Robert Sharman - Profile on Academia.edu (original) (raw)
Papers by Robert Sharman
npj climate and atmospheric science, Jul 14, 2023
Atmospheric turbulence at commercial aircraft cruising altitudes is a main threat to aviation saf... more Atmospheric turbulence at commercial aircraft cruising altitudes is a main threat to aviation safety worldwide. As the air transport industry expands and is continuously growing, investigating global response of aviation turbulence under climate change scenarios is required for preparing optimal and safe flying plans for the future. This study examines future frequencies of moderate-orgreater-intensity turbulence generated from various sources, viz., clear-air turbulence and mountain-wave turbulence that are concentrated in midlatitudes, and near-cloud turbulence that is concentrated in tropics and subtropics, using long-term climate model data of high-emissions scenario and historical condition. Here, we show that turbulence generated from all three sources is intensified with higher occurrences globally in changed climate compared to the historical period. Although previous studies have reported intensification of clear-air turbulence in changing climate, implying bumpier flights in the future, we show that intensification of mountain-wave turbulence and near-cloud turbulence can also be expected with changing climate.
16th Conference on Mountain Meteorology (17-22 August, 2014), Aug 18, 2014
Breaking topographically-induced gravity waves or mountain waves are a major source of turbulence... more Breaking topographically-induced gravity waves or mountain waves are a major source of turbulence encounters by commercial and general aviation aircraft. An empirical method for forecasting mountain wave-induced turbulence (MWT) over the continental U. S. is presented which uses a combination of MWT seasonal and regional climatologies, terrain characteristics, and turbulence diagnostics derived from operational numerical weather prediction (NWP) model output. Accuracy assessments are provided through comparisons to thousands of pilot reports of turbulence from mid troposphere to lower stratosphere over mountainous areas in the U.S. where the report specifically indicated that the turbulence was mountain-wave related.
Invited talk) Recent advances in the detection and understanding of turbulence associated with thunderstorms
14th Conference on Mesoscale Processes/15th Conference on Aviation, Range, and Aerospace Meteorology, Aug 1, 2011
Proceedings of SPIE, Aug 22, 2008
This paper describes how operational radar, satellite and lightning data may be used in conjuncti... more This paper describes how operational radar, satellite and lightning data may be used in conjunction with numerical weather model data to provide remote detection and diagnosis of atmospheric turbulence in and around thunderstorms. In-cloud turbulence is measured with the NEXRAD Turbulence Detection Algorithm (NTDA) using extensively qualitycontrolled, ground-based Doppler radar data. A real-time demonstration of the NTDA includes generation of a 3-D turbulence mosaic covering the CONUS east of the Rocky Mountains, a web-based display, and experimental uplinks of turbulence maps to en-route commercial aircraft. Near-cloud turbulence is inferred from thunderstorm morphology, intensity, growth rate and environment data provided by (1) satellite radiance measurements, rates of change, winds, and other derived features, (2) lightning strike measurements, (3) radar reflectivity measurements and (4) weather model data. These are combined via a machine learning technique trained using a database of in situ turbulence measurements from commercial aircraft to create a predictive model. This new capability is being developed under FAA and NASA funding to enhance current U.S. and international turbulence decision support systems, allowing rapid-update, highresolution, comprehensive assessments of atmospheric turbulence hazards for use by pilots, dispatchers, and air traffic controllers. It will also contribute to the comprehensive 4-D weather information database for NextGen.
