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- Author or Editor: KEITH W. JOHNSON x
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Abstract
The observed geopotential heights and temperatures (corrected for radiation effects) at the 100-, 50-, 30-, and 10-mb levels from most of the Northern Hemisphere radiosonde stations were compared with objectively analyzed heights and temperatures for February 1969. The 1-mo average root-mean-square (rms) height differences ranged from 51 m at 100 mb to 139 m at 10 mb. The rms temperature differences increased from 1.1°C at 100 mb to 2.9°C at 10 mb. Similar statistics are presented for North America and for different types of instruments.
Abstract
The observed geopotential heights and temperatures (corrected for radiation effects) at the 100-, 50-, 30-, and 10-mb levels from most of the Northern Hemisphere radiosonde stations were compared with objectively analyzed heights and temperatures for February 1969. The 1-mo average root-mean-square (rms) height differences ranged from 51 m at 100 mb to 139 m at 10 mb. The rms temperature differences increased from 1.1°C at 100 mb to 2.9°C at 10 mb. Similar statistics are presented for North America and for different types of instruments.
Abstract
The major stratospheric warming of December 1967–January 1968, which reached its peak nearly 1 mo earlier in the winter than any other major warming of record, is compared with other stratospheric warming events, especially with that of January 1963, through the use of rawinsonde and rocketsonde information. This information is presented in the form of time sections, spatial cross-sections, and constant-pressure synoptic charts at various stratospheric levels for representative dates before the warming and at various stages of its development. Synoptic density charts at 30 and 40 km are presented showing marked changes in stratospheric densities during the warming from both standard atmosphere and nonwarming conditions. Spherical harmonic analyses of height fields are used to show the importance of components of zonal wave number 2 in changes of stratospheric circulation associated with the warming.
Abstract
The major stratospheric warming of December 1967–January 1968, which reached its peak nearly 1 mo earlier in the winter than any other major warming of record, is compared with other stratospheric warming events, especially with that of January 1963, through the use of rawinsonde and rocketsonde information. This information is presented in the form of time sections, spatial cross-sections, and constant-pressure synoptic charts at various stratospheric levels for representative dates before the warming and at various stages of its development. Synoptic density charts at 30 and 40 km are presented showing marked changes in stratospheric densities during the warming from both standard atmosphere and nonwarming conditions. Spherical harmonic analyses of height fields are used to show the importance of components of zonal wave number 2 in changes of stratospheric circulation associated with the warming.
Abstract
The satellite infrared spectrometer aboard Nimbus 3 has provided a new source of temperature data and height data for the atmosphere. Problems of applying these data in synoptic stratospheric analysis are briefly reviewed. It is found that consistent summertime synoptic charts for the Northern Hemisphere (at 50, 30, and 10 mb) may be prepared using a 100-mb objective analysis as a base chart and thicknesses above 100 mb from SIRS retrievals. Some improvement is made possible by use of concurrent wind observations. It is noted that the SIRS observations have yielded a significant improvement in the data base for the stratosphere.
Abstract
The satellite infrared spectrometer aboard Nimbus 3 has provided a new source of temperature data and height data for the atmosphere. Problems of applying these data in synoptic stratospheric analysis are briefly reviewed. It is found that consistent summertime synoptic charts for the Northern Hemisphere (at 50, 30, and 10 mb) may be prepared using a 100-mb objective analysis as a base chart and thicknesses above 100 mb from SIRS retrievals. Some improvement is made possible by use of concurrent wind observations. It is noted that the SIRS observations have yielded a significant improvement in the data base for the stratosphere.
Abstract
Daily 50- and 10-mb. height and temperature values for 3 yr. (1964–1966) are interpolated for specific locations from objectively analyzed charts. Time sections are constructed using these values, and the relationship of the time sections to the sequence of synoptic charts is discussed. Values from weekly 5-, and 2, and 0.4-mb. synoptic analyses (1964–65) are used in making vertical comparisons with the 50- and 10-mb. values.
