Interannual Changes of 20-50 and 50-100 Day Climate Variability in the Indo-Pacific Sector in Austral Summer

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概要

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• Intraseasonal variations (ISV) of climate from the central Indian Ocean to the western Pacific are investigated at high frequencies (20-50 day period) and low frequencies (50-100 day period) in association with El Ninos, mainly using 7 years of zonal wind, 8 years of precipitation, and 31 years of outgoing longwave radiation (OLR) data observed from satellites. Zonal wind, validated against Tropical Atmosphere Ocean (TAO) buoy measurements at 147°E, 0°and 156°E, 0°, indicated a larger portion of ISV was contained in high frequencies during the 1999-2000, 2000-01, 2002-03, and 2003-04 seasons, as compared to the 1996-97 and 2001-02 seasons, with the latter seasons occurring a year before El Nino events. For 1996-97 and 2001-02, a particular frequency of 3 cycles per season (64-day period) explained a significant portion of the zonal wind ISV in a coherent band from the Indian Ocean to the western Pacific. Furthermore, it was found that the westerly wind signal in this region propagated eastward. Satellitebased precipitation was likewise examined, and showed a similar pattern in time and space. Consistently, OLR data indicated that the ratio of low-frequency ISV to high-frequency ISV was significantly correlated with the Nino 3.4 index at a one-year lead time. Low-frequency variance alone also showed a significant, albeit weaker, correlation, and high-frequency variance indicated no correlation. We suggest that high-frequency variance acts as noise, reducing the relationship between low-frequency ISV and El Nino/Southern Oscillation. Thus, a strong low-frequency variance in combination with a weak high-frequency variance (high ratio value) is important for understanding the initiation of El Ninos. Another interesting feature observed from OLR was the area with the largest ratios of low-frequency to high-frequency ISV had shifted westward during the 30-year record. The westward shift suggests that the eastern Indian Ocean is playing a more important role in ISV-El Nino relations in recent years.

• 社団法人日本気象学会の論文
• 2006-08-25

著者

• Salahuddin Ahmed

  Atmospheric Science Laboratory Coastal Resources Management East Carolina University

• Curtis Scott

  Atmospheric Sci. Lab. Dep. Of Geography East Carolina Univ. Greenville

• Curtis Scott

  Atmospheric Science Laboratory Department Of Geography East Carolina University

関連論文

• Interannual Changes of 20-50 and 50-100 Day Climate Variability in the Indo-Pacific Sector in Austral Summer
• 南方振動に関与する熱帯太平洋とAustralasia域における循環場と気候要素

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