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Comments on “New formulae for the equivalent night sky emissivity” by Melchor Centeno V
LETTERS TO THE EDITOR Comments on “New Formulae for the Equivalent Night Sky Emissivity” by Melchor Centeno V
Dear Sir, Centeno[l] has proposed a new equation for clear-sky atmospheric emittance which is based on three independent variables: ambient air temperature, relative humidity and altitude above mean sea level. I too have recently proposed such an equation[2], but have found that it is dependent on temperature, humidity and the dustiness of the air[3-51; and in testing it against the data provided by Centeno, I find that it requires no adjustment for altitude. The form of my equation is cII= A +5.95
x 10-5e,exp(1500/7’0)
happens much higher in the atmosphere, however; and this should, thus, be one of the prime objectives of future research in this area. SHERWOOD
B.
IDSO.
Water Conservation Laboratory USDA, ARS 4331 East Broadway Road Phoenix, AZ 85040, U.S.A. U.S.
(1)
REFERENCES 1. M. Centeno V, New formulae for the equivalent night sky emissivity. Solar Energy 28, 489498 (1982). 2. S. B. Idso, A set of equations for full spectrum and 8-14pm and 10.5-12.5pm thermal radiation from cloudless skies. Water Resourc. Res. 17, 195-304 (1981). 3. S. B. Idso, On the apparent incompatibility of different atmospheric thermal radiation data sets. Quart. J. Roy. Meteorol. Sot 106, 375-376 (1980). 4. S. B. Idso, An experimental determination of the radiative properties and climatic consequences of atmospheric dust under nonduststorm conditions. Atmos. Environ. 15, 1251-1259 (1981). 5. S. B. Idso, On calculating thermal radiation from cloudless skies. Arch. Meteorol. Geophys. Bioclim., Ser.
where T, is ambient air temperature in K, e,, is ambient vapor pressure in mb, and A is a constant dependent upon the dustiness of the air. Typical values of A that I have found to be applicable to different published data sets are: 0.700 for Phoenix, ArizonaI21. 0.682 for . ., 0.689 for Sidnev. MontanaIf. Kerang, AustraIia[6], 0.660 for ihe coast of O%gon[7], 0.637 for Aspendale, Australia[6], 0.627 for Minneapolis, Minnesota[8], 0.624 for the mid North Pacific[9], 0.601 for remote Arctic regions[lO], and 0.578 for the Indian Ocean [6]. Choosing a value of 0.569 for the Los Chorros, Maracaibo, Macuto and Carabelleda sites studied by Centeno, eqn (1) gives practically identical results, in the mean, to those given by Centeno’s new equation for clear skies at sea level: eqn (1) underpredicts his measurements, in the mean, by 0.52 per cent; while Centeno’s equation underpredicts, in the mean, by 0.53 per cent. At the Los Chorros site, however, eqn (I)--with no adjustment for the 900m altitude differencdoes much better than the Centeno equation with its altitude adjustment factor: eqn (1) overpredicts, in the mean, by only 0.18 per cent, while Centeno’s equation underpredicts, in the mean, by 1.2 1 per cent. Weighting the two data groupings equally, eqn (1) with a constant A of 0.569 and no altitude adjustment factor underpredicts both data sets, in the mean, by only 0.17 per cent; while Centeno’s equation-with its variable altitude factor-underpredicts, in the mean, by 0.87 per cent. In light of these findings, it would appear that eqn (1) may not need to bejgdjusted for altitude, as Centeno suggests is necessary for other equations, at least over the first kilometer above sea level. More good data sets from a greater range of altitudes will be needed before we can assess what
B, 32 53-57 (1983). 6. W. C. Swinbank, Long-wave radiation from clear skies. Quart. J. Roy. Meteorol. Sot. 89, 339-348 (1963). 7. R. K. Reed and D. Halpem, Insolation and net longwave radiation off the Oregon coast. J. Geophys. Res. SO, 839-844 (1975).
8. J. W. Ramsey, H. D. Chiang and R. J. Goldstine, A study of the incoming longwave atmospheric radiation from a clear sky. J. Appl. Meteorol. 21, 56578 (1982). 9. J. J. Simpson and C. A. Paulson, Mid-ocean observations of atmospheric radiation. Quart. J. Roy. Meteorol. Sot. 105, 487-502 (1979). 10. E. L. Andreas and S. F. Ackley, On the difference in ablation seasons of Arctic and Antarctic sea ice. J. Atmos. Sci. 39, 440447 (1982). 11. J. K. Aase and S. B. Idso, A comparison of two formula types for calculating long-wave radiation from the atmosphere. Water Resourc. Res. 14, 623-625 (1978).
Response to Dr. Sherwood B. Idso’s Letter Dear Sir, Your statement that your formula (1) for c, with A = 0.569 applies with equal accuracy to measurements I have carried out at various Venezuelan sites: Los Chorros, Maracaibo, Macuto and Caraballeda, is hereby questioned. Your argument that the same value of the constant A in your formula is not affected by the altitude of the site of observation is most surprising.
