El Niño衰退年印度洋海盆模态对印度夏季季风降水的影响
作者简介:吕梁宏(1989—), 男, 山西省太原市人, 主要从事海气相互作用。Email: tysllh@163.com
收稿日期: 2016-05-29
要求修回日期: 2016-07-25
网络出版日期: 2017-04-06
基金资助
国家重大科学研究计划项目(2012CB955600), 国家自然科学基金项目(47476003、41106010)
The effect of Indian Ocean Basin mode on Indian Summer Monsoon Rainfall in decaying year of El Niño
Received date: 2016-05-29
Request revised date: 2016-07-25
Online published: 2017-04-06
Supported by
National Basic Research Program of China (2012CB955600)
The National Natural Science Foundation of China (47476003, 41106010)
Copyright
采用全印度陆地降水资料、NCEP/NCAR大气资料以及HadISST资料集的SST资料, 使用经验正交函数分解(Empirical Orthogonal Function, EOF)和相关分析回归分析等统计方法, 在前人的基础上, 系统研究了厄尔尼诺-南方涛动(El Nino-Southern Oscillation, ENSO)及印度洋海盆模态(Indian Ocean Basin mode, IOB)对印度夏季季风降水的影响, 指出厄尔尼诺衰退年印度夏季降水在反对称模态和北印度洋二次增暖共同的作用下表现出初夏减少晚夏增加的特点。通过观测分析发现, 厄尔尼诺在其发展年和衰退年对印度夏季季风降水的影响截然不同。在发展年, 中东太平洋的异常增暖引起Walker环流的改变, 印度洋区域的下沉气流抑制印度大陆降水。在衰退年, 厄尔尼诺对印度洋进行“充电”, 产生印度洋海盆增暖模态。在这个过程中, 局地海气相互作用引起衰退年的印度降水有初夏减少晚夏增加的特点。其中春季印度洋的反对称风场(赤道以北为东北风异常, 赤道以南为西北风异常)对印度夏季风有一定的减弱作用, 这种异常环流减弱了初夏印度降水。同时反对称风场会造成在夏季北印度洋的二次增暖, 又会促进了晚夏降水的异常增加。通过水汽输运通量的诊断分析进一步验证了上述海盆模态对印度夏季降水的作用。
吕梁宏 , 郑小童 . El Niño衰退年印度洋海盆模态对印度夏季季风降水的影响[J]. 热带海洋学报, 2017 , 36(2) : 1 -11 . DOI: 10.11978/2016054
Based on the All India Rainfall data, NCEP/NCAR reanalysis data and HadISST data, we demonstrated a delayed effect of the El Nino-Southern Oscillation (ENSO) and Indian Ocean Basin (IOB) mode on Indian summer monsoon rainfall (ISMR). The results showed that decreased Indian rainfall in the early summer (Jun-Jul) and increased rainfall in the late summer (Aug-Sep) are influenced by the anti-symmetric mode and the second warming in the northern Indian Ocean (NIO). The responses of ISMR to El Niño are distinct between the developing and decaying years. In the developing year of El Niño, the ISMR decreases due to the change of Walker circulation in the tropical ocean. In the decaying year, the IOB mode decreases (increases) the ISMR in early (late) boreal summer. The anti-symmetric pattern of atmospheric anomalies with northeasterly (northwesterly) wind anomalies north (south) of the equator happens in spring. The northeasterly anomalies weaken the Indian Summer Monsoon and force the second anomalous sea surface temperature (SST) peak in the NIO by reducing wind speed and surface evaporation. The southwest monsoon brings more moisture (Q°), which is produced by the warm NIO SST to the India subcontinent, leading to increased monsoon rainfall in the late summer.
