ATCA Journal | Q4 2013 Preview

Winter 2013 | VOLUME 55, NO. 4

Consolidating Control Towers:

A Model of Collaboration Plus

• Avoiding Turbulence Near Thunderstorms • Time for a Paradigm Shift to Privatization and User Fees in the U.S.

www.atca.org

Winter 2013 | Vol. 55, No. 4 Published for:

Contents

ATCA members and subscribers have access to the online edition of The Journal of Air Traffic Control. Visit lesterfiles.com/ pubs/ATCA. Password: ATCAPubs (case sensitive).

Air Traffic Control Association 1101 King Street, Suite 300 Alexandria, VA 22314 Phone: 703-299-2430 Fax: 703-299-2437 info@atca.org www.atca.org Published by:

Feature 28 Consolidating Control Towers: A Model of Collaboration 140 Broadway, 46th Floor New York, NY 10005 Toll-free phone: 866-953-2189 Toll-free fax: 877-565-8557 www.lesterpublications.com President, Jeff Lester Vice-President & Publisher, Sean Davis EDITORIAL

How the Team at Oakland Control Tower Consolidated Two Aging Towers into One Modernized, Customizable Facility

40

Art Director, Myles O’Reilly Senior Graphic Designer, John Lyttle Graphic Designer, Gayl Punzalan Graphic Designer, Jessica Landry

ADVERTISING Sales Director, Danny Macaluso | 866-954-8168 Stephanie Allen | 866-954-8167 Quinn Bogusky | 888-953-2198 Louise Peterson | 866-953-2183 Walter Lytwyn | 866-953-2196

DISTRIBUTION Jennifer Holmes | 866-953-2189

© 2013 Air Traffic Control Association, Inc. All rights reserved. The contents of this publication may not be reproduced by any means, in whole or in part, without the prior written consent of the ATCA. Disclaimer: The opinions expressed by the authors of the editorial articles contained in this publication are those of the respective authors and do not necessarily represent the opinion of the ATCA. Printed in Canada. Please recycle where facilities exist.

Cover image and top photo by Chris Ruhaak/ Heartland Photo & Design.

Make your Connections at World ATM Congress 2014

Articles 10 Avoiding Turbulence Near Thunderstorms

Recent implementation of accurate turbulence observations from some commercial aircraft and results of high-resolution simulations using cloudresolving models are laying the groundwork to improve guidelines for en route thunderstorm-induced turbulence avoidable and forecasting

Editorial Director, Jill Harris Managing Editor, Kristy Rydz Editorial Assistant, Andrew Harris

DESIGN & LAYOUT

Be at the Hub of the Industry

18

Air Navigation Advances in Oceanic Airspace are Leading the Way for NextGen The FAA is Working with Airlines and International Partners to Exploit New Policies, Procedures, and Technologies

36

Time for a Paradigm Shift to Privatization and User Fees in the U.S. A Call for Change

42

Sense and Avoid for Unmanned Aircraft Systems

52

The Value of the Right Information at the Right Time

57

The Digital Ecosystem

Workshop Results and Conclusions for Airborne Separation The Angle of Attack Indicator – an Important Tool for Pilots A New Pathway for Innovation

Departments 3 From the President 5 From the Editor’s Desk 7 Member Benefits & Application

65

Directory of Member Organizations

Annual Statement 66 of Ownership

68

Index to Advertisers

The Journal of Air Traffic Control

1

FROM THE PRESIDENT

Making Strides On the cover of this Winter 2013 issue of The Journal of Air Traffic Control, we feature a photo of the control tower at Oakland International Airport. I had the privilege of traveling to Oakland in June to observe their process of consolidating two aging con-

By Peter F. Dumont President & CEO, ATCA

like the ATCA Annual Conference & Exposition and the World ATM Congress and walk away having interacted with the business professionals who will help them in their work. At this past ATCA Annual, I heard from several attendees that the level of government participants they came into contact with was a level higher than they were expecting. While we continue to welcome ALL from the industry, this was pleasant feedback.

