Origins of water vapor and precipitation throughout Japan in winter monsoon and extratropical cyclone events using a regional isotope circulation model

Abstract:

This study clarified the origins of water vapor and precipitation throughout Japan in winter (December to February) by a regional isotope circulation model with stable isotopes in water (δ¹⁸O and δD). Model simulation was conducted from 2000 to 2010. The simulated δ¹⁸O values of precipitation were verified by observational data with high correlation (0.897) and a significance level (p < 0.01), however the slope of the simulated latitude effect was (values decrease with increasing latitude) smaller than observed that. Simulated daily sea-level pressure patterns were divided into two types: winter monsoon (WM) type (19 days) and extratropical cyclone (EC) type (18 days). In the WM type, precipitation rate was high (low) along the Japan Sea side (the Pacific Ocean side) of Japan. The latitude effect was recognized in δ¹⁸O in precipitation around Japan. The d-excess (= δD – 8 × δ¹⁸O) in precipitation and evaporation were more than 15‰ around Japan. Simulated water vapor evaporated from the Japan Sea was predominant all over Japan, except for the southwestern islands of Japan. A portion of this moisture moved eastward to the Pacific Ocean; however, the moisture did not contribute to the total amount of precipitation along the Pacific Ocean side of Japan because of the small amount of precipitation there. In contrast, precipitation rate was high across Japan in the EC type. The δ¹⁸O in precipitation showed the latitude effect and the amount effect around Japan. The d-excess in precipitation and evaporation were below 15‰ around Japan, except for the East China Sea. Simulated water vapor evaporated from the Pacific Ocean was predominant all over Japan. Along the Japan Sea side of Japan, δ¹⁸O was 2‰ higher and d-excess was 9‰ higher in the WM type than in the EC type. We found the linkage between the isotopic composition and the precipitation origins in winter along the Japan Sea side of Japan. Such information is required for a variety of paleo-climate and hydrology studies.