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- Author or Editor: G. Russell x
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Abstract
A number of investigators have advanced the thesis that weather information has (or accrues) economic value because it makes possible “better” management decisions in a weather-sensitive process. A simulation model approach is used to modify this thesis, and to illustrate the necessity for the decision-maker to have a sufficiently precise method for translating weather information into operational terms.
Abstract
A number of investigators have advanced the thesis that weather information has (or accrues) economic value because it makes possible “better” management decisions in a weather-sensitive process. A simulation model approach is used to modify this thesis, and to illustrate the necessity for the decision-maker to have a sufficiently precise method for translating weather information into operational terms.
Abstract
A statistical analysis is performed of the tropical cyclone forecast advisories and bulletins issued by the Eastern Pacific Hurricane Center, Redwood City, California, during the 1971–78 seasons. Each forecast is normalized by comparison with the performance of an objective model (EPCLPR) that is based on climatology and persistence. The normalized official forecasts show an improvement in skill during the period. This improvement is attributed to the availability of satellite data for determining the storm positions and to the introduction of objective forecast techniques. Forecast errors are related to a number of storm-related variables, such as initial latitude and longitude and deviations from the climatological track. Stepwise discriminant analysis is used to classify the forecasts into groups of above or below average errors.
Abstract
A statistical analysis is performed of the tropical cyclone forecast advisories and bulletins issued by the Eastern Pacific Hurricane Center, Redwood City, California, during the 1971–78 seasons. Each forecast is normalized by comparison with the performance of an objective model (EPCLPR) that is based on climatology and persistence. The normalized official forecasts show an improvement in skill during the period. This improvement is attributed to the availability of satellite data for determining the storm positions and to the introduction of objective forecast techniques. Forecast errors are related to a number of storm-related variables, such as initial latitude and longitude and deviations from the climatological track. Stepwise discriminant analysis is used to classify the forecasts into groups of above or below average errors.
Abstract
A 10 year (1960–69) sample of observations in western North Pacific tropical cyclones over open ocean was used to derive statistical regression equations to forecast the maximum wind speed for 24, 48 and 72 h periods. Stratification of the dependent data by latitude bands, by months, and by maximum intensity were tested with both five-predictor and ten-predictor equations. An independent sample of tropical cyclones (July, August and September of 1955–59) was used to test the derived regression equations. Verification was in terms of the relative forecast error according to the acceptability criteria set by the Joint Typhoon Warning Center, Guam.
Equations derived from a combined dependent sample of July, August and September storms stratified into two bands (one north, one south of 20°N) produced forecasts which were equivalent or superior to equations derived from storms stratified by months or in three 10° bands from 5°N to 35°N. These two five-predictor equations for the 24 h period were also superior to equations derived for storms within the classes ≤65, 66–100 and ≥101 kt. Although not tested with a homogeneous set of forecasts using operational data rather than post-season data, the objective forecast technique appears to give results comparable to or better than recent official intensity forecasts, especially for the 72 h interval.
Abstract
A 10 year (1960–69) sample of observations in western North Pacific tropical cyclones over open ocean was used to derive statistical regression equations to forecast the maximum wind speed for 24, 48 and 72 h periods. Stratification of the dependent data by latitude bands, by months, and by maximum intensity were tested with both five-predictor and ten-predictor equations. An independent sample of tropical cyclones (July, August and September of 1955–59) was used to test the derived regression equations. Verification was in terms of the relative forecast error according to the acceptability criteria set by the Joint Typhoon Warning Center, Guam.
Equations derived from a combined dependent sample of July, August and September storms stratified into two bands (one north, one south of 20°N) produced forecasts which were equivalent or superior to equations derived from storms stratified by months or in three 10° bands from 5°N to 35°N. These two five-predictor equations for the 24 h period were also superior to equations derived for storms within the classes ≤65, 66–100 and ≥101 kt. Although not tested with a homogeneous set of forecasts using operational data rather than post-season data, the objective forecast technique appears to give results comparable to or better than recent official intensity forecasts, especially for the 72 h interval.
