Re: [ferret_users] How to flip a variable? U is read at reverse

["Ansley C. Manke" <ansley.b.manke@xxxxxxxx>]

Karen,

Also, this looks like a dataset where depth is not a simple z-axis coordinate variable but varies in location:

depth_u(z, lat, lon)

So depth is not a simple z-axis but data needs to be transformed so that the correct depth is used for any given location.  This is addressed by Ferret in "Auxiliary Coordinates"; see this documentation:

http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/Grids-Regions/GRIDS#_4.2.6


-- we need to do some more FAQ's on this topic.  Does anyone have an OPeNDAP URL pointing to data such as this?

Ansley


On 1/31/2018 1:32 PM, karen guihou wrote:

Hi all

I am struggling with some ROMS files that I try to read. The surface is at level 40, and the bottom at level 1.

When I import the netcdf, Ferret automatically flips (I do not understand how/why) the U,V,T,S variables so that k=1 is now at the surface and k=40 is at the bottom. However, it does not flip the depth variable. My depths levels are negative values.

If I do u*depth, I end up multiplying the bottom by the surface. If I plot a vertical section of U, the max velocities are at the bottom...

Any idea of option to give, or some missing attribute in the netcdf? I created the nc from a mat file.

Thank you in advance!

netcdf U_climato_CMM {

dimensions:

z = 40 ;

lat = 384 ;

lon = 349 ;

time = UNLIMITED ; // (1 currently)

variables:

float depth_u(z, lat, lon) ;

depth_u:units = "m" ;

float dz(z, lat, lon) ;

dz:units = "m" ;

float lat(lat) ;

lat:units = "degrees south" ;

float latitude(lat) ;

latitude:units = "degrees south" ;

float lon(lon) ;

lon:units = "degrees west" ;

float longitude(lon) ;

longitude:units = "degrees west" ;

float taux(time, lat, lon) ;

taux:units = "N/m2" ;

taux:cell_methods = "time: mean" ;

float time(time) ;

time:units = "days since 1980-01-01" ;

time:cell_methods = "time: mean" ;

float u(time, z, lat, lon) ;

u:units = "m/s" ;

u:cell_methods = "time: mean" ;

float ubar(time, lat, lon) ;

ubar:units = "m/s" ;

ubar:cell_methods = "time: mean" ;