Detailed description is coming soon...

Description

Computes geostrophic velocity using geostrophic balance. Additionally computes ageostrophic velocity as a vector subtraction of total velocity and geosprophic velocity.

Canonically the total velocity is the decomposition of geostrophic and ageostrophic velocity:

$\vec{V}=\vec{V_g}+\vec{V_a}$

Where the geostrophic velocity corresponds to synoptic motions and can be trivially derived using geostrophic balance

$\vec{V_g}=\frac{1}{\rho}\Delta{P}$

In order to gain the ageostrophic velocity as the mesoscale marker we compute geostrophic velocity first and then subtract it from total velocity.

For WRF output there is an option to compute the geostrophic velocity on model levels using fluctuation fields instead of total variables using numerical schemes taken from WRF. This increases the accuracy. You need to run this code upon true WRF output.

Requirements

NetCDF.

Building

Copy to your machine:

git clone https://github.com/alexavr/geostrophic.git
cd geostrophic
vi Makefile
make

You might need to edit Makefile :

NETCDF=/opt/netcdf4-hdf5       # path to your NetCDF
FC=ifort                       # your FORTRAN compiler

Cleaning in case anything went wrong:

make clean

Data preprocessing

If you're planing to compute geostrophic upon WRF output than you don't have to prepare anything.

If you're planing to compute upon other data (say reanalyse) only simple (or no-fluctuation) method is available. The source file has to contain u,v,p,rho variables along with lat, lon (or latitude, longitude) fields. This preparation could be accomplished by using the cdo library.

No moving grids supported yet.

Configuration

The configuration is done using the file namelist.geo.

The domain could be regional (regional = .TRUE.) or global (periodic boundary, regional = .FALSE.). You need also set the time interval using stime and etime (this interval has to be present in the source file!).

The particles could be initiated manually (pt_grid = .FALSE.) in ASCII file named init_particles.dat (see init_particles_Reykjavik.dat as an example). Or evenly spaced allover the domain (pt_grid = .TRUE.), pt_step is number of steps between particles in both directions, pt_height is elevation in meters.

Accuracy of the computations. There are two schemes provided:

Coarse scheme (accuracy = .FALSE.). Predicts particle location using time step from the source file. Fast but very inaccurate. Recommended only for test purposes.
Fine scheme (accuracy = .TRUE.). Interpolates data between source file time step. This option controlled by timestep (in minutes).

Running

./geostrophic.exe src_file.nc

where src_file.nc comes from the "Data reprocessing".