The Australian Monsoon: Projected changes of Australia’s Wet season www.cawcr.gov.au A. Moise , R. Colman, S. Ramasamy and L. Hanson Climate Change Science Team Climate Variability and Change Program The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Motivation � Fundamental component of SH summer circulation � Dominates rainfall distributions over northern Australia and adjacent regions. � Changes to the Australian monsoon over the coming century could have profound consequences for these regions (industries, agriculture, eco systems, human life) � We have reported earlier on projected changes in the Australian monsoon as simulated by CMIP3 coupled climate models, in which we found inconclusive results on changes in Australia’s wet season rainfall. � Here: results on changes in the strength of simulated convection associated with Australia’s monsoon rainfall in order to decrease the uncertainty in rainfall projections. � Here: assess the changes in these convective regimes under enhanced greenhouse conditions with the view of a more dynamical understanding of projected changes in monsoon rainfall over Australia. The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Overview of talk Starting point: Overview of mean monthly changes in PR, TAS PR annual cycle – large model spread Regime sorting of precipitation Convective regimes Changes in the regimes Monsoon Precipitation Domain? The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
TAS and PR changes under A2: djf and jja DJF JJA 2m air temp Multi Model Mean BOX precip The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Tropical Australia rainfall: t-series of change BOX The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
PR seasonality changes: AUSTRALIA months latitude ∆ (%) ∆ (mm) The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Change in zonal winds: tropical Australia BOX Height (hPa) months Low level : Easterlies � Westerlies @ onset similar Duration of Westerlies � slight extension (delay of retreat) Slight intensification High Level : Westerlies � Easterlies @ onset similar Weakening of Easterlies during monsoon The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Change in Monsoon Shear Line January Slightly southward extension of monsoon shear line (A2 vs 20c3m) March Delay in retreat of monsoon The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Precipitation changes Further focus on: � Simulated changes in annual cycles � Sub-setting � Inter-annual Variability � ENSO connection The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Model spread in DJF precipitation changes The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Spread in PR changes: tropical Australia MSLP 2m air temperature Annual cycle changes ALL models Subset The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Interannual variability Change in SD of precipitation across tropical Australia The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Interannual variability: ENSO correlation (SON)-nino3.4 SST’s correlated to wet season (ONDJFMA) precip in tropical Australia Change in correlation: COR(2080-99) - COR(1980-99) 2080-99 average 5 months before and after monsoon onset in Reanalysis The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Regime Sorting Motivation : � Understanding physical process. � What are the processes behind changes in PR: � changes in moisture (due to temperature increase in enhanced GHG world) or � changes in convection (due to changes in circulation)? Proxy measure for convection: vertical motion at 500hPa: ω 500 Part A : Stratification of rainfall along categories of convection Part B : Decomposition of changes of rainfall into process related terms Bony et al. (2004) The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Regime sorting along ω 500 ω 500 = measure of vertical motion (hPa/d) negative � up, convective regimes positive � down, subsidence regimes Projection of rainfall on ω 500 : which convective regimes produce low/high rainfall � model evaluation What rainfall amounts are seen at given convective regime? The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Regime sorting along ω 500 ω 500 = measure of vertical motion (hPa/d) negative � up, convective regimes positive � down, subsidence regimes Projection of rainfall on ω 500: which convective regimes produce low/high rainfall � model evaluation What is the distribution of convective regimes? The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Regime sorting along ω 500 ω 500 = measure of vertical motion (hPa/d) negative � up, convective regimes positive � down, subsidence regimes Projection of rainfall on ω 500: which convective regimes produce low/high rainfall � model evaluation Convective regime-sorted rainfall? The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Regime sorting along ω 500 ω 500 = measure of vertical motion (hPa/d) negative � up, convective regimes positive � down, subsidence regimes Projection of rainfall on ω 500: which convective regimes produce low/high rainfall � model evaluation The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Application of regime sorting: annual cycle Models with convection too weak Models with convection too strong The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Decomposition of rainfall changes +∞ P = precipitation ∫ = ω ω P P ( ) Wd P( ω 500) = precipitation at given regime 500 W = frequency of occurrence of regime − ∞ Change in Precipitation: nbin nbin nbin ∑ ∑ ∑ δ = Δ + Δ + Δ Δ P P W PW P W = = = bin 1 bin 1 bin 1 Thermodynamic Dynamic Co-variation component component component changes due to increased atmospheric moisture content with warmer temperatures changes due to altered atmospheric circulation Bony et al. (2004) The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Change in Precip for given omega500 ∆ P PRECIP regimes for given omega-500 35 delta 30 20c3m A2 25 Precip (mm/d) 20 15 10 5 0 -5 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 W 500 (hPa/d) The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Change in PDF for omega500 ∆ W The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Decomposition of rainfall changes: AUS The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Decomposition of rainfall changes: AUS The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Not just over land: The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
Summary of results • Small rainfall changes for DJF • Large uncertainty from model ensemble • Convective regimes in models and changes • Some model show too much rain in either very deep or very shallow convective regimes. • On average a slight increase in rainfall for deep convective regimes only • On average a slight increase in number of shallow-to medium convective regimes. Decrease in subsidence regimes. • In the GCMs the changes in rainfall over the wider region are mainly driven by the thermodynamic component, ie. Increased moisture content due to increased temperatures • Regime sorting is a powerful method to evaluate processes behind rainfall change in GCMs. The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Aurel Moise CAWCR, Climate Change Science Team Phone: 03 9669 4574 Email: a.moise@bom.gov.au Web: www.cawcr.gov.au Thank you www.cawcr.gov.au
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