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Improving the Initialization of Coupled Hurricane-Ocean Models by Feature-Based Assimilation of Mesoscale Oceanic Features Richard M. Yablonsky and Isaac Ginis URI Graduate School of Oceanography 18-20 June 2007 Third Northeast Tropical Workshop MIT Endicott House, Dedham, MA

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Improving the Initialization of Coupled Hurricane-Ocean Models by Feature-Based Assimilation of Mesoscale Oceanic Featur


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slide1

Improving the Initialization of Coupled Hurricane-Ocean Models by Feature-Based Assimilation of Mesoscale Oceanic Features

Richard M. Yablonsky and Isaac Ginis

URI Graduate School of Oceanography

18-20 June 2007

Third Northeast Tropical Workshop

MIT Endicott House, Dedham, MA

slide2

The Role of Numerical Models

Numerical models allow us to predict the future state of the atmosphere and ocean using mathematical equations based on physical laws…

Forecasters at NHC use output from the GFDL/URI coupled hurricane-ocean model and the coupled Hurricane WRF model (as well as other models) to help them make accurate 3-5 day hurricane forecasts

Image courtesy of Isaac Ginis

track errors cut in half in 17 years
Track errors cut in half in 17 years!

400

350

300

The

Good

News!

250

200

150

100

50

0

Image courtesy of James Franklin, NHC

no progress with intensity in 17 years
No progress with intensity in 17 years!

The

Bad

News!

Image courtesy of James Franklin, NHC

hurricane physics thermodynamics

Radiation to space

Radiation to space

OUTFLOW (Isothermal compression)

OUTFLOW (Isothermal compression)

Inward

component

of surface wind

Inward

component

of surface wind

Evaporation from ocean

Evaporation from ocean

Hurricane Physics & Thermodynamics

Image courtesy of http://hurricanes.noaa.gov

DOWNDRAFT

(Adiabatic

compression

& warming)

DOWNDRAFT

(Adiabatic

compression

& warming)

UPDRAFT

(Adiabatic

expansion

& cooling)

INFLOW (Isothermal expansion)

INFLOW (Isothermal expansion)

Hurricanes develop and are maintained by transportation of water vapor from the ocean surface up a natural chimney to the upper atmosphere.

is the ocean part simple
Is the ocean part simple?
  • Heat energy for the hurricane depends on evaporation from the sea surface
  • Evaporation rate depends on SST
  • So to initialize a hurricane model, all you need to know about the ocean is the SST ahead of the storm, right?
  • WRONG!!!
  • Let us now understand why…
slide8

Ocean’s Role in Hurricane Intensity

Satellite Infrared Image of Sea Surface Temperature Hurricane Gert (1999)

slide9

Image courtesy of Isaac Ginis

Typical of

Gulf of Mexico

in September

Typical of

Caribbean

in September

slide10

Answer: We must look

under the ocean surface!

Why is the cold wake

“not as cold” here?

importance of hurricane ocean interaction katrina rita nearly perfect storms
Importance of Hurricane-Ocean Interaction:Katrina & Rita -- Nearly “Perfect Storms”

Subsurface (75-m)

ocean temperature in

advance of Rita on

15 September 2005

Warm “Loop Current”

water and a “Warm

Core Ring” extend far

into the Gulf of Mexico

from the Caribbean…

Directly under Rita’s

and Katrina’s track!!!

capturing the loop current and rings
Capturing the Loop Current and Rings
  • You need real data to properly initialize the 3-D ocean temperature field…
  • You can start with a monthly ocean climatology and assimilate the daily SST…
  • But is a monthly climatology good enough to capture major oceanic fronts like the Gulf Stream, the Loop Current, & eddies (rings)?
  • Let’s find out!!!
slide13

The depth of the 26°C isotherm on

15 Sept. 2005 according to

GDEM climatology

The depth of the 26°C isotherm on

15 Sept. 2005 after we assimilate

mesoscale oceanic features (i.e. the

Loop Current and Rings)

Question: How do we know our

initialization is better than GDEM?

