Statistical Properties of Episodes of Enhanced 2–3-Day Convection in the Indian and Pacific Oceans

Jon M. Schrage Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana

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

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Brian Strahl Fleet Numerical Meteorology and Oceanography Center, Monterey, California

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Abstract

Using 9 yr of IR brightness temperature values as a proxy for tropical convection, the climatology and statistics of the 2–3-day convective oscillation signal are examined. These higher-frequency oscillations are shown to have a very different spatial distribution than the signal associated with the 25–70-day intraseasonal oscillation, making it quite unlikely that these oscillations simply represent a form of noise in the time series.

The characteristics of the oscillations are shown to be strong functions of latitude, season, and strength of the oscillation itself. Only the strongest of the 2–3-day oscillations prove to be in good agreement with the properties shown in previous studies, which were based on smaller spatial and temporal domains. These strong oscillations manifest a strong association with the intraseasonal oscillation and westerly wind bursts, particularly in the deep Tropics. Weaker oscillations, on the other hand, are found to be more stochastic and less dependent on larger-scale atmospheric structures.

Corresponding author address: Dr. Jon M. Schrage, Department of Earth and Atmospheric Sciences, Purdue University, 1397 Civil Engineering Bldg., West Lafayette, IN 47907-1397. Email: schragej@purdue.edu

Abstract

Using 9 yr of IR brightness temperature values as a proxy for tropical convection, the climatology and statistics of the 2–3-day convective oscillation signal are examined. These higher-frequency oscillations are shown to have a very different spatial distribution than the signal associated with the 25–70-day intraseasonal oscillation, making it quite unlikely that these oscillations simply represent a form of noise in the time series.

The characteristics of the oscillations are shown to be strong functions of latitude, season, and strength of the oscillation itself. Only the strongest of the 2–3-day oscillations prove to be in good agreement with the properties shown in previous studies, which were based on smaller spatial and temporal domains. These strong oscillations manifest a strong association with the intraseasonal oscillation and westerly wind bursts, particularly in the deep Tropics. Weaker oscillations, on the other hand, are found to be more stochastic and less dependent on larger-scale atmospheric structures.

Corresponding author address: Dr. Jon M. Schrage, Department of Earth and Atmospheric Sciences, Purdue University, 1397 Civil Engineering Bldg., West Lafayette, IN 47907-1397. Email: schragej@purdue.edu

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