UK and London Weather 09/01/2012-15/01/2012

Hello all,

As a student working with Dr Janet Barlow and Dr Omduth Coceal over the course of the Clearflo Project, I thought it would be helpful to provide a brief weekly discussion on the UK-wide and local weather during the course of the IOP’s and how it could potentially be affecting pollution, the Urban Heat Island (UHI), and the boundary layer dynamics in London.

We’ve had a chilly week in London so far, thanks to high pressure dominating across the UK, with the anticyclonic centre originally sitting over Northwestern France and persisting over Europe and towards the North Sea. This blocking high is inhibiting the progress of frontal systems into the UK, and leaving us in well- subsided air, giving us clear conditions and a freely-radiating surface.
In London the weather has grown colder since the start of the IOP. On the 11th of January there was still some cloud cover and maximum temperatures in the realm of 11?C. Then by the 13th there were spots of mist and patchy fog forming as temperatures dropped to freezing at night, followed by dry sunny spells and cooler maximum temperatures closer to 7?C.

By the weekend of the 14th-15th of January high pressure was still well established and influencing London’s weather, and mist and freezing fog has been clearing more slowly in the mornings. Weekend temperatures ranged between -2?C at night and 6?C during the day in the South east.
During such persistent clear periods London’s urban surface will have been warmed more rapidly than rural locations by the absorption of solar radiation, leading to a stronger UHI effect. Additionally, the stationary weather and low winds will have meant that in the past week London’s pollution was likely to be predominantly locally-driven.

It’s also worth noting that during weak-wind and clear-sky conditions, the thermal modification of the boundary layer in response to the UHI is likely to dominate the local meteorology, even over the increased surface roughness’ influence in urban areas. This is also conducive to the formation of a “mixing layer dome” or “dust dome” in which pollution accumulates over the urban landscape in calm meteorological conditions (Arya, 1998).

The 12 UTC Synoptic Analysis on the 15th of January 2012

Aryra, S. P., 1998: Introduction to Micrometeorology
Met Office Weather Forecast
WetterOnline UKMO

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