한국기상학회 학술대회 논문집, Apr 1, 2010
The forecast skill of upper-level turbulence diagnostics is evaluated using available turbulence ... more The forecast skill of upper-level turbulence diagnostics is evaluated using available turbulence observations [viz., pilot reports (PIREPs)] over East Asia. The six years of PIREPs used in this study include null, light, and moderate-or-greater intensity categories. The turbulence diagnostics used are a subset of indices in the Graphical Turbulence Guidance (GTG) system. To investigate the optimal performance of the component GTG diagnostics and GTG combinations over East Asia, various statistical evaluations and sensitivity tests are performed. To examine the dependency of the GTG system on the operational numerical weather prediction (NWP) model, the GTG system is applied to both the Regional Data Assimilation and Prediction System (RDAPS) analysis data and Global Forecasting System (GFS) analysis and forecast data with 30-km and 0.31258 (T382) horizontal grid spacings. The dependency of the temporal variation in the PIREP and GFS data and the forecast lead time of the GFS-based GTG combination are also investigated. It is found that the forecasting performance of the GTG system varies with year and season according to the annual and seasonal variations in the large-scale atmospheric conditions over the East Asia region. The wintertime GTG skill is the highest, because most GTG component diagnostics are related to jet streams and upper-level fronts. The GTG skill improves as the number of PIREP samples and the vertical resolution of the underlying NWP analysis data increase, and the GTG performance decreases as the forecast lead time increases from 0 to 12 h.
Gravity wave-induced mean flows and turbulence at the tropopause
AGU Fall Meeting Abstracts, Dec 1, 2012
Bulletin of the American Physical Society, Nov 19, 2012
Wave-induced mean flow at an interface JOHN MCHUGH, University of New Hampshire, ROBERT SHARMAN, ... more Wave-induced mean flow at an interface JOHN MCHUGH, University of New Hampshire, ROBERT SHARMAN, National Center for Atmospheric Research -A vertical packet of internal waves that are horizontally periodic will generate a mean flow that has the same sense as the group velocity of the incident waves. When the wave packet impinges on a density-gradient interface the waves are partially reflected and the wave-induced mean flow is enhanced just under the interface. A density-gradient interface has continuous density but discontinuous buoyancy frequency, and is an idealization of Earth's tropopause. Here we consider waves generated by flow past an isolated object, and maintain a vertical packet by introducing the obstacle gradually. The resulting waves are confined horizontally over a narrow interval and hence are not slowly varying in the horizontal. Nonlinear simulations show that the mean flow at the interface has a component with the same sense as the wave group velocity above the mean position of the interface, but also a component with the opposite sense just below the mean interfacial position. This combination establishes a wave-induced circulation at the interface.
Effects of Distant Organized Convection on Forecasts of Widespread Clear-Air Turbulence
Monthly Weather Review, Oct 1, 2022
Two cases of observed widespread moderate-or-greater (MOG) clear-air turbulence (CAT) in differen... more Two cases of observed widespread moderate-or-greater (MOG) clear-air turbulence (CAT) in different synoptic patterns are investigated using a nested high-resolution NWP model. Both of these cases occurred in confluent entrance regions of upper-tropospheric–lower-stratospheric (UTLS) jet streaks, where large-scale anticyclonic outflow from distant organized moist convection strengthened the UTLS jet. Both the strength and vertical sharpness of the resulting jet influence the altitudes of MOG turbulence and the details of simulated turbulence onset mechanisms. In a strong and narrow UTLS jet downstream of a weak synoptic ridge, MOG turbulence arises from Kelvin–Helmholtz (KH) waves that overturn in opposite directions on the vertical flanks of the jet. In broader UTLS jets, MOG turbulence arising from KH waves was favored in strong vertical shear layers beneath the wind maximum, but was inhibited above it due to static stability increases near the tropopause. However, vertically propagating internal gravity waves initiated above KH wave breaking beneath the UTLS jet amplify within the lower stratosphere above the jet, constituting another possible source of turbulence. Turbulence onset mechanisms were often apparent in simulations with minimum horizontal grid spacings of Δx = 1 km. However, amplitudes of the associated grid-resolved vertical motions were unreliable when compared with simulations having minimum horizontal grid spacings of Δx = 1/3 km. In spite of this, turbulence forecasting systems driven by input from coarser-resolution operational NWP models are demonstrated to provide good diagnoses of this type of convectively influenced CAT when the NWP model accurately forecasts upstream convection. Significance Statement In this study we document the role of distant convection on observed widespread strong clear-air turbulence near upper-level jet streams in different weather patterns. Results from nested NWP model simulations, together with similar examples from previous case studies, suggest a strong association of widespread turbulence with jet stream enhancements related to outflow from upstream convection. We also demonstrate how model horizontal grid spacings of <1 km are required to adequately resolve common turbulence onset mechanisms (e.g., Kelvin–Helmholtz instability, gravity wave breaking). Nevertheless, examples are provided showing that turbulence forecasting systems driven by lower-resolution operational NWP models can provide potentially valuable guidance on these widespread turbulence events when those models accurately forecast the timing and locations of upstream convection.
