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Briefing on Windshear and Turbulence Alerting Service

Briefing on Windshear and Turbulence Alerting Service. S.T. Chan & P.W. Chan 21 March 2005. Agenda. Understanding of WS & TURB in HK Freq. of occurrence Typical conditions conducive to WS & TURB Characteristics HKO WS & TURB alerting service Recent improvements How do we perform

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Briefing on Windshear and Turbulence Alerting Service

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  1. Briefing on Windshear and Turbulence Alerting Service S.T. Chan & P.W. Chan 21 March 2005 Hong Kong Observatory - 21 March 2005

  2. Agenda • Understanding of WS & TURB in HK • Freq. of occurrence • Typical conditions conducive to WS & TURB • Characteristics • HKO WS & TURB alerting service • Recent improvements • How do we perform • Operational aspects • Looking forward • Q&A Hong Kong Observatory - 21 March 2005

  3. What is windshear and turbulence? • Windshear – sustained change in wind direction/speed for more than a few seconds • change in headwind/tailwind • change in lift • Scale several hundred metres - 4 km Hong Kong Observatory - 21 March 2005

  4. What is windshear and turbulence? • Glide slope of aircraft on APP or DEP typically 3 – 6 deg.->Glide path in a plane close to horizontal • Systematic vertical shear (e.g. low-level jets) not the only reason for WS encountered • Most often horizontal shear (e.g. interface between different air masses) matters Hong Kong Observatory - 21 March 2005

  5. What is windshear and turbulence? • Turbulence – rapid irregular motion of air • Rapid bumps or jolts • effect on flight path relatively minimal • aircraft may be tossed about, momentarily out of control in severe events Hong Kong Observatory - 21 March 2005

  6. 2nd peak 1st peak Frequency Distribution by Month • Significant windshear: 1 in every 500 flights • Significant TURB: 1 in every 2,000 flights Hong Kong Observatory - 21 March 2005

  7. Decreasing freq. of occurrence In Hong Kong… • 5 typical weather scenarios • Winds blowing across terrain(terrain-induced) • Sea breeze • Gust fronts • Microbursts • Low-level jets Hong Kong Observatory - 21 March 2005

  8. Winds Blowing Across Terrain (Terrain-induced) • Windy occasions like during TC… • In lighter wind conditions, low-level temperature inversion also triggers windshear (spring months) Hong Kong Observatory - 21 March 2005

  9. Sea breeze • Usually develops under fine weather • Sea breeze converges with prevailing E’lies • Mostly in the form of headwind gains, but headwind losses also possible Hong Kong Observatory - 21 March 2005

  10. Gust front • Leading edge of cool air spreading out from the downdraft of intense storms • Headwind gain Hong Kong Observatory - 21 March 2005

  11. Microburst • Most violent form of downdraft from thunderstorms • Typical horizontal extent: a few km • Inc. headwind -> Downdraft -> Inc. tailwind Hong Kong Observatory - 21 March 2005

  12. Low-level jet • Narrow band of strong winds • Usually affects aircraft on departure (steeper glide path) • Relatively infrequent at HKIA Hong Kong Observatory - 21 March 2005

  13. Characteristics of WS & TURB in HK • Most are terrain-induced • Transient and sporadic • More significant on South RWY due to closeness to hills in general • Gain and loss events can co-exist Hong Kong Observatory - 21 March 2005

  14. Windshear is Sporadic!! • Small-scale disturbances over RWY 25L (multiple events) Cold colours(blue, green) – moving towards LIDAR Warm colours (yellow, orange, pink) – moving away from LIDAR Hong Kong Observatory - 21 March 2005

  15. LIDAR-Derived Headwind ProfileRWY 25L Departure Headwind profile @ 14:41 UTC Hong Kong Observatory - 21 March 2005

  16. LIDAR-Derived Headwind ProfileRWY 25L Departure Headwind profile @ 14:41 UTC Hong Kong Observatory - 21 March 2005

  17. Windshear is Transient!! Headwind profile @ 14:41 UTC Headwind profile @ 14:43 UTC • Sequence of headwind changes reversed in 2 minutes! Hong Kong Observatory - 21 March 2005

