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Unusual convection patterns were observed in snow-slush on a pond in Seattle, Wash., during January 1980 and again during February 1981. The patterns are reminiscent of spoke-type convection discovered experimentally by Busse and Whitehead (1974).
Unusual convection patterns were observed in snow-slush on a pond in Seattle, Wash., during January 1980 and again during February 1981. The patterns are reminiscent of spoke-type convection discovered experimentally by Busse and Whitehead (1974).
Abstract
Supercooling of the surface water on open leads in the Arctic Ocean has been suggested as a possible source of water for the observed subsurface freezing. Observations with an infrared radiometer at the shore-lead outside Pt. Barrow, Alaska, in April 1972, verify this supposition.
Abstract
Supercooling of the surface water on open leads in the Arctic Ocean has been suggested as a possible source of water for the observed subsurface freezing. Observations with an infrared radiometer at the shore-lead outside Pt. Barrow, Alaska, in April 1972, verify this supposition.
Abstract
Tracers were used to reveal the motions within the boundary layer on water in turbulent free convection. The technique of obtaining a thin sheet of light with an inexpensive laser and a cylindrical lens is suggested as a convenient tool for classroom demonstrations and research. Some facts about high Rayleigh number free convection, often not revealed by quantitative point sensors, which will be illustrated with the accompanying photographs are as follows: 1) the “whole” thermal boundary layer at the air-water interface participates in the convection through cyclic instabilities, 2) the form of the convection is predominantly vertical sheets originating from narrow lines in the interface (also observed with “schlieren” by Spangenberg and Rowland), 3) whether the boundary is rigid or free does not affect the appearance of these lines appreciably, 4) the lines move about in an unpredictable fashion and interact with each other, 5) entrainment away from the boundary very quickly broadens the convection elements and 6) presence of salt strongly affects the horizontal scales of the convection in evaporating water. The latter point is also demonstrated with horizontal wavenumber spectra, and compared to theory. Discussions of similarities between convective systems in atmosphere and ocean and these laboratory observations are included.
Abstract
Tracers were used to reveal the motions within the boundary layer on water in turbulent free convection. The technique of obtaining a thin sheet of light with an inexpensive laser and a cylindrical lens is suggested as a convenient tool for classroom demonstrations and research. Some facts about high Rayleigh number free convection, often not revealed by quantitative point sensors, which will be illustrated with the accompanying photographs are as follows: 1) the “whole” thermal boundary layer at the air-water interface participates in the convection through cyclic instabilities, 2) the form of the convection is predominantly vertical sheets originating from narrow lines in the interface (also observed with “schlieren” by Spangenberg and Rowland), 3) whether the boundary is rigid or free does not affect the appearance of these lines appreciably, 4) the lines move about in an unpredictable fashion and interact with each other, 5) entrainment away from the boundary very quickly broadens the convection elements and 6) presence of salt strongly affects the horizontal scales of the convection in evaporating water. The latter point is also demonstrated with horizontal wavenumber spectra, and compared to theory. Discussions of similarities between convective systems in atmosphere and ocean and these laboratory observations are included.
Abstract
A comprehensive closed-form parameterization has been developed for the contribution of the nonprecipitating marine atmosphere to microwave brightness temperatures observed by the Special Sensor Microwave/Imager (SSM/I). The variables considered in this model include viewing angle, integrated water vapor amount and scale height, effective tropospheric lapse rate and new-surface temperature, total cloud liquid water, effective cloud height, and surface pressure.
First an approximate closed-form formula is derived for the efficient calculation of upwelling brightness temperature at the top of the atmosphere and the downwelling brightness temperature at the surface. The independent variables include the viewing angle, separate optical depths and absorption scale heights for dry air and water vapor, effective surface temperature lapse rate, cloud height, and cloud optical depth. This parameterization is valid for all microwave frequencies for which the total optical depth of the atmosphere, excluding cloud liquid water, is less than unity.
Second, the dependence of the radiative variables listed above on meteorological variables is determined for each of the SSM/I frequencies 19.35, 22.235, 37.0, and 85.5 GHz, based on the values computed from 16 893 maritime temperature and humidity profiles representing all latitude belts and all seasons. Comparisons of the brightness temperatures predicted by the complete brightness-temperature model with brightness temperatures obtained by direct numerical integration of the radiative transfer equation for the radiosonde-profile dataset yield rms differences well below 1 K for all four SSM/I frequencies.