Journal of Applied Meteorology and Climatology, Apr 1, 2008
Output from the Army Test and Evaluation Command's Four-Dimensional Weather System's mesoscale mo... more Output from the Army Test and Evaluation Command's Four-Dimensional Weather System's mesoscale model is used to drive secondary-applications models to produce forecasts of quantities of importance for daily decision making at U.S. Army test ranges. Examples of three specific applications-a sound propagation model, a missile trajectory model, and a transport and diffusion model-are given, along with accuracy assessments using cases in which observational data are available for verification. Ensembles of application model forecasts are used to derive probabilities of exceedance of quantities that can be used to help range test directors to make test go-no-go decisions. The ensembles can be based on multiple meteorological forecast runs or on spatial ensembles derived from different soundings extracted from a single meteorological forecast. In most cases, the accuracies of the secondary-application forecasts are sufficient to meet operational needs at the test ranges.
Diagnosing hazardous turbulence associated with thunderstorms [presentation]
Journal of Applied Meteorology and Climatology, Mar 1, 2020
Strong turbulence was encountered by the German High-Altitude Long-Range Research Aircraft (HALO)... more Strong turbulence was encountered by the German High-Altitude Long-Range Research Aircraft (HALO) at flight level 430 (13.8 km) on 13 October 2016 above Iceland. In this event the turbulence caused altitude changes of the research aircraft of about 50 m within a period of approximately 15 s. Additionally, the automatic thrust control of the HALO could not control the large gradients in the horizontal wind speed and, consequently, the pilot had to switch off this system. Simultaneously, the French Falcon of Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE), flying 2 km below HALO, also encountered turbulence at almost the same location. On that day, mountain-wave (MW) excitation and propagation was favored by the alignment of strong surface winds and the polar front jet. We use a combination of in situ observations, ECMWF and empirical turbulence forecasts, and high-resolution simulations to characterize the observed turbulent event. These show that a pronounced negative vertical shear of the horizontal wind favored overturning and breaking of MWs in the area of the encountered turbulence. The turbulent region was tilted upstream and extended over a distance of about 2 km in the vertical. The analyses suggest that HALO was flying through the center of a breaking MW field while the French Falcon encountered the lower edge of this region. Surprisingly, the pronounced gradients in the horizontal wind speeds leading to the deactivation of the automatic thrust control were located north of the breaking MW field. In this area, our analysis suggests the presence of gravity waves that could have generated the encountered modulation of the horizontal wind field.
