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- Author or Editor: H. E. Fleming x
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Abstract
Artificial earth satellites offer a unique opportunity to exploit the possibility of deducing temperature profiles on a global scale from measurements of radiance in several narrow spectral intervals in a strongly absorbing band of an atmospheric gas whose mixture is uniform. In the earth's atmosphere the 4.3-micron and 15-micron bands of carbon dioxide and the 5-mm. band of oxygen may be used; only the 15-micron band is considered in detail, although the procedures are applicable to the other bands. The problem considered is the numerical solution of the integral form of the radiative transfer equation from measurements in a finite set of spectral intervals. It is shown that, by a suitable approximation of the Planck radiance, the radiative transfer equation can be reduced to an integral equation of the first kind. After a discussion of the kernel, which is associated with the transmittance of the gas, the equation is changed to a finite set of equations which is amenable to numerical solution. The solution is limited to about six pieces of information, which may be expressed as points along the vertical profile, or as coefficients of an expansion; the limitation in information is manifest in the transmittance curves for the several spectral intervals, the errors of measurement, and the approximations employed. However, even in this limited case the formal solution of the set of equations is unstable. A method of stabilizing the solution by smoothing is discussed. In this process the amount of smoothing remains small, so that the inherent properties of the temperature profile are not affected. Several possible forms of the solution are discussed, and it is concluded that empirical orthogonal functions are preferred because they contain the physical information lacking in analytical forms. Examples are shown of solutions for radically different profiles, both with “exact” simulated measurements and with random errors introduced.
Abstract
Artificial earth satellites offer a unique opportunity to exploit the possibility of deducing temperature profiles on a global scale from measurements of radiance in several narrow spectral intervals in a strongly absorbing band of an atmospheric gas whose mixture is uniform. In the earth's atmosphere the 4.3-micron and 15-micron bands of carbon dioxide and the 5-mm. band of oxygen may be used; only the 15-micron band is considered in detail, although the procedures are applicable to the other bands. The problem considered is the numerical solution of the integral form of the radiative transfer equation from measurements in a finite set of spectral intervals. It is shown that, by a suitable approximation of the Planck radiance, the radiative transfer equation can be reduced to an integral equation of the first kind. After a discussion of the kernel, which is associated with the transmittance of the gas, the equation is changed to a finite set of equations which is amenable to numerical solution. The solution is limited to about six pieces of information, which may be expressed as points along the vertical profile, or as coefficients of an expansion; the limitation in information is manifest in the transmittance curves for the several spectral intervals, the errors of measurement, and the approximations employed. However, even in this limited case the formal solution of the set of equations is unstable. A method of stabilizing the solution by smoothing is discussed. In this process the amount of smoothing remains small, so that the inherent properties of the temperature profile are not affected. Several possible forms of the solution are discussed, and it is concluded that empirical orthogonal functions are preferred because they contain the physical information lacking in analytical forms. Examples are shown of solutions for radically different profiles, both with “exact” simulated measurements and with random errors introduced.
Abstract
The method of real-time retrieval of atmospheric temperature profiles from Nimbus IV Satellite Infrared Spectrometer observations currently used in dynamical weather analysis-forecast operation is described. Each vertical temperature profile is determined by its deviation from a “guess” profile. The deviation is expressed as a linear combination of differences between the measured radiances and those computed from the guess profile. The coefficients are estimated, by matrix inversion, from the weighting functions (i.e., derivatives of atmospheric transmittance functions), which are regularized by the ratio of the expected variance of the measurement errors to the expected variance of the errors in the guess profile. The deviations are iterated until the variance of the radiance residuals is less than the expected variance of the measurement errors.
For weather analysis-forecast operation the dynamical forecast is used as the first guess; therefore, the calculated profiles should differ from the forecast profiles only when the measurable error in the forecast exceeds the instrumental noise level. The retrieved profiles are those which deviate least from the forecast in order to satisfy all the radiance observations. This property is well suited to dynamical forecasting in that it does not tend to produce erroneous atmospheric waves.