ATCA will continue to provide venues such as these and some enhanced events, resulting from strategic partnerships, in the coming year. We look forward to seeing you at these events and getting your feedback. Bringing you the type of content like what is included in this issue of the Journal, and conversations – the right conversations – presented and discussed at events throughout the year – is just one way the association can provide resources to enhance your professional experience and the ATC landscape.

Happy Holidays,

Peter F. Dumont President & CEO Air Traffic Control Association

Photographer: VitalyEdush/Photos.com

involved in the project, congratulate them on a successful transition to the new tower; this was not a simple feat.

Also in this issue, the theme of Unmanned Aerial Systems (UAS) are touched on several times – both from government participants and industry’s investment in future technological advances. Knowing Thanks to our redesign and publication team, The that the importance Journal of Air Traffic Control is now available online, in and relevancy of the addition to the print format. ATCA members – all of issue will only grow whom receive the Journal – and outside subscribers in the future, ATCA can find the download information in the Table of has planned a forum Contents. to discuss the policy, operations, manufacturing, and infratrol towers into one newly built facility. structure of UAS – including its involveAside from the impressive workflow ment in the National Airspace System. and intricate details carried out for the I am pleased this event is coming to switchover, I was even more struck by fruition – ATCA’s UAS Day will take the collaboration among team mem- place January 24, 2014 – I hope you can bers. Between the FAA at all levels, join us there. management, NATCA, engineers, and We had a very successful 58th tower vendors – the team exhibited an Annual Conference and Exposition ability to actively listen to departments with record floor traffic despite chaloutside their own and work together lenging times. We will follow that suctoward a successful end product. That cess with the World ATM Congress model should be applauded and I hope 2014 (March 4 to 6 in Madrid). In its replicated in our current aviation infra- second year, the Congress is already structure. When you read the Oakland shaping up to build on the inaugural case study (page 28), I think you will be year’s tremendous success. inspired by the example of teamwork It is rewarding to see individual it provides. And if you know someone and corporate members attend events

The Journal of Air Traffic Control

3

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from the editor’s desk

ATCA

Air Traffic Control Association

Winter 2013 | Vol. 55, No. 4 Air Traffic Control Association 1101 King Street, Suite 300 Alexandria, VA 22314 Phone: 703-299-2430 Fax: 703-299-2437 info@atca.org Air Traffic Control Association www.atca.org

ATCA

Formed in 1956 as a non-profit, professional membership association, ATCA represents the interests of all professionals in the air traffic control industry. Dedicated to the advancement of professionalism and technology of air traffic control, ATCA has grown to represent several thousand individuals and organizations managing and providing ATC services and equipment around the world.

Editor-in-Chief: Steve Carver Publisher: Lester Publications, LLC

Officers and Board of Directors Chairman: James H. Washington, B3 Solutions Chairman-Elect: Neil Planzer, The Boeing Company President & CEO: Peter F. Dumont, Air Traffic Control Association Treasurer, Director-At-Large: Rachel Jackson, ASRC Research & Technology Solutions Secretary, East Area Director: Jeff Griffith, Washington Consulting Group Northeast Area Director: Mike Headley, Apptis South Central Area Director: William Cotton Southeast Area Director: Robert Coulson, Harris Corporation North Central Area Director: Jim Crook, Retired, US Air Force Western Area Director: Mike Lewis, Jeppesen Canada, Caribbean, Central and South America, Mexico Area Director: John Crichton, NAV CANADA Europe, Africa, Middle East Area Director: Steve James Pacific, Asia, Australia Area Director: Bob Gardiner, ACMAT Consultants Directors-At-Large: Rick Day, CSC Charlie Keegan, Raytheon Sandra Samuel, Lockheed Martin

Staff Marion Brophy, Director, Communications Ken Carlisle, Director, Meetings and Expositions Jonathan Fath, Manager, New Media Jessica McGarry, Manager, Publications and Media Christine Oster, Chief Financial Officer Paul Planzer, Manager, ATC Programs Claire Rusk, Vice President of Operations Rugger Smith, Senior Account Manager Sandra Strickland, Events and Exhibits Coordinator Tim Wagner, Membership Manager

By Steve Carver Editor-in-Chief, The Journal of Air Traffic Control

Navigating Politics

Thomas Jefferson once said, “When angry, count to ten before you speak. If very angry, count to one hundred.” Living through the past few months watching Congress show their opposition to debating and evasiveness in passing a budget (not an approved budget in five years, I might add), while I felt the impact, and heard and saw the results of their lack of empathy, I extended President Jefferson’s angry count to one thousand after one hundred just didn’t do the trick.

