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- Author or Editor: R. T. Pinker x
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Abstract
Experiments were performed to examine the sensitivity of computed solar fluxes using a delta-Eddington model to recent parameterizations of cloud albedo of single scattering and asymmetry factor, In particular, the changes in the surface downward solar flux, the planetary albedo and the atmospheric shortwave absorption were investigated as a function of two parameterizations of cloud NIR albedo of single scattering and cloud asymmetry factor. It was shown that the computed downward solar fluxes could differ by as much as 37 W m−2 due to changes in cloud parameterization alone.
Abstract
Experiments were performed to examine the sensitivity of computed solar fluxes using a delta-Eddington model to recent parameterizations of cloud albedo of single scattering and asymmetry factor, In particular, the changes in the surface downward solar flux, the planetary albedo and the atmospheric shortwave absorption were investigated as a function of two parameterizations of cloud NIR albedo of single scattering and cloud asymmetry factor. It was shown that the computed downward solar fluxes could differ by as much as 37 W m−2 due to changes in cloud parameterization alone.
Abstract
The usefulness of satellites in climate research is primarily due to the ability to produce global, uniformly distributed, long term records of observations. To achieve efficiency in storing, there is a need to compromise on the spatial and temporal resolution of the data. Questions arise about the impact of the reduced resolution on the parameters to be derived. In this study the effect of different spatial sampling of satellite observations on retrieved surface solar irradiance (SW1) was studied. Our results indicate that sampled (8-km resolution) andareally averaged (50-km resolution) visible brightness is highly correlated; the correlation has a regional, seasonal,and diurnal dependence. Using the two different resolutions of satellite observations, SW1 was computed for awhole annual cycle. On the average, the results differed by about 8%-9%. Therefore, to validate satellite methodsagainst ground truth to an accuracy which exceeds 8%-9% of the mean, attention should be given to the typeof satellite data and ground truth used in the validation process. The scales selected for investigation are ofinterest to the International Satellite Goud Climatology Project (ISCCP) B3 sampling.
Abstract
The usefulness of satellites in climate research is primarily due to the ability to produce global, uniformly distributed, long term records of observations. To achieve efficiency in storing, there is a need to compromise on the spatial and temporal resolution of the data. Questions arise about the impact of the reduced resolution on the parameters to be derived. In this study the effect of different spatial sampling of satellite observations on retrieved surface solar irradiance (SW1) was studied. Our results indicate that sampled (8-km resolution) andareally averaged (50-km resolution) visible brightness is highly correlated; the correlation has a regional, seasonal,and diurnal dependence. Using the two different resolutions of satellite observations, SW1 was computed for awhole annual cycle. On the average, the results differed by about 8%-9%. Therefore, to validate satellite methodsagainst ground truth to an accuracy which exceeds 8%-9% of the mean, attention should be given to the typeof satellite data and ground truth used in the validation process. The scales selected for investigation are ofinterest to the International Satellite Goud Climatology Project (ISCCP) B3 sampling.
Abstract
In an earlier study, Pinker et al. have shown that the daily average net radiation at the top of the atmosphere is highly correlated with the daily average net radiation at the surface. A regression formalism was derived and tested on independent datasets; it proved to yield estimates of net radiation to accuracies required for climate studies. The objective of the present paper has been to simplify the regression approach for deriving surface net radiation from satellite observations. It was found that the scene brightness alone, as sensed by the GOES satellite, can serve as a predictor of the net radiation at the surface.
Abstract
In an earlier study, Pinker et al. have shown that the daily average net radiation at the top of the atmosphere is highly correlated with the daily average net radiation at the surface. A regression formalism was derived and tested on independent datasets; it proved to yield estimates of net radiation to accuracies required for climate studies. The objective of the present paper has been to simplify the regression approach for deriving surface net radiation from satellite observations. It was found that the scene brightness alone, as sensed by the GOES satellite, can serve as a predictor of the net radiation at the surface.
