THE DISTRIBUTION AND CLIMATOLOGICAL ANALYSIS OF THE DAILY MINIMUM TEMPERATURE IN AND AROUND THE TOKYO METROPOLITAN AREA

Abstract

Using the daily temperature values observed at 28 climatological stations (Fig. 1) within 30km from the civic center of Tokyo, the author prepared 270 patterns of the daily minimum temperature distribution for the winter months (December, January and February) of the years 1952/53, 1953/54 and 1954/55. These patterns were then classified into the following 5 types according to a) temperature difference between the civic center and its suburbs, and b) the general pattern of isotherms (Fig. 3): #1: Temperature differences are less than 2C……43 sheets (Fig. 3, (1) & (5)). #2: Temperature differences are 2°-4°C, with isotherms running in rough concentric circles around the highest temperature area of the central part of the city……92 sheets (Fig. 3, (2) & (6)). #3: Temperature differences are more than 4°C, with isotherms running in the same manner as in type #2, above……53 sheets (Fig. 3, (3)). #4: Marked temperature differences appear only at the northern margin of the built-up area……6 sheets. (Fig. 3, (7)). #5: Temperature differences of more than 2°C can be seen, but isotherms running irregulaly, and are not directly influenced by the built-up area……20 sheets (Fig. 3, (4) & (8)). 56 sheets were excluded before classification because of the irregular quality of their diurnal temperature changes. In order to discover the relationship between these 5 types of pattern and such meteorological factors as cloudiness, wind velocity wind direction, temperature and water-vapor pressure, all of which are considered important in the development of “city temperature”, a frequency distribution talbe (Tables 1, 3, 4, 5, and 6) of these factors for each of the 5 temperature distribution types explained above was compiled, and the results obtained are as follows (see Fig. 3): #1-patterns of this type are likely to occur on cloudy nights (especially those with precipitation) or on clear nights with strong wind (more than 5m/s). #3-patterns of this type have a tendency to develop on clear nights with weak wind or calm. #2-patterns of this type appear as intermediate between types #1 and #3. #4-patterns of this type appear in conditions of trong wind and relatively high temperatures without exception. Therefore, a partial analysis and explanation of this special pattern was made and is shown in Fig. 5. #5-patterns of this type are liable to appear on nights with marked changes of wind direction, but not in all cases. As for wind effect, somewhat different conclusion were drawn concrning this influence on “city temperatures”. Namely, that “calm” is not necessarily the most suitable condition for the development of “city temperature”. Weak wind conditions seem to be more appropriate (Fig. 4, Table 3). Finally, the synoptic weather situation most suitable for the development of “city temperature” is discussed (Table 7).