2023-09-23 07:33:16
This winter is expected to be mild with little snow on the Sea of Japan side, but there are still concerns regarding temporary heavy snow
September 23, 2023 16:33
This winter is expected to be mild due to the lingering effects of El Niño and the positive Indian Ocean Dipole. There will be little snow on the Sea of Japan side throughout the winter. However, it cannot be said that there is no risk of temporary cold air flowing in and causing heavy snow.
This winter is expected to be warm due to teleconnections such as the El Niño phenomenon
This winter (2023/2024) is expected to be warm due to the lingering effects of El Niño and the positive Indian Ocean Dipole. There will also be less snow on the Sea of Japan side.
Teleconnection is a phenomenon in which when a phenomenon appears, it is propagated to locations thousands or tens of thousands of kilometers away. The El Niño phenomenon is also a teleconnection in which a tropical phenomenon affects Japan and other areas.
An El Niño phenomenon, in which sea surface temperatures are higher than normal, has been occurring off the coast of Peru in South America since spring. The El Niño phenomenon will reach its peak in early winter. In the tropics, convective activity increases mainly in the central to eastern Pacific Ocean.
On the other hand, in the Indian Ocean, a positive Indian Ocean Dipole phenomenon, known as ocean fluctuations independent of El Niño and La Niña phenomena, is underway.
The positive Indian Ocean Dipole is a phenomenon that generally occurs from summer to autumn, when sea surface temperatures are lower than normal in the eastern part of the tropical Indian Ocean, and convective activity becomes inactive in this area. This phenomenon is also a teleconnection that affects Japan and other countries.
This winter (2023/2024), the positive Indian Ocean Dipole is expected to pass its peak, but its effects will remain.
Due to the residual influence of El Niño and the positive Indian Ocean Dipole, tropical convective activity becomes active in the western Indian Ocean, inactive from the eastern Indian Ocean to the Philippines, and active from the central to eastern Pacific Ocean. This situation affects the flow of westerly winds over Japan. The westerly winds will meander and flow norther than normal near Japan. Therefore, the cold air is expected to move south toward Japan.
Winter of 2019/2020 A very warm winter following the occurrence of the positive Indian Ocean Dipole phenomenon
The last time a positive Indian Ocean Dipole occurred was from summer to fall of 2019. This year’s positive Indian Ocean Dipole peaked in October and is said to be the strongest positive Indian Ocean Dipole since records were kept in 1950.
In the following winter (2019/2020), the effects of the positive Indian Ocean Dipole persisted until around December. Japan’s average winter temperature has a difference of +1.43℃ from the standard value, making Japan the warmest winter since statistics began in the winter of 1897/1898.
At this time, an El Niño phenomenon was not occurring, but a phenomenon called the “El Niño Modoki phenomenon” in which sea surface temperatures were higher than normal was occurring in the central part of the tropical Pacific Ocean. Due to this influence and the residual effect of the positive Indian Ocean Dipole, tropical convective activity became active in the western Indian Ocean, inactive from the eastern Indian Ocean to the Philippines, and active in the central Pacific Ocean. This is thought to have caused the westerly winds to meander and flow norther than normal near Japan, resulting in a warmer winter in Japan.
Reference: University of Tsukuba homepage
This winter (2023/2024) Although the forecast is for a warm winter, there is concern regarding a temporary influx of cold air.
This winter, cold air is expected to move south toward Japan, but long-term forecasts such as cold season forecasts do not reflect the Arctic Oscillation, which affects the flow of cold air.
The Arctic Oscillation is a phenomenon in which the atmospheric pressure near the North Pole and in mid-latitudes, including Japan, fluctuate in opposite directions in the north and south. When the atmospheric pressure near the North Pole is low and the atmospheric pressure at mid-latitudes is high, it is called a positive Arctic Oscillation, and the opposite case is called a negative Arctic Oscillation. Since the atmosphere flows from areas of high pressure to areas of low pressure, a positive Arctic Oscillation makes it easier for cold air to accumulate near the North Pole. On the other hand, a negative Arctic Oscillation makes it easier for cold air near the North Pole to flow into mid-latitude regions such as Japan.
Regarding the winter of 2019/2020 mentioned above, one of the reasons for the record warm winter is that the positive Arctic Oscillation became dominant towards the end of the winter.
At this stage, it is not possible to predict whether the Arctic Oscillation will be predominantly positive or negative this winter. There may be a period when cold air flows in due to the onset of the negative Arctic Oscillation. In this case, there is a risk of temporary heavy snow on the Sea of Japan side.
If a low-pressure system moves along the southern coast of Honshu in the latter half of winter, it will coincide with the influx of cold air, so it is possible that even the Pacific plains will need to be careful regarding snow.
Although the forecast is for a mild winter, it is a good idea to be prepared for the cold and snow.
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