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Shuyi S. Chen and CollaboratorsRosenstial School of Marine and Atmospheric Science
University of Miami
Recent Research on Hurricane Intensity
In the eye of Katrina
Hurricane Maximum Potential Intensity (MPI)Emanuel (1988), Holland (1997), …..
MPI = f { (Ck/CD), ε, SST, RH }
ε = (TB – TO)/TB (thermodynamic efficiency)
Ck and CD are exchange coefficients of enthalpy and momentum fluxes
Why most hurricanes do not reach their MPI?
Factors Controlling Intensity Change
Inner core (eye and eyewall) dynamics
Environmental conditions, including vertical wind shear, moisture distribution, and sea surface temperature (upper ocean heat content), etc.
• Inner core and rainband internactions• Concentric eyewalls and eyewall
replacement cycle
Hurricane Internal Dynmaics
• Vertical wind shear• Moisture distribution
Environment Rainbands Inner Core
Hurricane Rainband and Intensity Change Experiment (RAINEX)Houze, Chen, and co-authors (2006, BAMS)
• Ocean surface waves• SST and upper ocean
Atmosphere-Wave-Ocean Interactions
Coupled Boundary Layer Air-Sea Transfer (CBLAST)Chen et al. (2006, BAMS)
Schematic Reflectivity Structure(Hugh Willoughby)
Eyewall Replacement
RAINEX Science ObjectivesUse airborne observations to examine simultaneously the dynamic and thermodynamic structures of hurricane inner core and outer rainband regions where the positive potential vorticity associated with deep convective cores are located.
Use numerical model to investigate the interactions of the rainbands and primary hurricane vortex circulation and their role in hurricane intensity change.
•Use airborne Doppler radar to observe both eyewall and rainband internal vorticity structures simultaneously
•Use intensive dropsondes for thermodynamic environment of hurricane rainbands and eyewall to support both analysis and modeling/forecasting
•Use model to determine how the vorticityfeatures evolve and storm intensitychanges
Approach:
RAINEX is the first experiment using three-Doppler-aircraft flying in hurricanes.
High-Resolution Multi-nested Vortex-Following Numerical Models at University of Miami:
• UM/RSMAS Coupled Atmos-Wave-Ocean Model
• Weather Research and Forecast (WRF) Model
Katrina Ophelia Rita
8/27
8/28
15 km
1.67 km 5 km
45 km
9/19
9/22
9/23
9/21
9/20
21-sep-2005, 19:00:00
ELDORA composite reflectivity in Rita from 22 September 05
22 September 2005
Innerouter
22 September 2005
Inner outer
Innerouter
Inner
outer
N43 flight-level wind in Rita
Hurricane Rita (2005)
CBLAST-Hurricane Coupled Atmosphere-Wave-Ocean Modeling
Objective - To develop air-sea coupling parameterizations for fully coupled, high-resolution atmosphere-wave –ocean modeling systems for hurricane prediction. • Wind-Wave Coupling• Effects of Sea Spray• Atmosphere-Ocean Coupling
ATMOS. MODEL(MM5/COAMPS/WRF)
OCEAN MODEL(HYCOM or 3DUOM)
WAVE MODEL
(WAVEWATCH III or WAM)
Roughness lengthW
ind-induced stress
Surface fluxes
SST
SSH
& cu
rrent
velo
city
Wav
e-In
duce
d stre
ss
Coupled Atmosphere-Wave-Ocean Modeling System for Hurricane Predictions
Emanuel (1995):•Axisymetric model,•Bulk PBL•Use gradient wind
Questions in Atmos-Wave-Ocean Coupling:1) What are Ck and CDin high winds?2) What is the ratio of Ck and CD in hurricanes?
Ocean surface waves in Hurricane Frances (2004)
Hurricane Frances (2004)
CDCD
CkCk
RL RL
RR RRFR FR
FL FL
Hurricane Frances (2004)
Observation
Coupled Model
Obs Coupled model
Conclusions
To improve hurricane intensity forecast, we need
High-resolution (~1 km) to resolved the inner core
Fully coupled atmosphere-wave-ocean models
Accurate initial and lateral boundary conditions (data assimilation, etc.)