zenaz: Calculates position of the sun

In YplantQMC: Plant Architectural Analysis with Yplant and QuasiMC

Description

Calculates the zenith and azimuth angle of the position of the sun, based mostly on routines from Iqbal (1983).

By default, it is assumed that the time of day is not given in local apparent time (LAT, also known as 'solar time'). To convert the standard time to LAT, the longitude of the location, and the longitude of the nearest time zone border must be given.

Alternatively, use LAT=TRUE to specify that the time of day is in LAT (that is, solar maximum occurs exactly at noon).

The user can specify a number of timesteps (KHRS), so that the solar positions are calculated for the midpoint of each timestep (this is used within YplantQMC). Alternatively, specify timeofday directly.

Usage

zenaz(year = 2012, month = 4, day = 1, lat = -33.6, long = 150.7,
  tzlong = long, KHRS = 24, timeofday = NA, LAT = FALSE)

Arguments

year	YYYY - to account for eccentricity (small effect).
month	Month number
day	Day of month number
lat	Latitude, degrees.
long	Longitude, degrees. Optional (only used for local apparent time correction.)
tzlong	Longitude of the nearest timezone border
KHRS	Number of timesteps in a day (optional). See Details.
timeofday	Optional, time of day (in hours) (a vector of any length) to calculate the position of the sun
LAT	Logical (default=FALSE). Are the times of day given in 'local apparent time'?

Value

A list with the following components:

list("hour")

Time in decimal hours

list("altitude")

Solar altitude (degrees)

list("azimuth")

Solar azimuth (degrees. N=0, E=90)

list("daylength")

Day length in hours

list("sunset")

Time of sunset (hours)

list("zenrad")

Solar zenith position (radians)

Note

This routine is no doubt less accurate that the NOAA routines provided by the solarpos function in the maptools package. It is easier to use, though.

Author(s)

Remko Duursma, based mostly on original FORTRAN code by Belinda Medlyn.

References

Iqbal, B., 1983. An Introduction to Solar Radiation. Academic Press, New York, 386 pp

See Also

setHemi

Examples

# Simple use
zenaz(month=8, day=16, timeofday=12, lat=-33)

# Get half-hourly solar positions
hourpos <- zenaz(month=2, day=16, KHRS=48, lat=-33, long=155, tzlong=150)
with(hourpos, plot(hour, altitude, type='o',ylab=expression(Altitude~(degree))))

YplantQMC documentation built on May 29, 2017, 7:02 p.m.