subducted. The subducted water flows in the upper thermocline to feed the entrainment. During this cycle, heat is removed from warm pool to other region where it is released to the atmosphere. The implication of this cycle is that warm pool is a divergent rather than convergent region.