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- Author or Editor: C. L. Smith x
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Abstract
Low-level, ATS-3 satellite wind estimates are compared with values of wind direction and speed interpolated from analyses based on research aircraft observations of a synoptic tropical wave of moderate intensity on 26 July 1969 during BOMFX. The data were stratified according to whether a satellite estimate was positioned in one of three regions; namely, east or west of the wave trough or north of the disturbance center. When cloud and analysis vector magnitude deviations were computed, regional differences became apparent. These differences are attributed to the physical behavior of the cloud targets tracked under the influence of the surrounding large-scale environment.
Abstract
Low-level, ATS-3 satellite wind estimates are compared with values of wind direction and speed interpolated from analyses based on research aircraft observations of a synoptic tropical wave of moderate intensity on 26 July 1969 during BOMFX. The data were stratified according to whether a satellite estimate was positioned in one of three regions; namely, east or west of the wave trough or north of the disturbance center. When cloud and analysis vector magnitude deviations were computed, regional differences became apparent. These differences are attributed to the physical behavior of the cloud targets tracked under the influence of the surrounding large-scale environment.
Abstract
Cloud altitudes specified from the Infrared Temperature Profile Radiometer on the Nimbus 5 satellite are compared with simultaneous observations by radiosonde and ground-based ranging measurements conducted with the lidar system at CSIRO in Aspendale, Victoria, Australia, during September 1976. The results show that the cloud altitudes deduced by the CO2 channel absorption method are in general agreement with the lidar and radiosonde determinations, regardless of the cloud opacity and amount.
Abstract
Cloud altitudes specified from the Infrared Temperature Profile Radiometer on the Nimbus 5 satellite are compared with simultaneous observations by radiosonde and ground-based ranging measurements conducted with the lidar system at CSIRO in Aspendale, Victoria, Australia, during September 1976. The results show that the cloud altitudes deduced by the CO2 channel absorption method are in general agreement with the lidar and radiosonde determinations, regardless of the cloud opacity and amount.
Abstract
A multiple-parameter model has been formulated to estimate precipitable water profiles above the standard pressure levels from the satellite infrared spectrometer B (SIRS–B) radiation observations taken from the Nimbus 4 satellite. The method was verified with coincident radiosonde data. The relative error of SIRS-derived precipitable water above the 1000-mb level was approximately 20 percent. The 532-cm−1 water vapor channel alone explained 72 percent of the variance of the precipitable water. This method was used to specify the optimum SIRS–B spectral intervals for future water vapor sounding.
Abstract
A multiple-parameter model has been formulated to estimate precipitable water profiles above the standard pressure levels from the satellite infrared spectrometer B (SIRS–B) radiation observations taken from the Nimbus 4 satellite. The method was verified with coincident radiosonde data. The relative error of SIRS-derived precipitable water above the 1000-mb level was approximately 20 percent. The 532-cm−1 water vapor channel alone explained 72 percent of the variance of the precipitable water. This method was used to specify the optimum SIRS–B spectral intervals for future water vapor sounding.
Abstract
An attempt is made to resolve the difference in Nimbus II satellite-observed and calculated atmospheric radiances in the 6.7-μm water vapor band. Regression equations were calculated to relate the Nimbus II MRIR (medium resolution infrared radiometer) water vapor channel radiance measurements to radiances calculated assuming different values of the effective water vapor absorption coefficient. A value of log10 L *=2.4, where L * is the effective water vapor channel absorption coefficient, produced the maximum correlation between computed and observed values. The regression equation for this water vapor absorption co-efficient may be used to recalibrate the Nimbus II 6.7-μm radiance observations.
The radiance upwelling from the atmosphere in the 6.4–6.9 μm spectral region (the 6.7- μm channel of Nimbus II) arises mainly from the 200–600 mb atmospheric layer. However, assuming that the water vapor profile can be represented by a power function, the entire water vapor distribution can be estimated from these radiance observations. Results from 250 cases showed that a power law exponent of 3.9 yielded the best correspondence between radiance-calculated and radiosonde-observed water vapor profiles. RMS mixing ratio errors varied from 0.03 gm kg−1 at 300 mb to 1.3 gm kg−1 at 850 mb, yielding relative errors of 10–20%. The mixing ratio discrepancies in the sensed layer (200–600 mb) are close to the errors of radiosonde observations. The rms difference between the radiance-calculated and radiosonde-observed total precipitable water was 0.6 gm cm−2. The relatively large total precipitable water discrepancy is caused by the fact that the 6.7-μm radiance observations are relatively insensitive to the lower atmosphere where the majority of water vapor exists and where the variation of water vapor is largest.
Abstract
An attempt is made to resolve the difference in Nimbus II satellite-observed and calculated atmospheric radiances in the 6.7-μm water vapor band. Regression equations were calculated to relate the Nimbus II MRIR (medium resolution infrared radiometer) water vapor channel radiance measurements to radiances calculated assuming different values of the effective water vapor absorption coefficient. A value of log10 L *=2.4, where L * is the effective water vapor channel absorption coefficient, produced the maximum correlation between computed and observed values. The regression equation for this water vapor absorption co-efficient may be used to recalibrate the Nimbus II 6.7-μm radiance observations.
