Description
===========

The TIROS-N Operational Vertical Sounder (TOVS) Polar Pathfinder (Path-P) derived wind dataset consists of gridded daily wind fields north of 60 
degrees latitude. The dataset is  gridded at 100km spatial resolution on an Equal-Area Scalable Earth Grid (EASE-Grid). Daily Northern Hemisphere 
data are available from July 1979 through December 2005. The dataset is derived from TOVS Path-P temperature profiles 
(http://psc.apl.washington.edu/pathp/), combined with the National Centers for Environmental Prediction Reanalysis-1 10m winds and surface pressure. 
The dataset was derived based on the method described in Zou and Van Woert (2002) for the Antarctic and extended to the Arctic region in Francis et 
al. 2005. The wind vector is calculated for 7 levels at each grid point using the  standard thermal wind equation, TOVS temperature profiles and 
NCEP 10m winds. The data is further corrected using a Lagrange Multiplier approach subject to a mass conservation constraint appropriate for the 
pole.

The dataset was derived at the Institute for Marine and Coastal Sciences at Rutgers University in New Brunswick, NJ. It includes NCEP 10m winds 
(corrected) and surface pressure linearly interpolated to the EASE grid, as well as derived wind data at 7 levels. 

File Format
===========

Daily data are stored in NetCDF files according to the CF-1.1 convention. There is one file per year and each file is approximately 110M. 
File naming convention is TOVSWIND_yyyy.nc, where yyyy is the year.  

Variables
=========

Available variables:

        float r: EASE grid r-coordinate
        float s: EASE grid s-coordinate
        float plev: Pressure levels(Pa)
        float time: Days since 1900-01-01 00:00:00
        float lat: Latitude
        float lon: Longitude
        float ua: Eastward level wind (m/s)
        float va: Northward level wind (m/s)
        float ps: Surface Pressure(Pa)
        float uas: Eastward 10m wind (m/s)
        float vas: Northward 10m wind(m/s)

The dataset has grid dimensions of 67x67 with a horizontal resolution of ~100km. There are 7 pressure levels. The number of time steps in each 
file depends on the number of available data points for that particular year. More detailed meta data is available in each NetCDF file. 

Reading Data
============

TOVS derived wind data can be read using most commercial and open source programs which support the NetCDF libraries.  

IDL example: Reads in latitude, longitude and level wind variables using the built-in NetCDF tools.

IDL> fname='TOVSWIND_1980.nc'
IDL> cdfid=ncdf_open(fname)
IDL> latid=ncdf_varid(cdfid,'lat')
IDL> lonid=ncdf_varid(cdfid,'lon')
IDL> uaid=ncdf_varid(cdfid,'ua')
IDL> vaid=ncdf_varid(cdfid,'va')
IDL> ncdf_varget,cdfid,latid,lat
IDL> ncdf_varget,cdfid,lonid,lon
IDL> ncdf_varget,cdfid,uaid,ua
IDL> ncdf_varget,cdfid,vaid,va
IDL> ncdf_close,cdfid


MATLAB example:  Reads in latitude, longitude and level wind variables using MEXNC and SNCTOOLS (available at mexcdf.sourceforge.net).

>> fname='TOVSWIND_1980.nc';
>> lat=nc_varget(fname,'lat');
>> lon=nc_varget(fname,'lon');
>> ua=nc_varget(fname,'ua');
>> va=nc_varget(fname,'vaq');

References
==========

Francis, J.A., E. Hunter, and C.-Z. Zou, 2005: Arctic tropospheric winds derived from TOVS satellite retrievals. J. Clim., 18, 2270-2285.
Zou, C.-Z., and M. L. Van Woert, 2002: Atmospheric wind retrievals from satellite soundings over the middle- and high-latitude oceans. 
Mon. Wea. Rev., 130, 1771-1791.