Arran field course – live blog – Saturday 11th September

Our final day on Arran and our final occluded fronts from the dominant series of systems influencing our weather look to have passed during mid-morning. Yesterday (Friday 10th) we saw a really nice frontal progression in our weather station measurements as another occluded front passed around 10:30 local time. The transition in air mass was marked by a drop in temperature and dew point, a small amount of precipitation locally and a transition in wind direction (although there was little of the typical enhancement of wind speed, probably down to the strong local effects that we experienced in the valley all week).

Also in this blog, I have the long promised ozonesonde profile. The ozonesonde reached an impressive 31.5km sampling a large proportion of the high ozone concentrations in the stratosphere. The profile is shown below along with the temperature and dewpoint from the same sonde. A very sharp transition between the low partial pressure of ozone in the troposphere and the high partial pressure at the tropopause can be seen at around 350hPa. Ozone partial pressures increase rapidly above this point, with some interesting embedded smaller scale structure, perhaps associated with stratospheric gravity waves.

The wind speed and direction measured by the same ozonesonde is shown below, showing a remarkably consistent direction as the sonde ascends through the upper level jet near tropopause level and into the rather quiescent stratosphere, where the strong polar vortex is yet to develop.

Finally, there is also some data for readers to download and examine, from our instrumented walk up goat fell. This kml file can be downloaded and browsed at your leisure (you will also need the files in this directory which should be placed in the same location as the kml file. You can pan around our walk and look at the observations our students took as they ascended and descended Goat Fell. Some feature to look our for, the rapid change in wind speed, direction and humidity as groups leave the forested lower slopes of the hill at around 400m and the steering of the flow along the major ridge of the hill as we approach the summit. The mean wind direction for Tuesday can be deduced from the measurements we made both at the summit and at the beach at sea-level before and after the walk.

Leave a Reply

Your email address will not be published. Required fields are marked *