alerting of low-level windshear and turbulencealerting of low-level. windshear. and turbulence. s.t....

Alerting of LowAlerting of Low--LevelLevel WindshearWindshear and Turbulenceand Turbulence

S.T. ChanS.T. ChanHong Kong ObservatoryHong Kong Observatory

Hong Kong, ChinaHong Kong, China

26 July 200526 July 2005

Agenda

DefinitionsDefinitionsWMO/ICAO requirementsWMO/ICAO requirementsFreq. of occurrence of WS & TURBFreq. of occurrence of WS & TURBTypical conditions conducive to WS & TURBTypical conditions conducive to WS & TURBInstrumentation for WS & TURB alertingInstrumentation for WS & TURB alerting

WTWS (WTWS (WindshearWindshear and Turbulence Warning System)and Turbulence Warning System)TDWR (Terminal Doppler Weather Radar)TDWR (Terminal Doppler Weather Radar)Doppler LIDAR (Doppler LIDAR (LIghtLIght Detection And Ranging)Detection And Ranging)

Agenda (Cont.)

HKO WS & TURB alerting serviceHKO WS & TURB alerting serviceAutomatic alerts passed by ATCAutomatic alerts passed by ATCWarnings broadcast on ATISWarnings broadcast on ATIS

WS cases on TDWR/LIDARWS cases on TDWR/LIDARInterpretation of Doppler velocity Interpretation of Doppler velocity imagesimages

Definitions

What is windshear

and turbulence?

WindshearWindshear -- change in wind direction/speed change in wind direction/speed for more than a few secondsfor more than a few seconds

change in headwind/tailwindchange in headwind/tailwindchange in liftchange in lift

What is windshear

and turbulence?

Turbulence Turbulence –– rapid irregular motion of airrapid irregular motion of airRapid bumps or joltsRapid bumps or joltseffect on flight path relatively minimaleffect on flight path relatively minimalaircraft may be tossed about, momentarily out of aircraft may be tossed about, momentarily out of control in severe eventscontrol in severe events

WMO/ICAO Requirements

Reporting of WS & TURBReporting of WS & TURBPilots to report to ATS severe TURB Pilots to report to ATS severe TURB encounter and also WS if operationally sig. encounter and also WS if operationally sig. (Para. 5.6, WMO TR Ch. C.3.1/ICAO Annex (Para. 5.6, WMO TR Ch. C.3.1/ICAO Annex 3)3)

WMO/ICAO Requirements (Cont.)

Reporting of WS & TURBReporting of WS & TURBWS & moderate or severe TURB be WS & moderate or severe TURB be reported as supplementary info in local reported as supplementary info in local routine/special reports,routine/special reports,WS info added in METAR and SPECI if WS info added in METAR and SPECI if local circumstances so warrantlocal circumstances so warrant(Para. 4.8.1, Appendix 3, WMO TR Ch. C.3.1 (Para. 4.8.1, Appendix 3, WMO TR Ch. C.3.1 / ICAO Annex 3)/ ICAO Annex 3)

WMO/ICAO Requirements

WarningWarningWarnings of WS affecting operation of aircraft Warnings of WS affecting operation of aircraft below 500 m (1 600 ft) below 500 m (1 600 ft) (Para. 7.4, WMO TR Ch. C.3.1/ICAO Annex 3)(Para. 7.4, WMO TR Ch. C.3.1/ICAO Annex 3)Evidence of WS should be based onEvidence of WS should be based on

GroundGround--based remotebased remote--sensinigsensinig eqeq. (e.g. Doppler radars). (e.g. Doppler radars)GroundGround--based detection based detection eqeq. (e.g. wind sensor network). (e.g. wind sensor network)Aircraft observationsAircraft observationsOther met. info. (e.g. appropriate sensors near aerodrome)Other met. info. (e.g. appropriate sensors near aerodrome)