Finally, the global radiosonde dataset is used to compute expectation values and standard deviations of selected atmospheric variables on which the brightness-temperature model depends. These statistics are intended for use in constrained nonlinear retrieval algorithms and similar applications.
Abstract
A comprehensive closed-form parameterization has been developed for the contribution of the nonprecipitating marine atmosphere to microwave brightness temperatures observed by the Special Sensor Microwave/Imager (SSM/I). The variables considered in this model include viewing angle, integrated water vapor amount and scale height, effective tropospheric lapse rate and new-surface temperature, total cloud liquid water, effective cloud height, and surface pressure.
First an approximate closed-form formula is derived for the efficient calculation of upwelling brightness temperature at the top of the atmosphere and the downwelling brightness temperature at the surface. The independent variables include the viewing angle, separate optical depths and absorption scale heights for dry air and water vapor, effective surface temperature lapse rate, cloud height, and cloud optical depth. This parameterization is valid for all microwave frequencies for which the total optical depth of the atmosphere, excluding cloud liquid water, is less than unity.
Second, the dependence of the radiative variables listed above on meteorological variables is determined for each of the SSM/I frequencies 19.35, 22.235, 37.0, and 85.5 GHz, based on the values computed from 16 893 maritime temperature and humidity profiles representing all latitude belts and all seasons. Comparisons of the brightness temperatures predicted by the complete brightness-temperature model with brightness temperatures obtained by direct numerical integration of the radiative transfer equation for the radiosonde-profile dataset yield rms differences well below 1 K for all four SSM/I frequencies.
Finally, the global radiosonde dataset is used to compute expectation values and standard deviations of selected atmospheric variables on which the brightness-temperature model depends. These statistics are intended for use in constrained nonlinear retrieval algorithms and similar applications.
Abstract
Calculations are made of errors in the measurement of solar irradiance at the sea surface. which occur when pyranometers are tilled. Tilts due to buoy or ship motion caused by wave action or a preferential tilt due to drag are considered. Errors depend on sky condition and are maximum for clear skies. They depend on soar zenith angle and on the relative azimuth of sun and tilt directions, and vary, therefore, with latitude and season or time of day. Errors as large as ±10% to ±20% in the daily average (with sign dependent on azimuth of the tilt) could be encountered for clear skies poleward of 45°N or S in the winter half of the year for a 10° preferential tilt. Instantaneous errors due to wave action can be as large. Because of the difficulty of making corrections a posteriori, gimbal mounting of pyranometers is recommended.
Abstract
Calculations are made of errors in the measurement of solar irradiance at the sea surface. which occur when pyranometers are tilled. Tilts due to buoy or ship motion caused by wave action or a preferential tilt due to drag are considered. Errors depend on sky condition and are maximum for clear skies. They depend on soar zenith angle and on the relative azimuth of sun and tilt directions, and vary, therefore, with latitude and season or time of day. Errors as large as ±10% to ±20% in the daily average (with sign dependent on azimuth of the tilt) could be encountered for clear skies poleward of 45°N or S in the winter half of the year for a 10° preferential tilt. Instantaneous errors due to wave action can be as large. Because of the difficulty of making corrections a posteriori, gimbal mounting of pyranometers is recommended.
Abstract
A method of determining cloud liquid water path is developed using shortwave spectral measurements. The attenuation of shortwave radiant fluxes is due to scattering and absorption in the near-infrared band, but is caused only by scattering in the near-ultraviolet and visual band. The ratio of the reflectances in these two bands is defined as the reflectance ratio; the ratio of the transmittances as the transmittance ratio. Relationships between these ratios and the amount of cloud liquid water are developed. The use of reflectance ratio as a determinant of liquid water path has two advantages over the use of total shortwave reflectance alone. It minimizes the effect of droplet size distribution and the diagnostic curve is less sensitive to changes in reflectance than the curve based on total reflectance. The model is tested with data obtained by aircraft flights during the 1978 Joint Air-Sea Interaction Experiment (JASIN) and shows good agreement with measurements of liquid water path taken in the same area and with the results of other approximation formulas. Calculations show that this method could also be used to detect the extent of layering within a cloud deck.
