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DAYLENGTH procedure

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)

Parameters

DAYNUMBER = variate Days of year for which daylengths are required
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
Updated on March 8, 2019

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