A formula for wind chill, and more details about formula names, categories, and variable names
First review Basics of IDV Formulas.
wind chillwith the expression
13.12 + 0.6215*T - 11.37*WS**0.16 + 0.3965*T*WS**0.16
Contour Plan Viewdisplay.
13.12 + 0.6215*(T-273.15) - 11.37*(WS*3.6)**0.16 + 0.3965*(T-273.15)*(WS*3.6)**0.16
Here is a wind chill contour plot:
Description is listed in the
If you leave the
Description field empty, the name
of the formula will be used as the description.
Group is a way of categorizing your formulas and
Group does not already exist, it is added when
you save the new formula. If the
Group already exists,
the new formula will appear under that group's tab in the
Fields panel. If you
Group empty, the formula appears in the
The variable names in the formula definition, such as dpt, are dummy names, and in principle can be anything, such as "a" or "var2". It is best to use variable names that suggest the parameter data they represent so that later in the parameter selection step you remember what the variables should represent. Use names like Temp500m, RelHum_surf, absvort, sst_jan, or whatever makes sense to you. If you use a variable names like V1 and V2, then later when the formula requests which real parameter name goes with which dummy variable name you may be puzzled.
Once you have defined a formula, it is saved and will appear in future
runs of your IDV. It is saved in your personal copy of the derived.xml
file, which usually is in the file
on UNIX systems.
Holding the mouse pointer stationary over the formula name in the
Fields panel will cause a
tooltip box to appear showing the formula name and the mathematical formula.
Formulas are preserved by the IDV. Next time you start the IDV you will see formulas you created before. You can build up a library of your own formulas.
To remove a formula, click on
Remove formula in the
formula pull down menu.
This does not remove a display of calculations made with a formula, it removes
the formula itself from the
Field Selector window. Usually you leave formulas
in place until you are sure you will not use them again.