Determination of the Primary Diagnostics for the CAT (Clear-Air Turbulence) Forecast in Korea
Asia-pacific Journal of Atmospheric Sciences, Dec 1, 2003
In order to improve the CAT (clear-air turbulence) forecasts of KITFA (Korean Integrated Turbulen... more In order to improve the CAT (clear-air turbulence) forecasts of KITFA (Korean Integrated Turbulence Forecasting Algorithm), analyses and forecast fields of 12 CAT diagnostics included in KITFA, in which 5-㎞ RDAPS (Regional Data Assimilation and Prediction System) forecasts routinely ingested, are analyzed in comparison with PIREPs reported in Korea for Spring 2002. The ROC (Receiver Operating Characteristics) curves shown as the relationship between 1-PODn and PODy represent that NGM1, vertical shear (VWS), and the squared vorticy (Vort²) suggest somewhat meaningful statistics for detecting the turbulence potential area in the analysis fields. The areas under the ROC curves suggested that the significance of the CAT forecasts for the 12 indices decreased with lead times. Other statistical values such as FAR (False Alarm Ratio), Critical Success Index (CSI), and TSS (True Skill Statistics) for some specified thresholds of the indices suggest more validated statistics for the performance of the turbulence forecasts. Although the statistical results obtained by matching turbulence forecasts of the CAT diagnostics to the observations can be somewhat uncertain because of a limitation of the NWP model forecast and insufficient PIREPs, this intercomparison exercise contributes not only for the improvement of the CAT forecast, but also for the robustness of the verification methods for the KITFA.
한국의 청천난류 예보 시스템에 대한 연구 Part II: Graphical Turbulence Guidance (GTG) 시스템
대기, Sep 1, 2009
CAT (clear-air turbulence) forecasting algorithm, the Graphical Turbulence Guidance (GTG) system ... more CAT (clear-air turbulence) forecasting algorithm, the Graphical Turbulence Guidance (GTG) system developed at NCAR (national center for atmospheric research), is evaluated with available observations (e.g., pilot reports; PIREPs) reported in South Korea during the recent 5 years (2003-2008, excluding 2005). The GTG system includes several steps. First, 44 CAT indices are calculated in the domain of the Regional Data Assimilation and Prediction System (RDAPS) analysis data with 30 ㎞ horizontal grid spacing provided by KMA (Korean Meteorological Administration). Second, 10 indices that performed ten best forecasting scores are selected. Finally, 10 indices are combined by measuring the score based on the probability of detection, which is calculated using PIREPs exclusively of moderate-or-greater intensity. In order to investigate the best performance of the GTG system in Korea, various statistical examinations and sensitivity tests of the GTG system are performed by yearly and seasonally classified PIREPs. Performances of the GTG system based on yearly distributed PIREPs have annual variations because the compositions of indices are different from each year. Seasonal forecasting is generally better than yearly forecasting, because selected CAT indices in each season represent meteorological condition much more properly than applying the selected CAT indices to all seasons. Wintertime forecasting is the best among the four seasonal forecastings. This is likely due to that the GTG system consists of many CAT indices related to the jet stream, and turbulence associated with the jet stream can be activated mostly in wintertime under strong jet magnitude. On the other hand, summertime forecasting skill is much less than other seasons. Compared with current operational CAT prediction system (KITFA; Korean Integrated Turbulence Forecasting System), overall performance of the GTG system is better when CAT indices are selected seasonally.
