Quasi-2-Day and Diurnal Cloud Variation Timescales Over Convectively Active Regions

Climatological features of the cloud variability on quasi-2-day (Q2D) and diurnal cycle (DC) timescales are investigated by utilizing the high-resolution satellite infrared brightness temperature (IRBT) observations from January 1998 to December 2019. A distinct land-sea contrast between the distributions of Q2D and DC signals is evident. Diurnally driven cloud activity mainly occurs over land and mountainous regions, and the Q2D timescale is more prominent over tropical ocean basins and land where organized convection is usually observed, for example, Congo and Amazon Rainforests, the United States and subtropical South America during warm seasons. The long-term relationship between the Q2D variability and sea surface temperature (SST) shows that the clouds are more active on Q2D timescales over higher SST environments. The Q2D variability correlates well with both the Indian Ocean Dipole (IOD) and El Nino/Southern Oscillation (ENSO) from 1998 to 2019. The cloud variability associated with a range of convective available potential energy (CAPE) values is analyzed. The result over land shows that increased Q2D cloud variability emerges with higher CAPE, suggesting the coincidence of Q2D and organized convection, particularly given that this effect is strongest over regions with frequent mesoscale convective systems (MCSs) around the world. The cloud variability and the Q2D timescale analyses provide an alternative perspective to understand the global features of mesoscale convective systems. Overall, this study objectively examines the global variability of convective timescales related to the diurnal cycle and longer-lived convective systems to provide a greater understanding of how the global convection population varies in space and time.

Automated summary

This study investigates the climatological features of cloud variability on quasi-2-day (Q2D) and diurnal cycle (DC) timescales using high-resolution satellite data from 1998 to 2019. The results show a distinct land-sea contrast in the distributions of Q2D and DC signals, with Q2D being more prominent over tropical ocean basins and land where organized convection is observed, while DC activity mainly occurs over land and mountainous regions. The study also reveals a strong correlation between Q2D variability and sea surface temperature, as well as with the Indian Ocean Dipole (IOD) and El Nino/Southern Oscillation (ENSO) phenomena, providing valuable insights into the global features of mesoscale convective systems.