Wave Forecasting at ECMWF

Jean-Raymond Bidlot Marine Aspects Section Predictability Division of the Research Department European Centre for Medium-range Weather Forecasts (E.C.M.W.F.) Reading, UK

Slide 1 Ocean waves:

We are dealing with generated waves at the surface of the , from gentle to rough …

Ocean wave Forecasting at ECMWF Slide 2 Ocean Waves

Forcing: earthquake wind moon/sun Restoring: gravity surface tension force

10.0 1.0 0.03 3x10-3 2x10-5 1x10-5 Frequency (Hz)

Ocean wave Forecasting at ECMWF Slide 3 What we are dealing with?

Water surface elevation, η Wave Period, T Wave Length, λ , H

Ocean wave Forecasting at ECMWF Slide 4 Wave Spectrum

l The irregular water surface can be decomposed into (infinite) number of simple sinusoidal components with different frequencies (f) and propagation directions (θ ).

l The distribution of wave energy among those components is called: “wave spectrum”, F(f,θ).

Ocean wave Forecasting at ECMWF Slide 5 l Modern ocean wave prediction systems are based on statistical description of oceans waves (i.e. ensemble average of individual waves).

l The state is described by the two-dimensional wave spectrum F(f,θ).

Ocean Wave Modelling Ocean Wave Modelling

Ocean wave Forecasting at ECMWF Slide 6 Ocean Wave Modelling l For example, the mean variance of the sea surface elevation η due to waves is given by: 〈η2〉 = F( f ,θ)dfdθ ∫∫ l The mean energy associated with those waves is: 2 energy= ρηw g

l The statistical measure for wave height, called the (Hs): 2 H s = 4 η

The term significant wave height is historical as this value appeared to be well correlated with visual estimates of wave height from experienced observers. It can be shown to correspond to the average rd 1/3 highest waves (H1/3). Ocean wave Forecasting at ECMWF Slide 7 Ocean Wave Modelling l The ocean wave modelling at ECMWF is based on the wave mode WAM cycle 4 (Komen et al. 1994), albeit with frequent improvements (Janssen 2007: ECMWF Tech. Memo 529.). l Products from different configurations of WAM are currently available at ECMWF. l Wave model wave page:

http://www.ecmwf.int/products/forecasts/wavecharts/index.html#forecasts l General documentation: http://www.ecmwf.int/research/ifsdocs/CY36r1/index.html

Ocean wave Forecasting at ECMWF Slide 8 ECMWF Wave Model Configurations Global models

Tuesday20°E 14 March40°E 200660°E 00UTC80°E ECMWF100°E 120°E Forecast140°E t+36160°E VT: Wednesday180° 160°W 15 March140°W 2006120°W 12UTC100°W Surface:80°W significant60°W 40°W wave20°W height l Global from 81°S to 90°N, 10.29 70°N 70°N 9.75 60°N 60°N including all inland . 9 50°N 50°N

40°N 40°N 8.25

30°N 30°N 7.5

20°N 20°N 6.75 l Coupled to the atmospheric model 10°N 10°N 6 0° 0° 5.25 (IFS) with feedback of the sea 10°S 10°S 4.5 20°S 20°S 3.75 30°S 30°S 3 surface roughness change due to 40°S 40°S 2.25 50°S 50°S 1.5 60°S 60°S waves. 0.75 70°S 70°S 0 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W l The interface between WAM and Forecast wave height on 15/03/2006 12UTC. the IFS has been generalised to include air density and gustiness neutral wind effects on wave growth and more wind gustiness recently neutral . l Data assimilation Jason-2 air density altimeter wave heights. model Wave model Atmospheric roughness

Ocean wave Forecasting at ECMWF Slide 9 ECMWF Wave Model Configurations

Deterministic model Probabilistic forecasts (EPS) l 28 km grid spacing. l 55 km grid spacing. l 36 frequencies. l 30 25 frequencies *. l 36 directions. l 24  12 directions *. l Coupled to the TL1279 model. l Coupled to TL639  TL319 model *.

l (50+1) (10+5) day forecasts from l Analysis every 6 hrs and 10 day 0 and 12Z (monthly once a forecasts from 0 and 12Z. week).

* Change in resolutions after 10 days

NB: also in seasonal forecast at lower resolutions

Ocean wave Forecasting at ECMWF Slide 10 ECMWF Wave Model Configurations

Interim reanalysis (1979 to present)

(as a follow-up to ERA40 (45 year reanalysis) Comparison with buoys: l 1.0°x1.0°. l 30 frequencies. l 24 directions. l Coupled to TL255 model l Production is ongoing. l Very satisfactory performance:

Operations ¤ http://www.ecmwf.int/research/era/do/get/era-interim ERA-40 ¤ ECMWF Newsletters No. 110 (Winter 2006/07) & ERA Interim 111 (Spring 2007) http://www.ecmwf/publications/newsletters

