兩類El Nio不同衰減型的演變特征及其與我國夏季降水的聯(lián)系

陳圣劼，何金海

(1.江蘇省氣象臺，江蘇 南京 210008；2.南京信息工程大學(xué) 氣象災(zāi)害教育部重點實驗室，江蘇 南京 210044)

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陳圣劼1，何金海2*

(1.江蘇省氣象臺，江蘇 南京 210008；2.南京信息工程大學(xué) 氣象災(zāi)害教育部重點實驗室，江蘇 南京 210044)

利用中國氣象局743站日降水、NCEP-/NCAR大氣環(huán)流、英國氣象局Hadley中心全球月平均海表溫度(SST)等資料，探討了兩類El Nio不同衰減型的演變特征及其對衰減階段夏季(6-8月)我國降水異常分布的可能影響。根據(jù)海表溫度異常(SSTA)沿赤道(5°S～5°N)的演變特征，EP-El Nio存在兩種衰減型：自東向西(E-W)衰減(大于0.5℃的海溫正距平首先在南美沿岸消失，并向西擴展)和自西向東(W—E)衰減(大于0.5℃的海溫正距平首先在赤道中太平洋消失，并向東擴展)；CP-El Nio存在3種衰減方式：對稱(S)衰減(赤道中太平洋暖海溫的發(fā)展和衰減關(guān)于某一峰值對稱)、延遲(P)衰減(衰減階段緊接著呈現(xiàn)EP-El Nio分布)、突然(A)衰減(衰減階段緊接著發(fā)生EP-La Nia事件)。對于EP-El Nio，在華北、華南、長江和黃河(簡稱兩河)之間及兩河的上游地區(qū)，E-W與W-E衰減階段夏季降水呈現(xiàn)完全相反的異常分布特征。E-W衰減階段夏季兩河之間及上游地區(qū)偏旱的可能性顯著增大，華北地區(qū)降水異常偏多，長江以南略偏多；而W-E衰減階段夏季，兩河之間及上游地區(qū)降水偏多，降水異常大值中心主要位于沿江地區(qū)，華南大部和華北地區(qū)降水明顯偏少。對于CP-El Nio的3種衰減方式：夏季降水異常大值帶在S衰減方式下主要位于黃河和淮河之間；在P方式衰減時，出現(xiàn)在長江流域；而在A型衰減時，主要位于黃河下游地區(qū)。S和A衰減方式下，東北大部尤其東北北部降水偏少，而處于P衰減時，東北大部降水明顯偏多；在西南地區(qū)，S衰減時夏季降水總體偏多，A衰減時情況相反；在西北北部地區(qū)，A衰減時偏旱，而S和P衰減時降水總體偏多。不同的衰減方式均對應(yīng)不同的降水異?？臻g分布，區(qū)分衰減型使得兩類El Nio次年我國夏季降水異常顯著區(qū)的分布范圍和信號強度均較未區(qū)分衰減型時有較好的改善，為我國汛期降水短期氣候預(yù)測工作提供了重要依據(jù)。

兩類El Nio；不同衰減型；演變特征；夏季降水

1 引言

2 資料和方法

所使用的主要數(shù)據(jù)集包括(1)NCEP/NCAR(National Center for Environmental Prediction/National Center for Atmospheric Research)大氣環(huán)流再分析資料[22]，水平分辨率為2.5°×2.5° ；(2)英國氣象局Hadley中心全球月平均海表溫度(SST)資料[23]，空間分辨率為1°×1°；(3)日本氣象廳JMA海洋各層溫度資料(http://www.cgd.ucar.edu/cas/catalog/ocean/HistOcn_new.html)，水平分辨率為1°×1°，海溫垂向共分24層；(4)中國氣象局743站日降水資料。分析時段均為1960年1月至2015年12月。夏季降水是指6、7、8月3個月降水累積。

3 兩類El Nio不同衰減型的演變過程分析

圖1 5次EP-El Nio事件合成的SSTA隨時間的演變Fig.1 Evolution of composite SSTA of five EP-El Nio events等值線間隔0.5℃，橫坐標(biāo)數(shù)字0表示當(dāng)年，1表示次年，深(淺)色陰影表示正(負)異常通過信度0.10的顯著性檢驗The interval of contour is 0.5℃，the number 0 (1) in the longitudinal coordinate indicates the current (next) year，deep/shadow shaded denote positive /negative anomalies exceeding the 0.10 significance level

