鄧新林, 李 春??
(1.中國海洋大學(xué)物理海洋實驗室,山東 青島 266100; 2.青島海洋科學(xué)與技術(shù)協(xié)同創(chuàng)新中心,山東 青島 266100;3.海洋-大氣相互作用與氣候山東省高校重點實驗室,山東 青島 266100)
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鄧新林1,2,3, 李春1,2,3??
(1.中國海洋大學(xué)物理海洋實驗室,山東 青島 266100; 2.青島海洋科學(xué)與技術(shù)協(xié)同創(chuàng)新中心,山東 青島 266100;3.海洋-大氣相互作用與氣候山東省高校重點實驗室,山東 青島 266100)
摘要:基于HadISST海表溫度和NCEP/NCAR的海平面氣壓等再分析資料,研究了北太平洋海平面氣壓主模態(tài)與Elo的關(guān)系。結(jié)果發(fā)現(xiàn):阿留申低壓模態(tài)是對Elo事件的同期響應(yīng),而北太平洋濤動模態(tài)可以誘導(dǎo)熱帶太平洋產(chǎn)生類似中部型Elo的海溫異常,且具有提前4~12個月的預(yù)報意義。冬春季的北太平洋濤動處于正位相時,阿留申低壓與夏威夷高壓同時減弱,北太平洋背景風(fēng)場減弱。夏威夷高壓東南側(cè)西南風(fēng)異常減弱北太平洋東北信風(fēng),使加利福尼亞海區(qū)SST暖異常,在“風(fēng)-蒸發(fā)-SST”機制的作用下,異常暖海溫向熱帶太平洋傳播,使赤道地區(qū)海溫升高并產(chǎn)生西風(fēng)異常,熱帶太平洋產(chǎn)生類似中部型Elo的異常海溫。Elo類型的年代際變化可能受到北太平洋濤動的影響,當(dāng)北太平洋濤動信號活躍時,中部型Elo事件的發(fā)生頻率大。
關(guān)鍵詞:Elo;北太平洋濤動;“風(fēng)-蒸發(fā)-SST”機制;年代際變化
北太平洋大氣環(huán)流有兩個主模態(tài):阿留申低壓(Aleutian Low,AL)模態(tài)和NPO模態(tài),分別是對應(yīng)著海洋的太平洋年代際振蕩(Pacific Decadal Oscillation,PDO)模態(tài)和北太平洋環(huán)流振蕩(North Pacific Gyre Oscillation,NPGO)模態(tài)。在冬季,NPO可以強迫出一個海溫異常足跡,這個被強迫出來的海溫異常信號能持續(xù)到下一年的春夏季,進而產(chǎn)生類似ENSO模態(tài)的海溫異常,這種作用機制被稱為“留足跡”機制[12-13]。Di Lorenzo等[13]發(fā)現(xiàn),NPGO通過副熱帶北太平洋的海洋環(huán)流使熱帶太平洋中部海溫增暖。
1資料和方法
本文所用的資料已從1948年起去掉了線性趨勢以消除全球變暖對氣候的影響,并對海表面氣壓距平(SLPa)場進行了3個月的時間平滑以消除季節(jié)內(nèi)的變化信號。為得到北太平洋大氣環(huán)流的空間模態(tài),對1948—2014年月平均的SLPa進行了EOF分解,分解結(jié)果為第一模態(tài)的AL和第二模態(tài)的NPO,并定義此時的空間模態(tài)為AL/NPO正位相,對應(yīng)的時間序列為AL/NPO指數(shù)。用相關(guān)和回歸的方法探究了AL/NPO與熱帶太平洋SST的關(guān)系,并且通過滑動相關(guān)分析其年代際變化。
為分析北太平洋大氣環(huán)流的特征,首先對SLPa場進行了EOF分解(見圖1)。由圖1看出,第一模態(tài)表現(xiàn)為海盆尺度的異常中心,該異常中心位于阿留申低壓附近,稱之為AL。類似AL模態(tài)的大氣強迫能調(diào)整PDO的位相,與ENSO的低頻變化相關(guān)[14-15]。第一模態(tài)對應(yīng)的時間序列被稱為AL指數(shù)。第二模態(tài)表現(xiàn)為正負異常中心呈南北偶極分布(見圖1(b)),人們將其定義為NPO模態(tài)[15]。第二模態(tài)對應(yīng)的時間序列被稱為NPO指數(shù)。NPO可分為正負位相。當(dāng)NPO為正(負)位相時,南部為異常低壓(高壓)北部為異常高壓(低壓),夏威夷高壓與阿留申低壓同時減弱(增強),南北經(jīng)向氣壓梯度減弱。NPO型的大氣強迫對應(yīng)NPGO型的海洋環(huán)流[15]。
((a)第一模態(tài);(b)第二模態(tài);(c)第一時間序列(紅色)與第二時間序列(藍色);百分率為該模態(tài)的解釋方差。(a) First EOF mode of SLP; (b) Second EOF mode of SLP; (c) Standardized time series of the first (PC1, read) and second principal component (PC2, blue); The percentage represents explain variance.)
