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2–3-Day Convective Variability in the Tropical Western Pacific

Carol Anne ClaysonDepartment of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana

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Brian StrahlDepartment of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana

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Jon SchrageDepartment of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana

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Abstract

This paper is an examination of 2–3-day convective variability in the tropical Pacific region. The initial focus of the paper is on the western tropical Pacific during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) intensive observation period (IOP); high spatial and temporal resolution outgoing longwave radiation (OLR) data and sea surface temperatures are filtered to eliminate diurnal and lower-frequency variability. The propagation of the 2–3-day convective variability is also studied. Westward propagation appears to be favored in some regions, indicative of the events being influenced by westward-propagating inertio-gravity waves. However, many regions have 2–3-day events that divide fairly equally into eastward and westward propagations, indicating that both eastward- and westward-propagating inertio-gravity waves are influencing the oscillation. The SST data during the 4-month IOP dataset show evidence of a 2–3-day variability during those convective events occurring under low wind speed conditions during the suppressed phases of the MJO, indicative of a possible thermodynamic feedback between the ocean and atmosphere. The results of this 4-month dataset are then expanded by the use of an 11-yr IR brightness temperature dataset that is similarly filtered. Interannual variability in the occurrence of the 2–3-day events is also studied; the results indicate that for those regions in which convection strongly increases or decreases during the ENSO cycle, the occurrence of the 2–3-day variability also increases or decreases. The dependence of the 2–3-day convective episodes on large-scale convection and the intraseasonal oscillation (ISO) is also investigated. Results show that large-scale convection and the ISO are not necessary for these events, consistent with results for the 4-month IOP.

Corresponding author address: Dr. Carol Anne Clayson, Dept. of Earth and Atmospheric Sciences, Purdue University, 1397 CIVL Bldg., West Lafayette, IN 47907-1397. Email: clayson@purdue.edu

Abstract

This paper is an examination of 2–3-day convective variability in the tropical Pacific region. The initial focus of the paper is on the western tropical Pacific during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) intensive observation period (IOP); high spatial and temporal resolution outgoing longwave radiation (OLR) data and sea surface temperatures are filtered to eliminate diurnal and lower-frequency variability. The propagation of the 2–3-day convective variability is also studied. Westward propagation appears to be favored in some regions, indicative of the events being influenced by westward-propagating inertio-gravity waves. However, many regions have 2–3-day events that divide fairly equally into eastward and westward propagations, indicating that both eastward- and westward-propagating inertio-gravity waves are influencing the oscillation. The SST data during the 4-month IOP dataset show evidence of a 2–3-day variability during those convective events occurring under low wind speed conditions during the suppressed phases of the MJO, indicative of a possible thermodynamic feedback between the ocean and atmosphere. The results of this 4-month dataset are then expanded by the use of an 11-yr IR brightness temperature dataset that is similarly filtered. Interannual variability in the occurrence of the 2–3-day events is also studied; the results indicate that for those regions in which convection strongly increases or decreases during the ENSO cycle, the occurrence of the 2–3-day variability also increases or decreases. The dependence of the 2–3-day convective episodes on large-scale convection and the intraseasonal oscillation (ISO) is also investigated. Results show that large-scale convection and the ISO are not necessary for these events, consistent with results for the 4-month IOP.

Corresponding author address: Dr. Carol Anne Clayson, Dept. of Earth and Atmospheric Sciences, Purdue University, 1397 CIVL Bldg., West Lafayette, IN 47907-1397. Email: clayson@purdue.edu

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