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Abstract
A detailed, multisensor case study of mesoscale convective storms occurring in summer over the central and eastern Colorado Rockies is presented. This case study uses data obtained during the 1977 South Park Area Cumulus Experiment (SPACE) from surface meteorological stations, rawinsondes and tethered balloons, conventional and Doppler radars, powered aircraft and satellites.
On 19 July 1977, a north–south oriented line of intense convective cells formed and remained within South Park, an elevated plain 2.8 km above sea level located within the Rocky Mountains. Elevated surface heating in South Park created a region of low-level convergence which imported Pacific moisture from west of the Rockies into South Park. The mososcale thunderstorm line formed over this convergence zone. Subsequently, northerly surface flow, having the appearance of a “density current”, penetrated into South Park late in the afternoon, enhancing the intensity of convective storms. Various interactions of the storm system with the mesoscale environment were observed. A single large convective cell was then observed to grow on the southern end of the mesoscale line, exhibiting supercell characteristics and substantial modification of the environmental flow. A detailed description of this quasi-steady storm is given in Parts II and III (Knupp and Cotton, 1982a,b).
Abstract
A detailed, multisensor case study of mesoscale convective storms occurring in summer over the central and eastern Colorado Rockies is presented. This case study uses data obtained during the 1977 South Park Area Cumulus Experiment (SPACE) from surface meteorological stations, rawinsondes and tethered balloons, conventional and Doppler radars, powered aircraft and satellites.
On 19 July 1977, a north–south oriented line of intense convective cells formed and remained within South Park, an elevated plain 2.8 km above sea level located within the Rocky Mountains. Elevated surface heating in South Park created a region of low-level convergence which imported Pacific moisture from west of the Rockies into South Park. The mososcale thunderstorm line formed over this convergence zone. Subsequently, northerly surface flow, having the appearance of a “density current”, penetrated into South Park late in the afternoon, enhancing the intensity of convective storms. Various interactions of the storm system with the mesoscale environment were observed. A single large convective cell was then observed to grow on the southern end of the mesoscale line, exhibiting supercell characteristics and substantial modification of the environmental flow. A detailed description of this quasi-steady storm is given in Parts II and III (Knupp and Cotton, 1982a,b).
Abstract
An experiment was performed to measure the near-surface current by aiming horizontally two of the beams from an acoustic Doppler current profiler (ADCP) deployed at 0.6-m depth from an anchored (but rolling) ship. The results compare favorably with independent current measurements made at 2-m depth but appear to resolve as well a vertical current shear associated with the shallow wind-drift layer. The approach, therefore, has potential for investigating the current profile in the upper meter or two of the water column.
Abstract
An experiment was performed to measure the near-surface current by aiming horizontally two of the beams from an acoustic Doppler current profiler (ADCP) deployed at 0.6-m depth from an anchored (but rolling) ship. The results compare favorably with independent current measurements made at 2-m depth but appear to resolve as well a vertical current shear associated with the shallow wind-drift layer. The approach, therefore, has potential for investigating the current profile in the upper meter or two of the water column.
Abstract
On 20 May 1977 a periodic pressure disturbance over the upper Midwest was detected by synoptic and mesoscale microbarograph arrays. Analysis indicates that a pressure wave with an amplitude of approximately 1.0 mb, a phase speed of approximately 14 m s−1, a period of between 1.5 and 3 h, and a horizontal wavelength of approximately 100 km moved through Illinois, Iowa and Wisconsin from the south within the warm sector of an occluded cyclone. We interpret them pressure data as the signature of an internal atmospheric gravity wave. At several locations convective precipitation occurred coincident with the advancing ridges of the pressure wave, suggesting that the gravity wave influence convection. Openings in the cloud cover correlated with the location of the gravity wave. Simple modeling confirms the destabilization potential of the gravity wave.