Abstract
A model for computing global solar radiation at the surface was formulated for use with satellite observations. A compromise in the approach was necessary, whereby the model accuracy and the inherent limitations of satellite observations were made compatible. A three-layer model atmosphere was used. The part of the solar spectrum from 0.3 to 0.7 μm was split into four equally spaced spectral intervals; the region from 0.7 to 4 μm was divided into eight nonspectral intervals. Use was made of the Delta–Eddington approximation, and parameterization was applied to the optical properties of Rayleigh scattering, water vapor absorption, aerosol absorption and scattering, and cloud absorption and scattering. Ozone absorption was also accounted for. The primary driving input of the model is the cloud optical depth, which can be inferred either from satellite observations (Experiment A) or from surface cloud observations (Experiment B). In Experiment A, the model was run for the months of May–August 1982 to produce estimates of daily cumulative insulation for Toronto, Canada. The mean value of the daily estimate was 19.61 MJ m−2. While the mean measured value was 19.72 MJ m−2. The correlation between the predicted and measured daily totals was 0.944, and the standard error of estimate was 2.47 MJ m−2, which is 12.5% of the mean observed value. Experiment B was run for the months May–August of 1981 and 1982. The standard errors of estimate were 16 and 18% of the respective means.
Abstract
A model for computing global solar radiation at the surface was formulated for use with satellite observations. A compromise in the approach was necessary, whereby the model accuracy and the inherent limitations of satellite observations were made compatible. A three-layer model atmosphere was used. The part of the solar spectrum from 0.3 to 0.7 μm was split into four equally spaced spectral intervals; the region from 0.7 to 4 μm was divided into eight nonspectral intervals. Use was made of the Delta–Eddington approximation, and parameterization was applied to the optical properties of Rayleigh scattering, water vapor absorption, aerosol absorption and scattering, and cloud absorption and scattering. Ozone absorption was also accounted for. The primary driving input of the model is the cloud optical depth, which can be inferred either from satellite observations (Experiment A) or from surface cloud observations (Experiment B). In Experiment A, the model was run for the months of May–August 1982 to produce estimates of daily cumulative insulation for Toronto, Canada. The mean value of the daily estimate was 19.61 MJ m−2. While the mean measured value was 19.72 MJ m−2. The correlation between the predicted and measured daily totals was 0.944, and the standard error of estimate was 2.47 MJ m−2, which is 12.5% of the mean observed value. Experiment B was run for the months May–August of 1981 and 1982. The standard errors of estimate were 16 and 18% of the respective means.
Abstract
A unique set of micrometeorological data was obtained during a 1967–70 multidisciplinary environmental field program in a tropical forest environment. The program was under the sponsorship of the Advanced Research Project Agency (ARPA) and was known as Project TREND (Tropical Environmental Data). Wind variability parameters, which characterize the dispersion process within and above the forest canopy and over a nearby clearing under different stability conditions, were derived. Based on relations between σ y and σ z , it was found that in neutral condition, σ z ≈ 2Cd over the observed forest surface. This is in agreement with “universal” ratios in other studies over relatively smooth terrain. Over the clearing, σ z must be increased to account for “memory” of greater roughness upstream. Ratios of the values of σ z found in unstable conditions to those in neutral conditions agree with other studies. Values of turbulence intensity based on wind speed measurements support the above findings and show that dispersion rates within the forest canopy would be lager, relative to the mean transport velocity, than in the free air. A useful correspondence was found between Pasquill stability categories and the Richardson number or Monin-Obukhov z/L parameter. The ranges of those parameters corresponding to the Pasquill categories were found to be much narrower than those reported from studies over smoother terrain.
Abstract
A unique set of micrometeorological data was obtained during a 1967–70 multidisciplinary environmental field program in a tropical forest environment. The program was under the sponsorship of the Advanced Research Project Agency (ARPA) and was known as Project TREND (Tropical Environmental Data). Wind variability parameters, which characterize the dispersion process within and above the forest canopy and over a nearby clearing under different stability conditions, were derived. Based on relations between σ y and σ z , it was found that in neutral condition, σ z ≈ 2Cd over the observed forest surface. This is in agreement with “universal” ratios in other studies over relatively smooth terrain. Over the clearing, σ z must be increased to account for “memory” of greater roughness upstream. Ratios of the values of σ z found in unstable conditions to those in neutral conditions agree with other studies. Values of turbulence intensity based on wind speed measurements support the above findings and show that dispersion rates within the forest canopy would be lager, relative to the mean transport velocity, than in the free air. A useful correspondence was found between Pasquill stability categories and the Richardson number or Monin-Obukhov z/L parameter. The ranges of those parameters corresponding to the Pasquill categories were found to be much narrower than those reported from studies over smoother terrain.
