The variability of the Asian summer monsoon in warmer climate Ding Yihui* (National Climate Center, CMA) *Contributers: Wang Zunya, Sun Ying,Liu Yunyun, Liu Yanju, Song Yafang, Zhang Jin

Outline 1. The variability of Asian summer monsoon under global warming in last 100-years 2. Future change in Asian summer monsoon in a warmer world in next 100 years 3. Discussions and conclusions

1. The variability of Asian summer monsoon under global warming in last 100-years

Fig.1. The vertically integrated moisture flux transport (surface to 300hPa )averaged for summer (JJA: June, July and August) of (Unit ： kg.m -1.s -1 ） Climatology of the Asian summer monsoon

Fig.2. The vertically integrated field of divergence of moisture transport for JJA of Negative (positive) regions denotes the convergence (divergence) of moisture （ Unit ： kg.m -2.s -1 )

Fig.3. Climatological mean ( ) summer precipitation pattern ( Unit:mm.d -1 )

Fig.4. Schematic maps of the climatological mean moisture budgets of the Asian-Pacific summer monsoon region in summer (JJA) (Units:106kg/s). The shaded area refers to the Tibetan Plateau. The positive and negative values represent net moisture influx and efflux, respectively. SIO: South Indian Ocean(30S°-0°N, 40°E-120°E); AS: Arabian Sea(0°-22.5°N, 40°E-80°E); BOB: Bay of Bengal (0°-22.5°N, 80°E-100°E); SCS: South China Sea(0°-22.5°N, 100°E-120°E) ; SC: South China (22.5°N-27°N, 100°E-120°E); YHRB: Yangtze–Huaihe River Valleys(27°N-35°N, 100°E-120°E); NC: North China(35°N-42°N,100°E-120°E); NEC: Northeast China(42°N-54°N,120°E-135°E); NWNP: northwestern part of North Pacific (22.5°N- 45°N, 120°E-160°E); SWNP: southwestern part of North Pacific(0°-22.5N°, 120°E-160°E).(Liu, et al.,2009)

观测近百余年北半球（上图， Latif 等， 2009 ）和中国（下图，根据龚道溢，王绍武， 2009 计算绘制）年 平均气温距平变化（图中黑线是年平均距平，红线是线性趋势，兰线是 21 年滑动平均） Time series of observed mean surface temperature change for last 100 years Top panel: NH; bottom panel: China. Red: trends, blue:21-yr running average.

Correlation patterns of Asian-Pacific summer (JJA) monsoon 亚洲 - 太平洋季风降水的相关分布 西北太平洋关键区 6~8 月降水与亚洲 - 太平洋季风区降水的相关

季风子系统的遥相关（季节内变率的整体性）  夏季风爆发初期， ISM 通过 “ 南支 ” 遥相关型影响长江流域梅雨；  夏季风盛行期间， ISM 通过 “ 北支 ” 遥相关型影响华北地区降水；  WNPSM 主要通过经 30~60 天滤波的 CISO 影响中国夏季降水。 Teleconnection modes of various components of Asian summer system: holistic correlation for ISO

Fig.5. Long-term variation of the East summer monsoon index for (based on Guo’s monsoon index). Positive(negative)values denote stronger (weaker)summer monsoon than normal. (IPCC, 2007) Weakening of the Asian summer monsoon and superposed inter-annual and inter-decadal variability.

Inter-decadal variability for all India precipitation 12-18,30-40 and yr oscillation (Goswami,2005) 年代际变率： 年， 年， 60 与 80 年

降水距平 百分比 /% Long–tem of anomalous precipitation in Asian-African monsoon regions 西非 West Africa （ Trenberth, et al ） 东非 East Africa （ Trenberth, et al ） 南亚 South Africa （ Trenberth, et al ） 中国华北（ 71 个站序列） North China Ren and Feng (2009) 年亚非季风区降水量异常

