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METEO Air temperature

Air temperature

Bbo.temperature_air module calculates spatial interpolation of average and minimum air temperature in the area of interest. Digital elevation model, values of air temperature measured at the meteorological station, corrected solar irradiation and temperature gradient are used for calculation.

Input to module are first (day from) and last (day to) day of the year. For the range resulting from entered first and last day is calculation made. Outputs of the module are rasters of average (at_mean_d<xxx>) and maximal (at_mean_d<xxx>) air temperature.

Temperature gradient describes changes in temperature when altitude is changed. Indicates how much will air temperature (°C) change when altitude is change of 1m (°C/m). Temperature gradient is variable over time, it vary over the seasons. It is determined by values of time series, what is saved in tgrad_std.txt file. File contain two columns. In first column is number of the day of year stored and in second column is value of temperature gradient. Missing values of temperature gradient are added by linear interpolation from the known values of the two nearest days.

In meteo_station vector file saved in shp mapset is position of meteorogical stations stored. The module uses the position to derive the altitude of the meteorogical station from the digital elevation model layer and to derive value of current solar irradiation from sr_d <xxx> layers in solar mapset.
Average air temperature t(d) in raster cell for day d is calculated on the basis of the difference in altitude in the cell and altitude of meteorogical station elevmeteo multiply by value of temperature gradient c(d) for the day, to which is add average air temperature measured at the meteorogical station tmeteo(d):

t(d)=c(d)*(elev-elevmeteo)+tmeteo(d)

Maximal daily air temperature is calculated in an analogous manner. Furthermore is correction factor used. It is correcting the change of maximal temperature by coefficient calculated from values of current solar irradiation in cell sr(d) and meteorogical station srmeteo(d):

tmax(d)=c(d)*(sr(d)/srmeteo)*(elev-elevmeteo)+tmaxmeteo(d)