太平洋—印度洋海温异常对陕西夏季降水年际变化的影响

利用1961-2008年陕西78个气象站夏季(6-8月)降水资料、NOAA提供的全球逐月海表温度资料和NCEP/NCAR 500 h Pa位势高度场、风场月平均再分析资料,运用回归、SVD、交叉小波分析等方法分析了前期到同期不同季节太平洋、印度洋海温与陕西夏季降水的关系。结果表明,陕西夏季降水与前期秋、冬季节赤道中东太平洋、西印度洋海温呈正相关关系,与北太平洋海温呈负相关关系,太平洋海温分布为El Nino型;到同年夏季,显著正相关区西移到东印度洋和我国东部沿海,前期及同期太平洋、印度洋海温影响陕西的显著区域都位于关中和陕南东部。冬季Nino3海温与陕西夏季降水在4~5年时间尺度有显著的同位相共振周期,Nino3海温超前陕西夏季降水变化4~6个月。东亚、南海、东南亚夏季风指数与陕西夏季降水呈负相关关系,与Nino3海温也呈负相关关系,当前期Nino3海温偏高时,东亚夏季风减弱,西太平洋副热带高压偏强、偏西,陕西南部有异常西南风水汽输送,北部有异常北风,陕西处于冷暖空气的交汇区,夏季降水偏多,反之偏少。

Study on the relationship between ENSO and tropical Indian Ocean temperature

The relationship between ENSO and Indian Ocean Dipole was discussed by using the data set of sea temperature from Scripps Institute of Oceanography, the air temperature at 1000hPa from the NCEP reanalysis data and the Nino3 index from the Climate Prediction Center （CPC） of U.S.A. during the period from 1955 to 2001. The results show that there exists a Dipole on the maximum temperature anomalous level （MTAL） in the Indian Ocean, which close relates to ENSO in the Pacific Ocean. During El Nino periods there are good relationships between ENSO and Indian Ocean Dipole which maximum correlation occurring when ENSO leads by one month, but in La Nina periods the relationship is not so good. The distribution of Dipole in Indian Ocean is from northeast to southwest, which one （west） pole in 65°E - 75°E, 6°S - 10°S and the other in 85°E - 95°E, 2°N - 6°N, which is different from that defined by Saij. The correlation coefficients of Nino3 index with temperature anomalies in the west/east poles on the MTAL are over 0.4 - 0.15, respectively. It is a main sea temperature system in the tropical Indian Ocean. However, in the surface layer from sea surface to the depth of 20 m - 30 m there is no such a dipole with opposite sea temperature anomalies in the NE and SW of tropical Indian Ocean. The SSTA in the NE might be influenced by the sensible exchange process because the evolution of sea and 1 000 hPa air temperature anomaly time series of the NE of tropical Indian Ocean is quite similar except those during 1962 - 1963 and 1986. The periods of Indian Ocean Dipole are shorter than that of ENSO, and about 1 to 6-year.

Predicting Western Pacific Subtropical High Using a Combined Tropical Indian Ocean Sea Surface Temperature Forecast

Weather and climate in East China are closely related to the variability of the western Pacific subtropical high(WPSH), which is an important part of the Asian monsoon system. The WPSH prediction in spring and summer is a critical component of rainfall forecasting during the summer flood season in China. Although many attempts have been made to predict WPSH variability, its predictability remains limited in practice due to the complexity of the WPSH evolution. Many studies have indicated that the sea surface temperature(SST) over the tropical Indian Ocean has a significant effect on WPSH variability. In this paper, a statistical model is developed to forecast the monthly variation in the WPSH during the spring and summer seasons on the basis of its relationship with SST over the tropical Indian Ocean. The forecasted SST over the tropical Indian Ocean is the predictor in this model, which differs significantly from other WPSH prediction methods. A 26-year independent hindcast experiment from 1983 to 2008 is conducted and validated in which the WPSH prediction driven by the combined forecasted SST is compared with that driven by the persisted SST. Results indicate that the skill score of the WPSH prediction driven by the combined forecasted SST is substantial.