近 50 年来，西部地区降水约增加 15 ％ — 50 ％；东部地区频繁出现 “ 南涝北旱 ” ，华南地区降 水约增加 5 ％ — 10 ％，而华北和东北大部分地区约减少 10 ％ — 30 ％。 （图： 年 我国年降水量变化幅度） 我国降水分布发生了明显变化 Significant change in summer precipitation pattern in China ( ) unit:%/10yrs （中国气象局气候变化中心）

年和 年年平均干旱日数之差 （单位：天） Difference in drought days between and （第二次国家气候变化评估报告初稿， 2009 ）

近 50 年来中国大陆极端强降水日数的变化趋势（实心和虚心圆分别代表增 加和下降趋势，按半径大小分别为每 10 年变化 7.5% 以上， 7.5% ～ 2.5% ， 小于 2.5% ，显著变化的地区标有叉号） Numbers of days of heavy rainfall

Vulnerability of fresh water resources in the context of global climate change (high stress region in North China) IPCC ， 2007 气候变化下，全球现代淡水资源的脆弱性和他们的管理

华北 (a)(b) (c)(d) 123 年（ 1880 － 2003 ）中国东部分区降水的变化 Long –term (123yr)variation of summer precipitation in North China (a), Yangtze River basin (b), South China (c) and Meiyu season 长江 华南梅雨季

Period (years) Va ria nc e ( σ 2 ) Period (years) Va ria nc e ( σ 2 ) Period (years) Va ria nc e ( σ 2 ) Period (years) Va ria nc e ( σ 2 ) (a)(b) (c)(d) 小波分析功率谱： 年与 80 年周期趋势变化分析： 1978 和 1992 是两个突变点 Spectrum power of wavelet analysis:30-40-yr and yr oscillations 华北 (c)(d) 长江 华南 梅雨季

中国东部不同分区夏季降水的主要周期 Major periods of summer precipitation in different subregions of East China subdivision 分区 A 时段（ 123 年） B 时段（ 54 年） 华南 South China 4, 14*, 30*, 80*2*, 7, 30* 长江中下游 Yangtze 2*, 7*, 20*, 40*2*, 7,14, 40* 华北 North China 3, 9, 18*, 40*, 80 3*, 9, 18 长江中下游 5 站 (121 年 ) Meiyu Season 2, 7, 12, 40*, 80* 2, 7*, 12, 40* * 代表超过 50% 信度

中国东部三个地区夏季降水的突变点检验 Detection of abrupt change points for different subregions in East China Methods 方法 South China 华南 Yangte 长江中下 游 North China 华北 Meiyu 梅雨期长江中下 游 5 站 Running Test1980, , Yamamoto et al., (1986) 1980, , Mann-Kendall (1945; 1975) 所有的突变点都超过 95% 的信度

(a) (b) (c) (d) 中国夏季降水的 EOF 分析（ ） EOF modes of summer precipitation (JJA) for (a)(c): EOF1 ； (b)(d): EOF2 空间分布 时间系数

夏季风 水汽输 送向量 的 EOF 分析 下图是 时间系 数 Leading EOF model of moisture tranport for Asian summer monsoon

b 图 ~2005 年夏季 850hPa 风场的 EOF 分解的第 1 特征向量（ a ）及对应的时间系数（ b ） a

中国不同时段，夏季降水距平百分比分布 的变化。（阴影区是正距平，相对于 年平均值） In-decadal shifts of summer monsoon patterns in China shading: positive anomaly percentage

中国东部 ( °E) 平均夏季异常降水纬度 - 时间剖面图。单位 : mm Latitude-time cross-section of summer precipitation departure( °E)

850 hPa 平均经向风纬度时间剖面图 （ unit: ms -1 ）。阴影区是异常南风。 Latitude-time cross-section of 850hpa V-component departures, shading: South wind

