Lo op Current Resp onse to Hurricanes Isidore and Lili



Lynn K Shay and Eric W Uhlhorn

Monthly Weather Review In Press

Date December

Division of Meteorology and Physical Oceanography

Rosenstiel Scho ol of Marine and Atmospheric Science

University of Miami

Rickenbacker Causeway

Miami FL

email nshayrsmasmiamiedu



Hurricane Research Division

Atlantic Oceanographic and Meteorological Lab oratory

National Oceanographic Atmospheric Administration

Rickenbacker Causeway

Miami FL

email ericuhlhornnoaagov

Abstract

Recenthurricane activityover the Gulf of basin has underscored the imp ortance of the Lo op

CurrentLCand its deep warm thermal structure on hurricane intensity During hurricanes Isidore

and Lili in research ights were conducted from b oth NOAA WPD aircraft to observe pre in

and p oststorm ocean conditions using airb orne exp endable ocean prolers to measure temp erature

salinity and current structure Atmospheric thermo dynamic and wind proles and remotelysensed

surface winds were concurrently acquired as each storm moved over the LC

Observed upp er o cean co oling was ab out C as Isidore moved across the Yucatan Straits at a

 

sp eed of m s Given prestorm o cean heat content OHC levels exceeding kJ cm in the LC



currentvelo cities ms signicant co oling and deep ening of the o cean mixed layer OML did



not o ccur in the Straits Estimated surface enthalpy ux at Isidores eyewall was kW m where the



maximum observed wind was m s Spatially integrating these surface enthalpy uxes suggested



a maximum surface heat loss of kJ cm at the eyewall Over the Yucatan Shelf observed ocean

co oling of C was due to upwelling pro cesses induced by wind stress and an oshore winddriven

transp ort During o cean co oling in the LC was C compared to more than C in the



Gulf Common Water where the maximum estimated surface enthalpy ux was kW m asso ciated



with p eak surface winds of m s Due to Lilis asymmetric structure and rapid translational sp eed

 

ofms the maximum surface heat loss due to the surface enthalpy ux was less than kJ cm

In both hurricanes the weak o cean thermal resp onse in the LC was primarily due to the lack of

energetic nearinertial current shears that develop across thin OML observed in quiescent regimes Bulk

Richardson numb ers remained well ab ove criticality due to the strength of the upp er o cean horizontal

pressure gradient that forces northward current and thermal advection of warm water distributed

over deep layers As these o ceanic regimes are resistive to shearinduced mixing hurricanes sense a

more sustained surface enthalpy ux compared to storms moving over shallow quiescent mixed layers

Since o cean co oling levels induced byhurricane force winds dep end on the underlying o ceanic regimes

features must b e accurately initialized in coupled forecast mo dels

Intro duction

Coupled mo dels to predict hurricane intensity and structure change are b eing used to issue forecasts

to the public who will increasingly rely on the most advanced weather forecasting systems to prepare for

landfalling systems Marks and Shay Bender and Ginis For such mo dels it has b ecome

increasingly clear over the past decade that the o ceanic comp onent will have to include realistic initial

conditions to simulate not only the o ceanic resp onse to hurricane forcing Price Sanford et al

Shay et al Price et al DAsaro but also to simulate the atmospheric resp onse

to o ceanic forcing Shay et al Hong et al Lin et al Walker et al Wu et al

Shay

An imp ortant example of this latter eect was observed during s passage in

when atmospheric conditions were conducive for Opals rapid deep ening over hours over the Gulf of

Mexico GOM Bosart et al During this deep ening pro cess Opal passed over a Warm Core

Ring WCR shed earlier by the Lo op Current LC as detected by radar altimeter measurements of

the surface height anomaly SHA elds from NASAs TOPEXPoseidon Mission Shay et al

While satellitederived images revealed that sea surface temp eratures SST were to C there

was little evidence of this warm o cean features signature compared to the surrounding Gulf Common

Water GCW Using a coupled mo del Hong et al p erformed a series of sensitivity tests

with and without this observed WCR They found that Opal deep ened an additional mb over the

WCR compared to numerical exp eriments without it Walker et al found that cold core rings

lo cated on the p eriphery of the larger WCR help ed to weaken just prior to

More recently Shay showed that the LC and WCR did not signicantly co ol during

the passage of hurricanes Katrina and Rita where these hurricanes rapidly deep ened to category

status These studies emphasize the imp ortance of initializing mo dels with realistic o cean features to

couple to hurricane forecasting mo dels Jacob and Shay Falkovich et al Halliwell et al

The upp er o ceans transp ort from the NW Caribb ean Sea and through the Yucatan Straits signi

  

cantly inuences the GOM circulation patterns These transp orts Sv Sverdrup m s

through the straits forces LC variability and mo dulates WCR shedding events Maul Sturges

and Leb en Leb en The LC transp orts warm subtropical water with markedly dierent

temp erature and salinity structure into the GOM compared to the GCW Shay et al As the

LC intrudes north of N WCRs having diameters of to km separate from the LC at an

average interval of to months based on radar altimeterderived SHA elds Sturges and Leb en

By contrast when the LC retracts south of N this time envelop e for WCR shedding events

increases to an average of more than months Leb en Regardless of the northward LC p ene



tration these anticyclonically rotating WCRs propagate westward at sp eeds of to km d Elliot



Note that b oth the LC and WCR features contain upp er ocean currents of up to m s

Forristall et al Oey et al At any given time the GOM may have two or three WCRs

emb edded within its circulation pattern with smallerscale cold core rings lo cated along their p eriphery

The anticyclonic circulation around the LC exits the GOM through the Straits between the

United States and to form the Florida Currentandeventually the Gulf Stream These ribb ons

of deep er and warmer o cean current features transp ort heat p oleward representing an integral part of

the gyre circulation Gill

Central to the question of upp er o cean heat Leipp er and Volgenau develop ed a relationship

to estimate the hurricane heat p otential or o ceanic heat contentOHC

Z

dz z T z Q c

p

h



 

where z is the density structure c is sp ecic heat at constant pressure kJ kg K and

p

Tz is the observed temp erature less C integrated from the depth of the C isotherm h to





the surface In the subtropical regimes such as the LC OHC values exceed kJ cm Leipp er

and Volgenau That is the C and C isotherm depths are lo cated at m and

m depths in this subtropical water mass compared to m and m depths resp ectively in the

GCW

To improve our understanding of the LC resp onse to the passage of a mature hurricane a series

of exp eriments was conducted from National Oceanic Atmospheric Administration NOAA WPD

research ights NRF NRF and the NOAA GulfstreamIV NRF aircraft during the passage

of Hurricanes Isidore and Lili The exp erimental sampling strategy was designed to deploy Global Po

sitioning System GPS sondes Ho ck and Franklin and Airb orne eXp endable Current Prolers

AXCPs Airb orne eXp endable ConductivityTemp erature and Depth Prolers AXCTDs and Air

borne eXp endable Bathythermographs AXBTs prior during and subsequent to hurricane passage

This exp erimental eort in Hurricanes Isidore and Lili improved up on a previous Hurricane Gilb ert

exp erimentShay et al by measuring prestorm instorm and p oststorm currents temp eratures

and salinities along with detailed atmospheric temp erature humidity and wind soundings Table

The ob jective of this manuscript is to do cumenttheevolving thermal and momentum o cean resp onse

to the heat moisture and momentum uxes across the airsea interface based on the combination

of GPS sonde proler data Ho ck and Franklin and remotelysensed surface winds from the

Stepp ed Frequency Microwave Radiometer SFMR Uhlhorn et al To address this ob jective

this manuscript is organized as follows a description of the proler data including chronologies of

Hurricanes Isidore and Lili is Section the exp erimental approach including the surface wind forcing

and airsea parameters are describ ed in Section observational analysis and airsea uxes are given in

