Low cloud structure, variability, and patterns in the primary subtropical stratocumulus regimes using MODIS and ECMWF Analysis/Re-Analysis Data

The Terra satellite, containing Moderate Resolution Imaging Spectroradiometer (MODIS), was launched in late 1999, and Aqua in 2002, providing 10 years of cloud data, including top properties, fraction, and optical information. We evaluate the MODIS level-three dataset, which contains nearly daily global coverage at one-degree resolution with sub-grid statistics (e.g. standard deviation and histograms), in order to examine the variability of low clouds, including optical depth, effective radius, water path, and cloud fraction at the synoptic, monthly, and longer-term scales in climatological regimes with strong negative radiative forcing due to an abundance of low clouds. While the length of the data still may inhibit a clear quantification of longer-term trends of low clouds, we assess the interannual variability in the context of variability of the large- (temporal and spatial) scale circulation. We use ECMWF analyses and reanalyses to acquire insight on the short-temporal scale thermodynamics and dynamics, including SSTs, SST gradients, strength of the subtropical highs, wind-stress, and large-scale vertical velocity, and attempt to determine which factors correlate well with low clouds on short versus long temporal scales. We additionally assess our capacity to sample trade-wind regimes with MODIS, which are likely dominated by more scattered patches of clouds at the one-degree latitude-longitude scale. We also quantify the extent to which the local and non-local thermodynamics/dynamics are important to modulating these cloud populations, including any linkages with the stratocumulus regions.