Aviation Turbulence : Processes, Detection, Prediction
Springer eBooks, 2016
Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wo... more Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wonder why this is so difficult to avoid. The book includes papers by various aviation turbulence researchers and provides background into the nature and causes of atmospheric turbulence that affect aircraft motion, and contains surveys of the latest techniques for remote and in situ sensing and forecasting of the turbulence phenomenon. It provides updates on the state-of-the-art research since earlier studies in the 1960s on clear-air turbulence, explains recent new understanding into turbulence generation by thunderstorms, and summarizes future challenges in turbulence prediction and avoidance
Rising above the storm: Studies into convectively induced turbulence
Pentagon shield: Experiments with a nonoscillatory forward-in-time CFD code (EuLag) to simulate flow around the Pentagon [presentation]
![Research paper thumbnail of Probabilistic pilot-behavior models for clear-air turbulence avoidance maneuvers [presentation]](https://attachments.academia-assets.com/110939369/thumbnails/1.jpg)
](Determining the impact of Doppler LIDAR on transport and diffusion modeling applications: An observing system simulation experiment [presentation]
Gravity waves and gravity wave "breaking" as contributors to aviation turbulence
Investigation of mountain-wave induced turbulence (MWT) events over the Colorado region on 31 December 2011
npj climate and atmospheric science, Jul 14, 2023
Atmospheric turbulence at commercial aircraft cruising altitudes is a main threat to aviation saf... more Atmospheric turbulence at commercial aircraft cruising altitudes is a main threat to aviation safety worldwide. As the air transport industry expands and is continuously growing, investigating global response of aviation turbulence under climate change scenarios is required for preparing optimal and safe flying plans for the future. This study examines future frequencies of moderate-orgreater-intensity turbulence generated from various sources, viz., clear-air turbulence and mountain-wave turbulence that are concentrated in midlatitudes, and near-cloud turbulence that is concentrated in tropics and subtropics, using long-term climate model data of high-emissions scenario and historical condition. Here, we show that turbulence generated from all three sources is intensified with higher occurrences globally in changed climate compared to the historical period. Although previous studies have reported intensification of clear-air turbulence in changing climate, implying bumpier flights in the future, we show that intensification of mountain-wave turbulence and near-cloud turbulence can also be expected with changing climate.
16th Conference on Mountain Meteorology (17-22 August, 2014), Aug 18, 2014
Breaking topographically-induced gravity waves or mountain waves are a major source of turbulence... more Breaking topographically-induced gravity waves or mountain waves are a major source of turbulence encounters by commercial and general aviation aircraft. An empirical method for forecasting mountain wave-induced turbulence (MWT) over the continental U. S. is presented which uses a combination of MWT seasonal and regional climatologies, terrain characteristics, and turbulence diagnostics derived from operational numerical weather prediction (NWP) model output. Accuracy assessments are provided through comparisons to thousands of pilot reports of turbulence from mid troposphere to lower stratosphere over mountainous areas in the U.S. where the report specifically indicated that the turbulence was mountain-wave related.
Invited talk) Recent advances in the detection and understanding of turbulence associated with thunderstorms
14th Conference on Mesoscale Processes/15th Conference on Aviation, Range, and Aerospace Meteorology, Aug 1, 2011
Proceedings of SPIE, Aug 22, 2008
This paper describes how operational radar, satellite and lightning data may be used in conjuncti... more This paper describes how operational radar, satellite and lightning data may be used in conjunction with numerical weather model data to provide remote detection and diagnosis of atmospheric turbulence in and around thunderstorms. In-cloud turbulence is measured with the NEXRAD Turbulence Detection Algorithm (NTDA) using extensively qualitycontrolled, ground-based Doppler radar data. A real-time demonstration of the NTDA includes generation of a 3-D turbulence mosaic covering the CONUS east of the Rocky Mountains, a web-based display, and experimental uplinks of turbulence maps to en-route commercial aircraft. Near-cloud turbulence is inferred from thunderstorm morphology, intensity, growth rate and environment data provided by (1) satellite radiance measurements, rates of change, winds, and other derived features, (2) lightning strike measurements, (3) radar reflectivity measurements and (4) weather model data. These are combined via a machine learning technique trained using a database of in situ turbulence measurements from commercial aircraft to create a predictive model. This new capability is being developed under FAA and NASA funding to enhance current U.S. and international turbulence decision support systems, allowing rapid-update, highresolution, comprehensive assessments of atmospheric turbulence hazards for use by pilots, dispatchers, and air traffic controllers. It will also contribute to the comprehensive 4-D weather information database for NextGen.
