Supervisor: Prof' Ian Simmonds

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Global changes in synoptic activity with
increasing CO2- changes in the SH extratropical
cyclones -
Eun-Pa Lim

• Supervisor Prof. Ian Simmonds
• School of Earth Sciences
• The University of Melbourne

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Acknowledgement

• Many thanks are given to
• MY SUPERvisor Prof. Ian Simmonds
• Kevin Keay, Pandora Hope, Harun Rashid, Richard
  Wardle, Ross Murray, David Noone, Brett Holman
• Drs. John Bye, Kevin Walsh, Ian Smith, Alex Pezza
• Karen, Lyn Bettio, Vaughan, Malek, Belinda,
  Hilary, Jo, Andrew Barker, Tim Carter, Tim Butler
  previous/current PhD and honours students.
• Profs. Andy Gleadow and Janet Hergt, Dr. Malcolm
  Wallace, Helen Russell, Helen Thompson, Richard
  Young, Kerry Hambridge
• Melbourne Univ. Scholarship Office
• Dr. Xingren Wu Antarctic CRC
• Ms. Alison Griffiths

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Introduction

• EXTRATROPICAL
• CYCLONES do
• comprise daily weather
• patterns in the midhigh
• latitudes
  
• 
  
• 
  Australian weather chart on
  16/08/2005
• 
  at 1800 UTC taken from
  http//www.bom.gov.au
• play a key role in the redistribution of the
  atmospheric budgets of heat, momentum, and
  moisture across the globe

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• IPCC 2001 the scientific basis
• global atmosphere temperature 0.6C
• changes in precipitation and atmospheric
  circulations
• Levitus et al. (2000)
• The world ocean mean temperature 0.06C from
  1948 to 1998
• The top layer of 0-300 m 0.31C
• IPCC 2001 CDIAC
• CO2 concentration 90 ppmv (280 ppmv to
  370ppmv)
• Equivalent CO2 concentration 174 ppmv (330
  ppmv to 504 ppmv)

CO2
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Research Questions

• What changes in extratropical low
  pressure/geopotential height systems have
  occurred during the past 20 years?
• If global warming continues, what changes would
  occur in the low pressure/geopotential height
  systems? Do the changes that occur with enhanced
  greenhouse gases have any similarity with the
  observed changes?
• What would be physical mechanisms behind those
  changes?

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Q1. What changes in extratropical low
pressure/geopotential height systems have
occurred during the past 20 years?

• The No. of SH surface cyclones has decreased
  since the 1970s (Key and Chan (1999), Simmonds
  and Keay (2000), Pezza and Ambrizzi (2003), Fyfe
  (2003) )
• The characteristics of surface cyclones such as
  intensity, scale and depth have increased in the
  same period (Simmonds and Keay (2000)).
• The central pressure of MSLP cyclones has
  decreased (Jones and Simmonds (1993), Pezza and
  Ambrizzi (2003)).
• Similar changes have occurred in 500 hPa level
  cyclones (Key and Chan (1999), Keable et al.
  (2002)).

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Q1. What changes in extratropical low
pressure/geopotential height systems have
occurred during the past 20 years?

• Little amount of literature for the 500 hPa level
  cyclones found and tracked individually
• Hardly any studies investigating the mean
  characteristics of interaction between surface
  cyclones and upper level cyclones
• Detecting cyclones in various levels of the
  troposphere and examining the characteristics of
  cyclones at each of the levels.
• Tracing each surface cyclone vertically up to the
  500 hPa level - obtain the mean characteristics
  of the vertical interaction of lower and higher
  level cyclones.

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Q2. If global warming continues, what changes
would occur in the low pressure/geopotential
height systems?

• a decrease of baroclinicity in the lower
  troposphere by weaker temperature gradients
• an increase of baroclinicity in the upper
  troposphere by stronger temperature gradients
• ( Hall et al. 1994, Zhang and Wang 1997)

A latitude-pressure plot of the difference in the
zonal-mean temperature between 2xCO2 and control
experiments. (Taken from Hall et al. 1994 their
figure 1)
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Q2. If global warming continues, what changes
would occur in the low pressure/geopotential
height systems?

