OBSERVATION OF THE VERTICAL PROFILES OF WIND VELOCITY BY TWO DOPPLER LIDARS ABOVE CITY CENTER IN COASTAL CITY SENDAI, JAPAN (PART 1): INFLUENCE OF CHARACTERISTICS OF INLAND WIND AND SEA BREEZE ABOVE THE CITY ON AIR TEMPERATURE AND HUMIDITY NEAR THE GROUND

The use of sea breeze with a huge cool potential has been regarded as one of the effective countermeasures against urban heat island phenomenon, and many studies have reported the effect of sea breeze on reducing air temperature. On the other hand, atmospheric observations have been conducted to understand the characteristics of wind in the urban boundary layer. Especially, in recent years, with the development of remote sensing technology, many studies to measure the mean or turbulent characteristics of wind above the city have been conducted using Doppler lidars. However, the relationship between sea breeze above the city and temperature and humidity near the ground has not been clarified precisely. In this study, to examine the relationships between sea breeze and temperature near the ground in summer, a concurrent measurement of wind velocities above the city center using two Doppler lidars, and air temperature and humidity at multiple observation points was conducted in Sendai, a coastal city of Japan. The results were classified into days with wind from inland and sea breeze, and compared. A time series of the vertical distributions of wind direction, speed and the vertical component of wind velocity vector, and power spectrum of vertical fluctuations of the wind were analyzed with a time series of air temperature and humidity for each day. In the day with inland wind, the difference between the time series of air temperature measured at points located in inland to coastal areas was small. From the measurements taken by the Doppler lidars, the inland wind was observed at the height near the ground to over 1,000 m. The results also showed that the higher the altitude, the larger the scalar value of horizontal wind velocity. Until 9:30, small fluctuations in vertical wind velocity above the city were observed uniformly across all heights. From that time onward, the vertical fluctuations with large power were confirmed at the height of around 400 m and 600 m, while the power at the height of around 100 m and 200 m was low. In the day with sea breeze, the rise of air temperature stopped or moderated in order of distance from the coastal line. In the central part of the city, the temperature rise was stopped until 15:00. Based on the results of Doppler lidars, the sea breeze started to be observed at around 8:30, and in the afternoon, the layer of inland wind was observed on the layer of sea breeze. Regarding the vertical fluctuations of wind, though ther