Weather Conditions, Temperature and Pressure Pattern in July and August in the 1750's

Abstract

From long-term variations of weather hazards of Japan, Maejima and Tagami (1986) found the “Cold Age” from 15th to 19th century. During this period Japan had frequently suffered from severe famine due to cool summer weather. This paper attempts to reconstruct the summer weathers in the 1750's, including the notorious famine of 1755, the Horeki famine.
From the weather records as proxy data in 11 historical diaries the weather calendar diagrams for 1751-1760 were prepared. By means of synoptic view of weather distribution in those diagrams, the characteristics of the seasonal march of pressure pattern were estimated for each summer. Then, using the weather pattern, a method was introduced to estimate the temperature and the frequency of pressure pattern.
The formula to estimate the monthly mean temperature, by using present instrumental data, is follows:
y=c₁x₁+c₂x₂+…+c₁₅x₁₅+c₁₆x₁₆
where independent variables x₁, x₂, …x₁₅, x₁₆ denote sixteen types of weather pattern, and dependent variable y denote monthly mean temperature in a given location. Using the data for latest 30 years, coefficients c₁, c₂, …c₁₅, c₁₆ were calculated to estimate y with minimum error sum. Thus, we calculate the monthly mean temperature in the historical past by using the frequency of historical weather pattern.
Then, from the relationship between pressure pattern and weather pattern in the instrumental period, historical pressure pattern was inferred.
The results obtained are summarized as follows:
(1) In 1750's the summer weather was different from year to year. In July 1755, a notorious famine year, northern Japan suffered from cool air flow from the northeast, and it was rainy, because of the stagnation of stationary front, in central and southern Japan. On the contrary, in August 1755 it was rainy only in the northern part of northern Japan, while it was hot and dry in central and southern Japan.
(2) The temperature for July 1755 was 3°C lower than the present normal (1951-80) at Morioka and Ishinomaki in the eastern part of northern Japan. Standard deviation of error sum of estimation was 0.7°C (Morioka) and 0.6°C (Ishinomaki). In August 1755 the temperature at Morioka and Ishinomaki was not low.
(3) In July 1755 the frequency of summer monsoon pressure pattern was low, while the frequency of stationary type of front running along the Pacific coast was high. In August 1755, the frequency of summer monsoon pressure pattern was low, while the frequency of stationary type of front running over nothern Japan was high.