The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
George A. Isaac - One of the best experts on this subject based on the ideXlab platform.
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Aircraft Icing Study Using Integrated Observations and Model Data
Weather and Forecasting, 2019Co-Authors: Faisal S. Boudala, George A. IsaacAbstract:AbstractLight (LGT) to moderate (MOD) Aircraft Icing (AI) is frequently reported at Cold Lake, Alberta, but forecasting AI has been a big challenge. The purpose of this study is to investigate and ...
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Reply to ''Comments on 'Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification'''
Journal of Applied Meteorology and Climatology, 2013Co-Authors: Stewart G. Cober, George A. IsaacAbstract:Cober et al. (2009) and Cober and Isaac (2012) characterized Aircraft Icing environments that contained supercooledlargedrops (SLD).100mm indiameteron the basis of data collected during 134 research flights into winter storms in three geographic regions of North America. The characterization was designed to be supplemental to existing Aircraft Icing certification envelopes, given that existing envelopes do not explicitly incorporate SLD conditions. The U.S. Federal Aviation Administration is considering using the results from Cober et al. (2009) and Cober and Isaac (2012) as the basis for new certification regulations. Marwitz (2013) has suggested that the results of Cober and Isaac (2012) are deficient with respect to their application to the proposed new certification regulations, and he provided some criticisms. The purpose of this response is to address these criticisms. Marwitz (2013) suggested that the use of median volume diameter (MVD) and maximum diameter (Dmax) by Cober and Isaac (2012) as part of their characterization method is invalid because MVD and Dmax are not related to performance measurement. Cober and Isaac (2012) made no attempt to measure performance degradation of the research Aircraft. Rather the intent was to collect and analyze a sufficiently large dataset to characterize Icing environments that included SLD at the 99% and 99.9% levels (i.e., extreme values) so that manufacturers could subsequently determine the associated performance degradation on their instruments, Aircraft components, or engines. A justification for using MVD and Dmax follows. MVD is the 50% mass diameter, and hence large MVD values (i.e., .40mm) specifically identify Icing conditions that are outside the existing certifications standards and for which the majority of the mass is incorporated in drops that have higher collision efficiency (and corresponding performance degradation) with Aircraft surfaces. Aircraft, instrument, and engine manufacturers use different combinations of MVD (or other drop diameter characteristics), temperature, and liquid water content (LWC) to evaluate performance losses primarily through their use in wind-tunnel, naturalIcing, and numerical simulation experiments. Aircraft Icing envelopes have been based in part on MVD since their inception in the 1950s. It is an industry standard to correlate the analysis of Icing conditions against performance degradation, and MVD is one of the primary
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Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification
Journal of Applied Meteorology and Climatology, 2012Co-Authors: Stewart G. Cober, George A. IsaacAbstract:AbstractObservations of Aircraft Icing environments that included supercooled large drops (SLD) greater than 100 μm in diameter have been analyzed. The observations were collected by instrumented research Aircraft from 134 flights during six field programs in three different geographic regions of North America. The research Aircraft were specifically instrumented to accurately measure the microphysics characteristics of SLD conditions. In total 2444 SLD Icing environments were observed at 3-km resolution. Each observation had an average liquid water content (LWC) > 0.005 g m−3, drops > 100 μm in diameter, ice crystal concentrations 500 μm in diameter, each with median drop volume diameters 40 μm. For each SLD subset, the observations were used to develop envelop...
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Aircraft Icing in Glaciated and Mixed Phase Clouds
Journal of Aircraft, 2008Co-Authors: John Hallett, George A. IsaacAbstract:Aircraft are typically certified for flight into clouds containing entirely supercooled liquid particles. Nevertheless, mixed-phase clouds containing both supercooled water and ice particles occur not infrequently under similar atmospheric conditions at temperatures down to at least 30 C and, on occasion, to 40 C and are not included in the specification. Characterization of such clouds has proved a challenge to our understanding and measurement capability. As was recognized a decade ago, the role of such clouds in Aircraft Icing incidents is unclear and merits attention. Further, the definition of mixed-phase clouds depends on Aircraft-borne instruments, their ability to differentiate between ice and water separately, and their time response with respect to the actual spatial distribution of ice and water with respect to the Aircraft track. Such mixed phase clouds vary from an intimate mix of cirrus ice falling into a supercooled cloud layer to a consideration of a cumulonimbus system of a supercooled cloud updraft adjacent to an ice downdraft, butmany kilometers distant. The scale of themixmust therefore be considered in terms of physical processes of updraft and downdraft. The impact on Aircraft performance is highly dependent on the flight time in regions of any particular mix. Individual particles are investigated following impact on a heated 2-cm-diam sapphire opticalflat (the cloudscope),mounted normal to the airflowandhaving a central stagnation point, and video recorded from behind. Impacting particles diverge, melt, and/or evaporate, the rate of area change being a measure of particle density. The relative mix of particle phase, size, shape, and concentration provides insight on accretion scenarios for possible Aircraft structural or engine performance degradation.
