大气科学  2017, Vol. 41 Issue (5): 988-998 PDF

1 扬州大学物理科学与技术学院, 扬州 225002
2 兰州大学大气科学学院, 兰州 730000
3 国家气候中心, 北京 100081

Effects of Anomalous Water Vapor Transport from Tropical Indian Ocean-Western Pacific on Summer Rainfall in Eastern China
ZOU Meng1, QIAO Shaobo2, WU Yongping1, FENG Guolin1,3
1 College of Physical Science and Technology, Yangzhou University, Yangzhou 225002
2 College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000
3 National Climate Center, Beijing 100081
Abstract: Using monthly reanalysis datasets of NCEP/NCAR for 1979-2015, the impact of anomalous water vapor transport from the tropical Indian Ocean-western Pacific on summer precipitation in eastern China was analyzed in this paper. The results show that the summertime anomalous water vapor transport from the tropical India Ocean-western Pacific (10°S-30°N, 60°-140°E) to eastern China mainly includes two modes, which can explain 34% of the total water vapor transport variance. The first mode (EOF1) shows anomalous water vapor transport from the tropical western Pacific across the South China Sea and the Bay of Bengal to eastern China along the western flank of the anticyclone. The water vapor transport from the South China Sea and the Bay of Bengal both are abnormally high. Meanwhile, the WPSH (western Pacific subtropical high) is significantly stronger than normal, and anomalous water vapor convergence occurs over the middle and lower reaches of the Yangtze River valley accompanied with significant upward movements, which are favorable for precipitation over this region. The second mode (EOF2) shows anomalies of anticyclonic water vapor transport from the tropical India Ocean across the Arabia sea, India Peninsula, and Indo-China Peninsula and anomalies of cyclonic water vapor transport over southern China, which lead to anomalous water vapor convergence and ascending motions over southern China. As a result, more precipitation occurs in southern China. Furthermore, possible external causes for the above two modes were analyzed. Results indicate that the EOF1 is closely related to ENSO. SST (sea surface temperature) over the tropical eastern Pacific in the preceding winter was significantly warmer than normal, while SSTs over the tropical North India Ocean and the South China Sea in the subsequent summer were significantly warmer than normal. These SST anomalies resulted in a significantly strong WPSH and anomalously high water vapor mainly originated from the tropical western Pacific and the South China Sea. The EOF2 is related to the simultaneous positive phase of the tropical Indian Ocean Dipole (IOD). The anomalous easterly winds appeared over the tropical India Ocean when the IOD was positive phase, which was linked to anomalous cyclonic circulation and moisture convergence over South China. The anomalous water vapor mainly originated from the tropical southern India Ocean.
Key words: Tropical Indian Ocean-western Pacific      Anomalous water vapor      ENSO      Middle and lower reaches of the Yangtze River      South China
1 引言

2 资料和方法

 ${Q_u}(x, y, t) = \frac{1}{g}\int\limits_{300}^{{p_s}} {q(x, y, t)u(x, y, t){\rm d}p, }$ (1)
 ${Q_v}(x, y, t) = \frac{1}{g}\int\limits_{300}^{{p_s}} {q(x, y, t)v(} x, y, t){\rm d}p,$ (2)

3 热带印度洋—西太平洋夏季平均水汽输送路径和时空变化特征

 图 1 1981~2010年东亚地区夏季平均的水汽通量（单位：kg m-1 s-1）分布 Figure 1 Spatial pattern of mean summer water vapor fluxes (units: kg m-1 s-1) over eastern Asia for 1981–2010