Fig. 1 Correlation of India summer monsoon rainfall (blue bar) with NDJ Niño3.4 SST index (red dashed curve). a) In El Niño developing year; b) in El Niño decaying year; c) India summer monsoon rainfall delay index (ISMR-DI)图1 印度大陆夏季季风降水(ISMR)序列(蓝色柱状)和冬季(NDJ)Niño3.4指数序列(红色虚线) |
Fig. 2 Correlation (black solid curve) and regression (blue dashed curve) of ISMR and NDJ Niño3.4 index from developing year to decaying year of El Niño. Two horizontal red dashed lines show the 95% confidence level图2 El Niño发展年至衰退年印度降水与冬季(NDJ) Niño3.4指数相关(黑色实线; 红色虚线为95%置信度)、回归(蓝色虚线) |
Tab. 1 Correlation of ISMR with (1) NDJNiño3.4 index in decaying year; (2) the Indian Ocean basin SST anomalies (MAM); (3) NIO SST anomalies (MAM); and (4) AMI index. The number in bold font means exceeding the 95% confidence level表1 冬季(NDJ)Niño3.4指数(衰退年)、印度洋海盆春季整体增暖SST序列(IOB SST)、北印度洋二次增暖SST序列、反对称指数(AMI)与印度夏季季风降水(ISMR)的相关系数 |
ISMR(JJAS) | ISMR(6月) | ISMR(7月) | ISMR(8月) | ISMR(9月) | |
---|---|---|---|---|---|
Niño3.4 | 0.15 | -0.46 | 0.04 | 0.32 | 0.45 |
IOB SST | 0.19 | -0.32 | 0.03 | 0.24 | 0.45 |
NIO SST | 0.22 | -0.49 | 0.03 | 0.30 | 0.59 |
AMI | -0.10 | -0.61 | -0.08 | 0.28 | 0.40 |
注: 黑体字表示超过95%置信度系数。 |
Fig. 3 Correlation of Indian Ocean (SWIO, NIO, or IO) SST anomalies with NDJ Niño3.4 index. Two horizontal red dashed lines show the 95% confidence level图3 西南印度洋(SWIO)、北印度洋(NIO)、印度洋海盆(IO)SST与冬季(NDJ) Niño3.4指数的超前滞后相关(红色虚线为95%置信度) |
Fig. 4 Regression coefficients of SST anomalies with NDJ Niño3.4 index from October in developing year to September in decaying year (shading, ℃)图4 El Niño发展年10月到次年9月海表面温度异常对冬季(NDJ)Niño3.4指数回归系数分布(填色, ℃) |
Fig. 5 Regression coefficients of rainfall anomalies (shading) and 850hPa wind anomalies (vector) with NDJ Niño3.4 index from October in developing year to September in decaying year. Wind vectors are plotted only where the length of the vector exceeds 0.3 m•s-1图5 El Niño发展年10月到次年9月降水异常(填色)和风场异常(矢量)对冬季(NDJ)Niño3.4指数回归系数分布(图中只画出大于0.3m•s-1的风速) |
Fig. 6 Correlations of the first EOF mode of boreal rainfall in Indian Ocean and AMI index, boreal spring SWIO SST anomalies and AMI index. (a) Anomalies of rainfall (shading) and 850hPa winds (vector) in boreal spring (MAM) obtained from regression of the fields on the time series coefficient of the first EOF mode of boreal spring rainfall in the Indian Ocean (28°S-28°N, 40°-110°E). Wind vectors are plotted only where the length of the vector exceeds 0.3 m•s-1. (b) Time series coefficient of the first EOF mode (red dashed curve) and AMI index (blue solid curve). (c) AMI index (blue solid curve) and boreal spring (MAM) SWIO SST anomalies (red dashed curve, ℃)图6 印度洋春季降水异常EOF第一模态与反对称指数、西南印度洋春季海温异常相关图 |
Fig. 7 Correlations of ISMR anomalies, AMI index and NIO SST anomalies. (a) ISMR (Jun) anomalies (blue dashed curve) and AMI index (green solid curve). (b) ISMR (Sep) anomalies (blue dashed curve) and NIO SST anomalies (green solid curve) in boreal spring (MAM). (c) AMI index (blue dashed curve) and NIO SST anomalies (green solid curve) in boreal spring (MAM)图7 夏季季风降水异常、反对称指数与北印度洋春季海温异常相关图 |
Fig. 8 Regression of transport of specific humidity on NDJ Niño3.4 index at 850 hPa (units: 10-3kg•s-1•hPa-1•m-1) during June-September. Vectors are plotted only where the length of the vector exceeds 0.3 (units: 10-3kg•s-1•hPa-1•m-1)图8 850hPa异常风场与平均水汽的输运通量对冬季Niño3.4数回归分布 |
Fig. 9 Regression of transport of specific humidity on Niño3.4 index at 850 hPa during June-September. Vectors are plotted only where the length of the vector exceeds 0.3图9 6—9月850hPa平均风场与水汽异常的输运通量对冬季Niño3.4指数回归分布 |
Fig. 10 Regression of divergence of specific humidity (red line), (blue line) and (black line) on Niño3.4 index. The positive value means convergence图10 El Niño衰退年印度区域平均风场与水汽异常(红线)、异常风场与平均水汽(蓝线)、水汽通量异常()的散度(黑线)对Niño3.4指数的回归(正值表示辐合) |
The authors have declared that no competing interests exist.
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