Cyclone Classification: Internal Structure versus Energetics - An aplication to the Catarina Event....
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Cyclone Classification: Internal Structure versus Cyclone Classification: Internal Structure versus Energetics - An aplication to the Catarina Event. Energetics - An aplication to the Catarina Event.
Pedro Leite da Silva DiasNational Laboratory of Scientific ComputingMinistry of Science and TechnologyInstitute of Astronomy, Geophysics and Atmospheric Sciences University of São Paulo (USP)
LllLll Encontro internacional sobre ciclones do atlântico sul, previsão de trajetórias e avaliação de riscos
Rio de Janeiro, 19 a 21 de maio de 2008
Classical view:
But, on March 28 2004 …..
From Gan and Rao 2006
Pezza and Simmonds, 2005
03 UTC 22 March 03 UTC 23 March
03 UTC 24 March 03 UTC 25 March
0/ UTC 26 March 15 UTC 27 March 15 UTC 28 March15 UTC 26 March
15 UTC 2 March15 UTC 24 March
15 UTC 22 March 15 UTC 23 March
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How about satellite derived precipitation?
GOES/TRMM
(R.Gevaerd
27 March 2004 11 Z
5-8km
Vertical structure
Q
Relative humidity - shadedPotential temperature (isolines)
From Bonatti et al. 2006
Q
FF
From Bonatti et al. 2006 Relative humidity - shadedPotential temperature (isolines)
Relative humidity - shadedPotential temperature (isolines)
From Bonatti et al. 2006
Vertical Structure - FSU
http://www.moe.met.fsu.edu
Low troposphere vertical shear (warm x cold core)
Upper troposphere vertical shear
symmetry
Hart 2003 - Cyclone Phase
AVN – ANALYSIS
uppertroposphere
lower troposphere
CIRA AMSU retrieval
uppertroposphere
lower troposphere
Cross section at 29.3S
00Z28Mar2004
Q1
Q2
EYE
EYE
NCEP – High resolution GFS analysis
50km
Surface Fluxes
Sensible Heat Flux Anomaly
Surface
Latent Heat Flux Anomaly
Surface
How about the numerical guidance from the operational models?
162 h 136h 114h
CPTEC ETA forecast at 06 UTC 28 Mar 2004
90 h 66h 42h
CPTEC ETA forecast at 06 UTC 28 Mar 2004
Does increased resolution improve the numerical results?
BRAMS• Version 3.0
– Based on RAMS 5.04 – Maintained by CPTEC– Particular features:
• Shallow Cumulus Parameterization • Deep cumulus parametrization – “Grell-Ensemble”• Initialization of soil moisture• Option for surface processes: LEAD and SIB2 (with Carbon)• Surface data assimilation with internal quality control• CATT – dispersion module for gases and aerosols produced by
biomass burning and urban sources
• 2 grids: 32 km and 8 km (with cloud microphysics) – Previous experiments by Menezes et al. 2004- CBMET
3h Precipitation BRAMS at 8km resolution
SST Anomalies – High Resolution data -20km
Warm pools detached from Brazil Current are common but this one can’t be tracked …
This warm area may be important..
Effect of high
Resolution SST:
less intense system !!!!
See Renato Silva 2004 -XIIICBMet
Impact of perturbation in the latent heating vertical profile
2 fo2 2
p2 tfoV
g
2
fo+ f
f o2
R
p
V g T
pf o2
R
cp
pJp
Geopotential tendency is proportional to the vertical derivative of the diabatic heating
Possible Trajectories with perturbed convective heating
Better fit to obs
Better fit to obs
Summary
• Do tropical cyclones belong to a unique family?
• OR are we artificially separating a continuum of atmospheric vortices into groups?
• In Australia: subtropical lows with hurricane intensity winds
ENERGETICS
Brennan e Vincent (1980)
αω−=dt
dTCpQ
Cyclone tracking:
At each time, energetics at the box is computed
NCEP GFS operational Analysis (high resolution 50km) of Catarina
Other peculiar cases….
Typical baroclinic system…
Note large baroclinic conversion and increase of Ke
Increase of Ke also related to barotropic conversion
Small contribution of Q’T
This is the previous cyclone yesterday .ppt
Initial phase is typically baroclonic Latent heat picks up
later…
Strong energy conversion
Barotropic conversion from Ke to Kz except at the end
Ciclone off the S coast of Brazil - 13/Feb/2008
An interesting case of a schizophrenic cyclone…
(Santis et al. 2008)
Ciclone 31/12/2007
•Early moist baroclinic phase
•Latter barotropic conversion
Low predictability case:
Small Q’T
Ke->KZ
Typical barocliniic conversion
See www.master.iag.usp.br/intercomp
Conceptual view of the energetics
Q’T’
V’T’dU/dy
u’v’dU/dy KZ -> KE
barotropic
baroclinic
Bomb cyclone
Hurricane
Tropical storms
Few (hybrid)
most
AZ ->AE
Conclusions- I
•Vertical profile of diabatic heating in operational models is too high: global and regional
•Downscaling also lead to heating at higher levels: not enough pressure drop at low levels and therefore models underestimated the wind speed;
•Perturbations in the vertical heating profile lead to intensification of the system: in one case the trajectory was substantially changed – the low pressure veered to the north and eventually reached the Rio de Janeiro coast
•Energetics: early phase follows typical evolution of cold moist baroclinic perturbation. Later phase: barotropic conversion + moist conversion (not large).Hybrid system –subtropical low with hurricane intensity (1) at the end.
Recommendations• Need objective classification system for hybrid systems such as Catarina: energetics is a possible choice;
•The workshop organized by the Brazilian Meteorological Society
•Articulated solution with WMO should be sought in order to improve classification of cyclones (according to the WMO manual: hurricanes are non frontal structures…) , personnel training and dissemination of the information. - IWTC Costa Rica Nov. 2006
• recommended that in spite of the hybrid structure of the cyclone, if another case arises in the future, it is recommended that the systems be called “hurricane” when the estimated wind speed falls in the category I. This recommendation is based on the fact that the public perception that this type of event is significantly different from the regular extratropical and subtropical lows that regularly reach the southern part of Brazil