圖3 E-W衰減型(a)、W-E型(b)EP-El Nio事件沿赤道(5°S～5°N)次表層海溫異常垂向分布隨時間的演變Fig.3 Evolution of composite equatorial depth-longitude section of SSTA of EP-El Nio events decaying in E-W pattern (a) and W-E pattern (b) 0表示當(dāng)年，1表示次年，等值線間隔為0.3℃(a)和0.5℃(b), 深(淺)色陰影區(qū)表示海溫距平超過(低于)0.5℃(-0.5℃)The number 0 (1) indicates the current (next) year, the interval of contour is 0.3℃ in a and 0.5℃ in b, deep/ shadow shaded denote SSTA values exceeding /below 0.5/-0.5℃

由于E-W型和W-E型分別發(fā)生在20世紀(jì)80年代前后，可能對應(yīng)ENSO循環(huán)演變結(jié)構(gòu)的年代際變化。由于個例有限，這兩種衰減方式的普適性還需進一步驗證。

圖4 9次CP-El Nio事件合成的SSTA隨時間的演變Fig.4 Evolution of composite SSTA of nine CP-El Nio events 等值線間隔0.2℃，橫坐標(biāo)數(shù)字0表示當(dāng)年，1表示次年，深(淺)色陰影表示正(負)異常通過信度0.10的顯著性檢驗The interval of contour is 0.2℃，the number 0 (1) in the longitudinal coordinate indicates the current (next) year， deep/ shadow shaded denote positive /negative anomalies exceeding the 0.10 significance level

圖5 CP-El Nio事件的3種衰減型沿赤道(5°S～5°N)SSTA隨時間的演變，S型衰減(a)、P型(b)、A型衰減(c)Fig.5 Evolution of composite equatorial(5°S—5°N)SSTA of three types of CP-El Nio events, decaying in S type (a), decaying in P pattern (b), decaying in A pattern (c)縱坐標(biāo)數(shù)字0表示當(dāng)年，1表示次年，等值線間隔0.5℃, 深(淺)色陰影區(qū)表示海溫距平超過(低于)0.5℃(-0.5℃)The number 0 (1) in the longitudinal coordinate indicates the current (next) year，the interval of contour is 0.5℃，deep/shadow shaded denote SSTA values exceeding /below 0.5/-0.5℃

圖6

圖6 S型(a)、P型(b)、A型(c)CP-El Nio事件沿赤道(5°S～5°N)次表層海溫異常隨時間的演變Fig.6 Evolution of composite equatorial depth-longitude section of SSTA of CP-El Nio events decaying in S pattern (a)，P pattern (b) and A pattern (c) 0表示當(dāng)年，1表示次年，等值線間隔0.3℃, 深(淺)色陰影區(qū)表示海溫距平超過(低于)0.3℃(-0.3℃)The number 0 (1) indicates the current (next) year，the interval of contour is 0.3℃，deep/ shadow shaded denote SSTA values exceeding /below 0.3/-0.3℃

4 兩類El Nio的不同衰減型與我國夏季降水分布的聯(lián)系

與已有的研究成果[16—17]相一致，EP-El Nio和CP-El Nio事件在其衰減階段對我國夏季(6-8月)降水存在不同的影響：EP-El Nio次年，我國長江以南、黃河以北降水總體可能偏多，兩河之間及西北地區(qū)降水可能偏少。而CP-El Nio次年，淮河流域、西北大部降水異常與EP-El Nio事件相反，總體偏澇；偏少的區(qū)域主要位于長江以南、西南四川盆地及東北西北部等地(圖7)。與降水異常相對應(yīng)，兩類El Nio次年環(huán)流場也呈現(xiàn)不同的異常特征(圖略)。在EP-El Nio次年，低層850 hPa自西北太平洋沿東亞沿岸至鄂霍次克海附近，呈現(xiàn)反氣旋-氣旋-反氣旋環(huán)流異常分布，表現(xiàn)為較明顯的東亞—太平洋(EAP)遙相關(guān)負位相分布，其中西北太平洋反氣旋(WNPAC)異常中心約位于(18°N，135°E)附近。WNPAC西北側(cè)的西南風(fēng)距平與偏北風(fēng)距平的匯合區(qū)位于江南地區(qū)，西南風(fēng)距平給江南地區(qū)帶來豐富的水汽。WNPAC的存在同時使得西太平洋副熱帶高壓(WNPSH)較常年偏強偏西。另外，東北地區(qū)受一氣旋性環(huán)流異?？刂?，其北部偏東氣流有利于將鄂霍次克海的潮濕氣流輸送到我國東北地區(qū)，東北降水有區(qū)域性增加的可能。與EP-El Nio不同，在CP-El Nio次年，EAP型遙相關(guān)不明顯，WNPAC異常強大，中心位置也較EP-El Nio偏北，位于(25°N，135°E)，此時WNPSH異常偏強偏西。這個異常反氣旋的西南風(fēng)距平有利于水汽的進一步向北輸送，使得多雨區(qū)位于長江以北，而長江以南受反氣旋控制，降水偏少。

