5:15 PM - 6:45 PM
[ACG32-P05] Influence of spring snow cover over Eurasia on the climate of the Japanese region
Keywords:snow cover
In the winter in the Northern Hemisphere, there is a "snow cover" in which snow covers the ground surface in many places on the Eurasian continent. Once the snow cover decreases due to snow albedo feedback, the ground surface, which has a lower reflectivity than snow, is exposed, and the temperature near the ground surface rises, further reducing the snow cover. Yasunari et al. (1991) showed the effects of winter and spring snow accumulation anomalies on the Asian monsoon and teleconnection patterns during the warm season. In addition, Komatsu et al. (2023) evaluated the relationship between snow cover and ground surface temperature in autumn Eurasia. In this way, various studies have been given regarding the phenomena and regions affected by the continental snow cover. In this study, we focused on the presence or absence of snow cover in spring in Eurasia and examined the influence on the climate of Japan.
In this study, we used the weekly average data of snow cover from the National Snow & Ice Data Center as snow cover data. Daily mean data were used from JRA-55 (Kobayashi et al., 2015), a long-term reanalysis data of the Japan Meteorological Agency, as atmospheric field data. The analysis period is from February to May 1979-2022.
First, the 1st ~ 15th of each month of use was defined as the beginning of the month, and the 16th ~ the last day of the month was defined as the end of the month. Next, the 1000 hPa temperature on land in Japan was averaged for each season, and the Japan temperature index was created. We examined the correlation with the snow cover rate in the previous season and the previous season based on the Japan Temperature Index for each season, and investigated the correlation based on each season from early March to late April, and specified the region and time of the highest correlation. In the extracted area, the values of the snow cover were averaged over the area and a snow cover index was created. Years with a σ of 1.0 or more of the snow cover index were defined as snowy years, and years of -1.0σ or less were defined as low snowfall years. Subsequently, we compared the temporal variation of snow cover and the temporal variation of temperature in high and low snowy years.
As a result of investigating the correlation between the Japan temperature index and the snow cover of the previous season, the correlation between the snow cover in the east of the continent from early March to early April and the temperature in Japan in late April was higher than that of other seasons, suggesting that the relationship may be high. Next, we examined the correlation between the temperature in Japan in late April and the temperature of the entire continent in early April, and found a significant positive correlation in the area covering all areas that were correlated with snow cover. In addition, there was a stronger positive correlation in the lower layer, suggesting that the temperature anomaly in the lower layer due to the snow cover in the east of the continent affected the temperature in Japan in late April. We created a snow cover index for the eastern region of the continent described so far, and extracted high snow years and light snow years. Comparing the temporal changes in snow cover between the two, it was found that the snowmelt started earlier in the low snow years and the period of low snow cover tended to last longer, while the snowmelt started later in the snowy years and the snow melt occurred during the period when the snow cover was maintained in the low snow years. Next, we compared the temporal changes in the weekly mean temperature. It was found that the temperature in Japan tends to rise easily in late April in low snow years, and the temperature in Japan tends to rise less easily in late April in high snowy years. These results suggest that the atmosphere tends to warm up when the snow cover is low in early April, which affects the subsequent temperature in Japan, and that the temperature in Japan is unlikely to rise when the snow cover is melted in early April.
In this study, we investigated the effects of spring snow cover on the climate near Japan. It was suggested that if the snow cover in the eastern part of the continent is low in early April, the temperature in Japan tends to rise thereafter, and the temperature in Japan in late April may be difficult to rise in years when the snow is still melting at the end of April.
In this study, we used the weekly average data of snow cover from the National Snow & Ice Data Center as snow cover data. Daily mean data were used from JRA-55 (Kobayashi et al., 2015), a long-term reanalysis data of the Japan Meteorological Agency, as atmospheric field data. The analysis period is from February to May 1979-2022.
First, the 1st ~ 15th of each month of use was defined as the beginning of the month, and the 16th ~ the last day of the month was defined as the end of the month. Next, the 1000 hPa temperature on land in Japan was averaged for each season, and the Japan temperature index was created. We examined the correlation with the snow cover rate in the previous season and the previous season based on the Japan Temperature Index for each season, and investigated the correlation based on each season from early March to late April, and specified the region and time of the highest correlation. In the extracted area, the values of the snow cover were averaged over the area and a snow cover index was created. Years with a σ of 1.0 or more of the snow cover index were defined as snowy years, and years of -1.0σ or less were defined as low snowfall years. Subsequently, we compared the temporal variation of snow cover and the temporal variation of temperature in high and low snowy years.
As a result of investigating the correlation between the Japan temperature index and the snow cover of the previous season, the correlation between the snow cover in the east of the continent from early March to early April and the temperature in Japan in late April was higher than that of other seasons, suggesting that the relationship may be high. Next, we examined the correlation between the temperature in Japan in late April and the temperature of the entire continent in early April, and found a significant positive correlation in the area covering all areas that were correlated with snow cover. In addition, there was a stronger positive correlation in the lower layer, suggesting that the temperature anomaly in the lower layer due to the snow cover in the east of the continent affected the temperature in Japan in late April. We created a snow cover index for the eastern region of the continent described so far, and extracted high snow years and light snow years. Comparing the temporal changes in snow cover between the two, it was found that the snowmelt started earlier in the low snow years and the period of low snow cover tended to last longer, while the snowmelt started later in the snowy years and the snow melt occurred during the period when the snow cover was maintained in the low snow years. Next, we compared the temporal changes in the weekly mean temperature. It was found that the temperature in Japan tends to rise easily in late April in low snow years, and the temperature in Japan tends to rise less easily in late April in high snowy years. These results suggest that the atmosphere tends to warm up when the snow cover is low in early April, which affects the subsequent temperature in Japan, and that the temperature in Japan is unlikely to rise when the snow cover is melted in early April.
In this study, we investigated the effects of spring snow cover on the climate near Japan. It was suggested that if the snow cover in the eastern part of the continent is low in early April, the temperature in Japan tends to rise thereafter, and the temperature in Japan in late April may be difficult to rise in years when the snow is still melting at the end of April.