Urban Heat Island (UHI) quantification Sample Clauses

Urban Heat Island (UHI) quantification. During the night of the 4-5 July 2009, when the land breeze regime prevails, the UHI develops until reaching its maximum (0.82 ºC) at 3 UTC in the urban station. The maximum at the sub-urban hinterland station is 0.6 ºC at 4 UTC and at the coastal station is almost negligible (0.2 ºC at 3 UTC). At the early hours in the morning this effect disappears, when solar heating initiated fumigation and sea and up-valley breezes re-enter the stagnated air mass into the city around 6 UTC. At night a ground- based inversion could be formed in the bottom of the valleys by a combination of radiation cooling and the accumulation of cold down-slope drainage wind. A blocking of the stabilized air mass could occur over the surroundings of Bilbao due to the roughness and the heat island and the generation of upward motions in the urban zone. This effect can be observed in the wind difference between the urban and control simulations: while the wind is accelerated up to 1 ms-1 at the urban station, during the early hours, the wind difference range between -0.3 to -0.7 m-1 at sub-urban sites. The difference in the relative humidity shows a decrease during the development of the UHI phenomenon at night and, when the sea breezes penetrate in the city the relative humidity increases.