Abstract
In this study, four different meteorological models, one diagnostic and three prognostic, are used to develop meteorological inputs for a photochemical model, as applied to the peninsula of Athens, Greece. The comparison of meteorological models results pointed out significant differences in the calculated wind fields, mainly during the night period. These differences are linked to specific aspects of the models, such as model vertical resolution, hydrostatic versus nonhydrostatic formulation, and numerical diffusion. During the day hours, models produce quite similar wind fields, which agree correctly with the available observations related to the Athens center area. Using the different wind fields as input to a photochemical air quality model led to similar urban ozone levels in the Athens area. Outside of the city, the different wind fields transport the urban plume in different directions in a range of 50°. The more primary pollutants, for example CO and NO2 concentrations, varied significantly due to the different wind velocities predicted by meteorological models. The effect of the atmospheric deposition can be near zero or can go up to 25% for ozone and to 45% for NO2. The determination of the most appropriate wind field to be used for the photochemical modeling would have required a more comprehensive set of observed data. Therefore, when data are scarce, it may be recommended to use different wind field modeling techniques to assess the sensitivity and the robustness of the predicted concentrations.
Abstract
In this study, four different meteorological models, one diagnostic and three prognostic, are used to develop meteorological inputs for a photochemical model, as applied to the peninsula of Athens, Greece. The comparison of meteorological models results pointed out significant differences in the calculated wind fields, mainly during the night period. These differences are linked to specific aspects of the models, such as model vertical resolution, hydrostatic versus nonhydrostatic formulation, and numerical diffusion. During the day hours, models produce quite similar wind fields, which agree correctly with the available observations related to the Athens center area. Using the different wind fields as input to a photochemical air quality model led to similar urban ozone levels in the Athens area. Outside of the city, the different wind fields transport the urban plume in different directions in a range of 50°. The more primary pollutants, for example CO and NO2 concentrations, varied significantly due to the different wind velocities predicted by meteorological models. The effect of the atmospheric deposition can be near zero or can go up to 25% for ozone and to 45% for NO2. The determination of the most appropriate wind field to be used for the photochemical modeling would have required a more comprehensive set of observed data. Therefore, when data are scarce, it may be recommended to use different wind field modeling techniques to assess the sensitivity and the robustness of the predicted concentrations.
Abstract
During the passage of hurricane Norbert in 1984, the Hurricane Research Division of NOAA conducted a Planetary Boundary Layer Experiment that included the deployment of Airborne eXpendable Current Profilers (AXCP). A total of. 16 AXCPs provided for the fist time high-resolution vertical profiles of currents and temperatures in hurricane wind conditions. This study focuses on the vertical structure of the near-inertial baroclinic current excited by the passage of this hurricane.
The transient hurricane-induced currents are isolated from the AXCP profiles in Norbert by subtracting a spatially-averaged current. Near the center of hurricane Norbert, the WKBJ-scaled vertical wavenumber spectra are a decade greater than the Garrett-Munk spectra (GM75). The fist ten linear, baroclinic free modes are calculated from the spatially-averaged Brunt–Väisälä frequency. To allow a more direct comparison with the AXCP observations in the current wind regime, the near-inertial response for the three dimensional velocities is simulated by superposing a hurricane-like wind stress field onto the first ten baroclinic modes. About 70% of the current variance in hurricane Norbert can be explained by a sum of only the first four near-inertial modes. Most of the ocean current variability can be accounted for by the wind stress curl, although the direct effect of the wind stress and the soon divergence do contribute to the observed current variance within 30–60 km from the storm. However, these last two effects rapidly diminish after one inertial period. Although the energy input by the hurricane forcing is spread over all of the vertical wavelengths, most of the energy is contained in the gravest four vertical modes which then govern the dynamics in the wake region.
Abstract
During the passage of hurricane Norbert in 1984, the Hurricane Research Division of NOAA conducted a Planetary Boundary Layer Experiment that included the deployment of Airborne eXpendable Current Profilers (AXCP). A total of. 16 AXCPs provided for the fist time high-resolution vertical profiles of currents and temperatures in hurricane wind conditions. This study focuses on the vertical structure of the near-inertial baroclinic current excited by the passage of this hurricane.
