11:00 AM - 1:00 PM
[HQR04-P08] Climate reconstruction during the Little Ice Age based on weather records described in old diaries
- Number of lightning days in the Hokuriku district, Japan –
Keywords:old diary, climate reconstruction, lightning, the Little Ice Age, Hokuriku
Summary
> Reconstruction of the numbers of lightning days in Kanazawa and Toyama during the Little Ice Age (LIA) based on the weather records in the diaries.
> Reconstructed numbers of lightning days in Kanazawa and Toyama during LIA are fraction of the current number.
> This suggest that the increase in sea surface temperature has led to an increase in the number of lightning days.
Research Objective
Studies on paleoclimate reconstruction have been conducted from various viewpoints, such as reconstruction of the location of rainy season frontal zone, atmospheric pressure pattern, seasonal change in weather, flood scale and amount of precipitation, based on various data source. However, reconstructions of lightning have been limited. In this study we attempted to reconstruct the lightning in Hokuriku district during the Little Ice Age (LIA), and then compared the past and present weather records and discussed the factors of change.
Research Methods
The diaries were used to estimate the paleoclimate of the LIA. The weather records of Kanazawa City from 1827 to 1837 were obtained from “Kakuson Nikki (Diary written by Mr. Kakuson)”, and those of Himi City near Toyama City from 1827 to 1843 from “Ohkyo Zakki (Diary written by hostel owner)”. The weather records of the present-day Kanazawa City and Toyama City were also collected from the JMA database. The obtained weather records were entered was tabulated. In addition to the number of days per year, days each of the three periods: summer-1 (Mar. to Jun.), Summer-2 (Jul. to Oct.) and winter (Nov. to Feb.) were also tabulated.
Results
[ Days per Year: Present <--- LIA ]
Kanazawa: 47.4 days (3.2 times) <--- 14.8 days / Toyama: 33.9 days (2.5 times) <--- 13.4 Days
[ Days in Summer-1 ]
Kanazawa: 9.2 days (3.2 times) <--- 2.9 days / Toyama: 8.2 days (2.9 times) <--- 2.8 Days
[ Days in Summer-2 ]
Kanazawa: 10.7 days (1.6 times) <--- 6.8 days / Toyama: 13.0 days (1.7 times) <--- 7.5 Days
[ Days in Winter ]
Kanazawa: 27.5 days (6.5 times) <--- 4.3 days / Toyama: 12.8 days (4.2 times) <--- 3.0 Days
Discussion
The number of lightning days has been increasing from LIA to the present in both Kanazawa and Toyama. The increase in the number of days of lightning was particularly high in winter, indicating that lightning in summer was the dominant rather than in winter in LIA even the winter lightning is dominant in Hokuriku district at the present.
The winter lightnings in Hokuriku district are caused by formation of cumulonimbus clouds by vapor supplied by the difference in temperature (potential temperature, in particularly) between sea surface temperature (SST) of Sea of Japan affected by Tushima warm current and air temperature of the wind blowing from Siberian High. Then, the results of this study indicate that the winter temperature difference during LIA reduced compare to the present. In order to reduce the winter temperature difference, either an increase in air temperature or a decrease in SST, or both, must occur. Since LIA was a period of low temperature, and since global warming is currently underway, the former cannot be the reason. In addition, the inflow of the Tsushima warm current is thought to have continued during the Holocene, making it difficult to assume that SST decreased during LIA. Considering the fact that SST around Japan has been increasing in recent years, it suggests that the change in number of lightning days may have been caused by recent global warming.
> Reconstruction of the numbers of lightning days in Kanazawa and Toyama during the Little Ice Age (LIA) based on the weather records in the diaries.
> Reconstructed numbers of lightning days in Kanazawa and Toyama during LIA are fraction of the current number.
> This suggest that the increase in sea surface temperature has led to an increase in the number of lightning days.
Research Objective
Studies on paleoclimate reconstruction have been conducted from various viewpoints, such as reconstruction of the location of rainy season frontal zone, atmospheric pressure pattern, seasonal change in weather, flood scale and amount of precipitation, based on various data source. However, reconstructions of lightning have been limited. In this study we attempted to reconstruct the lightning in Hokuriku district during the Little Ice Age (LIA), and then compared the past and present weather records and discussed the factors of change.
Research Methods
The diaries were used to estimate the paleoclimate of the LIA. The weather records of Kanazawa City from 1827 to 1837 were obtained from “Kakuson Nikki (Diary written by Mr. Kakuson)”, and those of Himi City near Toyama City from 1827 to 1843 from “Ohkyo Zakki (Diary written by hostel owner)”. The weather records of the present-day Kanazawa City and Toyama City were also collected from the JMA database. The obtained weather records were entered was tabulated. In addition to the number of days per year, days each of the three periods: summer-1 (Mar. to Jun.), Summer-2 (Jul. to Oct.) and winter (Nov. to Feb.) were also tabulated.
Results
[ Days per Year: Present <--- LIA ]
Kanazawa: 47.4 days (3.2 times) <--- 14.8 days / Toyama: 33.9 days (2.5 times) <--- 13.4 Days
[ Days in Summer-1 ]
Kanazawa: 9.2 days (3.2 times) <--- 2.9 days / Toyama: 8.2 days (2.9 times) <--- 2.8 Days
[ Days in Summer-2 ]
Kanazawa: 10.7 days (1.6 times) <--- 6.8 days / Toyama: 13.0 days (1.7 times) <--- 7.5 Days
[ Days in Winter ]
Kanazawa: 27.5 days (6.5 times) <--- 4.3 days / Toyama: 12.8 days (4.2 times) <--- 3.0 Days
Discussion
The number of lightning days has been increasing from LIA to the present in both Kanazawa and Toyama. The increase in the number of days of lightning was particularly high in winter, indicating that lightning in summer was the dominant rather than in winter in LIA even the winter lightning is dominant in Hokuriku district at the present.
The winter lightnings in Hokuriku district are caused by formation of cumulonimbus clouds by vapor supplied by the difference in temperature (potential temperature, in particularly) between sea surface temperature (SST) of Sea of Japan affected by Tushima warm current and air temperature of the wind blowing from Siberian High. Then, the results of this study indicate that the winter temperature difference during LIA reduced compare to the present. In order to reduce the winter temperature difference, either an increase in air temperature or a decrease in SST, or both, must occur. Since LIA was a period of low temperature, and since global warming is currently underway, the former cannot be the reason. In addition, the inflow of the Tsushima warm current is thought to have continued during the Holocene, making it difficult to assume that SST decreased during LIA. Considering the fact that SST around Japan has been increasing in recent years, it suggests that the change in number of lightning days may have been caused by recent global warming.