Estimation of downwelling longwave irradiance under all‐sky conditions

Abstract

This work is focused on the characterization and parameterisation of the downward atmospheric irradiance (LW) for clear and cloudy skies. LW is a component of the surface radiation budget that is present throughout the day. Unlike solar irradiance, LW is not measured routinely in extended networks, so it must be estimated indirectly. We evaluated five parameterisations for estimating LW under clear skies. After some consideration regarding the local fitting of the parameterisations, we analysed their different behaviour during day and night and propose a correction model for this effect. We use measurements registered at Tabernas (Spain) from 2001 to 2003. For the locally adjusted parameterisations the root mean square deviation (RMSD) and the mean bias deviation (MBD) are smaller than 5.7 and 0.6%, respectively. The combination of the more complex correction parameterisation of the day/night differences with the locally adjusted formula of Brutsaert and the original formula of Berdalh and Martin leads to estimations with RMSD below 3.1%. Using data registered at Palaiseau (France) the proposed parameterisations yields MBD close to 0% and RMSD below 3.2%. Cloudy conditions were analysed and two different approaches were used to estimate the cloud effect. Both approaches determine all sky LW using a clear-sky formulae and a cloud modification factor, computed with the solar global irradiance on a horizontal surface. The results show that LW can be estimated under all-sky conditions during the daytime with a RMSD of 5.8 and 6.2%, and a MBD of 1.6 and −2.2% for the Crawford and Duchon scheme and the parameterisation in k t , respectively, at Tabernas. The application of the same parameterisations to Palaiseau yields RMSD of 6.7 and 7.7%, and MBD of −2.5 and 0.7%.

Parameterizing daytime downward longwave radiation in two Korean regional flux monitoring network sites

“…Bilbao and De Miguel (2007) Crawford and Duchon (1999)'s cloudiness factor with the Brunt (1932) model was recommended for all sky conditions in these eleven sites in Florida, US. Alados et al (2012) demonstrated that the locally calibrated scheme of Brutsaert and origonal scheme of Berdalh and Martin showed best R ld estimations with root mean square deviation (RMSD) below $3.0% for clear sky conditions and the Crwaford and Duchon showed the best R ld estimations with RMSD below $6.0% for all sky conditions in Spain. Gubler et al (2012) demonstrated that the typical form of all sky R ld model presented in Eq.…”

Effect of water–air heat transfer on the spread of thermal pollution in rivers

“…7and 8, there are many other formulae for atmospheric emissivity calculations. The new methods are usually juxtaposed with oldest formulae, see, for example, Alados et al (2012), Duarte et al (2006), Flerchinger et al (2009), Iziomon et al (2003), Marthews et al (2012) and Santos et al (2011). The selected, used herein, formulae are summarised in Table 4.…”

“…Since formula (7) is commonly used in water quality modelling, it has been calibrated for many sites around the world; see, for example, Berdahl and Martin (1984), Berger et al (1984), FAO (1990), Heitor et al (1991, Iziomon et al (2003), Kjaersgaard et al (2007), Monteith (1961), Sellers (1965), and Swinbank (1963). In summary, according to different studies (Alados et al 2012;Elsasser 1942;Iziomon et al 2003;Jiménez et al 1987), the values for a 1 and a 2 coefficients range from 0.34 to 0.7 and from 0.023 to 0.110, respectively. Since the clear night-time sky is more emissive than the daytime, some authors, for example, Berdahl and Fromberg (1982) and Li et al (2017), suggest using different coefficients for the daytime and night-time, or propose a correction depending on the hour of the day (Alados-Arboledas and Jimenez 1988).…”

Characteristics of Downward and Upward Longwave Radiation at Athalassa, an Inland Location of the Island of Cyprus

“…Dozens of parameterization formulas have been developed in which clear-sky effective emissivity is calculated as a function of the screen-level air temperature (T a ) and water vapor pressure (e), since about half the longwave radiation comes from the lowest 100 m of the atmosphere [1]. Details about the formulae for estimating emissivity are given by various authors [10][11][12]. Prata [13] found that the precipitable water content was much better to represent the effective emissivity of the atmosphere than the water vapor pressure.…”