Solar Radiation calculation for LGM

Question

I'm trying to calculate the area solar radiation for the Last Glacial Maximum using ArcGIS 10.3.

However, this seems not to be planned by Esri's Developers. Which option should I choose for the Time Configuration?

• The calculation should be for one year. However, when I choose "Whole year with monthly interval", there appears an option to specify the year. I am not sure how to interpret this documentation text[1]: Does it play a role which year I'll enter there?

• Furthermore, there is the option for "Special Days" which are then enumerated to be "Summer Solstice, Equinox, Winter Solstice".

This seems like a practical way to get the mean radiation values for one year. However, what exactly is done by the tool, using this option? Does it calculate means, does it build a sum....?

• And at least: Is the calculation which this tool performs suitable to model the situation during the Last Glacial Maximum?

Answer 1

Regarding what role the 'year' setting plays, it is only used to define if it is a leap year or not which is specified in the 'Tool Help' section:

"The year value for time configuration is used to determine a leap year. It does not have any other influence on the solar radiation analysis as the calculations are a function of the time period determined by Julian days."

If you select the option 'Create output for each interval', it'll create separate rasters for each interval range. This range itself will be a sum of the length of each interval. For example, if you want to know the amount of solar insolation for a certain week within a year with daily intervals, and have this option checked, it'll create daily sums, otherwise it'll create a sum of that week.

Regarding the last point, the model implemented in ArcMap does not include the reflected component, only the direct and diffuse components of solar radiation. It also uses a single latitude value across the same area, so its not recommended for very large areas. It also applies single values as modifiers to simulate atmospheric conditions and simulates an overcast sky. So it is not possible to use your own raster data for these modifiers, for example.

An implementation in GRASS GIS called r.sun allows for much more indepth specification in comparison: https://grass.osgeo.org/grass73/manuals/r.sun.html.