L. Stefanova,T. N. Krishnamurti, S. Pattnaik, L. Ramaswamy

Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
L. Stefanova, T. N. Krishnamurti, S. Pattnaik, L. Ramaswamy
Department of Meteorology,
Florida State University
Tallahassee, Florida
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Objective
Can an energetics aproach provide insight into
hurricane intensification?
What are the roles of the azimuthal mean,
asymmetry and cloud scales for hurricane
intensification?
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Motivation: Mean to Waves Kinetic Energy
Exchange (Felix 2001, genesis stage)
Kinetic energy mean to asymmetry
+
Asymmetric circulation gaining
energy from mean circulation
Kinetic energy mean to cloud-scale
Mean circulation gaining
energy from cloud-scales
–
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Katrina simulation
• Gridded observed data not available at
sufficient resolution (few kilometers);
therefore using model output
• NCAR PSU MM5 model: triply nested
(18km, 6km and 2km) two-way
interactive grid.
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Tangential wind:
θ
Defining Scales
r
• 
Size of analysis
the scaleinofthe
wave
numberdirection:
n at radiusf(θ,r)=Σ
R:
Fourier
azimuthal
Fn(r)einθ for tangential
S(R,n)=
π R/n
and radial wind, vertical velocity,
and temperature
• n=0: Azimuthal
Note that atMean;
different radii the same n corresponds to scales of different size
• 
If the smallest resolvable scale is Sres, the largest n adequately resolved is at
n=1, n=2: Large Scale Asymmetry;
most
n=3 and larger: “Cloud Scales” n (R)= π R/S
max
res
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Schematic of Energetics
Fa
Ka
K0
F0
Fc
Pa
Kc
K: Kinetic energy
P: Available potential energy
H: Heating
F: Friction
P0
Ha
H0
Pc
Hc
Scale indicated by subscript:
0: Azimuthal mean (wave number 0)
a: Asymmetry (wave numbers 1,2)
c: “Cloud scales” (wave numbers 3 and higher)
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Tangential wind component (spectral power) m2/s2
t
r
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Radial wind component (spectral power) m2/s2
t
r
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Vertical velocity component (spectral power) Pa2/s2
t
r
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Pa  P0
Pc  P0
Units: 10-4m2/s3
Pc  Pa
Pa
Pa
t
r
P0
Pc
P0
Pc
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
P0 K0
Pa Ka
Units: 10-4m2/s3
Pc Kc
Ka t
K0
Kc
Ka
K0 r
Kc
Pa
P0
Pc
Pa
P0
Pc
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Ka K0
Kc Ka
Kc K0
Units: 10-4m2/s3
Ka Ka
t
K0 r K0
Kc Kc
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
dK0/dt (energetics)
dK0/dt (energetics, time mean removed)
dK0/dt (centered differences)
t
r
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Summary
Pa
Ka
K0
Inward of maximum
winds
P0
Kc
Pc
Ka
Vicinity of maximum
winds
Pa
K0
Kc
P0
Pc
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Conclusions
•  Energetics can provide
reasonable indication of
hurricane intensification
•  In-scale conversion of potential
to kinetic energy is the
dominant contributor to kinetic
energy growth at the scale of
the mean
•  Near the radius of maximum
winds the asymmetry and cloud
scales act as sink for both
potential and kinetic energy of
the mean flow
questions? comments?:
•  Inwards of the radius of
maximum winds the asymmetry
and cloud scales act as a
source for the kinetic energy of
the mean flow
•  The kinetic energy budget
residual might indicate possible
unresolved cloud-scale-tomean kinetic energy transfer in
the region of maximum winds
•  Need to test on observed data!
stefanov@met.fsu.edu
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity
Units: 10-4m2/s3
Advection of K0 by mean
Interaction of Hurricane and Cloud Scales: Contribution to Hurricane
Intensity