Understanding the synoptic variability of stratocumulus cloud liquid water path over the Southeastern Pacific

Abstract

The spatial and temporal variance of stratocumulus cloud liquid water path (CLWP) over Southeastern Pacific has been investigated by combining satellite moderate resolution imaging spectroradiometer cloud products, CLWP from advanced microwave scanning radiometer-EOS observations and NCEP final analysis atmospheric products with empirical orthogonal function (EOF) Analysis. CLWP variance is the most complicated factor among three fundamental cloud quantities (the microphysical cloud droplet concentration, and the macrophysical CLWP and cloud fractional cover). The results show that EOF/PC1 of CLWP represents the variation of domain-averaged CLWP, which is mainly controlled by surface meteorological factors. Sea surface temperature and cold advection drive the synoptic and seasonal scales of variance of CLWP, while surface wind speed plays a fundamental role in stratocumulus cloud formation and daily variance of CLWP. EOF/PC2 of CLWP describes the spatial variance of CLWP. This daily spatial variance of CLWP is controlled by the factors of lower tropospheric stability and cloud top relative humidity, which determine cloud thickness and, consequently, CLWP through thermodynamic and entrainment processes. Further study indicates a twofold interaction of the surface wind speed on stratocumulus CLWP: (1) dynamically through modulation of surface latent heat and sensible heat fluxes and (2) microphysically through enhanced marine aerosol production.