Section the forced LC resp onse is discussed in Section with resp ect to ocean co oling and mixing

and results are summarized with concluding remarks given in Section

Hurricane Chronology

The tropical wave from which Isidore develop ed was of Cap e Verde origin where several p erio ds of

uctuating storm intensity o ccurred until this wave crossed the W meridian Pasch et al

However it was only when the tropical depression moved into the western Caribb ean Sea that it was

named TS Isidore on Sept Isidore then moved slowly along a northwest track and at UTC

Sept Isidore was upgraded to a hurricane with a central pressure of mb Isidore winds exceeded



ms on Sept as it approached the Isle of Youth and made landfall along the tip of western Cuba

The storm remained over Cuba for ab out hrs re emerging over the Yucatan Straits middayon



Sept This slowmoving hurricane ms traveled westward Fig in tensifying to a category

storm just north of the Yucatan Straits over the LC see Fig Isidore moved over the Yucatan Shelf

on Sept and made landfall on the Yucatan Peninsula for the next hrs weakening to a minimal

TS emb edded within a broad atmospheric circulation pattern Isidore subsequently moved northward

and created a co ol wakeof C SSTs across the central GOM Fig b making landfall on Sept

just west of Grande Isle

Hurricane Lili

Lili was also a tropical waveofCapeVerde origin starting Sept Pasch et al This wave



b ecame a tropical depression on Sept and as the system moved just westofnorthat ms

initial intensication to TS status o ccurred on Sept The TS subsequently weakened to an op en

tropical wave on Sept but as the wave slowed it redev elop ed into a TS late on Sept with a

minimum central pressure of mb Lili intensied to hurricane status at UTC Sept while

passing over the As Lili tracked along a northnorthwest tra jectory after emerging



o the Cuban coast Fig the hurricane intensied to category status m s over the LC



and to a category storm ms in the southcentral GOM just north of the b oundary b etween

LC and GCW During this p erio d Lilis radius of maximum winds R decreased from km over

max

the LC to km along the northern b oundary between the LC and GCW when the storm system



was movingatms Lili rapidly weakened to category status due to a combination of enhanced

atmospheric shear dryair intrusion along the western edge Pasch et al and interacting with

the shelf water co oled by Isidore Hurricane Lili made landfall at UTC Oct near Intracoastal

City Louisiana

Exp erimental Approach

During the NOAA Hurricane Research Divisions hurricane eld program a joint National

Science Foundation NSF and NOAA exp eriment measured b oth the kinematic and thermo dynamic

upp ero cean resp onse to a propagating mature tropical over the LC Motivated bythehurricane

Opal case the exp erimental ob jective was to measure the levels of upp er o cean co oling and shear

induced mixing in the LC circulation system To achieve this ob jective the exp eriment consisted of

sixteen researchights each deploying o ceanic and atmospheric exp endable prob es in the same lo cation

b efore during and after passage of Hurricanes Isidore and Lili Table A set of prestorm ights was

conducted from to Sept instorm ights o ccurred on Sept and Oct and p oststorm

surveys were acquired on Sept and Oct In addition there were also two landfall exp eriments

on Sept and Oct o the Yucatan Peninsula and along the Louisiana Coast for Isidore and Lili

resp ectively Success rates for the o ceanic prolers dened here as receiving radio frequency RF

signals on the aircraft were greater than GPS sondes were also concurrently deployed from the

aircraft including the GIV to map the regionalscale atmospheric structure over the GOM from ight

level to the surface in the storm and surrounding environment

This comprehensive set of measurements included both in situ and remotelysensed data Data

acquired include current and temp erature proles from AXCPs temp erature and salinity proles from

AXCTDs temp erature proles from AXBTs and surface directional wave sp ectra from the NASA

Scanning Radar Altimeter Wright et al Note that AXCPs AXCTDs and AXBTs all measure

temp erature however the temp erature measurements only p enetrate to m for the AXBTs compared

to and m for AXCTDs and AXCPs resp ectively A second dierence is that temp eratures

from AXBTs and AXCPs are measured with a thermistor with an an accuracy of C compared to

an AXCTDs thermistor accuracy of C Here SSTs from all exp endable prolers are dened to

b e nearsurface temp eratures within the rst few meters of the sea surface Also deep er proles allow

estimates of geostrophically balanced currents relative to m for assessing initialization schemes used

in o cean mo dels Halliwell et al Finally the surface wind eld was measured from observations

by GPS sondes Ho ck and Franklin and SFMR Uhlhorn et al These in situ data

are cast within a regionalscale context using SHA elds measured from radar altimetry Cheney et

al Sturges and Leb en TOPEX and Geosat FollowOnMission SHA data in Fig

were ob jectively analyzed at using Mariano and Brown based on parameters used on the

Hurricane Gilb ert data set

Isidore

prestorm o cean prolers were deployed from Given uncertainties in Isidores track two grids of

research aircraft in the northwest Caribb ean Sea and in the southcentral part of the GOM on and

Sept Fig ab Success rates in acquiring proles were from oceanic prob es In some

cases the comp ound surrounding the thermistor was compromised b elow m due to pressure eects

that caused bad temp erature proles from AXCPs A few AXCTDs also had incorrect calibration

co ecients and are not used in the analyses b elow On each of the prestorm ights there were eight

prob es with no radio frequency RF signals During the dualaircraft Isidore ighton Sept Fig

c there were eight failures out of deployed prolers and additional AXBTs deployed from

NRF with RF failures Several AXCPs malfunctioned along the western b oundary of the Yucatan

Straits where large currents and current shears caused thin wire connecting the prob e to the surface

unit to break Given the dualaircraft mission this is unprecedented coverage of the upp er o cean as a

hurricane intensied to category status On Sept there were additional AXBTs deployed over

the same regime where the instorm ights deployed prolers including over the Yucatan Shelf During

the p oststorm exp erimen tonSept days later sixtyfour prob es were deployed along similar

transects as the prestorm and instorm ights Seven of these prolers did not transmit data backto

the aircraft

Lili

One week later on Sept TS Lili moved to the northwest toward the Yucatan Straits following

a similar track as Isidore During this time a prestorm ightwas conducted in front of the pro jected

TS Lili and potential hurricane track on Sept not shown by deploying AXBTs On Sept

additional prolers were deployed from an instorm ightcentered on Lili at N W including six

AXCPs with four prob es providing proler data not shown As Lili continued along this northwest

tra jectory moving over the western tip of Cuba as a Category storm the instorm ight on Oct

Fig f was centered fortuitously on the preIsidore grid of Sept Fig b On this research

ight sixtythree prolers were deployed with twelve of them not providing any RF signals to the

aircraft It was during this early ight on NRF and the later NRF ight on Oct in supp ort

of a NOAANESDIS Ocean Winds exp eriment deploying AXBTs when Lili deep ened to a category

storm just northwest of the b oundary between the LC and the GCW in the central GOM basin A

p ostLili exp eriment was then conducted on Oct by deploying the same number of prolers with

only ve RF failures Thus these o ceanic and atmospheric measurements were acquired when two

hurricanes were intensifying over the same o ceanographic regime separated bydays

AirSea Parameters

Airsea parameters and scaling arguments dened in Table are used to place the observations into

a nondimensional framework based on Price The wavelength of the o ceanic resp onse induced

bya moving is prop ortional to the pro duct of the storm translation sp eed U and the

h



lo cal inertial p erio d IP Geisler Based on a ms translation sp eed and an IP of d

h the predicted wavelength for Isidore is km Table For Lili this wavelength is



km b ecause of faster translation sp eeds of ms and IPs ranging from d h to d

h over the LC and GCW resp ectively Radii of maximum wind R for these storms over the LC

max

ranged from to km however as Lili moved northwestward over the GCW R decreased to

max

km during a deep ening cycle to a category storm In this context along and crosstrack directions

are nondimensionalized in terms of and R to examine the forced ocean resp onse relative to the

max

observed storm structure Shay et al



ave phase sp eed in the LC is approximately m s whereas in the The rst baro clinic mo de w



