the wave train is out-of-phase and extends in a more southern path 2 in the higher level atmosphere during phase 3 a significant positive anoma

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1 34 3 Vol. 34 No Transactions of Atmospheric Sciences Jun J Yin Zhi-cong Wang Ya-fei Yuan Dong-min Analysis of the interannual variability of the Meiyu quasi-biweekly oscillation and its previous strong influence signal J. Trans Atmos Sci NCEP /NCAR Rossby P A Analysis of the interannual variability of the Meiyu quasi-biweekly oscillation and its previous strong influence signal YIN Zhi-cong 1 2 WANG Ya-fei 1 YUAN Dong-min 3 1. State Key Laboratory of Severe Weather China Academy of Meteorological Sciences Beijing China 2. Beijing Meteorological Bureau Beijing China 3. Huafeng Group of Meteorological Audio and Video Information China Meteorological Administration Beijing China Abstract Based on the 740 stations daily rainfall datasets in China from 1954 to 2005 and the NCEP / NCAR reanalysis data we analyzed interannual variability of the Meiyu quasi-biweekly oscillation over Yangtze-Huaihe River Valley and discussed the background features of atmosphere circulation and sea surface temperature in anomaly years. We divided each rainfall circle into 8 phases. Phase 3 corresponds to the largest positive rainfall while phase 7 corresponds to the largest negative rainfall. The results are as follows 1 the differences between strong and weak oscillation years showed that during phase 3 there is a Rossby wave-like train extending from South China Sea to Alaska via the Sea of Japan Sea of Okhotsk and Aleutian Island in lower atmosphere. The anti-cyclone over South China Sea coordinated with cyclone over Japan is conducive to rainfall over Yangtze-Huaihe River Valley. While in Phase JICA GYHY LASWZF congc84@ 163. com yfwang@ cams. cma. gov. cn.

2 the wave train is out-of-phase and extends in a more southern path 2 in the higher level atmosphere during phase 3 a significant positive anomaly of geopotential height occurred over Sea of Okhotsk. Together with the negative anomaly over Northeast China the anomaly supplied adequate cold and dry air for the rainfall. 3 The SST sea surface temperature of the Kuroshio and its extension zone from March to July showed a very significant positive correlation with the intensity of Meiyu quasi-biweekly oscillation. The lasting positive offshore SST anomaly strengthens Meiyu quasi-biweekly oscillation by regulating the position and intensity of the Western Pacific Subtropical High. Key words Meiyu quasi-biweekly oscillation low-frequent oscillation offshore sea surface temperature wavelet analysis ~ 25 d Lau et al d 2008a Yu and 2008b Ge He et al ~ 30 d Chen and Chen 1995 Chen and Yen ~ 24 d EOF % Wang 1992 Wang et al P-J 2008 OKJ Fukutomi and Yasunari ~ 122 E 28 ~ 34 N 10 ~ 25 d Wang and 2005 NCEP /NCAR Yamazaki ~ 10 d 30 d NOAA Morlet Lac-

3 3 299 zos QBWO quasi-biweekly oscillation 8 3 Yokoi and Satomura 2007 QBWO 7 1 I QAI 10 ~ 25 d d I QAI 9 a Chen and Yen a 10 ~ 25 d 27 QBWO WO 1998 I QAI 1 QBWO I QAI 20 ± 5 90 ± 4 60 QBWO 90 QBWO I QAI Mann-Kendall QBWO 90 QBWO I QAI hpa % QBWO hpa I QAI QBWO P-J 10 ~ 25 d QBWO ~ 25 d 6 7 a 77 QBWO 3 QB- 3 Rossby P-J 1 Fig I QAI 9 a The deviation series of I QAI from 1954 to 2005 and its 9-year filtered series solid curve 2 Fig ~ 25 d mm The d filtered rainfall series from May to August in 1991 units mm the numbers denote the sequence

4 Fig QBWO a b mm The phase composite of filtered rainfall series when QBWO was significant a strong and b weak from 1979 to 2005 Thick black curve indicates the time-averaged series units mm 4 Fig. 4 3 a 7 b 850 hpa QBWO m s - 1 The difference of 850 hpa wind field between strong and weak QBWO years in a Phase 3 and b Phase 7 units m s - 1 4b Rossby 7 Rossby QBWO QBWO ~ 25 d hpa QBWO

尹志聪等梅雨准双周振荡的年际变化及其前期强信号分析第3 期图5 301 低频降水第 3 位相 a 和第 7 位相 b 所对应的 500 hpa 高度场在 QBWO 活跃年和不活跃年差值单位 gpm Fig 5 The difference of 500 hpa geopotential height between strong and weak QBWO years in a

