The impact of stratospheric ozone depletion and CO
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The impact of stratospheric ozone depletion and CO 2 on AAO trends and regional climate change at surface of Southern Hemisphere. Syktus J., I. Smith 2 , G. McKeon 1, M. Dix 2 & W. Cai 2 1 Department of Natural Resources, Mines and Energy, Brisbane, Australia

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The impact of stratospheric ozone depletion and CO2 on AAO trends and regional climate change at surface of Southern Hemisphere

Syktus J.,I. Smith2, G. McKeon1, M. Dix2 & W. Cai2

1Department of Natural Resources, Mines and Energy, Brisbane, Australia

2CSIRO Atmospheric Research, Melbourne, Australia


Motivation

  • the source of observed 20thC trends in the SAM is a matter of scientific debate with stratospheric ozone losses, greenhouse gas increases and natural variability all possible players

  • my motivation is from practical point of view; does it influence regional climate trends and change

  • since it is difficult to separate the contribution of these various forcings in the observed record, a global climate model has been used


Southern hemisphere annular mode discussion
Southern Hemisphere Annular Mode - Discussion

  • It is a dominant mode of low frequency variation of the SH circulation. Characterized by zonally symmetric fluctuations in the extra-tropical atmospheric circulation that extends from surface to the stratosphere

  • The observation show that AOO index has trend towards a positive values since the late 1970s, coincident with occurrence of ozone depletion (Marshall 2003)

  • The issue here is whether AGCM forced with observed SST and radiative forcing factors such as CO2 & O3 can simulate the trends in surface MSLP and other surface characteristics at regional scales

  • Climate models forced by changing CO2 or by decreasing stratospheric ozone usually show a trend in the SH annular mode.

  • Still an open question how good a representation of stratosphere is needed to accurately model tropospheric climate and climate change, however link to stratosphere is not essential for MSLP to have SH annular mode like response


Martin Visbeck

Todd Mitchell


Problem and approach
Problem and approach

  • During the past decade large parts of eastern Australia experienced unprecedented and persisting drying trends

  • Drying trends in eastern Australia in recent decades  Water supply restrictions in major cities of Eastern Australia

  • Identification of possible forcing factors; GHG,O3, land cover change …

  • Limitations of the approach

  • Review of the current state of knowledge

  • Simulation results and discussion


Rainfall relative to historical records australia july 1992 to june 2003
Rainfall Relative to Historical Records Australia– July 1992 to June 2003

Percentiles

Red = Last 10 years are in the bottom 10% of all previous ten July to June year periods from 1890


Trends in annual rainfall expressed in terms of the trend correlation coefficient r not b
Trends in annual rainfall expressed in terms of the trend correlation coefficient (r, not b).

1952 to 2002

MJJASO

1952 to 2002

Annual

1952 to 2002 NDJFMA


All-Australian annual rainfall indices correlation coefficient (r, not b).

(a)area-averaged total, mean=461

1974 1902

2000 1905

1973 2002

1950 1961

1956 1994

r(SOI)=0.50

(b)area-averaged mean decile value

1974 1905

1973 1928

2000 1961

1975 1994

1917 2002

r(SOI)=0.44


  • Despite 2002 being one of the driest years on record, Australia appears to have become wetter

  • This positive trend in NW Aus appears because of relatively wet years in the second half of the record (e.g.1974, 2000).

  • The chances of these trends arising due to random fluctuations of the data are about 5%

  • We do not know:

  • where the trends have occurred

  • if there are any compensating negative trends

  • which seasons are involved


Second dominant EOT of Australian Observed Rainfall - S2 Central west (15%)

S2represents variability over that potion of the continent where rainfall stations are most sparse. It is possible that T2 may be dominated by the relatively small number of stations whose effect has been interpolated over large distances. (Smith 2004)

T2 has also positive & statistically significant trend during the 1900-2002 period, strongest over the past decade

NDJFMA


Summary Central west (15%)

  • Increases in all-Australian annual rainfall over the past 100 years are the result of increases in summer rainfall over much of the western half of the continent over the past 50 years.

  • The magnitude and pattern of the increases appears unusual and unlikely to be the result of “natural variability”.

  • It is not possible to describe winter rainfall trends as unusual.

  • Increases in summer rainfall have been suggested as a response to increased greenhouse gases.

  • Temperatures have risen substantially over both Australia and the Indian Ocean over recent decades.

  • These may be linked to the rainfall changes.

  • These may, in turn, be attributable to EGG - but earlier than expected.


March 2002 Rainfall Forecast Central west (15%) for July to September

IRI Net Assessment ForecastsNR&M contributes NCEP model output at monthly intervals to IRI consensus forecast since late 1998

  • Forecast skill assessment (Goddard et al., 2004, BAMS)

http://iri.columbia.edu/climate/forecast/net_asmt/



Gladstone and Gold Coast water restriction in place for number of years now.

