A182-0007
Circulation pattern dependence of heavy snowfall events in Sapporo, Japan and their projected response to climate change
Circulation pattern dependence of heavy snowfall events in Sapporo, Japan and their projected response to climate change
Tuesday, 15 December 2020
Poster
Abstract:
Future changes to heavy snowfall events in Sapporo city, Hokkaido, located in the northernmost island of Japan, is evaluated using the database for Policy Decision making for Future climate change (d4PDF) large ensemble simulations. The d4PDF provides over 3000 years of historical and future climate simulations from the 60 km Meteorological Research Institute-Atmospheric General Circulation Model (MRI-AGCM), and the 20 km dynamically downscaled regional simulations from the Non-Hydrostatic Regional Climate Model (NHRCM). For future experiments, a climate 4 K warmer than the pre-industrial period is produced. Additionally, a 5 km dynamically downscaled NHRCM is conducted covering the northern Japan region, which better resolves complex topography and local scale forcing compared to 20 km grid spacing. A total of 735 years of snowfall data from the 5 km NHRCM is used for this study.
As snowfall characteristics can differ based on circulation patterns, mean sea level pressure anomaly patterns that result in heavy snowfall in both the historical and 4 K climate are identified using self-organizing maps. Two synoptic patterns, one from extratropical cyclones over central Japan or north/east of Hokkaido, and one by high-pressure anomalies over the Siberian continent are identified as patterns that produce heavy snowfall days in the historical climate. Large decreases in future heavy snowfall days are seen in the former synoptic patterns, as surface temperatures are at or slightly below 0 °C in the historical climate and warming to several degrees above freezing in the 4 K climate, resulting in more rain events. The latter synoptic pattern is associated with events well below freezing in historical climates and remained mostly below freezing even in the 4 K climate. This pattern represents an enhancement of the East Asian winter monsoon, which transports cold and dry air from the Siberian continent over warmer waters of the Sea of Japan. Our results suggest that a warmer Sea of Japan will provide more moisture during these cold air outbreaks, producing more developed snow clouds, which leads to more frequent and more intense future snow events in Sapporo.
As snowfall characteristics can differ based on circulation patterns, mean sea level pressure anomaly patterns that result in heavy snowfall in both the historical and 4 K climate are identified using self-organizing maps. Two synoptic patterns, one from extratropical cyclones over central Japan or north/east of Hokkaido, and one by high-pressure anomalies over the Siberian continent are identified as patterns that produce heavy snowfall days in the historical climate. Large decreases in future heavy snowfall days are seen in the former synoptic patterns, as surface temperatures are at or slightly below 0 °C in the historical climate and warming to several degrees above freezing in the 4 K climate, resulting in more rain events. The latter synoptic pattern is associated with events well below freezing in historical climates and remained mostly below freezing even in the 4 K climate. This pattern represents an enhancement of the East Asian winter monsoon, which transports cold and dry air from the Siberian continent over warmer waters of the Sea of Japan. Our results suggest that a warmer Sea of Japan will provide more moisture during these cold air outbreaks, producing more developed snow clouds, which leads to more frequent and more intense future snow events in Sapporo.