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Impact of Stratospheric Ozone Depletion and CO2 on AAO Trends and Regional Climate Change in Southern Hemisphere

This study investigates the influence of stratospheric ozone depletion and CO2 on trends in the Southern Hemisphere Annular Mode (AAO) and regional climate change. The research uses a global climate model to explore the relationship between these forcings and surface characteristics such as mean sea-level pressure (MSLP) in the region. The study also examines the drying trends in eastern Australia and identifies possible forcing factors. The results highlight the impact of stratospheric ozone loss and greenhouse gas increases on the AAO and regional climate. The research provides valuable insights for understanding and predicting future climate changes.

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Impact of Stratospheric Ozone Depletion and CO2 on AAO Trends and Regional Climate Change in Southern Hemisphere

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  1. 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

  2. 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

  3. 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

  4. Martin Visbeck Todd Mitchell

  5. 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

  6. 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

  7. 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

  8. All-Australian annual rainfall indices (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

  9. 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

  10. 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

  11. Summary • 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.

  12. March 2002 Rainfall Forecastfor 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/

  13. Murray-Darling Basin – April-September rainfall and maximum temperature 1952 - 2002

  14. 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

  15. Natural Annual Flows into Hume Weir (MDBC) Lowest 4-year period on record Natural Annual Flows into Hume Weir (MDBC)

  16. CSIRO Mk3 AGCM Model • 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

  17. CSIRO T63/L18 C20C Experiments • 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

  18. Ozone scenario used in CSIRO AGCM simulations Observations

  19. Ozone recovery projections

  20. 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.

  21. CSIRO Mk2 Model, Warming Run

  22. Correlation between the AAO and JJA Rainfall CSIRO Mk2 Model, greenhouse run, showing when the AAO goes up rainfall over SWWA decreases, and vice-versa!

  23. MSLP change in Mk 3 JJA DJF SON MAM ANN

  24. SAM SWWA Rainfall Winter Spring

  25. Queensland summer rainfall in GHG scenario with Mk3 coupled AGCM

  26. Model Simulated and NCEP R1 JJA MSLP for JJA 1971-2000

  27. Annual Trend NCEP PSL 1971-2001

  28. Model Simulated MSLP difference for JJA 1971-2000

  29. Model Simulated MSLP difference for JJA 1971-2000

  30. Model Simulated MSLP difference for JJA 1971-2000

  31. Model Simulated MSLP difference for JJA 1971-2000

  32. Model Simulated MSLP difference for JJA 1971-2000

  33. Trends in the SAM: impact on Antarctic temperatures  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)

  34. Response of surface temperature Warming over Antarctic Peninsula and cooling over Eastern Antarctica seen in both CO2 and O3 forcing, but stronger in O3

  35. Response of surface temperature DJF 1993-2003 cooling over Eastern Australia due to CO2 effect and an opposite effect when O3 is added

  36. Response of precipitation 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

  37. Response of JJA precipitation 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

  38. SSTs only Observed Difference SSTs + Solar + CO2 SSTs + Solar + CO2 + Ozone Summer Rainfall Difference between1961-1994 and 1995-2002

  39. Observed Difference SSTs only SSTs + Solar + CO2 SSTs + Solar + CO2 + Ozone Summer Rainfall Difference between1961-2003 and 1998/9-2000/1

  40. Conclusions 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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