圖1北太平洋SLP場的EOF分解結(jié)果
Fig.1EOF analysis of North Pacific SLP
(橫坐標(biāo)<0表示AL/NPO指數(shù)超前CP/EP指數(shù)的相關(guān);灰色實線表示置信度為90%的臨界相關(guān)值。Negative lags imply that the NPO/AL index leads the CP/EP index; Gray line represents the 90% confidence limit(r=±0.204).)
圖2AL指數(shù)(紅色)/NPO指數(shù)(藍色)與冬季CP(a)及EP(b)指數(shù)的超前—滯后相關(guān)
Fig.2(a)Lead-lag Correlation of the AL (red)/NPO (blue) index with the CP(a) index and the EP(b) index
從北半球冬、春季起,NPO指數(shù)與次年冬季的CP指數(shù)有獨立的超置信度為90%的相關(guān)性,故在下文的研究中,取12月至次年5月(D(-1)JFMAM(0))平均的AL/NPO指數(shù)作為該年的AL/NPO指數(shù)(見圖6(a))。
為了驗證NPO能影響熱帶太平洋SST的這一結(jié)論,本文用1948—2014年的NPO指數(shù)對SST和海平面風(fēng)場進行回歸(見圖4,5),結(jié)果發(fā)現(xiàn),NPO型的大氣環(huán)流使北太平洋中緯度產(chǎn)生異常東風(fēng),副熱帶東部產(chǎn)生異常的西南風(fēng)(見圖4(a)),該異常東風(fēng)與西南風(fēng)減弱了背景風(fēng)場。當(dāng)背景風(fēng)場減弱后,海表面的水汽蒸發(fā)減少,海洋向大氣釋放的熱帶隨之減少,熱量收支平衡被打破,SST升高[5-9]。這種由“風(fēng)-蒸發(fā)-SST”機制產(chǎn)生的異常的暖海溫足跡能夠持續(xù)到次年的春季和夏季[8],并延伸至熱帶太平洋中西部(見圖5(a)),此時熱帶太平洋中西部產(chǎn)生異常西風(fēng)(見圖5(b)),該西風(fēng)異常減弱了赤道東風(fēng),赤道上翻流減弱,熱帶太平洋海水變暖。
厄爾尼諾發(fā)展年的夏季,秘魯西岸有暖海溫生成并向熱帶太平洋傳播(見圖4(b))。此時熱帶太平洋的暖海溫起源于兩個地方,一是來自受NPO影響的北太
(陰影部分表示SST經(jīng)過了信度為90%的回歸檢驗;箭頭表示風(fēng)場經(jīng)過了置信度為80%的回歸檢驗。Shaded areas and vector indicate 90% and 80% confidence level for SST and surface wind.)
圖4SST(彩色陰影及等值線,單位:℃)及海平面風(fēng)場(箭頭,單位:m/s)對NPO指數(shù)的回歸
Fig.4Regression maps of SST(shaded and contour, unit: ℃ ) and surface wind (vector, unit: m/s) against to the NPO index
((a)沿(0°,170°W)至(20°N,115°E)線剖面;(b)赤道地區(qū)(5°S,5°N)經(jīng)向平均的緯向-時間剖面。(a)Regression map along the line (0°,170°W)to (20°N,115°E); (b)Regression map in the tropical area(5°S, 5°N) average.)
圖5SST(等值線,單位:℃)、海表面風(fēng)場(矢量箭頭,單位:m·s-1)及海面凈潛熱通量(彩色陰影,單位:W·m-2)對NPO指數(shù)的回歸
Fig.5Regression maps of SST(contour, unit: ℃), surface wind (vector, unit: m·s-1) and latent heat net flux
(shaded, unit: W·m-2) against to the NPO index
4結(jié)語
參考文獻:
[4]Kao H Y, Yu J Y. Contrasting eastern-Pacific and central-Pacific types of ENSO [J]. Journal of Climate, 2009, 22(3): 615-632.
[5]Yu J Y, Lu M M, Kim S T. A change in the relationship between tropical central Pacific SST variability and the extratropical atmosphere around 1990[J]. Environmental Research Letters, 2012, 7(3): 034025.
[8]Wu L, Liu Z Y, Li C, et al. Extratropical control of recent tropical Pacific decadal climate variability: A relay teleconnection [J]. Climate Dynamics, 2007, 28(1): 99-112.
