Principle component analysis of marine stratocumulus drizzle and other in situ observations

Drizzle in marine stratocumulus exhibits substantial patchiness. We seek to understand the factors that produce this strong heterogeneity, which in turn we expect will clarify the mechanism(s) by which drizzle forms in stratocumulus. We choose to utilize Principal Component Analysis (PCA) on aircraft measurements of marine stratocumulus in two regions: (a) in the near-coastal region of Monterey, California during the MASE (Marine Stratus Experiment) in July 2005 and (b) in the near-coastal region of Iquique, Chile during the VAMOS Ocean-Cloud-Atmosphere-Land Study (VOCALS) in October-November 2008. Utilizing two different field projects allows us to compare and contrast results from stratocumulus layers with distinct macrophysical characteristics, e.g. boundary layer depth and liquid water path.

Our key measurement is the drop size distribution between 3 and 150 micrometers using the Artium Flight Phase-Doppler Interferometer, from which properties such as size-resolved drizzle rate can be derived. We combine a selected set of thermodynamic (e.g. theta_e), meteorological (e.g. vertical wind) observations with these cloud microphysical measurements (all at 1 Hz or ~50 m resolution) in order to elucidate those parameters that are most closely related to drizzle at different regions within the cloud. One a priori expectation is that parameters whose value exhibits some memory on the time scale of drizzle formation (e.g. theta_e) are more likely to matter than those which fluctuate on much faster time scales (e.g. instantaneous vertical wind). Interpreting which of these parameters tends to associate with drizzle will generate insight into the processes relevant to drizzle formation, and hopefully help explain the patchy nature of drizzle.