Enhancement: PSD broadening in radar calculations

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Introduce capability for temperature dependence of intercept parameter in 
particle size distribution. This will apply to the calculation of mixing ratios 
from precipitation fluxes, i.e. to the N_ax parameter in cosp_constants.

This will represent the observed broadening of the size spectra with increasing 
temperature for ice particles due to aggregation processes.

No need to represent this in radar_simulator itself, as the correct PSD 
constants will be calculated given the correct effective radius and mixing 
ratio.

Original issue reported on code.google.com by alejandr...@metoffice.gov.uk on 16 Aug 2013 at 10:27

[GoogleCodeExporter]

This should be simple. gbx now has a member for the particle concentration: 
Np(Npoints,Ncolumns,Nlevels), so if should be a matter of using that 
information in cosp_precip_mxratio. An open question is whether the input file 
needs an extra variable. My initial view is that an extra variable in the input 
file is not needed, but a test can be created in which that array is filled 
with sensible information.

Original comment by alejandr...@metoffice.gov.uk on 16 Aug 2013 at 10:59