5:15 PM - 6:45 PM
[MIS17-P12] Correspondence between weather record in diaries and sunshine duration examined with "detailed description rate" and "overlapping rate"
Keywords:Weather record of diaries, Paleoclimate proxy data, Quantification, Detailed description rate, Overlapping rate, Sunshine duration
Daily weather record of old diaries is very useful for climate reconstruction in historical times because of its exceptionally high temporal resolution as paleoclimate proxy data. Those data have been compiled for since the 11th century for the capital (Kyoto) area, and are widely available for since the 18th century for most part of Japan. However, there is difficulty in estimating quantitative meteorological variables such as precipitation from their qualitative and subjective weather description. In this study, we attempt to develop a method to quantify weather record of diaries by using old diaries written in Meiji and Taisho period (late 19th to early 20th centuries) that are comparable to instrumental meteorological data.
We have defined "detailed description rate" and "overlapping rate" as indices to extract objective and quantitative information from weather record of old diaries and have examined their usefulness. "Detailed description rate" is the ratio of the number of days of detailed weather records (i.e., weather records that contain information more than a single word such as "sunny" or "rainy", for example, degree of intensity of rainfall or weather changes within a day) to the total number of days of weather records in a certain period. This index has been shown to correlate negatively with the threshold for recording precipitation in the diary (Sho et al., 2017). By using this relationship, it is possible to compensate for differences in the threshold of precipitation records among diaris and compare the number of precipitation days between different diaries by converting the threshold value to 1 mm, for example. "Overlapping rate" is defined as the area of overlap between the relative frequency distribution of a meteorological parameter for each weather category when two weather categories are extracted from the daily weather records based on some criteria, such as "with precipitation" and "without precipitation" or "fine" and "cloudy." Smaller (nearer to 0) value of this index means better correspondence between selected weather categories and the meteorological parameter while larger (nearer to 1) value means worse correspondence. By using this index and comparing with hourly precipitation and cloud cover data, it became clear that the daily weather records of "with precipitation" and "without precipitation" mainly reflect daytime conditions, but also reflect nighttime conditions to some extent, and that records of "clear" and "cloudy" correspond well with daytime cloud cover and hardly reflect nighttime cloud cover.
In this presentation, focusing on the correspondence with sunshine duration (or sunshine rate), we examine the degree of correspondence with weather records such as "sunny," "cloudy," and "rainy," its differences by season and diary, and the accuracy and temporal resolution of sunshine duration estimated from weather records, using weather records in about 10 diaries collected in the Kinki and Tokyo areas.
We have defined "detailed description rate" and "overlapping rate" as indices to extract objective and quantitative information from weather record of old diaries and have examined their usefulness. "Detailed description rate" is the ratio of the number of days of detailed weather records (i.e., weather records that contain information more than a single word such as "sunny" or "rainy", for example, degree of intensity of rainfall or weather changes within a day) to the total number of days of weather records in a certain period. This index has been shown to correlate negatively with the threshold for recording precipitation in the diary (Sho et al., 2017). By using this relationship, it is possible to compensate for differences in the threshold of precipitation records among diaris and compare the number of precipitation days between different diaries by converting the threshold value to 1 mm, for example. "Overlapping rate" is defined as the area of overlap between the relative frequency distribution of a meteorological parameter for each weather category when two weather categories are extracted from the daily weather records based on some criteria, such as "with precipitation" and "without precipitation" or "fine" and "cloudy." Smaller (nearer to 0) value of this index means better correspondence between selected weather categories and the meteorological parameter while larger (nearer to 1) value means worse correspondence. By using this index and comparing with hourly precipitation and cloud cover data, it became clear that the daily weather records of "with precipitation" and "without precipitation" mainly reflect daytime conditions, but also reflect nighttime conditions to some extent, and that records of "clear" and "cloudy" correspond well with daytime cloud cover and hardly reflect nighttime cloud cover.
In this presentation, focusing on the correspondence with sunshine duration (or sunshine rate), we examine the degree of correspondence with weather records such as "sunny," "cloudy," and "rainy," its differences by season and diary, and the accuracy and temporal resolution of sunshine duration estimated from weather records, using weather records in about 10 diaries collected in the Kinki and Tokyo areas.