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- Author or Editor: C. E. Graves x
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Abstract
It has recently become clear through advances in both theoretical and experimental meteorology, that improvements in modeling the transport and dispersion of pollutants will require on-site measurements of the atmosphere. This requirement has in turn generated questions about 1) our ability to make such measurements both near the surface and through the first few hundred meters of the atmosphere and 2) the expected accuracy and precision of such measurements using current technology. To help answer these questions an experiment was conducted at the Boulder Atmospheric Observatory to assess the ability of in situ and remote sensors to measure the mean and turbulent properties of the lower atmosphere. Two categories of sensors were tested. One consisted of lightweight in situ sensors of types that have been frequently used in the recent past for boundary layer studies. The other category consisted of four commercially available Doppler sodars, with the capability to measure wind speed, wind direction, and vertical component of turbulence, at various heights above the ground. Part one of this two part study deals with comparisons of five in situ wind sensing systems with a three-axis sonic anemometer, all mounted on 10 m towers spaced approximately 5 m apart. Discussed in this paper are statistical measures of their accuracy, precision and spectral response to fluctuations in the wind.
Abstract
It has recently become clear through advances in both theoretical and experimental meteorology, that improvements in modeling the transport and dispersion of pollutants will require on-site measurements of the atmosphere. This requirement has in turn generated questions about 1) our ability to make such measurements both near the surface and through the first few hundred meters of the atmosphere and 2) the expected accuracy and precision of such measurements using current technology. To help answer these questions an experiment was conducted at the Boulder Atmospheric Observatory to assess the ability of in situ and remote sensors to measure the mean and turbulent properties of the lower atmosphere. Two categories of sensors were tested. One consisted of lightweight in situ sensors of types that have been frequently used in the recent past for boundary layer studies. The other category consisted of four commercially available Doppler sodars, with the capability to measure wind speed, wind direction, and vertical component of turbulence, at various heights above the ground. Part one of this two part study deals with comparisons of five in situ wind sensing systems with a three-axis sonic anemometer, all mounted on 10 m towers spaced approximately 5 m apart. Discussed in this paper are statistical measures of their accuracy, precision and spectral response to fluctuations in the wind.
Abstract
Measurements of wind speed, wind direction, and the vertical component of turbulence, from four different commercially available Doppler sodars, are compared with similar measurements from in situ sensors on a 300 m instrumented tower. Results indicate that the four sodars measure wind speed and direction accurately and with reasonably high precision. The sodars tended to overestimate the vertical component of turbulence at night and to underestimate it during the day. Precision in those measurements was considerably poorer than for the averaged speeds and directions. Analysis of the vertical wind speed measurements from the sodars indicates that the measurement inaccuracies arise from a combination of aliasing and spatial averaging. Comparison of five in situ wind systems with a sonic anemometer are presented in Part I of this two part series of papers.
Abstract
Measurements of wind speed, wind direction, and the vertical component of turbulence, from four different commercially available Doppler sodars, are compared with similar measurements from in situ sensors on a 300 m instrumented tower. Results indicate that the four sodars measure wind speed and direction accurately and with reasonably high precision. The sodars tended to overestimate the vertical component of turbulence at night and to underestimate it during the day. Precision in those measurements was considerably poorer than for the averaged speeds and directions. Analysis of the vertical wind speed measurements from the sodars indicates that the measurement inaccuracies arise from a combination of aliasing and spatial averaging. Comparison of five in situ wind systems with a sonic anemometer are presented in Part I of this two part series of papers.
Abstract
An algorithm to estimate monthly 5° × 5° area-averaged rain rate over the oceans from January 1973 to December 1976 using single-channel microwave data from the Nimbus-5 satellite has been developed. This study extends the work of Shin et al. by including the full width of scan angles (from −50° to 50°) in order to reduce sampling error. The scan-angle dependence of the estimated rain rate due to variable antenna sidelobe effects, surface emissivity, and propagation pathlength is eliminated using a statistical method. A globally uniform beam-filling correction factor of 2.2 is applied in this study. Comparison with island station rainfall measurements over the Pacific shows a remarkably high correlation between two data in the equatorial dry zone and South Pacific convergence zone (SPCZ) but a low correlation in the extratropics and equatorial western Pacific. It is also proved that the retrieved rain rates are statistically significant.
The rainfall deviations from non-El Niño years April 1973 to December 1975 reveal the temporal and spatial variations produced by the 1972–73 and 1976–77 El Niño episodes. We observe an increase of rainfall over the eastern and central equatorial Pacific Ocean and a decrease over the equatorial western Pacific Ocean and eastern Australia during these events. Consistent with previous work, the rainfall anomaly of the 1972–73 El Niño was much stronger than that of the 1976–77 El Niño.
Abstract
An algorithm to estimate monthly 5° × 5° area-averaged rain rate over the oceans from January 1973 to December 1976 using single-channel microwave data from the Nimbus-5 satellite has been developed. This study extends the work of Shin et al. by including the full width of scan angles (from −50° to 50°) in order to reduce sampling error. The scan-angle dependence of the estimated rain rate due to variable antenna sidelobe effects, surface emissivity, and propagation pathlength is eliminated using a statistical method. A globally uniform beam-filling correction factor of 2.2 is applied in this study. Comparison with island station rainfall measurements over the Pacific shows a remarkably high correlation between two data in the equatorial dry zone and South Pacific convergence zone (SPCZ) but a low correlation in the extratropics and equatorial western Pacific. It is also proved that the retrieved rain rates are statistically significant.
The rainfall deviations from non-El Niño years April 1973 to December 1975 reveal the temporal and spatial variations produced by the 1972–73 and 1976–77 El Niño episodes. We observe an increase of rainfall over the eastern and central equatorial Pacific Ocean and a decrease over the equatorial western Pacific Ocean and eastern Australia during these events. Consistent with previous work, the rainfall anomaly of the 1972–73 El Niño was much stronger than that of the 1976–77 El Niño.
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.
