高等大气动力学第10讲季风

1、第1010讲 季风动力学魏魏 科科, 中国科学院大气物理研究所, E-mail: 高等大气动力学NepalChinaTibet Plateau “这是喜马拉雅山脉，这是中国的青藏高原，这是尼泊尔，山脉的南坡缓缓的伸向印度洋，受印度洋暖湿气流的影响，尼泊尔王国气候湿润，四季如春，而山脉的北麓陡降，终年积雪，再加上深陷大陆的中部，远离太平洋，所以自然气候十分的恶劣”“如果我们把喜马拉雅山炸开一道五十公里的口子，世界屋脊还留着，把印度洋的暖风引到我们这里来，试想一想，那我们美丽青藏高原从此摘掉落后的帽子不算，还得变出多少个鱼米之乡！”1999年电影不见不散 葛优台词青藏高原对亚洲季风区而言是福是祸？

2、青藏高原对亚洲季风区而言是福是祸？亚洲季风是如何形成的？亚洲季风是如何形成的？Everest引子引子Outlinel季风概念和全球季风l季风的历史演变l季风的形成理论印度季风印度季风东亚季风东亚季风西北太平洋季风西北太平洋季风澳大利亚季风澳大利亚季风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月盛行风向变化超过120l1月和7月盛行风的平均频率超过40%l至少1月和7月中有一个月的平均合成风超过3 m/sl在5经纬度矩形内，这两个月中每个月气旋和反气旋的交替出现至少每两年一次 lWebster（1987）Monsoonl冬、夏风向的季节性反转和干、湿期的季节性交替出现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东南季风不特古代蕃舶借以北来，

8、而我国夏季雨泽甘霖之得以长驱直入而达黄河、长江流域，实亦利赖之也。在我国古籍所载东南季风之名称不一，风俗通谓：“五月有落梅风，江淮以为信风。”玉芝堂谈荟引风土记谓“南中六月则有东南长风号黄雀风”。苏东坡舶棹风诗：“三时已断黄梅雨，万里初来舶棹风。”其诗引中有云：“吴中梅雨既过，飒然清风弥旬，岁岁如此，湖人谓之舶棹风。是时海舶初回，此风自海上与舶俱至云尔。”盖信风可兼指冬夏季风，而舶棹风则专指夏至后东南季风而言 竺可桢 1934，东南季风与中国之雨量中国对于季风的记录l竺可桢，1916，“中国之雨量及风暴说”中指出，季风是由于陆地与海水的比热不同而引起的。l陆地的比热低，较海洋易热亦易冷，夏季大

9、陆比海洋热，冬季则相反。夏季水冷于陆，近陆的空气浮升，海面稍冷的空气群趋之，因此风常自海而陆；冬季则陆冷于水，大陆上的气压较在海面者为高，故风常由陆至海。这样就形成了季风。这就是国内外盛行的海陆分布季风形成说。 l1933，“中国气流之运行”l冬季西伯利亚高气压笼罩亚洲大陆，风从大陆吹入海中；夏季大陆上变成低气压区，风就从海洋吹向大陆；春秋两季都是风的转变时期。l1934，“东南季风与中国之雨量” l夏季季风带来水汽是中国雨泽的主要来源。当夏季东南季风强盛时，长江流域主旱，华北偏涝；当东南季风不强时，长江流域主涝而华北偏旱。 季风区季风区季风区季风区After Webster 1987Bin

10、Wang and LinHo 2002季风区季风区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为季风区Li and Zeng, 2001X热带季风系统：南亚季风、印度尼西亚季风、南海季风、澳洲季风、西北太平洋季风、西非季风和索马里-西印

11、度洋季风、南美季风区、中美季风区副热带季风系统：东亚季风、北美季风、北非季风、沿着伊朗高原和青藏高原北部边缘的中亚地区内陆季风、高原季风、南澳大利亚季风、南非季风温寒带季风区：远东季风、阿拉斯加北部地区、北极部分地区Monsoon indexsummerWang, B., et al 2008Monsoon indexwinterWang and Chen 2010东亚季风的历史演变l早第三纪无季风 (7040Ma B.P.)l第三纪准季风（东部沿海出现冬干夏湿的季节变化，且存在东西方向湿度差异，可能与气候转凉和海陆温度梯度增大有关）(40Ma10Ma B.P.)l第四纪早期海洋性季风l第四纪

12、中期以来大陆性季风l现代东亚季风是青藏高原隆升达到3000米以上，热力和动力作用相结合的产物，大致定性于1.00.2Ma B.P.板块运动状况准季风海洋性大陆性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，使得东亚冬夏季风都更强，冬季风影响可以到

15、北回归线以南，夏季风更加深入内陆和北方地区l即使在高原强烈隆起之前、地形高度还很低的情况下，南亚季风就已经存在，只是随着高原隆起加大了南亚地区由海陆分布所奠定的径向热力对比，从而使得南亚季风进一步加强季风的形成因素？l太阳辐射年变化所造成的行星热对流环流是热带季风的“第一推动力”l 地表特性差异所导致的准定常行星波(也有季节变化)为“第二推动力”l如以推动大气质量越赤道纬圈传输的效力来看， 二推动力之效力比在(北半球)夏季为4：(12)， 在冬季为3：(13)， 或者平均大体来说就是2：1曾庆存，2002季风动力学理论季风动力学理论l理想（干大气）季风模型（柯钦等，1956）l季风是由于大陆与

16、海洋受热不均匀后、引起力管而形成lGill模型（Gill，1980）l热源强迫lRodwell-Hoskins 的季风模型 (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涡度和涡度方程涡度和涡度方程 p Divergence Tilting Baroclinic Friction()()aaaapt VVVF左端的一项为绝对涡度的局地变化局地变化，第二项为平流项平流项，第三项为散度项散度项，第四项为扭转项扭转项，式中右端第一项为力管项力管项，第二项为摩擦耗散项摩擦耗散项 apt考虑涡旋的产生apt考虑涡旋的产生考虑涡旋的产生考虑干空气考虑干空气pRTdpddTpT10hPa100

18、0hPadpp10K300dTTKddTT水平面上气压变化相对较小，等压面近似水平，而温度和密度的变化大。于是等压面和等容面产生交角，这意味着涡旋的形成 atp考虑涡旋的产生ppp ABCDBD N p12ppddTTSurface temperaturelGill模型（Gill，1981）l热源强迫比较对称热源反对称热源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