solar_zenith_angle

solar_zenith_angle(fs, to_cosine=False)

New in Metview version 5.14.0.

Computes the solar zenith angle for each gridpoint in fs.

Parameters

  • fs (Fieldset) – input fieldset

  • to_cosine (bool) – when this argument is True the cosine of the solar zenith angle is returned

Return type

Fieldset

The result is the solar zenith angle in degrees. However, if to_cosine is set True the cosine of the solar zenith angle is returned. The computations are based on the following formula:

\[cos\theta_{s} = sin\phi\, sin\delta + cos\phi\, cos\delta\, cosh\]

where:

  • \(\theta_{s}\) is the solar zenith angle

  • \(\phi\) is the latitude

  • \(\delta\) is the declination of the Sun

  • h is the hour angle in local solar time

The declination of the Sun is computed as:

\[\delta = - arcsin\left(0.39779 cos(0.98565\unicode{xB0} (N+10) + 1.914\unicode{xB0} sin(0.98565\unicode{xB0} (N-2))\right)\]

where:

  • N is the day of the year beginning with N=0 at midnight Universal Time (UT) as January 1. It is a floating point number allowing for fractional days.

A missing value in any field in fs will result in a missing value in the corresponding grid point in the output fieldset.

The dates and times used in the computations are based on the “validityDate” and “validityTime” ecCodes keys. If these are not available for a given field the result will contain missing values for all the gridpoints for that field.

When to_cosine is False and the GRIB edition of the input field is 2 the ecCodes paramId in the output field is set to 260225 (shortName=”solza”). For GRIB edition 1 this parameter is not defined.

When to_cosine is True the ecCodes paramId in the output is set to 214001 (shortName=”uvcossza”).