异常夏季水汽输送 (a) 和水汽汇 (Q 2 ) (b) 纬度 - 时间剖面图。（地面到 300hPa 输送总量）。单位 : Kgm -1 g -1 (a) 和 Kgm -1 s -1 (b). Cross-sections of anomalous moisture (a) transport and divergence (Q2) (b) for East China (a) (b)

b c 1951~2005 年夏季 850hPa 风场的 EOF 分解的第 2 特征向量（ a ）、 时间系数（ b ）及时间系数的最大熵谱曲线（ c ） Interannual Variability: TBO and 4-7-yr oscillations 850hPa wind EOF2 Time coefficient

a d b c d 1951~2005 年夏季海平面气压场 EOF 分解 的第 1 和 2 特征向量（ a 、 c ）对应的时间系 数（ b 、 d ） EOF fields of (a)EOF1 (c) EOF2 and corresponding time coefficients (b)EOF 1,(d)EOF2 Sea level pressure

(a) (b) Time series of the anomalous vertically integrated (from surface to 100hPa) apparent heat source (Q1) averaged for all Tibetan Plateau (75 ～ 105°E ， 27.5~42.5°N ) for summer (a), and spring (b). Solid lines denote 9-yr running mean curves. Unit: Wm -2

a c b d 整层积分的大气热源分布（阴影为负值区） EOF fields of vertically integrated atmospheric heat source (Q1) (a) EOF1; (b) EOF2 and corresponding time coefficients; (b) EOF1 ； (d)EOF2

e d 能是亚洲 - 太平洋夏季风系统的一种固有振荡，它与暖洋面上的海气相互作用振荡密切关联。 季风强年海温的季节演变合成图（ a 、前一年冬季； b 、当年 春季； c 、当年夏季； d 、当年秋季； e 、当年冬季；虚线方框代表 印度洋偶极子关键区和 Nino3.4 区） a b c d e Composite SSTA (Nino 3.4) patterns for strong summer monsoon phase of the TBO cycle e a: preceding winter (year 0) b ； spring (year 1) c: summer (year1) d: autumn (year1) e: following winter (year2) Box: IOD and Nino 3.4.

亚洲 - 太平洋夏季风准两年振荡的异常场示意图 绿色阴影区代表亚洲 - 太平洋季风区夏季大气热源的正值区；黑色箭头代表 850hPa 环 流异常场；灰色阴影区代表异常水汽辐合场；红（蓝）色曲线代表海温异常场 Schematic of the anomalous fields for TBO of the Asian –Pacific forced by ENSO events.

2. Future change in Asian summer monsoon in a warmer world in next 100 years

模式名称模式和 CMAP 夏季平均 降水的相关 模式和 GPCP 夏季平 均降水的相关 模式和中国站点降水资 料 减去 降水变化的相关 分类情况 1CGCM3.1(T47) 类3类 2CGCM3.1(T63) 类3类 3CNRM-CM 类2类 4CSIRO 类2类 5GFDL-CM 类1类 6GFDL-CM 类2类 7GISS-EH 类3类 8GISS-ER 类3类 9FGOALS-g 类3类 10INM-CM 类2类 11IPSL-CM 类3类 12MIROC3.2(hires) 类1类 13MIROC3.2(medres) 类1类 14ECHAM 类3类 15MRI-CGCM 类3类 16CCSM 类3类 17PCM 类3类 18UKMO-HadCM 类2类 19UKMO_hadgem 类2类 Validations of IPCC model performance

中国东部降水变化百分率 EOF 分析结果 EOF analysis of summer precipitation in East China for

Fig.10. Future percentage changes(%) in summer precipitation for East Asia and its three sub-regions (South China, Yangtze River Valley(YRV) and North China), relative to climatological mean of Projections are based on 19 IPCC AR4 climate models.(Sun and Ding,2009)

中国东部降水时间 - 纬度剖面 Latitude-time cross-section of East Asian summer precipitation for

Fig.12. Future change of the East Asian summer index for next 100 years( based on the definition of monsoon index by Lu and Chan, with estimate of the V-component of wind). (Sun and Ding,2009)

东亚 850hPa 水汽输送变化时间 - 纬度剖面 Latitude –time cross-section of 850hpa moisture transport in East Asia for

