Field studies of the effect of entrainment upon the structure of clouds at Great Dun Fell

Some observations of airflow over a large hill of moderate slope

“…The Fell is well suited for study, being covered by rough grass with no trees and few other obstructions. It was found that the speed-up of the wind is dominated by the elevated stratification and generally agrees closely with the predictions of the model of Carruthers and Choularton (1982) except when the flow is blocked. On the hill summit, the turbulence is approximately in local equilibrium in at least the lowest 10 m and the turbulence measurements are similar to those obtained within the inner layer at other sites.…”

“…A clear indication of blocked flow in the Eden valley occurred towards the evening on the 25th with reasonable agreement between the two upwind sites, but with markedly different behaviour from the airflow model predictions, the observed speed-ups being much greater than the calculated values. The model of Carruthers and Choularton (1982) cannot reproduce the effects of blocking. The return to non-blocked flow during the early morning of the 26th is marked.…”

“…The Great Dun Fell site (GDF), shown in Figure la, has been described in, for example, Baker et al (1982). Essentially GDF is a large nearly two-dimensional ridge situated in the Northern Pennine ridge, which runs approximately NW-SE, overlooking the Eden Valley to the SW.…”

“…The airhow model of Carruthers and Choularton (1982) was used to compare predicted speed-ups with observations. This extends the Jackson-Hunt theory to include the effects of upper-level stability.…”

Acoustic sounder observations from an elevated location

“…These include orographic features due to the mountain itself. Baker et al (1982) have presented some observations using an acoustic sounder temporarily located at Great Dun Fell. More recently a sounder designed and built at UMIST has been permanently installed at the site and in this note we present results obtained using this system.…”