The Importance of the Horizontal Advection of Hydrometeors in a Single-Column Model

Abstract

Single-column models (SCMs) are typically forced with profiles of vertical velocity and the divergence of water vapor and temperature due to horizontal advection. Vertical profiles of wind speed are also usually included to provide information required by model physics routines. What is not usually considered, probably because it is not typically available, is the divergence of hydrometeors due to horizontal advection. This paper uses output from a mesoscale model to provide forcing for an SCM. The mesoscale model contained a bulk microphysical scheme and, therefore, the forcing dataset allows a sensitivity study into the effect of the divergence of hydrometeors due to horizontal advection on various parameters in the SCM. It is shown that although the divergence of hydrometeors is typically smaller than the divergence of water vapor, at times it can be larger, particularly at upper levels (above 500 mb). By forcing the SCM with and without the divergence of hydrometeors included, it is shown that the term can significantly affect cloud water content, specific humidity, temperature, and other fields in the model. Including the divergence of hydrometeors into the water vapor divergence term does not always give the same results as including it as a separate field; however, some of the time it does, and is more physically based than ignoring the term completely.