GCW this phase sp eed increases to ms due to stronger stratication at the base of the mixed

    

layer Reduced gravities g ranged from x m s in the LC to x m s within

the GCW eg Shay et al The STW stratication is weaker with large OMLs of O m

compared to the GCW stratication where initial OML depth lies b etween and m The Froude

number dened as the ratio of the translation sp eed to the rst baro clinic mo de wave phase sp eed



U c exceeds in b oth cases implying a predominant baro clinic o cean resp onse Geisler

h



The baro clinic radius of deformation was km in the LC compared to km in the GCW

When the length scale of the windstress forcing R km is greater than the deformation

max

radius asso ciated with the rst baro clinic mo de Gill a baro clinic time scale required for a phase

dierence of to develop b etween the rst baro clinic mo de and the other baro clinic mo des is given

by

f

t





k c

where k represents the horizontal wavenumb er of the wind stress f is the lo cal Coriolis parameter and

c is the rst baro clinic mo de phase sp eed The relevant time scales are to IP in the LC regime

compared to IP in the GCW This more rapid time scale is due to a decrease in R coupled with

max

a faster phase sp eed when Lili moved over the GCW Note that this time scale was O IP during

Gilb ert due to an R that was a factor of three times larger than either observed in Isidore or Lili

max

Shay et al

max

Isotherm displacements scale as or ab out m m in the exp ected Isidore Lili o cean

fU

o

h

g

are predicted to be weak resp onse The geostrophic velo city resp onse V prop ortional to

gs

fR

max

 

with values of to cm s in the LC compared to cm s in the GCW consistent with the

R

max max

Gilb ert data set Shay et al Winddriven o cean velo cityV scales as representing

ml

hU

o

h

h



a velo city of to cm s with similar values in the thermo cline based on the expression V

ml

b

where h is initial OML depth and b is the thermo cline thickness Weak upp er ocean stratication

distributed over deep er layers will cause the LC resp onse to be weaker than in the more stratied

GCW Price Shay and Elsb erry Shay et al In the GCW however the predicted



windforced thermo cline currentiscms due to stronger stratication and shallower OML depths

The magnitude of the o cean resp onse not only dep ends on the characteristics of the hurricane forcing

but it also crucially dep ends on background initial o cean conditions based on these scaling arguments

Price dened a mixedlayer Burger number as

 

S g h

M



R f

max

U

h

where S is the nondimensional storm sp eed and h is the OML depth For the LC M ranged

R f

max

between to due to large values of S for Lili and for Isidore Over the GCW

Lilis acceleration toward the northwest coupled with a smaller R caused S to increase to The

max

b

thermo cline Burger numb ers T M are nearly equal to M in the LC since the ratio of thermo cline

h

and OML thicknesses is O as noted ab ove In the GCW however T is or a magnitude larger

than in the LC representing more dynamical coupling b etween the OML and thermo cline layer The

M

resultant blueshift in the mixedlayer inertial frequency is prop ortional to Table equating to



frequencies shifted ab ove f by toconsistent with previous results Shay et al

Analysis Approach

Orbital Velo cities

To examine the current and shear measurements from the AXCPs the surfacewave induced orbital

velo city signals must be removed from the current proles observed from the instorm ights When

averaged over a cycle the resolved lowfrequency surface waves will not contribute signicantly to the

mean current with the exception of a small Stokes drift due to nonlinear wave structure Observed

current proles are t to the Sanford et al threelayer mo del with an assumed mono chromatic

linear deepwater surface gravitywave sup erimp osed

Z Z z z

i i

kz

z S sin e U S i uz C cos

i Z

i

W W

where uz is the mo deled eastwest current prole a similar expression holds for the northsouth

comp onentv z C and S are the amplitudes of the orbital velo cities asso ciated with surface waves

p



kg is the wave frequency for wavenumber k following from linear theory W m s is

the AXCP fall rate and U and S are the mean current and shear in layer i resp ectively Observed

i z

i

current proles are t to using a standard Levenb ergMarquardt nonlinear leastsquares regression

Marquardt by minimizing the error over a range of trial wave periods T from to s

T Additional constraints are that the current proles are continuous across layer interfaces

thereby reducing the numb er of free parameters from eightto six

Mo del ts to the Isidore Sept and Lili Oct current proles are listed in Tables and



resp ectively Instorm orbital velo city amplitudes were typically m s in accord with previous

exp erimental eorts Sanford et al As shown in Fig the RMS residual currents estimated

by calculating dierences between the mo del and observed prole to a depth when kz ie

wave amplitudes are reduced to ab out of their surface velo city amplitudes based on the ts



were generally less than cm s indicativeof a reasonably go o d t for strongly forced mixed layer

conditions However there were a few exceptions with relatively large residuals Vertical shears of the

 

horizontal velo city comp onents in the upp er twolayers Z Z were O s whereas the shears



in the lower layer Z decreased by an order of magnitude The orbital velo city amplitudes have b een



removed from the observed current proles to examine the observed upp er o cean resp onse Shay et al

Price et al

Ob jective Analyses

Ob jectivelyanalyzed elds of observed variables are pro duced using a statistical interp olation

metho dology The analysis pro cedure used here is the OAX package develop ed at Canada Bed

ford Institute of Oceanography and is based on the algorithm presented in Bretherton et al

This approach uses a linear optimal interp olation technique to estimate values at grid p oints based on

observations at nearest neighbors Acovariance mo del of the form Freeland and Gould



r

r

r e r

is used where r is the weighted nondimensional distance b etween an observation and gridp oint In the

absence of detailed climatological information available ab out LC structural and temp oral variability

over the scales of interest exp osed to severe forcing a quantitativedevelopment of the optimal parameter

scales is dicult eg Baker et al Therefore scales are chosen through trialanderror to

adequately resolve the mesoscale o cean structure As the largest variability is observed near the surface

during hurricane passage spatial scales here are smaller and increase with depth Table The

horizontal covariance mo del r is plotted for each layer as a function of dimensional distance rL

or the observed proles the grid structure used for all Lili Isidore analyses is Fig F

no des in the horizontal plane encompassing a domain in latitude and

longitude resp ectively The vertical grid contains p oints at m depth intervals from the surface to

m The Isidore Lili grids are rotated T north to align with the storm track direction

st th

Isidores Lilis storm track is aligned with the grid column from the South Southwest side

rd th

of the domain and the p eak surface wind travels along approximately the column Each

analysis uses an efolding time scale of da ys consistent with previously observed resp onse time

scales Shay et al

Assuming prop erlychosen scales for the interp olation uncertainty estimates for each gridded eld

are available based up on the input measurement noise For nominal measurement errors of surface

temp eratures maximum mapping errors are C in the northwest part of the preLili grid due to

data sparsity in that region compared to temp erature mapping errors of C not shown over the

remainder of the domain Similarly mapping errors for C isotherm depths range from to m



whereas those asso ciated with OHC values are a maximum of KJ cm Finally current mapping



errors are typically to m s with the larger values lo cated in the northwest corner of the preLili

domain In all of the mapp ed elds these mapping errors are much less than the observed o ceanic

signals eg high signal to noise ratios

AirSea Fluxes

Seasurface forcing is describ ed by the uxes of momentum heat and moisture These uxes

are estimated from bulk formulae utilizing nearsurface m atmospheric thermo dynamic and wind

measurements and upp ero cean thermal data Atmospheric data are measured from the large number

of GPSsondes deployed within the storm from both aircraft Table including sondes deployed

