Search Results
You are looking at 1 - 4 of 4 items for :
- Author or Editor: W. F. Dabberdt x
- Article x
- Refine by Access: All Content x
Abstract
Observations of boundary-layer flow within the Santa Barbara region taken on 20 September 1985 revel the presence of a wide variety of flow features, including mesoscale wind vortices sea/land breezes, and thermally driven upslope/downslope winds. Details of these features, in particular the mesoscale vortices, are documented with dual-Doppler radar, Doppler sodar, aircraft, surface mesonet, and rawinsonde data. Numerical simulations of flow in the region using a mixed-layer model show good agreement with the observations. Model simulations indicate that sea-/land-roughness differences and planetary vorticity are of minor importance in forming the midchannel eddy (MCE), an eddy that is observed in the channel during the early morning hours. MCE formation is, however, shown to be strongly dependent on the initial stratification of the atmosphere, with more intense eddies forming as the stability increases. A second independent mechanism for MCE formation appears to be the interaction of drainage flows with the large-scale flow. A daytime vortex, known as the Gaviota eddy, occurs as the result of surface heating that generates a sea-breeze flow opposing the large-scale ambient flow.
Abstract
Observations of boundary-layer flow within the Santa Barbara region taken on 20 September 1985 revel the presence of a wide variety of flow features, including mesoscale wind vortices sea/land breezes, and thermally driven upslope/downslope winds. Details of these features, in particular the mesoscale vortices, are documented with dual-Doppler radar, Doppler sodar, aircraft, surface mesonet, and rawinsonde data. Numerical simulations of flow in the region using a mixed-layer model show good agreement with the observations. Model simulations indicate that sea-/land-roughness differences and planetary vorticity are of minor importance in forming the midchannel eddy (MCE), an eddy that is observed in the channel during the early morning hours. MCE formation is, however, shown to be strongly dependent on the initial stratification of the atmosphere, with more intense eddies forming as the stability increases. A second independent mechanism for MCE formation appears to be the interaction of drainage flows with the large-scale flow. A daytime vortex, known as the Gaviota eddy, occurs as the result of surface heating that generates a sea-breeze flow opposing the large-scale ambient flow.
More than 120 scientists, engineers, administrators, and users met on 8–10 December 2003 in a workshop format to discuss the needs for enhanced three-dimensional mesoscale observing networks. Improved networks are seen as being critical to advancing numerical and empirical modeling for a variety of mesoscale applications, including severe weather warnings and forecasts, hydrology, air-quality forecasting, chemical emergency response, transportation safety, energy management, and others. The participants shared a clear and common vision for the observing requirements: existing two-dimensional mesoscale measurement networks do not provide observations of the type, frequency, and density that are required to optimize mesoscale prediction and nowcasts. To be viable, mesoscale observing networks must serve multiple applications, and the public, private, and academic sectors must all actively participate in their design and implementation, as well as in the creation and delivery of value-added products. The mesoscale measurement challenge can best be met by an integrated approach that considers all elements of an end-to-end solution—identifying end users and their needs, designing an optimal mix of observations, defining the balance between static and dynamic (targeted or adaptive) sampling strategies, establishing long-term test beds, and developing effective implementation strategies. Detailed recommendations are provided pertaining to nowcasting, numerical prediction and data assimilation, test beds, and implementation strategies.
More than 120 scientists, engineers, administrators, and users met on 8–10 December 2003 in a workshop format to discuss the needs for enhanced three-dimensional mesoscale observing networks. Improved networks are seen as being critical to advancing numerical and empirical modeling for a variety of mesoscale applications, including severe weather warnings and forecasts, hydrology, air-quality forecasting, chemical emergency response, transportation safety, energy management, and others. The participants shared a clear and common vision for the observing requirements: existing two-dimensional mesoscale measurement networks do not provide observations of the type, frequency, and density that are required to optimize mesoscale prediction and nowcasts. To be viable, mesoscale observing networks must serve multiple applications, and the public, private, and academic sectors must all actively participate in their design and implementation, as well as in the creation and delivery of value-added products. The mesoscale measurement challenge can best be met by an integrated approach that considers all elements of an end-to-end solution—identifying end users and their needs, designing an optimal mix of observations, defining the balance between static and dynamic (targeted or adaptive) sampling strategies, establishing long-term test beds, and developing effective implementation strategies. Detailed recommendations are provided pertaining to nowcasting, numerical prediction and data assimilation, test beds, and implementation strategies.
