A study of the hourly variability of the urban heat island effect in the Greater Athens Area during summer.
Measurements of air temperature and humidity in the urban canopy layer during July 2009 in 26 sites in Athens, Greece, allowed for the mapping of the hourly spatiotemporal evolution of the urban heat island (UHI) effect. City districts neighboring to the mountains to the east were the hottest during the afternoon, while being among the coolest during the early morning hours. While during the early morning some coastal sites were the hottest, the warm air plume slowly moved to the densely urbanized center of the city until 14:00-15:00, moving then further west, to the Elefsis industrial area in the afternoon. Results from the UrbClim model agree fairly well with the observations. Satellite-derived land surface temperature (LST) data from AATSR, ASTER, AVHRR and MODIS, for pixels corresponding to ground stations measuring Tair, showed that LST can be up to 5K lower than the respective Tair during nighttime, while it can be up to 15K higher during the rest of the day. Generally, LST during late afternoon as acquired from AATSR is very near to Tair for all stations and all days, i.e., the AATSR LST afternoon retrieval can be used as a very good approximation of Tair. The hourly evolution of the spatial Tair distribution was almost the same during days with NE Etesian flow as in days with sea breeze circulation, indicating that the mean wind flow was not the main factor controlling the diurnal UHI evolution, although it influenced the temperatures attained. No unambiguous observation of the urban moisture excess (UME) phenomenon could be made.
Laboratory of Atmospheric Pollution and Pollution Control Engineering of Atmospheric Pollutants, School of Engineering, Democritus University of Thrace, 12 Vas. Sofias str., 67100 Xanthi, Greece. Electronic address: kourtidi@env.duth.gr.
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Kourtidis
Laboratory of Atmospheric Pollution and Pollution Control Engineering of Atmospheric Pollutants, School of Engineering, Democritus University of Thrace, 12 Vas. Sofias str., 67100 Xanthi, Greece; Department of Meteorology and Climatology, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece. Electronic address: argeor@env.duth.gr.
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Georgoulias
Laboratory of Atmospheric Pollution and Pollution Control Engineering of Atmospheric Pollutants, School of Engineering, Democritus University of Thrace, 12 Vas. Sofias str., 67100 Xanthi, Greece. Electronic address: rapso@env.duth.gr.
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Rapsomanikis
Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens (NOA), Athens, Greece. Electronic address: vamoir@noa.gr.
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Amiridis
Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens (NOA), Athens, Greece. Electronic address: ik@noa.gr.
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Keramitsoglou
Flemish Institute for Technological Research (VITO), Boeretang 200,2400 Mol, Belgium. Electronic address: hans.hooyberghs@vito.be.
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Hooyberghs
Flemish Institute for Technological Research (VITO), Boeretang 200,2400 Mol, Belgium. Electronic address: bino.maiheu@vito.be.
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Maiheu
Laboratory of Atmospheric Physics, Physics Dept., Aristotle University of Thessaloniki, Greece. Electronic address: melas@auth.gr.
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Melas
Land surface temperature; Urban heat island; Urban moisture excess