The transient hurricane-induced currents are isolated from the AXCP profiles in Norbert by subtracting a spatially-averaged current. Near the center of hurricane Norbert, the WKBJ-scaled vertical wavenumber spectra are a decade greater than the Garrett-Munk spectra (GM75). The fist ten linear, baroclinic free modes are calculated from the spatially-averaged Brunt–Väisälä frequency. To allow a more direct comparison with the AXCP observations in the current wind regime, the near-inertial response for the three dimensional velocities is simulated by superposing a hurricane-like wind stress field onto the first ten baroclinic modes. About 70% of the current variance in hurricane Norbert can be explained by a sum of only the first four near-inertial modes. Most of the ocean current variability can be accounted for by the wind stress curl, although the direct effect of the wind stress and the soon divergence do contribute to the observed current variance within 30–60 km from the storm. However, these last two effects rapidly diminish after one inertial period. Although the energy input by the hurricane forcing is spread over all of the vertical wavelengths, most of the energy is contained in the gravest four vertical modes which then govern the dynamics in the wake region.
Abstract
Hemispherical backscattering cross sections σb of spherical particles are calculated using a recently derived analytic expression. Results are compared with σb values obtained by numerical integration. It is found that the analytic formula gives exact values of the hemispherical backscattering cross sections and also saves computer time. The behavior of σb in the limits of very small and very large spheres is discussed. As an aid in utilizing simple models of climate change due to aerosols, the percentage of incident solar radiation scattered into the backward hemisphere is calculated for a range of particle sizes and complex refractive indices. Similar results are also presented for the ratio of absorption to hemispheric backscattering, a critical parameter in many aerosol climate models.
Abstract
Hemispherical backscattering cross sections σb of spherical particles are calculated using a recently derived analytic expression. Results are compared with σb values obtained by numerical integration. It is found that the analytic formula gives exact values of the hemispherical backscattering cross sections and also saves computer time. The behavior of σb in the limits of very small and very large spheres is discussed. As an aid in utilizing simple models of climate change due to aerosols, the percentage of incident solar radiation scattered into the backward hemisphere is calculated for a range of particle sizes and complex refractive indices. Similar results are also presented for the ratio of absorption to hemispheric backscattering, a critical parameter in many aerosol climate models.
Abstract
This paper describes a comprehensive set of fully automated quality assurance (QA) procedures for observations of daily surface temperature, precipitation, snowfall, and snow depth. The QA procedures are being applied operationally to the Global Historical Climatology Network (GHCN)-Daily dataset. Since these data are used for analyzing and monitoring variations in extremes, the QA system is designed to detect as many errors as possible while maintaining a low probability of falsely identifying true meteorological events as erroneous. The system consists of 19 carefully evaluated tests that detect duplicate data, climatological outliers, and various inconsistencies (internal, temporal, and spatial). Manual review of random samples of the values flagged as errors is used to set the threshold for each procedure such that its false-positive rate, or fraction of valid values identified as errors, is minimized. In addition, the tests are arranged in a deliberate sequence in which the performance of the later checks is enhanced by the error detection capabilities of the earlier tests. Based on an assessment of each individual check and a final evaluation for each element, the system identifies 3.6 million (0.24%) of the more than 1.5 billion maximum/minimum temperature, precipitation, snowfall, and snow depth values in GHCN-Daily as errors, has a false-positive rate of 1%−2%, and is effective at detecting both the grossest errors as well as more subtle inconsistencies among elements.
Abstract
This paper describes a comprehensive set of fully automated quality assurance (QA) procedures for observations of daily surface temperature, precipitation, snowfall, and snow depth. The QA procedures are being applied operationally to the Global Historical Climatology Network (GHCN)-Daily dataset. Since these data are used for analyzing and monitoring variations in extremes, the QA system is designed to detect as many errors as possible while maintaining a low probability of falsely identifying true meteorological events as erroneous. The system consists of 19 carefully evaluated tests that detect duplicate data, climatological outliers, and various inconsistencies (internal, temporal, and spatial). Manual review of random samples of the values flagged as errors is used to set the threshold for each procedure such that its false-positive rate, or fraction of valid values identified as errors, is minimized. In addition, the tests are arranged in a deliberate sequence in which the performance of the later checks is enhanced by the error detection capabilities of the earlier tests. Based on an assessment of each individual check and a final evaluation for each element, the system identifies 3.6 million (0.24%) of the more than 1.5 billion maximum/minimum temperature, precipitation, snowfall, and snow depth values in GHCN-Daily as errors, has a false-positive rate of 1%−2%, and is effective at detecting both the grossest errors as well as more subtle inconsistencies among elements.
