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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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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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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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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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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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Serhad S. Ataktürk and Kristina B. Katsaros

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.

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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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Lynn A. McMurdie and Kristina B. Katsaros

Abstract

With the atmospheric water-vapor content information available from the SEASAT and Nimbus-7 Scanning Multichannel Microwave Radiometers (SMMR), differences in water-vapor distribution between cyclonic storms in different regions of the global ocean can be examined in more detail than previously possible from radiosondes. SMMR-derived integrated water vapor is a robust and dependable variable of the same accuracy as integrated radiosonde soundings. In this study, maximum and minimum water-vapor content in the vicinity of cold fronts of 80 storms that occurred in the North Atlantic, North Pacific and Southern oceans are compared. North Atlantic storms were found to have significantly higher maximum and minimum water-vapor content near cold fronts on average than North Pacific or Southern ocean storms for both the warm and cold seasons. These differences are attributed to warmer sea surface temperatures and air temperatures in the North Atlantic, and higher baroclinity and consequently stronger upward motion in North Atlantic storms. Additionally, some of the differences may be attributed to the fact that the North Atlantic storms generally occur at lower latitudes than the storms in the other regions. Furthermore, the North Pacific storms were found to have significantly higher maximum and minimum water-vapor content near cold fronts on average than the Southern Ocean storms for both the warm and cold seasons. These differences are attributable to warmer sea surface temperatures in the North Pacific during the warm season, and to less moisture transport by Southern Ocean storms and the poleward location of the Southern Ocean storms compared to North Pacific storms during the cold season. Two examples of water-vapor content in a South Atlantic storm are given to contrast with the Southern Ocean cases. The South Atlantic storm had much higher maximum water-vapor content near the cold front than most Southern Ocean storms.

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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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