Although the impact to aviation employees cannot compare to the impacts felt by our military families or to those impacted by delays in Federal aid, we looked with saddened eyes at those who lost their contractor support positions, the FAA employees who worked not knowing if they were to be paid for their labor, and the anxiety of FAA employees who were furloughed, not knowing if they would make their family budget for the next month. How is it possible to turn one’s back on those who strive to continue to make the National Airspace System the best in the world?

How can we move forward into the next generation of aviation when the U.S. industry doesn’t know how

long there will be money, if the money will be taken away after being provided, or if highly talented people can be retained? Are we doomed to a less capable aviation service due to the inabilities of Congress? Unfortunately, I don’t have the answers to these questions but I can tell you that in the past, the services of aviation have successfully moved forward during bad times through the desire of those who love aviation. It is always the people who innovate and find ways around political impacts.

Continued on next page

The Journal of Air Traffic Control (ISSN 0021-8650) is published quarterly by the Air Traffic Control Association, Inc. Periodical postage paid at Alexandria, VA and additional entries.

EDITORIAL, SUBSCRIPTION & ADVERTISING OFFICES at ATCA Headquarters: 1101 King Street, Suite 300, Alexandria, Virginia 22314. Telephone: (703) 299-2430, Fax: (703) 299-2437, Email: info@atca.org, Website: www.atca. org. POSTMASTER: Send address changes to The Journal of Air Traffic Control, 1101 King Street, Suite 300, Alexandria, Virginia 22314. © Air Traffic Control Association, Inc., 2013 Membership in the Air Traffic Control Association including subscriptions to the Journal and ATCA Bulletin: Professional, $130 a year; Professional Military Senior Enlisted (E6–E9) Officer, $130 a year; Professional Military Junior Enlisted (E1–E5), $26 a year; Retired fee $60 a year applies to those who are ATCA Members at the time of retirement; Corporate Member, $500–5,000 a year, depending on category. Journal subscription rates to non-members: U.S., its territories, and possessions—$78 a year; other countries, including Canada and Mexico—$88 a year (via air mail). Back issue single copy $10, other countries, including Canada and Mexico, $15 (via air mail).

Contributors express their personal points of view and opinions that are not necessarily those of their employers or the Air Traffic Control Association. Therefore The Journal of Air Traffic Control does not assume responsibility for statements made and opinions expressed. It does accept responsibility for giving contributors an opportunity to express such views and opinions. Articles may be edited as necessary without changing their meaning.

The Journal of Air Traffic Control

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from the editor’s desk I have something to say to the hard workers of our industry: don’t dismay, keep your chin up and your steps forward, and always remember this famous quote by Will Rogers: “This country has come to feel the same when Congress in in session as when the baby gets hold of a hammer.”

As we move into 2014, I look back on the past few years of The Journal of Air Traffic Control and remember how Interested in Contributing as an Author?

Contact: • Steve Carver, Editor-in-Chief, The Journal of Air Traffic Control, scarver@avmgt.com • Ed Stevens, Chair, ATCA Publications Committee • Marion Brophy, ATCA Director of Communications, marion.brophy@atca.org The Journal of Air Traffic Control Publications Committee Members • Edward Stevens, Chair, Retired, edwardhstevens@gmail.com • Steve Carver, Editor-in-Chief, Aviation Management Associates,

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Winter 2013

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LETTER FROM THE EDITOR

The Names & Faces of Air Traffic Gather at The Names & Faces of Air Traffic Gather at

The Names & Faces of Air Traffic

ATCA Members are part of the global air traffic dialogue. Your access to ATCA committees, publications, and meetings will increase your awareness of the current aviation landscape ATCA Members areATC part of the global airAirtraffic and current work towards improving safety, Trafficdialogue.

