1Graduate Program in Earth and Space Science, York University, Toronto, Ontario2Environment Canada, Cloud Physics and Severe Weather Research Section, Toronto, Ontario

Yi (Emily) Zhou1, George Isaac2, 1, Peter Taylor1

1. IntroductionLow level wind shear : change of horizontal wind

direction and/or speed with height ((∂U/∂z, where U is horizontal wind)

Dangerous: increase/decrease of head wind (tail wind), hence an increase /decrease of lifting force, causing the aircraft to fly above or below its intended flight path.

A survey conducted by the International Civil Aviation Organization showed that from 1964 to 1983, low level windshear caused at least 28 large transport aircraft accidents in the world that together resulted in over 500 fatalities and 200 injuries.

Tasks Study low level wind shear from models’ out put (GEM-15 Regional, GEM-2.5 LAM and RUC-13) Analysis of low level wind shear from AMDAR

(Aircraft Meteorological Data Reports) wind profile data for Pearson Airport

Case studyData:

From CAN-Now Archive Files: Pearson M300 Data (2007-07-13 to 2009-03-31) GEM-15 Regional (2007-02-27 to 2009-03-12) GEM-2.5 LAM (2007-03-13 to 2009-03-12) RUC-13 model data (2007-08-20 to 2009-03-11)

AMDAR data in netCDF from pftp.madis-data.noaa.gov (2007-07-13 to 2009-03-31)

2. Low level wind shear criteriaAccording to MANAIR 2.6.7(MANAIR - manual of standards

and procedures for aviation weather forecasts), the vertical non convective low level wind shear criteria are listed as:Wind vector change greater than 25 knots within 500 ft

AGL.Wind vector change greater than 40 knots within 1000 ft

AGL.Wind vector change greater than 50 knots within 1500 ft

AGL.A PIREP indicates a loss or gain of indicated airspeed of 20

knots or more, within 1500 ft AGL.

When any of the above guidelines are met, then the low level wind shear achieves the criterion, and this wind shear is classed as a wind shear case.

Low Level Wind Shear Criteria

Non metric unit metric unit

Height Criteria Height Criteria

feet kts m m/s

1st 500 ft 25 152.4 12.85

1st 1000ft 40 304.8 20.56

1st 1500ft 50 457.2 25.7

2. Low level wind shear criteria

3. Methods of InterpolationPurpose of interpolation:

to obtain particular 500ft, 1000ft, and 1500ft height wind

Methods: Cubic spline methodLinear method

Comparison 2 methods:

3. Methods of Interpolation

3. Methods of Interpolation

Comparison 2 methods: linear is better for interpolating AMDAR

data and RUC data than Cubic spline. For interpolating GEM-15 Regional and GEM-2.5 LAM, the two methods have roughly the same results.

Reason: uneven end points distance of AMDAR and RUC .

Method Chosen: Linear

3. Methods of Interpolation

4. AMDAR wind shear analysisWind shear cases monthly distribution

Wind shear cases time distribution

4. AMDAR wind shear analysis

Local Time?

Wind shear cases distribution in different levels

4. AMDAR wind shear analysis

5. Frequency of low level wind shearwithin 500ft above ground level

Wind Shear Criterion: 12.8m/s

5. Frequency of low level wind shearWithin 1000ft above ground level

Wind Shear Criterion: 20.56m/s

5. Frequency of low level wind shearWithin 1500ft above ground level

Wind Shear Criterion: 25.7m/s

5. Frequency of low level wind shearConclusion:

within 500 , 1000 feet height above ground level, the GEM-15 Regional has the best capability for low level wind shear forecasting, the second is GEM-2.5 LAM. For 1500 feet height above ground level, RUC is the best one. Low level wind shears predicted from models are lower than those observed.

