|Calculating the freezing point of seawater|
|Algorithms - Seawater|
|Written by Jan Schulz|
|Tuesday, 03 June 2008 16:47|
Calculating the freezing point of seawater
The freezing point of sea water depends on salinity and pressure. Millero and Leung (Millero & Leung 1976) give a formula for the calculation of this temperature. Here a function is given to compute the freezing point in °C for seawater at given values of practical salinity and pressure in decibars.
The adopted equation given in the UNESCO handbook ‘Algorithms for computation of fundamental properties of seawater’ (UNESCO 1983) is:
In this equation tf is the freezing point in °C, S the salinity in PSS-78 and p the pressure in decibars. The equation is valid in the practical salinity range of 4 to 40 at atmospheric pressure. Measurements at elevated pressures showed no significant dependence of the pressure coefficient on salinity in the range of 27 to 35 (Fujino et al. 1974). The estimated error to pressure of 500 decibars is 0.003°C .
The below algorithm in object Pascal is equal to the original Fortran code (UNESCO 1983). For given values of salinity and pressure the freezing point of sewater is returned.
Function TF (S, P : Double): Double;
Fujino K., Lewis E.L., Perkin R.G. (1974): The freezing point of seawater at pressures up to 100 bars. Journal of Geophysic Research 79:1792-1797.
Millero F.J., Leung W.H. (1976): The thermodynamics of seawater at one atmosphere. American Journal of Science 276:1035-1077.
UNESCO (1983): Algorithms for computation of fundamental properties of seawater. UNESCO technical papers in marine science 44:1-55.
|Last Updated on Friday, 18 March 2011 18:10|