Abstract
The method of real-time retrieval of atmospheric temperature profiles from Nimbus IV Satellite Infrared Spectrometer observations currently used in dynamical weather analysis-forecast operation is described. Each vertical temperature profile is determined by its deviation from a “guess” profile. The deviation is expressed as a linear combination of differences between the measured radiances and those computed from the guess profile. The coefficients are estimated, by matrix inversion, from the weighting functions (i.e., derivatives of atmospheric transmittance functions), which are regularized by the ratio of the expected variance of the measurement errors to the expected variance of the errors in the guess profile. The deviations are iterated until the variance of the radiance residuals is less than the expected variance of the measurement errors.
For weather analysis-forecast operation the dynamical forecast is used as the first guess; therefore, the calculated profiles should differ from the forecast profiles only when the measurable error in the forecast exceeds the instrumental noise level. The retrieved profiles are those which deviate least from the forecast in order to satisfy all the radiance observations. This property is well suited to dynamical forecasting in that it does not tend to produce erroneous atmospheric waves.
Abstract
The statistical minimum-rms inversion method used to obtain temperature profiles, requires estimates of covariance matrices and means for Planck function profiles of the atmosphere. In order to obtain these estimates over the pressure range of IWO to 0.01 mb, it was necessary to combine data from temperature measurements by radiosondes, rocketsondes and grenadesondes. Radiosonde data reaching the 10-mb level were extended to higher levels by means of a modified regression technique. Matrices and means have been obtained by this method for seasonal and geographical groupings in the Northern Hemisphere and the tropics. Details of the geographical and time changes in the matrices and the means are presented.
Abstract
The statistical minimum-rms inversion method used to obtain temperature profiles, requires estimates of covariance matrices and means for Planck function profiles of the atmosphere. In order to obtain these estimates over the pressure range of IWO to 0.01 mb, it was necessary to combine data from temperature measurements by radiosondes, rocketsondes and grenadesondes. Radiosonde data reaching the 10-mb level were extended to higher levels by means of a modified regression technique. Matrices and means have been obtained by this method for seasonal and geographical groupings in the Northern Hemisphere and the tropics. Details of the geographical and time changes in the matrices and the means are presented.
Abstract
Satellite-radiance data (Nimbus 5, 6; ≤80 km) and the MSIS-83 model have been used to prepare global zonal-mean gradient winds (30–120 km) for the new CIRA-1986. Here these are supplemented by planetary-wave morphology from the same Nimbus data to provide local gradient winds—the zonal wind and the eddy portion of the meridional wind are calculated by this method. These data are then compared with radar-derived wind contours (∼60–110 km), extending the comparisons done earlier (Manson et al.) for heights below 80 km. Overall the agreement for the zonal winds is good, especially below 80 km; differences are shown so the user can evaluate each product. The comparison of meridional winds is particularly valuable and unique as it reveals considerable ageostrophy, particularly in summer months near the height of the zonal wind's reversal from west- to eastward flow. Coriolis torques due to this meridional flow are available from Saskatoon (52°), Poker Flat (65°), and Tromsö (70°) in the Northern Hemisphere, and Adelaide (35°), Christchurch (44°), and Mawson (68°) in the Southern Hemisphere. Values of 60–100 m s−1 day−1 are generally consistent with estimates of the balancing gravity wave momentum deposition made by direct methods at the same locations.
