Convective Coupling in Tropical-Depression-Type Waves
Abstract
Tropical-depression (TD)-type waves are synoptic-scale disturbances embedded with deep convection over the western North Pacific. The present study investigates the rainfall and moisture features of TD-type waves using TRMM-derived rainfall products and the ERA-Interim reanalysis data during the period June-October 1998-2013. The rainfall features a north-south asymmetrical pattern with respect to a TD-type disturbance, that enhanced convective and stratiform rainfall occur in the southern portion. Along with the northwestward propagation, deep convective and stratiform rainfall occurs in-phase with the TD-type disturbance without significant preceding shallow convective rainfall. Following the deepest convection, shallow convective rainfall increases in the anomalous southerlies. Such a rainfall progression differs from the paradigm from shallow, to deep convection, then to stratiform rainfall, which is suggested in other convectively coupled equatorial waves. The rainfall progression and the atmospheric moisture anomaly are phase-locked to the TD-type disturbances that the relative displacements change little when the disturbances propagate northwestward.
Then, the large-scale controls on the convective rainfall progression have been investigated through budgets of moist static energy (MSE) and moisture. The MSE recharge-discharge is controlled by horizontal processes, whereby horizontal moisture advection causes net MSE import prior to deep convection. Such moistening by horizontal advection creates a moist mid-troposphere, which helps destabilize the atmospheric column, leading to the development of deep convective rainfall. Following the heaviest rainfall, negative horizontal moisture advection dries the troposphere, inhibiting convection. Such moistening and drying processes explain why deep convection can develop without preceding shallow convection. The advection of moisture anomalies by the mean horizontal flow controls the tropospheric moistening and drying processes. As the TD-type waves propagate northwestward in coincidence with the northwestward environmental flow, the moisture, or convective rainfall, is phase-locked to the waves.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA155.0006F
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3371 Tropical convection;
- ATMOSPHERIC PROCESSES