The radiance upwelling from the atmosphere in the 6.4–6.9 μm spectral region (the 6.7- μm channel of Nimbus II) arises mainly from the 200–600 mb atmospheric layer. However, assuming that the water vapor profile can be represented by a power function, the entire water vapor distribution can be estimated from these radiance observations. Results from 250 cases showed that a power law exponent of 3.9 yielded the best correspondence between radiance-calculated and radiosonde-observed water vapor profiles. RMS mixing ratio errors varied from 0.03 gm kg−1 at 300 mb to 1.3 gm kg−1 at 850 mb, yielding relative errors of 10–20%. The mixing ratio discrepancies in the sensed layer (200–600 mb) are close to the errors of radiosonde observations. The rms difference between the radiance-calculated and radiosonde-observed total precipitable water was 0.6 gm cm−2. The relatively large total precipitable water discrepancy is caused by the fact that the 6.7-μm radiance observations are relatively insensitive to the lower atmosphere where the majority of water vapor exists and where the variation of water vapor is largest.
Abstract
TOPEX/Poseidon (T/P) altimeter data over the period 1992–98 have been analyzed to examine annual variability of sea surface elevation and currents over the Scotian Shelf and Slope. A modified orthogonal response analysis is used to derive the annual cycle while simultaneously removing the residual tides and other dynamical processes at the appropriate T/P alias periods. An evaluation of the M 2 and K 1 alias variations is carried out, suggesting notable tidal correction errors off Cape Cod and over Georges Bank. The along-track sea surface slopes, which represent surface geostrophic current components normal to the track, are estimated on selected T/P ascending and descending ground tracks. The annual altimetric sea level harmonic is compared with steric height anomalies and wind-driven setup. The comparison indicates that the altimetric sea surface elevation variability is dominated by the baroclinic (and associated barotropic) component and supplemented by the wind-driven and remotely forced components. Altimetric elevations agree favorably with tide-gauge data at Halifax, Nova Scotia, and well with those at St. John's, Newfoundland. Wintertime intensification of the shelf-break flows is indicated in the altimetric surface currents, consistent with the solutions of regional diagnostic model forced by baroclinicity and boundary flows. Altimetric results clearly demonstrate seasonal variability of northeastward slope current stronger in fall and winter and weaker in spring and summer, which is less well resolved in the model. Assimilation of altimetric data into regional circulation models could help improve their prognostic ability to hindcast and nowcast seasonal variability of shelf-edge and slope water circulation. This study also implies a demand for better shelf tidal models to detide altimetric data for extraction of semiannual and shorter-period processes.
Abstract
TOPEX/Poseidon (T/P) altimeter data over the period 1992–98 have been analyzed to examine annual variability of sea surface elevation and currents over the Scotian Shelf and Slope. A modified orthogonal response analysis is used to derive the annual cycle while simultaneously removing the residual tides and other dynamical processes at the appropriate T/P alias periods. An evaluation of the M 2 and K 1 alias variations is carried out, suggesting notable tidal correction errors off Cape Cod and over Georges Bank. The along-track sea surface slopes, which represent surface geostrophic current components normal to the track, are estimated on selected T/P ascending and descending ground tracks. The annual altimetric sea level harmonic is compared with steric height anomalies and wind-driven setup. The comparison indicates that the altimetric sea surface elevation variability is dominated by the baroclinic (and associated barotropic) component and supplemented by the wind-driven and remotely forced components. Altimetric elevations agree favorably with tide-gauge data at Halifax, Nova Scotia, and well with those at St. John's, Newfoundland. Wintertime intensification of the shelf-break flows is indicated in the altimetric surface currents, consistent with the solutions of regional diagnostic model forced by baroclinicity and boundary flows. Altimetric results clearly demonstrate seasonal variability of northeastward slope current stronger in fall and winter and weaker in spring and summer, which is less well resolved in the model. Assimilation of altimetric data into regional circulation models could help improve their prognostic ability to hindcast and nowcast seasonal variability of shelf-edge and slope water circulation. This study also implies a demand for better shelf tidal models to detide altimetric data for extraction of semiannual and shorter-period processes.
Abstract
A seven-channel Multi-spectral Scanning Radiometer (MSR) was flown aboard the NASA Convair-990 aircraft during the GARP Atlantic Tropical Experiment (GATE) from June–September, 1974. The radiometer measures the total shortwave (0.2–5 μm) and longwave (5–50 μm) components of radiation and the radiation in specific absorption band and window regions that modulate the total radiation flux. Measurements of the angular distribution of radiation, including the upward and downward components, were obtained. The principal scientific objective of the MSR experiment was to obtain the atmospheric absorption data required for precise computations of radiative heating profiles from atmospheric state parameters. The method used to construct the infrared radiation heating computational model based on in situ GATE MSR observations is described. Radiative heating profiles computed with this model for both cloudy and cloudless atmospheres were compared with direct observations by flux radiometers and with profiles computed with the Rodgers and Walshaw model. The results indicate that the empirically based computational model should provide tropospheric radiative heating profiles sufficiently accurate for diagnostic and prognostic applications of GATE data.