한국기상학회 학술대회 논문집, Apr 1, 2010
The forecast skill of upper-level turbulence diagnostics is evaluated using available turbulence ... more The forecast skill of upper-level turbulence diagnostics is evaluated using available turbulence observations [viz., pilot reports (PIREPs)] over East Asia. The six years of PIREPs used in this study include null, light, and moderate-or-greater intensity categories. The turbulence diagnostics used are a subset of indices in the Graphical Turbulence Guidance (GTG) system. To investigate the optimal performance of the component GTG diagnostics and GTG combinations over East Asia, various statistical evaluations and sensitivity tests are performed. To examine the dependency of the GTG system on the operational numerical weather prediction (NWP) model, the GTG system is applied to both the Regional Data Assimilation and Prediction System (RDAPS) analysis data and Global Forecasting System (GFS) analysis and forecast data with 30-km and 0.31258 (T382) horizontal grid spacings. The dependency of the temporal variation in the PIREP and GFS data and the forecast lead time of the GFS-based GTG combination are also investigated. It is found that the forecasting performance of the GTG system varies with year and season according to the annual and seasonal variations in the large-scale atmospheric conditions over the East Asia region. The wintertime GTG skill is the highest, because most GTG component diagnostics are related to jet streams and upper-level fronts. The GTG skill improves as the number of PIREP samples and the vertical resolution of the underlying NWP analysis data increase, and the GTG performance decreases as the forecast lead time increases from 0 to 12 h.
Gravity wave-induced mean flows and turbulence at the tropopause
AGU Fall Meeting Abstracts, Dec 1, 2012
Bulletin of the American Physical Society, Nov 19, 2012
Wave-induced mean flow at an interface JOHN MCHUGH, University of New Hampshire, ROBERT SHARMAN, ... more Wave-induced mean flow at an interface JOHN MCHUGH, University of New Hampshire, ROBERT SHARMAN, National Center for Atmospheric Research -A vertical packet of internal waves that are horizontally periodic will generate a mean flow that has the same sense as the group velocity of the incident waves. When the wave packet impinges on a density-gradient interface the waves are partially reflected and the wave-induced mean flow is enhanced just under the interface. A density-gradient interface has continuous density but discontinuous buoyancy frequency, and is an idealization of Earth's tropopause. Here we consider waves generated by flow past an isolated object, and maintain a vertical packet by introducing the obstacle gradually. The resulting waves are confined horizontally over a narrow interval and hence are not slowly varying in the horizontal. Nonlinear simulations show that the mean flow at the interface has a component with the same sense as the wave group velocity above the mean position of the interface, but also a component with the opposite sense just below the mean interfacial position. This combination establishes a wave-induced circulation at the interface.
Effects of Distant Organized Convection on Forecasts of Widespread Clear-Air Turbulence
Monthly Weather Review, Oct 1, 2022
Two cases of observed widespread moderate-or-greater (MOG) clear-air turbulence (CAT) in differen... more Two cases of observed widespread moderate-or-greater (MOG) clear-air turbulence (CAT) in different synoptic patterns are investigated using a nested high-resolution NWP model. Both of these cases occurred in confluent entrance regions of upper-tropospheric–lower-stratospheric (UTLS) jet streaks, where large-scale anticyclonic outflow from distant organized moist convection strengthened the UTLS jet. Both the strength and vertical sharpness of the resulting jet influence the altitudes of MOG turbulence and the details of simulated turbulence onset mechanisms. In a strong and narrow UTLS jet downstream of a weak synoptic ridge, MOG turbulence arises from Kelvin–Helmholtz (KH) waves that overturn in opposite directions on the vertical flanks of the jet. In broader UTLS jets, MOG turbulence arising from KH waves was favored in strong vertical shear layers beneath the wind maximum, but was inhibited above it due to static stability increases near the tropopause. However, vertically propagating internal gravity waves initiated above KH wave breaking beneath the UTLS jet amplify within the lower stratosphere above the jet, constituting another possible source of turbulence. Turbulence onset mechanisms were often apparent in simulations with minimum horizontal grid spacings of Δx = 1 km. However, amplitudes of the associated grid-resolved vertical motions were unreliable when compared with simulations having minimum horizontal grid spacings of Δx = 1/3 km. In spite of this, turbulence forecasting systems driven by input from coarser-resolution operational NWP models are demonstrated to provide good diagnoses of this type of convectively influenced CAT when the NWP model accurately forecasts upstream convection. Significance Statement In this study we document the role of distant convection on observed widespread strong clear-air turbulence near upper-level jet streams in different weather patterns. Results from nested NWP model simulations, together with similar examples from previous case studies, suggest a strong association of widespread turbulence with jet stream enhancements related to outflow from upstream convection. We also demonstrate how model horizontal grid spacings of <1 km are required to adequately resolve common turbulence onset mechanisms (e.g., Kelvin–Helmholtz instability, gravity wave breaking). Nevertheless, examples are provided showing that turbulence forecasting systems driven by lower-resolution operational NWP models can provide potentially valuable guidance on these widespread turbulence events when those models accurately forecast the timing and locations of upstream convection.