from Air Force Reserve reconnaissance and NOAA GIV synoptic ights Surface winds are estimated

from SFMR measurements by sensing brightness temp eratures at multiple frequencies as thoroughly

describ ed in Uhlhorn et al

From each GPS dropwindsonde Ho ck and Franklin m values of temp erature and sp ecic

humidity are acquired and ob jectively analyzed using Bretherton et al pro jected onto a storm

relative grid aligned with the direction of storm motion SFMR wind observations are ob jectively

analyzed following Powell and then interp olated bilinearly to a stormrelative grid

as for the GPS atmospheric thermo dynamic variables See Fig Finally sea surface temp erature

observations are also optimally interp olated to the same stormrelative grid as noted ab ove resulting

in a set of variables at a common lo cation from which the spatial distribution of the bulk surface

momentum sensible and latent heat uxes are estimated



j j C jU j

a 

d

Q c C jU jT

s a p 

h

Q L C jU jq

a v q 

l

where is the atmospheric density C C and C are exchange co ecients of momentum sensible and

a q

d h

latent heat resp ectively U is the m wind sp eed c is sp ecic heat of air at constant pressure L is

 p v

the latentheatofvap orization T T T is the dierence b etween SST and m air temp erature

s a

SSTs are dened to b e nearsurface temp eratures within the rst few meters of the sea surface from the

exp endables and q q q is the dierence between the saturated sp ecic humidityat the SST

s a

and unsaturated m atmospheric sp ecic humidity The surface drag co ecient C is computed

d



from the Large and Pond relationship but capp ed at a maximum value of based on



recent results indicating a threshold or saturation value of C between to m s wind sp eeds

d

Powell et al Donelan et al Shay and Jacob Jarosz et al Heat exchange

co ecients C are set equal to C which is conservative compared to the theory prop osed byEmanuel

k d

That is Emanuels theoretical results suggest that this enthalpy and drag co ecient ratio lies

between to in severe hurricanes An additional o cean forcing mechanism is due to the surface

precipitation ux rain rate Freshwater input by rain can alter the o ceans resp onse both by direct

co oling due to rain at lower temp erature than the SST and reducing the salinity which stabilizes the

OML and reduces the rate of vertical mixing Jacob and Kolinsky TRMM satellite microwave

imager TMI derived rain rates Fig are used to estimate surface precipitation uxes for Isidore

 

and Lili where maximum rainrates were mm hr and mm hr resp ectively

Surface ux distributions during the Isidore instorm ight Sept are shown in Fig Peak



kW m as a result of high enthalpy ux is found in the rightrear quadrant of the storm to b e

 

The temp erature of a bulk OML dened as the depth where the temp erature decreases by more than C isgiven

bya vertical average from nearsurface to this depth During p erio ds of strong wind forcing the upp er o cean is well mixed

in temp erature which represents a bulk OML temp erature as observed during hurricanes Sanford et al Shay et

al



SSTs that show negligible decrease from prestorm conditions Maximum momentum ux Nm

is lo cated in the rightfront quadrant and is asso ciated with a highly symmetric storm due its fairly



slow m s translational sp eed Similarly the estimated surface uxes in Lili are shown in Fig

Lilis surface wind eld Oct indicates marked asymmetry due to the more rapid storm motion



toward the NW m s and corresp ondingly surface uxes are enhanced on the right of track



Compared to Isidore the maximum surface enthalpy ux in Lili is weak er kW m despite p eak



surface winds of m s This lower ux is due primarily to SSTs of ab out Clower observed in

the LC regime This is an imp ortant p oint highlighting how mo dest surface temp eratures dierences

can eectively alter surface heat uxes under hurricane wind conditions Cione and Uhlhorn

To improve our understanding for how these estimated uxes relate to seaair heat exchange en

thalpy heat and moisture uxes are integrated in the alongtrack direction to obtain a crosstrack

radial distribution of the o cean heat loss through the sea surface Alongtrack spatial co ordinate is

used to convert to time using the steadily moving storm assumption based on the observed storm sp eed

 

Table Estimated surface heat losses kJ cm for Isidore and Lili are shown in Fig At the

 

eyewall surface heat loss in Isidore is kJ cm compared to kJ cm value found during Lili



These dierences are due to higher enthalpy uxes versus kW m and slower storm sp eeds



versusms in Hurricane Isidore

Based on the TRMM data see Fig net freshwater input precipitation minus evap oration

PE is estimated for b oth storms byintegrating these data in the alongtrack direction Fig b As

suggested by the uxes the PE rate in Isidore was a factor of three times larger than in Lili b etween

mm within Isidores core rain impacted the OML balance through the R At levels of

max

PE rate By contrast the PE rate in Lilis core was mm due to a faster translation sp eed Such

rain events induce changes in the OML salinity balance of to practical salinity units psu as

do cumented by CTD measurements acquired in typho on wakes in the western Pacic Ocean Pudov

and Petrichenko Thus the OML salinity balance and the surface buoyancy ux that must

be accounted for in ocean resp onse mo dels for light and strong winds Price et al Jacob and

Koblinsky

Temp erature and Velo city Proles

Current and temp erature proles from the BB transect see Fig g along to R to the

max

right of the track are shown in Fig or IPs h following Lilis passage over the domain

Current proles along the northern part of transect B in the GCW indicated an anticyclonic rotation

with depth suggestive of vertical energy propagation out of the windforced OML Leaman

During Gilb erts passage this observed anticyclonic rotation with depth was found to b e a factor of four

times more energetic than the cyclonically rotating comp onent Shay and Jacob This current

vector rotation forced strong current shears b eneath the OML that induces co oling by entrainment

mixing pro cesses This eect lowers Richardson numb ers to b elow criticality for a deep ening and co oling

OML Pollard et al Price Jacob et al In the center of the BB transect OML



currents approach m s owing toward the east Notice the warmer thermal structure approaches

the currents remained relatively constant with depth in the LC This baro clinic m depth where

current structure tends to be in geostrophic balance with a current reversal at m and weaker

currents extending to a depth of m By contrast the current structure at point B is shallower



with maximum OML currents of m s

In the GCW lo cated in the northwest corner of the analysis domain OML co oling and deep ening

are typical signatures of a stronger o cean resp onse that often lead to negative feedback to hurricane

passage Chang and Anthes Bender and Ginis However in the LC this negative feedback

is minimized compared to that observed over the GCW Since the assumption of to the atmosphere

horizontal homogeneity is violated in the LC and WCR regime Halliwell et al stresses the

imp ortance that threedimensional oceanic mo dels must be initialized to accurately predict intensity

from coupled forecasting mo dels In fact Falkovich et al intro duced a numerical approach for

featurebased o cean mo deling that involves crossfrontal sharp ening of the background temp erature and

salinity and hence density elds These studies underscore the need for dimensional exp erimental

data to improve o ceanic mo del initialization schemes

Temp erature and Velo city Sections

Background o cean ows are set up by horizontal pressure gradients due to nonzero r Tandr s

h h

where s is salinity and mayplay a signicant role in aecting the development of strong winddriven

current shears within the LC and WCR regime Fig Pre and p ostIsidore measurements across

the Yucatan Straits indicate strong density and pressure gradients asso ciated with the LC PreIsidore



measurements suggested a northward owing LC of m s skewed toward the western b oundary of

the Yucatan Straits This is the region where the horizontal density and pressure gradients sharp en due

to a strong bottom slop e The initial C isotherm depth was a maximum of m depth in the

Straits but was near the b ottom over the Yucatan Shelf These spatial variations were sharp ened since

Isidore co oled the shelf waters by more than C compared to C across the Yucatan Straits