Monthly means and standard deviations of daily values from these monthly means are calculated and are compared with similar parameters derived directly from data. Comparisons of these statistical parameters are made for three geographical sections: 1) a north-south section near 80°W., 2) an east-west section across North America in middle latitudes, and 3) an east-west section across the Western Hemisphere at high latitudes. Vertical differences in variability and standard deviation are discussed.
Abstract
Daily 50- and 10-mb. height and temperature values for 3 yr. (1964–1966) are interpolated for specific locations from objectively analyzed charts. Time sections are constructed using these values, and the relationship of the time sections to the sequence of synoptic charts is discussed. Values from weekly 5-, and 2, and 0.4-mb. synoptic analyses (1964–65) are used in making vertical comparisons with the 50- and 10-mb. values.
Monthly means and standard deviations of daily values from these monthly means are calculated and are compared with similar parameters derived directly from data. Comparisons of these statistical parameters are made for three geographical sections: 1) a north-south section near 80°W., 2) an east-west section across North America in middle latitudes, and 3) an east-west section across the Western Hemisphere at high latitudes. Vertical differences in variability and standard deviation are discussed.
Abstract
The vertical structure of traveling planetary-scale waves is investigated using spherical harmonics of the geopotential field at levels from 1000 mb. to 10 mb., obtained from ESSA analyses. Fluctuations of the large-scale harmonics are analyzed using vector regression methods.
Westward-moving planetary-scale waves are shown to be present throughout the year at all the levels analyzed, with upward increasing amplitude in winter.
Abstract
The vertical structure of traveling planetary-scale waves is investigated using spherical harmonics of the geopotential field at levels from 1000 mb. to 10 mb., obtained from ESSA analyses. Fluctuations of the large-scale harmonics are analyzed using vector regression methods.
Westward-moving planetary-scale waves are shown to be present throughout the year at all the levels analyzed, with upward increasing amplitude in winter.
Abstract
Two indices are proposed that characterize and quantify the circulation and temperature fields at stratospheric constant-pressure levels. The circulation index is calculated at 60° N. latitude as a normalized difference of the squared amplitudes of wave numbers 2 and 1 of the height field. The temperature index is the mean temperature gradient hetween the North Pole and 60° N.
Comparisons of values of these parameters during several stratospheric warming episodes are utilized to show the difference between small-scale and large-scale warming events. Comparisons of values at different levels lead to the possibility of studying tropospheric-stratospheric interactions during periods of stratospheric warming.
Abstract
Two indices are proposed that characterize and quantify the circulation and temperature fields at stratospheric constant-pressure levels. The circulation index is calculated at 60° N. latitude as a normalized difference of the squared amplitudes of wave numbers 2 and 1 of the height field. The temperature index is the mean temperature gradient hetween the North Pole and 60° N.
Comparisons of values of these parameters during several stratospheric warming episodes are utilized to show the difference between small-scale and large-scale warming events. Comparisons of values at different levels lead to the possibility of studying tropospheric-stratospheric interactions during periods of stratospheric warming.
Abstract
The usefulness of Nimbus 4 satellite infrared spectrometer (SIRS)-derived temperature and height data for constant-pressure analyses at stratospheric levels is investigated by comparing SIRS data with rawinsonde observations and objective analyses of those data. Results from the various methods of comparison are difficult to interpret since systematic and random errors of observations at stratospheric altitudes do not permit the observed data to be used as an unquestioned standard. In addition, conclusions must be qualified by the fact that the SIRS information derived to date has depended in part on analyses of rawinsonde data.
The following conclusions were reached from the various comparison studies: (1) SIRS data are useful for constant-pressure analyses at stratospheric levels, (2) mean differences between analyzed rawinsonde temperatures and SIRS derivations are generally less than 3°C, (3) differences are greater during stratospheric warmings, but SIRS data generally indicate the proper trend of the temperature changes, thus adding information about the temperature of the real atmosphere to an analysis, and (4) stratospheric SIRS data after Nov. 5, 1971, can be used with more confidence than those derived before that date.
