POSSIBLE RELATIONSHIP BETWEEN ENSO AND BLOCKING IN KEY REGIONS OF EURASIA

LI Yan; JIN Rong-hua; WANG Shi-gong

Abstract:

Using reanalysis data provided by the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research, the potential relationship between the El Niño-Southern Oscillation (ENSO) cycle and blocking highs in three key regions of Eurasia (Ural, Baikal, and Okhotsk) from 1950 to 2008 is analyzed. Composite analysis of 500 hPa geopotential height field during different stages of ENSO reveals that in the winters of El Niño (EN) years, there is significant negative anomaly of geopotential height in the three key regions. In the winters of La Niña (LN) years, on the other hand, significant positive anomaly of geopotential height is observed in Eastern Ural, Baikal, and Okhotsk. In summer, Okhotsk exhibits positive anomaly, which is significant at a confidence level of 90% by Student’s t-test during the developing stage of an LN year. In the developing stage of an EN year, geopotential height field at 500 hPa manifests positive (negative) anomaly in Baikal (Ural and Okhotsk), while the geopotential height field at 500 hPa exhibits positive (negative) anomaly in Ural and Okhotsk (Baikal) during the decaying stage of both EN and LN years. However, these abnormities are insignificant in a developing EN year, decaying EN year, and the summer of a decaying LN year. By analyzing 500 hPa geopotential height field during different phases of the ENSO cycle, it is observed that results of the case study are consistent with those of composite analysis. Annual average blocking is likewise examined during the different stages of ENSO from 1950 to 2008. Combined with composite analysis and case study, results indicate that blockings in the three key regions are suppressed (enhanced) during the winters of EN (LN) years. In summer, the influence of ENSO on the blockings in the three key regions is not as significant as that in winter. Evidently, developing LN may enhance blockings in Okhotsk. Influence factors on blockings are various and complex. This paper indicates that the influence of ENSO on blockings cannot be neglected, and that it is crucial to related operational forecasting as a potential signal.

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LI Yan, JIN Rong-hua, WANG Shi-gong. POSSIBLE RELATIONSHIP BETWEEN ENSO AND BLOCKING IN KEY REGIONS OF EURASIA [J]. Journal of Tropical Meteorology, 2010, 16(3): 221-230.

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POSSIBLE RELATIONSHIP BETWEEN ENSO AND BLOCKING IN KEY REGIONS OF EURASIA

Key Laboratory of Semi-Arid Climate Change of Ministry of Education, College of Atmospheric Sciences, Lanzhou University

Abstract: Using reanalysis data provided by the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research, the potential relationship between the El Niño-Southern Oscillation (ENSO) cycle and blocking highs in three key regions of Eurasia (Ural, Baikal, and Okhotsk) from 1950 to 2008 is analyzed. Composite analysis of 500 hPa geopotential height field during different stages of ENSO reveals that in the winters of El Niño (EN) years, there is significant negative anomaly of geopotential height in the three key regions. In the winters of La Niña (LN) years, on the other hand, significant positive anomaly of geopotential height is observed in Eastern Ural, Baikal, and Okhotsk. In summer, Okhotsk exhibits positive anomaly, which is significant at a confidence level of 90% by Student’s t-test during the developing stage of an LN year. In the developing stage of an EN year, geopotential height field at 500 hPa manifests positive (negative) anomaly in Baikal (Ural and Okhotsk), while the geopotential height field at 500 hPa exhibits positive (negative) anomaly in Ural and Okhotsk (Baikal) during the decaying stage of both EN and LN years. However, these abnormities are insignificant in a developing EN year, decaying EN year, and the summer of a decaying LN year. By analyzing 500 hPa geopotential height field during different phases of the ENSO cycle, it is observed that results of the case study are consistent with those of composite analysis. Annual average blocking is likewise examined during the different stages of ENSO from 1950 to 2008. Combined with composite analysis and case study, results indicate that blockings in the three key regions are suppressed (enhanced) during the winters of EN (LN) years. In summer, the influence of ENSO on the blockings in the three key regions is not as significant as that in winter. Evidently, developing LN may enhance blockings in Okhotsk. Influence factors on blockings are various and complex. This paper indicates that the influence of ENSO on blockings cannot be neglected, and that it is crucial to related operational forecasting as a potential signal.

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POSSIBLE RELATIONSHIP BETWEEN ENSO AND BLOCKING IN KEY REGIONS OF EURASIA

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