observations of the coastal ocean response to ivan: implications for hurricane intensity change lynn...

Observations of the Coastal Ocean Response to Ivan: Implications for Hurricane Intensity Change

Lynn “Nick” Shay, G. Halliwell, and W. Teague

MPO, RSMAS, Univ. of MiamiOceanography Department, NRL-Stennis

http://iwave.rsmas.miami.edu/~nick

MOTIVATION:

SHA field from GFO altimeter (left panels) and SST Image from TMI (right)Relative to Katrina’s track & intensity.

Severe Storm (Cat 3 or above) Tracks (red) relative to the posit of the LC and WCR complex based on satellite data in Aug 05.

LC

In addition to thermal structure,measuring current and shear is central for mixing and oceanic cooling and hence feedback to the storm.(from Shay 2007)

Ivan’s Track and Intensity Relative to OHC (left) NRL SEED Mooring Locations in Northern Gulf of Mexico Relative

to Bottom Depth (Right) (Teague et al., JPO, 2007).

14 ADCP moorings!

NRL Mooring Specifics (Teague et al., JPO, 2007).Note ADCP provides absolute velocity (u,v,w)

Array # LatoN

LongoW

StartDate2004

EndDate2004

Δt(hr)

DepthRange

(m)

Δz(m)

BottomDepth

(m)

InstrumentType

2 29.43 88.01 05/01 10/31 0.25 4-54 2 60 TRBM

8 29.14 88.11 05/03 11/07 1.0 42-492 10 518 LR

9 29.19 87.94 05/03 11/07 1.0 40-500 10 518 LR

14 29.20 87.65 05/05 11/07 1.0 42-502 10 1029 LR/RCM9

Ivan’s eye of over the moorings (dots) at 00 UTC on 16 Sept 04.

(a) Wind stress (Pa) with winds, (b) frictional wind velocity (m s-1), (c) wind stress divergence (s-1) (d) wind stress curl (s-1). Based on HWIND fields.

Intense Forcing (upper) and Relaxation Stages (lower) for NRL SEED moorings 7-14

7-10 Red ~500 m

11-14 Yellow~1000 m

(Teague et al. JPO, 2007).

Temperature time series at the bottom of each ADCP for M1-M14

A11-A14 are Aanderaa CM

M8 (Track) and M9 (1.5 Rmax) Near-Inertial Current Response (Rmax= 32 km)

BP 22 to 29 h ; normalized by 20 cm s-1 based on (max Rmax)/(0bUh)

M8 (Track) Observed and Near-Inertial Current Shear Response (Rmax= 32 km)

Normalized shear by 10-2 s-1 based on (max Rmax)/(0bUh)

M9 (1.5 Rmax) Observed and Near-Inertial Current Shear Response (Rmax= 32 km)

Normalized shear by 10-2 s-1 based on (max Rmax)/(0bUh)

Depth-Averaged Current at Mooring 8

Depth-averaged response in near-inertial wave band at 12 hours for a few days.

White-Obs, Black-OA

Color is log of the depth-averaged KE cm2 s-2.

Oceanic Response and Intensity Impacts

Ivan a clear example of negative feedback (cooling/mixing induced by strong winds and Cold Core Ring) as opposed to positive feedback over the Loop Current and Warm Core Rings (i.e. Katrina, Rita and Wilma-the Trifecta).

To evaluate state-of-the-art coupled models, temperatures and currents needed to assess mixing schemes and evaluate initialization schemes.

We have only had 7 sets of T(z), V(z) data since 1984 from the NOAA WP-3D and USAF deployments.

Aircraft expendables (AXCP, AXCTD) conduct targeted measurements of ocean.

SST is not enough for ocean’s influence on hurricanes:

1. Implement optimal ocean sampling schemes for pre, during and post hurricanes; 2. Initialize ocean models with Loop Current and Warm/Cold Core Rings.

Shay’s Top 5 Reasons Why We Need to Understand The LC/WCR/CCR in GOM:

1. Improve intensity predictions at Operational Centers.

2. When in phase with hurricane season…Rapid Deepening spells DISASTER.

3. Sustained air-sea fluxes (>1.5 Kw m-2) with little SST cooling and OHC change .

4. Deep warm thermal layers (>100 m) with OHC values exceeding 100 kJ cm-2.

5. Part of the natural ocean variability (gyre circulation) with strong currents (1-1.5 m s-1 ) advecting warm water (advective time scale is O(day)).

Models need good 3-D Ocean Data to evaluate the coupled models-operations.