亚洲和北美干湿变化及其与海表温度异常的关系

利用多通道奇异谱方法（MSSA）分析了1953~2003年亚洲和北美Palmer干旱指数（PDSI）与热带和北半球温带海洋海表面温度异常（SSTA）的主要周期振荡特征及其相互联系.结果表明：亚洲和北美PDSI以及SSTA均存在明显的3~6年的年际以及10年左右的年代尺度振荡；此外，亚洲PDSI还存在显著的6~8年的年际振荡.SSTA的年际振荡主要体现了ENSO的变化特征，而其年代尺度振荡的空间分布具有热带太平洋和北太平洋共同作用的类ENSO型.同时，MSSA的分析结果给出了亚洲和北美主要振荡信号的时间和空间演变特征.相关性分析表明，亚洲和北美PDSI的年际及年代尺度振荡均显示明显的对SSTA强迫信号的响应.对于年际振荡，亚洲PDSI对SSTA响应强于北美，但年代尺度振荡则反之.此外，亚洲和北美PDSI对于SSTA信号响应的关键区域也随时间尺度的不同而发生变化.亚洲的西西伯利亚、青藏高原东西两侧以及中西伯利亚东部在年际和年代尺度上均为受SSTA影响最显著的区域；在年际尺度上，北美中部地区的干湿变化与SSTA存在显著相关，而在年代尺度上，美国西部更易受SSTA年代尺度振荡的影响.

The evolution of dry and wet periods in Asia and North America and its relationship with SSTA

The Multichannel Singular-Spectrum Analysis (MSSA) was used to analyze the variability of Palmer Drought Severity Index (PDSI) across the Asia and North America, and the relation between PDSI and the Sea Surface Temperature Anomaly (SSTA) in the tropical and Northern temperate ocean. The results indicated that the interannual (3~6 years) and the quasi-decadal time scales (longer than 8 years) oscillations existing in the evolution of PDSI and SSTA. Further investigation indicated that the Asian PDSI showed significant 6~8 years time scales signal. It was found that the 3~6 years oscillation of SSTA displayed the characteristics of ENSO signal, while the ENSO-like or Pacific Decadal Oscillation (PDO) dominated the variability on the quasi-decadal timescale variation of SSTA. The results further presented the spatio-temporal characteristics of wet and dry signals in Asia and North America. The ENSO signal was more correlative to the wet-dry signals of Asia than those of North America on the interannual timescale (3~6 years). But on the quasi-decadal timescale, the ENSO-like seemed to have stronger influence in North America than other signals. From the spatial distribution of the correlation between the PDSI and SSTA, west Siberia, the north and south sides of Tibetan Plateau and the area east to Central Siberian Plateau had the strongest response to SSTA signals. Although the central parts of North America were influenced by SSTA on the interannual timescale, the west part of North America had stronger response to the quasi-decadal SSTA forcing signals.