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Characterizations of Aircraft Icing Environments that Include Supercooled Large Drops
Journal of Applied Meteorology, 2001Co-Authors: Stewart G. Cober, George A. Isaac, J. Walter StrappAbstract:Abstract Measurements of Aircraft Icing environments that include supercooled large drops (SLD) greater than 50 μm in diameter have been made during 38 research flights. These flights were conducted during the First and Third Canadian Freezing Drizzle Experiments. A primary objective of each project was the collection of in situ microphysics data in order to characterize Aircraft Icing environments associated with SLD. In total there were 2793 30-s averages obtained in clouds with temperatures less than or equal to 0°C, maximum droplet sizes greater than or equal to 50 μm, and ice crystal concentrations less than 1 L−1. The data include measurements from 12 distinct environments in which SLD were formed through melting of ice crystals followed by supercooling in a lower cold layer and from 27 distinct environments in which SLD were formed through a condensation and collision–coalescence process. The majority of the data were collected at temperatures between 0° and −14°C, in stratiform winter clouds assoc...
Stewart G. Cober - One of the best experts on this subject based on the ideXlab platform.
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Reply to ''Comments on 'Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification'''
Journal of Applied Meteorology and Climatology, 2013Co-Authors: Stewart G. Cober, George A. IsaacAbstract:Cober et al. (2009) and Cober and Isaac (2012) characterized Aircraft Icing environments that contained supercooledlargedrops (SLD).100mm indiameteron the basis of data collected during 134 research flights into winter storms in three geographic regions of North America. The characterization was designed to be supplemental to existing Aircraft Icing certification envelopes, given that existing envelopes do not explicitly incorporate SLD conditions. The U.S. Federal Aviation Administration is considering using the results from Cober et al. (2009) and Cober and Isaac (2012) as the basis for new certification regulations. Marwitz (2013) has suggested that the results of Cober and Isaac (2012) are deficient with respect to their application to the proposed new certification regulations, and he provided some criticisms. The purpose of this response is to address these criticisms. Marwitz (2013) suggested that the use of median volume diameter (MVD) and maximum diameter (Dmax) by Cober and Isaac (2012) as part of their characterization method is invalid because MVD and Dmax are not related to performance measurement. Cober and Isaac (2012) made no attempt to measure performance degradation of the research Aircraft. Rather the intent was to collect and analyze a sufficiently large dataset to characterize Icing environments that included SLD at the 99% and 99.9% levels (i.e., extreme values) so that manufacturers could subsequently determine the associated performance degradation on their instruments, Aircraft components, or engines. A justification for using MVD and Dmax follows. MVD is the 50% mass diameter, and hence large MVD values (i.e., .40mm) specifically identify Icing conditions that are outside the existing certifications standards and for which the majority of the mass is incorporated in drops that have higher collision efficiency (and corresponding performance degradation) with Aircraft surfaces. Aircraft, instrument, and engine manufacturers use different combinations of MVD (or other drop diameter characteristics), temperature, and liquid water content (LWC) to evaluate performance losses primarily through their use in wind-tunnel, naturalIcing, and numerical simulation experiments. Aircraft Icing envelopes have been based in part on MVD since their inception in the 1950s. It is an industry standard to correlate the analysis of Icing conditions against performance degradation, and MVD is one of the primary
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Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification
Journal of Applied Meteorology and Climatology, 2012Co-Authors: Stewart G. Cober, George A. IsaacAbstract:AbstractObservations of Aircraft Icing environments that included supercooled large drops (SLD) greater than 100 μm in diameter have been analyzed. The observations were collected by instrumented research Aircraft from 134 flights during six field programs in three different geographic regions of North America. The research Aircraft were specifically instrumented to accurately measure the microphysics characteristics of SLD conditions. In total 2444 SLD Icing environments were observed at 3-km resolution. Each observation had an average liquid water content (LWC) > 0.005 g m−3, drops > 100 μm in diameter, ice crystal concentrations 500 μm in diameter, each with median drop volume diameters 40 μm. For each SLD subset, the observations were used to develop envelop...
