## 2 Measurements and Quality Control Processes
### Longwave Radiation Quality Control  
The process of quality control for the longwave radiation is based on range tests which were suggested by the Baseline Surface Radiation Network (BSRN) group. BSRN has proposed globally physical possible, extremely rare, and climatological configurable limits as well as global cross-comparisons for the surface longwave radiation measurements [32] (Table 2). The \"physically possible\" tests detect extremely large errors in the radiation data. The radiation data falling in the intervals defined by the range between 40 and 700 W/m\({}^{2}\) for downward longwave irradiance and between 40 and 900 W/m\({}^{2}\) for the upward longwave irradiance are considered \"physically possible\". The data set passed the suggested physical limits. The \"extremely rare\" limits are narrower than those of the \"physically possible\" limits, since they usually occur over very short time periods under very extreme conditions. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Site** & **Location** & **Latitude** & **Longitude** & **Altitude (m, m.s.l)** \\ \hline Athalassa & Inland & 35.141\({}^{\circ}\) N & 33.396\({}^{\circ}\) E & 165 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Site parameters for the Athalassa meteorological station. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test** & **Limits** & & \(L_{dn}\) **(W/m\({}^{2}\))** & \(L_{up}\) **(W/m\({}^{2}\))** \\ \hline PPL & Physically Possible Limits & & Min & 40 & 40 \\  & & Max & 700 & 900 \\ \hline ERL & Extremely Rare Limits & & Min & 60 & 60 \\  & & Max & 500 & 700 \\ \hline \hline \multirow{3}{*}{CCL} & \multirow{3}{*}{Climatological Configurable Limits} & \multirow{3}{*}{1 st Level} & Min & 190 & 240 \\  & & Max & 465 & 590 \\ \cline{3-5}  & & & Min & 145 & 210 \\  & & Max & 500 & 630 \\ \hline \hline \multirow{3}{*}{GCC} & \multirow{3}{*}{Global Cross-Comparisons vs. \(T_{a}\)} & Min & \(0.4^{\circ}\)\(\mathrm{\SIUnitSymbolDegree}_{a}\)\({}^{4}\) & \(\mathrm{\SIUnitSymbolDegree}_{a}\)\({}^{4}\) (\(\mathrm{\SIUnitSymbolDegree}_{a}-15\))\({}^{4}\) \\  & & Max & \(\mathrm{\SIUnitSymbolDegree}_{a}\)\({}^{4}\) + 25 & \(\mathrm{\SIUnitSymbolDegree}_{a}\)\({}^{4}\) (\(\mathrm{\SIUnitSymbolDegree}_{a}+25\))\({}^{4}\) \\ \hline \hline \multirow{3}{*}{\(R_{nl}\)} & \multirow{3}{*}{Net Long wave irradiance} & Min = \(-\)300 W/m\({}^{2}\) \\  & & Max = +25 W/m\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physically possible and extremely rare global limits recommended by BSRN and user configurable climatological limits, as well as global cross-comparisons based on air temperature (\(T_{a}\)) (in Kelvin) and between the two longwave variables. \(\sigma\) is the Stefan–Boltzman constant = 5.67 \(\times\) 10\({}^{-8}\) Wm\({}^{-2}\) K\({}^{-4}\). Therefore, \"good quality\" is assumed to be inside the \"extremely rare\" limits. Figure 2 shows that downward longwave irradiances (\(L_{dn}\)) are within the specified limits. However, about 0.4% of data of the upward longwave irradiances (\(L_{up}\)) have values slightly above 700 W/m\({}^{2}\), with a maximum value of 738 W/m\({}^{2}\) (Figure 2). The suggested climatological limits are based on data obtained from the Great Plains in the United States. The limits are classified in two levels. The 1 st level has the \"smallest\" testing limits, while those referred as \"2 nd level\" give the second lower limits. Downward longwave irradiances passed all the given criteria, while the upward longwave irradiances showed slightly higher values than the suggested upper limits (Table 2). It has to be noted that some of the downward longwave values are as high as the outgoing longwave radiation. These values may be attributed to high aerosol optical depth values from warm layers above the planetary boundary layer [18]. The global cross comparison tests are referred to various comparisons between the two longwave irradiances and their relationships with air temperature data (\(T_{a}\)) at the screen level.