Abstract
The interannual variability of the tropical tropopause region between 14 and 18 km is examined using observations of convection, winds, and tropopause temperatures from reanalyses and water vapor from satellites. This variability is compared to a simulation using the Community Climate Model version 3 (CCM3) general circulation model forced by observed sea surface temperatures. A coherent picture of the effect of the El Niño–Southern Oscillation (ENSO) on the tropopause region is presented in the NCEP–NCAR reanalyses and CCM3. ENSO modifies convection in the Tropics, and the temperature and circulation of the tropical tropopause region, in agreement with idealized models of tropical heating. CCM3 reproduces most details of these changes, but not the zonal mean temperature variations present in the analysis fields, which are not related to ENSO. ENSO also forces significant changes in observed and simulated water vapor fields. In the upper troposphere water vapor is at maximum near convection, while in the tropopause region water vapor is at minimum in the regions of convection and surrounding it. Convection, cirrus clouds, temperatures, and transport are all linked to describe the water vapor distribution and highlight the role of transport in the tropopause region.
Abstract
The interannual variability of the tropical tropopause region between 14 and 18 km is examined using observations of convection, winds, and tropopause temperatures from reanalyses and water vapor from satellites. This variability is compared to a simulation using the Community Climate Model version 3 (CCM3) general circulation model forced by observed sea surface temperatures. A coherent picture of the effect of the El Niño–Southern Oscillation (ENSO) on the tropopause region is presented in the NCEP–NCAR reanalyses and CCM3. ENSO modifies convection in the Tropics, and the temperature and circulation of the tropical tropopause region, in agreement with idealized models of tropical heating. CCM3 reproduces most details of these changes, but not the zonal mean temperature variations present in the analysis fields, which are not related to ENSO. ENSO also forces significant changes in observed and simulated water vapor fields. In the upper troposphere water vapor is at maximum near convection, while in the tropopause region water vapor is at minimum in the regions of convection and surrounding it. Convection, cirrus clouds, temperatures, and transport are all linked to describe the water vapor distribution and highlight the role of transport in the tropopause region.
Abstract
Numerical simulations are used to study transitions between boundary layer rolls and more cellular convective structures observed during a lake-effect snow event over Lake Michigan on 17 December 1983. Weak lake-effect nonroll convection was observed near the eastern (downwind) shore preceding passage of a secondary cold front. After frontal passage horizontal wind speeds in the convective boundary layer increased, with subsequent development of linear convective patterns. Thereafter the convective pattern became more three-dimensional as low-level wind speeds decreased. Little directional shear was observed in any of the wind profiles. Numerical simulations with the Advanced Regional Prediction System model were initialized with an upwind sounding and radar-derived wind profiles corresponding to each of the three convective structure regimes. Model-derived reflectivity fields were in good agreement with the observed regimes. These simulations differed primarily in the initial wind speed profiles, and suggest that wind speed and shear in the lower boundary layer are critical in determining the linearity of convection. Simulation with an upwind-overlake wind profile, with strong low-level winds, produced the most linear model reflectivity structure. Fluxes and measures of shear-to-buoyancy ratio for this case were comparable to observations.
Model sensitivity tests were conducted to determine the importance of low-level wind speed and speed shear in determining the linearity of convection. Results are consistent with trends expected from ratios of buoyancy to shear (but not proposed numerical threshold values). Eliminating all directional shear from the initial wind profile for the most linear case did not reduce the degree of linearity, thus showing that directional shear is not a requirement for rolls in lake-effect convection. Elimination of clouds (principally latent heating) reduced the vertical velocities by about 50%. It was found that variations in wind speed shear below 200-m height played a major role in determining the degree of linearity of the convection.
