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[MIS01-P06] Japanese Winter Orographic Precipitation and ENSO – Case of Sapporo –
Keywords:precipitation, Hokkaido, ENSO
Heavy winter snowfall in northern Japan is well known worldwide. This is because the winter pressure pattern of high-West and low-East brings cold and dry air from the Siberian plain southward, and the cold air is replenished with the water vapor when it crosses the Sea of Japan, causing heavy snowfall on the Sea side in northern Japan.
Sapporo City is located on the Sea side of Hokkaido, with plains extending from north to east and mountainous areas from south to west. With these two topographic features, Sapporo also has many regional differences in snowfall.
In this study, Empirical orthogonal functions (EOF) analysis is used to analyze the main variations of precipitation patterns in Sapporo during the winter season (December to March), and meteorological considerations are made regarding the occurrence of specific precipitation patterns. Daily precipitation data from the Sapporo Multi-Sensor and AMeDAS around Sapporo City were used as the grid data. The total period of precipitation data is 2788 days for 23 winters from December 1992 to March 1993.
The first EOF is the pattern of precipitation increase/decrease, the second EOF is the mountain snow type (A) and the low-land snow type (B), and the third EOF is the seaward precipitation type (C) and the inland precipitation type (D). Then, we focused on the four patterns with regional differences and examined their meteorological characteristics. Sea Level Pressures showed that patterns A and D were precipitation caused by a south-coast low pressure system, while patterns B and C were precipitation caused by a winter pressure system.
Then, we used as an index the difference between the sum of the number of days of appearance of each winter type, B and C (with an absolute EOF score greater than 1), and the sum of the number of days of appearance of A and D, which are characteristic of snowfall by a south-coast low pressure system. A comparison between this index and the NINO.3 region SST, one of the indicators of El Niño-Southern Oscillation (ENSO), showed a negative correlation between the two: the correlation coefficient R=-0.27 in winter 23, but R=-0.58 except in the very strong El Niño (Super El Niño) winter of 1998, with 99% confidence level.
In other words, during El Niño events (when NINO.3 is positive), many days with heavy precipitation occur in the mountains and inland areas west of Sapporo, while during La Niña events, many days with heavy precipitation occur along the coast and in the plains (low-lands). Therefore, even when precipitation anomalies for El Niño and La Niña winters are composited, the El Niño winter anomalies shows more precipitation in the mountainous areas to the south, while the La Niña winter anomalies shows more precipitation in the plains to the northeast and along the sea.
Sapporo City is located on the Sea side of Hokkaido, with plains extending from north to east and mountainous areas from south to west. With these two topographic features, Sapporo also has many regional differences in snowfall.
In this study, Empirical orthogonal functions (EOF) analysis is used to analyze the main variations of precipitation patterns in Sapporo during the winter season (December to March), and meteorological considerations are made regarding the occurrence of specific precipitation patterns. Daily precipitation data from the Sapporo Multi-Sensor and AMeDAS around Sapporo City were used as the grid data. The total period of precipitation data is 2788 days for 23 winters from December 1992 to March 1993.
The first EOF is the pattern of precipitation increase/decrease, the second EOF is the mountain snow type (A) and the low-land snow type (B), and the third EOF is the seaward precipitation type (C) and the inland precipitation type (D). Then, we focused on the four patterns with regional differences and examined their meteorological characteristics. Sea Level Pressures showed that patterns A and D were precipitation caused by a south-coast low pressure system, while patterns B and C were precipitation caused by a winter pressure system.
Then, we used as an index the difference between the sum of the number of days of appearance of each winter type, B and C (with an absolute EOF score greater than 1), and the sum of the number of days of appearance of A and D, which are characteristic of snowfall by a south-coast low pressure system. A comparison between this index and the NINO.3 region SST, one of the indicators of El Niño-Southern Oscillation (ENSO), showed a negative correlation between the two: the correlation coefficient R=-0.27 in winter 23, but R=-0.58 except in the very strong El Niño (Super El Niño) winter of 1998, with 99% confidence level.
In other words, during El Niño events (when NINO.3 is positive), many days with heavy precipitation occur in the mountains and inland areas west of Sapporo, while during La Niña events, many days with heavy precipitation occur along the coast and in the plains (low-lands). Therefore, even when precipitation anomalies for El Niño and La Niña winters are composited, the El Niño winter anomalies shows more precipitation in the mountainous areas to the south, while the La Niña winter anomalies shows more precipitation in the plains to the northeast and along the sea.