Diurnal variations of cloud and relative humidity profiles across the tropics

Abstract

Even though the diurnal cycle of solar forcing on the climate system is well defined, the diurnal evolutions of water vapor and clouds induced by the solar forcing are not yet established across the tropics. Here we combine recent satellite observations of clouds profiles and relative humidity profiles to document the diurnal variations of the water vapor and clouds vertical distributions over all the tropics in June-July-August. While the daily mean water vapor and cloud profiles are different between land and ocean, their diurnal variations with respect to their daily means exhibit similar features. Relative humidity profiles and optically thin cloud fraction profiles vary together which maximize during night-time in the entire troposphere and a minimize in day-time. The fraction of optically opaque clouds peak in the free troposphere in the early afternoon, transforms into a high altitude positive anomaly of optically thin clouds from nightfall to sunrise. In addition, land regions exhibit a daily low thin cloud positive anomaly, while oceanic regions exposed to subsidence air motions exhibit positive anomalies of opaque clouds in the lower atmosphere during the second half of the night, which grow until sunrise.

Measurements of sky brightness at Bosscha Observatory, Indonesia

“…However, the solar force exerted by the longer incoming radiation from the sunshine duration corresponds to the RH profile ( Figure 2 c and 2f). The varying seasonal phases or lag of local climatology variables do not exhibit a strong relationship with high cloud amounts ( Chepfer et al., 2019 ).…”

“…In the convective mechanism, the cold cloud coverage is dominated by spatially large, long-lived cloud systems in the near surface. They tend to form in the early evening (2–7 PM) and reach a maximum areal extent of very cold cloud tops before dawn to early morning (0–6 AM) ( Chen and Houze, 1997 ; Hong et al., 2008 ; Chepfer et al., 2019 ).…”

Assessment of Simulated Solar Irradiance on Days of High Intermittency Using WRF-Solar

“…Errors in RH and T can make the atmospheric column drier or wetter influencing stability of the atmospheric column and the updraft of air parcels affecting cloud formation by limiting the height of supersaturation of parcels and the amount of convective available potential energy to drive convection [76]. In the tropics, satellite observations have shown that RH and thick clouds vary daily by as much as 20% and 10%, respectively, at any altitude over land [77]. Given RH errors in this study are as much as 20% which can be associated with errors in T [78], it is sufficient to say thick clouds will be influenced significantly during a daily cycle.…”

Oxygen, reactive oxygen species and developmental redox networks: Evo-Devo Evil-Devils?

“…In addition to altitude, another fundamental factor is the water vapor contained in the air that evidently contributes with its partial pressure and affects the partial pressure of the other gases in the atmosphere (Wenger et al, 2015). In the real-world atmospheric water vapor concentration varies throughout the day (Chepfer et al, 2019). It can also vary depending on geographic location since it is not the same to live in the most humid regions of the world like the Amazon rainforest or in the driest deserts like the Atacama in South America.…”