Individual Time Period Analyses over the GATE Ship Array

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  • 1 Department of Atmospheric Science, Colorado State University, Ft. Collins 80523
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Abstract

Diagnostic moisture and dry static energy budgets for the GATE A/B-scale area are performed for individual time periods using rawinsonde and satellite data. The data are sufficiently accurate to permit quantitative analysis of that area with 3–6 h time resolution. Each budget is used to estimate the net condensation rate for every time period.

The budget condensation rates slightly exceed radar rainfall estimates for the GATE master array and the radar values lag the budget condensation by 4–6 h during major rainfall episodes. Storage of liquid water and unsampled vapor in clouds can account for a large portion of the observed lag. The present results indicate that observed 3–6 h lags between, low-level mass convergence and echo growth during GATE result primarily from the lag between condensation and precipitation during convective system evolution. The release of latent heat in a tropical convective system appears to be closely related to the instantaneous mass convergence below 700 mb.

Budget-derived condensation is maximum at about 0900 GMT (∼0730 LT). This agrees well with long-term gage measurements in many other tropical oceanic regimes, but contradicts the GATE radar rainfall. Part of the discrepancy is due to the storage of liquid water and cloud vapor, but solar heating of the rawinsonde also contributes.

Abstract

Diagnostic moisture and dry static energy budgets for the GATE A/B-scale area are performed for individual time periods using rawinsonde and satellite data. The data are sufficiently accurate to permit quantitative analysis of that area with 3–6 h time resolution. Each budget is used to estimate the net condensation rate for every time period.

The budget condensation rates slightly exceed radar rainfall estimates for the GATE master array and the radar values lag the budget condensation by 4–6 h during major rainfall episodes. Storage of liquid water and unsampled vapor in clouds can account for a large portion of the observed lag. The present results indicate that observed 3–6 h lags between, low-level mass convergence and echo growth during GATE result primarily from the lag between condensation and precipitation during convective system evolution. The release of latent heat in a tropical convective system appears to be closely related to the instantaneous mass convergence below 700 mb.

Budget-derived condensation is maximum at about 0900 GMT (∼0730 LT). This agrees well with long-term gage measurements in many other tropical oceanic regimes, but contradicts the GATE radar rainfall. Part of the discrepancy is due to the storage of liquid water and cloud vapor, but solar heating of the rawinsonde also contributes.

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