Krzysztof E. Haman

A New Ultrafast Thermometer for Airborne Measurements in Clouds

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 mm 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 1024 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 21. 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.

Two New Types of Ultrafast Aircraft 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 instrum...

A New Thermometric Instrument for Airborne Measurements in Clouds

Abstract A new instrument for measuring the temperature of air in clouds from an aircraft is described. The instrument uses a very fine thermometric sensor located behind a thin rod that protects the sensor from direct contact with cloud droplets. Because the airflow is less disturbed than in more massive protective housings the accuracy and speed of the sensor are relatively less affected than in other types of airborne contact thermometers. Details of the construction of a prototype unit and results of preliminary flight and wind tunnel tests are given.

Temperature measurements in clouds on a centimetre scale Preliminary results

Abstract Preliminary results of the temperature measurements in Cumulus mediocris clouds with a new ultra-fast airborne thermometer installed on a motor-glider are presented. The time constant of the thermometer is about 2 × 10 −4 s but due to limitations of the recorder the data were conditioned with the use of a 300 Hz low-pass filter and sampled with 999 Hz rate, giving spatial resolution of 3 cm at 30 m/s cruising speed. Records taken whilst penetrating various parts of Cumulus clouds on 23 and 25 August 1994 in the vicinity of Warsaw show a number of unexpected features such as single and multiple sharp jumps of temperature over layers only a few centimetres thick. Measurements of this kind are throwing a new light on the process of mixing in convective clouds.

Theoretical and Experimental Characterization of the Ultrafast Aircraft Thermometer: Reduction of Aerodynamic Disturbances and Signal Processing

Abstract The ultrafast aircraft thermometer, built for measuring temperature in clouds at flight speeds up to 100 m s−1, employs a 2.5-μm-thick platinum-coated tungsten wire as a sensing element. When temperature increases, the wire resistance increases. The changes are amplified by an electronic system. Temperature measurements made in a wind tunnel and during flights show noise that is related to the von Karman vortex street generated behind the shield that protects the sensing element against the impact of cloud droplets. To reduce both the level of turbulence and the amount of water collected on the shield, suction is applied through the slits in its sides. The effect of suction on the flow field is twofold. First, at the Reynolds numbers that the thermometer is operated suction eliminates aerodynamic disturbances. Second, suction diverts the inner part of the boundary layer into the slit. This inner part is a region of strong shear and, therefore, a region where intensive viscous heating takes place....

Observations of cooling tower and stack plumes and their comparison with plume model ALINA

Abstract Aircraft observations of stack and cooling tower plumes taken at a big power plant are compared with corresponding outputs of one-dimensional plume model ALINA, yielding certain improvements to the entrainment parametrization and dynamics of the model. Some observations of plume-plume and plume-environment interactions are reported.

Visualization of small density fluctuations of the atmosphere with spatial frequency filters

The recently improved ultra-fast aircraft resistance thermometer measures with a time constant of the order 0.1 ms. For an aircraft speed of 100 m/s this time constant corresponds to a spatial resolution of a few centimeters. Measurements made both in the atmosphere and in the low-turbulence wind tunnel at air speed 80 m/s are corrupted with noise of a few kHz frequency. Authors of the thermometer suggest that this noise results from turbulence introduced by vortex shedding from the protective shield. To achieve further improvement of the instrument we have to understand the nature of these aerodynamic disturbances. The present study is carried in two complementary directions. In the first, flow modeling is made with the FEATFLOW 1.2d - a finite element software for the incompressible Navier-Stokes equations. The results of flow simulation are in qualitative agreement with the experiment. In the second, we simulate visualization of the flow using two optical spatial filters: the Foucault filter that gives output intensity signal where bright bias is modulated with 1-D Hilbert transform of an object phase function and modified Zernike phase filter that shifts phase of the spectrum dc term by 0.2π.

Radar-echo tracking by use of invariant moments

A number of techniques to track rainfall patterns by use of radar observations have been developed over the years. We present a method for radar-echo tracking based on Hu invariant moments. The method has been tried on several sequences of test images, and the derived displacement fields were in good agreement with the real motions of the tested objects. For the real data obtained from the conventional meteorological radar in Legionowo the method occasionally failed when changes in the radar echo between observations were too large.

Hygrometry with Temperature Stabilization

Abstract A method is presented for stabilizing the temperature of air to allow the use of temperature-sensitive, humidity sensors for direct determination of an invariant humidity characteristic such as specific humidity and/or its fluctuations. Problems connected with such measurements are discussed in detail, and outlines of their theory are given. One instrument of this type that has been built and used is briefly described.

Optimization of the atmospheric temperature field measurements

Small-scale inhomogeneities of the atmospheric temperature field are caused by air turbulence and result in refractive index fluctuations, which in turn influence the propagation of optical beams. Understanding small density fluctuations in the atmosphere is important for the free-space laser communication and for high-resolution imaging through the atmosphere. The ultra-fast aircraft resistance thermometer constructed in the Institute of Geophysics, Warsaw University, measures the temperature of cloudless air and of warm clouds with 10 kHz sampling frequency. During a flight at the speed of 100 m/s, at low altitudes up to 2 km, this corresponds to the spatial resolution of the order of one centimeter. This resolution is sufficient for studying small density fluctuations in the atmospheric boundary layer. A streamlined shield protects the sensing wire of the thermometer from cloud droplets and other small particles suspended in the air but introduce aerodynamic disturbances in the form of vortices. The thermometer records the resulting fluctuations of temperature as noise. The shield sucks air and water collected on its surface through the suction slits. This suction also suppresses the disturbances. In this paper we analyze how the temperature measurements are influenced by: (i) turbulence generated behind the shield placed in front of the sensing wire; (ii) suction of air through the shield slits; (iii) cloud droplets of various space distributions, masses and velocities. We have carried out the 2D numerical simulations of the time-dependent, incompressible, viscous flow (the Navier-Stokes equation) around the shield placed in a uniform stream. We solved the particle path equations for an ensamble of droplets in the Stokes approximation. All the simulations are oriented toward optimization of the shield shape in order to (i) reduce noise in measurements at low and high altitudes and (ii) protect the sensing wire against ice crystals in flights at high altitudes.