WMO/ICAO Guidance

Manual on Wind ShearManual on Wind Shear (ICAO Doc 9817) (ICAO Doc 9817) -- to be publishedto be publishedReplacing Replacing Wind ShearWind Shear, ICAO Circular , ICAO Circular 186186--AN/122AN/122

Frequency of Occurrence in HK

Aircraft report Aircraft report collectioncollection

Launched 2 rounds of Launched 2 rounds of IOP exercises in IOP exercises in 20002000Repeatedly appealing Repeatedly appealing for pilot reportsfor pilot reportsDeveloped a WS & Developed a WS & TURB report formTURB report form

Frequency Distribution by Month

77--year period year period (Jul 98 (Jul 98 –– Jun 05)Jun 05)

0.21% reported 0.21% reported WS (~1 in 500 WS (~1 in 500 flights)flights)0.05% reported 0.05% reported TURB (~1 in TURB (~1 in 2,000 flights)2,000 flights)

1st peak

2nd peak

Typical Weather Conditions for WS & TURB

Intense convective activitiesIntense convective activitiesThunderstormsThunderstormsMicroburstsMicroburstsGust frontsGust frontsTornadoesTornadoesWaterspoutsWaterspouts

Typical Weather Conditions for WS & TURB (Cont.)

Frontal surfacesFrontal surfacesStrong winds across topographyStrong winds across topographySea breeze frontsSea breeze frontsMountain wavesMountain wavesLowLow--level inversionslevel inversions

In Hong Kong…

5 typical weather scenarios5 typical weather scenariosWinds blowing across terrainWinds blowing across terrain(terrain(terrain--induced)induced)Sea breezeSea breezeGust frontsGust frontsMicroburstsMicroburstsLowLow--level jetslevel jets

Decreasing freq. of occurrence

HKIA

Winds Blowing Across Terrain (Terrain-induced)

Lin Fa Shan

(756m)

Yi Tung Shan

(748m)Sunset Peak

(869m)

Lantau Peak

(933m)

Nei

Lak Shan

(751m)

Castle Peak

(583m)

(507m)


Fresh or strong winds from E through SWFresh or strong winds from E through SW……


Strong winds from NW through NEStrong winds from NW through NE……

Wind flow across complex terrain on Lantauas simulated by computer model

LANTAULANTAU

HKIAHKIA


Windy occasions Windy occasions like during TClike during TC……Aircraft may Aircraft may encounter encounter headwind losses headwind losses and gainsand gains

In lighter wind conditions, lowIn lighter wind conditions, low--level level temperature inversion also triggers temperature inversion also triggers windshearwindshear(spring months)(spring months)

Sea breezeUsually develops under fine Usually develops under fine wxwx and light windsand light windsSea breeze converges with prevailing Sea breeze converges with prevailing EE’’liesliesMostly in the form of headwind gains, but Mostly in the form of headwind gains, but headwind losses also possibleheadwind losses also possible

Gust frontThe leading edge of cool air spreading out The leading edge of cool air spreading out from a downdraft of intense stormsfrom a downdraft of intense stormsHeadwind gainsHeadwind gains

MicroburstMost violent form of downdraft from Most violent form of downdraft from thunderstormsthunderstormsTypical horizontal extent: a few kmTypical horizontal extent: a few kmInc. headwind Inc. headwind --> Downdraft > Downdraft --> Inc. tailwind> Inc. tailwind

Low-level jetNarrow band of strong windsNarrow band of strong windsUsually affects aircraft on departure Usually affects aircraft on departure (steeper glide path)(steeper glide path)Relatively infrequent at HKIARelatively infrequent at HKIA

Characteristics of WS & TURB in HK

Most are terrainMost are terrain--induced induced Transient and sporadicTransient and sporadic

Phenomenon affects aircraft differentlyPhenomenon affects aircraft differently

In general more significant on S RWY due to In general more significant on S RWY due to closeness to hillscloseness to hillsGain and loss events can coGain and loss events can co--existexist

