Climate Divisions for Alaska Based on Objective Methods

Alaska encompasses several climate types because of its vast size, high-latitude location, proximity to oceans, and complex topography. There is a great need to understand how climate varies regionally for climatic research and forecasting applications. Although climate-type zones have been established for Alaska on the basis of sea- sonal climatological mean behavior, there has been little attempt to construct climate divisions that identify regions with consistently homogeneous climatic variability. In this study, cluster analysis was applied to monthly-average temperature data from 1977 to 2010 at a robust set of weather stations to develop climate divisions for the state. Mean-adjusted Advanced Very High Resolution Radiometer surface temperature estimates were employed to fill in missing temperature data when possible. Thirteen climate divisions were identified on the basis of the cluster analysis and were subsequently refined using local expert knowledge. Divisional boundary lines were drawn that encompass the grouped stations by following major surrounding topographic boundaries. Correlation analysis between station and gridded downscaled temperature and precipitation data supported the division placement and boundaries. The new divisions north of the Alaska Range were the North Slope, West Coast, Central Interior, Northeast Interior, and Northwest Interior. Divisions south of the Alaska Range were Cook Inlet, Bristol Bay, Aleutians, Northeast Gulf, Northwest Gulf, North Panhandle, Central Panhandle, and South Panhandle. Correlations with various Pacific Ocean and Arctic climatic teleconnection indices showed numerous significant relationships between seasonal division average temperature and the Arctic Oscillation, Pacific-North American pattern, North Pacific index, and Pacific decadal oscillation.阿拉斯加州幅员辽阔、地处高纬度、毗邻海洋且地形复杂，因此拥有多种气候类型。开展气候研究与预报应用时，亟需明晰该区域的气候分异规律。尽管此前已基于季节气候平均特征为阿拉斯加州划定了气候类型带，但鲜有研究尝试构建能够识别气候变率持续均一区域的气候分区方案。本研究针对1977至2010年间多组可靠气象站的月平均气温数据开展聚类分析，以此构建阿拉斯加州的气候分区。研究采用经均值校正的先进甚高分辨率辐射计（Advanced Very High Resolution Radiometer, AVHRR）地表温度反演数据，在可行条件下填补气温数据的缺失值。经聚类分析共识别出13个气候分区，随后结合当地专家知识对分区方案进行了优化调整。各分区的边界线均围绕聚类得到的气象站组划定，并贴合周边主要地形界线。通过对气象站数据与格点降尺度气温、降水数据开展相关性分析，验证了本次气候分区的划定位置与边界合理性。阿拉斯加山脉以北的新增气候分区分别为：北坡区、西海岸区、中部内陆区、东北内陆区以及西北内陆区；阿拉斯加山脉以南的分区则包括库克湾、布里斯托尔湾、阿留申群岛、东北海湾区、西北海湾区、北狭长地带区、中狭长地带区以及南狭长地带区。通过与多组太平洋及北极气候遥相关指数开展相关性分析，研究发现各气候分区的季节平均气温与北极涛动、太平洋-北美遥相关型、北太平洋指数以及太平洋年代际振荡均存在大量显著关联。