日最低・最高気温の統計値における日界変更の影響  [in Japanese] Time of Observation Bias in the Climatological Data of Daily Minimum and Maximum Temperature in Japan  [in Japanese]

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Abstract

日界とは,気象観測における1日の区切りの時刻である.日本の気象観測における日最低・最高気温の日界は,現在は00時であるが,1953∼63年は日最低気温について09時であり,1939年までは多くの地点で22時であった.こうした日界の違いが統計値に与える影響を,アメダスの毎時資料を使って調べ,以下の結果を得た.(1) 09時日界による日最低気温は,00時日界の値に比べて高い傾向がある.偏差の大きさは,全国平均の年平均値で0.41℃である.(2) 22時日界による日最低気温も,00時日界の値に比べて高く,偏差の大きさは全国平均の年平均値で0.17℃である.(3) これらの偏差は,気温の日変化特性と日々変化の大きさに依存し,季節や地域によっては上記の値の2倍を超えることもある.(4) 09時・22時日界による日最高気温の偏差は小さい. また,過去100年間の日最低気温の経年変化率を計算する場合には09時日界よりも22時日界による偏差のほうが影響が大きく,地点や季節によっては0.4℃/(100年)に達する評価誤差を生じ得ることが指摘された.

Observation of daily minimum and maximum temperature at meteorological stations in Japan is currently made for the 24 hours between 0000 and 2400 JST (Japan Standard Time), whereas it was made for 2200-2200 JST at many stations until 1939, and for 0900-0900 JST as to minimum temperature from 1953 to 1963. In order to evaluate the bias arising from different observation times, hourly data at 830 AMeDAS stations for 1979-1997 were analyzed. The results are summarized as follows: (1) The 0900-0900 minimum temperature tends to deviate positively from the 0000-2400 value. The bias is 0.41℃ on the annual average over the whole country. (2) The 2200-2200 minimum temperature, which has been believed to be unbiased so far, has also some positive bias. The annual average bias over the whole country is 0.17℃. (3) The bias has considerable seasonal and spatial differences according to the diurnal and synoptic temperature variations. At some stations and in some seasons, the bias can exceed twice of the average values mentioned above. (4) The bias of 0900-0900 and 2200-2200 maximum temperatures are generally small. It is also shown that the 2200-2200 bias can be more serious than the 0900-0900 bias in evaluating the rising rate of minimum temperature during the last hundred years, with a maximum possible error of 0.4℃/(100 years).

Journal

  • 天気

    天気 46(12), 819-830, 1999-12-01

    日本気象学会

References:  12

Cited by:  5

Codes

  • NII Article ID (NAID)
    110001814070
  • NII NACSIS-CAT ID (NCID)
    AN00151568
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    05460921
  • NDL Article ID
    4935210
  • NDL Source Classification
    ZM43(科学技術--地球科学--気象)
  • NDL Call No.
    Z15-35
  • Data Source
    CJP  CJPref  NDL  NII-ELS  NDL-Digital 
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