You find that your formula underpredicts my sea level measurements, in the mean, by 0.52 per cent; and that it overpredicts, in the mean, by 0.18 per cent the values of the measurements I carried out at the Los Chorros site. Since your formula refers to the clear sky emissivity, it should be tested with those measurements taken when the degree of turbidity or nebulosity N of the atmosphere is zero (N = 0). I presume that you have done so with my measurements. 203
Dear Sir, Centeno[l] has proposed a new equation for clear-sky atmospheric emittance which is based on three independent variables: ambient air temperature, relative humidity and altitude above mean sea level. I too have recently proposed such an equation[2], but have found that it is dependent on temperature, humidity and the dustiness of the air[3-51; and in testing it against the data provided by Centeno, I find that it requires no adjustment for altitude. The form of my equation is cII= A +5.95
x 10-5e,exp(1500/7’0)
happens much higher in the atmosphere, however; and this should, thus, be one of the prime objectives of future research in this area. SHERWOOD
B.
IDSO.
Water Conservation Laboratory USDA, ARS 4331 East Broadway Road Phoenix, AZ 85040, U.S.A. U.S.
(1)
REFERENCES 1. M. Centeno V, New formulae for the equivalent night sky emissivity. Solar Energy 28, 489498 (1982). 2. S. B. Idso, A set of equations for full spectrum and 8-14pm and 10.5-12.5pm thermal radiation from cloudless skies. Water Resourc. Res. 17, 195-304 (1981). 3. S. B. Idso, On the apparent incompatibility of different atmospheric thermal radiation data sets. Quart. J. Roy. Meteorol. Sot 106, 375-376 (1980). 4. S. B. Idso, An experimental determination of the radiative properties and climatic consequences of atmospheric dust under nonduststorm conditions. Atmos. Environ. 15, 1251-1259 (1981). 5. S. B. Idso, On calculating thermal radiation from cloudless skies. Arch. Meteorol. Geophys. Bioclim., Ser.
where T, is ambient air temperature in K, e,, is ambient vapor pressure in mb, and A is a constant dependent upon the dustiness of the air. Typical values of A that I have found to be applicable to different published data sets are: 0.700 for Phoenix, ArizonaI21. 0.682 for . ., 0.689 for Sidnev. MontanaIf. Kerang, AustraIia[6], 0.660 for ihe coast of O%gon[7], 0.637 for Aspendale, Australia[6], 0.627 for Minneapolis, Minnesota[8], 0.624 for the mid North Pacific[9], 0.601 for remote Arctic regions[lO], and 0.578 for the Indian Ocean [6]. Choosing a value of 0.569 for the Los Chorros, Maracaibo, Macuto and Carabelleda sites studied by Centeno, eqn (1) gives practically identical results, in the mean, to those given by Centeno’s new equation for clear skies at sea level: eqn (1) underpredicts his measurements, in the mean, by 0.52 per cent; while Centeno’s equation underpredicts, in the mean, by 0.53 per cent. At the Los Chorros site, however, eqn (I)--with no adjustment for the 900m altitude differencdoes much better than the Centeno equation with its altitude adjustment factor: eqn (1) overpredicts, in the mean, by only 0.18 per cent, while Centeno’s equation underpredicts, in the mean, by 1.2 1 per cent. Weighting the two data groupings equally, eqn (1) with a constant A of 0.569 and no altitude adjustment factor underpredicts both data sets, in the mean, by only 0.17 per cent; while Centeno’s equation-with its variable altitude factor-underpredicts, in the mean, by 0.87 per cent. In light of these findings, it would appear that eqn (1) may not need to bejgdjusted for altitude, as Centeno suggests is necessary for other equations, at least over the first kilometer above sea level. More good data sets from a greater range of altitudes will be needed before we can assess what
B, 32 53-57 (1983). 6. W. C. Swinbank, Long-wave radiation from clear skies. Quart. J. Roy. Meteorol. Sot. 89, 339-348 (1963). 7. R. K. Reed and D. Halpem, Insolation and net longwave radiation off the Oregon coast. J. Geophys. Res. SO, 839-844 (1975).
8. J. W. Ramsey, H. D. Chiang and R. J. Goldstine, A study of the incoming longwave atmospheric radiation from a clear sky. J. Appl. Meteorol. 21, 56578 (1982). 9. J. J. Simpson and C. A. Paulson, Mid-ocean observations of atmospheric radiation. Quart. J. Roy. Meteorol. Sot. 105, 487-502 (1979). 10. E. L. Andreas and S. F. Ackley, On the difference in ablation seasons of Arctic and Antarctic sea ice. J. Atmos. Sci. 39, 440447 (1982). 11. J. K. Aase and S. B. Idso, A comparison of two formula types for calculating long-wave radiation from the atmosphere. Water Resourc. Res. 14, 623-625 (1978).
Response to Dr. Sherwood B. Idso’s Letter Dear Sir, Your statement that your formula (1) for c, with A = 0.569 applies with equal accuracy to measurements I have carried out at various Venezuelan sites: Los Chorros, Maracaibo, Macuto and Caraballeda, is hereby questioned. Your argument that the same value of the constant A in your formula is not affected by the altitude of the site of observation is most surprising.
You find that your formula underpredicts my sea level measurements, in the mean, by 0.52 per cent; and that it overpredicts, in the mean, by 0.18 per cent the values of the measurements I carried out at the Los Chorros site. Since your formula refers to the clear sky emissivity, it should be tested with those measurements taken when the degree of turbidity or nebulosity N of the atmosphere is zero (N = 0). I presume that you have done so with my measurements. 203