Abstract
The usefulness of Nimbus 4 satellite infrared spectrometer (SIRS)-derived temperature and height data for constant-pressure analyses at stratospheric levels is investigated by comparing SIRS data with rawinsonde observations and objective analyses of those data. Results from the various methods of comparison are difficult to interpret since systematic and random errors of observations at stratospheric altitudes do not permit the observed data to be used as an unquestioned standard. In addition, conclusions must be qualified by the fact that the SIRS information derived to date has depended in part on analyses of rawinsonde data.
The following conclusions were reached from the various comparison studies: (1) SIRS data are useful for constant-pressure analyses at stratospheric levels, (2) mean differences between analyzed rawinsonde temperatures and SIRS derivations are generally less than 3°C, (3) differences are greater during stratospheric warmings, but SIRS data generally indicate the proper trend of the temperature changes, thus adding information about the temperature of the real atmosphere to an analysis, and (4) stratospheric SIRS data after Nov. 5, 1971, can be used with more confidence than those derived before that date.
Abstract
The Marine Optical System is a spectrograph-based sensor used on the Marine Optical Buoy for the vicarious calibration of ocean color satellite sensors. It is also deployed from ships in instruments used to develop bio-optical algorithms that relate the optical properties of the ocean to its biological content. In this work, an algorithm is applied to correct the response of the Marine Optical System for scattered, or improperly imaged, light in the system. The algorithm, based on the measured response of the system to a series of monochromatic excitation sources, reduces the effects of scattered light on the measured source by one to two orders of magnitude. Implications for the vicarious calibration of satellite ocean color sensors and the development of bio-optical algorithms are described. The algorithm is a one-dimensional point spread correction algorithm, generally applicable to nonimaging sensors, but can in principle be extended to higher dimensions for imaging systems.
Abstract
The Marine Optical System is a spectrograph-based sensor used on the Marine Optical Buoy for the vicarious calibration of ocean color satellite sensors. It is also deployed from ships in instruments used to develop bio-optical algorithms that relate the optical properties of the ocean to its biological content. In this work, an algorithm is applied to correct the response of the Marine Optical System for scattered, or improperly imaged, light in the system. The algorithm, based on the measured response of the system to a series of monochromatic excitation sources, reduces the effects of scattered light on the measured source by one to two orders of magnitude. Implications for the vicarious calibration of satellite ocean color sensors and the development of bio-optical algorithms are described. The algorithm is a one-dimensional point spread correction algorithm, generally applicable to nonimaging sensors, but can in principle be extended to higher dimensions for imaging systems.
Abstract
The Marine Optical System (MOS) is a dual charge-coupled device (CCD)-based spectrograph system developed for in-water measurements of downwelling solar irradiance E d and upwelling radiance L u . These measurements are currently used in the calibration and validation of satellite ocean color measurement instruments such as the moderate resolution imaging spectroradiometer (MODIS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). MOS was designed to be deployed from a ship for single measurements and also integrated into the Marine Optical Buoy (MOBY) for longer time series datasets. Measurements with the two spectrographs in the MOS systems can be compared in the spectral interval from about 580 to 630 nm. In this spectral range, they give different values for L u or E d at a common wavelength. To better understand the origin of this observation and the sources of uncertainty in the calibration of MOBY, an MOS bench unit was developed for detailed radiometric characterization and calibration measurements in a laboratory setting. In the work reported here, a novel calibration approach is described that uses a tunable-laser-based, monochromatic, spatially uniform, Lambertian, large area integrating sphere source (ISS). Results are compared with those obtained by a conventional approach using a lamp-illuminated ISS. Differences in the MOS bench unit responsivity between the two calibration approaches were observed and attributed to stray light. A simple correction algorithm was developed for the lamp-illuminated ISS that greatly improves the agreement between the two techniques. Implications for water-leaving radiance measurements by MOS are discussed.
