高等大氣動力學(xué)第10講季風(fēng)

1、第1010講 季風(fēng)動力學(xué)魏魏 科科, 中國科學(xué)院大氣物理研究所, E-mail: 高等大氣動力學(xué)NepalChinaTibet Plateau “這是喜馬拉雅山脈，這是中國的青藏高原，這是尼泊爾，山脈的南坡緩緩的伸向印度洋，受印度洋暖濕氣流的影響，尼泊爾王國氣候濕潤，四季如春，而山脈的北麓陡降，終年積雪，再加上深陷大陸的中部，遠(yuǎn)離太平洋，所以自然氣候十分的惡劣”“如果我們把喜馬拉雅山炸開一道五十公里的口子，世界屋脊還留著，把印度洋的暖風(fēng)引到我們這里來，試想一想，那我們美麗青藏高原從此摘掉落后的帽子不算，還得變出多少個魚米之鄉(xiāng)！”1999年電影不見不散 葛優(yōu)臺詞青藏高原對亞洲季風(fēng)區(qū)而言是福是禍？

2、青藏高原對亞洲季風(fēng)區(qū)而言是福是禍？亞洲季風(fēng)是如何形成的？亞洲季風(fēng)是如何形成的？Everest引子引子Outlinel季風(fēng)概念和全球季風(fēng)l季風(fēng)的歷史演變l季風(fēng)的形成理論印度季風(fēng)印度季風(fēng)東亞季風(fēng)東亞季風(fēng)西北太平洋季風(fēng)西北太平洋季風(fēng)澳大利亞季風(fēng)澳大利亞季風(fēng)Monsoon circulation and precipitation in Asian-Australian Region (Boreal summer minus boreal winter)Monsoon: derived from the Arabic word for seasonCharacter: Seasonal reversa

3、l of the wind directionWhat is Monsoon?WinterSummerDefinition of monsoonlRamage（1971）Monsoon Meteorotogyl1月和7月盛行風(fēng)向變化超過120l1月和7月盛行風(fēng)的平均頻率超過40%l至少1月和7月中有一個月的平均合成風(fēng)超過3 m/sl在5經(jīng)緯度矩形內(nèi)，這兩個月中每個月氣旋和反氣旋的交替出現(xiàn)至少每兩年一次 lWebster（1987）Monsoonl冬、夏風(fēng)向的季節(jié)性反轉(zhuǎn)和干、濕期的季節(jié)性交替出現(xiàn)American meteorological society glossary of monsoon

4、lmonsoon(Derived from Arabic mausim, a season.) A name for seasonal winds. lIt was first applied to the winds over the Arabian Sea, which blow for six months from northeast and for six months from southwest, but it has been extended to similar winds in other parts of the world. lEven in Europe the p

5、revailing west to northwest winds of summer have been called the “European monsoon.” lThe primary cause is the much greater annual variation of temperature over large land areas compared with neighboring ocean surfaces, causing an excess of pressure over the continents in winter and a deficit in sum

6、merlbut other factors such as the relief features of the land have a considerable effect. lThe monsoons are strongest on the southern and eastern sides of Asia, the largest landmass, but monsoons also occur on the coasts of tropical regions wherever the planetary circulation is not strong enough to

7、inhibit them. They have been described in Spain, northern Australia, Africa except the Mediterranean, Texas, and the western coasts of the United States and Chile. lIn India the term is popularly applied chiefly to the southwest monsoon and, by extension, to the rains which it bringsl東南季風(fēng)不特古代蕃舶借以北來，

8、而我國夏季雨澤甘霖之得以長驅(qū)直入而達(dá)黃河、長江流域，實(shí)亦利賴之也。在我國古籍所載東南季風(fēng)之名稱不一，風(fēng)俗通謂：“五月有落梅風(fēng)，江淮以為信風(fēng)?！庇裰ヌ谜勊C引風(fēng)土記謂“南中六月則有東南長風(fēng)號黃雀風(fēng)”。蘇東坡舶棹風(fēng)詩：“三時已斷黃梅雨，萬里初來舶棹風(fēng)?！逼湓娨杏性疲骸皡侵忻酚昙冗^，颯然清風(fēng)彌旬，歲歲如此，湖人謂之舶棹風(fēng)。是時海舶初回，此風(fēng)自海上與舶俱至云爾?！鄙w信風(fēng)可兼指冬夏季風(fēng)，而舶棹風(fēng)則專指夏至后東南季風(fēng)而言 竺可楨 1934，東南季風(fēng)與中國之雨量中國對于季風(fēng)的記錄l竺可楨，1916，“中國之雨量及風(fēng)暴說”中指出，季風(fēng)是由于陸地與海水的比熱不同而引起的。l陸地的比熱低，較海洋易熱亦易冷，夏季大