The LC resp onse was an increase of m s consistent with the exp ected current resp onse of m



s as p er scaling arguments in Table On the western side of the Straits the C isotherm upwelled

toward the sea surface whereas this isotherm depth increased to more than m in the eastern part

of the Y ucatan Straits due to downwelling of the isotherms

As shown in Fig mean crosstrackvariability in the alongtrack direction prior to and subsequent

to Lilis passage revealed similar features except that the currents and horizontal temp erature density

gradients were not impacted quite as muchby the steep b ottom terrain Maximum upp er o cean currents



were directed toward the north at sp eeds of more than ms There was co oling in the northern

part of the domain where the C isotherm depth was lo cated at m depth b efore Lili which then

decreased by ab out m on Oct due in part to upwelling along the track Spatially averaged



baro clinic currents increased to m s in resp onse to Lili As in the o ceanic resp onse to Isidore

there was little evidence of signicant upp er o cean co oling b etween snapshots While the time envelop e

between the pre and p ostLili measurements was nearly twoweeks there was not much evidence that

this category hurricane impacted the LC even just two days following passage By contrast forced

nearinertial current shears deep ened and co oled the OML byabout C in the GCW during Hurricane

Gilb erts passage Shay et al

Forced Resp onse in the Lo op Current

An imp ortant question emerging from recent studies is the upp er o cean co oling levels during hur

ricane passage While early studies have fo cused on the concept of negative feedback during hurricane

passage ie Chang and Anthes observational evidence has suggested that the STW mass as

so ciated with the LC and WCR do esnt signicantly co ol compared to the GCW Based on proler

measurements b efore and after Rita the o ceanic co oling was minimized suggesting less negative feed

backeven though Rita was a category hurricane over the LC Shay Historical records suggests

that once a hurricane enters the GOM basin it will likely intensify prior to making a landfall Marks

and Shay Contrasting the details of the o ceanic resp onse dierences b etween the LC and WCR

versus the GCW water masses has implications with resp ect to negative feedback to the atmosphere

The fo cus here is on examining the observed o ceanic resp onse to Hurricanes Isidore and Lili

SST

Pre and p ostIsidore and Lili SST elds are shown in Fig PreIsidore SSTs ranged from

to C over the exp erimental domain During the p ostIsidore exp eriment on Sept SST

changes were observed along these b ottom top ographical gradients with the largest SST changes of

C o ccurring over the Yucatan Shelf Fig c That is SSTs decreased to less than C due to

alongshelf wind stress forcing a net surface oshore ow and transp ort to force upwelling of a shallow

seasonal thermo cline While signicant SST co oling and upward isotherm displacements o ccurred over

the shelf just prior to landfall only small thermal structure and isotherm depth changes were observed

across the Straits to the western tip of Cuba Thus SSTs remained ab ove C in the Straits a day

after Isidore suggestive of less negative feedbacktothestorm Given the d interval b etween Isidore

and Lili preLili SSTs were to Cover most of the exp erimental domain After Lilis passage

SSTs decreased to only C in the LC however along the northwest part of the measurement

domain SSTs co oled to less than C in the GCW Consistent with the NDBC measurements

see Fig this observed SST change equates to more than C co oling Fig f as Lili intensied

to a category storm in the southcentral GOM Pasch et al

C Isotherm Depths

Prior to Isidore a strong horizontal gradient of the C isotherm depth was observed such that

depths were found to b e more than m in the Yucatan Straits to less than m over the Yucatan Shelf

Fig These horizontal dierences are constrained by strong crossstream top ographical gradients

separating the Yucatan Straits from the Yucatan Shelf Consistent with these large SST changes over

the shelf isotherm depths decreased along these b ottom top ographical gradients after Isidore However

in the center and eastern part of the deep er Yucatan Straits isotherm depth increased by mFig

c whichmay be a manifestation of the do wnwelling cycle This alternating upwelling cycle along

the steep b ottom slop e and over the shelf and downwelling cycle in the Straits is an integral part of

the o ceanic resp onse to hurricane forcing Geisler These pro cesses result in a tightening of the

isotherm depths and hence thermo cline and their gradients across the abrupt top ographical changes

The corresp onding C isotherm depths for preLili conditions were lo cated at more than m depth

in the southeast part of the LC Fig d and decreased to m along the northwest p eriphery in the

GCW Compared to a monthly climatology Teague et al these isotherm depths seem to be

anomalously deep but they were consistent with satellitederived isotherm depths derived from satellite

altimetry based on a seasonal climatology Halliwell et al Given Lilis rapid translation sp eed

p oststorm isotherm depths changed little compared to the preLili values in the LC Fig e That

is isotherm depths ranged between to m in the LC compared to ab out to m range

before the storm The isotherm displacements induced by Lili were m which is consistent with

scaling arguments using b oth the maximum wind stress and translation sp eed values in Table

OHC Variability

Pre and p oststorm OHC distributions Fig reect these SSTs and C isotherm depths Pre

Isidore OHC in the NW Caribb ean basin and through the eastern part of the Y ucatan Straits exceeded



kJ cm in accord with satellitederived OHC values derived from radar altimetry Halliwell et al



Over the Yucatan Shelf preIsidore OHC values were ab out kJ cm Fig a suggestive

of a shallow seasonal thermo cline maintained by the trade winds Gill In the p ostIsidore

distributions the OHC values were less than those observed during prestorm conditions but by less



than kJ cm along the western parts of the Straits and along the eastern part the OHC increased



by ab out kJ cm consistentwithadownwelling signal ie deep ening of the C isotherm Fig



c Over the shelf however the OHC losses were more than kJ cm where SSTs co oled by C

hange presumably due to northward heat In the center of the straits there was essentially no OHC c

transp ort by the LC Evidently these large spatial gradients in SSTs and OHC across the Yucatan

Straits impacted the enthalpy uxes that aected Isidores intensication to category status Since

isotherm depths decreased by ab out m in the LC with a C SST co oling the LC essentially



maintained OHC levels of more than kJ cm prior to Lili Fig d Maximum OHC levels



from proler measurements exceeded kJ cm compared to satelliteinferred values of kJ



cm not shown By contrast in the GCW OHC values after Lili decreased by more than kJ

 

cm compared to less than kJ cm in the LC regime This larger OHC loss asso ciated with

an SST decrease of more than C may have been due to enhanced vertical shears as the surface



enthalpy uxes only accounted for ab out to kJcm of heat loss through the surface Given that

the p ostLili survey was conducted IP h after passage Fig e the OHC loss may have

b een more than this value since a ma jor contributor to the o ceanic heat budget is asso ciated with the

northward advection of heat by the LC Dierencing pre and p ostLili OHC elds indicates that average

  

uxes were signicantly less than kJ cm d kW m due to hurricane passage Along the

northwest part of the Lili domain ie GCW thin OMLs co ol and deep en quickly during hurricane

passage where the SST decreases typically range from to C Price Shay et al Jacob et

al and induce a negative feedback Chang and Anthes Bender and Ginis Price et

al argued that the North Atlantic Subtropical Front over which Hurricanes Josephine

and Gloria passed are inconsequential to the simulated o cean resp onse In the threedimensional

LC regime however the horizontal pressure gradients and balanced currents are considerably stronger

than in the North Atlantic Ocean subtropical front Thustosimulate the resp onse o cean mo dels must

b e initialized with these basic state ows Marks and Shay Halliwell et al

Vertical Current Shear

The most eective pro cess for OML co oling and decreasing SST is byentrainment mixing downward

heat ux across the base of the OML asso ciated with vigorous nearinertial current shears eg Price

Schade and Emanuel This pro cess is parameterized in numerical mo dels and has b een

Jacob shown to pro duce widely varying results dep ending up on the chosen mixing parameterization

et al Jacob and Shay The results presented here suggest that strong prestorm current

regimes may limit the development of windforced nearinertial currents and their vertical shears