Time Aircraft Type Intensity Location03:50 - None reported -04:00 A330 15 kt loss 3MF04:02 B747-400 25-29 kt gain 2MF04:04 B747-400 None reported -04:10 B767 15 kt gain 2MF

A day in March 2000Landings on RWY 07L

Instrumentation for WS & TURB Alerting

AWS

Wx buoy

Wind profiler

TDWR

LIDAR

Windshear

and Turbulence Warning System (WTWS)

An integrated system automatically An integrated system automatically integrates alerts from integrates alerts from

Microburst/Microburst/WindshearWindshear alerts from TDWRalerts from TDWRWindshearWindshear/Turbulence alerts generated by /Turbulence alerts generated by WTWS algorithmsWTWS algorithms

WTWS Algorithms

WindshearWindshearDifferences in wind speed and direction Differences in wind speed and direction measured at adjacent anemometersmeasured at adjacent anemometersImproved algorithm to reImproved algorithm to re--process TDWR process TDWR data (radial wind speed, signal to noise ratio) data (radial wind speed, signal to noise ratio) and detect and detect windshearwindshear in clear airin clear airNew algorithm based on LIDAR New algorithm based on LIDAR dopplerdopplervelocities in the pipelinevelocities in the pipeline

Rule: Runway-oriented wind difference in any pair >= 15 kt

WTWS Algorithms

TurbulenceTurbulenceWind speed and direction and their Wind speed and direction and their fluctuations at various anemometers in HK; fluctuations at various anemometers in HK; magnitude of turbulence determined by magnitude of turbulence determined by correlationcorrelationReRe--process radial wind speed, spectrum process radial wind speed, spectrum width, signal to noise ratio data from width, signal to noise ratio data from TDWR to detect turbulence in clear airTDWR to detect turbulence in clear air

WTWS DisplaysAlphanumeric Alarm Display (AAD)Alphanumeric Alarm Display (AAD)

WTWS alerts in textual format for direct WTWS alerts in textual format for direct readout to pilots by ATCreadout to pilots by ATC

TURBTURB

WTWS DisplaysGeographical Geographical Situation Situation Display (GSD)Display (GSD)

For reference For reference by ATC by ATC supervisors and supervisors and aviation aviation forecastersforecastersShows Shows geographical geographical distribution of distribution of WS & TURBWS & TURB

TDWR

TDWR

To detect To detect microburst and WS microburst and WS associated with associated with convective stormsconvective storms~12 km NE of HKIA~12 km NE of HKIARadar antenna ~60 m Radar antenna ~60 m AMSLAMSLRunways approx. Runways approx. aligned with TDWR aligned with TDWR radialradial

Special features of TDWRNarrow antenna Narrow antenna beamwidthbeamwidth

0.5 deg.0.5 deg.Good Good sidelobesidelobe performanceperformanceExcellent target differentiationExcellent target differentiation

Highly stable KlystronHighly stable Klystron--based based transmittertransmitter

Able to detect reflectivity below Able to detect reflectivity below --20 20 dBZdBZ(can detect some returns even in rainless (can detect some returns even in rainless conditions)conditions)

Special features of TDWR (Cont.)

Advanced velocity Advanced velocity dealiasingdealiasing algorithmalgorithmEmploys dual Employs dual PRFsPRFs in the lowest scan to in the lowest scan to uniquely determine unambiguous velocity uniquely determine unambiguous velocity datadataVelocity Velocity dealiasingdealiasing at higher elevations at higher elevations based on assumption of vertical continuity based on assumption of vertical continuity of velocityof velocityUnambiguous velocity range Unambiguous velocity range --80 80 m/sm/s to 80 to 80 m/sm/s


Range Range dealiasingdealiasing algorithmalgorithmLow PRF scan at lowest elevation to provide Low PRF scan at lowest elevation to provide initial view of radar echo returns from the initial view of radar echo returns from the longest rangelongest rangeThis information is then used to predict This information is then used to predict the expected degree of obscuration in the expected degree of obscuration in higher level scanshigher level scans