Abstract
On 20 May 1977 a periodic pressure disturbance over the upper Midwest was detected by synoptic and mesoscale microbarograph arrays. Analysis indicates that a pressure wave with an amplitude of approximately 1.0 mb, a phase speed of approximately 14 m s−1, a period of between 1.5 and 3 h, and a horizontal wavelength of approximately 100 km moved through Illinois, Iowa and Wisconsin from the south within the warm sector of an occluded cyclone. We interpret them pressure data as the signature of an internal atmospheric gravity wave. At several locations convective precipitation occurred coincident with the advancing ridges of the pressure wave, suggesting that the gravity wave influence convection. Openings in the cloud cover correlated with the location of the gravity wave. Simple modeling confirms the destabilization potential of the gravity wave.
Abstract
A new radiosonde system considerably improves the detection of fine temperature structure in the lower atmosphere. Special features of the system include a simple, inexpensive radiosonde which uses a monolithic timer in a rapid-response, temperature sensing audio oscillator circuit, a receiver which uses an integrated-circuit phase-lock-loop to track the audio-frequency pulses, and a simple, barometric release mechanism. The system has been used extensively in recent field investigations of the planetary boundary layer.
Abstract
A new radiosonde system considerably improves the detection of fine temperature structure in the lower atmosphere. Special features of the system include a simple, inexpensive radiosonde which uses a monolithic timer in a rapid-response, temperature sensing audio oscillator circuit, a receiver which uses an integrated-circuit phase-lock-loop to track the audio-frequency pulses, and a simple, barometric release mechanism. The system has been used extensively in recent field investigations of the planetary boundary layer.
Abstract
As part of the joint National Oceanic and Atmospheric Administration–National Aeronautics and Space Administration (NOAA–NASA) Pathfinder program, the NOAA/National Environmental Satellite, Data and Information Service (NESDIS) has created a research-quality atmospheric, climate-scale dataset through the reprocessing of archived Advanced Very High Resolution Radiometer (AVHRR) observations from four afternoon satellites, in orbit since 1981. The raw observations were recalibrated using a vicarious calibration technique for the AVHRR reflectance channels and an improved treatment of the nonlinearity of the three infrared emittance channels. State-of-the-art algorithms are used in the Pathfinder Atmosphere (PATMOS) project to process global AVHRR datasets into statistics of channel radiances, total cloud amount, components of the earth's radiation budget, and aerosol optical thickness over oceans. The radiances and earth radiation budget components are determined for clear-sky and all-sky conditions. The output products are generated on a quasi-equal-area grid with a spatial resolution of approximately 110 km, with twice-a-day temporal resolution, and averaged over 5-day (pentad) and monthly time periods. The quality of the products is assessed relative to independent surface or satellite observations of these parameters. This analysis shows that the PATMOS data are sufficiently accurate for studies of the interaction of clouds and aerosol with solar and terrestrial radiation, and of climatic phenomena with large signals, for example, the annual cycle, monsoons, and the four ENSOs and two major volcanic eruptions that occurred during the 19-yr PATMOS period. Analysis also indicates that smaller climate signals, such as those associated with longer-term trends in surface temperature, may be difficult to detect due to the presence of artifacts in the time series that result from the drift of each satellite's observation time over its mission. However, a simple statistical method is employed to remove much of the effect caused by orbital drift. The uncorrected PATMOS dataset is accessible electronically.
Abstract
As part of the joint National Oceanic and Atmospheric Administration–National Aeronautics and Space Administration (NOAA–NASA) Pathfinder program, the NOAA/National Environmental Satellite, Data and Information Service (NESDIS) has created a research-quality atmospheric, climate-scale dataset through the reprocessing of archived Advanced Very High Resolution Radiometer (AVHRR) observations from four afternoon satellites, in orbit since 1981. The raw observations were recalibrated using a vicarious calibration technique for the AVHRR reflectance channels and an improved treatment of the nonlinearity of the three infrared emittance channels. State-of-the-art algorithms are used in the Pathfinder Atmosphere (PATMOS) project to process global AVHRR datasets into statistics of channel radiances, total cloud amount, components of the earth's radiation budget, and aerosol optical thickness over oceans. The radiances and earth radiation budget components are determined for clear-sky and all-sky conditions. The output products are generated on a quasi-equal-area grid with a spatial resolution of approximately 110 km, with twice-a-day temporal resolution, and averaged over 5-day (pentad) and monthly time periods. The quality of the products is assessed relative to independent surface or satellite observations of these parameters. This analysis shows that the PATMOS data are sufficiently accurate for studies of the interaction of clouds and aerosol with solar and terrestrial radiation, and of climatic phenomena with large signals, for example, the annual cycle, monsoons, and the four ENSOs and two major volcanic eruptions that occurred during the 19-yr PATMOS period. Analysis also indicates that smaller climate signals, such as those associated with longer-term trends in surface temperature, may be difficult to detect due to the presence of artifacts in the time series that result from the drift of each satellite's observation time over its mission. However, a simple statistical method is employed to remove much of the effect caused by orbital drift. The uncorrected PATMOS dataset is accessible electronically.
