Atmospheric turbulence
10 Mar 2011




Atmospheric Turbulence

Atmospheric turbulence

The Doppler capability of the Chilbolton radar makes it possible for researchers to determine the radial wind field around the site. Project teams from Reading University have made remarkable observations of atmospheric billows. These structures are called Kelvin-Helmholtz Instabilities. They occur in regions of a vertical shear in the wind and involve the formation of ripples and overturning billows. The process has the effect of converting kinetic energy from the original orderly flow into turbulent kinetic energy and heat.

The picture to the left is a vertical cross-section of the atmosphere observed at around 9 p.m. on the 6th September, 1995 when a surface warm front was present. The reflectivity (dBZ) in the top image shows regions of strong rain. However, the dynamical structure within the region of the front is even more interesting and can be studied by looking at the Doppler velocity, shown in the bottom image.

A disturbance with a wavelength of 4 km is present in the image- these circular structures are known as Kelvin-Helmholtz Billows. Further study shows that it is the velocity shear that is important, and interesting braided structures are found which have previously been associated with Kelvin-Helmholtz billows in clear air observations.

Contact: Jeffery, Judith (STFC,RAL,RALSP)