Powerful clutter removal mechanismPowerful clutter removal mechanismA 55 A 55 dBZdBZ filter to low velocity data (filter to low velocity data (--2 to 2 to 2 2 m/sm/s) to remove stationary clutter) to remove stationary clutterA pointA point--target removal algorithm to remove target removal algorithm to remove moving objects (aircraft, birds and ships) moving objects (aircraft, birds and ships) UserUser--defined 30 defined 30 dBZdBZ clutter polygons to clutter polygons to remove areas contaminated with moving remove areas contaminated with moving clutters (traffic, trees)clutters (traffic, trees)

Example: Clutter Polygon over Lantau Island

TDWR Products

Graphical productsGraphical productsPrecipitation and storm motionPrecipitation and storm motionMicroburst shapesMicroburst shapesGust frontsGust frontsWind shift predictionWind shift prediction

Alphanumeric alertsAlphanumeric alertsMicroburstMicroburstWindshearWindshear

Doppler LIDAR

To supplement To supplement TDWR in detecting TDWR in detecting WS under clearWS under clear--air air conditionsconditionsInstalled at roofInstalled at roof--top top of ATC Complexof ATC Complex~43 m above runway~43 m above runwayA good view of both A good view of both arrival/departure arrival/departure corridorscorridors

LIDAR

LIDAR Coverage

Out to 3 NM from TDZ

Out to 3 NM from TDZ

LIDAR Principle

LIDAR versus TDWR

LIDAR works best in

fine weather

TDWR works bestin

rainy weather

Major Parameters of LIDAR

Peak pulse energy 2 Peak pulse energy 2 mJmJWavelength 2 Wavelength 2 μμmmRange resolution ~100 mRange resolution ~100 mMaximum range ~10 km (weather Maximum range ~10 km (weather dependent)dependent)Unambiguous velocity range Unambiguous velocity range --20 20 m/sm/s to to 20 20 m/sm/s (extendable to (extendable to --40 40 m/sm/s to 40 to 40 m/sm/s with reduction in range)with reduction in range)

Safety Issues

Classified as Class 1M under IEC Classified as Class 1M under IEC 6082560825--1 (IEC 2001) and Class 3b under 1 (IEC 2001) and Class 3b under ANSI Z136.1ANSI Z136.1--20002000

Could be harmful if viewed with optical aidsCould be harmful if viewed with optical aidsSafety measuresSafety measures

Sector blankingSector blankingScan rate interlockScan rate interlockLaser Safety Officer appointedLaser Safety Officer appointed

HKO WS & TURB Alerting Service

Types of WS & TURB Warnings

Automatic WS & TURB alerts passed by Automatic WS & TURB alerts passed by ATCATCWS & TURB warnings broadcast on WS & TURB warnings broadcast on ATIS (Automatic Terminal Information ATIS (Automatic Terminal Information System)System)

Automatic Alerts

Issued by WTWS covering 3 NM from Issued by WTWS covering 3 NM from runway thresholdsrunway thresholdsNominal update rate 1 min.Nominal update rate 1 min.

Automatic WS Alerts

Microburst Alert (MBA)Microburst Alert (MBA)RunwayRunway--oriented wind speed loss >= oriented wind speed loss >= 30 30 ktkt and accompanied by precipitationand accompanied by precipitationGenerated by TDWR and integrated into Generated by TDWR and integrated into WTWSWTWS

WindshearWindshear Alert (WSA)Alert (WSA)RunwayRunway--oriented wind speed loss or gain >= oriented wind speed loss or gain >= 15 15 ktkt (except microburst)(except microburst)

Automatic WS Alerts (Cont.)