Abstract
Satellite-radiance data (Nimbus 5, 6; ≤80 km) and the MSIS-83 model have been used to prepare global zonal-mean gradient winds (30–120 km) for the new CIRA-1986. Here these are supplemented by planetary-wave morphology from the same Nimbus data to provide local gradient winds—the zonal wind and the eddy portion of the meridional wind are calculated by this method. These data are then compared with radar-derived wind contours (∼60–110 km), extending the comparisons done earlier (Manson et al.) for heights below 80 km. Overall the agreement for the zonal winds is good, especially below 80 km; differences are shown so the user can evaluate each product. The comparison of meridional winds is particularly valuable and unique as it reveals considerable ageostrophy, particularly in summer months near the height of the zonal wind's reversal from west- to eastward flow. Coriolis torques due to this meridional flow are available from Saskatoon (52°), Poker Flat (65°), and Tromsö (70°) in the Northern Hemisphere, and Adelaide (35°), Christchurch (44°), and Mawson (68°) in the Southern Hemisphere. Values of 60–100 m s−1 day−1 are generally consistent with estimates of the balancing gravity wave momentum deposition made by direct methods at the same locations.
Abstract
Air quality and heat are strong health drivers, and their accurate assessment and forecast are important in densely populated urban areas. However, the sources and processes leading to high concentrations of main pollutants, such as ozone, nitrogen dioxide, and fine and coarse particulate matter, in complex urban areas are not fully understood, limiting our ability to forecast air quality accurately. This paper introduces the Clean Air for London (ClearfLo; www.clearflo.ac.uk) project’s interdisciplinary approach to investigate the processes leading to poor air quality and elevated temperatures.
Within ClearfLo, a large multi-institutional project funded by the U.K. Natural Environment Research Council (NERC), integrated measurements of meteorology and gaseous, and particulate composition/loading within the atmosphere of London, United Kingdom, were undertaken to understand the processes underlying poor air quality. Long-term measurement infrastructure installed at multiple levels (street and elevated), and at urban background, curbside, and rural locations were complemented with high-resolution numerical atmospheric simulations. Combining these (measurement–modeling) enhances understanding of seasonal variations in meteorology and composition together with the controlling processes. Two intensive observation periods (winter 2012 and the Summer Olympics of 2012) focus upon the vertical structure and evolution of the urban boundary layer; chemical controls on nitrogen dioxide and ozone production—in particular, the role of volatile organic compounds; and processes controlling the evolution, size, distribution, and composition of particulate matter. The paper shows that mixing heights are deeper over London than in the rural surroundings and that the seasonality of the urban boundary layer evolution controls when concentrations peak. The composition also reflects the seasonality of sources such as domestic burning and biogenic emissions.
Abstract
Air quality and heat are strong health drivers, and their accurate assessment and forecast are important in densely populated urban areas. However, the sources and processes leading to high concentrations of main pollutants, such as ozone, nitrogen dioxide, and fine and coarse particulate matter, in complex urban areas are not fully understood, limiting our ability to forecast air quality accurately. This paper introduces the Clean Air for London (ClearfLo; www.clearflo.ac.uk) project’s interdisciplinary approach to investigate the processes leading to poor air quality and elevated temperatures.
Within ClearfLo, a large multi-institutional project funded by the U.K. Natural Environment Research Council (NERC), integrated measurements of meteorology and gaseous, and particulate composition/loading within the atmosphere of London, United Kingdom, were undertaken to understand the processes underlying poor air quality. Long-term measurement infrastructure installed at multiple levels (street and elevated), and at urban background, curbside, and rural locations were complemented with high-resolution numerical atmospheric simulations. Combining these (measurement–modeling) enhances understanding of seasonal variations in meteorology and composition together with the controlling processes. Two intensive observation periods (winter 2012 and the Summer Olympics of 2012) focus upon the vertical structure and evolution of the urban boundary layer; chemical controls on nitrogen dioxide and ozone production—in particular, the role of volatile organic compounds; and processes controlling the evolution, size, distribution, and composition of particulate matter. The paper shows that mixing heights are deeper over London than in the rural surroundings and that the seasonality of the urban boundary layer evolution controls when concentrations peak. The composition also reflects the seasonality of sources such as domestic burning and biogenic emissions.
