Significance of the South Pacific Convergence Zone in Energy Conversions of the Southern Hemisphere during FGGE, 10–27 January 1979

Huo-Jin Huang Department of Geosciences, Purdue University, West Lafayette, IN 47907

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Dayton G. Vincent Department of Geosciences, Purdue University, West Lafayette, IN 47907

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Abstract

A modified set of Level III-b grid point analyses, originally produced by ECMWF, is used to diagnose the circulation features and energy conversions in the Southern Hemisphere during the FGGE SOP-1 period of 10–27 January 1979. One of the dominant features during the period was the South Pacific Convergence Zone (SPCZ), a large-scale, quasi-stationary, convectively-active cloud band over the South Pacific Ocean. The study focuses on the significance of the SPCZ on Southern Hemisphere energy conversions by partitioning the conversions into zonal and eddy (transient and standing) components. The mean state is examined for a 15-day period, 10–24 January, when the SPCZ was most active. After 24 January it dissipated. In addition, daily variations are examined for the entire period and a zonal wavenumber analysis fox. wavenumbers 1–15 is performed.

The major findings are that 1) the baroclinic conversion of eddy potential to eddy kinetic energy (CE) is the dominant conversion term in the tropics (0–30°S), and it is particularly important in the vicinity of the SPCZ; 2) all conversion terms in middle latitudes (30–60°S) are comparable and equally important; 3) standing (transient) eddies make the most significant contribution to CE (all eddy conversion terms) in the tropics and SPCZ area (midlatitudes); 4) wavenumber 4 dominates the CE conversion in the tropics, whereas wavenumbers 5–8 dominate all the eddy conversions in middle latitudes; 5) one of the four waves in the n=4CE conversion in the tropics coincides with the SPCZ, while the remaining three correspond to the continental areas of Africa, Australia and South America; and 6) during the last three days, when the SPCZ is decaying, the importance of the n=4 contribution to CE is negligible.

Abstract

A modified set of Level III-b grid point analyses, originally produced by ECMWF, is used to diagnose the circulation features and energy conversions in the Southern Hemisphere during the FGGE SOP-1 period of 10–27 January 1979. One of the dominant features during the period was the South Pacific Convergence Zone (SPCZ), a large-scale, quasi-stationary, convectively-active cloud band over the South Pacific Ocean. The study focuses on the significance of the SPCZ on Southern Hemisphere energy conversions by partitioning the conversions into zonal and eddy (transient and standing) components. The mean state is examined for a 15-day period, 10–24 January, when the SPCZ was most active. After 24 January it dissipated. In addition, daily variations are examined for the entire period and a zonal wavenumber analysis fox. wavenumbers 1–15 is performed.

The major findings are that 1) the baroclinic conversion of eddy potential to eddy kinetic energy (CE) is the dominant conversion term in the tropics (0–30°S), and it is particularly important in the vicinity of the SPCZ; 2) all conversion terms in middle latitudes (30–60°S) are comparable and equally important; 3) standing (transient) eddies make the most significant contribution to CE (all eddy conversion terms) in the tropics and SPCZ area (midlatitudes); 4) wavenumber 4 dominates the CE conversion in the tropics, whereas wavenumbers 5–8 dominate all the eddy conversions in middle latitudes; 5) one of the four waves in the n=4CE conversion in the tropics coincides with the SPCZ, while the remaining three correspond to the continental areas of Africa, Australia and South America; and 6) during the last three days, when the SPCZ is decaying, the importance of the n=4 contribution to CE is negligible.

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