# Presentation: 167373

## Scatterometer Wind Forcing of an Eddy-Resolving North Atlantic Model

- Matthew Hecht (Los Alamos)
- Bill Large (NCAR)
- Patrice Klein (IFREMER)

## Wind Stress, Oceanic Kinetic Energy and Inertial Resonance

- Wind stress depends weakly on **u**ocn
****  (**u**atm - **u**ocn)
- Kinetic Energy input to ocean can depend strongly on **u**ocn
- KE = ∫ (**** · **u**ocn) dt
- The ocean responds to strong wind forcing by setting up inertial currents, changing direction with frequency f. **If**
**If** the ocean model is eddy resolving **and** the wind forcing includes inertial frequencies **then** we may see inertial resonance, where KE is large because **** and **u**ocn rotate together

**Notes:**
Note dot product within the time integral!

**Notes:**
Note difference in mixed layer depths between roughly 50 and 60oS, where the model mixed layer is on the order of 50m, and the obs has a highly variable, and, in some places, much deeper mixed layer, possibly from inertial freq wind events finding eddies

- Observed deepening of mixed layer (top)

- not captured by
- non-eddy-resolving
- ocean (bottom)

- 50oS

- 50oS

**Notes:**
Say that this is Temperature!
Note difference in mixed layer depths around 50oS, where the model mixed layer is on the order of 50m, and the obs has a highly variable, and, in some places, much deeper mixed layer, possibly from inertial freq wind events finding eddies

## Forcing of Eddy-Resolving North Atlantic Ocean Model, with Daily and 12-hourly QSCAT Winds

- 1/10o POP (Los Alamos’ Parallel Ocean Program) Ocean of Smith et al. (JPO 2000), but with
- KPP vertical mixing, 1/2x horz viscosity and diffusivity
- 2 branch runs,  from ECMWF daily wind forced case, using QSCAT/NCEP blended winds
- Daily winds (inertial frequencies absent)
- 12-hourly winds (preserves significant fraction of inertial frequency range)
- Concentration on one extreme event, January 21, 2002
- Winds produced by Ralph Milliff and Jan Morzel at Colorado Research Associates (CoRA)
- http://www.colorado-research.com/~morzel/blendedwinds.qscat.dirth.2002.html

**Notes:**
Note: with QSCAT we only have 12-hourly coverage, but the instrument resolves more extreme events.
Note: inertial frequency is f (=2sin(lat)); rotation is clockwise in NH.
Run on computers at LANL and at NCAR.

## Slide 6

## Histograms of work done by wind on ocean over 3 hour diagnostic periods, daily vs. 12-hourly-forced cases

*daily*

*12-hourly*

*12-hourly*

- Work

- Log(# grid cells)

- January, 2002

*Work is*
- ∫ (**** · **u**ocn) dt

- 0

- 4000

- 2000

- -2000

- 106

- 104

- 102

**Notes:**
Note: no difference, to the eye, over first 3 decades in terms of frequency of occurrence! It’s the tails that are different -- a relatively few events forced by very strong winds.

## Work done by Wind Stress -- January 21, 2002 

- daily

- 12-hourly

**Notes:**
Note: didn’t pick this because of dramatic difference between 12-hourly and daily cases -- this was just the single biggest event in January of 2002.
Notice the small spatial scales.

## Small Scales in Ocean, Larger Scales in Wind

- QSCAT Stress

- 64
- dynes/
- cm^2!

- Vorticity

- January 21, 2002

**Notes:**
Z-component of vorticity in k=1 layer, from ZVORT.h.14q2x.20020121.h0_30-50N. Units are 10^6/sec.
This is an illustration of the disparity in Rossby length scales between ocean and atmosphere.

## Conclusions

- Mean input of kinetic energy O.K. with daily winds
- Direct influence of higher wind frequencies on linear dynamics is minimal
- Need eddy-resolving ocean and high-frequency winds (higher than daily) to resolve extreme events
- Could have a major impact on non-linear mixing

**Notes:**
Note: it’s a great disappointment not to have the additional coverage of second satellite-born scatterometer. The period for which there is 6-hourly coverage does not include northern winter.

## Continuing Work

- What’s the *impact* of resolving these extreme, inertial-frequency events?
- How much impact is there when higher frequency *reanalysis winds* are used?
- “Extreme” events will be less extreme, but...
- Can compare daily to 6-hourly