圖7 EP-El Nio事件(a)、CP-El Nio(b)衰減階段我國夏季降水距平百分率合成Fig.7 Composite summer percentage of precipitation anomalies during the decaying phase of EP-El Nio events (a) and CP-El Nio events (b) 等值線間隔: 10%, 深(淺)色陰影區(qū)表示正(負)異常分別通過信度0.20、0.10的顯著性檢驗The interval of contour is 10%，deep/ shadow shaded denote positive /negative anomalies exceeding the 0.20 and 0.10 significance level, respectively

圖8 E-W型(a)、W-E型(b)EP-El Nio次年夏季我國降水距平百分率合成和E-W型(c)、W-E型(d)EP-El Nio衰減階段夏季合成的850 hPa風(fēng)場距平合成Fig.8 Composite summer percentage of precipitation anomalies during the decaying phase of EP-El Nio events decaying in E-W pattern (a) and W-E pattern (b) and composite of summer 850 hPa winds anomalies during the decaying phase of EP-El Nio events decaying in E-W pattern (c) and W-E pattern (d)等值線間隔：20%, 深(淺)色陰影區(qū)表示正(負)異常分別通過信度0.20、0.10的顯著性檢驗, 加粗箭頭表示通過信度0.10的顯著性檢驗， A表示反氣旋性異常，C表示氣旋性異常The interval of contour is 20%，deep/ shadow shaded denote positive /negative anomalies exceeding the 0.20 and 0.10 significance level, respectively. Bold arrows denote values exceeding the 0.10 significance level. A: anticyclonic anomalies, C: cyclonic anomalies

圖9 E-W型(長虛線)、W-E型EP-El Nio(實線)衰減階段夏季合成的500 hPa 588位勢什米等值線(短虛線為1981—2010年的氣候均值)Fig.9 Composite of summer 5 880 gpm at 500 hPa height during the decaying phase of EP-El Nio events decaying in E-W pattern (long dashed line) and W-E pattern (solid line) (short dashed line denotes the climatic summer 5 880 gpm height averaged from 1981 to 2010)

圖10 S型(a)、P型(b)、A型(c)CP-El Nio衰減階段夏季中國降水距平百分率合成和S型(d)、P型(e)、A型(f)CP-El Nio衰減階段夏季合成的850 hPa風(fēng)場距平Fig.10 Composite summer percentage of precipitation anomalies during the decaying phase of CP-El Nio events decaying in S pattern(a), P pattern(b) and A pattern (c) and composite of summer 850 hPa winds anomalies dur-ing the decaying phase of CP-El Nio events decaying in S pattern (d), P pattern (e) and A pattern (f)a、b中等值線間隔20%，c中等值線間隔10%；深(淺)色陰影區(qū)表示正(負)異常分別通過信度0.20、0.10的顯著性檢驗；加粗箭頭表示通過信度0.10的顯著性檢驗；A：反氣旋性異常The interval of contour in a and b is 20%. The interval of contour in c is 10%. Deep/ shadow shaded denote positive/negative anomalies exceeding the 0.20 and 0.10 significance level, respectively. Bold arrows denote values exceeding the 0.10 significance level. A: anticyclonic anomalies