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Characterizations of Aircraft Icing Environments that Include Supercooled Large Drops
Journal of Applied Meteorology, 2001Co-Authors: Stewart G. Cober, George A. Isaac, J. Walter StrappAbstract:Abstract Measurements of Aircraft Icing environments that include supercooled large drops (SLD) greater than 50 μm in diameter have been made during 38 research flights. These flights were conducted during the First and Third Canadian Freezing Drizzle Experiments. A primary objective of each project was the collection of in situ microphysics data in order to characterize Aircraft Icing environments associated with SLD. In total there were 2793 30-s averages obtained in clouds with temperatures less than or equal to 0°C, maximum droplet sizes greater than or equal to 50 μm, and ice crystal concentrations less than 1 L−1. The data include measurements from 12 distinct environments in which SLD were formed through melting of ice crystals followed by supercooling in a lower cold layer and from 27 distinct environments in which SLD were formed through a condensation and collision–coalescence process. The majority of the data were collected at temperatures between 0° and −14°C, in stratiform winter clouds assoc...
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An Intercomparison of Mesoscale Forecasts of Aircraft Icing Using SSM/I Retrievals
Weather and Forecasting, 1996Co-Authors: André Tremblay, George A. Isaac, Stewart G. Cober, Anna Glazer, Jocelyn MailhotAbstract:Abstract A technique for the detection of supercooled liquid water (SLW) from Special Sensor Microwave/ (SSM/I) data is discussed. For this study, these SLW retrievals depict areas of Icing that are used to compare against different Aircraft Icing forecast algorithms. It is shown that currently used automated algorithms give incorrect distributions of SLW events with temperature and include systematically glaciated clouds in Icing forecasts. This problem is eliminated when an explicit SLW scheme is used. With this scheme the Canadian forecast system can detect roughly 75% of the SLW signal within an accuracy of 100 km when compared to SSM/I retrievals. The scheme also detects 99% of nonIcing events within the same accuracy.
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Aircraft Icing Measurements in East Coast Winter Storms
Journal of Applied Meteorology, 1995Co-Authors: Stewart G. Cober, George A. Isaac, J. W. StrappAbstract:Abstract Analysis of the Aircraft Icing environments of East Coast winter storms have been made from 3 1 flights duringthe second Canadian Atlantic Storms Program. Microphysical parameters have been summarized and are compared to common Icing intensity envelopes and to other Icing datasets. Cloud regions with supercooled liquid water had an average horizontal extent of 4.3 km, with average droplet concentrations of 130 μ, liquid water contents of 0.13 g m-3, and droplet median volume diameters of 18 pm. In general, the Icing intensity observed was classified as light, although moderate to severe Icing was observed in several common synoptic situationsand several cases are discussed. Freezing drizzle was observed on four flights, and represented the most severeIcing environment encountered.
Frank Mcdonough - One of the best experts on this subject based on the ideXlab platform.
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Surface weather features associated with freezing precipitation and severe in-flight Aircraft Icing
Atmospheric Research, 1998Co-Authors: Ben C. Bernstein, Tiffany A. Omeron, Marcia K. Politovich, Frank McdonoughAbstract:Surface observations of freezing precipitation and pilot reports of severe in-flight Aircraft Icing for the continental United States are compared to the location of surface weather features, including airmasses of different origin and position relative to fronts, low-pressure centers and troughs. Statistics are calculated to determine where freezing precipitation and severe Aircraft Icing occur most often, and are produced most efficiently (number of occurrences per unit area). Airmasses found along the east and west coasts of the US are the most efficient producers of freezing precipitation and pilot reports of severe Icing, respectively, while the areas ahead of surface warm fronts are the most efficient producers of both of these phenomena. The weather conditions typically found in these locations, and others that are of interest for freezing precipitation and Aircraft Icing, are discussed.
