Extratropical cyclone - RTC, Regional Training Centre - Turkey

EUMETSAT
Monitoring weather, climate
and the environment
Dr. Jochen Kerkmann
Satellite Meteorologist
Training Officer

Medicanes: case study of a Tropical Storm in the
Mediterranean
Objective:
blur that (once-perceived) fine line between
tropical and extratropical cyclones

Motivation
Jack Beven (Tropical Prediction Center, Miami, 2002)
People don't normally use 'The Mediterranean Sea' and
'hurricane' in the same breath. However, on rare occasions
the Mediterranean has seen cyclones that resemble tropical
storms or hurricanes.
Such system occurred in September 1947, September 1969,
January 1982, September 1983, and January 1995.

16 Jan 1995 07 Oct 1996
27 May 2003 15 Dec 2005
From Fita et al, 2007

“Tropical storm-like MCS in the Mediterranean”
MSG, 18 Oct 2007, 12:00 UTC
Email from Kornel Kollath (OMSZ)

Terra MODIS
18 Oct 2007, 09:50 UTC

Loop 07:30 – 15:45 UTC

Tropical Cyclones: the four major cloud
patterns
Système en bandes
incurvées
Système cisaillé
Curved
band pattern
Sheared pattern
Système à masse
nuageuse centrale
dense
Système à
oeil
From:
Philippe Caroff
(Meteo France)
CDO pattern
Eye pattern

Shear pattern examples (westerly flow)
Source: Philippe Caroff (Meteo France)
TC TC BINDU BINDU ::
IR IR +ERS +ERS windfield windfield
15/01/2001 15/01/2001 at at 1841Z 1841Z (above) (above)
16/01/2001 16/01/2001 at at 0547Z 0547Z (right) (right)

Shear pattern examples (easterly flow)
Source: Joint Typhoon Warning Center
1 Nov 2007, 05:30 UTC
23 Oct 2008, 05:30 UTC

17 October 12:00 UTC
500 hPa Geop. + Temp. Surface Pressure
from Kornel Kollath (OMSZ)

18 October 12:00 UTC
500 hPa Geop. + Temp. 500 & 1000 hPa Geop.
W

Hurricane Gustav (for comparison)
W
1 Sep 2008, 00:00 UTC: 500 hPa Geop. + Temp. (ECMWF)

Classic warm-core cyclone
AMSU-based
temperature
anomaly in
Hurricane Bonnie
(1998)
Source: Mark DeMaria (CIRA)

NOAA, 26 January 1982
• The simulated cyclone
possessed a warm, dry
core, which extended to
400 mb, with a structure
similar to that of a tropical
cyclone.
• The surface energy fluxes
are found to be crucial for
the mesoscale
cyclogenesis
From Kuo et al., NCAR

NOAA, 27 March 1999
From Meneguzzo, Italy

Met-5, 07 October 1996
Similar in their scale, satellite
imagery, precipitation rates,
wind strength, vertical
structure and the
cyclogenetic process to
tropical cyclones that
develop outside the tropical
atmosphere
Importance of surface fluxes !
From Reale and Atlas, 2001

Most outstanding Medicane case ?

Loop 14-17 January 1995

Terra MODIS
15 Dec 2005, 11:25 UTC, True Colour RGB

Met-9, 26 September 2006, 15:00 UTC
RGB Airmass
HRV Channel
From Miglietta et al., 2008
Surface pressure
Radar reflectivity at 9:23 UTC

MSC/COMET NORLAT Workshop October 2006
Hurricanes:
From mid-life crisis to death with a
focus on the afterlife
Robert Hart
Department of Meteorology
Florida State University
rhart@met.fsu.edu
http://moe.met.fsu.edu

Contents
1. Hurricane basics
2. Cyclone phase space
3. Baseline lifecycles
4. Nonconventional lifecycles
4.1 Tropical to Extratropical: Warm-core
symmetric to cold-core asymmetric
4.2 Extratropical/subtropical to tropical transition
…

Structural transition
• Tropical and extratropical cyclones historically have
been viewed as two discrete, mutual exclusive
cyclone groups
• Warm SSTs, increased surface fluxes, enhanced
convection, enhanced latent heat release & warmseclusion
within extratropical cyclones can blur that
once-perceived fine line between tropical and
extratropical cyclones

Classic warm-core cyclone: TC
Intensifies through: sustained convection, surface fluxes.
Cyclone strength greatest near the top of the PBL
Stratosphere
Cold
- +
Z
Troposphere
W
a
r
m
L
Height perturbation

Classic cold-core cyclone: extratropical
Intensifies through: baroclinic development, tropopause lowering.
Cyclone strength greatest near tropopause
Stratosphere
Warm
Cold
- +
Z
Troposphere
Cold
Warm
L
Height perturbation

Hybrid (non-conventional) cyclone
What if an occluded extratropical cyclone moves over warm water?
Characteristics of tropical and extratropical cyclones.
- +
Stratosphere
Warmer
Z
Troposphere
Colder
Warmer
L
Height perturbation

