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Proceedings of the Estonian Academy of Sciences

ISSN 1736-7530 (electronic)   ISSN 1736-6046 (print)
Formerly: Proceedings of the Estonian Academy of Sciences, series Physics & Mathematics and  Chemistry
Published since 1952

Proceedings of the Estonian Academy of Sciences

ISSN 1736-7530 (electronic)   ISSN 1736-6046 (print)
Formerly: Proceedings of the Estonian Academy of Sciences, series Physics & Mathematics and  Chemistry
Published since 1952
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Longwave radiation at the earth’s surface in Estonia; pp. 480–487

(Full article in PDF format) doi: 10.3176/proc.2015.4.03


Authors

Viivi Russak, Ingrid Niklus

Abstract

Solar radiation has been continuously measured in Estonia since 1950, but the recordings of longwave radiation began only about ten years ago. This paper presents the first description of the characteristic features of up- and downwelling longwave radiation in the Baltic Sea region. In the radiation balance the longwave fluxes have an important role. In the annual totals of radiation incident upon the ground surface in Estonia, the longwave atmospheric downwelling radiation Ll↓ exceeds the direct solar radiation Eg↓ about three times, and this ratio has an essential seasonal run. In the total upwelling radiation Ll­, the infrared part is still greater, up to 92%. Comparing the measured and calculated (according to the Stefan–Boltzmann law) hourly totals of Ll­ for snow (emissivity ε = 0.85) we found a good linear relationship (R2 = 0.96). However, the measured totals systematically exceeded the calculated values (on average by 18%). Dependence of the downwelling infrared radiation Ll↑ on the near-surface water vapour pressure e is approximated by a power function (R2 = 0.73). This is in good accordance with the results of studies carried out at other geographical sites. The influence of clouds on the fitted power function is noteworthy. Separate analysis of the hours with full cloudiness of low clouds and the cloudless hours confirmed the validity of the power function. However, a difference was found in their parameters (for overcast sky the exponent b = 0.20, R2 = 0.91 and for cloudless sky b = 0.25 and R2 = 0.93).

Keywords

longwave radiation, upwelling radiation, downwelling radiation, water vapour pressure, cloudiness, annual course, diurnal course, frequency.

References

Kannel , M. , Ohvril , H. , and Okulov , O. 2012. A shortcut from broadband to spectral aerosol optical depth. Proc. Estonian Acad. Sci. , 61 , 266–278.
http://dx.doi.org/10.3176/proc.2012.4.02

Okulov , O. 2003. Variability of Atmospheric Transparency and Precipitable Water in Estonia During the Last Decades. PhD dissertation. Tartu University Press.

Rosa , R. and Stanhill , G. 2014. Estimating long-wave radia­tion at the Earth’s surface from measurements of specific humidity. Int. J. Climatol. , 34 , 1651–1656.
http://dx.doi.org/10.1002/joc.3793

Ruckstuhl , C. , Philipona , R. , Morland , J. , and Ohmura , A. 2007. Observed relationship between surface specific humidity , integrated water vapor , and longwave downward radiation at different altitudes. J. Geophys. Res.–Atmos. , 112(D3) , D03302.
http://dx.doi.org/10.1029/2006JD007850

Russak , V. and Kallis , A. 2003. Eesti kiirguskliima teatmik [Handbook of Estonian Solar Radiation Climate]. Eesti Vabariigi Keskkonnaministeerium , Tallinn (in Estonian).

Stanhill , G. 2011. The role of water vapor and solar radiation in determining temperature changes and trends measured at Armagh , 1881–2000. J. Geophys. Res.–Atmos. , 116 , D03105.
http://dx.doi.org/10.1029/2010JD014044

 
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Current Issue: Vol. 68, Issue 3, 2019




Publishing schedule:
No. 1: 20 March
No. 2: 20 June
No. 3: 20 September
No. 4: 20 December