Robert Sharman - Academia.edu (original) (raw)
Papers by Robert Sharman
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.
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.
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
![Research paper thumbnail of Probabilistic pilot-behavior models for clear-air turbulence avoidance maneuvers [presentation]](https://attachments.academia-assets.com/110939369/thumbnails/1.jpg)
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Monthly Weather Review, 2019
Convectively induced turbulence (CIT) is an aviation hazard that continues to be a forecasting ch... more Convectively induced turbulence (CIT) is an aviation hazard that continues to be a forecasting challenge as operational forecast models are too coarse to resolve turbulence affecting aircraft. In particular, little is known about tropical maritime CIT. In this study, a numerical simulation of a tropical oceanic CIT case where severe turbulence was encountered by a commercial aircraft is performed. The Richardson number (Ri), subgrid-scale eddy dissipation rate (EDR), and second-order structure functions (SF) are used as diagnostics to determine which may be used for CIT related to developing and mature convection. Model-derived subgrid-scale EDR in past studies of midlatitude continental CIT was shown to be a good diagnostic of turbulence but underpredicted turbulence intensity and areal coverage in this tropical simulation. SF diagnosed turbulence with moderate to severe intensity near convection and agreed most with observations. Further, SF were used to diagnose turbulence for de...
Bulletin of the American Meteorological Society, 2018
For the next generation of the World Area Forecast System (WAFS), the global Graphical Turbulence... more For the next generation of the World Area Forecast System (WAFS), the global Graphical Turbulence Guidance (G-GTG) has been developed using global numerical weather prediction (NWP) model outputs as an input to compute a set of turbulence diagnostics, identifying strong spatial gradients of meteorological variables associated with clear-air turbulence (CAT) and mountain-wave turbulence (MWT). The G-GTG provides an atmospheric turbulence intensity metric of energy dissipation rate (EDR) to the 1/3 power (m2/3 s–1), which is the International Civil Aviation Organization (ICAO) standard for aircraft reporting. Deterministic CAT and MWT EDR forecasts are derived from ensembles of calibrated multiple CAT and MWT diagnostics, respectively, with the final forecast provided by the gridpoint-by-gridpoint maximum of the CAT and MWT ensemble means. In addition, a probabilistic EDR forecast is produced by the percentage agreement of the individual CAT and MWT diagnostics that exceed a certain E...
AccessScience
Turbulence is a well-known hazard to the aviation sector. It is responsible for numerous injuries... more Turbulence is a well-known hazard to the aviation sector. It is responsible for numerous injuries ea…
Aviation Turbulence, 2016
The current state of our understanding of aviation-scale turbulence processes and overviews of cu... more The current state of our understanding of aviation-scale turbulence processes and overviews of current detection and forecasting methods were provided in previous chapters of this book. Future progress will require a multipronged multidisciplinary approach from the academic, engineering, and user communities underpinned by advances in our fundamental understanding of turbulence process. The chapter outlines the required research and development, as well as operational needs, required to better understand, observe, and predict turbulence regions
AIAA Guidance, Navigation, and Control Conference, 2015
In this paper, we research the feasibility of using high rate Automatic Dependent Surveillance – ... more In this paper, we research the feasibility of using high rate Automatic Dependent Surveillance – Broadcast (ADS-B) aircraft altitude and velocity information to detect the presence of mountain waves and Mountain Wave Turbulence (MWT) in the vicinity of steep terrain as well as atmospheric waves and turbulence from other sources that are of interest to aviation, for instance, Convective Induced Turbulence (CIT). The key element of ADS-B that enables the research is a 1 second update rate on ADS-B position reports, and aircraft position and altitude being reported based on Global Positioning System (GPS) accuracy. This frequency is much faster than today’s standard of reporting meteorological data via the Aircraft Meteorological Data Relay (AMDAR) or Meteorological Data Collection and Reporting System (MDCRS), and as we show, is fast enough to estimate the location of mountain wave events, MWT, and CIT. When combined with other weather state information gained by in situ sensors, satellite, and radar-based technology in the National Airspace System (NAS), a total situational awareness of mountain wave, MWT, and CIT information in the Continental United States (CONUS) can be achieved for supporting airline flight planning and Air Traffic Management (ATM) decision making.
