Transcript Mapping wind speed and direction in Antarctica

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.
Step 2:
Create the point file (b)
• 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 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.