Characteristics of Variation of Mean Temperature with Different Averaging Periods, and the Confidence Limits of Return Period by an Empirical Method

Abstract

Characteristics of year to year change in mean air temperature with different averaging period were analysed, and the confidence limits of return periods determined by an empirical method were discussed in relation to the averaging period, season and the place. Results are summarized as follows:
(1) Both annual and monthly mean air temperatures for the warm season with the return period of 50 years are found to be nearly equal to the temperature (M-2σ), where M and σ are the mean and standard deviation of the yearly change in annual and monthly mean temperatures. Monthly mean temperatures for the return period of 10 years are lower by about 0.4°C than the temperature (M-σ) in average.
(2) Air temperatures for the same return period are decreased with the decrease of the averaging period, and the difference between monthly and half-decade mean air temperatures for the return period of 10 years are in the range of 1 to 2°C.
(3) Empirical relations were obtained to explain the change in relative standard deviation of yearly fluctuation of period-mean temperature (Eq. 4). These values of the relative standard deviation are somewhat smaller than those predicted by the -1/2 power law of averaging days.
(4) Significant values of return periods (T_j) estimated by the empirical method (Eq. 1) vary with season, place, and the averaging period. T_j for half-decade and decade mean temperatures in the case of statistical period of 78 years, are considered to be about 15 and 20 years, respectively.