四川盆地春旱日数准2年周期特征及其对东亚冬季风的响应

本研究利用1961-2016年四川盆地气象干旱综合监测指数(MCI)和同期NCEP/NCAR再分析资料,使用MTM-SVD方法,分析了四川盆地春旱周期特征,并研究了其准2年周期对东亚冬季风的响应情况.结果表明:在年际尺度上,四川盆地春旱日数有准2年和准3年周期,其中准2年周期更加显著.准2年周期的典型循环表现为春旱全区一致偏轻和偏重的交替演变,并且准2年周期信号在1990年代以后最明显, 1960年代次之, 1970-1990年代中期几乎消失.利用MTM-SVD方法对春旱日数和海平面气压耦合场重建准2年周期,研究其协同变化关系,发现四川盆地春旱偏轻年的1-2月东亚冬季风显著偏强, 3月突然减弱, 4月持续偏弱;春旱偏强年的1-2月东亚冬季风显著偏弱,而3月略减弱,但是仍较常年偏强, 4月继续偏强.环流分析表明,在冬春季节转换过程中,当东亚冬季风出现先强后弱(先弱后强)的突然(缓慢)转换时,春季500 hPa高度场激发欧亚遥相关负(正)位相,导致东亚大槽偏弱(强),东亚中东部出现异常南(北)风分量,有(不)利于产生降水,四川盆地春旱偏轻(重).

Characteristics of Quasi-2-Year Cycle of the Number of Spring Drought Days in Sichuan Basin and Its Response to East Asian Winter Monsoon

Periodic characteristics of spring drought in Sichuan Basin and its response to East Asian Winter Monsoon on a quasi-2-year cycle are examined with the Multi-Taper Method-Singular Value Decomposition (MTM-SVD) method, using the MCI data in 1961-2016 from 104 meteorological stations in Sichuan Basin and the NCEP/NCAR reanalysis data in the same period The results show that the number of spring drought days in the Sichuan Basin has a quasi-2-year and a quasi-3-year cycle on the inter-annual scale, of which the quasi-2-year cycle is more significant. The typical cycle of the quasi-2-year cycle presents a pattern of alternating light and heavy spring drought, and the quasi-2-year period signal is most obvious after 1990s, 1960s takes the second place, and it almost disappeared from 1970s to the middle of 1990s. Through the analysis of coordinate change of the number of spring drought days and atmospheric pressure at sea level with the method of MTM-SVD, it is found that the East Asian Winter Monsoon has response to the number of spring drought days in a quasi-2-year cycle. In years of light spring drought, the East Asian Winter Monsoon is strong in January and February, but weakens abruptly in March and remains weak in April. In years of heavy spring drought, the East Asian Winter Monsoon is weak in January and February, and it slightly weakens in March, yet being still stronger than usual and continuing to be strong in April. Circulation analysis shows that in the seasonal transition process when the East Asian Winter Monsoon presents an abrupt (slow) change from strong (weak) to weak (strong), the spring 500 hPa height field excites a Eurasian teleconnection negative (positive) phase, leading to the weak (strong) East Asian Trough, appearing anomalous south (north) wind component in East Asia, resulting in a light (heavy) spring drought.