Ocean wave Forecasting at ECMWF Slide 11 Wave Model Products

Wave model The complete description of the is given by the 2-D spectrum, however, it is a fairly large amount of data (e.g. 24x30 values at each grid point in the global model). It is therefore reduced to integrated quantities: 2-D Ø 1-D spectrum obtained spectrum by integrating the 2-D spectrum over all directions and/or over a 1-D frequency range. spectrum

Ocean wave Forecasting at ECMWF Slide 12 Wave Model Products

When simple numbers are required, the following

parameters are available: ) peak f Ø The significant wave height ( E (Hs). Ø The peak period (period of the peak of the 1-D spectrum). area under spectrum = <η2>

Ø Mean period(s) obtained 2 H = 4 η from weighted integration of s the 2-D spectrum. Ø Integrated mean direction. f fp < f > Ø Few others. (peak frequency) (mean frequency)

T = 1 / f Complete list at: http://www.ecmwf.int/services/archive/d/parameters/order=/table=140/

Ocean wave Forecasting at ECMWF Slide 13 Wave Model Products Use simple parameters: total wave height and mean propagation direction

10m winds and mean pressure: Wave height and mean direction: Analysis : 14 February 2009, 00 UTC Analysis : 14 February 2009, 00 UTC

Ocean wave Forecasting at ECMWF Slide 14 Wave Model Products

Wave periods: at the peak of the spectrum or in the mean

PEAK PERIOD: MEAN WAVE PERIOD: Analysis : 14 February 2009, 00 UTC Analysis : 14 February 2009, 00 UTC

Ocean wave Forecasting at ECMWF Slide 15 Wave Model Products

Wave height and mean direction: Analysis : 14 February 2009, 00 UTC

PEAK PERIOD: Analysis : 14 February 2009, 00 UTC

Ocean wave Forecasting at ECMWF Slide 16 Wave Model Products Situation might be more complicated !

10m winds and mean sea level pressure: Wave height and mean direction: Analysis : 15 February 2009, 00 UTC Analysis : 15 February 2009, 00 UTC

Ocean wave Forecasting at ECMWF Slide 17 Wave Model Products Situation might be more complicated:

Wave height and mean direction: Analysis : 15 February 2009, 00 UTC

Ocean wave Forecasting at ECMWF Slide 18 Wave Model Products A scheme is used to split the global wave fields into waves which are under the direct influence of the forcing wind, the so-called windsea or wind waves, and those waves that are no longer bound to the forcing wind, generally referred to as . Period and mean direction are also determined for these split fields.

Wave height and windsea mean direction: Wave height and swell mean direction: Analysis : 15 February 2009, 00 UTC Analysis : 15 February 2009, 00 UTC

Ocean wave Forecasting at ECMWF Slide 19 Wave Model Products

Windsea and swell: opposing sea

Ocean wave Forecasting at ECMWF Slide 20 Wave Model Products

Windsea and swell: cross sea

swell

Ocean wave Forecasting at ECMWF Slide 21 Wave Model Products on the web:

Currently on our web: significant wave height and mean direction

Ocean wave Forecasting at ECMWF Slide 22 Wave Model Products on the web

Currently on our web: mean wave period and direction

Ocean wave Forecasting at ECMWF Slide 23 Wave Model Products on the web: For the Severe Weather Forecast Demonstration Projects (SWFDP) for South Africa, East Africa and the Pacific windsea and swell plots are also available: e.g.: Swell Mean period and direction Swell wave height and direction

Significant wave height and direction

http://www.ecmwf.int/products/forecasts/d/charts/medium/special Ocean wave Forecasting at ECMWF Slide 24 Wave Model Products: EPS From the EPS wave forecasts it is possible to derive probabilities for certain wave conditions.

Tuesday 6 November 2001 12UTC ECMWF EPS Probability Forecast t+120 VT: Sunday 11 November 2001 12UTC Surface: significant wave height probability >8 25°W 20°W 15°W 10°W 5°W 0° 5°E 10°E 15°E 20°E 25°E 54.47

25°E 50 50%

MIKE HEIDRUN 45

DRAUGEN 40

65°N 35 20°E 25°W

30

25 25%

20

60°N 15 Significant wave height (m) at Heidrun 15°E 55°N 14 10 12 5

0 20°W 15°W 10°W 5°W 0° 5°E 10°E 10 06 Nov. 2001 12 UTC ECMWF EPS probability forecast t+120 8 8 m Significant wave height above 8 m 6 4 2 0 1 2 3 4 5 6 7 8 9 10 ECMWF Newsletter 95 – Autumn 2002 Forecast day

Ocean wave Forecasting at ECMWF Slide 25 Wave Model Products on the web

Currently on our web: probability for set thresholds (2m)

Ocean wave Forecasting at ECMWF Slide 26 Wave Model Products on the web

Currently on our web: probability for set thresholds (4m)

Ocean wave Forecasting at ECMWF Slide 27 Wave Model Products on the web

Currently on our web: probability for set thresholds (6m)

Ocean wave Forecasting at ECMWF Slide 28 A bit more compact: Wave EPSgram:

Like normal EPSgram but for wind direction, wind speed, significant wave height, mean wave direction and mean period.

