Plotting scatterometer data in McIdas-V

If you are on  twitter people tend to tag nice scatterometer images with #ASCAT

I am using McIDAS-V 1.4 to plot scatterometer data. I get the data from http://opendap.jpl.nasa.gov/opendap/catalog.xml.

So in the McIdas-V data explorer I select http://opendap.jpl.nasa.gov/opendap/catalog.xml as the cataolg (under general),  netCDF as the data sources type and the find my data.

I usually plot ASCAT A or B coastal winds which are found under:

OceanWinds > ascat > preview >  L2 > metop a OR metop b > coastal opt > YYYY > DOY >

(Latest Day of Year will be last)

YYYY is the year e.g. 2014 DOY is the day of the year (Today is 148).

The files end with .nc.gz. The files have the date YYYYMDD and then a time HHMMSS which is the end of the orbit in UTC. so for a place on each you most likely want the orbit that finishes just after 0930 or 2130  local time.

Select your .nc.gz file and “add source” .

You may have done all of this via another data source such as EUMETCast.

The coastal winds are a 12.5km product, that get about 12.5km from the coast.  More details on the winds can be found on the KNMI scatterometer page (http://www.knmi.nl/scatterometer/publications/pdf/ASCAT_Product_Manual.pdf)

You can plot the winds barbs or vectors in a single colour in Mc-V, or plot the wind speeds using a colour table but what if you want coloured wind barbs?

Add a new formula that looks like:

WindsFormula

The formula line is:

combineFields(windVector,newName(WindCol,"colourParam"))

Now plot the data – select formula and your formula then choose your data twice (once for the wind barbs and then for the colour – most likely wind speed at 10m)

I use a binned colour scale that approximatly matches the Beufort scale my xml is here: http://bit.ly/OPCwinds. The colours are close to the set used by NWS/OPC, warning thresholds are clear and the bins help see structures.

Also under main window > tools > parameters > defaults Tab: User defaults I have a line

ColWindBarbs BeaufortOPC 0.0 – 40.0 m/s

which means that any winds plotted using my formula (which generates ColWindBarbs uses the BeufortOPC colour table with default range 0-40 m/s) – save a few clicks each time.

Here is an example from the Aral sea – the 50knt wind in the centre is most likely a land contamination effect.

AralSeaAscat-Ex

Within the ASCAT products there is also backscatter distance or MLE. This is a product of the wind estimation process and high positive values can be related to wind variability.

Here is an example the winds over plotted (from southern indian ocean) with backscatter distance  the winds with high positive MLE are plotted in red.

MLEexample

It’s very nice for surface front positioning.

So that is how I plot data with Mc-Idas-V. If you need help with the actual data here is a good place to start http://www.knmi.nl/scatterometer/ and there is always oops@eumetsat.int for help from the EUMETSAT helpdesk.

 

 

 

 

 

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