  18. Gain & Loss Events Co-exist! • Gain followed by loss or vice versa • Common for terrain-induced cases Hong Kong Observatory - 21 March 2005

  19. Terrain-Induced MBA • Terrain-induced events in rain could be so strong that (i.e. loss of 30 kt or greater) TDWR captures them as MICROBURST! • Don’t expect the typical sequence of events (gain preceding downdraft followed by loss) Hong Kong Observatory - 21 March 2005

  20. WS & TURB Alerting Service Hong Kong Observatory - 21 March 2005

  21. Automatic Alerts • Issued by WTWS (Windshear and Turbulence Warning System) covering 3 NM from runway thresholds • Nominal update rate 1 min. Hong Kong Observatory - 21 March 2005

  22. Automatic WS Alerts • Microburst Alert (MBA) • Generated by TDWR (Terminal Doppler Weather Radar) and integrated into WTWS • Runway-oriented wind speed loss >= 30 kt and accompanied by precipitation • Windshear Alert (WSA) • Runway-oriented wind speed loss or gain >= 15 kt Hong Kong Observatory - 21 March 2005

  23. Automatic TURB Alerts • Moderate or severe in intensity • With reference to heavy category aircraft Hong Kong Observatory - 21 March 2005

  24. Warnings Provided on ATIS • Issued by Aviation Met. Forecasters • Based on pilot reports, forecasting rules developed from case studies, real-time conditions as revealed by TDWR, LIDAR, etc. Hong Kong Observatory - 21 March 2005

  25. Performance of WS Warnings(12-month Running Means) • POD approaching upper limit, FAR keeps decreasing Hong Kong Observatory - 21 March 2005

  26. Improvements Implemented Hong Kong Observatory - 21 March 2005

  27. TMT Runway anemometers Weather buoy Weather buoys New Member of WTWS Algorithms - AWARE • AWARE (Anemometer-based Windshear Alerting Rules – Enhanced) launched in mid-2004 • Replaced old LLWAS module • Based on wind readings at 6 runway anemometers & TMT & 5 weather buoys • Alerts out of ground truths Hong Kong Observatory - 21 March 2005

  28. Merits of AWARE… • More extensive coverage compared with LLWAS • Enhanced detection of WS associated with: • Sea breeze • Gust front • Shear line • More sensitive in depicting gain events than WTWS/TDWR Hong Kong Observatory - 21 March 2005

  29. Shear Line Case WS Episode in July 2004 • WS reports over 25RA:0530 B772 +15kt0535 A343 +15kt0546 A306 -10 to +15 kt0619 A306 +15kt0625 B773 ±10 to 15kt • All captured by AWARE Cold colours(blue, green) – moving towards LIDAR Warm colours (yellow, orange, pink) – moving away from LIDAR Hong Kong Observatory - 21 March 2005

  30. Successful Detection by AWARE (Previously gone undetected with WTWS) Hong Kong Observatory - 21 March 2005

  31. AWARE – Point to Note • AWARE alerts updated at 10 sec. intervals • There may be brief alerts lasting a few sec. in marginal cases • They are genuine alerts! Hong Kong Observatory - 21 March 2005

  32. LIDAR Scanner ATCX Building Roof-top LIght Detection And Ranging(LIDAR) system – Fully Operational in Mid-2004 Installed in mid-2002 IR (2 μm) → eye-safe Hong Kong Observatory - 21 March 2005

  33. 100 How the LIDAR works … Hong Kong Observatory - 21 March 2005

  34. Merits of LIDAR… • Demonstrated capability in WS detection in non-rainy conditions -> indispensable reference tool for issuance of forecaster WS warnings on ATIS • Better definition on location of WS detected-> runway-specific WS warnings • Automatic windshear detection-> new alerting algorithms developed Hong Kong Observatory - 21 March 2005

  35. Windshear algorithms for automatic alerting based on LIDAR data • Adaptation of TDWR approach (shear along radar beams) – the radial shear algorithm • Direct view of glide paths – glide-path scan windshear algorithm Hong Kong Observatory - 21 March 2005