WTWS consolidates MBA and WSA and WTWS consolidates MBA and WSA and issues an integrated alert according to issues an integrated alert according to prioritypriority

MicroburstMicroburstTDWR WS of +30 TDWR WS of +30 ktkt or moreor moreWTWS WS of WTWS WS of --30 30 ktkt or moreor moreWTWS WS of +30 WTWS WS of +30 ktkt or moreor moreTDWR WS of TDWR WS of --15 to 15 to --29 29 ktktTDWR WS of +15 to +29 TDWR WS of +15 to +29 ktktWTWS WS of WTWS WS of --15 to 15 to --29 29 ktktWTWS WS of +15 to +29 WTWS WS of +15 to +29 ktkt

Automatic WS Alerts (Cont.)

Content of MBA & WSAContent of MBA & WSAType of alert (MBA or WSA)Type of alert (MBA or WSA)Magnitude of runwayMagnitude of runway--oriented wind speed oriented wind speed differencedifferenceLocation (final approach / departure area)Location (final approach / departure area)E.g.E.g.

(Call sign) caution microburst minus 30 (Call sign) caution microburst minus 30 ktkt on final on final approachapproach(Call sign) caution (Call sign) caution windshearwindshear plus 15 plus 15 ktkt on on departuredeparture

Automatic TURB Alerts

Issued by WTWS based on derived Issued by WTWS based on derived eddy dissipation rate (EDR)eddy dissipation rate (EDR)Alert of Moderate TURB Alert of Moderate TURB –– EDR between EDR between 0.3 and 0.50.3 and 0.5Alert of Severe TURB Alert of Severe TURB –– EDR reached EDR reached 0.50.5With reference to heavy category With reference to heavy category aircraftaircraft

Automatic TURB Alerts (Cont.)

Content of TURB AlertsContent of TURB AlertsIntensity of turbulence (moderate/severe)Intensity of turbulence (moderate/severe)Location (final approach / departure area)Location (final approach / departure area)E.g.E.g.

(Call sign) caution severe turbulence on final (Call sign) caution severe turbulence on final approachapproach(Call sign) caution moderate turbulence on (Call sign) caution moderate turbulence on departuredeparture

Warnings Broadcast on ATIS

Issued by Aviation ForecastersIssued by Aviation ForecastersBased on pilot reports, forecasting rules Based on pilot reports, forecasting rules developed from case studies, latest developed from case studies, latest situation as revealed by TDWR, LIDAR, situation as revealed by TDWR, LIDAR, etc.etc.Warning message broadcast at the Warning message broadcast at the beginning of ATIS message right after beginning of ATIS message right after the runway in use at the beginningthe runway in use at the beginning

Warnings Broadcast on ATIS (Cont.)

E.g.E.g.

““Significant Significant windshearwindshear forecast 07L and 07R. forecast 07L and 07R. Moderate turbulence forecast 07L and 07RModerate turbulence forecast 07L and 07R””

““Significant Significant windshearwindshear forecast and REPORTED forecast and REPORTED 07L and 07R07L and 07R”” (to add credibility to the warning (to add credibility to the warning when substantiated with actual reports)when substantiated with actual reports)

““Significant Significant windshearwindshear forecast 07Lforecast 07L”” (warning (warning specific to individual runways, launched in early specific to individual runways, launched in early 2005)2005)

Development of Windshear Alerting Techniques

Spring RulesMonitor weather

situation

WTWS : WSA 20K-

3MF ATIS : SIG WS FORECAST

WS Cases as Revealed by TDWR / LIDAR

Terrain-Induced CaseStrong winds blowing across Lantau during S.T.S Strong winds blowing across Lantau during S.T.S HagupitHagupit (0218)(0218)Closest to HK to the SSW in the afternoon of 11 Closest to HK to the SSW in the afternoon of 11 Sep 2002Sep 2002

StrongESE winds

HKIA

Terrain-Induced Case (Cont.)Strong Strong ESEESE’’lieslies over HKIA, gale to storm force over HKIA, gale to storm force winds over hilltopswinds over hilltops23 aircraft conducted go23 aircraft conducted go--around due to WSaround due to WS