• Development of extratropical cyclones is
  driven by strong baroclinicity which is
  characterised by large meridional temperature
  gradient (vertical shear) and low static
  stability.

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Q2. If global warming continues, what changes
would occur in the low pressure/geopotential
height systems?

• An overall reduction of cyclonic activity over
  the SH
• - due to decreasing baroclinicity at the lower
  troposphere
• reduction in meridional temperature
  gradient (Zhang and Wang 1997, Carnell and
  Senior 1998, Sinclair and Watterson 1999, Ulbrich
  and Christoph 1999)
• increase in static stability in the
  Southern Ocean (Geng and Sugi 2003)
• - due to incresing baroclinicity in the upper
  troposphere by pushing the main storm tracks
  poleward (Yin 2005)

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Q2. If global warming continues, what changes
would occur in the low pressure/geopotential
height systems?

• Detecting changes of cyclone features at
  different levels of the troposphere find the
  response of each level cyclone to increasing CO2
• Tracing each cyclone from the surface to the 500
  hPa level through the 850 and 700 hPa levels
  examine any changes in the interaction between
  the vertical levels with enhanced CO2

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Q3. What would be physical mechanisms behind
those changes?

• Conducting idealised experiments modelling
  latitudinal temperature gradients see the
  influence of each of the upper and lower level
  latitudinal temperature gradient change on the
  changes of cyclone features

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Data and Methods

• NCEP-DOE Reanalysis II 6-hourly data (NCEP2)
• - 2.5lat x 2.5lon resolution (T62) 28
  vertical levels
• - MSLP, Z925, Z850, Z700, Z600, Z500, Z400,
  Z300
• - 1979-2000
• The CSIRO MARK2 AOGCM 6-hourly data
• - 3.2lat x 5.6lon resolution (R21) 9
  vertical levels
• - MSLP, Z850, Z700 and Z500
• - CO2 forcing
• gt in the control run equivalent CO2
  330 ppmv

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gt in the transient run historical
increase of equivalent CO2 1
increase per annum
(IPCC IS92a) no further CO2 forcing
(Wu et al. 1999)
3xCO2
STAB
22 year time slice 2xCO2
Equivalent CO2 concentration used in the CSIRO
Mark2 transient model
1xCO2
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• The Melbourne University AGCM
• - 3.3lat x 5.6lon resolution (R21) 9
  vertical levels
• - mslp, Z850, Z700 and Z500
• - equivalent CO2 330 ppmv
• - 20 year simulation for the control
  experiment
• 8 year simulation for the transient
  experiments

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• The Melbourne University cyclone finding and
  tracking scheme (Murray and Simmonds 1991,
  Simmonds et al. 1999)
• Cyclone Features
  
• System Density the mean number of cyclones
  
• found in
  a 103( lat)2

Intensity ?2Z (m/( lat)2)
?2Z0
Radius ( lat)
Depth (m)
Depth 0.25intensityradius2
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Results
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NCEP2Mean characteristics of cyclone system
density and depth

• The No. of cyclones tends to decrease as the
  height increases up to the 850 hPa level but
  increase again above that level
• Cyclone depth increases with height

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• NCEP2
• Climatology of MSLP cyclone frequency

System Density
Depth
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• NCEP2
• Climatology of Z500 cyclone frequency

System Density
Depth
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NCEP2Trends in the SH winter cyclone properties
in 1979-2000
statistically significant at the 95 c.l.
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CSIRO Mean changes in SH winter cyclone features
with increasing CO2
System Density
Depth
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CSIRO Spatial distribution of MSLP cyclone
features between 2xCO2 and 1xCO2 experiments
System Density
Depth
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CSIRO Spatial distribution of Z500 cyclone
features between 2xCO2 and 1xCO2 experiments
System Density
Depth
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• MSLP Cyclone System Density