Abstract
Using approximately 25 years of rehabilitated global solar radiation measurements, an analysis of the asymmetry of global solar radiation around solar noon was performed for three climatic regions of the United states represented by Miami, Florida; Fort Worth, Texas; and Washington, DC.
An asymmetric distribution of the global solar radiation during the summer months was found at all three regions. The most pronounced asymmetry occurred at Miami during July and August: radiation in excess of 12% was received in the morning as compared to the afternoon. At the other station the morning totals exceed the afternoon totals by 3%–4%. At Fort Worth. a reversal in the asymmetry was observed during the spring: the afternoon hours received 3% more radiation than the morning hours. Similar analyses were performed using hourly observations of clouds and resulted in consistent findings.
Abstract
Using approximately 25 years of rehabilitated global solar radiation measurements, an analysis of the asymmetry of global solar radiation around solar noon was performed for three climatic regions of the United states represented by Miami, Florida; Fort Worth, Texas; and Washington, DC.
An asymmetric distribution of the global solar radiation during the summer months was found at all three regions. The most pronounced asymmetry occurred at Miami during July and August: radiation in excess of 12% was received in the morning as compared to the afternoon. At the other station the morning totals exceed the afternoon totals by 3%–4%. At Fort Worth. a reversal in the asymmetry was observed during the spring: the afternoon hours received 3% more radiation than the morning hours. Similar analyses were performed using hourly observations of clouds and resulted in consistent findings.
Abstract
During the last few years, the feasibility of deriving surface radiation budget (SRB) components from satellite observations has been demonstrated and a better understanding of the need for SRB information in climate research was formulated. Much attention has been given to the scales at which such information is needed and to the accuracies required at different spatial and temporal scales. Recently, global acts of satellite observations became available, allowing implementation of satellite models for SRB on a global scale, and international frameworks were established for validating such models. To respond to these developments, we modified and expanded an early version of a physical model to derive surface solar irradiance from satellite observations. The model is based on radiative transfer theory, and can produce both direct and diffuse spectral components in the 0.2–4.0-μm interval. Attention is given to the absorption and scattering processes in the atmosphere and the interaction of radiation with the surface. The bidirectional nature of the exiting radiation at the top of the atmosphere is also accounted for. In this paper the emphasis will be on describing the current status of the model and its implementation on a global scale with the International Satellite Cloud Climatology Project (ISCCP) C1 data.
Abstract
During the last few years, the feasibility of deriving surface radiation budget (SRB) components from satellite observations has been demonstrated and a better understanding of the need for SRB information in climate research was formulated. Much attention has been given to the scales at which such information is needed and to the accuracies required at different spatial and temporal scales. Recently, global acts of satellite observations became available, allowing implementation of satellite models for SRB on a global scale, and international frameworks were established for validating such models. To respond to these developments, we modified and expanded an early version of a physical model to derive surface solar irradiance from satellite observations. The model is based on radiative transfer theory, and can produce both direct and diffuse spectral components in the 0.2–4.0-μm interval. Attention is given to the absorption and scattering processes in the atmosphere and the interaction of radiation with the surface. The bidirectional nature of the exiting radiation at the top of the atmosphere is also accounted for. In this paper the emphasis will be on describing the current status of the model and its implementation on a global scale with the International Satellite Cloud Climatology Project (ISCCP) C1 data.
Abstract
Computations of sensible and latent heat fluxes over forest and crop canopies using the Thornthwaite-Holzman equations require an a priori knowledge of roughness and data displacement heights. If the values of these parameters are not representative of the wind structure above the canopy, then errors will be induced in the heat flux calculations.
A detailed error transfer analysis is derived and tested against tower data taken in a tropical dry ever-green forest in Thailand. It is shown that significant errors may occur in heat flux computations if mean values of roughness parameter and datum displacement height are used during periods of significant variation of those parameters. Further, the sensitivity of a heat flux calculation to the discrepancy in the profile parameters used may be either suppressed or amplified.
A simple model is derived to estimate this error transfer from estimates of the mean values and variances of the roughness parameter and data displacement height.
Abstract
Computations of sensible and latent heat fluxes over forest and crop canopies using the Thornthwaite-Holzman equations require an a priori knowledge of roughness and data displacement heights. If the values of these parameters are not representative of the wind structure above the canopy, then errors will be induced in the heat flux calculations.
