1. Overview

The SAMSON-like export produced by WindRose Studio is generated from the processed hourly dataset built during the Process Data phase.

The exported file is designed to be compatible with AERMET/CALMET surface input requirements and is constructed exclusively from variables physically present in the imported GRIB file.

The export requires the presence of the following ERA5 variables:

• 10u (10m u-component of wind)

• 10v (10m v-component of wind)

• 2t (2m temperature)

• 2d (2m dew point temperature)

• sp (surface pressure)

• tcc (total cloud cover)

If one or more required variables are missing, the SAMSON export cannot be generated.

2. Hourly Timeline Construction

The exported file is based on a continuous hourly timeline reconstructed from the first to the last hourly GRIB message in the dataset.

For each hour:

• a row is generated,

• missing variables are assigned AERMET/CALMET-compliant missing codes,

• no temporal interpolation is applied.

The hourly dataset used for export is the same validated reference table used for wind rose and statistical analyses.

3. Variable-by-Variable Transformations

All transformations are deterministic and explicitly defined:

Air Temperature (TD)

Derived from ERA5 2m temperature:

TD [°C] = 2t [K] − 273.15

Dew Point Temperature (TDEW)

Derived from ERA5 2m dew point temperature:

TDEW [°C] = 2d [K] − 273.15

Wind Speed (WS)

WS [m/s] = √(10u² + 10v²)

Wind Direction (WD)

Meteorological convention (“from where the wind blows”):

WD [°] = (atan2(−10u, −10v) · 180/π + 360) mod 360

Relative Humidity (RH)

Relative humidity is derived from TD and TDEW using a standard psychrometric formulation (e.g., Magnus–Tetens approximation), then:

• rounded appropriately,

• limited to the physical range 0–100 %.

Surface Pressure (SLVP)

Derived from ERA5 surface pressure:

SLVP [hPa] = sp [Pa] / 100 

WindRoseStudio_ProcessData_AERM…

Total Sky Cover (TSKC)

Derived from ERA5 total cloud cover:

TSKC = round(tcc · 10)

Resulting in integer tenths (1–10) 

4. AERMET/CALPUF Compliance

The exported variables follow the Samson reference structure published by Lakes Environmental/WebMet, including:

• required units,

• acceptable value ranges,

• missing value conventions.

Unit conversions (e.g., K → °C, Pa → hPa) are applied before formatting.

The final file is therefore:

• temporally complete,

• physically consistent,

• formally compliant with AERMET/CALMET surface input expectations.