梅雨の遅れの原因は、偏西風と黒潮の蛇行です。
今年は、梅雨が遅れています。既に梅雨入りした沖縄地方でも、平年より１１日遅れで梅雨入りしています。平年、近畿地方で６月６日ころ、関東甲信地方で６月７日ごろに梅雨入りします。今年は６月１３日現在、本州では梅雨入りしていません。また、日本各地で夏日を記録するなど、気温も上昇しています。梅雨前線が北上しないため、梅雨が遅れているのですが、偏西風の蛇行が一番の原因とされています。また、気温が上がっている原因は、黒潮の蛇行と言われています。なぜ、このような異常気象が発生しているのでしょうか？
偏西風の蛇行の原因は、北極の気温上昇です。
偏西風は、北極と赤道付近の温度差と地球の自転により発生していると考えられています。近年、地球温暖化による北極の気温上昇により、赤道付近と北極の温度差が小さくなり、北極を起点とする気流が大きく乱れています。一つの指標として、北極振動指数が挙げられます。北極振動指数は、北半球の海面気圧から算出される指数です。この指数が、１９８０年から正の値を示してしています。北極振動指数が正の値の時、北極と北半球中緯度の気圧差が大きいことを示しています。これは、"warm phase"と呼ばれ、中・高緯度では寒気の流れ込みが弱まって温暖な気候が多いとされています。偏西風の蛇行も、北極の気温上昇によるものでしょう。
黒潮の蛇行が気温上昇や豪雨の原因となっています。
黒潮は南方から日本列島に流れてくる海流です。南から流れ込むため、水温が高い海水を運んできます。黒潮が日本列島付近で蛇行すると、暖かい海水が日本列島の南側で広がり、海水温が上昇した結果、暖かい水蒸気が日本列島に流れ込みます。最近、「南から暖かい湿った空気が流れ込みます。」というコメントを天気予報でよく耳にすると思います。これは黒潮が大きく蛇行していることが原因です。実は、黒潮大蛇行が始まって約6年11か月目となり、過去最長期間になっています。これからも黒潮大蛇行が続けば、期間が7年を越えることになります。気象現象は積み重なりにより、より大きな事象になることが多く、黒潮大蛇行も年月を重ねると、日本への影響が大きくなるでしょう。
もうすぐ梅雨入りするかもしれません。
６月１５日から１６日にかけて、梅雨前線が日本列島に近づき、梅雨入りする可能性があります。沖縄地方が１１日遅れて梅雨入りしたことを考えると、近畿地方や関東地方も同じくらい遅れているのかもしれません。６月は本州で少雨の傾向があり、降水量が平年の５０％未満の所が多く、農作物に被害を与えています。気象庁の３カ月予報では、本州の降水量が平年より少ない確率は２０％でした。気象庁の３カ月予報は、あまり当たりませんね。
#梅雨 #偏西風の蛇行 #黒潮大蛇行
The rainy season is delayed due to the westerly winds and the meandering of the Kuroshio Current.
The rainy season is delayed this year. Even in Okinawa, where the rainy season has already started, it is 11 days later than normal. In normal years, the rainy season starts around June 6th in the Kinki region and around June 7th in the Kanto-Koshin region. As of June 13th this year, the rainy season has not started in Honshu. In addition, temperatures are rising, with summer days recorded in various parts of Japan. The rainy season is delayed because the rainy season front does not move north, but the meandering of the westerly winds is said to be the main cause. It is also said that the rise in temperature is due to the meandering of the Kuroshio Current. Why is this abnormal weather occurring?
The meandering of the westerly winds is caused by the rise in temperature in the Arctic.
It is believed that the westerly winds are caused by the temperature difference between the Arctic and the equator and the rotation of the Earth. In recent years, the temperature rise in the Arctic due to global warming has reduced the temperature difference between the equator and the Arctic, causing significant disturbance in the air currents originating from the Arctic. One indicator is the Arctic Oscillation Index. The Arctic Oscillation Index is an index calculated from sea level pressure in the Northern Hemisphere. This index has been showing positive values since 1980. When the Arctic Oscillation Index is positive, it indicates that the pressure difference between the Arctic and the mid-latitudes of the Northern Hemisphere is large. This is called a "warm phase," and it is said that the inflow of cold air in mid- and high-latitude areas is weakened, resulting in a warm climate. The meandering of the westerly winds is also likely due to the rise in temperature in the Arctic.
The meandering of the Kuroshio Current is the cause of rising temperatures and heavy rains.
The Kuroshio Current is an ocean current that flows into the Japanese archipelago from the south. Because it flows in from the south, it carries seawater with high water temperatures. When the Kuroshio Current meanders near the Japanese archipelago, warm seawater spreads to the south of the Japanese archipelago, and as a result of the rise in seawater temperature, warm water vapor flows into the Japanese archipelago. Recently, you may often hear the comment "Warm humid air is flowing in from the south" in weather forecasts. This is because the Kuroshio Current meanders greatly. In fact, it has been about 6 years and 11 months since the Kuroshio Current began to meander, making it the longest period on record. If the Kuroshio Current continues to meander, it will last more than 7 years. Meteorological phenomena often become larger events due to accumulation, and as the Kuroshio Current meander continues to meander over the years, its impact on Japan will become greater.
The rainy season may soon begin.
The rainy season front will approach the Japanese archipelago from June 15th to 16th, and the rainy season may begin. Considering that the rainy season began 11 days late in the Okinawa region, the Kinki and Kanto regions may be delayed by the same amount. In June, there is a tendency for little rain in Honshu, and many places have precipitation less than 50% of the average, causing damage to agricultural crops. According to the Japan Meteorological Agency's three-month forecast, there is a 20% chance that precipitation in Honshu will be less than average. The Japan Meteorological Agency's three-month forecasts aren't very accurate.
#rainySeason #MeanderingOfTheWesterlyWinds #LargeMeanderingOfTheKuroshioCurrent
