The Australian Monsoon: Projected changes of Australias Wet season - - PowerPoint PPT Presentation

The Centre for Australian Weather and Climate Research

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The Australian Monsoon:

Projected changes of Australia’s Wet season

• A. Moise, R. Colman, S. Ramasamy and L. Hanson

Climate Change Science Team Climate Variability and Change Program www.cawcr.gov.au

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

2m air temp precip JJA DJF Multi Model Mean BOX

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

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PR seasonality changes: AUSTRALIA

latitude months ∆ (mm) ∆ (%)

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Change in zonal winds: tropical Australia

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 BOX Height (hPa) months

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Change in Monsoon Shear Line

Slightly southward extension of monsoon shear line (A2 vs 20c3m) Delay in retreat of monsoon

January March

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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

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A partnership between CSIRO and the Bureau of Meteorology

Model spread in DJF precipitation changes

The Centre for Australian Weather and Climate Research

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Spread in PR changes: tropical Australia

Annual cycle changes

ALL models Subset MSLP 2m air temperature

The Centre for Australian Weather and Climate Research

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Interannual variability

Change in SD of precipitation across tropical Australia

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Interannual variability: ENSO correlation

(SON)-nino3.4 SST’s correlated to wet season (ONDJFMA) precip in tropical Australia

2080-99 average

Change in correlation: COR(2080-99) - COR(1980-99)

5 months before and after monsoon onset in Reanalysis

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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: ω500 Part A: Stratification of rainfall along categories of convection Part B: Decomposition of changes of rainfall into process related terms

Bony et al. (2004)

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A partnership between CSIRO and the Bureau of Meteorology

Regime sorting along ω500

ω500 = measure of vertical motion (hPa/d) negative up, convective regimes positive down, subsidence regimes Projection of rainfall on ω500: 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 ω500

ω500 = measure of vertical motion (hPa/d) negative up, convective regimes positive down, subsidence regimes Projection of rainfall on ω500: 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 ω500

ω500 = measure of vertical motion (hPa/d) negative up, convective regimes positive down, subsidence regimes Projection of rainfall on ω500: 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 ω500

ω500 = measure of vertical motion (hPa/d) negative up, convective regimes positive down, subsidence regimes Projection of rainfall on ω500: 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 strong Models with convection too weak

The Centre for Australian Weather and Climate Research

A partnership between CSIRO and the Bureau of Meteorology

Decomposition of rainfall changes

∑ ∑ ∑

= = =

Δ Δ + Δ + Δ =

nbin bin nbin bin nbin bin

W P PW W P P

1 1 1

δ

Bony et al. (2004)

Change in Precipitation: changes due to increased atmospheric moisture content with warmer temperatures changes due to altered atmospheric circulation

∫

+∞ ∞ −

= ω ω Wd P P ) (

500

P = precipitation P(ω500) = precipitation at given regime W = frequency of occurrence of regime Dynamic component Thermodynamic component Co-variation component

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Change in Precip for given omega500

PRECIP regimes for given omega-500

• 5

5 10 15 20 25 30 35

• 200 -180 -160 -140 -120 -100
• 80
• 60
• 40
• 20

20 40 60 80 100 W500 (hPa/d)

Precip (mm/d)

delta 20c3m A2

∆P

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A partnership between CSIRO and the Bureau of Meteorology

Change in PDF for omega500

∆W

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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
• nly
• 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

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

The Centre for Australian Weather and Climate Research

A partnership between CSIRO and the Bureau of Meteorology

Pattern Matching

MPI = Monsoon Precipitation Index Distinguishes monsoon climate from equatorial perennial rainfall regime where AR is small compared to annual mean. Distinguishes monsoon climate from subtropical arid and semi-arid regimes where annual means are small.

For Monsoon Precipitation-Domain

AnnualMean MJJAS PR NDJFM PR Mean AR MPI ) ( ) ( − = =

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A partnership between CSIRO and the Bureau of Meteorology

Changes in MPI

Biggest change is Expansion by ~ 35%

• slightly north-west
• stronger south-east