# Data for TMY

The standard TMY climate data in Meteonorm represents the period **2001–2020**.
To create a robust and globally consistent dataset, data from ground stations are
carefully blended with gridded satellite and reanalysis datasets.

![data-tmy-fig1](./data-tmy-fig1.png)
**Figure 1:** _Global data coverage in Meteonorm, showing ground station locations
with (white crosses) and without irradiance data (dots), and the footprint of the five
geostationary satellites._

## Ground Weather Station Data

Ground stations provide the most direct and accurate measurements of local weather
conditions. They serve as the primary source of truth in our database.

### Irradiance

The primary source for global horizontal irradiance (GHI) measurements is the
[**Global Energy Balance Archive (GEBA)**](https://geba.ethz.ch/) by ETH Zurich.
This is supplemented with high-quality data from several national weather
services (e.g. MeteoSwiss, DWD), as well as the
**Baseline Surface Radiation Network (BSRN)** and the **SURFRAD network**.

* Approximately **400 high-quality irradiance stations** are included in Meteonorm.
* Stations are **carefully selected** based on criteria such as quality and completeness.

### Other Meteorological Parameters

For non-irradiance parameters, the station network is primarily based on the
[**Global Surface Summary of the Day (GSOD)**](https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00516) database from NOAA.
For precipitation, this is enhanced with high-resolution data from national weather services
like MeteoSwiss and the German DWD.

* Over **9,000 stations** provide data for non-irradiance parameters.
* Included Parameters:
  * Air temperature
  * Dew point temperature
  * Wind speed
  * Precipitation
  * Number of days with precipitation

## Gridded Data

Gridded data provides complete spatial coverage, filling the gaps between ground stations.

### Satellite Data

Satellite data is the primary source for irradiance in regions without dense station
networks. Meteonorm incorporates data from five geostationary satellites, providing
nearly global coverage (see [Figure 1](#data-tmy-fig1)).

* **MSG** (Meteosat Second Generation): 2008 – 2023 (Europe, Africa, Atlantic)
* **IODC** (Indian Ocean Data Coverage): 2018 – 2023 (Indian Ocean region)
* **HIMAWARI**: 2018 – 2023 (East Asia, Australia)
* **GOES-East**: 2018 – 2023 (Americas, Eastern Pacific)
* **GOES-West**: 2011 – 2016 (Western Americas, Pacific)

To ensure consistency, the satellite data is homogenized to the 2001-2020 reference
period using ERA5 data and is then adjusted with a large-scale bias correction based
on trusted ground stations to account for regional biases.

### ERA5 Reanalysis Data

For regions not covered by satellites (primarily the polar regions), Meteonorm uses the
[ERA5 reanalysis dataset](https://www.ecmwf.int/en/forecasts/dataset/ecmwf-reanalysis-v5)
as a fallback.

* The ERA5 data used in Meteonorm covers the climate **reference period of 2001–2020**.
* The following parameters are sourced from ERA5:
  * Global horizontal irradiance
  * Air temperature
  * Dew point temperature
  * Precipitation
  * Wind speed
  * Wind direction