Abstract
FAGE (fluorescence assay with gas expansion) was developed as a sensitive technique for the detection of low-concentration free radicals in the atmosphere. The application of FAGE to tropospheric hydroxyl (H0) and hydroperoxyl (H02) radicals has yielded calibrated measurements of both species in both clean air and highly polluted urban air. For HO calibration, a continuously stirred tank reactor provides a uniform external HO concentration, which can be measured by gas chromatography of an HO-reactive hydrocarbon. The aerodynamics of the air-sampling process has been modeled computationally, with results that agree with empirical observations of the effects of nozzle diameter on HO loss during sampling. The authors have also modeled airborne fluid dynamics of a FAGE probe. They have recently obtained FAGE sensitivity as high as ± 1 × 106 cm−3 for a 6-minute averaging period, during field studies in highly polluted Los Angeles air, yielding a 7:1 signal-to-noise ratio near midday. Multipass excitation can further improve this sensitivity. The authors summarize their recent field studies of HO and HO2, current work on improved calibration methods, other improvements, and future plans.
Abstract
FAGE (fluorescence assay with gas expansion) was developed as a sensitive technique for the detection of low-concentration free radicals in the atmosphere. The application of FAGE to tropospheric hydroxyl (H0) and hydroperoxyl (H02) radicals has yielded calibrated measurements of both species in both clean air and highly polluted urban air. For HO calibration, a continuously stirred tank reactor provides a uniform external HO concentration, which can be measured by gas chromatography of an HO-reactive hydrocarbon. The aerodynamics of the air-sampling process has been modeled computationally, with results that agree with empirical observations of the effects of nozzle diameter on HO loss during sampling. The authors have also modeled airborne fluid dynamics of a FAGE probe. They have recently obtained FAGE sensitivity as high as ± 1 × 106 cm−3 for a 6-minute averaging period, during field studies in highly polluted Los Angeles air, yielding a 7:1 signal-to-noise ratio near midday. Multipass excitation can further improve this sensitivity. The authors summarize their recent field studies of HO and HO2, current work on improved calibration methods, other improvements, and future plans.
Abstract
Using data collected during Colorado State University's South Park Area Cumulus Experiment in 1977, a sequence of multi-scale convective events leading to the formation of a mesoscale convective complex is described. In the first phase, surface-based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges. The second phase was earmarked by the formation of convective precipitation echoes at “hot spots” over the high mountain terrain. Two groups of cells then propagated. eastward across the mountain basin, forming a line of discrete cells which moved across the foothills toward the High Plains. The cells further intensified at the. foothills/High Plains interface and formed a still larger, north-south line of thunderstorms. In the third phase, this north–south line of thunderstorms evolved into an expanding meso-β-scale convective cluster as it continued its eastward propagation over eastern Colorado. The convective intensity of the line was apparently modulated by moisture availability over the plains, with the southern cells being most intense initially. As the northern end of the line encountered greater low-level moisture in western Kansas, the convection rapidly intensified to severe levels and produced in excess of 50 mm of precipitation over a large area. In Part II of this article it is shown that this meso-β-scale system participated in the formation of a meso-&α-scale convective complex.
