Cold and Warm Rain Simulated Using a Global Nonhydrostatic Model without Cumulus Parameterization, and their Responses to Global Warming

Abstract

 A global nonhydrostatic model was used to evaluate the reproduction skill of cold and warm rain over the ocean at low latitudes and investigate their responses to global warming. In response to global warming, surface precipitation at low latitudes (30°S-30°N) in the simulations using mesh sizes of 7 and 14 km (R7 and R14, respectively) increased by 1.9 % and 2.6 %, respectively. It was found that the increase in precipitation in the higher horizontal resolution model R7 was caused by the increase in cold and warm rain and that in R14 was due to the increase in cold rain. In R7, the net increase in cold rain occurred due to the increase in stronger precipitation (> 40 mm hr^-1), most of which compensated for the decrease in weaker precipitation (< 40 mm hr^-1). In contrast, warm rain increased in almost all ranges of precipitation intensity. The fractional coverage of warm (cold) rain increased (decreased) robustly for both mesh sizes in the simulations. Analysis of the contribution of dynamic and thermodynamic environmental changes to the changes in cold and warm rain revealed a strong dependency on dynamic regimes in their effects.
 The lifespans of cold and warm clouds at low latitudes (defined by the ratio of the sum of cloud water and cloud ice paths to the precipitation flux) and possible changes related to global warming were also evaluated. On an average, in all precipitation intensities, there was no significant change in the longevity of cold clouds in response to global warming. In contrast, the lifespan of warm clouds was reduced in most of the sea surface temperature anomaly regimes.