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gsw_N2sol.m
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gsw_N2sol.m
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function N2sol = gsw_N2sol(SA,CT,p,long,lat)
% gsw_N2sol solubility of N2 in seawater
%==========================================================================
%
% USAGE:
% N2sol = gsw_N2sol(SA,CT,p,long,lat)
%
% DESCRIPTION:
% Calculates the nitrogen, N2, concentration expected at equilibrium with
% air at an Absolute Pressure of 101325 Pa (sea pressure of 0 dbar)
% including saturated water vapor. This function uses the solubility
% coefficients as listed in Hamme and Emerson (2004).
%
% Note that this algorithm has not been approved by IOC and is not work
% from SCOR/IAPSO Working Group 127. It is included in the GSW
% Oceanographic Toolbox as it seems to be oceanographic best practice.
%
% INPUT:
% SA = Absolute Salinity [ g/kg ]
% CT = Conservative Temperature (ITS-90) [ deg C ]
% p = sea pressure [ dbar ]
% ( i.e. absolute pressure - 10.1325 dbar )
% long = longitude in decimal degrees [ 0 ... +360 ]
% or [ -180 ... +180 ]
% lat = latitude in decimal degrees north [ -90 ... +90 ]
%
% SA & CT need to have the same dimensions. p, lat and long may have
% dimensions 1x1 or Mx1 or 1xN or MxN, where SA and CT are MxN.
%
% OUTPUT:
% N2sol = solubility of nitrogen in micro-moles per kg [ umol/kg ]
%
% AUTHOR: Roberta Hamme, Paul Barker and Trevor McDougall
% [ help@teos-10.org ]
%
% VERSION NUMBER: 3.05 (27th January 2015)
%
% REFERENCES:
% 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 http://www.TEOS-10.org
%
% Hamme, R., and S. Emerson, 2004: The solubility of neon, nitrogen and
% argon in distilled water and seawater. Deep-Sea Research, 51,
% 1517-1528.
%
% The software is available from http://www.TEOS-10.org
%
%==========================================================================
%--------------------------------------------------------------------------
% Check variables and resize if necessary
%--------------------------------------------------------------------------
if nargin ~= 5
error('gsw_N2sol: Requires five inputs')
end %if
[ms,ns] = size(SA);
[mt,nt] = size(CT);
[mp,np] = size(p);
if (mt ~= ms | nt ~= ns)
error('gsw_N2sol: SA and pt must have same dimensions')
end
if (mp == 1) & (np == 1) % p scalar - fill to size of SA
p = p*ones(ms,ns);
elseif (ns == np) & (mp == 1) % p is row vector,
p = p(ones(1,ms), :); % copy down each column.
elseif (ms == mp) & (np == 1) % p is column vector,
p = p(:,ones(1,ns)); % copy across each row.
elseif (ns == mp) & (np == 1) % p is a transposed row vector,
p = p.'; % transpose, then
p = p(ones(1,ms), :); % copy down each column.
elseif (ms == mp) & (ns == np)
% ok
else
error('gsw_N2sol: Inputs array dimensions arguments do not agree')
end %if
[mla,nla] = size(lat);
if (mla == 1) & (nla == 1) % lat is a scalar - fill to size of SA
lat = lat*ones(ms,ns);
elseif (ns == nla) & (mla == 1) % lat is a row vector,
lat = lat(ones(1,ms), :); % copy down each column.
elseif (ms == mla) & (nla == 1) % lat is a column vector,
lat = lat(:,ones(1,ns)); % copy across each row.
elseif (ns == mla) & (nla == 1) % lat is a transposed row vector,
lat = lat.'; % transpose, then
lat = lat(ones(1,ms), :); % copy down each column.
elseif (ms == mla) & (ns == nla)
% ok
else
error('gsw_N2sol: Inputs array dimensions arguments do not agree')
end %if
[mlo,nlo] = size(long);
long(long < 0) = long(long < 0) + 360;
if (mlo == 1) & (nlo == 1) % long is a scalar - fill to size of SA
long = long*ones(ms,ns);
elseif (ns == nlo) & (mlo == 1) % long is a row vector,
long = long(ones(1,ms), :); % copy down each column.
elseif (ms == mlo) & (nlo == 1) % long is a column vector,
long = long(:,ones(1,ns)); % copy across each row.
elseif (ns == mlo) & (nlo == 1) % long is a transposed row vector,
long = long.'; % transpose, then
long = long(ones(1,ms), :); % copy down each column.
elseif (ms == mlo) & (ns == nlo)
% ok
else
error('gsw_N2sol: Inputs array dimensions arguments do not agree')
end %if
if ms == 1
SA = SA.';
CT = CT.';
p = p.';
lat = lat.';
long = long.';
transposed = 1;
else
transposed = 0;
end
%--------------------------------------------------------------------------
% Start of the calculation
%--------------------------------------------------------------------------
SP = gsw_SP_from_SA(SA,p,long,lat);
x = SP; % Note that salinity argument is Practical Salinity, this is
% beacuse the major ionic components of seawater related to Cl
% are what affect the solubility of non-electrolytes in seawater.
pt = gsw_pt_from_CT(SA,CT); % pt is potential temperature referenced to
% the sea surface.
y = log((298.15 - pt)./(gsw_T0 + pt)); % pt is the temperature in degress C
% on the 1990 International Temperature Scale ITS-90.
% The coefficents below are from Table 4 of Hamme and Emerson (2004)
a0 = 6.42931;
a1 = 2.92704;
a2 = 4.32531;
a3 = 4.69149;
b0 = -7.44129e-3;
b1 = -8.02566e-3;
b2 = -1.46775e-2;
N2sol = exp(a0 + y.*(a1 + y.*(a2 + a3*y)) + x.*(b0 + y.*(b1 + b2*y)));
if transposed
N2sol = N2sol.';
end
end