Each octant is coloured based on the distribution of the significant wave height associated with each mean direction. The coloured areas correspond to the fractional number of ensemble members with wave height in the range specified by the coloured ruler. South of Grindavik, Iceland

Ocean waves at ECMWF Slide 29 EPS Wave Model Products on the web: SWFDP Pacific wave EPSgrams:

Set of locations where wave EPSgram are available

Ocean wave Forecasting at ECMWF Slide 30 EPS Wave Model Products on the web: SWFDP East Africa wave EPSgrams :

Set of locations where wave EPSgram are available

Ocean wave Forecasting at ECMWF Slide 31 Individual Waves, Significant Wave Height, Hs, Maximum Individual Wave Height, Hmax, and Freak Wave

Individual waves

… etc. Hmax Hs= H1/3

If Hmax > 2 Hs  freak wave event Ocean wave Forecasting at ECMWF Slide 32 Wave Model Products: Extreme Waves We have recently introduced a new parameter to estimate

the height of the highest individual wave (Hmax) one can expect:

Friday 7 March 2008 00UTC ECMWF 20°W Forecast t+84 VT: Monday 10 March 2008 12UTC Surface: Significant0° wave height (Exp: 0001 ) 17.44 Hs 17 Friday 7 March 2008 00UTC ECMWF Forecast t+84 VT: Monday 10 March 2008 12UTC Surface: (Exp: 0001 ) 16 20°W 0° 34.79 15 Expected H max 34 14 60°N 60°N 32 13 in 3 hour records 30 12 28 11 60°N 60°N 26 10 24 9 22 8

50°N 50°N 20 7 18 6 16 5 50°N 50°N 14 4 12 3 10 2 8 40°N 40°N 1 6 0 20°W 0° 4 th 40°N 40°N 2 March 10 , 2008, 12UTC 0 20°W 0° Forecasts fields from Friday 7th March, 2008, 0 UTC See ECMWF Tech Memo 288 for derivation and discussion http://www.ecmwf.int/publications/library/do/references/list/14 Ocean wave Forecasting at ECMWF Slide 33 Large swell reaching la Réunion, May 2007: the aftermath

Lagon de Trou d’Eau Coastal flooding Fisherman who was swept out to sea rescued by helicopter.

Saint-Leu. Photo Ludovic Lai-Yu Hotel hit hard Sea front destroyed

All pictures courtesy of CLICANOO (www.clicanoo.com)

Ocean wave Forecasting at ECMWF Slide 34 Large Swell Reaching la Réunion: The Model Sig. wave height and mean propagation direction valid on May 12, 2007, 18UTC. The model has nicely predicted significant wave height in excess of 5m in the evening of the 12th.

analysis forecast t+30

H1/3 (m) Hs model analysis (m)

7

6

5

4

3

forecast t+54 forecast t+782

1

0 11/05/2007 12/05/2007 12/05/2007 13/05/2007 13/05/2007 14/05/2007 14/05/2007 12:00 00:00 12:00 00:00 12:00 00:00 12:00

Ocean wave Forecasting at ECMWF Slide 35 Case study: long swell affecting the western Pacific in December 2008

Coastal flooding linked to high , barometric surge and long swell, e.g. Nukutoa on Takuu :

Pictures courtesy of John Hunter Antarctic Climate & Ecosystems Hobart, Tasmania, Australia

Ocean wave Forecasting at ECMWF Slide 36 Case study: long swell affecting the western Pacific in December 2008

10m winds (arrows) Sfc pressure th Dec. 6th, 2008, 0UTC (contours) Dec. 5 , 2008, 0UTC Sig. wave height (shading)

Dec. 8th, 2008, 0UTC Dec. 8th, 2008, 0UTC

Ocean wave Forecasting at ECMWF Slide 37 Case study: long swell affecting the western Pacific in December 2008 Dec. 9th, 2008, 12 UTC

Windsea Swell wave height wave height and and direction direction

Long swell reaching South !

Windsea Swell Mean period Mean period and and direction direction

Ocean wave Forecasting at ECMWF Slide 38 Case study: long swell affecting the western Pacific in December 2008 Wave condition north of New Ireland (PNG07) for 2008, based on ECMWF analysis ! Conditions were exceptional !

Sig. wave height Dec. 10th, 2008, 0 UTC

Ocean wave Forecasting at ECMWF Slide 39 Case study: long swell affecting the western Pacific in December 2008: EPS Wave Epsgram from Dec. 6th, 2008 at PNG07 Wave Epsgram from Dec. 8th, 2008 at PNG07

Ocean wave Forecasting at ECMWF Slide 40

Questions?

Ocean wave Forecasting at ECMWF Slide 41Duck, North Carolina