Antarctica has some of the harshest weather on the planet. One of the causes is the Katabatic winds, which blow cold air from the higher elevations of Antarctica's interior ice sheets down toward the coasts. These winds can reach nearly 200 miles per hour, and they are so strong that they routinely blow the snow out of the coastal valleys. And when they blew over water, they could cause choppy seas that often made it impossible to go ashore.

During our expedition through Antarctica's Ross Sea, we were given weather forecasts at least once a day. Usually people think of temperature as one of the important parts of a weather forecast, but temperature was mostly irrelevant for us: if it was colder, we would wear more layers, but this didn't affect our ability to get off the ship. The one factor that mattered more than anything was the wind speed. And since wind contains both a magnitude and a direction, it is essentially a vector. This means that the wind charts we used were an excellent example of vector fields!

Take a look at the wind charts above. There are a lot of things going on. First, the charts are filled with little figures that look like flags. These vectors represent the wind. The magnitude is represented by the little notches, which are called barbs: each full barb represents 10 knots of wind; each half barb represents 5 knots; and a triangular barb represents 50 knots. The charts are also color-coded, with blue and green areas corresponding to lesser winds, red areas corresponding to stronger winds, and grey and black areas corresponding to hurricane-strength winds. This color coding makes them easier to read, as well as providing information for the parts of the chart between the data points.

The barbs give the speed or magnitude of the wind: but the orientation gives the direction of the wind. Each little vector points in the direction of the wind, with the wind coming from the side of the segment with the barbs and moving in the direction of the segment without the barbs. Notice in the charts below that the winds are usually moving in a northerly direction, either northwest, northeast, or due north. This is because of the momentum from the katabatic winds coming from the ice sheets. If there isn't a particularly strong storm in the Ross Sea, the katabatic winds generally push the air in a northerly direction. However, a strong storm can completely change that.

Next, note the contour lines, which are the curves on the chart. These do not correspond to points on the chart with the same wind speed. They correspond to isobars, or points on the chart with the same atmospheric pressure. We largely ignored this data, as it was not as important to us as wind speeds.

Also, the curves that look more jagged represent the boundary between land and water. In each of these charts, the bottom-left corners are on land in Antarctica and the top-right corners are in the Ross Sea. For a map of what the actual area looks like, go to Google Maps and search for Ross Sea.

And finally, note that weather forecasts in Antarctica are approximately as accurate as they are in the rest of the world: not very accurate at all. On February 28th and March 1st, though the forecast called for winds of 20 knots or less in McMurdo Sound (the bay in the center of the bottom of the charts below), both days had winds of 50-60 knots, making it impossible for us to get off the ship. In our experiences, the weather was often worse than predicted, but sadly, it was never better than predicted.

Sample Problems

1. Look at the wind charts above. How strong (in knots) is the strongest wind forecasted in these charts?

2. Look at wind charts below, which represent the western portion of the Ross Sea on four consecutive days. What major change is forecasted in the area during this time? What might account for this?

3. Which areas(s) had the most variation in wind from day to day? Why might this be?

4. Which area(s) consistently have a forecast of ten or fewer knots of wind? Why might this be? Look at satellite imagery to determine what these areas have in common.