Meteorology

Ultrasonic anemometry

The aims of the measurements were to investigate:

• the relationship between street level (constrained) and roof top (WCC) as in DAPPLE 2003, but also to take this further by having unconstrained winds in DAPPLE 2004 from the BT Tower and Lidar. Note, DAPPLE 2003 had a predominance of winds from the W, SW and NW so maintaining the sonic anemometer configuration at the intersection was to allow documentation of all component winds during the longer DAPPLE 2004;
• how the horizontal advection compares with the vertical mixing in urban environments - possible in DAPPLE 2004 as the 6 fixed in-street sonics (Sites 1-4) had GPS time synchronization that will allow accurate correlations to be undertaken;
• the turbulent fluxes and mean flows across the intersection in the centre of the road (Sites 1 & 2) - DAPPLE 2004 used pairs of sonics, at 2 heights on both sites 1 & 2, rather than just single sonics as in the first campaign, to investigate further the results of flow switching and to measure the vertical turbulent fluxes in the central reservation (the previous campaign investigated pavement side fluxes at sites 4 and 5);
• the variation in flow either side of Marylebone Road (sites 3 & 4) - in DAPPLE 2003 site 3 failed and so we did not have this information - hence the deployment was repeated;
• how the more commonly measured synoptic, undisturbed greater London and disturbed urban roof top stations compare to each other and to the flow within the streets.

An album of anemometer installations is included in the Fieldwork 2003 pages.

Lidar anemometry

A team from QinetiQ made wind profile measurements with a Doppler LIDAR on June 3rd, the day of the first PMCH tracer experiment. The LIDAR was located on the NE corner of the Library roof and provided wind profiles from 10 to 200 m. The aims of these measurements were to investigate:

• the issue of how to provide a reliable wind speed reference in an urban environment;
• the relationship between the lidar data and the output from the fixed sonics on the WCC roof and BT tower, as well as output from the Met Office model profiles;
• the appropriateness of the technique in urban areas.