Abstract
AbstractThis work seeks evidence for convective–radiative interactions in satellite measurements, with a focus on the variability over the life cycle of tropical convection in search of the underlying processes at a fundamental level of the convective dynamics. To this end, the vertical profiles of cloud cover and radiative heating from the CloudSat–CALIPSO products are sorted into a composite time series around the hour of convective occurrence identified by the TRMM PR. The findings are summarized as follows. Cirrus cloud cover begins to increase, accompanied by a notable reduction of longwave cooling, in moist atmospheres even 1–2 days before deep convection is invigorated. In contrast, longwave cooling stays efficient and clouds remain shallow where the ambient air is very dry. To separate the radiative effects by the preceding cirrus clouds on convection from the direct effects of moisture, the observations with enhanced cirrus cover are isolated from those with suppressed cirrus under a moisture environment being nearly equal. It is found that rain rate is distinctly higher if the upper troposphere is cloudier regardless of moisture, suggesting that the cirrus radiative effects may be linked with the subsequent growth of convection. A possible mechanism to support this observational implication is discussed using a simple conceptual model. The model suggests that the preceding cirrus clouds could radiatively promote the moistening with the aid of the congestus-mode dynamics within a short period of time (about 2 days) as observed.
Highlights
The latent heat released by vapor condensation is the primary heat source being balanced against the net radiative cooling in the global atmospheric energy budget (Trenberth et al 2009; L’Ecuyer et al 2015), underscoring the central importance of moist convection and radiative processes, and in particular the mechanism underlying their coupling
It is difficult to separate the direct moisture effects from the radiative effects in the results presented so far
Satellite observations are exploited in search of possible evidence for radiative–convective interactions with focus on the hourly to daily variability intrinsic to the life time of convective systems over tropical oceans
Summary
The latent heat released by vapor condensation is the primary heat source being balanced against the net radiative cooling in the global atmospheric energy budget (Trenberth et al 2009; L’Ecuyer et al 2015), underscoring the central importance of moist convection and radiative processes, and in particular the mechanism underlying their coupling. Perturbations to the cloud and moisture fields brought by moist convection radiatively modify its ambient thermodynamics, which has the potential to promote or suppress the convective activity in return. Such a radiative–convective feedback is arguably at work in aspects of the global or tropical climate The averaging over a large domain can dilute the predominance of latent heating over radiative cooling to the extent that, for instance, radiation can offset 20% of net condensation in the large-scale temperature budget (Tao et al 2004; Li et al 2013).
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