Abstract
In this study, two years of hourly longwave downward and upward irradiance measurements at Athalassa, an inland location, are used to analyze and compare them. A detailed quality control process was followed according to the suggested tests proposed by the Baseline Surface Radiation Network (BSRN) group. The criteria involved are based on physically possible, extremely rare and climatological limits. Furthermore, comparison tests were also applied between the two longwave components as well as with air and ground surface temperatures. Additionally, time consistency and persistency tests were applied. All the suspect data were excluded from the analysis. The data showed that the frequency distribution of downward longwave irradiances follows a normal distribution function, while the upward longwave follows an almost normal distribution but with a long positive tail. The annual mean daily downward longwave irradiation is 27.3 MJ m−2 and the annual mean daily upward longwave irradiation is 37.8 MJ m−2. The net longwave irradiation is always negative ranging from −5.9 to −12.1 MJ/m2. Various models were tested to estimate daylight and all day downward and upward longwave irradiances under clear-sky and all-sky conditions. For the comparison of measured and estimated values the root-mean-square errors and linear regression correlations have been used. The results of this comparison showed that Idso’s and Brunt’s models perform well, and they can be used to estimate downward longwave irradiance under clear-sky conditions. Furthermore, both models were extended to estimate the daylight downward longwave irradiance under all-sky conditions by taking into account the ratio of global to the clear-sky global solar irradiance. In this case, the RMSE of the local calibrated coefficients scheme of Idso’s model was 30.6 W m−2, while Brunt’s model showed slightly lower value (29.0 W m−2).
Highlights
The radiation budget at the ground surface is important to understand the climate system and its variability
The net shortwave is the difference between the incoming global solar radiation (G) and the reflected radiation (R) from the ground, while the net longwave radiation is the difference between the downward (Ldn) and upward (Lup) radiation components
The net longwave radiation is calculated from the difference of downward and upward longwave irradiances and estimated from other models based on air temperature, relative humidity and global solar radiation
Summary
The radiation budget at the ground surface is important to understand the climate system and its variability. The net longwave radiation is calculated from the difference of downward and upward longwave irradiances and estimated from other models based on air temperature, relative humidity and global solar radiation. 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 intervals for the downward and upward irradiances calculated by the mean ± 3*StDev, have the following ranges which are closed to the extremely rare limits: Ldn: 166–467 W m−2, Lup: 161–713 W m−2. The graph shows that long missing data for both the downward and upward longwave irradiances are observed in the year 2017. Meloannghwoauvrelyirrnaedtialonncegw( Ranvle irLraddn i anLcuep()Risnla=lwaLydsn hSiignhceerLthupanisLadnl,wthaeysmheaignhheorutrhlyanneLtdn, the n−egLautipv)ei,sralnwgianygsfnroemga−ti4v7eW, ramn−g2 iinng from wt−hh4edth7iuhcehrWoimnuagormrlerymn−rieRi2ndcgnidonltaroddythu−eae2drri6emna5gtaoWstmrhsnomeiicdnsi−a2dtgtaiaenttydioothawn−erei(2tmFh6aii5sgdtshudWoeraceyihma.6itgTce−h,hdd2ee)riw.lnogSiwrttiohhmeuertinhlnmadeerigshdvauidatgrirfvahaieyaec.terviToagtelhnrumoeeoupslfoneotwrdhfaetteshuruaerbrnehfoseaovgcwueearhtlvtyiiecvamhreRiapavnbrealelrleausteuwsraoessf aalnsrtdoaeiconsohberddtoaewfidonsreatdsthlteifhgoephresttrtlhaiyoteidolpon2ew0r(1Fieo3irg–du2v20rae10l51u63c[e9–,sd]2.)d0.T1Suh5iremi[na9ilvg]a.errTtvahhgaeereiwaahtvoiioneunrtraeloygrfeemtmhhoeiosnausbtirvholiysvtyeeam(vn adiarsi)saaiibrvsolie0tusy.7nw7(dεa±as0)0a..i80lss8o0da.uo7nbr7di-n±g0t.h08e susmhomwesrsmligohnttlyhslowwherevnatlhueeswdeuaritnhgerthceowndinitteior nmsoanrtehsmanodreasrotaubnlde 0(.F8igduurrieng6et)h.e summer months when the weather conditions are more stable (Figure 6e)
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