# gsw_geostrophic_velocity

    geostrophic velocity

## Contents

- USAGE:
- DESCRIPTION:
- INPUT:
- OUTPUT:
- EXAMPLE:
- AUTHOR:
- VERSION NUMBER:
- REFERENCES:

## USAGE:

    [geostrophic_velocity, mid_lat, mid_long] =
                                gsw_geostrophic_velocity(geo_strf,long,lat,p)

## DESCRIPTION:

    Calculates geostrophic velocity relative to the sea surface, given a
    geostrophic streamfunction and the position (longitude, latitude and
    pressure (long, lat & p)) of each station in sequence along an ocean
    section.  The data can be from a single isobaric or "density" surface,
    or from a series of such surfaces.

    Click for a more detailed description of geostrophic
    velocity.

## INPUT:

    geo_strf = geostrophic streamfunction. This geostrophic streamfunction
               can be any of, for example,
               (1) geo_strf_dyn_height (in an isobaric surface)
               (2) geo_strf_Montgomery (in a specific volume anomaly surface)
               (3) geo_strf_Cunninhgam (in an approximately neutral surface
                   e.g. a potential denisty surface).
               (4) geo_strf_McD_Klocker (in an approximately neutral surface
                   e.g. a potential denisty surface, a Neutral Density
                   surface or an omega surface (Klocker et al., 2009)).

    long     = longitude in decimal degrees                   [ 0 ... +360 ]
                                                        or [ -180 ... +180 ]
    lat      = latitude in decimal degrees north             [ -90 ... +90 ]

    OPTIONAL:
    p      =  sea pressure ( default is 0 )                         [ dbar ]
             ( i.e. absolute pressure - 10.1325 dbar )
     Note. This optional input is used to obtain an accurate distance,
       "dist", taking into account that the radius from the centre of the
       Earth depends on the depth below the sea surface.

    There needs to be more than one station.
    geo_strf has dimensions (M(bottles) x N(stations)).
    lat & long need to have dimensions 1xN or MxN, where geo_strf is MxN.
    p may have dimensions 1x1 or Mx1 or 1xN or MxN, where geo_strf is MxN.

    Note. The ith bottle of each station (i.e. the ith row of geo_strf)
      must be on the same ith surface, whether that surface be,
       (1) an isobaric surface,
       (2) a specific volume anomaly surface,
           or some type of approximately neutral surface (cases (3) & (4)).

## OUTPUT:

    geostrophic_velocity  =  geostrophic velocity RELATIVE to the sea
                             surface.  It has dimensions (Mx(N-1))
    mid_lat               =  mid point latitude,             [ -90 ... +90 ]
                             (in decimal degrees north)
    mid_long              =  mid point longitude
                             (the range corresponds to that entered)

## EXAMPLE:

    geo_strf(:,1) = [ -0.600766; -2.959872; -6.705156; -9.991887; -14.285795; -17.893004;]
    geo_strf(:,2) = [ -0.558086; -2.746335; -6.163343; -8.846621; -11.307648; -12.775731;]
    long = [189 189];
    lat = [-20 -22];
    p =  [     10;      50;     125;     250;     600;    1000;]

    geostrophic_velocity = gsw_geostrophic_velocity(geo_strf,long,lat,p)

    geostrophic_velocity  =

      -0.003671955871408
      -0.018371680712397
      -0.046615489829472
      -0.098536165938139
      -0.256247175421439
      -0.440330269693261

## AUTHOR:

    Paul Barker, Trevor McDougall and Phil Morgan    [ help@teos-10.org ]

## VERSION NUMBER:

    3.01 (14th May, 2011)

## REFERENCES:

    Cunningham, S. A., 2000: Circulation and volume flux of the North
     Atlantic using syoptic hydrographic data in a Bernoulli inverse.
     J. Marine Res., 58, 1-35.

    IOC, SCOR and IAPSO, 2010: The international thermodynamic equation of
     seawater - 2010: Calculation and use of thermodynamic properties.
     Intergovernmental Oceanographic Commission, Manuals and Guides No. 56,
     UNESCO (English), 196 pp.  Available from the TEOS-10 web site.
      See sections 3.27 - 3.3.30 of this TEOS-10 Manual.

    Jackett, D. R. and T. J. McDougall, 1997: A neutral density variable
     for the world’s oceans. Journal of Physical Oceanography, 27, 237-263.

    Klocker, A., T. J. McDougall and D. R. Jackett, 2009: A new method for
     forming approximately neutral surfaces.  Ocean Sci., 5, 155-172.

    McDougall T.J., P.M. Barker, R. Feistel and D.R. Jackett, 2011:  A
     computationally efficient 48-term expression for the density of
     seawater in terms of Conservative Temperature, and related properties
     of seawater.  To be submitted to Ocean Science Discussions.

    McDougall, T. J. and A. Klocker, 2010: An approximate geostrophic
     streamfunction for use in density surfaces.  Ocean Modelling, 32,
     105-117.
      See Eqn. (62), of this paper, for definition of the
      McDougall-Klocker geostrophic streamfunction.

    Montgomery, R. B., 1937: A suggested method for representing gradient
     flow in isentropic surfaces.  Bull. Amer. Meteor. Soc. 18, 210-212.

    The software is available from http://www.TEOS-10.org