5 尹志聪等梅雨准双周振荡的年际变化及其前期强信号分析第3 期图5 301 低频降水第 3 位相 a 和第 7 位相 b 所对应的 500 hpa 高度场在 QBWO 活跃年和不活跃年差值单位 gpm Fig 5 The difference of 500 hpa geopotential height between strong and weak QBWO years in a Phase 3 and b Phase 7 units gpm 梅雨准双周振荡的前期海温场特征 temperature 海表温度影响梅雨准双周振荡强度的物理机制还计算了 I QAI 和 6 7 月平均的 500 hpa 有研究指出热带地区和中国近海的海温异常对江淮梅雨降水都具有重要的影响为了寻找前期高度场的相关系数图 7 除了中低纬度波列形式的相关分布之外两个显著正相关中心分别对应西和同期影响梅雨准双周振荡强度的强海温信号计算了年的 I QAI 和前期 3 5 月及同期太平洋副热带高压和鄂霍次克海高压这两个高压系统本身就具有显著的准双周振荡特征其发展变 6 7 月北太平洋 SST 的相关系数图 6 从 3 月开始日本东部海区开始出现正的相关中心随着时化必然会影响梅雨降水的准双周振荡根据吴国雄等 1999 的理论分析和 He et al 2001 的数值试间的推移该正相关中心逐渐变强并向南扩展至黑潮及其延伸区为了讨论中国近海 SST sea surface 验结果中国近海海温正异常引起的感热加热能在其西侧激发一个异常的反气旋环流从而影响西太 4 图6 Fig 6 I QAI 和 3 7 月 a e 太平洋海温的相关系数分布阴影表示超过 95% 置信水平的检验 The correlations between I QAI and SST of the Pacific a e from March to July The shaded areas denote the significance at 95% confidence level

6 Fig. 7 I QAI hpa 95% The correlations between I QAI and June-July averaged 500 hpa geopotential height The shaded areas denote the significance at 95% confidence level SST hpa ENSO Rossby hpa hpa gpm hpa Rossby 1 3 Rossby

7 Fig hpa gpm 850 hpa The gpm line in unfiltered 500 hpa geopotential height and the centers of anti-cyclone square and cyclone circle in filtered 850 hpa wind field The different colors denote the sequence of the phases. The gpm lines in phases 1 4 are indicated by solid lines while those in the other 4 phases are indicated by dot lines and the average position are shown by long dashed line. The arrows indicate the direction in which the anti-cyclone cyclone moves hpa Rossby 3 3 SST 1986 Yokoi and Satomura ~

8 J Chen T C Yen M C Interaction between the summer monsoons in J East Asia and the South China Sea Intraseasonal monsoon modes J. J Atmos Sci J Fukutomi Y Yasunari T day intraseasonal variations of ENSO convection and circulation over East Asia and Western North Pacific J M during early summer J. J Meteor Soc Japan Fukutomi Y Yasunari T Tropical-extratropical interaction associat ed with the day oscillation over the Western Pacific during J J ture interannual variation feature and variation mechanism of West ern Pacific subtropical high J. Adv Atmos Sci J Lau K M Yang G J Shen S H Seasonal and intraseasonal climatol ogy of summer monsoon rainfall over East Asia J. Mon Wea Rev J a. Wang Y Effects of blocking anticyclones in Eurasia in the rainy J b. J J. Mon Wea Rev Climate J Yu Z H Ge X Z Numerical simulated of seasonal movement of subtropical high line Ⅱ J. Acta Oceanol Sinica J J Chen T C Chen J M The day mode of global precipitation the northern summer J. J Meteor Soc Japan He Jinhai Zhou Bing Wen Min et al Vertical circulation struc season Meiyu /Baiu season J. J Meteor Soc Japan 70 5 Wang Y Yamazaki N The relationship between the movement of the Meiyu / Baiu rain belt and the periodic northwestward propagation Ⅰ J of the convective activity from tropical west Pacific J. Acta Meteor Sinica J Wang Y Yamazaki K Fujiyoshi Y The interaction between two Ⅰ separate propagation of Rossby Waves J. Mon Wea Rev 135 SSTA J M. Yokoi S Satomura T Climatological characteristics of the intraseasonal variation of precipitation over the Indochina Peninsula J. J

~ a 3 h NCEP ~ 24 3 ~ ~ 8 9 ~ km m ~ 500 m 500 ~ 800 m 800 ~ m a 200

~ a 3 h NCEP ~ 24 3 ~ ~ 8 9 ~ km m ~ 500 m 500 ~ 800 m 800 ~ m a 200 31 1 2013 3 Journal of Arid Meteorology Vol. 31 No. 1 March 2013. J. 2013 31 1 62-69. doi 10. 11755 /j. issn. 1006-7639 2013-01 - 0062 211101 2000 ~ 2010 3 h 2. 5 2. 5 NCEP 2 5 ~ 7 02 11 05 ~ 08 2 ~ 8