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The Relationship between Aircraft Icing and Synoptic-Scale Weather Conditions
Weather and Forecasting, 1997Co-Authors: Ben C. Bernstein, Tiffany A. Omeron, Frank Mcdonough, Marcia K. PolitovichAbstract:Abstract More than 2700 Aircraft Icing pilot reports are compared to analyses of operationally available data for 37 cases of winter weather. Statistical results regarding the number of occurrences of Icing reports with airmass origin, location relative to fronts, troughs and low pressure centers, precipitation type, cloud cover, lightning/thunder, fog, radar reflectivity, and synoptic-scale forcing mechanisms are developed. Statistics are created for several combinations of Icing severity and type, including a category for some of the worst Icing encountered by Aircraft (clear or mixed Icing of moderate or greater severity), then normalized by the areal extent of the weather features. Results indicate that the locations most conducive to Icing conditions were arctic, West Coast, and East Coast air masses; 250–600 km ahead of active and stationary warm fronts; in areas of freezing drizzle, freezing rain, and ice pellets when precipitation was occurring; and in areas with obscured and overcast sky conditio...
Marcia K. Politovich - One of the best experts on this subject based on the ideXlab platform.
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A Numerical Weather Model’s Ability to Predict Characteristics of Aircraft Icing Environments
Weather and Forecasting, 2017Co-Authors: Gregory Thompson, Marcia K. Politovich, Roy RasmussenAbstract:AbstractRecent advances in high-performance computing have enabled higher-resolution numerical weather models with increasingly complex data assimilation and more accurate physical parameterizations. With respect to Aircraft and ground Icing applications, a weather model’s cloud physics scheme is responsible for the direct forecasts of the water phase and amount and is a critical ingredient to forecasting future Icing conditions. In this paper, numerical model results are compared with Aircraft observations taken during Icing research flights, and the general characteristics of liquid water content, median volume diameter, droplet concentration, and temperature within Aircraft Icing environments are evaluated. The comparison reveals very promising skill by the model in predicting these characteristics consistent with observations. The application of model results to create explicit forecasts of ice accretion rates for an example case of Aircraft and ground Icing is shown.
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Progress Towards the Remote Sensing of Aircraft Icing Hazards
Remote Sensing Applications for Aviation Weather Hazard Detection and Decision Support, 2008Co-Authors: Andrew L. Reehorst, Marcia K. Politovich, David J. Brinker, David Serke, Charles C. Ryerson, Andrew L. Pazmany, Frederick SolheimAbstract:NASA has teamed with the FAA, DoD, industry, and academia for research into the remote detection and measurement of atmospheric conditions leading to Aircraft Icing hazards. The ultimate goal of this effort is to provide pilots, controllers, and dispatchers sufficient information to allow Aircraft to avoid or minimize their exposure to the hazards of in-flight Icing. Since the hazard of in-flight Icing is the outcome of Aircraft flight through clouds containing supercooled liquid water and strongly influenced by the Aircraft's speed and configuration and by the length of exposure, the hazard can't be directly detected, but must be inferred based upon the measurement of conducive atmospheric conditions. Therefore, Icing hazard detection is accomplished through the detection and measurement of liquid water in regions of measured sub-freezing air temperatures. The Icing environment is currently remotely measured from the ground with a system fusing radar, lidar, and multi-frequency microwave radiometer sensors. Based upon expected ice accretion severity for the measured environment, a resultant Aircraft hazard is then calculated. Because of the power, size, weight, and view angle constraints of airborne platforms, the current ground-based solution is not applicable for flight. Two current airborne concepts are the use of either multi-frequency radiometers or multi-frequency radar. Both ground-based and airborne solutions are required for the future since ground-based systems can provide hazard detection for all Aircraft in airport terminal regions while airborne systems will be needed to provide equipped Aircraft with flight path coverage between terminal regions.
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Surface weather features associated with freezing precipitation and severe in-flight Aircraft Icing
Atmospheric Research, 1998Co-Authors: Ben C. Bernstein, Tiffany A. Omeron, Marcia K. Politovich, Frank McdonoughAbstract:Surface observations of freezing precipitation and pilot reports of severe in-flight Aircraft Icing for the continental United States are compared to the location of surface weather features, including airmasses of different origin and position relative to fronts, low-pressure centers and troughs. Statistics are calculated to determine where freezing precipitation and severe Aircraft Icing occur most often, and are produced most efficiently (number of occurrences per unit area). Airmasses found along the east and west coasts of the US are the most efficient producers of freezing precipitation and pilot reports of severe Icing, respectively, while the areas ahead of surface warm fronts are the most efficient producers of both of these phenomena. The weather conditions typically found in these locations, and others that are of interest for freezing precipitation and Aircraft Icing, are discussed.