A detailed error transfer analysis is derived and tested against tower data taken in a tropical dry ever-green forest in Thailand. It is shown that significant errors may occur in heat flux computations if mean values of roughness parameter and datum displacement height are used during periods of significant variation of those parameters. Further, the sensitivity of a heat flux calculation to the discrepancy in the profile parameters used may be either suppressed or amplified.
A simple model is derived to estimate this error transfer from estimates of the mean values and variances of the roughness parameter and data displacement height.
Abstract
Concern about possible effects of a steady increase in CO2 on the earth's climate, and the fact that current estimates of sources and sinks of CO2 do not balance, generated interest to improve knowledge of rates at which carbon is cycled between the oceans, land, and atmosphere. The net primary productivity (NPP)—namely, the rate at which inorganic carbon is transformed into organic matter—is strongly controlled by the availability and intensity of photosynthetically active radiation (PAR); the distribution of photoactive pigments; the efficiency with which the light is absorbed; and the efficiency of its conversion into organic matter. In this study the feasibility to derive one of the above parameters is demonstrated—namely, PAR on a global scale. In the past, information on PAR was obtained from local ground measurements in the 0.4−0.7-µm spectral interval. In the absence of such measurements, PAR was estimated from measured total solar irradiance, using empirical “conversion factors.” It is demonstrated that this important bigeophysical parameter can now be derived from satellite observations. The inference model is implemented with global satellite data that are available ftom the International Satellite Cloud Climatology Project (ISCCP) to produce for the fire time global fields of PAR and corresponding “conversion factors.”
Abstract
Concern about possible effects of a steady increase in CO2 on the earth's climate, and the fact that current estimates of sources and sinks of CO2 do not balance, generated interest to improve knowledge of rates at which carbon is cycled between the oceans, land, and atmosphere. The net primary productivity (NPP)—namely, the rate at which inorganic carbon is transformed into organic matter—is strongly controlled by the availability and intensity of photosynthetically active radiation (PAR); the distribution of photoactive pigments; the efficiency with which the light is absorbed; and the efficiency of its conversion into organic matter. In this study the feasibility to derive one of the above parameters is demonstrated—namely, PAR on a global scale. In the past, information on PAR was obtained from local ground measurements in the 0.4−0.7-µm spectral interval. In the absence of such measurements, PAR was estimated from measured total solar irradiance, using empirical “conversion factors.” It is demonstrated that this important bigeophysical parameter can now be derived from satellite observations. The inference model is implemented with global satellite data that are available ftom the International Satellite Cloud Climatology Project (ISCCP) to produce for the fire time global fields of PAR and corresponding “conversion factors.”
Abstract
Surface solar irradiance (SW↓) was derived over the extended Amazon Basin using AVHRR observations from polar-orbiting satellites during four July months (1983–1986). Observations from the geostationary satellite GOES for July 1983 were also used to assess diurnal effects. Both satellite datasets are part of the Satellite Cloud Climatology Project (ISCCP) B3 product. It was demonstrated that it is now possible to derive long-term surface SW↓, which can be useful in climate studies, and that the accuracy of the derived fields is sufficient to detect interannual differences that can exceed at times 70 W m−2. The variability of the daily totals of SW↓ from the monthly means was similar during three of the four years investigated, yet, during the El Niño year of 1982–83, north of 10°N such variability increased drastically. This increase could be attributed to a changed pattern of convective activity as a result of higher SST off the coast of Peru. For the first time, the El Niño influence on the large-scale variability of the SW↓ was demonstrated.
Abstract
Surface solar irradiance (SW↓) was derived over the extended Amazon Basin using AVHRR observations from polar-orbiting satellites during four July months (1983–1986). Observations from the geostationary satellite GOES for July 1983 were also used to assess diurnal effects. Both satellite datasets are part of the Satellite Cloud Climatology Project (ISCCP) B3 product. It was demonstrated that it is now possible to derive long-term surface SW↓, which can be useful in climate studies, and that the accuracy of the derived fields is sufficient to detect interannual differences that can exceed at times 70 W m−2. The variability of the daily totals of SW↓ from the monthly means was similar during three of the four years investigated, yet, during the El Niño year of 1982–83, north of 10°N such variability increased drastically. This increase could be attributed to a changed pattern of convective activity as a result of higher SST off the coast of Peru. For the first time, the El Niño influence on the large-scale variability of the SW↓ was demonstrated.
