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[ACG32-P07] Why are summers in Japan becoming longer?
Keywords:summer, season, sea surface temperature
Japan has four seasons, and there have long been unique cultures and events that take advantage of the scenery and climatic characteristics that differ depending on the season.
However, the four seasons in Japan are collapsing.
In recent years, there have been many days reported as "hot as midsummer" even in spring and autumn, and along with this, there are some claims that "summer in Japan is getting longer" and "spring and autumn have disappeared".
Varies depending on the high temperature in spring and autumnFor example, the risk of heat stroke increases due to the high temperature in spring, when people are not accustomed to the heat. In addition, the severe residual heat and dryness last year affected the planting of autumn and winter vegetables and subsequent work. And since the volume of the ocean increases as it warms, the risk of sea level rise is also increasing due to the prolonged summer. It is very important to elucidate the cause.
According to Lin and Wang, 2022, the Northern Hemisphere summer started about 0.19 days earlier per year from 1960 to 2014, and the summer ended by about 0.19 However, since the discussion was centered on the North American continent, Europe, and Eurasia, there was no mention of the prolongation of the summer in the oceans surrounding island nations such as Japan Japan.
Therefore, the primary purpose of this study is to investigate the characteristics of summer and elucidate the trend of prolonged summer in recent years Japan.
In this study, we used daily data of 2 m temperature and 10 m wind from JRA-55 and daily sea surface temperature analysis data from the Japan Meteorological Agency (JMA) 55-year long-term reanalysis data JRA-55 and daily sea surface temperature (SST) from the Japan Meteorological Agency (JMA) and MGDSST for a period of 42 years from 1982 to 2023.
First, the temperature of the hottest day of the year (maximum temperature) and the temperature of the coldest day (minimum temperature) were extracted for each year, and the average value of each was obtained. Next, the average temperature range of the grid was set using the difference between the average values.
The first day (the last day) when the five-day moving average of daily temperature exceeded the threshold in each year was defined as the start date (end date) of the summer of that year, and the number of days from the start date to the end date was defined as the summer period.
First, in order to investigate the characteristics of summer in Japan, we examined the days when the temperature reaches its maximum value (hereinafter referred to as the peak temperature day), the start and end dates of summer, and the number of days of the period for each year.Finally, we investigated why summers in Japan are longer and investigate the relationship between the oceans and the seasonal progression of temperatures, based on the results shown in the next chapter.
The peak date of the temperature tends to be July on the continent and August at sea, and the Japan is in August Japan.
Next, the trend analysis showed the trend of change in summer: Japan, the central North Pacific, and the Arctic Ocean were confirmed in places where the start date was brought forward, the end date was pushed back, and the period was lengthened.
From this, it is considered that Japan is the only place in the mid-latitude region where there are four seasons, and the summer period is prolonged both forward and backward.
Finally, we will consider the cause of the prolonged summer in Japan because the seasonal change in temperature in Japan is like the seasonal change in the ocean.
Both near the start and end dates, an uptrend and temperature trend of SST were confirmed near Japan.
From the above results, it is possible that the atmosphere from the continent is not cooled by the ocean due to the rise of SST and is carried to Japan when the start date is brought forward, and that the warm air is carried to Japan by SST when the start date is delayed.
The purpose of this study was to understand the characteristics of summer in Japan and to elucidate the trend of prolongation of summer in recent years Japan.
Furthermore, from these results, we investigated the cause of Japan's prolonged summer in relation to the ocean and showed that the increase in SST may be one of the causes of Japan's prolonged summer.
However, the four seasons in Japan are collapsing.
In recent years, there have been many days reported as "hot as midsummer" even in spring and autumn, and along with this, there are some claims that "summer in Japan is getting longer" and "spring and autumn have disappeared".
Varies depending on the high temperature in spring and autumnFor example, the risk of heat stroke increases due to the high temperature in spring, when people are not accustomed to the heat. In addition, the severe residual heat and dryness last year affected the planting of autumn and winter vegetables and subsequent work. And since the volume of the ocean increases as it warms, the risk of sea level rise is also increasing due to the prolonged summer. It is very important to elucidate the cause.
According to Lin and Wang, 2022, the Northern Hemisphere summer started about 0.19 days earlier per year from 1960 to 2014, and the summer ended by about 0.19 However, since the discussion was centered on the North American continent, Europe, and Eurasia, there was no mention of the prolongation of the summer in the oceans surrounding island nations such as Japan Japan.
Therefore, the primary purpose of this study is to investigate the characteristics of summer and elucidate the trend of prolonged summer in recent years Japan.
In this study, we used daily data of 2 m temperature and 10 m wind from JRA-55 and daily sea surface temperature analysis data from the Japan Meteorological Agency (JMA) 55-year long-term reanalysis data JRA-55 and daily sea surface temperature (SST) from the Japan Meteorological Agency (JMA) and MGDSST for a period of 42 years from 1982 to 2023.
First, the temperature of the hottest day of the year (maximum temperature) and the temperature of the coldest day (minimum temperature) were extracted for each year, and the average value of each was obtained. Next, the average temperature range of the grid was set using the difference between the average values.
The first day (the last day) when the five-day moving average of daily temperature exceeded the threshold in each year was defined as the start date (end date) of the summer of that year, and the number of days from the start date to the end date was defined as the summer period.
First, in order to investigate the characteristics of summer in Japan, we examined the days when the temperature reaches its maximum value (hereinafter referred to as the peak temperature day), the start and end dates of summer, and the number of days of the period for each year.Finally, we investigated why summers in Japan are longer and investigate the relationship between the oceans and the seasonal progression of temperatures, based on the results shown in the next chapter.
The peak date of the temperature tends to be July on the continent and August at sea, and the Japan is in August Japan.
Next, the trend analysis showed the trend of change in summer: Japan, the central North Pacific, and the Arctic Ocean were confirmed in places where the start date was brought forward, the end date was pushed back, and the period was lengthened.
From this, it is considered that Japan is the only place in the mid-latitude region where there are four seasons, and the summer period is prolonged both forward and backward.
Finally, we will consider the cause of the prolonged summer in Japan because the seasonal change in temperature in Japan is like the seasonal change in the ocean.
Both near the start and end dates, an uptrend and temperature trend of SST were confirmed near Japan.
From the above results, it is possible that the atmosphere from the continent is not cooled by the ocean due to the rise of SST and is carried to Japan when the start date is brought forward, and that the warm air is carried to Japan by SST when the start date is delayed.
The purpose of this study was to understand the characteristics of summer in Japan and to elucidate the trend of prolongation of summer in recent years Japan.
Furthermore, from these results, we investigated the cause of Japan's prolonged summer in relation to the ocean and showed that the increase in SST may be one of the causes of Japan's prolonged summer.