Coarsetime

Gainttime

1st 500ft Shear m/s

1st 1000ftShear m/s

1st 1500ftShear m/s

2008Dec271304 13:03:50 11.0 21.0 26.0

2008Dec271331 13:30:50 13.9 14.2 14.6

2008Dec271415 14:14:50 13.9 13.5 13.0

2008Dec271809 18:08:56 14.3 16.5 17.6

6. Case study1. From OBS

2. From LAM

Date ValidTime1st 500ft

Shear m/s

1st 1000ftShear m/s

1st 1500ftShear m/s

2008-12-27-12_lam.tar.gz

2008-12-27-13:05Z 6 11 15

2008-12-27-12_lam.tar.gz

2008-12-27-13:30Z 7 11 14

2008-12-27-12_lam.tar.gz

2008-12-27-14:05Z 7 11 14

2008-12-27-12_lam.tar.gz

2008-12-27-18:05Z 9 11 13

Date ValidTime1st 500ft

Shear m/s1st 1000ftShear m/s

1st 1500ftShear m/s

2008-12-27-12_reg.tar.gz

2008-12-27-13:00Z 8 13 17

2008-12-27-12_reg.tar.gz

2008-12-27-13:30Z 9 14 17

2008-12-27-12_reg.tar.gz

2008-12-27-14:00Z 8 14 17

2008-12-27-12_reg.tar.gz

2008-12-27-18:00Z 8 11 15

6. Case study1. From REG

2. From RUC

Date Forecast and ValidTime1st 500ft

Shear m/s

1st 1000ftShear m/s

1st 1500ftShear m/s

2008-12-27-ruc.tar.gz

20081227ruc2.t11z.pgrb13f02.grib2.txt 3 9 13

2008-12-27-ruc.tar.gz

20081227ruc2.t11z.pgrb13f03.grib2.txt 6 12 19

2008-12-27-ruc.tar.gz

20081227ruc2.t16z.pgrb13f02.grib2.txt 3 8 14

6. Case studyHourly Surface Data Report (December 27, 2008) Sfc wind from models

Time Time Temp TdRH

Wind dir

Wind Spd

LAMWind SPD

REGWind SPD

RUCWind SPD

LST UTC °C °C % 10's deg m/s m/s m/s m/s

6:00 11:00 1.6 0.8 94 0 6 6 2

7:00 12:00 2.1 1.4 95 0 8 4 3

8:00 13:00 3.3 2.3 93 13 1 8 6 3

9:00 14:00 4.2 3.2 93 0 8 6 7

10:00 15:00 5.7 5 95 18 1 8 7 6

11:00 16:00 7 6.5 97 20 1 7 6 5

12:00 17:00 9 8.3 95 22 4 6 6 5

SFC OBS From: www.climate.weatheroffice.gc.ca

6. Case studyEvent overview

From: http://www.hpc.ncep.noaa.gov/dailywxmap/index.html

07AM, EST, Dec 27, 2008

6. Case studyEvent overview

Data from : http://nomads.ncdc.noaa.gov/cgi-bin/ncdc-ui/define-collection.pl?model_sys=narr&model_name=narr-a&grid_name=221

NARR DATA

6. Case studyEvent overview

6. Case study

6. Case studyM300 DATA

AMDAR DATACYYZ(Dn) 1330 27Dec08Descent sounding from 140° into Toronto Intl, ON (CYYZ)lasting 30 min, and covering 46 nautical miles (Aircraft #7189) P_alt mb t/td w_dir/w_spd Time Bng/Rng (ft) (°C) (kts) (UTC) (nm)

490 995 6.0/----- 233°/026 1330 268°/001980 978 10.1/----- 238°/043 1329 239°/003

1870 947 10.3/----- 245°/052 1328 233°/0052499 925 11.3/----- 245°/0512890 912 12.0/----- 245°/051 1327 231°/0092920 911 11.0/----- 237°/042 1325 218°/0132950 910 10.8/----- 240°/049 1326 229°/0123020 907 11.1/----- 245°/031 1324 206°/013

4000 875 11.6/----- 250°/030 1323 200°/0114780 850 9.8/----- 246°/0325280 834 8.6/----- 243°/034 1322 187°/008

Data from: http://amdar.noaa.gov/demo_java/

COARSETIME GAINTTIMEPROFILE

TIMEWINSPEED

m/s kts WINDIR

2008Dec271304 13:03:50 12303830300.54 1 146.3

2008Dec271331 13:30:50 12303846500.54 1 174.4

2008Dec271415 14:14:50 12303872901.07 2.1 188.4

2008Dec271809 18:08:56 12304013361.61 3.1 153.8

6. Case studyAMDAR profile

From: http://amdar.noaa.gov/demo_java/

6. Case studyConclusionFront passage passing stationClose to surface ground, an inversion layer

existsRH>90%Surface wind is small; above surface, wind

speed increase quickly

7 SummaryLinear interpolation method is better for interpolating

particular height wind.Wind shear cases exhibit features: 1. more cases happen in

autumn and winter; 2. cases occur mostly during night or morning (local time); 3. most wind shear happen within 1st 500ft AGL.

Within 500 and 1000 ft, GEM Regional has the best capability for low level wind shear forecasting, the second is LAM. For 1500 ft AGL, RUC is better.

Frontal passage passing station, strong low level T inversion support low level wind shear development.