# Auxiliary Data

## Topography

Location altitudes and horizon lines (shading profiles) are automatically derived from the
[**Copernicus GLO-30 Digital Elevation Model (DEM)**](https://dataspace.copernicus.eu/explore-data/data-collections/copernicus-contributing-missions/collections-description/COP-DEM).
The spatial resolution at the equator is 30 metres.

## Atmospheric Composition

Meteonorm includes monthly climatologies of key atmospheric components, which are
essential for its advanced radiation modeling. These parameters allow for a more accurate
calculation of solar radiation under clear-sky conditions. The data is based on the
[**MERRA-2 reanalysis**](https://gmao.gsfc.nasa.gov/reanalysis/merra-2/)[^1] for the
reference period of 2001–2020, with a spatial resolution of 0.5° x 0.625°.

**Included Climatologies:**
* Aerosol Optical Depth (AOD) at 550 nm (see [Figure 1](#data-ancillary-fig1))
* Linke Turbidity Factor
* Total Column Precipitable Water
* Total Column Ozone

![data-ancillary-fig1](./data-ancillary-fig1.png)
**Figure 1:** _Yearly average climatology of total column aerosol optical depth at 550 nm from MERRA-2_

## Time Zone

Meteonorm automatically determines the local time zone for any given location. To provide
a stable and consistent time series for modeling, all timestamps are based on the
location's **standard time**. This means a single, constant UTC offset is used year-round,
without applying daylight saving time (DST).

The time zone boundaries are based on
[timezone-boundary-builder](https://github.com/evansiroky/timezone-boundary-builder)
, with data from the official
[IANA time zone database](https://data.iana.org/time-zones/releases/).

An exception is made for the rare cases where standard time is active for only a small
portion of the year (e.g. less than three months). In these locations, the DST offset
is applied to the standard time to better represent the local civil time.


## Albedo

Albedo, or surface reflectivity, is a key parameter for calculating the amount of solar
radiation reflected from the ground. Meteonorm uses monthly mean surface albedo values
sourced from the
[**ERA5 reanalysis dataset**](https://www.ecmwf.int/en/forecasts/dataset/ecmwf-reanalysis-v5).

[^1]:
    Global Modeling and Assimilation Office (GMAO) (2015), inst3_3d_asm_Cp: MERRA-2 3D
    IAU State, Meteorology Instantaneous 3-hourly (p-coord, 0.625x0.5L42), version
    5.12.4, Greenbelt, MD, USA: Goddard Space Flight Center Distributed Active Archive
    Center (GSFC DAAC), Accessed June 2024 at doi: 10.5067/VJAFPLI1CSIV.