Control Association access toand ATCA committees, publications, and meetings will increase your awareness efficiency, capacity.

ATCA Members are part of the global air traffic dialogue.

#6%#

Your ofYour the access currenttoaviation landscape and current work improving ATC safety, efficiency ATCA committees, publications, andtowards meetings will increase your awareness and capacity. of the current aviation landscape and current work towards improving ATC safety, efficiency

What do you get an ATCA Member? andas capacity.

What you get as an ATCA Member What you get as an ATCA Member

• PARTNERSHIPS. ATCA collaborates with • CONNECTIONS. Meet with other industry Connections. Meet with other industry professionals at networking events throughout the year. the U.S. Department of Defense, Federal professionals at networking events Expert Opinions.

Members have exclusive access to ATCA Publications including: Connections.

Meet at networking events throughout Administration, ICAO, CANSO, the year. throughout thewith year.other industry professionalsAviation Valuable Content.

Daily Headline News, the ATCA Bulletin, & The Journal of Air Traffic Control Expert Opinions. Members have exclusive access to ATCA Publications academic institutions, and manyincluding: other • EXPERT OPINIONS. Members have Partnerships. with the the ATCA U.S. Department of Defense, Federal Aviation Valuable Content.ATCA Dailycollaborates Headline News, Bulletin, & The Journal of Air Traffic Control global organizations. exclusive access to ATCA publications.

Administration, ICAO, CANSO, academic institutions, and many other global organizations.

Partnerships. ATCA collaborates with the U.S. Department of Defense, Federal Aviation • REDUCED RATES. Members getconferences.

Reduced Rates.

Members get significant discounts to allmany ATCAother events and • VALUABLE CONTENT. Daily Headline Administration, ICAO, CANSO, academic institutions, and global organizations. significant discounts to all ATCA events News, the ATCA Bulletin, & The Journal Reduced Rates. Members get significant discounts to all ATCA events and conferences. and conferences. of Air Traffic Control.

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avoiding turbulence

Avoiding Turbulence Near Thunderstorms

Recent implementation of accurate turbulence observations from some commercial aircraft and results of high-resolution simulations using cloud-resolving models are laying the groundwork to improve guidelines for en route thunderstorminduced turbulence avoidance and forecasting 10

Winter 2013

Avoiding Turbulence

It is well known that severe turbulence is ubiquitous within the cloudy air of thunderstorms, motivating efforts to avoid their penetration through visual identification, remote sensing through onboard or ground-based radar, and reports from air traffic control. Yet, turbulence generated by thunderstorms is not necessarily confined to areas within the cloud and evading cloudy air can be an insufficient turbulence avoidance strategy.

By Drs. Robert Sharman, Todd Lane, and Stanley Trier, University Corporation for Atmospheric Research (UCAR)

Figure 1. Schematic of known regions of turbulence above and around thunderstorms; red areas indicate locations of expected CIT away from convective cores

improvement in forecasting and avoiding turbulence near thunderstorms requires better observations of NCT encounters and advances in fundamental understanding of the conditions associated with turbulence generation, its extent and intensity, and life cycle. Recent progress has been made in both these areas – automated in situ measurements of turbulence (Cornman et al. 1995, 2004) can help precisely identify regions of NCT while high-resolution computer simulations of idealized scenarios and well-observed cases have helped elucidate NCT processes. Such modeling is computationally expensive; to resolve turbulent processes that affect commercial aircraft, simulations may require grid spacings to be as small as 100 meters; i.e., far smaller than possible with current operational weather prediction models. The challenge is then to use computer models in a high-resolution research mode to guide improvements in future forecasting and thunderstorm avoidance procedures.

Current Guidelines for En Route Avoidance It is well known that severe turbulence is ubiquitous within the cloudy air of thunderstorms, motivating efforts to avoid their penetration through visual identification, The Journal of Air Traffic Control

Photographer: UCAR; welcomia/Photos.com

Turbulence is an important safety and operational hazard for the aviation industry. It is responsible for hundreds of injuries around the world each year, occasionally causes aircraft damage, occupant injuries, is the source of millions of dollars of additional operational costs for commercial airlines (which ultimately increases the cost of air travel), and can cause major disruptions to air traffic. Aircraft generally attempt to avoid turbulence – especially regions of severe turbulence – whenever possible through the strategic use of aviation weather forecasts and/or tactical maneuvers.

