Abstract
Abstract. The East Asian winter monsoon causes orographic snowfall over the windward side of the Japanese islands (facing the Sea of Japan and the northwesterly winter monsoon flow) and negative temperature anomalies around Japan. Daily weather information recorded in old Japanese diaries can provide useful information on the historical occurrences of snowfall days. Here, this information was combined with recently recovered early daily instrumental temperature data collected during the 19th century to reconstruct the occurrence of winter monsoon outbreak days (WMDs) from the 1840s to the early 1850s in Japan. Analyses of interannual and intra-seasonal variations in WMDs revealed active winter monsoon outbreaks in the early 1840s. In 1840/41 and 1841/42, these synchronously occurred with extreme snow events reported in central and southern China. However, winter monsoon outbreaks were absent during the middle to late winters of the mid-1840s and 1853/1854. Freezing records of Lake Suwa in central Japan showed that it did not freeze during 1844/1845 and 1853/1854, which was in agreement with our finding of inactive winter monsoons in these years. Comparing the occurrences of WMDs with early instrumental surface pressure data revealed that WMDs were associated with the active phases of the winter monsoon, as represented by an east–west surface pressure gradient over East Asia.
Highlights
Determining climate conditions before the 20th century is important for evaluating natural background climate variability because the anthropogenic effects on climate during this time were negligible
4.1 Circulation and precipitation patterns associated with winter monsoon outbreak days (WMDs)
A strong east–west sea level pressure (SLP) gradient appeared over Japan from day 1 to day 0, representing an active phase of the East Asian winter monsoon
Summary
Determining climate conditions before the 20th century is important for evaluating natural background climate variability because the anthropogenic effects on climate during this time were negligible. Various kinds of documentary data, such as the timing of grain and wine harvests, plant phenology, the freezing of water bodies, and daily weather documents, have been used to reconstruct past climate conditions; these approaches have been mainly applied in Europe (Brázdil et al, 2005; Labbé et al, 2019), China (Ge et al, 2016), and Japan (Mikami, 2008). These documentary data are important because they deal with short-term climatic fluctuations from the most recent past (Bradley, 2014). There are no official meteorological data from the Japan Meteorological Agency (JMA) prior to the construction of the Published by Copernicus Publications on behalf of the European Geosciences Union
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