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The Relationship between Aircraft Icing and Synoptic-Scale Weather Conditions
Weather and Forecasting, 1997Co-Authors: Ben C. Bernstein, Tiffany A. Omeron, Frank Mcdonough, Marcia K. PolitovichAbstract:Abstract More than 2700 Aircraft Icing pilot reports are compared to analyses of operationally available data for 37 cases of winter weather. Statistical results regarding the number of occurrences of Icing reports with airmass origin, location relative to fronts, troughs and low pressure centers, precipitation type, cloud cover, lightning/thunder, fog, radar reflectivity, and synoptic-scale forcing mechanisms are developed. Statistics are created for several combinations of Icing severity and type, including a category for some of the worst Icing encountered by Aircraft (clear or mixed Icing of moderate or greater severity), then normalized by the areal extent of the weather features. Results indicate that the locations most conducive to Icing conditions were arctic, West Coast, and East Coast air masses; 250–600 km ahead of active and stationary warm fronts; in areas of freezing drizzle, freezing rain, and ice pellets when precipitation was occurring; and in areas with obscured and overcast sky conditio...
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Toward the Improvement of Aircraft-Icing Forecasts for the Continental United States
Weather and Forecasting, 1992Co-Authors: Paul Schultz, Marcia K. PolitovichAbstract:Abstract An automated procedure is developed for detecting and forecasting atmospheric conditions conductive to Aircraft Icing over the continental United States. The procedure uses gridded output from the Nested-Grid Model, and is based on the manual techniques currently in use at the National Aviation Weather Advisory Unit in Kansas City, Missouri. Verification of the procedure suggests forecasting performance on par with the human forecasters. Unfortunately, efforts at more-rigorous performance analysis are hindered by the inadequacies of the verification database, which consists of pilots’ subjective reports of airframe ice buildup. In general, no-ice conditions are not reported. The physics of Aircraft Icing are reviewed, and the current manual techniques are discussed. The automated procedure provides an infrastructure for implementing incremental improvements in the algorithm as observations and numerical models improve.
Felix Yanovsky - One of the best experts on this subject based on the ideXlab platform.
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Efficiency estimation for the parametric radar algorithm of detection of probable Aircraft Icing zones
2014 International Conference on Mathematical Methods in Electromagnetic Theory, 2014Co-Authors: A.a. Pitertsev, Felix YanovskyAbstract:Icing is one of the most dangerous meteorological phenomena in civil aviation. The best Icing protection method is to prevent it formation. To do this, the pilot needs information about a zone of probable Icing on the route of the Aircraft flight. This information can be obtained using of airborne polarimetric radar data. This paper deals with the modeling and analysis of experimental data, synthesis of parametric algorithm for detection of the probable Aircraft Icing areas and the estimation of its effectiveness.
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Polarimetric radar as a device for detecting potentially dangerous zones of Aircraft Icing
2014 IEEE Microwaves Radar and Remote Sensing Symposium (MRRS), 2014Co-Authors: A.a. Pitertsev, Felix YanovskyAbstract:This paper is dedicated to remote detection of one of the most dangerous meteorological phenomena that significantly influences to all types of Aircraft both civil and military. The best Icing protection method is to prevent it formation. To do this, the pilot needs information about a zone of possible Icing on the Aircraft path. Such information can be obtained using airborne polarimetric radar. Here we discuss the results of modeling and data analysis that are necessary for development of signal processing algorithms to detect potentially dangerous zones in the atmosphere to avoid Aircraft Icing-inflight.
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Polarimetric approach to detection of probable Aircraft Icing zones. Icing detection algorithms
2007 European Radar Conference, 2007Co-Authors: A.a. Pitertsev, Felix YanovskyAbstract:Aircraft Icing is a dangerous meteorological phenomenon. Most important conditions for growing of ice coating on Aircraft body or wings are presence of supercooled liquid water (SLW) drops, high humidity and negative temperature of air. Remote sensing of the clouds with the help of polarimetric radar can detect the SLW in cloud. It can be used to avoid dangerous situations during the flight. Mathematical simulation of microwave backscattering from ice crystals of different forms and water drops in rain and clouds have been done. Different Icing detection algorithms are described and analyzed.