Yet, turbulence owes its existence to a variety of atmospheric processes (e.g., jet streams, terrain-induced flows, and thunderstorms) and each of these processes requires its own unique forecasting or avoidance strategy tailored to the mechanisms underlying the source. Unfortunately, progress in improving avoidance methods for a number of these sources is hampered by an incomplete understanding of the governing atmospheric dynamics, especially with respect to Convectively Induced Turbulence (CIT), which occurs in and around thunderstorms. CIT has been estimated to be responsible for 60 percent of turbulence-related aircraft accidents (Cornman and Carmichael 1993). In another study by Kaplan et al. (2005), 86 percent of 44 aviation accident cases were found to be within 100 km of convection.

CIT can occur within cloud or in the clear-air environment above or around the cloud. To distinguish in-cloud convective turbulence from out-of-cloud CIT, the term Nearcloud Turbulence (NCT) can be used. To pilots, NCT can seem like well-known Clear-Air Turbulence (CAT), since it is invisible and often leads to unexpected turbulence encounters. Figure 1 is a schematic of known NCT regions. The downwind wake can be turbulent and sections of the anvil can also be unstable. This instability may extend above or below the visible anvil cloud as well. But as indicated in the figure as wavy areas, thunderstorms can also generate buoyancy or gravity waves, which may propagate laterally and/or vertically away from the storm and subsequently break, much like water waves, leading to turbulence.

NCT can exist at small scales and short time periods, and the dynamic evolution of thunderstorms makes it notoriously difficult to accurately diagnose or forecast (Lane et al. 2012). A recent study by Williams (2013) shows promise in diagnosing conditions conducive to NCT, but further

11

Photo credit: UCAR

avoiding turbulence

Figure 3. Results from a three-dimensional numerical simulation of a thunderstorm. It shows the volume of cloud that exceeds 10 km altitude and surfaces of potential temperature at 15 km and 20 km, identifying gravity waves. The horizontal dimensions are 100 km x 50 km and the grid spacing is 150 m.

Figure 2. (a) Distributions of MOG relative risk as a function of (a) lateral distance to convection and (b) vertical proximity to cloud top.

The distribution is based on in situ turbulence reports between 7.6and 12.8-km altitudes (flight levels 25,000-42,000 ft) from May to October of 2004 and 2005.

remote sensing through onboard or ground-based radar, and reports from air traffic control. Yet, turbulence generated by thunderstorms is not necessarily confined to areas within the cloud and evading cloudy air can be an insufficient turbulence avoidance strategy. The Federal Aviation Administration (FAA) has a set of guidelines for pilots flying near thunderstorms (FAA, 2012), including: • Avoid by at least 20 miles any thunderstorm identified as severe or giving an intense radar echo. This is especially true under the anvil of a large cumulonimbus. • Clear the top of a known or suspected severe thunderstorm by at least 1,000 feet altitude for each 10 knots of wind speed at the cloud top.

Although these guidelines are simple in concept, in practice interpretation of them is subjective and limited by the information available to airline dispatchers, pilots, and air traffic controllers. Moreover, recent studies have shown that significant NCT may occur outside these prescribed 12

Winter 2013

margins and may be dependent on environmental factors invisible to a pilot (Lane et al. 2012), suggesting that these guidelines are inadequate, especially considering recent advances in the understanding of the important underlying processes.

Climatology of NCT To better understand the relation between NCT and cloud/ environmental properties that may be relevant, precise high-resolution observations of the turbulence event location, intensity, and timing relative to cloud boundaries is required. For events associated with injuries, the Flight Data Recorder (FDR) is often available for analysis. However, (fortunately) not all NCT encounters lead to injuries and other observations are required to identify NCT events.

Traditionally, these observations have been in the form of pilot reports (PIREPs), but these are inadequate to monitor NCT encounters because of the large time and position uncertainties associated with them (e.g. Williams 2013).

