Short Temporal Scale Variability of Low Cloud Regimes/Vertical Structures and Large-Scale Thermodynamics and Dynamics over the Southeastern Pacific Using MODIS and ERA-Reanalysis Data

While oceanic boundary layer clouds are well-correlated with SST, ω500, and various stability metrics over particular tropical and subtropical dynamic regimes particularly when at least 10-15 days are averaged together or when examining the annual cycle characteristics, the coherence of clouds with controlling variables is imperfect at smaller temporal and spatial scales for which cloud properties also exhibit significant variability. By utilizing a plethora of novel satellite cloud data of daily observations of MODIS level-3 data in conjunction with state-of-the-art reanalysis data from ERA-Interim, synoptic variability of low-level clouds and their relationships with potential controlling factors are quantified through examination of Hovmoller diagrams as well as empirical orthogonal function (EOF) and harmonic analysis to better elucidate the horizontal structure and temporal evolution of boundary layer clouds and the environment. The focus on the southeastern Pacific along cross-sections between near the equator to the north and the southern hemisphere mid-latitudes south of the primary VOCALS region encompasses multiple SST and large-scale dynamic regimes. This includes the cold tongue near the equator, a large latitude band of subsidence and predominant low clouds near the VOCALS region, and greater synoptic variability and fewer isolated low clouds further south. For fixed latitudes between the equator and ~30°S, SSTs decrease significantly from west to east from ~140°W to ~70°W by 5-10°C, and low-level cloud fraction histograms screened to exclude upper-level cloudiness reveal predominantly scattered low clouds to the west, a cloud fraction transition zone between about 110°W to 90°W, to frequent solid cloud cover scenes especially east of 90°W as stability and inversion strength both increase. Synoptic-scale analyses reveal that enhanced estimated inversion strength (EIS) anomalies tend to be geographically and temporally located with suppressed boundary layer depths as observed from MODIS, especially between 110°W and 80°W. Maximum coherence between the vertical gradient of equivalent potential temperature or EIS and cloud depth is achieved with zero-day lag, whereas positive pressure vertical velocity anomalies (ω) tend to lead EIS and also cloud depths by a few days, albeit with weaker temporal correlations. Inversion strength co-varies with low cloud fraction at the synoptic scale more weakly than inversion strength or stability does with cloud depth. Physical interpretation of synoptic-scale anomalies of the large-scale dynamics and boundary layer cloud properties over the southeast Pacific is provided, with shorter time-scale variability of clouds better explained by vertical velocity anomalies and slightly longer time-scale variability associated with inversion strength and low-level thermodynamic properties. Finally, since boundary layer cloud heights/depths appear to be intrinsically related to stability/inversion properties, a thorough cloud height/depth climatology is examined with MODIS, GPS, and Calipso for closer comparison with GCM low cloud heights/fraction as a function of boundary layer regime.