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In these exercises we will look at a case study of the interaction between a Hurricane and Atlantic cut-off low in the context of ensemble forecasting. During the course of the exercises, we will explore the scientific rationale for using forecast ensembles, why they are necessary and how ensemble forecasts can be visualized. We will also use principle component analysis (PCA) and clustering to analyse the behaviour of the ensemble. In this interesting case study, the HyMEX field campaign was also underway. We will see how the forecast products were used during this campaign.
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Pantillon, F., Chaboureau, J.-P. and Richard, E. (2015), 'Vortex-vortex interaction between Hurrican Nadine and an Atlantic cutoff dropping the predictability over the Mediterranean, http://onlinelibrary.wiley.com/doi/10.1002/qj.2635/abstract |
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In practise many cases are aggregated in order to evaluate the forecast behaviour of the ensemble. However, it is always useful to complement such assessments with case studies of individual events, like the one in this exercise, to get a more complete picture of IFS performance and identify weaker aspects that need further exploration. |
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With the edit window open, find the line that defines 'plot1':
Change this line to:
The suffix '.s' means plot the 500hPa geopotential as a shaded plot instead of using contours (this style is not available for all fields) |
As above, click the play button and then animate the map that appears.
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Wind parameters can be shown either as arrows or as wind flags ('barbs') by adding 'f.flag' to the end of variable name e.g. "wind10fwind10.flag".
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Plotting may be slow depending on the computer used. This reads alot of data files. |
Task 5: Satellite images
Open the folder 'satellite' by doubling clicking (scroll the window if it is not visible).
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Q. What do you notice about the SST?
TODO
Task
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6: Cross-sections
The last task in this exercise is to look at cross-sections through the storm and
Hurricane Nadine and the cut-off low.
Right click on the icon 'an_xs.mv', select 'Edit' and push the play 
button.
This generates a plot with a map of MSLP, a red line and underneath a cross-section plot along that red-line.
The default plot shows potential vorticity (PV) and potential temperature roughly through the centre of the Hurricane and the cut-off low.
Changing forecast time
Cross-section data is only available every 24hrs, not every 3 hrs for the horizontal maps.
This means the steps in the macro is only valid for the times: [2012-09-20 00:00], [2012-09-21 00:00], [2012-09-22 00:00], [2012-09-23 00:00], [2012-09-24 00:00], [2012-09-25 00:00]
Changing fields
Note that a smaller set of fields is available for cross-sections: temperature (t), potential temperature (pt), relative humidity (r), potential vorticity (pv), vertical velocity (w), wind-speed (speed; sqrt(u*u+v*v))
Changing cross-section location
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#Cross section line [ South, West, North, East ]
line = [30,-29,45,-15] |
The red line indicating the cross-section location can be changed in this macro by defining the end points of the line as shown above. Remember that if the forecast time is changed, the storm centres will move and the cross-section line will need to be repositioned to follow specific features. This is not computed automatically, but must be changed by altering the coordinates above.
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This completes the first exercise. You have now learnt how to use the key macros, alter fields for plotting and animate fields. The next exercises use similar macros |
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This completes the first exercise. You have now learnt how to use the key macros, alter fields for plotting and animate fields. |
- Plot and animate MSL + 500hPa maps showing track of Nadine
> 1 : Nadine MSLP and T2m (or better SST) tracking 15-20 september
> 2 : Satellite views on the 20th (provided by Etienne, if possible to put on the VM)
> 3 : Studying of the horizontal maps (analysis + forecasts)
> 4 : Studying and building of the vertical x-sections (analysis + forecasts)
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