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.
![Research paper thumbnail of Turbulence forecast for manned and unmanned aerial vehicle [presentation]](https://attachments.academia-assets.com/110939266/thumbnails/1.jpg)
](
Spatial and temporal distributions of Clear‐Air Turbulence (CAT) in the Northern Hemisphere were ... more Spatial and temporal distributions of Clear‐Air Turbulence (CAT) in the Northern Hemisphere were investigated using 41 years (1979–2019) of the European Centre for Medium‐range Weather Forecast Reanalysis version 5 (ERA5) data. We used two groups of CAT diagnostics to determine occurrence frequencies: (a) commonly used empirical turbulence indices (TI1, TI2, and TI3) and their components [vertical wind shear (VWS), deformation, ‐divergence, and divergence tendency], and (b) theoretical instability indicators [Richardson number (Ri), potential vorticity (PV), and Brunt‐Vӓisӓlӓ frequency]. The empirical indices showed high frequencies of moderate‐or‐greater (MOG)‐level CAT potential over the East Asian, Eastern Pacific, and Northwestern Atlantic regions in winter. Over East Asia, the entrance region of strong upper‐level jets showed the highest frequencies in TI1, TI2, and TI3 due mainly to strong VWS. The Eastern Pacific and Northwestern Atlantic areas near the exit region of jets had relatively high frequencies of these indices and also Ri. PV frequency was high on the southern side of jet primarily due to negative relative vorticity. Long‐term increasing trends of MOG‐level CAT potential also appeared in those three regions mainly due to warming in lower latitudes. The most significant increasing trend was found over East Asia, due to the strengthening of the East Asian jet and increased VWS due to the strong meridional temperature gradients in the mid‐troposphere induced by warming in the tropics and cooling in eastern Eurasia. These trends over East Asia, if continued, are expected to be of importance to efficient aviation operations across the northwestern Pacific Ocean.
Weather and Forecasting, 2022
A global Korean deterministic aviation turbulence guidance (G-KTG) system and a global Korean pro... more A global Korean deterministic aviation turbulence guidance (G-KTG) system and a global Korean probabilistic turbulence forecast (G-KPT) system are developed using outputs from the operational Global Data Assimilation and Prediction System of the Korea Meteorological Administration, and the performance skill of the systems are evaluated against in situ flight eddy dissipation rates (EDRs) recorded for one year (September 2018–August 2019). G-KTG and G-KPT consider clear-air turbulence (CAT) and mountain wave turbulence diagnostics, while G-KTG additionally considers near-cloud turbulence (NCT) diagnostics. In the G-KTG system, the various combinations of deterministic EDR forecasts are tested by different ensemble means of individual turbulence diagnostics. In the G-KPT system, the probabilistic forecast is established by counting the number of diagnostics that exceed a certain threshold for strong intensity turbulence on the given model grid. The evaluation results of the G-KTG syst...
avoidance guidelines include restrictions on flight in and around thunderstorms whose aim is to r... more avoidance guidelines include restrictions on flight in and around thunderstorms whose aim is to reduce the
Journal of the Atmospheric Sciences, 2020
A large midlatitude cyclone occurred over the central United States from 0000 to 1800 UTC 30 Apri... more A large midlatitude cyclone occurred over the central United States from 0000 to 1800 UTC 30 April 2017. During this period, there were more than 1100 reports of moderate-or-greater turbulence at commercial aviation cruising altitudes east of the Rocky Mountains. Much of this turbulence was located above or, otherwise, outside the synoptic-scale cloud shield of the cyclone, thus complicating its avoidance. In this study we use two-way nesting in a numerical model with finest horizontal spacing of 370 m to investigate possible mechanisms producing turbulence in two distinct regions of the cyclone. In both regions, model-parameterized turbulence kinetic energy compares well to observed turbulence reports. Despite being outside of hazardous large radar reflectivity locations in deep convection, both regions experienced strong modification of the turbulence environment as a result of upper-tropospheric/lower-stratospheric (UTLS) convective outflow. For one region, where turbulence was i...