Current proles are used to assess the vertical shear using proles with vertical resolution of

m after removal of the orbital velo cities x Based on current shears at the OML base are

estimated from the mo deltted shear co ecients in layer S from Tables and Mean and

Z

standard deviation of S are compared to Norb ert and Gilb ert shear measurements in Table Within

Z

measurement error Gregg et al weaker shears were observed in the current proles acquired

during two severe hurricanes These estimated shear values in Layer are ob jectively analyzed for

both in and p oststorm elds only Fig Evident in these elds is the weaker shear observed

in the LC regime compared to measured shears in the GCW Within the LC for example current

   

shears ranged from s whereas outside the LC the shears were s or

to times larger This eect is obvious in the instorm Isidore and p oststorm Lili current elds Figs

ad That the current shear resp onse is lagged in Lili may also be due to rapid storm motion and

its asymmetric wind stress distribution compared to the symmetric and slower moving Isidore Given

these wide ranging results between two distinct water masses considerably more current and shear

measurements are needed to fully assess mo del parameterizations

Bulk Richardson Number

The bulk Richardson numb er is estimated from the following expression

ghT

Ri

b



V

 

where C is the co ecient of thermal expansion Kraus and Businger h is the

OML depth T is the temp erature dierence between the bulk OML and averaged temp erature in

Layer and the magnitude of the bulk current shears jV j are determined from the mo deltted

mean current dierences b etween layers and as p er Tablesand Pollard et al used

avalue of unity for the bulk Richardson numb er as a condition for the onset of mixing pro cesses at the

OML base whereas Ellison and Turner found that more appropriate values ranged b etween

to for the initiation of vertical mixing Price used a Ri of as the critical value for mean

b

current shearinduced mixing based on a scaled entrainmentlaw from exp erimental lab oratory results

Small values of Ri indicate regions where shearinduced mixing is likely to overwhelm the damping

b

eect of stratication during the co oling pro cess Fig However instorm measurements in Isidore

indicate Ri over most of the domain These values in the LC are consistent with the observed

b



C co oling and OHC change of kJ cm Even where the maximum SST co oling of C was

observed bulk Richardson numb ers were ab ove critical values Fig ab suggesting that upwelling

of colder thermo cline water induced by the wind stress curl was the dominant mechanism over the

shelf The results for Lili are similar Fig cd although more evident in the p oststorm analysis of

current shear measurements Both of these cases pointto a reduction in shearinduced mixing events

in regions of strong background currents That is deep warm layers coupled with strong background



m s due to horizontal density and pressure gradients precludes the generation of strong ows of

shears observed in the nearinertial wave wake Shay et al These results p oint to a physical

mechanism that must b e well understo o d in coupled mo dels that predict hurricane intensity

Summary and Concluding Remarks

The goal of the aircraftbased exp erimentwas to measure the dimensional current temp erature

and salinity resp onses excited byhurricane passage with a fo cus on assessing the resp onses in and over

the LC The aircraftbased sampling strategy resulted in several snapshots of upp er o cean current

temp erature and salinity structure required to examine the resp onse to the passage of two category

hurricanes moving over the same domain over a day p erio d Given inherent uncertainties of storm

track prediction for the preIsidore ights this exp erimental ob jectivewas achieved with a high degree

of success for Isidore and Lili This is one of a few data sets where currents and shears are directly

measured during hurricane passages Sanford et al Shay et al Price et al Sanford et

al In this case the GPS sondes and SFMR data complement these in situ o cean measurements

in understanding the mutual resp onse

The o cean resp onse to the passage of hurricanes Isidore and Lili was investigated using in situ

observations from o ceanic and atmospheric sondes and remotely sensed o cean surface winds Uhlhorn

et al These hurricanes intensied to ma jor hurricane status Category and ab ove over the

LC and Lilis deep ening cycle continued into the central GOM basin as the storm reached Category

status just northwest of the LC b oundary Atmospheric conditions were conducive for deep ening as

noted by Pasch et al over an ocean where the extent of the co oling was O C and the



upp er o cean heat loss was less than kJ cm Even after b oth hurricanes the upp er o cean was still



warm with SSTs of to C with OHC levels exceeding kJ cm These results are similar to

t to that followed a track close to Katrina observations acquired prior and subsequen

over the LC and WCR Shay Based on these proler data lessons learned from Isidore and Lili

were

The threedimensional LC precludes the development of strong vertical current shears to force



mixing and deep ening of the OML despite applied wind stresses of N m due to the strength

of the current and depth of the warm isotherms

Co oling of Cover the Yucatan Shelf to Isidore was due to windforced upwelling while more

than C co oling during Lili was due to shearinduced mixing events in the GCW and



Maximum surface heat loss from the ocean was less than kJ cm at R where enthalpy

max



uxes ranged from to kW m for Lili and Isidore resp ectively

The rst p oint is imp ortant with regard to initialize o cean mo dels with realistic background conditions

Halliwell et al Mainelli et al Emanuel argues that the upp er o cean can b e treated

as a series of onedimensional column mo dels for coupled hurricane forecasting The results rep orted

and other recent studies suchasWu et al imply that dimensional advective tendencies must

be accounted for in such mo dels Since the o cean resp onse is weakest in strong frontal regimes the

negative feedback to the atmosphere is m uch less than over quiescent ocean regimes Point has

direct relevance to the threshold value to sustain a hurricanes intensity Leipp er and Volgenau

 

suggested a value of kJ cm d this threshold must b e revisited to understand howmuch o ceanic

heat loss is related to surface enthalpy uxes versus entrainment heat loss to the thermo cline In this

context Cione and Uhlhorn argue that it is just innercore SSTs that are necessary for intensity

forecasting but their results are inconclusive since OHC was held constant even though SSTs were

changing With temp erature proles OHC changes relativetothe C isotherm can b e estimated at

ner scales than currently available from coarse altimeter tracks Cheney et al

The scientic issue is not just the OHC magnitude but the depth of the C isotherms in the LC

and WCR regime are of equal imp ortance in determining the value of the OHC as p er The deep er

this layer of warm water more turbulent mixing is required to overturn and co ol the OML Signicant

in ternal wave shears asso ciated with nearinertial motions were not observed in the LC during Isidore

and Lili due to the strength of the horizontal pressure gradients that force the background currents

If shearinduced mixing is arrested then signicant OML co oling and deep ening will not occur By

contrast when current shears are large they lower the bulk Richardson numb ers to b elow critical

values which co ol the SST a proxy for OML temp eratures under high winds as the OML deep ens

Price Shay et al Entrainment heat uxes into the thermo cline will result in lower

surface enthalpy uxes that feed the hurricane and impact hurricane intensity Chang and Anthes

Schade and Emanuel Bender and Ginis For coupled mo del forecasting currents

and shears momentum resp onse are as imp ortant as thermal proles for simulating OML co oling

and deep ening pro cesses Given the number of vertical mixing mo dels using bulk and turbulence

closure schemes Jacob and Shay exploring parameter space under diering o cean conditions

water masses will require more current and shear measurements than has b een previously acquired

under hurricane conditions that could b e integrated into the NOAA IntensityForecasting Exp eriments

Rogers et al The o ceans momentum resp onse to hurricane forcing has b een used to determine

the b ehavior of the surface drag co ecientShay and Jacob Jarosz et al These data are

needed to test and evaluate innovative forecasting schemes involving b oth airsea and vertical mixing

parameterizations This is a crucial test for coupled mo dels designed for op erational hurricane intensity

forecasts Marks and Shay

Acknowledgments

LKS acknowledges the supp ort of the National Science Foundation for b oth the exp eriment and data

analysis through grants ATM ATM and ight hours were provided by NOAAs

Hurricane Research Division HRD and National Hurricane Center E Uhlhorn was supp orted by

b oth NOAA and ONRCBLAST under the leadership of Dr Peter Black We gratefully acknowledge

