Interannual shift of tropical high cloud diurnal cycle under global warming

This research focuses on the observed tropical oceanic high clouds above the 300 hPa level, to investigate their diurnal cycles and radiative effects at the top of atmosphere. The diurnal centroid is used to quantify the diurnal cycle based on circular statistics to indicate the daily peaking time of cloud cover. It is found that the diurnal cycle of the tropical oceanic high clouds can significantly impact their cloud radiative effects, with a correlation coefficient of - 0.63 at the 95% significant level and a slope of - 14.5 Wm(-2) h(-1) between the net cloud radiative effects and the diurnal centroid shifting from midnight towards noon. This implies that the changes of the diurnal cycle can strongly influence the Earth radiative budget, and thus possibly impose radiative feedbacks to affect atmospheric circulations under global climate warming. It is also found that the strength of convection and the cold point temperature are two major environmental factors in influencing the diurnal-cycle centroid of the tropical oceanic high clouds. Furthermore, according to observations, the correlation coefficient between the diurnal-cycle centroid of the tropical oceanic high clouds and the global mean temperature is 0.75 at the 95% significant level, indicating a 2-h shift of the tropical oceanic high clouds towards noon with 1celcius increases of the global mean temperature.

Automated summary

This research focuses on the diurnal cycles and radiative effects of tropical oceanic high clouds above the 300 hPa level. The study finds that the diurnal cycle of these clouds significantly impacts their radiative effects, with the shifting of the diurnal centroid from midnight towards noon correlating with a decrease in net cloud radiative effects. The strength of convection and cold point temperature are identified as major factors influencing the diurnal-cycle centroid of these clouds. Additionally, observations show a correlation between the diurnal-cycle centroid of these clouds and the global mean temperature, with a 2-hour shift towards noon for every 1 degree Celsius increase in global mean temperature.