POSSIBLE INFLUENCE OF FEBRUARY-APRIL ARCTIC OSCILLATION ON THE ITCZ ACTIVITY OF WESTERN-CENTRAL PACIFIC

HU Miao; GONG Dao-yi; MAO Rui

Abstract:

The daily patterns and activity of Intertropical Convergence Zone (ITCZ) in the Western-Central Pacific Ocean are analyzed using NOAA interpolated Outgoing Longwave Radiation dataset during the period from 1979 to 2008, and the relationships between ITCZ patterns and Arctic Oscillation (AO) is investigated in this paper. In accordance with the central activity region the daily ITCZ can be divided into six patterns―north, south, equator, double, full and weak pattern, respectively. The statistic result shows that the north (accounting for 30.98% of the total observations), south (31.11%) and weak (24.05%) ITCZ patterns are the most active daily patterns within a 30-year period, while the other three ITCZ patterns occur infrequently. Results show that the February-April AO index has a significant positive (negative) correlation with the frequency of the north (weak) ITCZ pattern from March-May to August-October, with the strongest correlation in April-June (March-May). At the same time, the lower tropospheric atmosphere circulation (850-hPa wind field) and SST anomalies corresponding to the AO change significantly in the tropical Pacific. When AO is in the positive phase, there is an anomalous westerly from the equator to 15°N and warmer SST in the critical north ITCZ active region, while there is an anomalous easterly and insignificant change of SST from the equator to 15°S. The wind and SST anomalies share the same characteristics of the equatorial asymmetry and thus enlarge the gradient between the south and north of equator, which would help reinforce convection in the north of equator and result in more frequent occurrence of the northern type of ITCZ.

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HU Miao, GONG Dao-yi, MAO Rui. POSSIBLE INFLUENCE OF FEBRUARY-APRIL ARCTIC OSCILLATION ON THE ITCZ ACTIVITY OF WESTERN-CENTRAL PACIFIC [J]. Journal of Tropical Meteorology, 2014, 20(3): 218-227.

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POSSIBLE INFLUENCE OF FEBRUARY-APRIL ARCTIC OSCILLATION ON THE ITCZ ACTIVITY OF WESTERN-CENTRAL PACIFIC

State Key Laboratory of Earth Surface Processes and Resource Ecology, Academy of Disaster Reduction and Emergency Management, Beijing Normal University, Beijing 100875 China Wuhan Regional Climate Center, Wuhan 430074 China

Rev Recd Date: 2014-06-11

Abstract: The daily patterns and activity of Intertropical Convergence Zone (ITCZ) in the Western-Central Pacific Ocean are analyzed using NOAA interpolated Outgoing Longwave Radiation dataset during the period from 1979 to 2008, and the relationships between ITCZ patterns and Arctic Oscillation (AO) is investigated in this paper. In accordance with the central activity region the daily ITCZ can be divided into six patterns―north, south, equator, double, full and weak pattern, respectively. The statistic result shows that the north (accounting for 30.98% of the total observations), south (31.11%) and weak (24.05%) ITCZ patterns are the most active daily patterns within a 30-year period, while the other three ITCZ patterns occur infrequently. Results show that the February-April AO index has a significant positive (negative) correlation with the frequency of the north (weak) ITCZ pattern from March-May to August-October, with the strongest correlation in April-June (March-May). At the same time, the lower tropospheric atmosphere circulation (850-hPa wind field) and SST anomalies corresponding to the AO change significantly in the tropical Pacific. When AO is in the positive phase, there is an anomalous westerly from the equator to 15°N and warmer SST in the critical north ITCZ active region, while there is an anomalous easterly and insignificant change of SST from the equator to 15°S. The wind and SST anomalies share the same characteristics of the equatorial asymmetry and thus enlarge the gradient between the south and north of equator, which would help reinforce convection in the north of equator and result in more frequent occurrence of the northern type of ITCZ.

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POSSIBLE INFLUENCE OF FEBRUARY-APRIL ARCTIC OSCILLATION ON THE ITCZ ACTIVITY OF WESTERN-CENTRAL PACIFIC

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