圖11 S型(長虛線)、P型(實線)、A型(點劃線)CP-El Nio衰減階段夏季合成的500 hPa副熱帶高壓588位勢什米等值線(短虛線為1981—2010年的氣候均值)Fig.11 Composite of summer 5 880 gpm at 500 hPa height during the decaying phase of CP-El Nio events decaying in S pattern (long dashed line), P pattern (long dashed line) and A pattern (dash dot line) (short dashed line denotes the climatic summer 5 880 gpm height averaged from 1981 to 2010)

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Different decaying characteristics for two types of El Nio and their relationships with the summer rainfall in China

Chen Shengjie1，He Jinhai2

(1.JiangsuMeteorologicalObservatory,Nanjing210008,China；2.KeyLaboratoryofMeteorologicalDisasterofNUIST,Nanjing210044,China)

Different decaying characteristics for two types of El Nio and their relationships with the summer rainfall in China were investigated by using 743 stations daily precipitation data from China Meteorological Administration, NCEP circulation reanalysis datasets and the monthly mean Met Office Hadley Center sea surface temperature (SST) analyses data. Based on the evolution of the SST anomalies (SSTA) across the equator(5°S-5°N), two types of decaying patterns are identified for EP-El Nio: (1) An evolution pattern that SSTA decaying from east to west (E-W). The positive SSTA larger than 0.5℃ first disappear in offshore of South America and the disappearance extends to the west. (2) An evolution pattern that SSTA decaying from west to east (W-E). The positive SSTA larger than 0.5℃ first disappear in the central Pacific and the disappearance extends to the east. The decaying evolution of CP-El Nio is classified into three patterns: (1) A symmetric (S)—decaying pattern whose SSTA grows and decays symmetrically with respect to a peak phase, (2) A prolonged(P)-decaying pattern that is followed by a EP-El Nio type, (3) An abrupt(A)—decaying pattern that is followed by a EP-La Nia type. In the following summer of EP-El Nio in two different decaying patterns, there are almost completely opposite rainfall anomalies in North China, South China，the region between and the upstream area of the Yangtze River and the Yellow River Valley (they are called the Two River for short). In the following summer for E-W pattern, suppressed rainfall appears in the region between and the upstream area of the Two River , while the rainfall in North China is abundant and rainfall of the area to the south of the Yangtze River is slightly more. However, there are significantly positive anomalies in the region between and the upstream area of the Two River with the center of positive anomalies located along the Yangtze River, but the negative rainfall anomalies in most region of South China and North China for W-E pattern. As for three decaying patterns of CP-El Nio, the positive anomalies are present in the region between the Huaihe River and the Yellow River Valley for S pattern, in the Yangtze River Valley for P pattern, while in the lower reaches of the Yellow River for A pattern. Rainfall in the Northeast China, especially in the northern of Northeast China, is below normal for S and A pattern, while above normal for P pattern. In the Southwest China, wet (dry) signal appears for S (A) pattern. And in the northern of Northwest China，there is less (more) precipitation for A pattern (S and P pattern). Different distribution of summer rainfall anomalies in the decaying phase of El Nio is closely associated with their different decaying patterns. When inspecting the impacts of the two types of El Nio on the following summer rainfall, it would be better to consider their different decaying patterns in view of the larger significant area and T-inspection value of rainfall anomalies. All these will provide important reference for the short-term climate prediction of summer rainfall.

two “flavors” of El Nio; different decaying patterns; evolution characteristics; summer rainfall

10.3969/j.issn.0253-4193.2017.01.002

2016-05-12；

2016-07-15。

國家重點基礎(chǔ)研究發(fā)展計劃(973計劃)子課題——熱帶太平洋海洋環(huán)流與暖池的結(jié)構(gòu)特征、變異機理和氣候效應(yīng)”(2012CB417403)。

陳圣劼(1987—)，女，江蘇省如東縣人，工程師，從事海氣相互作用研究。E-mail：chenshengjieshiz@163.com

*通信作者：何金海(1941—)，男，江蘇省鎮(zhèn)江市人，教授，主要研究東亞季風(fēng)變化規(guī)律、大氣低頻振蕩和旱澇機理。E-mail：hejhnew@nuist.edu.cn

P732.6

A

0253-4193(2017)01-0011-17

Chen Shengjie，He Jinhai. Different decaying characteristics for two types of El Nio and their relationships with the summer rainfall in China[J]. Haiyang Xuebao, 2017, 39(1): 11-27, doi:10.3969/j.issn.0253-4193.2017.01.002