ensemble global ocean wave forecast system (egowafs)

ENSEMBLE GLOBAL OCEAN WAVE FORECAST SYSTEM

(EGOWaFS)

For 2nd NAEFS Workshop

November 16-18, 2004

H. S. Chen

NCEP/EMC/MMAB

Status

of

1. Introduction.

- Meteorological Forecast System (FS ) vs. Ocean Wave FS.

- NCEP ocean wave model, NWW3 :

Directional, spectral wave model,

http://polar.ncep.noaa.gov/waves

- Deterministic FS vs. Ensemble FS.

2. The Ensemble Global Ocean Wave FS (EGOWaFS).

3. Preliminary Results.

1. Introduction.

Meteorological FS:

- chaotically nonlinear,

- the butterfly effect.

Ocean Wave FS:

- weakly nonlinear,

- highly dissipative.

Initial Condition

Initial ConditionSea surface forecast wind

Forecast wave field

  Figure 1.1 A schematic illustration of the growth of an isopleth of the forecast error probability distribution function, from (a) initial phase, to (b) linear growth phase, to (c) nonlinear growth phase, to (d) loss of predictability. (borrow from ???)

Remark:

The initial wave field has a significant impact on the forecast waves only up to the first 24 hours and the wind forcing is the most dominant factor throughout the forecast period.

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2. The Ensemble Global Ocean Wave FS (EGOWaFS).

- 10 ensemble wind fields + 1 control wind field (operational),

- NWW3 wave model,

- 10 ensemble wave fields + 1 control wave field (operational).

- use a considerable amount of computer resource.

- Ensemble parameters: Ens Mean, Ens Spread and Ens Probability.

- Output only up to 84 hour forecast, will increase in the future.

- In Parallel Run. Hopefully, operational next spring.

3. Some results for 2004 June.

Green thin lines: ensembles,

Red dash line with + sign: control,

Blue line with + sign: ensemble mean

Black dot with o sign: observed data.

F10,11, (>=24.67 m/s)

F9, (>= 21.07 m/s)

F8, (>= 17.48 m/s)

F7, (>= 14.39 m/s) 18 45 55 9

F6, (>= 11.31 m/s) 82 55 36 9 9 9 9 18 9

F5, (>= 8.74 m/s) 36 9 64 9 9 64 64 64 73 82 82 73 46

F4, (>= 5.65 m/s) 64 27 55 82 18 27 36 9 18 18 27 45

F3, (>= 3.60 m/s) 27 9

F0~2, (<3.60 m/s)

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84

forecast hour

Ensemble U10 Forecasts at Buoy 46006 at 2004 06 03 00

Table 1. Ensemble and NWW3 U10 forecasts and Observed Data in the Beaufort Scale.numerics: ensemble forecast in percentage,

box with a diagonal: NWW3 forecast,yellow box: observed data.

F10,11, (>=9.0m)

F9, (>= 7.0 m)

F8, (>= 5.5 m)

F7, (>= 4.0 m) 36 9 9 9 18 73 64 27 9

F6, (>= 3.0 m) 55 64 91 91 64 36 27 64 73 18 36 73 91

F5, (>= 2.0 m) 73 45 9 36 64 64 27 9 9

F4, (>= 1.0 m) 100 27

F3, (>= 0.6 m)

F0~2, (< 0.6 m)

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84

forecast hour

Ensemble Hs Forecasts at Buoy 46006 at 2004 06 03 00

Table 2. Ensemble and NWW3 Hs forecasts and Observed Data in the Beaufort Scale.numerics: ensemble forecast in percentage,

box with a diagonal: NWW3 forecast,yellow box: observed data.

Some Remarks:

The ensemble FS is more reliable and realistic than the deterministic FS.

A long list of works need to be done, such as verifications, postprocessors, score analysis, …etc.

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