[9]Li C, Wu L X. Dynamic linkage between the north pacific and the tropical pacific: Atmosphere-ocean coupling [J]. Advances in Atmospheric Sciences, 2013, 30(2): 306-314.
[10]Yu J Y, Kao H Y, Lee T. Subtropics-related interannualsea surface temperature variability in the central equatorial Pacific [J]. Journal of Climate, 2010, 3(11): 2869-2884.
[12]Vimont D J, Wallace J M, Battisti D S. The seasonal footprinting mechanism in the Pacific: implications for ENSO[J]. Journal of Climate, 2003, 16(16): 2668-2675.
[14]Di Lorenzo E, Combes V, Keister J E, et al. Synthesis of Pacific Ocean climate and ecosystem dynamics[J]. Oceanography, 2013, 26(4): 68-81.
[15]張立鳳, 呂慶平, 張永垂. 北太平洋渦旋振蕩研究進展[J]. 地球科學(xué)進展, 2011, 26(11): 1143-1149.
Zhang Lifeng, Lu Qingping, Zhang Yongchui. Advances in the study of North Pacific gyre oscillation [J]. Advance in Earth Sciences, 2011, 26(11): 1143-1149.
[16]Walker G T, Bliss E W. World weather V[J]. Memoirs of the Royal Metrological Society, 1932, 4: 53-84.
[17]Shukla J, Wallace J M. Numerical simulation of the atmospheric response to equatorial Pacific sea surface temperature anomalies [J]. Journal of the Atmospheric Sciences, 1983, 40(7): 1613-1630.
[18]Anderson B T. Tropical Pacific sea-surface temperatures and preceding sea level pressure anomalies in the subtropical North Pacific[J]. Journal of Geophysical Research: Atmospheres (1984-2012), 2003, 108(D23): 1-17.
[19]Vimont D J. The seasonal footprinting mechanism in the CSIRO coupled general circulation models and in observations [D]. Washington: University of Washington, 2002.
[20]Li C, H. Ma. Relationship between ENSO and Winter Rainfall over Southeast China and Its Decadal Variability[J]. Advances in Atmospheric Sciences, 2012, 29(6): 1129-1141.
責(zé)任編輯龐旻
Its Decadal Variability
DENG Xin-Lin1,2,3, LI Chun1,2,3
(1.Physical Oceanography Laboratory, Ocean University of China, Qingdao 266100, China; 2.Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China; 3.Key Laboratory of Ocean-Atmosphere Interaction and Climate in Universities of Shandong, Qingdao 266100, China)
Abstract:This study used the HadISST and NCEP/NCAR reanalysis dataset to examine the relationship between the North Pacificsea level pressure andtwo types of Elo. It is found that the Aleutian Low mode is the real-time correspond to Elo; the North Pacific Oscillation mode may give rise to central Pacific Elo, which can forecast the Elo for about 4~12 months ahead. When the North Pacific Oscillation is on the positive (negative) phase, the Hawaii High and Aleutian Low is enhanced (weakened), which relaxing (strengthening) the background circulation. The positive phase of North Pacific Oscillation in winter and spring weakens the trade wind, generating positive SST anomaly in the California sea area by the wind-evaporation-SST mechanism. The positive SST anomaly spread to the central tropical Pacific in spring and summer and forces a pattern of atmosphere circulation anomaly includingwesterly wind anomaly along the central and westerntropical Pacific, which contributes to the occurrence of CP Elo. It is interesting that the root mean square of North Pacific Oscillation has significant decadal variability, corresponding to the decadal variability of two type of Elo. From 1950s to 1970s and after 1990s, the North Pacific Oscillation is active, the occurrence of central PacificElo is more frequent; From 1970s to 1990s, the Aleutian Low is more active, the tropical Pacific is dominated by the easternPacificElo.
Key words:Elo; North Pacific oscillation; wind-evaporation-SST mechanism; interdecadal variation
基金項目:? 國家自然科學(xué)基金項目(41276002;41130859);國家重大研究計劃發(fā)展項目(2012CB955603;2013CB956201);國家自然科學(xué)基金—山東海洋科學(xué)研究中心聯(lián)合基金項目(U1406401)資助
收稿日期:2015-09-21;
修訂日期:2015-12-31
作者簡介:鄧新林(1991-),女,碩士生。E-mail:deng_xinlin@126.com ??通訊作者:E-mail:lichun7603@ouc.edu.cn
中圖法分類號:P732.6
文獻標(biāo)志碼:A
文章編號:1672-5174(2016)06-042-10
DOI:10.16441/j.cnki.hdxb.20150327
Supported by the National Natural Science Foundation of China (NSFC) (41276002; 41130859); the National Basic Research Program of China (2012CB955603; 2013CB956201); the NSFC-Shandong Joint Fund for Marine Science Research Centers (U1406401)