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Kristina B. Katsaros

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.

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Kristina B. Katsaros

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).

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Kristina B. Katsaros

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.

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Gerald Geernaert and Kristina B. Katsaros

Abstract

Based on the assumption that, over the sea, the roughness length of the wind profile scales with the wind stress, a new formulation that describes the drag coefficient as a function of the given neutral drag coefficient and stability is derived. The new formulation is compared to an earlier formulation where roughness changes with stability were ignored. The two are then illustrated with data collected from both the Marine Remote Sensing Project (1979) and the Tower Ocean Wave and Radar Dependence Experiment (1984). It was found that when the surface roughness was allowed to depend on wind stress (and therefore stability), the stratification correction to the neutral drag coefficient was larger than for the case when the roughness length was not allowed to vary.

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Kristina B. Katsaros and John E. Devault

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.

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Kristina B. Katsaros and W. Timotry Liu

Abstract

Sodium chloride solutions were cooled from above in the laboratory. Supercooling of the order of 1C was always observed at the surface prior to freezing. The magnitude of the supercooling varied and is inferred to be dependent upon the boundary layer thickness and the availability of freezing nuclei.

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Grant W. Petty and Kristina B. Katsaros

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.

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Douglas K. Miller and Kristina B. Katsaros

Abstract

The aim of this article is to estimate surface latent heat fluxes in the vicinity of a rapidly deepening cyclone before and during its period of most rapid intensification. This is done with a bulk parameterization scheme and remotely sensed input data.

A method for estimating the difference in specific humidity between the surface and a 10-m height is investigated using the Special Sensor Microwave/Imager (SSM/I)-observed integrated water vapor field and a sea surface temperature analysis.

The surface latent beat flux fields generally have estimated errors below 40% south of 40°N and outside the region of high integrated water vapor values associated with frontal bands. The method of estimating surface latent beat fluxes for the case study was found to be usable in most regions of the northwest Atlantic Ocean except for those locations directly adjacent to coastlines in instances of offshore flow and in the vicinity of surface fronts.

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Lynn A. McMurdie and Kristina B. Katsaros

Abstract

Rapidly deepening cyclones in midlatitudes are characterized by large cloud shields and abundant condensation qualitatively evident in infrared and visible satellite images. With the availability of passive microwave measurements from polar-orbiting satellites, it is now possible to characterize rapidly deepening cyclones quantitatively in terms of integrated water vapor and precipitation intensity. In this study, fields of integrated water vapor, integrated water vapor anomaly (defined as the observed water vapor content minus the monthly mean water vapor content at the particular location), and rainfall intensity index derived from the Special Sensor Microwave Imager (SSM/I) on the F-8 satellite of the Defense Meteorological Satellite Program are examined for 12 North Atlantic rapidly deepening and 11 North Atlantic non-rapidly deepening storms that occurred during the 1988 and 1989 winter months. By correlating concurrent 6-h deepening rates with the satellite-derived parameters for a region within 550 km of the surface low pressure center, signatures of rapid cyclogenesis are identified in the SSM/I fields. Maximum water vapor anomaly and average precipitation index have correlations with concurrent 6-h deepening rates of 0.56 and 0.55, respectively. The correlations improve dramatically when two outliers are removed, becoming 0.68 and 0.70, respectively. These results indicate that, although most rapidly deepening cyclones have high water vapor anomaly and stronger precipitation index than non-rapidly deepening cyclones, there are storms that deepen rapidly in the absence of high water vapor anomaly or heavy precipitation. In addition, occasionally there are storms that have exceptionally high water vapor anomalies yet do not deepen rapidly. In these unusual cases, it is suggested that atmospheric water vapor and condensation play a secondary role and that dynamical processes are dominant.

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John E. DeVault and Kristina B. Katsaros

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.

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