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.
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.
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
Monthly Weather Review, 2019
Convectively induced turbulence (CIT) is an aviation hazard that continues to be a forecasting ch... more Convectively induced turbulence (CIT) is an aviation hazard that continues to be a forecasting challenge as operational forecast models are too coarse to resolve turbulence affecting aircraft. In particular, little is known about tropical maritime CIT. In this study, a numerical simulation of a tropical oceanic CIT case where severe turbulence was encountered by a commercial aircraft is performed. The Richardson number (Ri), subgrid-scale eddy dissipation rate (EDR), and second-order structure functions (SF) are used as diagnostics to determine which may be used for CIT related to developing and mature convection. Model-derived subgrid-scale EDR in past studies of midlatitude continental CIT was shown to be a good diagnostic of turbulence but underpredicted turbulence intensity and areal coverage in this tropical simulation. SF diagnosed turbulence with moderate to severe intensity near convection and agreed most with observations. Further, SF were used to diagnose turbulence for de...
Bulletin of the American Meteorological Society, 2018
For the next generation of the World Area Forecast System (WAFS), the global Graphical Turbulence... more For the next generation of the World Area Forecast System (WAFS), the global Graphical Turbulence Guidance (G-GTG) has been developed using global numerical weather prediction (NWP) model outputs as an input to compute a set of turbulence diagnostics, identifying strong spatial gradients of meteorological variables associated with clear-air turbulence (CAT) and mountain-wave turbulence (MWT). The G-GTG provides an atmospheric turbulence intensity metric of energy dissipation rate (EDR) to the 1/3 power (m2/3 s–1), which is the International Civil Aviation Organization (ICAO) standard for aircraft reporting. Deterministic CAT and MWT EDR forecasts are derived from ensembles of calibrated multiple CAT and MWT diagnostics, respectively, with the final forecast provided by the gridpoint-by-gridpoint maximum of the CAT and MWT ensemble means. In addition, a probabilistic EDR forecast is produced by the percentage agreement of the individual CAT and MWT diagnostics that exceed a certain E...
AccessScience
Turbulence is a well-known hazard to the aviation sector. It is responsible for numerous injuries... more Turbulence is a well-known hazard to the aviation sector. It is responsible for numerous injuries ea…
Aviation Turbulence, 2016
The current state of our understanding of aviation-scale turbulence processes and overviews of cu... more The current state of our understanding of aviation-scale turbulence processes and overviews of current detection and forecasting methods were provided in previous chapters of this book. Future progress will require a multipronged multidisciplinary approach from the academic, engineering, and user communities underpinned by advances in our fundamental understanding of turbulence process. The chapter outlines the required research and development, as well as operational needs, required to better understand, observe, and predict turbulence regions
AIAA Guidance, Navigation, and Control Conference, 2015
In this paper, we research the feasibility of using high rate Automatic Dependent Surveillance – ... more In this paper, we research the feasibility of using high rate Automatic Dependent Surveillance – Broadcast (ADS-B) aircraft altitude and velocity information to detect the presence of mountain waves and Mountain Wave Turbulence (MWT) in the vicinity of steep terrain as well as atmospheric waves and turbulence from other sources that are of interest to aviation, for instance, Convective Induced Turbulence (CIT). The key element of ADS-B that enables the research is a 1 second update rate on ADS-B position reports, and aircraft position and altitude being reported based on Global Positioning System (GPS) accuracy. This frequency is much faster than today’s standard of reporting meteorological data via the Aircraft Meteorological Data Relay (AMDAR) or Meteorological Data Collection and Reporting System (MDCRS), and as we show, is fast enough to estimate the location of mountain wave events, MWT, and CIT. When combined with other weather state information gained by in situ sensors, satellite, and radar-based technology in the National Airspace System (NAS), a total situational awareness of mountain wave, MWT, and CIT information in the Continental United States (CONUS) can be achieved for supporting airline flight planning and Air Traffic Management (ATM) decision making.