Instead, NCT encounters can be identified using the new in situ turbulence measurements mentioned above that are now available from some U.S. airlines. These reports have positional accuracy better than 12 km and time accuracies of at least one minute, and are therefore well suited for case

Photo credit: UCAR

Avoiding Turbulence

Figure 4. Four frames of a 2-D simulation showing cloud, gravity waves, and turbulence. In the model gravity waves can be seen developing early.

An aircraft attempting to top the cell in frame 1 at FL 390 would already be at elevated risk. By frame 2, radar would likely have crews diverting away from main (center) cell; but breaking waves are present in clear air 3-5 thousand feet above the cells to the right. Frames 3 and 4 show how dissipating storms can be as dangerous as rapidly developing storms.

and statistical studies of NCT. The in situ turbulence measurement and recording system provides reports of eddy dissipation rate (EDR), an aircraft-independent atmospheric turbulence metric, including both the median and peak EDR encountered over each one-minute time interval. For NCT studies, the peak EDR value is preferable because it supplies a good indication of the hazard and provides more samples at the higher intensities.

To gain a better understanding of the frequency of occurrence of NCT relative to radar-derived cloud boundaries, 7 million peak EDR reports were compared to cloud locations derived from radar observations. Figure 2 depicts the distribution of distances to convection in terms of “relative risk” of encountering “moderate-or-greater” (MOG) turbulence for mid-sized commercial aircraft (FAA 2012) relative to its overall frequency (from all sources). Figure 2a shows the MOG relative risk with lateral distance away from the storm boundaries. The risk of turbulence encounters increases as the aircraft nears a thunderstorm (laterally), and the risk of MOG turbulence is almost twice the background value as far as 70 km (38 nmi) from a storm. Figure 2b shows the MOG relative risk relative to the aircraft’s dis-

tance above the cloud top. Although the risk of turbulence decreases with distance above cloud, the relative risk of MOG turbulence is still 10 times the background value 3.6 km (~12,000 ft) above the cloud top. Thus, in comparison to the background atmosphere, MOG turbulence is significantly more likely above and adjacent to thunderstorms.

Turbulence Above Thunderstorms One NCT case for which Flight Data Recorder (FDR) information was available was a severe turbulence encounter that resulted in 26 injuries above a developing thunderstorm over North Dakota in 1997. This case served as the motivation for a number of high-resolution numerical modeling studies to better identify turbulence generation mechanisms above deep convection (Lane et al. 2012).

These studies identified breaking gravity (or buoyancy) waves as an important turbulence generation mechanism relevant to aviation.

Developing convective clouds are known to generate internal gravity waves that can propagate horizontally and vertically away from the cloud itself. As shown by a computer simulation (from Lane and Sharman 2006) in Figure 3, the The Journal of Air Traffic Control

13

avoiding turbulence

Photo credit: UCAR

is more complicated, with maximum volumes of above-cloud turbulence occurring at intermediate shears. Stronger vertical shears lead to more intense turbulence, but over smaller volumes that are confined closer to the cloud top. The results of this work are promising and suggest that scientifically based avoidance guidelines for minimum vertical separation should incorporate parameters such as wind shear and stability. Other parameters (e.g., convection intensity) are likely to be important as well. Our ongoing research is exploring the variations in turbulence characteristics and occurrences in a variety of other atmospheric conditions and scenarios.

A key point to note is that the minimum vertical separation distance recommended by the current FAA guidelines is based entirely on the cloud-top wind speed and not the wind shear or cloud top stability, and therefore these wave-breaking processes are not accounted for. Furthermore, gravity waves and their dissipation rely strongly on the atmospheric thermodynamic stability – another process not incorporated in the FAA guidelines.

Figure 5. Results from three different simulations of turbulence above thunderstorms. Blue is the concentration of cloud and shades of orange represent simulated turbulence intensity.

waves emanating from the active region of a thunderstorm closely resemble ripples on a pond. Another similar simulation (reported in Lane et al. 2003) shows that these waves initially propagate upward from the cloud top as the storm penetrates the tropopause, then steepen, and break, generating turbulence at substantial distances above the cloud as shown in the sequence of images in Figure 4. Although this sequence was based on a mid-latitude summertime thunderstorm, it has been recently shown that the same mechanism can occur with convective clouds in the wintertime as well (Trier et al. 2012).