Extratropical Transition (ET)
The conversion of
Tropical cyclone to Extratropical cyclone
symmetric to asymmetric
nonfrontal to frontal
warm-core cyclone to cold-core cyclone
energy source
energy source
surface fluxes
convection
baroclinicity
QG dynamics

ET example
5 Aug 6 Aug 7 Aug
Tropical Phase Transformation Phase Re-Intensification Phase
Hurricane Alex makes the transition from a category 3
hurricane to an extra-tropical cyclone (5-7 August 2004)

See CAL module !
Verification
Hurricane Alex 2004

Extratropical to tropical transition
The conversion of
Extratropical cyclone to Tropical cyclone
asymmetric to symmetric
frontal to nonfrontal
cold-core cyclone to warm-core cyclone
energy source
energy source
baroclinicity
QG dynamics
surface fluxes
convection

NOMEK Course, Iceland, May 2009
Potential Vorticity (PV) in Weather Forecasting
Bjoern Roesting
Met.no

Max. winds at
tropopause level

Max. winds at
surf. level

Example: Hurricane Olga 2001
1800 UTC 24 November
1800 UTC 27 November

Verification
Hurricane Olga 2001

Example: Hurricane Vince 2005
8 Oct, 12:00 UTC 9 Oct, 12:00 UTC

Verification
Hurricane Vince 2005

Example: Hurricane Epsilon 2005
5 Dec, 06:00 UTC

Example: Hurricane Epsilon 2005
29 Nov/00:00 Z 29 Nov/12:00 Z
30 Nov/00:00 Z 30 Nov/18:00 Z

Example: “Comma Cloud” over the Atlantic
2 June 2009, 18:00 UTC

Example: “Comma Cloud” over the Atlantic
2 June 2009, 18:00 UTC, Showalter Index

Example: Tropical Storm Grace 2009
Met-8 5-min loop
Met-9 15-min loop
Met-9 60-min loop
1 Oct 2009, 18:00 UTC, Met-9, Airmass RGB

Example: Tropical Storm Grace 2009
5 Oct 2009, 10:25 UTC, Metop-A, AVHRR, RGB Ch134

Example: Tropical Storm Grace 2009
6 Oct 2009, 16:45 UTC, Met-8, HRV

Example: Tropical Storm Canaries 2010
RGB Ch124
RGB Ch134
2 Feb 2010, 10:46 UTC, Metop-A AVHRR

Example: Tropical Storm Canaries 2010
Met-9 HRV loop
Met-9 Dust RGB loop
6 Oct 2009, 16:45 UTC, Met-8, HRV
2 Feb 2010, 12:00 UTC, Met-9, Airmass RGB

Verification
6 Oct 2009, 16:45 UTC, Met-8, HRV

Special case: warm seclusion
Warm seclusion:
• the trapping of warm air near cyclone center as
a result of explosive development
• usually limited to below approx. 600 hPa

Double Bomb storm 2003
Extratropical cyclone that undergoes two periods of extremely rapid
intensification, leading to a warm seclusion of astonishing intensity.
Minimum pressure of 924 hPa with a drop of 55 hPa in 24 h. Deepest
Atlantic non-tropical low since Braer storm of 1993 (916hPa).

Verification
Double Bomb 2003

Back to case study

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Analysis of vorticity maxima
J. Kerkmann
P. Chadwick X X
09 Oct 2007, 12:00 UTC

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10 Oct 2007, 12:00 UTC

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Without animation… can’t be sure but I wonder whether the X is a bit slower than you position. This is
based solely on the cyclonic curvature of the moisture bands. :>) Phil
10 Oct 2007, 18:00 UTC

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11 Oct 2007, 18:00 UTC

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12 Oct 2007, 12:00 UTC

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13 Oct 2007, 12:00 UTC

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Phil: I think the convection is reforming the PV… latent heat release should lower the hgts around the PV anomaly
This increases the circulation at trop level. I think that is how it works.
It appears as though the X has made a right turn toward the convection.
14 Oct 2007, 12:00 UTC

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Phil: I am trying to place the main X between the cyclonic cusps.
The eastern cusp is not as clear as I would like.
15 Oct 2007, 12:00 UTC

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Phil: the x is in the middle of the convection.
Pointing at it with the arrow.
16 Oct 2007, 12:00 UTC

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Phil: the red x is in the middle of the convection
with good cyclonic curvature.
17 Oct 2007, 12:00 UTC

Summary
• No strict line between tropical and extratropical cyclones:
transitions in both directions possible
• Strong surface fluxes over relatively warm sea can turn a
quasi-stationary cut-off low to a hurricane-like cyclone
• Generally, small horizontal scale, but
• Can reach Hurricane strength (Saffir-Simpson scale 1);
strong surface winds
• Typical period: autumn and winter
• Name problem: Medicane or Tropical Storm/Cyclone?
• Warning Centre for Mediterranean Sea needed! =>
Medicanes should get a name

Thank you for your attention
More information: www.eumetsat.int

Official TC Centres
From: WMO Severe Weather Information Centre

Quiz: Separate the 5 tropical cyclones from the 5 extratropical
Images
courtesy NCDC