Moisture and heat budgets within atmospheric rivers in January 2009

This work performs case studies on the moisture and heat budgets associated with convection embedded in two "Atmospheric Rivers" (ARs) that impacted the North America in January 2009. The ECMWF Year of Tropical Convection data and global gridded precipitation data sets were used to construct the three-dimensional spatial structures of kinematic and thermodynamic fields. AR case 1 had west-east oriented shape, and AR case 2 had north-south oriented shape. In both cases, an AR was formed by merging a primary band of humid air and a secondary band. While this process served as a moisture source of the ARs, precipitating convective systems initiated in the latter acted as moisture sinks. By computing the apparent heat source (Q1) and apparent moisture sink (Q2), we estimated the locations of these precipitating convective systems as they propagated upstream in an AR. By comparing the Q1 and Q2 profiles, we found that as an AR emerged, convective heating prevailed; in later stages when an AR weakened, stratiform heating dominated. The evolution of these convective systems determined the magnitudes and locations of heating/cooling and drying/moistening, thus impacting the ambient thermodynamic fields and the moisture transport process of ARs. The two AR cases had different fractional areal coverage of precipitating convection: around 48% in case 1 and 81% in case 2. We therefore compared the integrated heat and moisture budgets between them. Our results suggested that case 1 had less vertically integrated heating and drying than case 2. Moreover, Northeastern Pacific was a heat sink and moisture sink in case 1, but it was a heat source and moisture sink in case 2.->