Urban thermal plume

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An urban thermal plume describes rising air in the lower altitudes of the Earth's atmosphere caused by urban areas being warmer than surrounding areas. Over the past thirty years there has been increasing interest in what have been called urban heat islands (UHI),^[1] but it is only since 2007 that thought has been given to the rising columns of warm air, or ‘thermal plumes’ that they produce. Common on-shore breezes at the seaside on a warm day, and off-shore breezes at night are caused by the land heating up faster on a sunny day and cooling faster after sunset, respectively. Thermals, or warm airs, that rise from the land and sea affect the local microscale meteorology; and perhaps at times the mesometeorology.^{[original research?]} Urban thermal plumes have as powerful although less localized an effect.

London is generally 3 to 9 Celsius hotter than the Home Counties.^[2][3] London’s meteorological aberrations were first studied by Luke Howard, FRS in the 1810s,^[4] but the notion that this large warm area would produce a significant urban thermal plume was not seriously proposed until very recently.

Microscale thermal plumes, whose diameters may be measured in tens of metres, such as those produced by industrial chimney stacks, have been extensively investigated, but largely from the point of view of the plumes dispersal by local micrometeorology.^[5] Though their velocity is generally less, their very much greater magnitude (diameter) means that urban thermal plumes will have a more significant effect upon the mesometeorology and even continental macrometeorology.^[6]