Programme 2/64 (supersedes 2/63) PES/TU.1206/3493/63


Project No.33

The Penetration of Built-Up Areas by Aerosols at Night

INTRODUCTION

1. When an aerosol cloud is generated in the atmosphere above a temperature inversion, it diffuses downward only slowly, and at night-time therefore it may drift over a wide area without penetrating to the ground to an appreciable extent. It has been suggested however, that in the vicinity of a large town the inversion is destroyed by the heat emitted from factory furnaces, domestic heating appliances, etc., and that sufficient turbulence is set up for aerosol material to be brought to ground level in larger concentrations than in open country far outside the town.

2. An attempt was made to verify this hypothesis by trials in Salisbury, but the results were inconclusive: the smallness of the town and the unevenness of the surrounding country were such that any effect of the type sought was masked by topographical effects. The experiments are being repeated in another, larger, town, which is a more powerful heat source, and which is situated in a district as free as possible from topographical irregularities; the City of Norwich has been selected for this purpose.

3. It has been found that opportunities to stage a trial on the basis of a 36 hr weather forecast occur with insufficient frequency; accordingly the programme has been modified to allow a decision to be made on a 9 hr or 10 hr forecast. In an effort to improve the value of a trial, the programme has been further modified so as to permit the fixing of Trial Zero at a time later than ½ hr after evening crossover, whenever flying conditions are favourable.

DATE AND TIME

4. It is aimed to carry out two trials in each of the weeks commencing on the following dates:-
January 13th; February 10th; March 16th; and April 13th, 1964.

R.A.F. Swanton Morley are not able to confirm the dates February 10th, March 16th, and April 13th so far in advance. These must, therefore, be considered subject to cancellation if necessary.

A trial will normally extend from midday on the “day of the trial” until the early morning of the following day.
PLACE

5. Norwich and its environs.