Observed Oceanic and Atmospheric Interactions During Hurricane Earl (2010) From Satellite and In-Situ Data

L.K. Shay, B. Jaimes, P. Meyers, E. Uhlhorn and J. Brewster

Goal: Using satellite, in situ data, build an improved ocean model to couple to HWRF and carefully assess the oceanic role in intensity

changes (deepening and weakening).

Objective and Hypothesis

In support of NASA ROSES-2008 program, this project is relevant to two key science questions of this program: (1) What environmental, oceanic, and inner core factors govern rapid intensification?; and (2) What is the predictability of rapid intensification and what observations are most critical to its prediction?

The scientific hypothesis: combining SSTs from NASA’s TRMM microwave imager (TMI) with the surface SHA fields from multiple satellite platforms (e.g., NASA Jason-1,2) will provide insights of ocean-atmosphere interactions during rapid deepening and weakening events using measurements acquired from NASA/NOAA aircraft during in Earl’s life cycle.

Here we estimate the air-sea fluxes and the net oceanic heat loss through the air-sea interface using satellite (SMARTS)/in situ data.

Motivation and Background

• Minimum sea surface temperature threshold for hurricane formation: SST >26ºC (Palmen, 1948)

• Leipper (1972) introduced Ocean Heat Content

– Integrated thermal energy from surface to 26º isotherm

• Empirical approach to estimate OHC from satellite altimetry (Shay and Brewster, 2010)

• Ocean thermal structure is important feedback mechanism (Chang and Anthes, 1978)

• Warm core eddies inhibit mixing and provide deep energy source for hurricanes (Shay et al., 2000; Jaimes and Shay, 2009)

MLD

D26

OHC

SST26°C

dzTcOHCD zp )26(

26

Key Air-Sea Parameters

StormRmax

(km)max

(N m-2)Uh

(m s-1)h

(m)g'

(m s-2)c1

(m s-1)1

(km)Fr

Uh/c1

SUh/(2Rmaxf)

Earl 24 10.5 8.0 22 0.03 2.2 38 3.6 2.9

Karl 17 9.4 5.0 20 0.03 1.6 34 3.0 3.0

Satellite Altimetry Availability Since 1998(14-year daily data set)

Over 50,000 Thermal Profiles From Multiple Platforms Used In Evaluation (Meyers et al., 2012)

SMARTS Performance (Meyers, 2011)

Satellite-Estimated MLD Considerations and Error Sources

• Improvement to OHC regression slope. More realistic variability.

• Decreased accuracy after strong wind-forcing events (entrainment mixing either through stress or shear).

• Most useful during hurricane season when there is more variability of MLD.

• Trapezoidal technique -Thermostads and standard profile shape. • SST errors account for 50% of OHC differences (surface boundary condition).• Climatology lacks sharp thermocline due to oversmoothing.

Hurricane Earl (2010): SST (TMI: Courtesy of RSS) and OHC (Jason, Envisat Altimeters)

Hurricane Earl (2010): satellite and ARGO Float Measurements (Pre/Post)

OML Depth~22 m SST Change~1.8CD26 Change~10 m

SST Cooling induced by Earl from TMI relative to Earl’s Track and Intensity.

Altimeter-derived surface height depression (~20 cm) along Earl’s Track and Intensity consistent with theory (Shay et al., 1990; Shay and Chang, 1996).

Constrains ocean model dynamics - interaction between barotropic and baroclinic modes.

Momentum and Enthalpy fluxes Emanuel (1995): ck/cd ≥ 1 (50 m/s); Black et al. (2007): ck/cd ~ 0.7

lsk

dqh

qval

hpas

QQQ

ccc

qcLyxQ

TcCyxQ

10

10

),(

),(

U

U

5.2 ,065.049.0max10

),(

103

1010

U

UUτ

d

da

c

cyx

Stress measurements from hot- film anemometer, particle velocimetry and laser line scan cameras at the surface (From Donelan et al. GRL (2004)).

Earl’s Track (and Intensity), SST (C: color), OHC (contours), and GPS Sondes

Momentum Flux Estimates From SSTs, GPS and SFMR Data During GRIP

Enthalpy Flux Estimates From SST, GPS and SFMR Data During GRIP

15-hr along-track integration of estimated enthalpy fluxes at stages C1 (Cat 1) , C2 (RI), and C4 (Cat 4).

Cross-track integration from +/- 6Rmax of surface presure, pre-storm OHC, Post-Pre OHC and SST. Average OHC loss is ~20 kJ/cm2 per day.

Summary: Work In Progress

• Extensive in-situ temperature profile data (~50,000 profiles) used to evaluate SMARTS regionally and seasonally in Atlantic Ocean basin. (14 year continuous data set 98-2011).

From Earl’s Extensive GPS Sonde Coverage:

• High OHC values (>100 kJ /cm2)-juxtaposed with high cross-gradient enthalpy fluxes of 1.2 to 1.4 kW/m2 during Earl’s RI cycles (including RW) based on SST, GPS sondes and SFMR data.

• Assess impact of SST and OHC gradients on fluxes.

• Conduct sensitivity testing with the ratio of Ck/Cd following Bryan (MWR, 2012) from these data sets.

• Examine the impact of the oceanic response in this region including SST cooling (1.5-3C), Barotropic trough (~20 cm), OML deepening and OHC loss.

• Include additional GRIP measurements balances in the ABL.