Answer: We use satellite altimetry and real-time AXBT instruments

for assimilation and/or validation!

sea surface height assimilation
Sea surface height assimilation
  • Satellite altimetry is used daily by the National Hurricane Center to calculate the depth of the 26°C isotherm
  • Using maps of the 26°C isotherm depth, we obtain a “first-guess” for the Loop Current shape and position
  • We also obtain a “first-guess” for the location of any warm & cold core rings in the Gulf of Mexico
  • We then modify the GDEM climatology accordingly
  • If there are real-time AXBTs, we assimilate them too…
airborne expendable bathythermograph axbt
Airborne eXpendable BathyThermograph(AXBT)
  • AXBT drops
  • from a plane
  • and floats on the
  • ocean surface
  • (2) Temperature
  • probe is released
  • and takes
  • measurements
  • as it sinks
  • (3) Surface
  • transmitter
  • relays the ocean
  • temperature
  • profile to
  • the airplane

Images courtesy of US Coast Guard International Ice Patrol

http://www.uscg.mil/lantarea/iip/General/ocean2.shtml

assimilating axbt temperature profiles
Assimilating AXBT temperature profiles
  • When available, we can adjust the shape and position of the Loop Current and rings from the form suggested by altimetry using AXBT profiles
  • This is helpful because altimetry is not perfect…
  • Also, AXBT profiles can be used to define the temperature profile in the core of the Loop Current & rings, rather than relying on the GDEM profile from the source region (i.e. the Caribbean)
  • We call modified initialization “data-assimilated”
  • But how exactly do we “modify” the GDEM climatology to obtain our “data-assimilated” initialization?...
how we modify gdem climatology feature based modeling

Data-assimilated

GDEM

Or… define using real

data: e.g. AXBT 6 for

LC and AXBT 13 (14)

for WCR (CCR)

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

Altimetry

How we modify GDEM Climatology:Feature-based modeling!
  • Start with
  • GDEM
  • Look at
  • altimetry/axbts
  • Define LC &
  • ring positions
  • Use Caribbean
  • water along
  • LC axis & in
  • warm core
  • ring center

Finally, assimilate SST

and integrate ocean

model for 48 hrs for

geostrophic adjustment

  • Make center
  • of cold core
  • ring colder than
  • surroundings
  • Blend features
  • w/ surroundings
slide18

Our feature-based model

Continuous data

assimilation

slide19

Our feature-based model

Continuous data

assimilation

slide20

Our feature-based model

Continuous data

assimilation

slide21

Our feature-based model

Continuous data

assimilation

slide22

Our feature-based model

Continuous data

assimilation

slide23

Our data-assimilated tropical

cyclone heat potential: 9/15/05

Tropical Cyclone Heat Potential:

integrated oceanic heat content from

the surface down to the 26°C isotherm

RSMAS HYCOM’s tropical

cyclone heat potential: 9/15/05

slide24

Tropical Cyclone Heat Potential:

RMS Error for all 18 AXBT locations

GDEM

climatology

RSMAS

HYCOM

Data-

assimilated

operational implementation
Operational Implementation
  • Our feature-based ocean initialization with data assimilation was incorporated into the 2006 operational version of the GFDL model (along with other improvements from 2005)
  • This initialization is now being used operationally in both the GFDL model and the Hurricane WRF model for the 2007 Atlantic hurricane season
intensity errors in recent seasons

We are

improving

this model

at URI…

Note the

reduced

GFDL

intensity

error in

2006!!!

Intensity Errors in Recent Seasons
future work
Future Work
  • Analyze more historical ocean temperature profiles for validation and perhaps further improvements to the initialization procedure
  • Consider using Pressure/Inverted Echo Sounder (PIES) instruments and/or drifters to supplement altimetry and AXBTs for defining the location of fronts (e.g. Loop Current & rings) in real time
  • Extend the feature-based modeling procedure to the western North Pacific Ocean for typhoons and the western Indian Ocean for cyclones
acknowledgements
Acknowledgements
  • Biju Thomas, Yalin Fan, Zhitao Yu (GSO)
  • Aleksandr Falkovich (NCEP)
  • Eric Uhlhorn (HRD)
  • Michelle Mainelli and Stephen Baig (NHC)
  • HYCOM Consortium (RSMAS)
thank you for your time and attention

THANK YOU FOR YOUR TIME AND ATTENTION!

QUESTIONS???

For more information, please go to: http://www.gso.uri.edu/~richard/publications.html

Yablonsky, R. M., and I. Ginis, 2007: Improving the

initialization of coupled hurricane-ocean models

by feature-based assimilation of mesoscale oceanic

features. Mon. Wea. Rev.,135, submitted.