Journal of Applied Meteorology and Climatology, Apr 1, 2008
Output from the Army Test and Evaluation Command's Four-Dimensional Weather System's mesoscale mo... more Output from the Army Test and Evaluation Command's Four-Dimensional Weather System's mesoscale model is used to drive secondary-applications models to produce forecasts of quantities of importance for daily decision making at U.S. Army test ranges. Examples of three specific applications-a sound propagation model, a missile trajectory model, and a transport and diffusion model-are given, along with accuracy assessments using cases in which observational data are available for verification. Ensembles of application model forecasts are used to derive probabilities of exceedance of quantities that can be used to help range test directors to make test go-no-go decisions. The ensembles can be based on multiple meteorological forecast runs or on spatial ensembles derived from different soundings extracted from a single meteorological forecast. In most cases, the accuracies of the secondary-application forecasts are sufficient to meet operational needs at the test ranges.
Diagnosing hazardous turbulence associated with thunderstorms [presentation]
Journal of Applied Meteorology and Climatology, Mar 1, 2020
Strong turbulence was encountered by the German High-Altitude Long-Range Research Aircraft (HALO)... more Strong turbulence was encountered by the German High-Altitude Long-Range Research Aircraft (HALO) at flight level 430 (13.8 km) on 13 October 2016 above Iceland. In this event the turbulence caused altitude changes of the research aircraft of about 50 m within a period of approximately 15 s. Additionally, the automatic thrust control of the HALO could not control the large gradients in the horizontal wind speed and, consequently, the pilot had to switch off this system. Simultaneously, the French Falcon of Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE), flying 2 km below HALO, also encountered turbulence at almost the same location. On that day, mountain-wave (MW) excitation and propagation was favored by the alignment of strong surface winds and the polar front jet. We use a combination of in situ observations, ECMWF and empirical turbulence forecasts, and high-resolution simulations to characterize the observed turbulent event. These show that a pronounced negative vertical shear of the horizontal wind favored overturning and breaking of MWs in the area of the encountered turbulence. The turbulent region was tilted upstream and extended over a distance of about 2 km in the vertical. The analyses suggest that HALO was flying through the center of a breaking MW field while the French Falcon encountered the lower edge of this region. Surprisingly, the pronounced gradients in the horizontal wind speeds leading to the deactivation of the automatic thrust control were located north of the breaking MW field. In this area, our analysis suggests the presence of gravity waves that could have generated the encountered modulation of the horizontal wind field.