Abstract
Using data collected during Colorado State University's South Park Area Cumulus Experiment in 1977, a sequence of multi-scale convective events leading to the formation of a mesoscale convective complex is described. In the first phase, surface-based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges. The second phase was earmarked by the formation of convective precipitation echoes at “hot spots” over the high mountain terrain. Two groups of cells then propagated. eastward across the mountain basin, forming a line of discrete cells which moved across the foothills toward the High Plains. The cells further intensified at the. foothills/High Plains interface and formed a still larger, north-south line of thunderstorms. In the third phase, this north–south line of thunderstorms evolved into an expanding meso-β-scale convective cluster as it continued its eastward propagation over eastern Colorado. The convective intensity of the line was apparently modulated by moisture availability over the plains, with the southern cells being most intense initially. As the northern end of the line encountered greater low-level moisture in western Kansas, the convection rapidly intensified to severe levels and produced in excess of 50 mm of precipitation over a large area. In Part II of this article it is shown that this meso-β-scale system participated in the formation of a meso-&α-scale convective complex.
Abstract
Hurricane Claudette was successfully tracked for three days using the 2-s (7 m) surface wave direction field mapped by the U.S. Air Force OTH-B over-the-horizon radar 2400 km away on the coast of Maine. Inflow and fine structure of the surface circulation are apparent in streamline plots derived from surface wave direction measured with 60-km resolution in the vicinity of the storm for five radar runs. The radar-derived track is within 60 km of that published by the NOAA National Hurricane Center.
Abstract
Hurricane Claudette was successfully tracked for three days using the 2-s (7 m) surface wave direction field mapped by the U.S. Air Force OTH-B over-the-horizon radar 2400 km away on the coast of Maine. Inflow and fine structure of the surface circulation are apparent in streamline plots derived from surface wave direction measured with 60-km resolution in the vicinity of the storm for five radar runs. The radar-derived track is within 60 km of that published by the NOAA National Hurricane Center.
Abstract
The new concept of an ensemble bred vector (EBV) algorithm is introduced to assess the sensitivity of model outputs to changes in initial conditions for weather forecasting. The new algorithm is based on collective dynamics in essential ways. As such, it keeps important geometric features that are lost in the earlier bred vector (BV) algorithm. By construction, the EBV algorithm produces one or more dominant vectors and is less prone to spurious results than the BV algorithm. It retains the attractive features of the BV algorithm with regard to being able to handle legacy codes, with minimal additional coding.
The performance of the EBV algorithm is investigated by comparing it to the BV algorithm as well as the finite-time Lyapunov vectors. With the help of a continuous-time adaptation of these algorithms, a theoretical justification is given to the observed fact that the vectors produced by the BV, EBV algorithms, and the finite-time Lyapunov vectors are similar for small amplitudes. The continuum theory establishes the relationship between the two algorithms and general directional derivatives.
Numerical comparisons of BV and EBV for the three-equation Lorenz model and for a forced, dissipative partial differential equation of Cahn–Hilliard type that arises in modeling the thermohaline circulation demonstrate that the EBV yields a size-ordered description of the perturbation field and is more robust than the BV in the higher nonlinear regime. The EBV yields insight into the fractal structure of the Lorenz attractor and of the inertial manifold for the Cahn–Hilliard-type partial differential equation.
Abstract
The new concept of an ensemble bred vector (EBV) algorithm is introduced to assess the sensitivity of model outputs to changes in initial conditions for weather forecasting. The new algorithm is based on collective dynamics in essential ways. As such, it keeps important geometric features that are lost in the earlier bred vector (BV) algorithm. By construction, the EBV algorithm produces one or more dominant vectors and is less prone to spurious results than the BV algorithm. It retains the attractive features of the BV algorithm with regard to being able to handle legacy codes, with minimal additional coding.
The performance of the EBV algorithm is investigated by comparing it to the BV algorithm as well as the finite-time Lyapunov vectors. With the help of a continuous-time adaptation of these algorithms, a theoretical justification is given to the observed fact that the vectors produced by the BV, EBV algorithms, and the finite-time Lyapunov vectors are similar for small amplitudes. The continuum theory establishes the relationship between the two algorithms and general directional derivatives.
Numerical comparisons of BV and EBV for the three-equation Lorenz model and for a forced, dissipative partial differential equation of Cahn–Hilliard type that arises in modeling the thermohaline circulation demonstrate that the EBV yields a size-ordered description of the perturbation field and is more robust than the BV in the higher nonlinear regime. The EBV yields insight into the fractal structure of the Lorenz attractor and of the inertial manifold for the Cahn–Hilliard-type partial differential equation.