Terrain-Induced Case (Cont.)TDWR PPI scan at 07:03 UTC (15:03 HKT)TDWR PPI scan at 07:03 UTC (15:03 HKT)Streaks of highStreaks of high-- and lowand low--speed of airflow speed of airflow emerged downwind of Lantauemerged downwind of Lantau

Cold colours

(blue, green) –

moving

towards

TDWR

Warm colours (yellow, orange, pink)

– moving away from TDWR

Origin of Low-speed air streaks traced back to individual peaks on Lantau Island

Terrain-Induced Case (Cont.)LIDAR also captured similar conditions when LIDAR also captured similar conditions when rain temporarily subsidedrain temporarily subsided

Sea Breeze Case (21 August 2002)

WW’’lyly sea breeze developed from west sea breeze developed from west of HKIA towards noonof HKIA towards noonWS reports received respectively at WS reports received respectively at 12:01, 14:22 and 14:29 HKT12:01, 14:22 and 14:29 HKTMovement of sea breeze front clearly Movement of sea breeze front clearly depicted on LIDARdepicted on LIDAR

Sea Breeze Case (Cont.)11:24 HKT 12:00 HKT

Onset of sea breeze at 1253H on 31 Jan 2002, windshear

occurrence started at 1327H

1200H 1253H WB1 registered onset of sea breeze

1327H start of 15 consecutive windshear reports

1409H R1W registered onset of sea breeze

Gust Front Case (10 September 2002)

TD TD HagupitHagupit (0218) over NE part of South China Sea(0218) over NE part of South China SeaNN’’lieslies affected HK under the outer circulation of affected HK under the outer circulation of HagupitHagupit

Gust Front Case (Cont.)Inland thunderstorms triggered by Inland thunderstorms triggered by insolationinsolationmoved SE to affect HKmoved SE to affect HKThunderstorms and wind change ahead well Thunderstorms and wind change ahead well captured by TDWRcaptured by TDWR

Gust Front Case (Cont.)Gust front ahead of the thunderstorms Gust front ahead of the thunderstorms also captured by LIDARalso captured by LIDAR

Advance of gust front as seen on LIDAR

Gust front on 4 Aug 2003 – Well Ahead of Main Convection

Microburst Case (30 June 2004)

HK under subsidence zone of T. HK under subsidence zone of T. MindulleMindulleLocalized thunderstorms triggered in HKLocalized thunderstorms triggered in HK

Microburst Case (Cont.)Intense convection developed just Intense convection developed just off SW of TDWRoff SW of TDWR

3 km CAPPI, HKO Doppler Radar 0.6 deg. PPI, TDWR Doppler vel.11:54 HKT

3 km CAPPI, HKO Doppler Radar 0.6 deg. PPI, TDWR Doppler vel.12:30 HKT

Microburst Case (Cont.)Convection continued to intensifyConvection continued to intensifyMicroburst alert issued by TDWRMicroburst alert issued by TDWR

Microburst Case

Low-Level Jet Case (6 October 2002)

Strong NE monsoon behind a cold front Strong NE monsoon behind a cold front prevailed over HKprevailed over HK

Low-Level Jet Case (Cont.)Fresh N to Fresh N to NENE’’lyly at HKIA, strong to at HKIA, strong to gale on hilltopsgale on hilltops

Low-Level Jet Case (Cont.)LIDAR RHI animation revealed lowLIDAR RHI animation revealed low--level jet ~1 km above groundlevel jet ~1 km above ground

Small Quiz on Interpretation of Doppler Velocity Images

Q.1 Q.1 –– PPI, radar at centrePPI, radar at centre

N


N

Wind direction

o


N

Wind speed

o


Q.2 Q.2 –– PPI, radar due south of displayPPI, radar due south of display

N


N

Wind pattern

o



N


N

o



N

Thank You

A landing aircraft

alerting of low-level windshear and turbulencealerting of low-level. windshear. and turbulence. s.t....

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