Abstract
A seven-channel Multi-spectral Scanning Radiometer (MSR) was flown aboard the NASA Convair-990 aircraft during the GARP Atlantic Tropical Experiment (GATE) from June–September, 1974. The radiometer measures the total shortwave (0.2–5 μm) and longwave (5–50 μm) components of radiation and the radiation in specific absorption band and window regions that modulate the total radiation flux. Measurements of the angular distribution of radiation, including the upward and downward components, were obtained. The principal scientific objective of the MSR experiment was to obtain the atmospheric absorption data required for precise computations of radiative heating profiles from atmospheric state parameters. The method used to construct the infrared radiation heating computational model based on in situ GATE MSR observations is described. Radiative heating profiles computed with this model for both cloudy and cloudless atmospheres were compared with direct observations by flux radiometers and with profiles computed with the Rodgers and Walshaw model. The results indicate that the empirically based computational model should provide tropospheric radiative heating profiles sufficiently accurate for diagnostic and prognostic applications of GATE data.
Abstract
This paper describes and compares various methods for calculating radar reflectivity factors in numerical cloud models that use bulk methods to characterize the precipitation processes. Equations sensitive to changes in the parameters of the particle size distributions are favored because they allow simulation of phenomena causing such changes. Marshall-Palmer-type functions are established to represent hailstone size distributions because the previously available distributions lead to implausibly large reflectivity factors. Simplified equations are developed for calculating reflectivity factors for both dry and wet hail. Some examples are given of the use of the various equations in numerical cloud models.
Abstract
This paper describes and compares various methods for calculating radar reflectivity factors in numerical cloud models that use bulk methods to characterize the precipitation processes. Equations sensitive to changes in the parameters of the particle size distributions are favored because they allow simulation of phenomena causing such changes. Marshall-Palmer-type functions are established to represent hailstone size distributions because the previously available distributions lead to implausibly large reflectivity factors. Simplified equations are developed for calculating reflectivity factors for both dry and wet hail. Some examples are given of the use of the various equations in numerical cloud models.
Abstract
The local, linear, least squares derivative (LLSD) approach to radar analysis is a method of quantifying gradients in radar data by fitting a least squares plane to a neighborhood of range bins and finding its slope. When applied to radial velocity fields, for example, LLSD yields part of the azimuthal (rotational) and radial (divergent) components of horizontal shear, which, under certain geometric assumptions, estimate one-half of the two-dimensional vertical vorticity and horizontal divergence equations, respectively. Recent advances in computational capacity as well as increased usage of LLSD products by the meteorological community have motivated an overhaul of the LLSD methodology’s application to radar data. This paper documents the mathematical foundation of the updated LLSD approach, including a complete derivation of its equation set, discussion of its limitations, and considerations for other types of implementation. In addition, updated azimuthal shear calculations are validated against theoretical vorticity using simulated circulations. Applications to nontraditional radar data and new applications to nonvelocity radar data including reflectivity at horizontal polarization, spectrum width, and polarimetric moments are also explored. These LLSD gradient calculations may be leveraged to identify and interrogate a wide variety of severe weather phenomena, either directly by operational forecasters or indirectly as part of future automated algorithms.
Abstract
The local, linear, least squares derivative (LLSD) approach to radar analysis is a method of quantifying gradients in radar data by fitting a least squares plane to a neighborhood of range bins and finding its slope. When applied to radial velocity fields, for example, LLSD yields part of the azimuthal (rotational) and radial (divergent) components of horizontal shear, which, under certain geometric assumptions, estimate one-half of the two-dimensional vertical vorticity and horizontal divergence equations, respectively. Recent advances in computational capacity as well as increased usage of LLSD products by the meteorological community have motivated an overhaul of the LLSD methodology’s application to radar data. This paper documents the mathematical foundation of the updated LLSD approach, including a complete derivation of its equation set, discussion of its limitations, and considerations for other types of implementation. In addition, updated azimuthal shear calculations are validated against theoretical vorticity using simulated circulations. Applications to nontraditional radar data and new applications to nonvelocity radar data including reflectivity at horizontal polarization, spectrum width, and polarimetric moments are also explored. These LLSD gradient calculations may be leveraged to identify and interrogate a wide variety of severe weather phenomena, either directly by operational forecasters or indirectly as part of future automated algorithms.
Abstract
In Part 1 of the two-part paper, we present an analysis of a portion of a tropical wave in the BOMEX Phase IV ship network on a much smaller sale than normally attempted using conventional observations and data from a number of research aircraft. The results indicate the existence of a strong mesoscale cyclone with a lifetime of less than 12 h within the synoptic-scale wave. At the time of maximum data density, the analysis time, the system was near its maximum intensity.
Abstract
In Part 1 of the two-part paper, we present an analysis of a portion of a tropical wave in the BOMEX Phase IV ship network on a much smaller sale than normally attempted using conventional observations and data from a number of research aircraft. The results indicate the existence of a strong mesoscale cyclone with a lifetime of less than 12 h within the synoptic-scale wave. At the time of maximum data density, the analysis time, the system was near its maximum intensity.
