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Preparation

In this exercise we will apply the basic Metview techniques to produce the plot shown above: a map showing part of North America with precipitation and mean sea level pressure fields plotted during the time of Hurricane Sandy. We will also attach a marker to show a specific location on the map (New York City) and customise the legend and title.

XXX Download data

Verify that the data are as expected.

We will prepare the plot interactively using icons. Then, at the end, we will put it all together into a macro.

Setting the View

With a new Geographical View icon, set up a cylindrical projection with its area defined by its lower-left corner [20oN, 110oW] and its upper-right corner [70oN, 30oW].

Set up a new Coastlines icon with the following:

  • The land coloured in cream
  • The coastlines in grey
  • The grid as a grey dashed line

Plotting the Mean Sea Level Pressure field

Plot the GRIB file msl.grib into this view using a new Contouring icon. Plot black isolines with an interval of 5 hPa between them. Since this will be plotted on top of another field, it would also be a good idea to increase the thickness of the isolines. Activate the legend in the Contouring icon and set the legend text for this icon to "MSLP".

Plotting the Precipitation Field

The GRIB file precip.grib contains a pre-processed field of precipitation accumulated over 3 hours before and after the time of the MSLP field (a total of 6 hours of precipitation).

GRIB files store their fields in SI units. For precipitation this is metres, which is not what meteorologists tend to use. Metview will normally automatically scale such parameters into their 'normal' units (in this case mm), but if a field is the result of some post-processing (as this one is) then this scaling will not be applied because the processing may have changed the nature of the field. Here, the field is still precipitation, so we would like the normal scaling to be applied. The Contouring icon has a parameter called Grib Scaling of Derived Fields which should be set to On in this case.

 

 

 

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