9、陸比海洋熱，冬季則相反。夏季水冷于陸，近陸的空氣浮升，海面稍冷的空氣群趨之，因此風(fēng)常自海而陸；冬季則陸冷于水，大陸上的氣壓較在海面者為高，故風(fēng)常由陸至海。這樣就形成了季風(fēng)。這就是國內(nèi)外盛行的海陸分布季風(fēng)形成說。 l1933，“中國氣流之運(yùn)行”l冬季西伯利亞高氣壓籠罩亞洲大陸，風(fēng)從大陸吹入海中；夏季大陸上變成低氣壓區(qū)，風(fēng)就從海洋吹向大陸；春秋兩季都是風(fēng)的轉(zhuǎn)變時期。l1934，“東南季風(fēng)與中國之雨量” l夏季季風(fēng)帶來水汽是中國雨澤的主要來源。當(dāng)夏季東南季風(fēng)強(qiáng)盛時，長江流域主旱，華北偏澇；當(dāng)東南季風(fēng)不強(qiáng)時，長江流域主澇而華北偏旱。 季風(fēng)區(qū)季風(fēng)區(qū)季風(fēng)區(qū)季風(fēng)區(qū)After Webster 1987Bin

10、Wang and LinHo 2002季風(fēng)區(qū)季風(fēng)區(qū)January climatological wind vectorMonthly wind vectorMean of January and July climatological wind vector Static normalized seasonality (SNS) indexDynamical normalized seasonality (DNS)Li and Zeng, 2001d 2為季風(fēng)區(qū)Li and Zeng, 2001X熱帶季風(fēng)系統(tǒng)：南亞季風(fēng)、印度尼西亞季風(fēng)、南海季風(fēng)、澳洲季風(fēng)、西北太平洋季風(fēng)、西非季風(fēng)和索馬里-西印

11、度洋季風(fēng)、南美季風(fēng)區(qū)、中美季風(fēng)區(qū)副熱帶季風(fēng)系統(tǒng)：東亞季風(fēng)、北美季風(fēng)、北非季風(fēng)、沿著伊朗高原和青藏高原北部邊緣的中亞地區(qū)內(nèi)陸季風(fēng)、高原季風(fēng)、南澳大利亞季風(fēng)、南非季風(fēng)溫寒帶季風(fēng)區(qū)：遠(yuǎn)東季風(fēng)、阿拉斯加北部地區(qū)、北極部分地區(qū)Monsoon indexsummerWang, B., et al 2008Monsoon indexwinterWang and Chen 2010東亞季風(fēng)的歷史演變l早第三紀(jì)無季風(fēng) (7040Ma B.P.)l第三紀(jì)準(zhǔn)季風(fēng)（東部沿海出現(xiàn)冬干夏濕的季節(jié)變化，且存在東西方向濕度差異，可能與氣候轉(zhuǎn)涼和海陸溫度梯度增大有關(guān)）(40Ma10Ma B.P.)l第四紀(jì)早期海洋性季風(fēng)l第四紀(jì)

12、中期以來大陸性季風(fēng)l現(xiàn)代東亞季風(fēng)是青藏高原隆升達(dá)到3000米以上，熱力和動力作用相結(jié)合的產(chǎn)物，大致定性于1.00.2Ma B.P.板塊運(yùn)動狀況準(zhǔn)季風(fēng)海洋性大陸性ABCsummerwinterAn et al. 2001A. Slight trendsB. Intensification of both summer and winter monsoons：incremental plateau uplift or extensionC. Winter monsoon become strongerlFirst, enhanced aridity in the Asian interior an

13、d onset of the Indian and east Asian monsoons, about 98Myr ago; lNext, continued intensification of the east Asian summer and winter monsoons, together with increased dust transport to the North Pacific Ocean, about 3.6-2.6Myr ago;lLast, increased variability and possible weakening of the Indian and

14、 east Asian summer monsoons and continued strengthening of the east Asian winter monsoon since about 2.6Myr ago.An et al. 2001From An et al. 2001Solar radiationGlacial boundary conditionMountain elevationCO2 experimentPrell, 1992Jiang 2008Jiang 2008Kitoh, 2004Kitoh, 2004l青藏高原的存在，使得東亞冬夏季風(fēng)都更強(qiáng)，冬季風(fēng)影響可以到

15、北回歸線以南，夏季風(fēng)更加深入內(nèi)陸和北方地區(qū)l即使在高原強(qiáng)烈隆起之前、地形高度還很低的情況下，南亞季風(fēng)就已經(jīng)存在，只是隨著高原隆起加大了南亞地區(qū)由海陸分布所奠定的徑向熱力對比，從而使得南亞季風(fēng)進(jìn)一步加強(qiáng)季風(fēng)的形成因素？l太陽輻射年變化所造成的行星熱對流環(huán)流是熱帶季風(fēng)的“第一推動力”l 地表特性差異所導(dǎo)致的準(zhǔn)定常行星波(也有季節(jié)變化)為“第二推動力”l如以推動大氣質(zhì)量越赤道緯圈傳輸?shù)男Я砜矗?二推動力之效力比在(北半球)夏季為4：(12)， 在冬季為3：(13)， 或者平均大體來說就是2：1曾慶存，2002季風(fēng)動力學(xué)理論季風(fēng)動力學(xué)理論l理想（干大氣）季風(fēng)模型（柯欽等，1956）l季風(fēng)是由于大陸與