  36. Shear line Shear line Radial shear algorithm Shear line discernible on LIDAR velocity picture Shear line identified by algorithm Hong Kong Observatory - 21 March 2005

  37. Glide-Path Scan WS Algorithm • “Tube” cross-section: 2000 feet x 400 feet • Only points within the “tube” will be considered • Points closest to the flight path will be used to create the headwind profile Hong Kong Observatory - 21 March 2005

  38. Successful detection of a sig. gain event Glide-Path Scan WS Algorithm Hong Kong Observatory - 21 March 2005

  39. Trial Operation of LIDAR-based Alerting Algorithms Hong Kong Observatory - 21 March 2005

  40. Runway-specific WS Warnings(on ATIS) • LIDAR/TDWR/wind sensors, etc., reveal weather systems conducive to WS • Weather systems moving and evolving slowly? • WS affects only certain runway corridors -> runway-specific warning issued (e.g. warning for APP corridors only)-> more specific and accurate warnings Hong Kong Observatory - 21 March 2005

  41. Example - Spring Easterly Flow(Terrain-induced) Gap flows only affect southern corridors → ATIS windshear warning issued for southern corridors only Cold colours(blue, green) – moving towards LIDAR Warm colours (yellow, orange, pink) – moving away from LIDAR Hong Kong Observatory - 21 March 2005

  42. Sea breeze front Background flow Sea Breeze Example - Sea Breeze Sea breeze front over western corridors → ATIS windshear warning will be issued for all western corridors Hong Kong Observatory - 21 March 2005

  43. Gap Flow Example - Autumn/Winter Northerly Flow Gap flows extend to affect eastern approach corridor of north runway only → ATIS windshear alert will be issued for that corridor Hong Kong Observatory - 21 March 2005

  44. Some Operational Aspects Hong Kong Observatory - 21 March 2005

  45. Revision to WS/TURB Info on ATIS(Ref.: AIC 03/05) • Wef 27 January 2005 • New terminology: “FORECAST” (“EXPECT” previously) for forecast warnings by HKO. “FORECAST AND REPORTED” for warnings confirmed by pilot reports. • Estimated 2 500 ft wind based on hilltop wind on Lantau be given (Arrival ATIS) when wind speed reaches 35 kt:“2500 ft estimated wind 160 degree 40 kt” Hong Kong Observatory - 21 March 2005

  46. New Format of WS/TURB Info in Local Routine Report / MET Page • Revised WS/TURB warning terminology under “ADDN INFO” following new ICAO template • New “ATIS WS/TURB WRNG” contains consolidated warnings for inclusion in ATIS • “FCST AND REP” for warnings validated by pilot reports Hong Kong Observatory - 21 March 2005

  47. Alert Phraseology • Very common to have multiple occurrences of WS on same corridor in HK • WTWS consolidates multiple events into ONE integrated alert • TDWR alerts higher priority than WTWS alerts • Sinking shear (loss events) higher priority than lifting shear (gain events) • Max intensity given in alerts Hong Kong Observatory - 21 March 2005

  48. Alert Phraseology • E.g. APP to RWY 25L • ‘Caution Microburst Minus 30 knots on final approach’ (instead of specific location as in US) • Note: • The max intensity (-30 kt) can occur anywhere along the corridor • First encounter (+15 kt @ 3NM) not the worst encounter (-30 kt @ 1NM) RWY 25L  -30 +15 Hong Kong Observatory - 21 March 2005

  49. Alert Phraseology • E.g. APP to RWY 25L • ‘Caution WindshearMinus 15 knots on final approach’ • Note: • Some may report -15 kt, while others +20 kt (especially those who conducted a missed APP on encounter of the lifting shear) RWY 25L  +20 -15 Hong Kong Observatory - 21 March 2005

  50. Looking Forward • Validation and tuning of LIDAR-based alerting algorithms – integration with WTWS • Backup LIDAR • Uplink of WS & TURB information to cockpit Hong Kong Observatory - 21 March 2005

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