The wind, my mobile and the Space Shuttle

Last week's post was about the fluctuations in wind and solar with time.  The week is an attempt to understand how wind speed varies with location.  What might be called a reference for wind speed in our area is the METAR reports from an airfield approximately 10 km to the west, Most of the time, this is upper limit of the wind speed which will be found in the wider town and country where the variations are significant. This is can be seen in the observations from personal weather stations on the Weather Underground, these are a valuable source of data, but as many of them are located in urban areas it is difficult to separate out the effects of terrain from rooftops.

The research plan was simple, go for a walk in the countryside with a wind speed meter and record the location of the readings using the GPS on my mobile phone.  As an aside, if you want perfect isolation from your fellow man, simply wander around with a clipboard and a measuring device and no one will come near you, this also works with sheep.  After several days locked in mortal combat with VB.net I managed to plot the results of the expedition on Google Earth together with contours derived from data made available from the Space Shuttle's SRTM mission.  I would like to express my appreciation of the openness of NASA and NOAA for placing fascinating datasets in the public domain, apart from hikes and cycle rides most of my knowledge of renewable energy comes from studying this material.

The results of the first attempt are shown in the screenshot from Google Earth:

The colour gradient chosen for the contours makes the valleys yellowish and the ridges reddish.  The numbers by the placemarks are the ratio of the observed wind speed to that of the nearest source of METAR reports.  On this occasion, the wind was blowing more or less steadily at 5 m/s from the south west.

The direction of travel was from South to North.  The first couple of kilometres were along a main road through an urban area where trees were rustling, but the wind speed meter was not registering, thus the wind speed was probably less than 2.5 m/s.    The next stage was along a ridge leading to the crest of The Downs, the start of this was sheltered wna the wind was approximately 4 m/s and turbulent, however, once on crest of the ridge the wind was steady at around 5 m/s.  The route had been chosen to include an descent into a valley through which runs a four lane highway but which is crossed a convenient bridge where a track goes up the eastern side.  During this stretch, the trees were rustling, but the wind speed meter was lifeless.  Once on the crest of The Downs, the wind was back to 5 m/s.  Carrying on to the North takes you down a steep scarp leasing to the relatively smooth Low Weald where only a gentle breeze was experienced.

Whilst this approach is simplistic, it does provide an insight into the relationship between wind speed and terrain.  I will test the tolerance of the local sheep population with some more hikes.