Dr Jim McFadden of the Oce of Aircraft Op erations OAO and Drs Hugh Willoughby and Frank

Marks NOAA HRD in orchestrating these aircraft exp eriments Dr Paul Chang of NOAANESDIS

directed the Ocean Winds ights on NRF and provided supp ort for b oth Isidore and Lili ights

Mr Michael Black HRDeld director directed all eld supp ort for these ights We appreciate the

extraordinary eorts of the OAO pilots engineers and technicians during these exp erimental eorts

Tom Co ok and Scott Guhin assisted in the aircraft based exp eriments Jo di Brewster provided graphical

supp ort Reviews from three anonymous reviewers signicantly improved the manuscript

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Isidore Lili

Date Flight GPS BTs CPs CTDs Date Flight GPS BTs CPs CTDs

Sep NSF Sep OW

Sep OW Sep NSF

Sep NSF Sep NSF

Sep OW Sep OW

Sep NSF Oct OW

Sep OW Oct NSF

Sep LF Oct LF

Sep NSF Oct NSF

Total

Table Deployed prob es RF failures in parentheses Isidore and Lili research ights from

NOAANESDIS Ocean Winds OW NSF and Landfall LF Flights Note that the and Sep

ights represent preLili conditions in the Gulf of Mexico based on RF signals success rates

Isidore Lili

Parameter LC LC GCW

Radius of maximum winds km R

max



Maximum wind m s W

max



Maximum wind stress N m

max



Sp eed of the hurricane m s U

h

Wavelength km



First mo de phase sp eed m s c



First Mo de Deformation Radius km

n

Time scale IP t

Inertial Perio d d IP

 

Reduced gravityms x g

Mixed layer depth m h

NonDimensional Numb ers

U

h

Froude Number Fr

c



U

h

Nondimensional storm sp eed S

R f

max



S g h

Mixed Layer Burger Numb er M

R f

max

b

Thermo cline Burger Number T M

h

R

max

Nondimensional Forcing Fo



Scales

R



max max

WindDriven Velo cityV ms

ml

hU

o

h

h



Thermo cline Velo cityV ms V

th ml

b

max

Isopycnal Displacements m

s

fU

h

g



s

Geostrophic Velo cityV cm s

gs

fR

max

M

Frequency Shift



Table AirSea parameters nondimensional numb ers and scales in Isidore and Lili Lo op Currentand

Gulf Common Water based up on Price scaling arguments Maximum wind stress is estimated

from the Stepp ed Frequency Microwave Radiometer data

Time Var T C S Z V S Z V S Z V S Z R

      

        

UTC s cm s cm s m cm s s m cm s s m cm s s m cm s

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

Table Co ecients from ts with the Sanford et al mo del and the Isidore Storm AXCP

proles in the upp er m where Z is the start depth of the go o d data used in the t T is the p erio d

o



of the surface wave with co ecients of C and S Z V and S x representlayer depth

  

layeredaveraged currents and current gradients in each layer resp ectively R is the residual current



not explained by the mo del to a depth of e

Time Var T C S Z V S Z V S Z V S Z R

      

        

UTC s cm s cm s m cm s s m cm s s m cm s s m cm s

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

Table Same as Table except for Lili Storm AXCP proles in the upp er m

Time Var T C S Z V S Z V S Z V S Z R

      

        

UTC s cm s cm s m cm s s m cm s s m cm s s m cm s

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

u

v

Table Same as Table except for Lili PostStorm AXCP proles

Depth range m Horiz Scale Ldeg Vert Scale m

Table Horizontal and vertical correlation scales used in the ob jective analyses

 

Storm Shear s

Norb ert

Gilb ert

Isidore

Lili

Table Observed current shear from AXCP proles deployed in TCs Means and standard deviations a)

CAT 5 CAT 4 CAT 3 CAT 2 CAT 1 26 Sept

03 Oct

42001

Loop Florida Current Current

30 Sept 22 Sept 20 Sept

b) ISIDORE LILI

30

C) 29

°

28

SST ( 27

26

16 Sept 19 22 25 28 01 Oct 04 07 10

Figure a LC red contour p osition relativeto the b est tracks of Isidore blue and Lili black in

SeptOct with intensities in the Gulf of Mexico relative to NDBC blue dot and b observed

o

SSTs C at NDBC with the gray shading for Isidore and Lili 50 a 24 45

40

23 35

30

22 25

20

21 15

10

20 5

0 −88 −87 −86 −85 −84

50 b 26 45

40

25 35

30

24 25

20

23 15

10

22 5

0

−88 −87 −86 −85 −84

Figure HWIND surface wind analysis of Hurricanes a Isidore at UTC Sept and b Lili



at UTC Oct Isotachs are contoured every ms Data used to generate this analysis

include observations from SFMR GPS dropwinsondes QuikSCAT scatterometer and available hourly

buoy rep orts The storm track is indicated by the solid line and box shows the ocean data analysis

region considered for this research Longitude (˚W) 90˚W 88˚W 86˚W 84˚W 82˚W 80˚W 90˚W 88˚W 86˚W 84˚W 82˚W 80˚W a) b) 26˚N

24˚N

22˚N

20˚N BT CP CTD 18 Sep 02 19 Sep 02 18˚N c) d) 26˚N

24˚N

22˚N

20˚N

21 Sep 02 22 Sep 02 18˚N e) f) 26˚N Latitude (˚N)

24˚N

22˚N

20˚N

23 Sep 02 02 Oct 02 18˚N g) 26˚N B’

24˚N B 22˚N

20˚N -20 0 20 SHA (cm) 04 Oct 02

18˚N

Figure SHA eld color cm from radar altimetry and o ceanic prole AXBTtriangles AXCP

boxes and AXCTDcircles deployments blacksymb ols go o d data white symb ols prob e failure for

a preIsidore in NW Caribb ean Sea b preIsidore in the south central GOM c Isidore instorm across

the Yucatan Straitsand d p ostIsidore day e p ostIsidore day on Sept f Lili instorm over

the grid in panel b and g PostLili on Oct relative to Isidore and Lili tracks with hurricane category

levels in Fig −1 −0.5 0 0.5 1 −1 −0.5 0 0.5 1 −50 −25 0 25 50 0 0 a b c

−50 −50

−100 −100 Depth (m) −150 −150 U T = 8.5 s T = 9.0 s V −200 −200

0 0 d e f

−50 −50

−100 −100 Depth (m) −150 −150 U T = 10.0 s T = 14.0 s V −200 −200 −1 −0.5 0 0.5 1 −1 −0.5 0 0.5 1 −50 −25 0 25 50

U (m s−1) V (m s−1) Resid. (%)

Figure Example of mo del ts dashed using a threelayer approach of Sanford et al for



Isidore top panels and Lili lower panels for the u and vcomp onents m s in panels abde

compared to observed prole solid Panels c and f represent dierences b etween observed and mo del

proles for both velo city comp onents normalized by the surface wave amplitudes from Tables

Note that the RMS dierences are smaller in Lili panel f but since the surface wave is less energetic

the normalized dierences are larger than for the Isidore proles 1

0.9

0.8

0.7

(r) 0.6 ρ

0.5

° 0.4 L=0.5 Covariance ° L=1.5 ° 0.3 L=2.0 ° L=2.5 0.2 ° L=3.0 ° 0.1 L=4.0 ° L=5.0 0 0 1 2 3 4 5

Distance (r⋅L, deg.)