As a first step towards improving thunderstorm turbulence guidelines, recent work has used numerical models to explore changes in above-cloud turbulence associated with systematic changes in the environmental wind shear and thermodynamic stability (which helps inhibit vertical motion). An example is shown in Figure 5 (derived from simulations reported in Lane and Sharman 2008); as expected, lower atmospheric stabilities produce more extensive regions of turbulence. The response to changes in wind shear (viz., vertical shear, i.e., the change in horizontal wind with height)

Turbulence Adjacent to Thunderstorms Combining automated in situ turbulence measurements with radar and satellite imagery has confirmed the large frequency of NCT encounters laterally away from active thunderstorm regions. For example, on August 5, 2005 over the Midwestern U.S., moderate-to-severe turbulence occurred 10 to 20 km southeast of the cloud associated with a relatively isolated region of intense thunderstorms (Figure 6a). On June 17, 2005, longer lasting and more widespread turbulence occurred along the outer cirrus anvil of a mesoscale convective system (MCS) over the southern Great Plains of the U.S. (Figure 6b); the turbulence was several hundred kilometers north of the MCS thunderstorm region.

Turbulence measurements are often correlated with the cir-

Figure 6. Turbulence measurements along the tracks of EDR-equipped commercial aircraft superposed on (a) 0240 UTC 5 August 2005 and (b) 0732 UTC 17 June 2005 GOES-12 infrared satellite images. Each dot represents a 1-min peak EDR measurement, with colors indicating EDR values nominally categorized as smooth (green), light (yellow), moderate (orange), and moderate-to-severe (red) turbulence.

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Photo credit: UCAR

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Figure 7. Simulated column-maximum radar reflectivity (coloured shading), 13-km MSL horizontal winds using the standard meteorological convention (half barb = 2.5 m s-1, full barb = 5 m s-1, pennant = 25 m s-1), and 12-km MSL turbulence kinetic energy (thick brown contours, 1 m2 s-2 contour intervals starting at 1 m2 s-2) at 0730 UTC 17 June 2005.

rus cloud bands that extend radially outward from the edge of thunderstorm anvils (Lenz et al. 2009), and in this case are present in the NE sector of the MCS (Figure 6b).

The mesoscale environment of the June 17th event was investigated using high-resolution computer simulations (Trier and Sharman 2009). These models specifically predict the location and intensity of areas of turbulence (as turbulent kinetic energy, TKE) that might affect aircraft.

Simulated TKE in this case is widespread within the MCS outflow, several hundred kilometers north of the heavy rainfall region (Figure 7), consistent with observations (Figure 6b). As in many large mid-latitude storms, the MCS outflow is asymmetric due to the superposition of the storm-induced upper-level outflow and a mid-latitude jet stream near the MCS. In regions where the MCS outflow reinforces the jet stream, enhanced vertical shears and turbulence can occur.

Conversely in regions where they oppose, vertical shears are reduced and turbulence is less likely. In this particular case, on the north side of the simulated MCS (at point ‘N’, Figure 7), the predicted turbulence was strongest at flight levels between 11.5 and 12 km MSL. Higher resolution simulations (Trier et al. 2010) indicated radial cirrus bands developing in this area as well (see Figure 5b). In contrast, there was no such cirrus banding and very little turbulence on the south side (near ‘S’, Figure 7).

High-resolution simulations of the August 5th case (Figure 6a) also showed large vertical shears and low stability where the turbulence was encountered. But in this event, these effects were accentuated due to the presence of horizontally propagating gravity waves and breaking in the region to the southeast of the storm (for more details, see Lane et al. 2012).

Toward Improved Forecasting and New Guidelines Many modern numerical weather prediction models can be

configured at high enough resolution to explicitly resolve the key moist convection (thunderstorm) processes. Such convection-permitting models are still too coarse, however, to even start to properly resolve turbulent processes relevant to aviation since this would require grid spacings of about an order of magnitude smaller than those presently used operationally – well beyond current capabilities.

