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Abstract This study describes a new mechanism governing the diurnal variation of vertical motion in tropical oceanic heavy rainfall zones, such as the intertropical convergence zone. In such regions, the diurnal heating of widespread anvil clouds due to shortwave radiative absorption enhances upward motion in these upper layers in the afternoon. This radiatively driven ascent promotes an afternoon maximum of anvil clouds, indicating a diurnal cloud‐radiative feedback. The opposite occurs at nighttime: While rainfall exhibits a dominant peak at night‐early morning, the boundary layer rooted upward motion and latent heating tied to this peak are forced to be more bottom heavy by the nighttime anomalous radiative cooling at upper levels. This mechanism therefore favors the stratiform top‐heavy heating mode during daytime and suppresses it nocturnally. These diurnal circulation signatures arise from microphysical‐radiative feedbacks that manifest on the scales of organized deep convection, which may ultimately impact the daily mean radiation budget.
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Island Rainfall Enhancement in the Maritime Continent
Abstract The hypothesis that the islands of the Maritime Continent (MC) enhance total rainfall and time‐mean upward motion is tested using a convection‐permitting regional model. Sensitivity experiments with the islands removed greatly diminish both rainfall and upward motion, supporting the hypothesis. We examine the individual factors in this enhancement, isolating the impacts of the diurnal cycle from those of basic‐state (i.e., constant) forcing of orography and the land surface. We find that the basic‐state forcing by land is the only factor that substantially enhances total island rainfall, specifically through the enhancement of mean surface heat fluxes. The diurnal cycle and orographic forcing, however, substantially enhance rainfall in the seas surrounding the islands. Moreover, the diurnal cycle is found to be essential for promoting mesoscale circulations on the spatial scales of the islands, which are critical to both the upscale growth of deep convection and the most extreme rainfall rates.
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- Award ID(s):
- 1712290
- PAR ID:
- 10455441
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 47
- Issue:
- 5
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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