Figure Covariance mo del weighting function r as a function of dimensional distance r L

deg applied to observations for the ob jective analyses as p er Table for diering length scales L 10 40 10 a b

5 30 5

max 0 20 0 max y/R y/R

−5 10 −5

−10 0 −10 −10 −5 0 5 10 −10 −5 0 5 10 x/R x/R

max max



Figure Rain rates mm hr based on TRMM data during a Isidore and b Lili −10−8 −6 −4 −2 0 2 4 6 8 10 300 1400 10 a b 8 250 1200 6 1000 4 200 2 800

max 0 150 600 y/R −2 100 −4 400 −6 −8 50 200 −10 0 0

7 1800

1600 c 6 d 1400 5 1200

4 1000 max 3 800 y/R 600 2 400 1 200

0 0 x/R x/R

max max

Figure Airsea heat moisture and momentum uxes derived from GPS sondes and SFMR from

 

Isidore on Sept for a sensible heat W m b latentheatWm c momentum or wind

 

stress Nm and d enthalpy a b Wm in a stormco ordinate system normalized by R

max −10−8 −6 −4 −2 0 2 4 6 8 10 300 1400 10 a b 8 250 1200 6 1000 4 200 2 800

max 0 150 600 y/R −2 100 −4 400 −6 −8 50 200 −10 0 0

7 1800

1600 c 6 1400 5 1200

4 1000 max 3 800 y/R 600 2 400 1 200

0 0 x/R x/R

max max

Figure As in Figure except for Lili on Oct x/R max

) −10 −8 −6 −4 −2 0 2 4 6 8 10 −2 12 a Isidore 09/21 Lili 10/02 10

8

6

4

2

0 Surface flux−induced heat loss (kJ cm 350 b 300

250

200

150

100

50

Precip. minus Evap. (mm) 0

−50 −10 −8 −6 −4 −2 0 2 4 6 8 10 x/R

max

Figure Crosstrack distribution of the a surface heat loss induced by surface uxes upp er panel



KJ cm and b precipitationevap oration rain uxes lower panel mm observed during hurricane

Isidore solid and Lili dashed with the appropriate error bars based on measurements 50 cm/s B' B 5 10 15 20 25 30 Temp (oC) 0

-30

-60

-90 Depth (m) -120

-150

-200

-300

-400

-500

-600 Depth (m) -700

-800

-900

-1000 2.11 2.06 2.10 2.15 2.29 2.35 2.39 2.44 2.47 2.57

Inertial Period



Figure Section BB currentvector stickplotcms and temp erature C color section at

R to the right of Lilis track on Oct PostStorm Time is scaled in terms of inertial period

max

Black dots represent the OML depth in the upp er panel extending from surface to m depth −88 −87.5 −87 −86.5 −86 −85.5 −85 −84.5 0

0.2 0.8 −100 0.6 0.2

0 0.4

0

Depth (m) −200 a −300

Temp. ( °C) 10 15 20 25 30

0

1.2 1 −100 0.8 0.6 0

0.2

Depth (m) −200 0.4 0.2 b −300 −88 −87.5 −87 −86.5 −86 −85.5 −85 −84.5

Longitude

Figure Pre upp er p ost lower Isidore alongtrack section of temp erature color C and north



ward geostrophic velo city dashed contours ms across the Yucatan Straits The heavy black line

depicts the depth of the C isotherm Latitude 24.6 24.4 24.2 24.0 23.8 23.6 0 0.5

0.4 −100 0.2 0.3 0 0.1

Depth (m) −200

0.1 a −300

Temp. ( °C) 10 15 20 25 30

0

0.6

0.6 0.2 0.5 0.2 −100

0.5 0.1

0.1 0.3 0.4

0 Depth (m) −200

0 0.3 b −300 −87 −86.5 −86 −85.5 −85 −84.5

Longitude

Figure Pre upp er p ost lower Lili crosstrack section of temp erature color C and geostrophic



velo cityms across the Yucatan Straits Heavy black line depicts the depth of the C isotherm Lon. −88 −87 −86 −85 −84 0.25 0 −0.25 0.25 0 −0.25 0.25 0 −0.25 24 28 28 29 27 −1 −1 8 29 8 −2 8 −1 28 27 −2 23 4 4 −4 4 25

max −3 29 26

29

22 0 0 x/R 0 Lat. −1 −4 −4 −4 21 −8 −8 −8 20 a b c y/Λ

y/ 26 Λ

29 −1 28 max

25 x/R −2

27 12 12 −1 12

29

28 24 −1 29 8 8 8 Lat. 4 4 4 0 23 0 29 0 0 0 0 0 22 d e f −0.125 −0.125 −0.125 −0.25 −0.25 −0.25 −88 −87 −86 −85 −84

Lon.

Figure Pre a p ost b Isidore and c SST C and Pre d Post e and SST f Lili

b ottom relative to Isidores and Lilis track black line across the Yucatan Straits and the southeast

GOM relative to b ottom top ography dotted for the and m depth contours Storm motion



arrows in panels a d for Isidore and Lili resp ectively and its co ordinate system crosstrack xR

max



alongtrack y dimensions are relative to the mean storm lo cations from instorm ights where

the R and values are given in Table

max Lon. −88 −87 −86 −85 −84 0.25 0 −0.25 140 140 24 60 60 60

0 8 0 0 20 23 20 100 100 4

0

max 40 140 x/R 22 40 20 0 140 Lat.

140 −4 21

140 0 −8 20 Λ a b c y/

y/ 26 Λ

60 25 60 max 100 x/R 0 100 12 100 60 20 24 8 Lat. 140 140 0

60 0

0 4

23 0 0

22 d e f −0.125 −0.25 −88 −87 −86 −85 −84

Lon.

Figure Similar to Fig except for C isotherm depth m Lon. −88 −87 −86 −85 −84 0.25 0 −0.25

20 24 140

−20 60 −40 8 −20 60 0

23 20 60 60 0 180 4 max

100 100 20 22 x/R −40 0 140 Lat.

140 140 −4 21 −20 0 −8 20 a b c y/Λ

y/ 26 Λ

−20

max 60 60 25 100 20 x/R −40 12 100

100 −20 −20 24 60 140

140 8 Lat.

60 0 4

−20 23 0 0

22 d e f −0.125 −0.25 −88 −87 −86 −85 −84

Lon.



Figure Similar to Fig except for OHC kJ cm relative to the depth of the C isotherm in

Fig Lon.

−88 −87 −86 −85 −84 5 0.25 0 −0.25 24 4.5 2 4 3 1 1 8

1.5 23 1.5 3.5

4

2.5

3 max x/R 22 2.5 1.5 0 Lat. 2 −4 2.5 2 21 1.5

2 1 −8

1.5 20 0.5 a b y/Λ 0 5

4.5 26 y/ Λ 1 4

3.5 max 25 0.5 x/R

2 2 1.5 3 12

1.5

3 1 2 1.5 2.5 24 1 8 Lat.

2.5

2 1.5 1.5 4 1.5 23 0 1

1 0

−0.125 22 0.5 c d −0.25 0 −88 −87 −86 −85 −84

Lon.

 

Figure Similar to Fig except for instorm and p oststorm current shears x s for Isidore

ab and Lili cd relative to storm tracks solid the bottom top ography dotted for the and

m depth contours Lon.

−88 −87 −86 −85 −84 5 0.25 0 −0.25 24 4.5

1.5 4 4.5 2.5 8 3.5

1.5 3.5 1 2 23 4 1 3 4 3

3 max 2 x/R 22 2.5 2.5 0 3.5 Lat.

2.5 1.5 2 1.5 −4

21 1.5 2 1 −8

20 0.5 a b y/Λ 0 5

4.5 y/ 26 Λ

4 5 4 3

max 1.5

1 3.5 25 2 x/R 2.5 4.5 3 2.5 3 12 2 3.5 2 2.5 1.5 2 24 8 Lat. 1.5 2.5 2.5 3 2 1 3.5 3 2.5 4 1.5 23 0

1 0

−0.125 22 0.5 c d −0.25 0 −88 −87 −86 −85 −84

Lon.

Figure Similar to Fig except Ri

b