5:15 PM - 6:30 PM
[AAS13-P02] Nocturnal Temperature Distribution under Fine and Weak Wind Conditions Based on Spatially High Density Observation Data in the Tokyo Metropolitan Area: Features in Summer
Keywords:urban heat island, nocturnal temperature distribution, spatially high density observation, Tokyo wards area, summer
The observation networks used for temperature distribution analyses were the Automated Meteorological Data Acquisition System (AMeDAS) of the Japan Meteorological Agency (JMA), air pollution monitoring system (APMS) of the Tokyo Metropolitan Government and adjacent prefectures, and Meteorological Environmental Temperature and Rainfall Observation System (Extended-METROS). The AMeDAS and APMS datasets were also used to obtain the wind data.
The results obtained in this study are summarized as follows:
(1) According to multiple regression analysis (stepwise method), wind speed and cloud amounts showed equally large effects on TD between central Tokyo (Otemachi, JMA) and the outside of Tokyo wards area (average temperature from four AMeDAS stations). This result was different from that of winter nights, indicating that cloud amounts have a larger effect than wind speed on TD.
(2) A steep horizontal temperature gradient zone (HTGZ) in the western part of Tokyo wards area was unclear even during nights with fine and low wind speeds in comparison with winter nights, where the steep HTGZ was clear under the same conditions. This may be related to the relatively lower decrease rate of temperature in summer, especially around sunset when the wintertime HTGZ begins to become conspicuous. It is considered that the difference in radiation cooling by season is one of the key factors. In addition, because high-temperature areas tended to remain in the northwestern part of Tokyo wards area in summer, central Tokyo did not become the highest-temperature area until after midnight, which was also different from the findings of winter nights.
(3) To identify effective factors for large differences in TD for fine and weak wind nights, the corresponding cases were divided into three categories in accordance with the observed values of TD at 04:00 JST just before sunrise. For cases of large TD, in which high-temperature areas were concentrated in central Tokyo, inland wind systems initiated relatively earlier and showed a relatively larger wind speed before midnight. Subsequently, the local wind front migrated to the coastal area of Tokyo Bay by early morning. For cases of low TD, inland winds were weak, and the local wind front could not be clearly observed. For cases of intermediate TD, a large amount of solar radiation and a relatively strong sea breeze system were observed during the preceding daytime. Clear high-temperature areas remained from the northern part of Tokyo wards area to southern Saitama prefecture throughout the night, and the local wind front stagnated in this area. We conclude that the nocturnal TD in and around the Tokyo wards area in summer is affected by inland wind systems and the location of the local wind front.