METEOROLOGY HOMEWORK

Satellite images are frequently shown on TV forecasts but are never held for long enough to let you study them or compare them with current weather charts. It takes some experience to appreciate what satellite pictures at different wavelengths can show, and to interpret the results. You have a very good opportunity to get some of this experience because you have been thinking about meteorology for a couple of months and compared with the general public are privileged to obtain free access to both satellite images and weather charts through the WWW.

In the traditions of some of the best learning experiences, this is a teach-yourself exercise. Exactly what you learn will depend quite a lot on the weather during the period of study. Choose a period of at least 5 days. On each day obtain visible and IR satellite pictures appropriate to some time when you can observe the sky. Also obtain the weather chart for the day, which may well be a mid-day forecast. Print-out 2 satellite pictures (one visible and one IR) and the chart. [This will cost 3 x 4 = 12p, a small sum to pay for an enjoyable occupation, and very cheap compared with the cost of supplying the information].

Now, can you see differences between the visible and IR pictures? Remember that in IR pictures, cold (high) clouds show white and warm (low) clouds show grey. Can you identify thick and thin cloud regions? Can you distinguish the fronts marked on the weather map? Are the fronts in the same place as on the chart?

Make a brief note to accompany the day's pictures of what the clouds actually look like outside. It is important to correlate observed appearance on the ground with satellite views so you can appreciate what the satellite is telling you about weather in places where you aren't present. Maybe you have friends or colleagues in a remote place, or maybe you want to assess the weather in a proposed holiday location or possible place of work. Notice that on the ground you perceive the clouds covering the dome of the sky, whereas the satellite looks down on a landscape as if it were a map.

You should be able to identify obvious features such as clear skies and broken clouds behind cold fronts. Looking successively at pictures for a few days, you can estimate how fast features travel and how quickly the chart, and hence the weather, changes from day to day. This can be harder than it might seem because features change as well as travel. What you'll find will depend pretty much on the weather but I think you'll enjoy the exercise. You can also try your hand at "nowcasting", namely forecasting over the next 6 - 12 hours how the clouds in particular and the weather in general will change. This is a useful activity at the beginning of a day's outing.

The course web-page at http://www.abdn.ac.uk/physics/meteo gives you access to forecast charts, observed weather charts and satellite images from polar-orbiting and geostationary satellites. If you haven't yet explored the course pages, start in the section under UK weather and obtain the Press Association's forecast charts by checking on Atlantic and UK weather maps. Then go to the Meteorology links page from the end of the UK weather section and locate the Dundee Satellite Receiving Station. Register as a user of this service, for free, and read the help file that explains what imaging wavelengths the different channels correspond to (http://www.sat.dundee.ac.uk/avhrr.html). Now explore the images available.