In addition to these computational demands, it is well known that predicting the timing and location of deep convective development is extremely challenging and, depending on the scenario, the limit of predictability may only be a few hours. Add to this the potentially more restrictive predictability limits associated with turbulence and it is clear that single deterministic forecasts would be inappropriate, making probabilistic forecasts essential. For weather prediction applications, one popular technique for providing probabilistic information uses an ensemble of prediction models; the range of forecast values given by the different models provides some measure of the probability of occurrence for a particular scenario. Yet, the computational demands place operational ensemble predictions of turbulence well out of reach and alternatives to explicit forecasting are required.

A viable alternative to explicit forecasting can be achieved through improved avoidance guidelines. An improved guideline might be a complicated function of quantities like wind shear, thermodynamic stability and storm energy, which would probably be too demanding for pilots to appreciate and comprehend at short notice. Yet, operational forecasts (or analyses such as described in Williams 2013) could be used to provide maps of calculated minimum vertical and horizontal separation distance from clouds based on new guidelines, which could then be followed in the event that a thunderstorm develops. These maps could then be used for tactical avoidance – for example, providing information about whether one sector of a storm might be more hazardous than another and/or recommending increased lateral separations for storms more likely to produce widespread NCT. Moreover, when coupled with operational forecasts of thunderstorms, such maps could also facilitate route planning and air traffic control. Finally, such improved approaches are likely to be a necessary component of future automated systems like NextGen in the U.S. and SESAR in Europe, especially given that the likely future increase in air traffic will impose pressures on an already overcrowded airspace.

Such pressures are exacerbated with the limitations placed on routing by hazards such as thunderstorms.

About the Authors Dr. Robert Sharman is a Project Scientist in the Research Applications Laboratory, National Center for Atmospheric Research, Boulder CO USA. Email: sharman@ucar.edu Dr. Todd Lane is an Australian Research Council Future Fellow in the School of Earth Sciences, The University of Melbourne, Australia. Email: tplane@unimelb.edu.au Dr. Stanley Trier is a Project Scientist in the Earth System Laboratory, MMM Division, National Center for Atmospheric Research, Boulder, Colo., U.S. Email: trier@ucar.edu The Journal of Air Traffic Control

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• Cornman, L. B. and Carmichael, B., 1993, Varied research efforts are under way to find means of avoiding air turbulence, ICAO Journal, 48, 10-15.

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• Lane, T. P., Sharman, R. D. Trier, S. B., Fovell, R. G. and Williams, J. K., 2012, Recent advances in the understanding of near-cloud turbulence, Bulletin of the American Meteorological Society, 93, 499-515.

• Lenz, A., K.M. Bedka, W.F. Feltz, and S.A. Ackerman, 2009, Convectively-induced transverse band signatures in satellite imagery. Weather and Forecasting, 24, 1362-1373.

• Sharman, R., C. Tebaldi, G. Wiener and J. Wolff, 2006, An integrated approach to mid-and upper-level turbulence forecasting.

Weather and Forecasting, 21, 268-287.

• Trier, S.B., and R.D. Sharman, 2009, Convection-permitting simulations of the environment supporting widespread turbulence within the upper-level outflow of a mesoscale convective system, Monthly Weather Review, 137, 1972-1990.

• Trier, S.B., R.D. Sharman, R.G. Fovell, and R.G. Frehlich, 2010, Numerical simulation of radial cloud bands within the upper-level outflow of an observed mesoscale convective system, Journal of the Atmospheric Sciences, 67, 2990-2999.

• Trier S. B., R. D. Sharman, and T. P. Lane, 2012, Influences of moist convection on a cold-season outbreak of clear-air turbulence (CAT), Monthly Weather Review, 140, 2477–2496.

• Williams, J. K., 2013, Using random forests to diagnose aviation turbulence. Machine Learning, DOI: 10.1007/s10994-013-5346-7, Published in Springer “Online First.”

• Wolff, J.K., and R.D. Sharman, 2008, Climatology of upper-level turbulence over the contiguous United States, Journal of Applied Meteorology and Climatology, 47, 2198-2214.

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Photographer: Anton Foltin/Photos.com

References and further reading