16、海洋受熱不均勻后、引起力管而形成lGill模型（Gill，1980）l熱源強(qiáng)迫lRodwell-Hoskins 的季風(fēng)模型 (Rodwell and Hoskins, 2001)lChao-Chen （2001）lThe monsoon is interpreted as an intertropical convergence zone (ITCZ) substantially away (more than 108) from the equator land the existence of the ITCZ does not have to rely on landsea contra

17、st.lTP SHAP (Sensible heat driven Air-Pump) (Wu et al., 1997, 2007)luplifted heating/cooling渦度和渦度方程渦度和渦度方程 p Divergence Tilting Baroclinic Friction()()aaaapt VVVF左端的一項(xiàng)為絕對渦度的局地變化局地變化，第二項(xiàng)為平流項(xiàng)平流項(xiàng)，第三項(xiàng)為散度項(xiàng)散度項(xiàng)，第四項(xiàng)為扭轉(zhuǎn)項(xiàng)扭轉(zhuǎn)項(xiàng)，式中右端第一項(xiàng)為力管項(xiàng)力管項(xiàng)，第二項(xiàng)為摩擦耗散項(xiàng)摩擦耗散項(xiàng) apt考慮渦旋的產(chǎn)生apt考慮渦旋的產(chǎn)生考慮渦旋的產(chǎn)生考慮干空氣考慮干空氣pRTdpddTpT10hPa100

18、0hPadpp10K300dTTKddTT水平面上氣壓變化相對較小，等壓面近似水平，而溫度和密度的變化大。于是等壓面和等容面產(chǎn)生交角，這意味著渦旋的形成 atp考慮渦旋的產(chǎn)生ppp ABCDBD N p12ppddTTSurface temperaturelGill模型（Gill，1981）l熱源強(qiáng)迫比較對稱熱源反對稱熱源Gill模型模型 ut12yv pxvt12yu pyptuxvy Q uteu12yv pxvtev12yu pypte puxvy Qwe pQ tteInclude Rayleigh friction and Newtonian coolingSteady-state

19、eu12yv pxev12yu pye puxvy Qwe pQGill 1980pwSolution for heating symmetric about the equator in the region |x|2 Q(x,y) F(x)exp(14y2) F(x) coskx,xLSolution for heating antisymmetric about the equator in the region |x| QVq q0 QVq q0 QVq qBoos & Kuang: Dominant control of the South Asian monsoon by

20、orographic insulation versus plateau heating, Nature, 2010, doi:10.1038/nature08707no elevated topographystandard topographysurface elevations north of the Himalayas set to zeroFigure 1 | Distributions from the atmospheric model of mass-weighted vertical mean temperature (shading, interval is 1K) an

21、d wind for 200400 hPa (left panel), equivalent potential temperature on a terrain-following surface level (middle panel, interval is 5K), and precipitation rate (colour shading, interval is 2 mmd-1) and 850 hPa winds (vectors) (right panel) for a, control experiment CON with full topography; b, expe

22、riment TOP-NS in which sensible heating at the top of the Tibetan Plateau was removed; c, experiment HIM in which surface elevations north of the Himalayas set to zero; and d, experiment HIM-NS which is the same as the HIM run except the surface sensible heating on the Himalayas is set to zero. All

23、panels are for JuneAugust, and thick black contours surround elevations higher than 1500 m and 3000 m. CONTOP-NSHIMHIM-NSq q 1 1q q 2 2PumpingPumpingq q 1 1q q 2 2PumpingPumpingq q 1 1q q 2 2PumpingPumpingq q 1 1q q 2 2No PumpingNo PumpingdL_ScNMTbOBSCONaImpacts of landsea thermal contrast on the As

24、ian summer monsoond. Land-Sea thermal contrastc. No Mountainb. OBSa. CONDIFFaRequired Circul. and Precip. to make up the Asian summer monsoonIPTP thermal forcingcIPTP_SHDIFF = TOTAL - (L_S)bIPTP_MaCONcHIMdHIM_Ma. CONb. Iran Plateau and Tibetan Plateau, only mechanical forcingc. HIM sensitive heating

25、 and mechanical forcingd. HIM-No Sensitive heating, only mechanical forcingFigure 5 Structure of the South Asian summer monsoon, showing 80E90E abCONIPTP_MWith TP surface sensible heatingWithout TP surface sensible heatingS SE EZ (Z (km) )510Eq.Eq.IndiaChinaTibetan PlateauIran PlateauSASM North BranchSASM South BranchMeridional CirculationTo EASMIP IP T TP PTP TP L_SL_SL_L_S SFigure 6 Schematic diagram showing the gross structure of the South Asian summer monsoonThermal Control of th