Possible Influence of February-April Arctic Oscillation on the ITCZ Patterns of Western-Central Pacific

The daily patterns and activity of Intertropical Convergence Zone(ITCZ) in the Western-Central Pacific Ocean has been analyzed using NOAA interpolated Outgoing Longwave Radiation dataset during the period from 1979 to 2008, and the relationships between ITCZ patterns with Arctic Oscillation(AO) have been investigated in this paper based on the AO dataset from Climate Prediction Center. 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 north (30.98%), south (31.11%) and weak (24.05%) ITCZ patterns are the most active among the ITCZ daily patterns within a 30-year period, while the other three ITCZ patterns occur infrequently. Results show that Feb-Apr AO index has a pronounced positive (negative) correlation with north (weak) ITCZ from Mar-May to Aug-Oct, with a strongest correlation in Apr-Jun (Mar-May). At the same time, the lower tropospheric atmosphere circulation (850hPa wind field) and SST anomalies corresponding to the AO change significantly in the tropical Pacific Ocean. When AO is in the positive phase, from equator to 15°N there is an anomalous westerly and warmer SST in the critical north ITCZ active region, while from equator to 15°S there is an anomalous easterly and insignificant change of SST. The wind and SST anomalies share the same character of the equatorial asymmetry and thus enlarge the gradient between south and north of equator, which can result in the reinforced convection in the north of the equator, as well as the more frequencies of north ITCZ.