Prediction and mechanistic analysis of May precipitation in North China based on April Indian Ocean SST and the Northwest Pacific Dipole

North China May precipitation(NCMP)accounts for a relatively small percentage of annual total precipitation in North China,but its climate variability is large and it has an important impact on the regional climate and agricultural production in North China.Based on observed and reanalysis data from 1979 to 2021,a significant relationship between NCMP and both the April Indian Ocean sea surface temperature(IOSST)and Northwest Pacific Dipole(NWPD)was found,indicating that there may be a link between them.This link,and the possible physical mechanisms by which the IOSST and NWPD in April affect NCMP anomalies,are discussed.Results show that positive(negative)IOSST and NWPD anomalies in April can enhance(weaken)the water vapor transport from the Indian Ocean and Northwest Pacific to North China by influencing the related atmospheric circulation,and thus enhance(weaken)the May precipitation in North China.Accordingly,an NCMP prediction model based on April IOSST and NWPD is established.The model can predict the annual NCMP anomalies effectively,indicating it has the potential to be applied in operational climate prediction.

MEAN SQUARE DEVIATION ANALYSIS OF INTERANNUAL SST VARIABILITY IN TROPICAL PACIFIC AND INDIAN OCEAN

Using the SST data series in tropical ocean (20N ~ 20S, 50E ~ 80W) during 1951 ~ 1997 to calculate its monthly mean square deviation, the work obtains results showing that interannual SST variability of the Pacific is more significant than that of the Indian Ocean, especially near the central and eastern equatorial Pacific (165W～90W, 6N～6S), where it ranges from 2C to 4C. The interannual SST variability is obvious in November and December but small in March and April. The interannual variability of 搘arm pool?SST is not so obvious as that of the eastern equatorial Pacific. However, interannual SST variability of the Indian Ocean ranges from 1C to 2C or so, being smaller than that of the Pacific. In the Indian Ocean, interannual SST variability of the Southern Hemisphere is more obvious than that of the Northern Hemisphere. According to above characteristics of interannual SST variability, the key sectors are determined.

Interdecadal change in the South Asian summer monsoon rainfall in 2000 and contributions from regional tropical SST

The drying trend in the South Asian summer monsoon(SASM)area has been a focus of monsoon rainfall studies in the last two decades.However,this study reveals that a signi cant interdecadal change in the SASM rainfall occurred in approximately the year 2000.Obvious spatial inhomo-geneity was a feature of this change,with increased rainfall over the southern part of the India Pakistan border area that extends from the Arabian Sea,as well as in the western Bay of Bengal.Furthermore,there was decreased rainfall over the southern SASM and the western coast of the Indian Peninsula.Numerical experiments using CAM4 show that global SST changes can induce general changes in the SASM circulation consistent with observations.The tropical Pacific/Indian Ocean SST anomalies dominated the Walker and the regional Hadley circulation changes,respectively,while the descending motion anomalies over the southern SASM were further enhanced by the warmer tropical Atlantic SSTs.Moreover,the spatial inhomogeneity of this interdecadal change in the SASM rainfall needs further study.

New Metrics of the Tropospheric Biennial Oscillation in the East Asian Summer Monsoon and Its Interdecadal Shift

This study designed a simple index for measuring irregular tropospheric biennial oscillation(TBO) activities, which was used to determine that the TBO in the East Asian Summer Monsoon(EASM), the most important summer precipitation system for China, has strengthened rather than weakened since the late 1970s. The lead/lag correlations between the EASM and tropical Indian-Pacific sea surface temperature(SST) suggest a relationship between interbasin SST and EASM coupling processes and that this alternative correlation pattern is likely related to TBO. Significant correlation occurred only in recent decades, which implies a reinforcement of TBO in the EASM. From records of representative points in the Indian-Pacific, the interdecadal intrinsic SST modes of the areas can be obtained with ensemble empirical mode decomposition owing to its good temporal locality. Statistical results show Indian-Pacific SST interdecadal trends that include out-of-phase and in-phase warming before and after the late 1970s, respectively, which may be responsible for the TBO interdecadal augmentation present since the late 1970s.