Calculates daylengths at a given period of the year (R.J. Reader & K. Phelps).
Option
LATITUDE = scalar |
Latitude at which the daylength is to be calculated, positive for northern hemisphere and negative for southern hemisphere; default 52.205 N (Wellesbourne) |
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Parameters
DAYNUMBER = variate |
Days of year for which daylengths are required |
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DAYLENGTH = variate |
Calculated daylengths in hours |
Description
DAYLENGTH calculates a set of daylengths at a given latitude. The numbers of the days during the year for which the daylengths are required should be specified, in a variate, using the DAYNUMBER parameter. The lengths will then be stored in the variate specified by the DAYLENGTH parameter. The latitude is defined by the LATITUDE option, by default LATITUDE=52.205 which is the latitude of Wellesbourne.
Option: LATITUDE.
Parameters: DAYNUMBER, DAYLENGTH.
Method
The formula by which the daylengths is calculated is given in Sellers (1965).
Action with RESTRICT
If either the DAYNUMBER or the DAYLENGTH variate is restricted, the calculations will be done only for the units not excluded by the restriction.
Reference
Sellers W.D. (1965). Physical Climatology. University of Chicago Press, Chicago, Illinois.
See also
Procedure: HEATUNITS.
Commands for: Calculations and manipulation.
Example
CAPTION 'DAYLENGTH example'; STYLE=meta VARIATE Dayno; !(1...31); DECIMALS=0 DAYLENGTH [LATITUDE=52.205] DAYNUMBER=Dayno; DAYLENGTH=Daylength CALCULATE Sunset = 12 + Daylength / 2 CALCULATE Sunrise = 12 - Daylength / 2 CAPTION 'Sunrise and Sunset times for January at Wellesbourne,UK.' PRINT Dayno,Sunrise,Sunset; DECIMALS=2