The Advanced Very High Resolution Radiometer Pathfinder Atmosphere (PATMOS) Climate Dataset: A Resource for Climate Research
A Resource for Climate Research
As part of the joint National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) Pathfinder program, the NOAA National Environmental Satellite, Data, and Information Service (NESDIS) has created a research-quality global atmospheric dataset through the reprocessing of Advanced Very High Resolution Radiometer (AVHRR) observations since 1981. The AVHRR is an imaging radiometer that flies on NOAA polar-orbiting operational environmental satellites (POES) measuring radiation reflected and emitted by the earth in five spectral channels. Raw AVHRR observations were recalibrated using a vicarious calibration technique for the reflectance channels and an appropriate treatment of the nonlinearity of the infrared channels. The observations are analyzed in the Pathfinder Atmosphere (PATMOS) project to obtain statistics of channel radiances, cloud amount, top of the atmosphere radiation budget, and aerosol optical thickness over ocean. The radiances and radiation budget components are determined for clear-sky and all-sky conditions. The output products are generated on a quasi-equalarea grid with an approximate 110 km × 110 km spatial resolution and twice-a-day temporal resolution, and averaged over 5-day (pentad) and monthly time periods. PATMOS data span the period from September 1981 through June 2001. Analyses show that the PATMOS data in their current archived form are sufficiently accurate for studies of the interaction of clouds and aerosol with solar and terrestrial radiation, and of climatic phenomena with large signals (e.g., the annual cycle, monsoons, ENSOs, or major volcanic eruptions). Global maps of the annual average of selected products are displayed to illustrate the capability of the dataset to depict the climatological fields and the spatial detail and relationships between the fields, further demonstrating how PATMOS is a unique resource for climate studies. Smaller climate signals, such as those associated with global warming, may be more difficult to detect due to the presence of artifacts in the time series of the products. Principally, these are caused by the drift of each satellite's observation time over its mission. A statistical method, which removes most of these artifacts, is briefly discussed. Quality of the products is assessed by comparing the adjusted monthly mean time series for each product with those derived from independent satellite observations. The PATMOS dataset for the monthly means is accessible at www.saa.noaa.gov/.
As part of the joint National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) Pathfinder program, the NOAA National Environmental Satellite, Data, and Information Service (NESDIS) has created a research-quality global atmospheric dataset through the reprocessing of Advanced Very High Resolution Radiometer (AVHRR) observations since 1981. The AVHRR is an imaging radiometer that flies on NOAA polar-orbiting operational environmental satellites (POES) measuring radiation reflected and emitted by the earth in five spectral channels. Raw AVHRR observations were recalibrated using a vicarious calibration technique for the reflectance channels and an appropriate treatment of the nonlinearity of the infrared channels. The observations are analyzed in the Pathfinder Atmosphere (PATMOS) project to obtain statistics of channel radiances, cloud amount, top of the atmosphere radiation budget, and aerosol optical thickness over ocean. The radiances and radiation budget components are determined for clear-sky and all-sky conditions. The output products are generated on a quasi-equalarea grid with an approximate 110 km × 110 km spatial resolution and twice-a-day temporal resolution, and averaged over 5-day (pentad) and monthly time periods. PATMOS data span the period from September 1981 through June 2001. Analyses show that the PATMOS data in their current archived form are sufficiently accurate for studies of the interaction of clouds and aerosol with solar and terrestrial radiation, and of climatic phenomena with large signals (e.g., the annual cycle, monsoons, ENSOs, or major volcanic eruptions). Global maps of the annual average of selected products are displayed to illustrate the capability of the dataset to depict the climatological fields and the spatial detail and relationships between the fields, further demonstrating how PATMOS is a unique resource for climate studies. Smaller climate signals, such as those associated with global warming, may be more difficult to detect due to the presence of artifacts in the time series of the products. Principally, these are caused by the drift of each satellite's observation time over its mission. A statistical method, which removes most of these artifacts, is briefly discussed. Quality of the products is assessed by comparing the adjusted monthly mean time series for each product with those derived from independent satellite observations. The PATMOS dataset for the monthly means is accessible at www.saa.noaa.gov/.
