Wavelet analysis of properties of marine boundary layer mesoscale cells
observed from AMSR-E
Abstract
Marine boundary layer clouds tend to organize into closed or open
mesoscale cellular convection (MCC). Here, two-dimensional wavelet
analysis is applied for the first time to passive microwave retrievals
of cloud water path (CWP), water vapor path (WVP), and rain rate from
AMSR-E in 2008 over the Northeast and Southeast Pacific, and the
Southeast Atlantic subtropical stratocumulus to cumulus transition
regions. The (co-)variability between CWP, WVP, and rain rate in 160x160
km2 analysis boxes is partitioned between four
mesoscale wavelength octaves (20, 40, 80, and 160 km). The cell scale is
identified as the wavelength of the peak CWP variance. Together with a
machine-learning classification of cell type, this allows the
statistical characteristics of open and closed MCC of various scales,
and its relation to WVP, rain rate and potential environmental
controlling factors to be analyzed across a very large set of cases.
The results show that the cell wavelength is most commonly 40-80 km.
Cell-scale CWP perturbations are good predictors of the WVP and rain
rate perturbations. A universal cubic dependence of rain rate on CWP is
found in closed and open cells of all scales. This suggests that aerosol
control on precipitation susceptibility is not as important for open
cell formation as are processes that cause increases in cloud water. For
cells larger than 20 km, there is no obvious dependence of cell scale on
the environmental controlling factors tested, suggesting that the cell
scale may depend more on its historical evolution than the current
environmental conditions.