Transcript Hurricane Microphysics: Ice vs Water

Hurricane Microphysics: Ice vs
Water
A presenation of papers by Willoughby et al.
(1984) and Heymsfield et al. (2005)
Derek Ortt
April 17, 2007
Background
• Previous research on TC structure and intensity
has focused on the interaction with the large scale
environment (e.g. Gray 1968, DeMaria 1996, Ortt
and Chen 2007) or TC internal dynamics (e.g.
Schubert et al. 1999 and Kossin et al. 2000)
• Recent work has focused on the inetraction of the
large scale environment and internal dynamics
(e.g. Nong and Emanuel 2003, Lonfat 2004, and
Ortt and Chen 2006)
• The role of microphysics on internal features has
not been well studied (and will be discussed
today)
Objectives
• To determine theoretically the differences
on TC structure of ice vs water
• To determine if observed hurricanes match
the theoretical model
Theoretical Results
(Willoughby et al.)
Model Specifics
• Non-hydrostatic and axissymmetric
• 2km horizontal resolution for inner 100km, 55km from 1001500km from center, 1km vertical resolution
• Governed by following equations
Time Marching Scheme
Computational Grid
Experiments
• W5A: Water microphysics, moist
troposphere
• W5F: Water microphysics, dry troposphere
• I7A: Ice Microphysics, moist troposphere
W5A
W5F
MSLP
MAX
WIND
RMW
MEAN
RAIN
W5F 34HR
WF5 54HR
I7A
MSLP
MAX
WIND
RMW
MEAN
RAIN
44 HR
WF5
I7A
Summary
• The use of ice microphysics produces structures similar to
observed TCs
– Convective rings in the ice microphysical simulations
produce structures and inward propagation similar to
observed TCs
– Downdrafts are caused by melting of ice
– Water microphysics produce fewer convective rings and
faster inward propagation of secondary eyewalls
• Not all convective rings produce a secondary wind
maximum
• Do observed TCs have characteristics similar to these
model results?
Observed Results
(Heymsfield et al.)
Data and Method
• In situ observations from Hurricane Humberto,
part of CAMEX (see Jan, 2006 JAS)
– Particle Size distribution (PSD) probes with 25 and 100
micrometer resolution
– FSSP probe that records data from 3 to 45 micrometers
– Cloud particle imager
– DC-8 Doppler Radar with 60m vertical resolution
• Gamma and exponential functions fitted to the
data
• Only fitted distributions with r2 > .8 used
• Vertical motions determined by subtracting
vertical motions of the DC-8 from the data
FSSP Particle Size Distributions
Imaging Probe Particle Size Distributions
Slope of Fitted Exponential Distributions
IWC
AVHRR Satellite imagery
Ice particles from cloud
particle imager probe on
9/23
9/23
9/25 (0019-0032 UTC)
Frozen
Rain
Slanted lines: Constant IWC
Summary
• Hurricane Humberto had high
concentrations of ice particles
• Supercooled water droplets were confined
to the strong updraft regions
• These updrafts match the results of
Willoughby et al. in the numerical model
simulations