Determination of the Primary Diagnostics for the CAT (Clear-Air Turbulence) Forecast in Korea
Asia-pacific Journal of Atmospheric Sciences, Dec 1, 2003
In order to improve the CAT (clear-air turbulence) forecasts of KITFA (Korean Integrated Turbulen... more In order to improve the CAT (clear-air turbulence) forecasts of KITFA (Korean Integrated Turbulence Forecasting Algorithm), analyses and forecast fields of 12 CAT diagnostics included in KITFA, in which 5-㎞ RDAPS (Regional Data Assimilation and Prediction System) forecasts routinely ingested, are analyzed in comparison with PIREPs reported in Korea for Spring 2002. The ROC (Receiver Operating Characteristics) curves shown as the relationship between 1-PODn and PODy represent that NGM1, vertical shear (VWS), and the squared vorticy (Vort²) suggest somewhat meaningful statistics for detecting the turbulence potential area in the analysis fields. The areas under the ROC curves suggested that the significance of the CAT forecasts for the 12 indices decreased with lead times. Other statistical values such as FAR (False Alarm Ratio), Critical Success Index (CSI), and TSS (True Skill Statistics) for some specified thresholds of the indices suggest more validated statistics for the performance of the turbulence forecasts. Although the statistical results obtained by matching turbulence forecasts of the CAT diagnostics to the observations can be somewhat uncertain because of a limitation of the NWP model forecast and insufficient PIREPs, this intercomparison exercise contributes not only for the improvement of the CAT forecast, but also for the robustness of the verification methods for the KITFA.
한국의 청천난류 예보 시스템에 대한 연구 Part II: Graphical Turbulence Guidance (GTG) 시스템
대기, Sep 1, 2009
CAT (clear-air turbulence) forecasting algorithm, the Graphical Turbulence Guidance (GTG) system ... more CAT (clear-air turbulence) forecasting algorithm, the Graphical Turbulence Guidance (GTG) system developed at NCAR (national center for atmospheric research), is evaluated with available observations (e.g., pilot reports; PIREPs) reported in South Korea during the recent 5 years (2003-2008, excluding 2005). The GTG system includes several steps. First, 44 CAT indices are calculated in the domain of the Regional Data Assimilation and Prediction System (RDAPS) analysis data with 30 ㎞ horizontal grid spacing provided by KMA (Korean Meteorological Administration). Second, 10 indices that performed ten best forecasting scores are selected. Finally, 10 indices are combined by measuring the score based on the probability of detection, which is calculated using PIREPs exclusively of moderate-or-greater intensity. In order to investigate the best performance of the GTG system in Korea, various statistical examinations and sensitivity tests of the GTG system are performed by yearly and seasonally classified PIREPs. Performances of the GTG system based on yearly distributed PIREPs have annual variations because the compositions of indices are different from each year. Seasonal forecasting is generally better than yearly forecasting, because selected CAT indices in each season represent meteorological condition much more properly than applying the selected CAT indices to all seasons. Wintertime forecasting is the best among the four seasonal forecastings. This is likely due to that the GTG system consists of many CAT indices related to the jet stream, and turbulence associated with the jet stream can be activated mostly in wintertime under strong jet magnitude. On the other hand, summertime forecasting skill is much less than other seasons. Compared with current operational CAT prediction system (KITFA; Korean Integrated Turbulence Forecasting System), overall performance of the GTG system is better when CAT indices are selected seasonally.
Aviation Turbulence : Processes, Detection, Prediction
Springer eBooks, 2016
Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wo... more Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wonder why this is so difficult to avoid. The book includes papers by various aviation turbulence researchers and provides background into the nature and causes of atmospheric turbulence that affect aircraft motion, and contains surveys of the latest techniques for remote and in situ sensing and forecasting of the turbulence phenomenon. It provides updates on the state-of-the-art research since earlier studies in the 1960s on clear-air turbulence, explains recent new understanding into turbulence generation by thunderstorms, and summarizes future challenges in turbulence prediction and avoidance
Rising above the storm: Studies into convectively induced turbulence
Pentagon shield: Experiments with a nonoscillatory forward-in-time CFD code (EuLag) to simulate flow around the Pentagon [presentation]
Determining the impact of Doppler LIDAR on transport and diffusion modeling applications: An observing system simulation experiment [presentation]
Gravity waves and gravity wave "breaking" as contributors to aviation turbulence
Investigation of mountain-wave induced turbulence (MWT) events over the Colorado region on 31 December 2011