Function Td = mollier_Td_magnus(pv,[],pb);
Td = mollier_Td_magnus(pv);
Td = mollier_Td_magnus(T,F);
returns the dew-point temperature in degrees C for
either the given partial vapour pressure of air in
Pa and total pressure (or barometric pressure)
pb in Pa, or the given air temperature in
degrees C and relative humidity F (as a fraction
0...1).
The following adaptation of the approximation
in Magnus form is used:
ps = K(pb) * A * exp( B * T / (C + T) ), (1)
where A, B and C are constants, and K(pb) is an
function of pb, as proposed by Alduchov and
Eskridge 1996 in equations 21 and 22 of their
paper.
The validity ranges of T and ps of this approximation
are obtained by calling m-file mollier_ps_lim_magnus.m.
The dew point temperature Td is the temperature at
which the partial vapour pressure at saturation, ps,
equals to the partial vapour pressure pv of the
air mixture:
ps(Td,pb) = pv. (2)
Alternatively, we can characterise the air mixture
by its air temperature T and relative humidity F,
instead of by its partial vapour pressure:
ps(Td,pb) = F * ps(T,pb). (3)
Solving eq. 2 given the Magnus form in eq. 1, we
get:
Td = C/( -1 + B/(ln(pv/(K(pb)*A))) ).
Solving eq. 3 given the Magnus form in eq. 1, we
get:
Td = C / (-1 + B/(ln(F) + ( B * T / (C + T) ))).
If the second input argument is empty or not
given, the input of pv is assumed. If in that case
the third input argument is not given, K(pb) is set
to 1.
If the first and second arguments are non-empty,
the input of T and F is assumed (and the input
of a third argument is irrelevant).
See also the m-files:
mollier_ps_magnus.m
mollier_Td_ashrae2013.m
mollier_Td_baehr.m
Reference:
Alduchov, O.A.; Eskridge, R.E. (1996). "Improved Magnus
form approximation of saturation vapor pressure".
Journal of Applied Meteorology, vol. 35 (4), pp. 601–609.
(c) 2026 fabien van mook
2026.08.20 release of this file within package "fvm-mollier" under GNU GPLv3+
