Diagnosis of the marine stratocumulus cloud variability in the annual cycle over the eastern tropical Pacific and Atlantic oceans

This research identifies dominant modes of annual variability of the marine stratocumulus (MSc) cloud in the eastern tropical Pacific and Atlantic. These modes are extracted from observational data using the cyclostationary empirical orthogonal function (CSEOF) technique, which retrieves the evolution of each mode together with its amplitude time series. This, in combination with comprehensive analysis of the many key physical variables associated with these modes help to depict the underlying dynamic and thermodynamic processes for the cloud formation/dissipation over the eastern tropical Pacific and Atlantic.;The main goal of this study is to investigate the timing, location, strength, and moving direction of the SST and the cloud throughout the year and gain some insights for parameterization of cloud properties using the evolution of SST and the interaction relationship between SST and cloud over these eastern tropical oceans. The most pronounced features of the evolution of the SST and cloud property anomalies are equatorward expansion along the coastal regions of the eastern tropical Pacific and Atlantic, and westward propagation along the equator. In the view of large-scale environment at the surface, the "trough-like" discontinuity of distorted SLP anomaly due to the land-sea distribution causes the persistently strong southerly surface wind anomaly blowing outward from the contour of SLP anomaly. This southerly surface wind anomaly pumps up the coastal upwelling that drags the cold water from the lower depths of the ocean. This describes schematically the surface wind-SST process occurring over the coastal region. The onset of cooling in the region is conducive to more clouds and less surface insolation, which further promotes southerly wind anomalies. This southerly induces locally stronger, more extensive dynamical and evaporative cooling. This cooling expands to northwest via southerly wind. This is a schematic description of the wind-SST-MSc relationship. The lag/lead pattern between variables supports this relationship. The meridional wind component (V) leads SST about one month in the region. The increasing (decreasing) shielding effect of shortwave radiation at the cloud top drives the cold (warm) SST anomaly. CA also leads SST about one month. Results of this analysis may lead to improvement of diagnostic model/parameterization for the MSc cloud properties in GCMs.