Several ground-based remote sensors were operated together in Colorado during February and March 1991 to obtain continuous profiles of the kinematic and thermodynamic structure of the atmosphere. Instrument performance is compared for five different wind profilers. Each was equipped with Radio Acoustic Sounding System (RASS) capability to measure virtual temperature. This was the first side-by-side comparison of all three of the most common wind-profiler frequencies: 50, 404, and 915 MHz. The 404-MHz system was a NOAA Wind Profiler Demonstration Network (WPDN) unit. Dual-frequency microwave radiometers that measured path-integrated water vapor and liquid water content were also evaluated. Frequent rawinsonde launches from the remote-sensor sites provided an extensive set of in situ measurements for comparison. The winter operations provide a severe test of the profiler/RASS capabilities because atmospheric scattering is relatively weak and acoustic attenuation is relatively strong in cold, dry conditions. Nevertheless, the lower-frequency systems exhibited impressive height coverage for wind and virtual temperature profiling, whereas the high-frequency units provided higher-resolution measurements near the surface. Comparisons between remote sensor and rawinsonde data generally showed excellent agreement. The results support more widespread use of these emerging technologies.
Several ground-based remote sensors were operated together in Colorado during February and March 1991 to obtain continuous profiles of the kinematic and thermodynamic structure of the atmosphere. Instrument performance is compared for five different wind profilers. Each was equipped with Radio Acoustic Sounding System (RASS) capability to measure virtual temperature. This was the first side-by-side comparison of all three of the most common wind-profiler frequencies: 50, 404, and 915 MHz. The 404-MHz system was a NOAA Wind Profiler Demonstration Network (WPDN) unit. Dual-frequency microwave radiometers that measured path-integrated water vapor and liquid water content were also evaluated. Frequent rawinsonde launches from the remote-sensor sites provided an extensive set of in situ measurements for comparison. The winter operations provide a severe test of the profiler/RASS capabilities because atmospheric scattering is relatively weak and acoustic attenuation is relatively strong in cold, dry conditions. Nevertheless, the lower-frequency systems exhibited impressive height coverage for wind and virtual temperature profiling, whereas the high-frequency units provided higher-resolution measurements near the surface. Comparisons between remote sensor and rawinsonde data generally showed excellent agreement. The results support more widespread use of these emerging technologies.
Abstract
Urbanization modifies atmospheric energy and moisture balances, forming distinct features [e.g., urban heat islands (UHIs) and enhanced or decreased precipitation]. These produce significant challenges to science and society, including rapid and intense flooding, heat waves strengthened by UHIs, and air pollutant haze. The Study of Urban Impacts on Rainfall and Fog/Haze (SURF) has brought together international expertise on observations and modeling, meteorology and atmospheric chemistry, and research and operational forecasting. The SURF overall science objective is a better understanding of urban, terrain, convection, and aerosol interactions for improved forecast accuracy. Specific objectives include a) promoting cooperative international research to improve understanding of urban summer convective precipitation and winter particulate episodes via extensive field studies, b) improving high-resolution urban weather and air quality forecast models, and c) enhancing urban weather forecasts for societal applications (e.g., health, energy, hydrologic, climate change, air quality, planning, and emergency response management). Preliminary SURF observational and modeling results are shown (i.e., turbulent PBL structure, bifurcating thunderstorms, haze events, urban canopy model development, and model forecast evaluation).
Abstract
Urbanization modifies atmospheric energy and moisture balances, forming distinct features [e.g., urban heat islands (UHIs) and enhanced or decreased precipitation]. These produce significant challenges to science and society, including rapid and intense flooding, heat waves strengthened by UHIs, and air pollutant haze. The Study of Urban Impacts on Rainfall and Fog/Haze (SURF) has brought together international expertise on observations and modeling, meteorology and atmospheric chemistry, and research and operational forecasting. The SURF overall science objective is a better understanding of urban, terrain, convection, and aerosol interactions for improved forecast accuracy. Specific objectives include a) promoting cooperative international research to improve understanding of urban summer convective precipitation and winter particulate episodes via extensive field studies, b) improving high-resolution urban weather and air quality forecast models, and c) enhancing urban weather forecasts for societal applications (e.g., health, energy, hydrologic, climate change, air quality, planning, and emergency response management). Preliminary SURF observational and modeling results are shown (i.e., turbulent PBL structure, bifurcating thunderstorms, haze events, urban canopy model development, and model forecast evaluation).