Abstract
A method of determining cloud liquid water path is developed using shortwave spectral measurements. The attenuation of shortwave radiant fluxes is due to scattering and absorption in the near-infrared band, but is caused only by scattering in the near-ultraviolet and visual band. The ratio of the reflectances in these two bands is defined as the reflectance ratio; the ratio of the transmittances as the transmittance ratio. Relationships between these ratios and the amount of cloud liquid water are developed. The use of reflectance ratio as a determinant of liquid water path has two advantages over the use of total shortwave reflectance alone. It minimizes the effect of droplet size distribution and the diagnostic curve is less sensitive to changes in reflectance than the curve based on total reflectance. The model is tested with data obtained by aircraft flights during the 1978 Joint Air-Sea Interaction Experiment (JASIN) and shows good agreement with measurements of liquid water path taken in the same area and with the results of other approximation formulas. Calculations show that this method could also be used to detect the extent of layering within a cloud deck.
Abstract
A twin propeller-vane anemometer developed at the University of British Columbia was successfully used for unattended measurements of atmospheric turbulence over extended periods of time during moderate to high winds in the presence of sea spray. In this paper, a new design in twin propeller-vane anemometers is introduced. The instrument consists of two Gill anemometers mounted on a vane. The propeller shafts, one pointing up and the other pointing down, make an angle of 45° with the horizontal (hence, the name K-Gill). In addition to the desirable characteristics of the earlier design the K-Gill has symmetry, so that updraft and downdraft winds are measured with equal sensitivity. A built-in level sensor allows till corrections. In order to reduce the flow distortion the electronics housing at the base of the instrument has been removed and the propellers have been mounted further away from the main vertical shaft. An algorithm for obtaining the vertical and downstream horizontal components of the wind velocity is described. Various sources of error and their magnitudes are discussed.
Abstract
A twin propeller-vane anemometer developed at the University of British Columbia was successfully used for unattended measurements of atmospheric turbulence over extended periods of time during moderate to high winds in the presence of sea spray. In this paper, a new design in twin propeller-vane anemometers is introduced. The instrument consists of two Gill anemometers mounted on a vane. The propeller shafts, one pointing up and the other pointing down, make an angle of 45° with the horizontal (hence, the name K-Gill). In addition to the desirable characteristics of the earlier design the K-Gill has symmetry, so that updraft and downdraft winds are measured with equal sensitivity. A built-in level sensor allows till corrections. In order to reduce the flow distortion the electronics housing at the base of the instrument has been removed and the propellers have been mounted further away from the main vertical shaft. An algorithm for obtaining the vertical and downstream horizontal components of the wind velocity is described. Various sources of error and their magnitudes are discussed.
The polar-orbiting satellite, Seasat, had been designed as an oceanographic satellite with little advance thought being given to atmospheric uses. However, the microwave instruments provided a rich source of data for studying atmospheric conditions. The simultaneous sampling by several instruments generated special benefits, a situation which to date has not been repeated. In this review we emphasize studies of midlatitude and tropical cyclones and regional weather and climate analyses. We also touch upon studies of long swell, sea ice, and continental ice sheets with Seasat data.
Many of these results of the Seasat mission were serendipitous. In preparation for the major NASA initiative for the next decade, the Earth Observing Satellite (EOS) program, we thought it timely to bring some of the Seasat experiences to the fore, since valuable lessons can be learned from the successes and the failures (or omissions) of the Seasat program. We have learned of: 1) the synergistic value of integrated, overlapping sampling by several instruments, 2) the invaluable contribution of carefully planned surface measurements, and 3) the importance of retaining flexibility in the system (enough data retention) to allow unexpected and innovative analysis techniques.
The polar-orbiting satellite, Seasat, had been designed as an oceanographic satellite with little advance thought being given to atmospheric uses. However, the microwave instruments provided a rich source of data for studying atmospheric conditions. The simultaneous sampling by several instruments generated special benefits, a situation which to date has not been repeated. In this review we emphasize studies of midlatitude and tropical cyclones and regional weather and climate analyses. We also touch upon studies of long swell, sea ice, and continental ice sheets with Seasat data.
