Observations of Convection Aggregation Under Seasonal Radiative Convective Equilibrium Over the Northwest Pacific Monsoon Region

Abstract

This study aims to use reanalysis and satellite data to reconcile the perspectives among the energetics of monsoon evolution, the convection-circulation relation on moisture space, and the occurrence of organized convection systems before and after monsoon onset. The observed characteristics of seasonally achieved regional radiative convective equilibrium (RCE) state over the eastern edge of the northwest Pacific region are investigated. The target region exhibits a sharp transition of energy balance from a strong energy-losing state before summer to a near-balance state in late summer with a west-to-east dry static energy transport. We then define the non-RCE and RCE periods to derive and contrast the statistics of convective cloud from CloudSat and precipitation events from IMERG data. During the RCE period, upward mass flux and cloud frequency (CF) increase in moist conditions, while downward flux strengthens with the top-heavy structure and CF at nearly all altitudes decreases in dry conditions. The longwave cloud radiative effect shows a similar change as the CF. The precipitation event of all sizes tends to be suppressed in dry conditions, while only the development of the large-sized event is more active than during the non-RCE period in moist conditions. We also found that over 20% of the large-sized events are associated with tropical cyclones during the RCE period, while the ratio drops to 1.6% during the non-RCE period. We propose a diagnostic framework by combining the series of analyses to evaluate convection-circulation coupling under the constraint of regional RCE in global models with various resolution scales.