Association of the occurrence of deep convective cloud cores with sea surface temperatures over the equatorial Indian and the western Pacific oceans

In the tropical region, convection is highly associated with sea surface temperature (SST). The convective cores of the deep convective clouds, which exclude the non-precipitating anvils, account for a significant fraction of tropical rainfall and strongly impact large-scale dynamics of the free troposphere. In the present study, associ-ation between the occurrence of deep convective cloud cores (DCCCs) and SST over the tropical region is examined using three years (2012-2014) brightness temperature (TB) data of the water vapour absorption channels of Sondeur Atmosphe & PRIME;rique du Profil d'Humidite & PRIME; Intertropicale par Radiome & PRIME;trie (SAPHIR), aboard Megha-Tropiques satellite. Occurrence frequency of DCCCs (OFD) increases when SST increases above 26.5 & LCIRC;C. The increase in OFD is apparent up to 30.5 & LCIRC;C and decreases for the further increase in SST. The association between OFD with SST, surface latent heat flux, free tropospheric humidity, and downwelling shortwave flux are examined over two dedicated deep convective regions, namely the equatorial Indian Ocean (EIO) and the western Pacific Ocean (WPO), for all seasons by applying the lead-lag correlation. The present study shows that the response of DCCCs to SST is faster over the EIO than over the WPO. Over the EIO and the WPO, DCCCs lag SST by 7 days and 12 days, respectively. When the SST-DCCC relation is analysed after removing the response time or lag, occurrence of DCCCs increases with SST even above 30.5 & LCIRC;C. Though similar studies have been done with precipitation, the tropical DCCCs are attempted for the first time. The observed lags are a few days shorter than those derived for precipitation since the present method considers only DCCCs and excludes the adjoining anvils and stratiform precipitation.

Automated summary

Convection in the tropical region is closely related to sea surface temperature (SST), and the occurrence of convective cores is influenced by SST. The study finds that the occurrence frequency of convective cores increases with SST until it reaches 30.5°C, after which it decreases. The response of convective cores to SST is faster in the equatorial Indian Ocean compared to the western Pacific Ocean, with lags of 7 days and 12 days, respectively. When considering only convective cores, the occurrence still increases with SST above 30.5°C after removing the lag.