Ambient Data Interpolation
The temperature is the only variable for which hourly data are available in addition to monthly averages. So for the temperature a double interpolation is performed to get a temperature profile for every time in a year depending on the date and the hour. For other data the interpolation is based on date only. This interpolation provides:
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The annual fluctuation of the dew point temperature, the relative humidity, the wind speed, and the direct and diffuse solar irradiances.
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The annual and diurnal fluctuation of the temperature.
In all cases, the interpolation is of second order, with continuous first-order derivative.