Many of these results of the Seasat mission were serendipitous. In preparation for the major NASA initiative for the next decade, the Earth Observing Satellite (EOS) program, we thought it timely to bring some of the Seasat experiences to the fore, since valuable lessons can be learned from the successes and the failures (or omissions) of the Seasat program. We have learned of: 1) the synergistic value of integrated, overlapping sampling by several instruments, 2) the invaluable contribution of carefully planned surface measurements, and 3) the importance of retaining flexibility in the system (enough data retention) to allow unexpected and innovative analysis techniques.
Abstract
Mesoscale cloud clusters near the northwestern coast of Borneo were observed by the Scanning Multichannel Microwave Radiometer (SMMR) on three occasions during the Winter Monsoon Experiment in December 1978. A nondimensional form of the SMMR 37 GHz polarization difference is introduced and used to identify regions of precipitation, and these are compared with visible and infrared imagery from the GMS-1 geostationary satellite. For two of the three cloud cluster cases, quantitative comparisons are made between nearly simultaneous SMMR observations and reflectivity observations made by the MIT WR-73 digital weather radar at Bintulu. Though limited in scope, these represent the first known direct comparisons between digital radar-derived rain parameters and satellite passive microwave observations of new-equatorial precipitation. SMMR 37 GHz observations are found to be much better indicators of fractional coverage of each SMMR footprint by rain than of average rain rate within the footprint. Total area coverage by precipitation is estimated for all three clusters using this result.
Abstract
Mesoscale cloud clusters near the northwestern coast of Borneo were observed by the Scanning Multichannel Microwave Radiometer (SMMR) on three occasions during the Winter Monsoon Experiment in December 1978. A nondimensional form of the SMMR 37 GHz polarization difference is introduced and used to identify regions of precipitation, and these are compared with visible and infrared imagery from the GMS-1 geostationary satellite. For two of the three cloud cluster cases, quantitative comparisons are made between nearly simultaneous SMMR observations and reflectivity observations made by the MIT WR-73 digital weather radar at Bintulu. Though limited in scope, these represent the first known direct comparisons between digital radar-derived rain parameters and satellite passive microwave observations of new-equatorial precipitation. SMMR 37 GHz observations are found to be much better indicators of fractional coverage of each SMMR footprint by rain than of average rain rate within the footprint. Total area coverage by precipitation is estimated for all three clusters using this result.
Abstract
Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) normalized 37-GHz polarization differences P were compared with surface digital radar observations of oceanic precipitation made daring the Taiwan Area Mesoscale Experiment (TAMEX). Four cases were found for which SMMR and radar coverage of significant precipitation features were nearly simultaneous. These yielded 518 SMMR-radar data pairs, of which over half included precipitation. An empirical method was used to correct the radar data for range-dependent errors, and relationships were then sought between the corrected pixel-averaged radar rainfall parameters and the SMMR-observed microwave polarization P. Because of the small sample size and large statistical uncertainties associated with the direct comparisons, the latter were most useful as a means to validate and tune a theoretically derived relationship between 37-GHz P and radar reflectivity factor Z. This relationship in turn was used to generate a large set of simulated SMMR observations from all available TAMEX radar scans in order to produce histograms and mean values of pixel-averaged rain rate as a function of P. An Appendix also describes an attempt to compare SMMR estimates of integrated cloud liquid water with coincident aircraft data during TAMEX.
Abstract
Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) normalized 37-GHz polarization differences P were compared with surface digital radar observations of oceanic precipitation made daring the Taiwan Area Mesoscale Experiment (TAMEX). Four cases were found for which SMMR and radar coverage of significant precipitation features were nearly simultaneous. These yielded 518 SMMR-radar data pairs, of which over half included precipitation. An empirical method was used to correct the radar data for range-dependent errors, and relationships were then sought between the corrected pixel-averaged radar rainfall parameters and the SMMR-observed microwave polarization P. Because of the small sample size and large statistical uncertainties associated with the direct comparisons, the latter were most useful as a means to validate and tune a theoretically derived relationship between 37-GHz P and radar reflectivity factor Z. This relationship in turn was used to generate a large set of simulated SMMR observations from all available TAMEX radar scans in order to produce histograms and mean values of pixel-averaged rain rate as a function of P. An Appendix also describes an attempt to compare SMMR estimates of integrated cloud liquid water with coincident aircraft data during TAMEX.
