Synoptic Air Mass Controls on Global and Regional Precipitation

Abstract

Despite the complexity of the physical mechanisms behind precipitation, many studies linking precipitation to weather types or atmospheric circulation focus on a single variable, oversimplifying the interactions involved. An alternative approach to examining precipitation involves the use of synoptic air masses, which provide a multivariate perspective. The gridded weather typing classification (GWTC-2) is a synoptic weather typing and air mass classification scheme that captures the holistic nature of weather at any given time and location. This study examined the association between precipitation and GWTC-2 air masses (AMs) on regional to global scales—marking the first use of the GWTC-2 AMs in precipitation studies. Although regional differences exist, land precipitation is better modulated by AMs than oceanic precipitation. There is a noticeably weaker association between AMs and tropical precipitation than extratropical precipitation, with extratropical regions showing up to 60% of summer precipitation variability explained. Regarding individual air mass influences, humid warm AMs show a surprisingly poor correlation with land precipitation, likely because water vapor does not increase linearly with increasing land temperatures. Also, compared to the other two humid AMs, humid cool AMs contribute five times more precipitation in deserts. More interestingly, the frontal AMs, defined to capture migrating extratropical cyclones, are strongly associated with tropical precipitation and capture the West African monsoon remarkably well. The association between GWTC-2 AMs and precipitation has potential applicability in ensemble precipitation forecasting and downscaling GCM simulations of daily precipitation.