Abstract
Numerical simulations are used to study transitions between boundary layer rolls and more cellular convective structures observed during a lake-effect snow event over Lake Michigan on 17 December 1983. Weak lake-effect nonroll convection was observed near the eastern (downwind) shore preceding passage of a secondary cold front. After frontal passage horizontal wind speeds in the convective boundary layer increased, with subsequent development of linear convective patterns. Thereafter the convective pattern became more three-dimensional as low-level wind speeds decreased. Little directional shear was observed in any of the wind profiles. Numerical simulations with the Advanced Regional Prediction System model were initialized with an upwind sounding and radar-derived wind profiles corresponding to each of the three convective structure regimes. Model-derived reflectivity fields were in good agreement with the observed regimes. These simulations differed primarily in the initial wind speed profiles, and suggest that wind speed and shear in the lower boundary layer are critical in determining the linearity of convection. Simulation with an upwind-overlake wind profile, with strong low-level winds, produced the most linear model reflectivity structure. Fluxes and measures of shear-to-buoyancy ratio for this case were comparable to observations.
Model sensitivity tests were conducted to determine the importance of low-level wind speed and speed shear in determining the linearity of convection. Results are consistent with trends expected from ratios of buoyancy to shear (but not proposed numerical threshold values). Eliminating all directional shear from the initial wind profile for the most linear case did not reduce the degree of linearity, thus showing that directional shear is not a requirement for rolls in lake-effect convection. Elimination of clouds (principally latent heating) reduced the vertical velocities by about 50%. It was found that variations in wind speed shear below 200-m height played a major role in determining the degree of linearity of the convection.
Abstract
Three drifting buoys were successfully air-dropped ahead of Hurricane Josephine. This deployment resulted in detailed simultaneous measurements of surface wind speed, surface pressure and subsurface ocean temperature during and subsequent to storm passage. This represents the first time that such a self-consistent data set of surface conditions within a tropical cyclone has been collected. Subsequent NOAA research overflights of the buoys, as part of a hurricane planetary boundary-layer experiment, showed that aircraft wind speeds, extrapolated to the 20 m level, agreed to within ±2 m s−1, pressures agreed to within ±1 mb, and sea-surface temperatures agreed to within ±0.8°C of the buoy values. Ratios of buoy peak 1 min wind (sustained wind) to one-half h mean wind > 1.3 were found to coincide with eyewall and principal rainband features.
Buoy trajectories and subsurface temperature measurements revealed the existence of a series of mesoscale eddies in the subtropical front. Buoy data revealed storm-generated, inertia-gravity-wave motions superposed upon mean current fields, which reached a maximum surface speed > 1.2 m s−1 immediately following storm passage. A maximum mixed-layer-temperature decrease of 1.8°C was observed to the right of the storm path. A temperature increase of 3.5°C at 100 m and subsequent decrease of 4.8°C following storm passage indicated a combination of turbulent mixing, upwelling and horizontal advection processes.
Abstract
Three drifting buoys were successfully air-dropped ahead of Hurricane Josephine. This deployment resulted in detailed simultaneous measurements of surface wind speed, surface pressure and subsurface ocean temperature during and subsequent to storm passage. This represents the first time that such a self-consistent data set of surface conditions within a tropical cyclone has been collected. Subsequent NOAA research overflights of the buoys, as part of a hurricane planetary boundary-layer experiment, showed that aircraft wind speeds, extrapolated to the 20 m level, agreed to within ±2 m s−1, pressures agreed to within ±1 mb, and sea-surface temperatures agreed to within ±0.8°C of the buoy values. Ratios of buoy peak 1 min wind (sustained wind) to one-half h mean wind > 1.3 were found to coincide with eyewall and principal rainband features.
Buoy trajectories and subsurface temperature measurements revealed the existence of a series of mesoscale eddies in the subtropical front. Buoy data revealed storm-generated, inertia-gravity-wave motions superposed upon mean current fields, which reached a maximum surface speed > 1.2 m s−1 immediately following storm passage. A maximum mixed-layer-temperature decrease of 1.8°C was observed to the right of the storm path. A temperature increase of 3.5°C at 100 m and subsequent decrease of 4.8°C following storm passage indicated a combination of turbulent mixing, upwelling and horizontal advection processes.