Projection of South Asian summer monsoon The land-sea thermal contrast for June-July-August- September (JJAS) between the TP region(20o-40°N, 60o- 100°E) and the tropical Indian Ocean (TIO, 10°S-10°N, 60o-100°E) (see the black boxes in Fig. 1a) was computed for both the upper and lower troposphere using TCupper= Thickness( hPa, TP) – Thickness( hPa, TIO) and TClower = Temperature (near-surface [2m], TP) – Temperature ( hPa, TIO). The hPa temperature over the TIO is used as a proxy of near- surface temperature after height adjustment for comparison with 2m air temperature over the TP, which is 2-5km above the mean sea level. (Sun, Ding and Dai,2010)

Long-term ( ) mean of June-July-August (JJAS) 850hPa winds (arrows, in m s-1) and hPa thickness anomaly (colors, in geopotential meter [gpm]) relative to the mean of the domain (10°S- 45°N, 30°-140°E).

Temporal evolution of (a) JJAS MI (black, in m s-1), TCupper (red, gpm), and TClower(blue, gpm), and (b) JJAS -U200 (black, m s-1) and U850 (green, m s-1) anomalies (relative to mean) averaged over 0°-20°N and 40°-110°E, and TCupper (red, gpm), and TClower (blue, gpm) from 1951 to 2099 based on IPCC AR4 7- model arithmetic mean under observation-based forcing during and the A1B scenario for U200 anomalies in (b) were multiplied by -1 to show the weakening of 200hPa easterly winds.

IPCC 7-model averaged (a) time- height cross-section of JJAS temperature departures (K, from mean) averaged over the TIO during (b) Latitude-height cross- section of JJAS temperature change (K) from to averaged between 60°E and 100°E. The topography along 90°E is shown by the black areas. (c) Longitude-height cross-section of change (K, from mean) in JJAS meridional temperature gradient (temperature changes averaged from 20o-40°N minus that from 10°S-10°N) for The topography along 35°N is shown by the black areas. (d) Time series of JJAS hPa thickness anomalies (gpm, from mean) over the TP (solid line) and TIO (dashed line) during

3. Discussions and conclusions

(1) In recent three decades, North and Northeast China have suffered from severe and persistent droughts while the Yangtze River basin and South China have undergone much more significant heavy rainfall/floods events. This long-term change in the summer precipitation and associated large-scale monsoon circulation features have been examined by using about 123-yr (1880–2002) records of precipitation in East Asia. One dominating mode of the inter-decadal variability of the summer precipitation in China is the near-80-yr oscillation. Then, on this basis, a possible explanation of this long- term change in relation to significant weakening of the Asian summer monsoon, possibly due to the abrupt increase in the preceding winter and spring snow over the Tibetan Plateau and warming of the sea surface temperature in tropical central and eastern Pacific since about 1978,has been set forward.

But we cannot answer whether the anthropogenic forcing has caused the changes of patterns of rainfall, floods/droughts in China, and East Asian monsoon. Natural fluctuation of climate change can also play an important role. It needs the further studies.

(2) It seems that the major rainfall belts would move northward by about 2040, but unstable. Afterwards, the summer precipitation in North China would increase considerably and stably. Furthermore, this anthropogenically-driven precipitation shift would appear to be consistent with the occurrence of rainfall peak period caused by the natural near-80-yr cycle. But this coincidence will be reliable?

(3)The above analyses show that the differential increases of the upper-tropospheric temperature over the TIO and TP lead to the changed relationship between the SASM intensity and tropospheric thermal contrasts over the SASM regions in a GHG-induced warmer climate. The weakening of the SASM circulation is directly related to the decrease of upper-tropospheric TP-TIO thermal contrast, which in turn is caused by the larger upper- tropospheric warming over the TIO than over the TP. The fact that the SASM weakens as the lower-tropospheric thermal contrast increases in the 21st century implies a smaller role of this thermal contrast in determining the SASM intensity than suggested by previousstudies for the 20th century.

(4) Uncertainty of modeling the enhancement of water vapour in upper troposphere in tropics and subtropics