Combined analysis of early pressure observation data and historical daily weather documents for winter climate reconstruction in Japan
Abstract. The East Asian winter monsoon is characterized by a strong east–west surface pressure gradient and the outbreak of cold air around Japan. It causes heavy snowfall in the Sea of Japan side of the Japanese Islands. Meanwhile, fine weather prevails over the Pacific Ocean side owing to topographical effects. Documents pertaining to daily weather in Japan often provide useful weather information regarding the appearance of typical “winter-monsoon-type weather patterns” in the historical period. In addition to historical daily weather documents, we recovered several early pressure observation series in Japan and China from the 19th century. A combined analysis of historical daily weather documents and early surface pressure observation may result in an effective detection of outbreaks arising from the East Asian winter monsoon in the historical period. Knowledge regarding atmospheric circulation fields associated with “winter-monsoon-type weather patterns” is essential for this combined analysis. We first investigate temporal evolutions of circulation fields associated with “winter-monsoon-type weather patterns” for the present day (1968–1980). The result indicates that the southward expansion of the Siberian High and eastward movement of extratropical cyclones around Japan result in a significant east–west surface pressure gradient in East Asia. This pressure gradient causes “winter-monsoon-type weather patterns” in Japan. Subsequently, we attempted to reconstruct the outbreak of the winter monsoon around Japan for the winter of 1851/52 using both historical weather documents and newly recovered early instrumental pressure data of Japan and China. The reconstructed results show that the outbreak of the East Asian winter monsoon can be reasonably detected by focusing on the sequence of reconstructed daily weather patterns and the east–west pressure gradient calculated using early instrumental pressure data.