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.
Spatial and temporal distributions of Clear‐Air Turbulence (CAT) in the Northern Hemisphere were ... more Spatial and temporal distributions of Clear‐Air Turbulence (CAT) in the Northern Hemisphere were investigated using 41 years (1979–2019) of the European Centre for Medium‐range Weather Forecast Reanalysis version 5 (ERA5) data. We used two groups of CAT diagnostics to determine occurrence frequencies: (a) commonly used empirical turbulence indices (TI1, TI2, and TI3) and their components [vertical wind shear (VWS), deformation, ‐divergence, and divergence tendency], and (b) theoretical instability indicators [Richardson number (Ri), potential vorticity (PV), and Brunt‐Vӓisӓlӓ frequency]. The empirical indices showed high frequencies of moderate‐or‐greater (MOG)‐level CAT potential over the East Asian, Eastern Pacific, and Northwestern Atlantic regions in winter. Over East Asia, the entrance region of strong upper‐level jets showed the highest frequencies in TI1, TI2, and TI3 due mainly to strong VWS. The Eastern Pacific and Northwestern Atlantic areas near the exit region of jets had relatively high frequencies of these indices and also Ri. PV frequency was high on the southern side of jet primarily due to negative relative vorticity. Long‐term increasing trends of MOG‐level CAT potential also appeared in those three regions mainly due to warming in lower latitudes. The most significant increasing trend was found over East Asia, due to the strengthening of the East Asian jet and increased VWS due to the strong meridional temperature gradients in the mid‐troposphere induced by warming in the tropics and cooling in eastern Eurasia. These trends over East Asia, if continued, are expected to be of importance to efficient aviation operations across the northwestern Pacific Ocean.
Weather and Forecasting, 2022
A global Korean deterministic aviation turbulence guidance (G-KTG) system and a global Korean pro... more A global Korean deterministic aviation turbulence guidance (G-KTG) system and a global Korean probabilistic turbulence forecast (G-KPT) system are developed using outputs from the operational Global Data Assimilation and Prediction System of the Korea Meteorological Administration, and the performance skill of the systems are evaluated against in situ flight eddy dissipation rates (EDRs) recorded for one year (September 2018–August 2019). G-KTG and G-KPT consider clear-air turbulence (CAT) and mountain wave turbulence diagnostics, while G-KTG additionally considers near-cloud turbulence (NCT) diagnostics. In the G-KTG system, the various combinations of deterministic EDR forecasts are tested by different ensemble means of individual turbulence diagnostics. In the G-KPT system, the probabilistic forecast is established by counting the number of diagnostics that exceed a certain threshold for strong intensity turbulence on the given model grid. The evaluation results of the G-KTG syst...
avoidance guidelines include restrictions on flight in and around thunderstorms whose aim is to r... more avoidance guidelines include restrictions on flight in and around thunderstorms whose aim is to reduce the
Journal of the Atmospheric Sciences, 2020
A large midlatitude cyclone occurred over the central United States from 0000 to 1800 UTC 30 Apri... more A large midlatitude cyclone occurred over the central United States from 0000 to 1800 UTC 30 April 2017. During this period, there were more than 1100 reports of moderate-or-greater turbulence at commercial aviation cruising altitudes east of the Rocky Mountains. Much of this turbulence was located above or, otherwise, outside the synoptic-scale cloud shield of the cyclone, thus complicating its avoidance. In this study we use two-way nesting in a numerical model with finest horizontal spacing of 370 m to investigate possible mechanisms producing turbulence in two distinct regions of the cyclone. In both regions, model-parameterized turbulence kinetic energy compares well to observed turbulence reports. Despite being outside of hazardous large radar reflectivity locations in deep convection, both regions experienced strong modification of the turbulence environment as a result of upper-tropospheric/lower-stratospheric (UTLS) convective outflow. For one region, where turbulence was i...