Numerical study of water origins within explosive cyclone system developing in the vicinity of Japan

Abstract:

To clarify water origins within warm and cold front systems of explosive extratropical cyclones developing in the vicinity of Japan. A colored moisture analysis (CMA) with isotopic regional spectral model (isoRSM) developed by Yoshimura et al. in 2010 was conducted to track water origins in an explosive extratropical cyclone occurred in December 2014. To validate isoRSM’s performance, observations of isotopic composition in precipitation at Sapporo were conducted in the event.

The isoRSM successfully simulated precipitation rate and isotopic composition at Sapporo (Fig. 1). In the first half event during warm front and warm sector passage, both simulations and observations showed decrease in δD and d-excess, and increase in precipitation rate and total precipitable water. According to the CMA, moisture from northwest Pacific was dominant and increased. In the second half event during cold front passage, the simulations exhibited uptrend in δD and d-excess, and decline in precipitation rate and total precipitable water. Regarding water origins, moisture from the Sea of Japan and East Asian Continent gradually increased and became dominant.

The decrease of δD and d-excess in precipitation of warm front and warm sector is attributable to increasing moisture transported along the warm conveyor belt from the northwest Pacific and other tropical oceans with low δD and d-excess, resulting from relatively weak maritime wind with high humidity and temperature during evaporation and subsequent relatively heavy precipitation in the upstream. In contrast, the uptrend of δD and d-excess in cold front precipitation is due to increased moisture from the Sea of Japan with high δD and d-excess, arising from relatively strong continent-origin wind with low humidity and temperature during evaporation and subsequent light rainfall in the upstream.

Our results indicated that moisture of warm front and warm sector was mainly originated from the northwest Pacific and other tropical oceans with low δD and d-excess, whereas moisture from the Sea of Japan and East Asian Continent contributed more to cold front with high δD and d-excess. We will further examine whether the phenomenon described in this study can also be found in other explosive cyclones.

Fig. 1 Observed and simulated precipitation rate (a), δD (b) and d-excess (c) at Sapporo