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- Author or Editor: Szymon P. Malinowski x
- Journal of Atmospheric and Oceanic Technology x
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Abstract
Cloud–clear air mixing at scales from 1 mm to 1 m is observed in a laboratory chamber. Cross sections through the volume in which the mixing takes place are obtained by illuminating a planar sheet of cloud with laser light (λ = 0.488 μm, 1.2-mm thickness); the light is scattered by cloud droplets and photographed. Images indicate that complicated filament-like structures are created during mixing. Due to the properties of Mie scattering, this technique is in principle more sensitive to the larger cloud drops, and volumes with the small droplets may be underrepresented in the images. After digitization of the images, an interface between cloudy and clear-air filaments is investigated. Preliminary results indicate that at the scale of 2 cm the nature of the interface changes: at larger scales it exhibits self-similar properties, whereas at smaller scales it has a simple geometrical structure.
Abstract
Cloud–clear air mixing at scales from 1 mm to 1 m is observed in a laboratory chamber. Cross sections through the volume in which the mixing takes place are obtained by illuminating a planar sheet of cloud with laser light (λ = 0.488 μm, 1.2-mm thickness); the light is scattered by cloud droplets and photographed. Images indicate that complicated filament-like structures are created during mixing. Due to the properties of Mie scattering, this technique is in principle more sensitive to the larger cloud drops, and volumes with the small droplets may be underrepresented in the images. After digitization of the images, an interface between cloudy and clear-air filaments is investigated. Preliminary results indicate that at the scale of 2 cm the nature of the interface changes: at larger scales it exhibits self-similar properties, whereas at smaller scales it has a simple geometrical structure.
Abstract
A new aircraft device for measuring temperature in clouds is described. Its sensor is a resistance thermometer made of platinum-coated tungsten wire 5 mm long and 2.5 μm in diameter. The sensor is located on a rotatable vane behind a thin rod aimed at protecting it against the impact of cloud droplets, which according to limited experience gathered until now seems to be sufficiently effective as an antiwetting protection for the speeds of motorgliders. Contrary to the massive housings usually adopted in other constructions, the rod creates only negligible disturbances in the thermodynamic properties of the ambient air. The time constant of the sensor is of the order 10−4 s, which permits measurements of temperature in clouds with a resolution of a few centimeters, depending on aircraft velocity. The thermometer was tested in a wind tunnel, and on an Ogar motorglider and a Do-228 aircraft. Its present version performs fairly well at low airspeeds of up to about 40 m s−1. For faster aircraft further improvements seem necessary. The paper presents a detailed description of the instrument, discussion of test results, and examples of centimeter-scale features of temperature fields in clouds measured with the thermometer.
Abstract
A new aircraft device for measuring temperature in clouds is described. Its sensor is a resistance thermometer made of platinum-coated tungsten wire 5 mm long and 2.5 μm in diameter. The sensor is located on a rotatable vane behind a thin rod aimed at protecting it against the impact of cloud droplets, which according to limited experience gathered until now seems to be sufficiently effective as an antiwetting protection for the speeds of motorgliders. Contrary to the massive housings usually adopted in other constructions, the rod creates only negligible disturbances in the thermodynamic properties of the ambient air. The time constant of the sensor is of the order 10−4 s, which permits measurements of temperature in clouds with a resolution of a few centimeters, depending on aircraft velocity. The thermometer was tested in a wind tunnel, and on an Ogar motorglider and a Do-228 aircraft. Its present version performs fairly well at low airspeeds of up to about 40 m s−1. For faster aircraft further improvements seem necessary. The paper presents a detailed description of the instrument, discussion of test results, and examples of centimeter-scale features of temperature fields in clouds measured with the thermometer.
Abstract
A new version of an ultrafast aircraft resistance thermometer (UFT-F) with a time constant of the order 10−4 s,for use in both cloudy and cloudless air, is described. It evolved from an earlier version (UFT-S). Its sensing element is similar to that in UFT-S and consists of a 5-mm-long and 2.5-μm-thick platinum-coated tungsten wire, located on a rotatable vane behind a thin vertical rod that protects the sensor against direct impact of cloud droplets and other objects. Such construction introduces much smaller thermal disturbances than do more massive housings of other types of immersion thermometers and permits taking full advantage of low thermal inertia of the sensing wire. However, aerodynamic disturbances created by vortex shedding from the protective rod induce adiabatic fluctuations of temperature, which appear on the temperature records as “noise.” In the case of the UFT-S the level of this noise has become intolerable at airspeeds of about 40 m s−1, limiting applicability of this instrument to slow aircraft or gliders. For UFT-F the shape of the protective rod has been redesigned and endowed with a special system of reducing aerodynamic disturbances behind it, which made it usable at airspeeds up to 100 m s−1 in cloudless air or warm clouds. For use in supercooled clouds, a special variety of UFT-F (denoted here UFT-D) has been designed. As in its predecessor, its sensing element is a 5-mm-long, 2.5-μm-thick, platinum-coated tungsten resistive wire protected against impact of cloud droplets by an airfoil-shaped rod, but all its icing-sensitive parts are electrically heated to prevent buildup of ice. This modification required a total change of mechanical structure of the instrument. Tests during the Third Canadian Freezing Drizzle Experiment showed that UFT-D can perform fairly well in water clouds supercooled down to at least −8°C and that its heating system introduces no intolerable disturbances into the record. Use of UFT-D in ice or mixed clouds is limited by the fact that the protective rod is not effective enough against ice crystals bigger than about 200 μm, which can quickly destroy the delicate sensing element.
The paper gives details of construction as well as results of wind tunnel and in-flight tests of these instruments.
Abstract
A new version of an ultrafast aircraft resistance thermometer (UFT-F) with a time constant of the order 10−4 s,for use in both cloudy and cloudless air, is described. It evolved from an earlier version (UFT-S). Its sensing element is similar to that in UFT-S and consists of a 5-mm-long and 2.5-μm-thick platinum-coated tungsten wire, located on a rotatable vane behind a thin vertical rod that protects the sensor against direct impact of cloud droplets and other objects. Such construction introduces much smaller thermal disturbances than do more massive housings of other types of immersion thermometers and permits taking full advantage of low thermal inertia of the sensing wire. However, aerodynamic disturbances created by vortex shedding from the protective rod induce adiabatic fluctuations of temperature, which appear on the temperature records as “noise.” In the case of the UFT-S the level of this noise has become intolerable at airspeeds of about 40 m s−1, limiting applicability of this instrument to slow aircraft or gliders. For UFT-F the shape of the protective rod has been redesigned and endowed with a special system of reducing aerodynamic disturbances behind it, which made it usable at airspeeds up to 100 m s−1 in cloudless air or warm clouds. For use in supercooled clouds, a special variety of UFT-F (denoted here UFT-D) has been designed. As in its predecessor, its sensing element is a 5-mm-long, 2.5-μm-thick, platinum-coated tungsten resistive wire protected against impact of cloud droplets by an airfoil-shaped rod, but all its icing-sensitive parts are electrically heated to prevent buildup of ice. This modification required a total change of mechanical structure of the instrument. Tests during the Third Canadian Freezing Drizzle Experiment showed that UFT-D can perform fairly well in water clouds supercooled down to at least −8°C and that its heating system introduces no intolerable disturbances into the record. Use of UFT-D in ice or mixed clouds is limited by the fact that the protective rod is not effective enough against ice crystals bigger than about 200 μm, which can quickly destroy the delicate sensing element.
The paper gives details of construction as well as results of wind tunnel and in-flight tests of these instruments.
