Entrainment rate diurnal cycle in marine stratiform clouds estimated from geostationary satellite retrievals and a meteorological forecast model

Abstract

AbstractThe mean diurnal cycle of cloud entrainment rate (we) over the northeast Pacific region is for the first time computed by combining, in a mixed‐layer model framework, the hourly composited GOES‐15 satellite‐based cloud top height (HT) tendency, advection, and large‐scale vertical velocity (w) during May to September 2013, with horizontal winds and w taken from the European Centre for Medium‐Range Weather Forecasts (ECMWF) model. The tendency term dominates the magnitude and phase of the we diurnal cycle, with a secondary role of w, and a modest advective contribution. The peak and minimum in we occur between 20:00–22:00 LT and 9:00–11:00 LT, respectively, in close agreement with the diurnal cycle of turbulence driven by cloud top longwave cooling. Uncertainties in HT and ECMWF fields are assessed with in situ observations and three meteorological reanalysis data sets. This study provides the basis for constructing nearly global climatologies of we by combining a suite of well‐calibrated geostationary satellites.