Abstract
The Marine Optical System (MOS) is a dual charge-coupled device (CCD)-based spectrograph system developed for in-water measurements of downwelling solar irradiance E d and upwelling radiance L u . These measurements are currently used in the calibration and validation of satellite ocean color measurement instruments such as the moderate resolution imaging spectroradiometer (MODIS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). MOS was designed to be deployed from a ship for single measurements and also integrated into the Marine Optical Buoy (MOBY) for longer time series datasets. Measurements with the two spectrographs in the MOS systems can be compared in the spectral interval from about 580 to 630 nm. In this spectral range, they give different values for L u or E d at a common wavelength. To better understand the origin of this observation and the sources of uncertainty in the calibration of MOBY, an MOS bench unit was developed for detailed radiometric characterization and calibration measurements in a laboratory setting. In the work reported here, a novel calibration approach is described that uses a tunable-laser-based, monochromatic, spatially uniform, Lambertian, large area integrating sphere source (ISS). Results are compared with those obtained by a conventional approach using a lamp-illuminated ISS. Differences in the MOS bench unit responsivity between the two calibration approaches were observed and attributed to stray light. A simple correction algorithm was developed for the lamp-illuminated ISS that greatly improves the agreement between the two techniques. Implications for water-leaving radiance measurements by MOS are discussed.
Abstract
Multiscale convection-allowing precipitation forecast perturbations are examined for two forecasts and systematically over 34 forecasts out to 30-h lead time using Haar Wavelet decomposition. Two small-scale initial condition (IC) perturbation methods are compared to the larger-scale IC and physics perturbations in an experimental convection-allowing ensemble. For a precipitation forecast driven primarily by a synoptic-scale baroclinic disturbance, small-scale IC perturbations resulted in little precipitation forecast perturbation energy on medium and large scales, compared to larger-scale IC and physics (LGPH) perturbations after the first few forecast hours. However, for a case where forecast convection at the initial time grew upscale into a mesoscale convective system (MCS), small-scale IC and LGPH perturbations resulted in similar forecast perturbation energy on all scales after about 12 h. Small-scale IC perturbations added to LGPH increased total forecast perturbation energy for this case. Averaged over 34 forecasts, the small-scale IC perturbations had little impact on large forecast scales while LGPH accounted for about half of the error energy on such scales. The impact of small-scale IC perturbations was also less than, but comparable to, the impact of LGPH perturbations on medium scales. On small scales, the impact of small-scale IC perturbations was at least as large as the LGPH perturbations. The spatial structure of small-scale IC perturbations affected the evolution of forecast perturbations, especially at medium scales. There was little systematic impact of the small-scale IC perturbations when added to LGPH. These results motivate further studies on properly sampling multiscale IC errors.
Abstract
Multiscale convection-allowing precipitation forecast perturbations are examined for two forecasts and systematically over 34 forecasts out to 30-h lead time using Haar Wavelet decomposition. Two small-scale initial condition (IC) perturbation methods are compared to the larger-scale IC and physics perturbations in an experimental convection-allowing ensemble. For a precipitation forecast driven primarily by a synoptic-scale baroclinic disturbance, small-scale IC perturbations resulted in little precipitation forecast perturbation energy on medium and large scales, compared to larger-scale IC and physics (LGPH) perturbations after the first few forecast hours. However, for a case where forecast convection at the initial time grew upscale into a mesoscale convective system (MCS), small-scale IC and LGPH perturbations resulted in similar forecast perturbation energy on all scales after about 12 h. Small-scale IC perturbations added to LGPH increased total forecast perturbation energy for this case. Averaged over 34 forecasts, the small-scale IC perturbations had little impact on large forecast scales while LGPH accounted for about half of the error energy on such scales. The impact of small-scale IC perturbations was also less than, but comparable to, the impact of LGPH perturbations on medium scales. On small scales, the impact of small-scale IC perturbations was at least as large as the LGPH perturbations. The spatial structure of small-scale IC perturbations affected the evolution of forecast perturbations, especially at medium scales. There was little systematic impact of the small-scale IC perturbations when added to LGPH. These results motivate further studies on properly sampling multiscale IC errors.