 图 2 1979~2015年热带印度洋—西太平洋夏季水汽输送标准化场的（a）EOF第一模态的空间分布型及其对应的（c）标准化时间系数（PC1），（b）EOF第二模态的空间分布型及其对应的（d）标准化时间系数（PC2）。图a、b中阴影表示风场分量u或者v的值通过99%信度水平检验，黄（蓝）色阴影表示t检验中的t值小于（大于）负（正）的临界值，下同 Figure 2 (a) Spatial pattern of the first EOF mode and (c) the corresponding normalized time coefficients (PC1), (b) spatial pattern of the second EOF mode and (c) the corresponding normalized time coefficients (PC2) of standardized water vapor transport fluxes over the tropical Indian Ocean–western Pacific for 1979–2015. In Figs. a and b, shaded areas indicate values of component u or component v pass the test t at 99% confidence level, yellow (blue) shaded areas represent values of t less (more) than negative (positive) thresholds, the same below

 图 3 PC1与（a）整层的水汽通量（单位：kg m-1 s-1）、（c）500 hPa的水汽通量（单位：g m-1 s-1 Pa-1）、（e）850 hPa的水汽通量（单位：g m-1 s-1 Pa-1）的一元线性回归分布；PC2与（b）整层的水汽通量（单位：kg m-1 s-1）、（d）500 hPa的水汽通量（单位：g m-1 s-1 Pa-1）、（f）850 hPa的水汽通量（单位：g m-1 s-1 Pa-1）的一元线性回归分布 Figure 3 Linear regression maps of PC1 with water vapor fluxes for (a) the entire troposphere (units: kg m-1 s-1), (c) 500 hPa (units: g m-1 s-1 Pa-1), (e) 850 hPa (units: g m-1 s-1 Pa-1). (b), (d), (f) As in (a), (c), (e), but for PC2
4 热带印度洋—西太平洋水汽异常输送与中国东部夏季降水关系

 图 4 （a）PC1与中国东部夏季降水距平百分率的一元线性回归分布；（b）同（a），但为PC2。图中黑点区域代表降水距平百分率通过90%信度水平的检验 Figure 4 (a) Linear regression maps of PC1 with percentage of summer precipitation anomalies over eastern China. (b) As in (a), but for PC2. Black dotted areas indicate the percentage of precipitation anomalies significance at 90% confidence level

 图 5 PC1对（a）500 hPa、（c）850 hPa水汽输送通量的辐散（红色阴影）、辐合（蓝色阴影）一元线性回归分布。（b、d）同（a、c）但为PC2。图中黑点区域代表通过90%信度水平的检验 Figure 5 Linear regression maps of PC1 with the divergence (red shadings) and convergence (blue shadings) of water vapor fluxes at (a) 500 hPa, (c) 850 hPa. (b, d) As in (a, c), but for PC2. Black dotted areas indicate regression significance at 90% confidence level

 图 6 （a）PC1与不同位势高度垂直速度（单位：10−2 Pa s-1）的一元线性回归分布。（b）同（a），但为PC2。图中阴影代表通过95%信度水平的检验 Figure 6 (a) Linear regression maps of PC1 with the vertical velocity (units: 10-2 Pa s-1) at different geopotential height. (b) As in (a), but for PC2. Shaded areas indicate regression significance at 95% confidence level
5 热带印度洋—西太平洋异常水汽输送与海温、蒸发的关系

 图 7 PC1与（a）前冬海温（单位：℃）、（c）春季海温（单位：℃）、（e）夏季海温（单位：℃）的一元线性回归分布。（b、d、f）同（a、c、e），但为PC2。图中黑点区域代表通过90%信度水平的检验 Figure 7 Linear regression maps of PC1 with the SST (units: ℃) in the (a) preceding winter, (d) spring, and (f) summer. (b, d, f) As in (a, c, e), but for PC2. Black dotted areas indicate regression significance at 90% confidence level

 图 8 （a）PC1与夏季热带印度洋—西太平洋蒸发量（单位：mm d-1）的一元线性回归分布。（b）同（a），但为PC2。图中黑点区域代表通过90%信度水平的检验 Figure 8 (a) Linear regression maps of PC1 with summer evaporation (units: mm d-1) over the tropical India Ocean–western Pacific. (b) As in (a), but for PC2. Black dots areas indicate regression significance at 90% confidence level
6 结论与讨论