## 2 Measurements and Quality Control Processes
### Longwave Radiation Quality Control
Using the data set, the intervals for the downward and upward irradiances calculated by the mean \(\pm\) 3*_StDev_, have the following ranges which are closed to the extremely rare limits: \(L_{th}\): 166-467 W m\({}^{-2}\), \(L_{up}\): 161-713 W m\({}^{-2}\). Regarding the range test of the net longwave irradiance (\(R_{nl}\)), Table 3 shows that the data point values are within the suggested limits shown in \[0.4*\sigma*T_{a}^{4}<L_{dn}<\sigma*T_{a}^{4}+25\text{W}\,\text{m}^{-2} \tag{4}\]1 The annual mean value of \(R_{nl}\) is \(-\)105 W m\({}^{-2}\). Another quality control test is the step test. This test is based on time consistency which compares the difference between successive measurements. If the difference exceeds an allowed value, then both observations are flagged as suspects. For example, [PERSON] et al. (2018) proposed the following values for different variables: for hourly global irradiance they proposed the value of 555 W m\({}^{-2}\) and for hourly air temperature the value of 7 \({}^{\circ}\)C, while for relative humidity the value of 45%. The data set confirms the limits of the above variables. For the longwave irradiances there is no information in the literature for the difference of two successive measurements. According to the available data set the rate of changes of downward and upward irradiances are \(<\)50 W m\({}^{-2}\) and \(<\)65 W m\({}^{-2}\), respectively. Finally, the persistency test was applied to check the variability of the measurements. When a sensor fails, it will often report a constant value. There is no evidence of such constant values of the given variables through the time series plots (Figure 5). The graph shows that long missing data for both the downward and upward longwave irradiances are observed in the year 2017. The higher values of both variables are recorded during the summer period, while the lower during the winter period, since both of them are related to the air or ground surface temperatures. The variability of upward irradiance is higher than that of downward irradiance. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Variable** & **Unit** & **N** & **Mean** & **StDev** & **Min** & **Q1** & **Median** & **Q3** & **Max** \\ \hline \(G\) & W/m\({}^{2}\) & 7834 & 403.1 & 302.69 & 0.0 & 113.3 & 384.6 & 659.9 & 1020.7 \\ \(R\) & W/m\({}^{2}\) & 8135 & 91.0 & 58.89 & 0.0 & 39.4 & 89.8 & 136.9 & 227.8 \\ \(R_{ns}\) & W/m\({}^{2}\) & 7029 & 355.9 & 230.23 & 7.1 & 145.1 & 344.3 & 551.5 & 850.1 \\ \(L_{dn}\) & W/m\({}^{2}\) & 13,414 & 316.5 & 50.22 & 185.5 & 278.2 & 315.4 & 351.7 & 469.6 \\ \(L_{up}\) & W/m\({}^{2}\) & 16,121 & 436.9 & 92.04 & 292.7 & 367.0 & 414.8 & 476.1 & 738.0 \\ \(R_{nl}\) & W/m\({}^{2}\) & 13,412 & \(-\)105.4 & 57.51 & \(-\)293.5 & \(-\)133.6 & \(-\)93.4 & \(-\)71.3 & 3.6 \\ \(T_{a}\) & \({}^{\circ}\)C & 17,457 & 20.1 & 8.65 & \(-\)19 & 13.4 & 20.0 & 26.5 & 44.2 \\ \(T_{g}\) & \({}^{\circ}\)C & 17,424 & 17.9 & 10.13 & \(-\)6.2 & 10.0 & 17.5 & 24.8 & 46.2 \\ \(R\)\(H\) & \% & 17,460 & 60.9 & 21.42 & 10.0 & 43.0 & 63.0 & 79.0 & 99.0 \\ \(e\) & hPa & 17,457 & 14.2 & 5.58 & 3.2 & 10.0 & 13.1 & 17.4 & 31.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Annual basic statistics of the hourly global (\(G\)), reflected (R), net shortwave (\(R_{ns}\) ), downward (\(L_{dn}\) ), upward (\(L_{up}\) ) and net longwave (\(R_{nl}\) ) irradiances in W m\({}^{-2}\), air temperature at the screen level (\(T_{a}\)), air temperature near the ground surface (\(T_{g}\)), relative humidity (\(R\)\(H\)), and actual vapor pressure (\(e\)) for the period of two years (2016–2017). and the lowest values in January (330 W m\({}^{-2}\)). Since \(L_{up}\) is always higher than \(L_{dn}\), the mean hourly net longwave irradiance (\(R_{nl}=L_{dn}-L_{up}\)) is always negative, ranging from \(-47\) W m\({}^{-2}\) in the morning to \(-265\) W m\({}^{-2}\) in the midday. The lower negative values of the hourly \(R_{nl}\) during midday are associated with the higher ground surface temperatures which are recorded at the station (Figure 6c,d).