December: 21 NSW

towns required

water carting

Canberra: First

water restrictions

since 1966

Melbourne: First

water restrictions

since 1982

Follows a 6-year

dry spell in southern

Australia

Water Storages Levels

Gladstone

Gold Coast


Natural annual flows into hume weir mdbc
Natural Annual Flows into Hume Weir (MDBC) number of years now.

Lowest 4-year period on record

Natural Annual Flows into Hume Weir (MDBC)


Csiro mk3 agcm model

CSIRO Mk3 AGCM Model number of years now.

• Atmosphere

Grid: T63 (1.88o x 1.88o) 18 levels - hybrid ,p with top at 4.5 hPa (~ 36 km)

Semi-Lagrangian moisture transport

UKMO convection (Gregory & Rowntree)

Liquid water clouds (Rotstayn)

• Land surface

Soil model - 6 levels

Temperature, water, ice

9 soil types

13 land surface and/or vegetation types

Snow-cover model - 3 layers


Csiro t63 l18 c20c experiments
CSIRO T63/L18 C20C Experiments number of years now.

  • 5 runs: 1949-2003 SST only

  • 5 runs: 1961-2003 SST and O3

  • 5 runs: 1871-2003 SST only

  • 5 runs: 1871-2003 SST and solar

  • 5 runs: 1871-2003 SST, solar and CO2

  • 5 runs: 1961-2003 SST, solar, CO2 and O3

  • 10 runs: 1949-2003 SST, solar, CO2 and O3 in progress


Ozone scenario used in csiro agcm simulations
Ozone scenario used in CSIRO AGCM simulations number of years now.

Observations


Ozone recovery projections
Ozone recovery projections number of years now.


Trends in the Southern Hemisphere annular mode in CSIRO Mk2 transient greenhouse runs reverse when the forcing is stabilised. However, this may take several centuries to take place, depending on the emission scenario used.


CSIRO Mk2 Model, Warming Run transient greenhouse runs reverse when the forcing is stabilised. However, this may take several centuries to take place, depending on the emission scenario used.


Correlation between the AAO and JJA Rainfall transient greenhouse runs reverse when the forcing is stabilised. However, this may take several centuries to take place, depending on the emission scenario used.

CSIRO Mk2 Model, greenhouse run, showing when the AAO goes up

rainfall over SWWA decreases, and vice-versa!


MSLP change in Mk 3 transient greenhouse runs reverse when the forcing is stabilised. However, this may take several centuries to take place, depending on the emission scenario used.

JJA

DJF

SON

MAM

ANN


SAM transient greenhouse runs reverse when the forcing is stabilised. However, this may take several centuries to take place, depending on the emission scenario used.

SWWA Rainfall

Winter

Spring










Trends in the sam impact on antarctic temperatures
Trends in the SAM: impact on Antarctic temperatures AGCM

Time series of the SAM based on NCEP-NCAR

Z850 data and Z500 Antarctic radiosonde data

(Thompson & Solomon, 2002). Data are normal-

ized to 1968-98.

Source: Todd Mitchell (http://tao.atmos.washington.edu/aao/)

Regression of Antarctic surface

temperature anomalies vs unit

change in the SAM, 1982-98.

(Kwok & Comiso, 2002)


Response of surface temperature
Response of surface temperature AGCM

Warming over Antarctic Peninsula and cooling over Eastern Antarctica seen in both CO2 and O3 forcing, but stronger in O3


Response of surface temperature1
Response of surface temperature AGCM

DJF 1993-2003 cooling over Eastern Australia due to CO2 effect and an opposite effect when O3 is added


Response of precipitation
Response of precipitation AGCM

NDJFM 1993-2003 wetter over Eastern Australia due to CO2 effect and an opposite effect when O3 is added, follows from surface temperature changes in previous slide. SPCZ changes


Response of jja precipitation
Response of JJA precipitation AGCM

JJA 1993-2003 weaker Asian monsoon due to CO2 effect and an lesser effect when O3 case is considered. The area of precipitation decrease/increase in Southern Ocean consistant with AAO trend is visible


Summer rainfall difference between 1961 1994 and 1995 2002

SSTs only AGCM

Observed Difference

SSTs + Solar + CO2

SSTs + Solar + CO2 + Ozone

Summer Rainfall Difference between1961-1994 and 1995-2002


Summer rainfall difference between 1961 2003 and 1998 9 2000 1

Observed Difference AGCM

SSTs only

SSTs + Solar + CO2

SSTs + Solar + CO2 + Ozone

Summer Rainfall Difference between1961-2003 and 1998/9-2000/1


Conclusions
Conclusions AGCM

Both CO2 and O3 forcing have contributed to pressure changes in Southern Hemisphere

These changes are similar to SH Annular Mode

The model has rather weak response to a radiative forcing when 30-40 years long ensemble mean climatology climatology is compared

Model show some systematic response in surface air temperature and precipitation, significance of which needs to be assessed

At regional scale contribution of CO2 and O3 to simulated rainfall anomalies is positive


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