Mapping wind speed and direction in Antarctica An example of the work of the BAS Mapping and Geographic Information Centre

The data:

Step 1: Format the data Spreadsheet with latitude, longitude, wind-speed and direction. Ensure the format is GIS compatible (no spaces in the column title and only numeric values in the columns). Save as a.csv file. Make sure that you close the spread-sheet after you have saved it. In this spreadsheet we have the required geographic information (latitude and longitude) and two attributes; wind magnitude (magnitude) and wind direction (dir).

Step 2: Create the point file (a) Open ArcCatalogue. Click on create feature class, and then from Xytable. This should bring up a dialogue box as shown on the next slide.

Make sure that the X field is Longitude and the Y is Latitude. Click the Coordinate System button. Navigate to select Geographic Coordinate Systems/World/WGS84.prj. Save this file in an appropriate directory as XYwinds and press OK. This operation will transform the spreadsheet into points. Step 2: Create the point file (b)

Step 3: Bring into Arcmap Open ArcMap. Let's add some data to the map. First we will add a coastline as a reference. Use the Add data button, navigate to your folder and add the coastline file. Now using the same button add the newly created point data-set. When that has come in click on the XYwinds file in the table of contents on the left hand side and drag it so that it is below the coastline. The result should look like the next slide.

detail

Step 4: Visualize the coastline The next step is to visualize the various datasets. Let’s do the coastline first. In the table of contents on the left hand side left click on the coastline layer. At the bottom click on Properties, then click on the Symbology tab at the top of the resulting box. This will bring up a dialogue box similar to the one below. By clicking on the Symbol button you can change the coastline colour and thickness to a style you prefer.

Step 5: Visualize the wind data - by size (a) Now lets do the same with the wind data. We will change the symbol to an arrow and turn the arrow to the direction based on the pol_direction attribute in the dataset. At the same time we can change the size of the arrow to reflect the magnitude of the wind.

Step 5: Visualize the wind data - by size (b) Right click on the layer and go into the Properties and open the Symbology tab. In the panel on the left hand side of the box change from the default of Features, to the Quantities option. Choose the middle option of Graduated Symbols. Then in the box that reads Value change the field to Magnitude - this changes the symbol size to reflect the magnitude of the wind. Click OK and if necessary use the zoom and pan tools to investigate the data.

Step 6: Visualize the wind data - by direction (a) Go back into your symbology. On the right hand side there is a button called Template. Click on this, it will bring up the Symbol selector.

Step 6: Visualize the wind data - by direction (b) Click on More Symbols and tick the Business symbol set. Using the scroll bar scroll down until you reach the arrows and choose Arrow Up (circled in red left). Now click on the Advanced button at the bottom of the main panel and choose Rotation. Change the field selector to dir and ensure the radio button is on Arithmetic. Click ok, this links the direction to the attribute in the data-set. Change the symbol size boxes so that the symbols range between 3 to 10 points. Check that your symbology window looks similar to the one below and click ok.

Step 7: Investigate the data Your data should now look like the next slide. Have a look at the detail of the data to see how the size and direction of the arrows face.

Step 8: Add a digital elevation model (DEM) Use the Add Data button to add the digital elevation model called Dem. Go into the data frame properties as before (View > dataframe properties), but this time into the Dem file. Experiment with colour ramp in the symbology until you are happy with the colours. Have a look at the result. Does the wind direction follow the topography in any way?

Step 9: Investigation in detail Look in detail at the data. Can you see any relationship between the wind and the topography? The answer is that winds in Antarctica, especially winter winds are Katabatic; they flow downhill and are fastest where the slopes are steepest. On the coast they are affected by local cyclonic winds which then divert them anticlockwise.