NCEP2 (1979-2000)
CSIRO (2CO2-1CO2)
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MSLP Cyclone Depth
NCEP2 (1979-2000)
CSIRO (2CO2-1CO2)
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Z500 Cyclone System Density
NCEP2 (1979-2000)
CSIRO (2CO2-1CO2)
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Z500 Cyclone System Density
NCEP2 (1979-2000)
CSIRO (2CO2-1CO2)
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(No Transcript)
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• Vertical organization of cyclones
• Vertical tracking

500

600

700

444 km
850

925

MSL
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Vertical structure of cyclones NCEP2

• -The vertically organized (MSL-500) cyclones
  have
• stronger intensity
• larger scale
• greater depth
• longer lifespan
• slower movement
• than the shallow structured
• (MSL-700) ones
• (99 confidence level).

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• Vertical structure of cyclones NCEP2
• About 36 of SH winter surface extratropical
  cyclones have vertically well organized structure
  connecting to Z500 cyclones

Ratio of vertically well organized cyclones to
the entire population of extratropical cyclones
in JJA (in )
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• Vertical structure of cyclones NCEP2
• The ratio of these kinds of cyclones has
  increased by
• 0.26 per annum from 1979 to 2000
• 
  (99 confidence level)

Time series of the ratio of the number of well
organized cyclones to the entire mslp
extratropical cyclones in JJA 1979-2000
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Vertical structure of cyclones NCEP2
- Mean distance between mslp and Z500 cyclones
centres
- This has decreased with the rate of 2 km per
year (99)
Z500
mslp
384 km
Time series of the average distance between Z500
and mslp cyclones in 1979-2000
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Vertical structure of cyclones CSIRO

• - About 50 of SH winter surface extratropical
  cyclones from the control run have vertically
  consistent depression connecting up to the 500
  hPa level.
• - The ratio of these kinds of cyclones increases
  
  with increasing CO2.

Ratio of the number of well organized cyclones to
all mslp extratropical cyclones in JJA
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Vertical structure of cyclones CSIRO
- Mean distance between the mslp and Z500
cyclones centres
- This decreases with increasing CO2 (95c.l.)

Z500
mslp
450 km (in the control run)
Averaged distance between Z500 and mslp cyclone
centres
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Temperature nudging experiments
A latitude-sigma level plot of the difference in
22 year averaged zonal-mean temperature between
2xCO2 and the control experiments from the CSIRO
Mark2 Model
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• Three experiments introducing temperature warm
  anomaly at the locations where CSIRO model shows
  warm anomalies

Tropics at 330 hPa High latitudes at 990 and
925 hPa TUHL
Tropics at 330 hPa TU
High latitudes at 990 and 925 hPa HL

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Comparison of the zonal averages of Z500 cyclone
features between the CSIRO and MUGCM models
System Density CSIRO GCM
MUGCM
65S 52 S
74S 54S
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• Depth
• CSIRO GCM
  MUGCM

61S 41S
61S 51S

• Increase of vertically well organized cyclones
  a decrease of the distance between mslp and Z500
  cyclones Tropical warming in the upper
  troposphere (TU)
• SH surface cyclone features
• HL warming - in the reduction of high latitude
  cyclones
• TU warming in the reduction of midlatitude
  cyclones

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Concluding remarks

• SH winter extratropical cyclones have been fewer
  in their number, but deeper in their maximum
  depth for the last two decades.
• Overall similarities in the changes in cyclone
  system density and depth simulated with doubled
  CO2 to the observed trends
• Increased greenhouse gases could result in
  further changes in extratropical cyclones in the
  future
• Cyclones have been vertically better organized in
  the observation
• Cyclones are vertically better organized as CO2
  increases
• More extreme weather events in the mid and high
  latitudes in the next centuries
• Latitudinal temperature gradients in the upper
  troposphere over the tropics appear to be
  responsible for the changes in Z500 cyclone
  features in the SH and the vertical structure of
  surface cyclones.

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• Thank you for your attention,
• Thank you for having me _at_ BMRC,
• and
• Thank you for your non-difficult questions in
  advance!!