Drivers of Climate at Mildura Dale Grey DPI Cobram Mildura Cropping Agronomist Tuesday, 29th June 2010

Annual

Annual- 5 year moving average WWII Federation Annual- 5 year moving average

Summer Autumn Winter Spring

Summer Autumn demise Winter Spring

Top of the Goulburn Catchment Autumn

Averaged over the whole year temperature doesn’t actually vary by that much. Mildura A 1 degree difference over a year is a massive change. It could mean the equivalent of 38 extra winter days or 15 extra summer days crammed into the year.

Previous droughts have not been as hot. 5 Year moving average of annual rainfall (Mildura) Previous droughts have not been as hot. 5 Year moving average of annual Max temp anomaly (Mildura)

Factors affecting Climate at Mildura El Niño / La Niña Indian Ocean Dipole IOD (+/-) Southern Annular Mode SAM (+/-) Sub Tropical Ridge STR Madden Julian Oscillation (phases 1-8) Pacific Decadal Oscillation (+/-) North West Cloud Bands Cut Off Lows

Word for the Day Anomaly- deviation from normal

First Some Oceanography 101

Argo Robotic Buoy Satellite Ships of Opportunity RAMA

29oC 13oC

Young Endeavour, March 2006 “The Rip” taken by M.Pardy

El Niño surface temperature anomaly November 2006 El Niño Cold off Darwin-Qld El Niño surface temperature anomaly

Classic horseshoe shape of warm water for La Niña December 31st 2007 La Niña Warm off Darwin-Qld Classic horseshoe shape of warm water for La Niña

The Walker Circulation A major influence on the Australian climate El Niño Cool water north Australia Warm Pacific Ocean Weak easterly trade winds Convection near date line SOI negative La Niña The opposite Neutral Sea temperatures are neutral across the pacific Trade winds extend from East (South Africa) to West (Australia) Create reasonable rainfall over Eastern Australia, particularly the northern half El Nino Warm water in eastern pacific Cool water around Australia Reduced trade winds Reduced rainfall in Australia La Nina Cool water in eastern pacific Warm water around australia Strong trade winds bring rainclouds to australia Higher rainfall in Australia Notice Darwin and Tahiti

PNG Ecuador Thermocline flat El Niño Sub-surface

La Niña Sub-surface Thermocline sloped

World Cloudiness, 2002 El Niño Becomes cloudier at the dateline cloudy clear World Cloudiness, 2002 El Niño Becomes cloudier at the dateline

World Cloudiness. 2007 La Niña Lack of cloud at the date line cloudy clear World Cloudiness. 2007 La Niña Lack of cloud at the date line

Equatorial Wind El Niño top, trade winds switch to the West La Niña bottom, winds strengthen to the East

Worldwide effects of La Niña and El Niño

Indian Ocean Dipole Positive (IOD +ve)

Indian Ocean Dipole Negative (IOD -ve) No IOD- since 1992

August 2006 Cool Broome-Brisbane IOD+

September 26th 2007 IOD+ Weak one

June 30th 2008 Cool Broome-Brisbane IOD+

September 29th 2008 IOD’s tend to decay from east to west in late September-October

El niño 19 years 23 years 1890-2010 La niña 27 years 16 years

El niño 17 years 20 years 1901-2010 La niña 24 years 16 years

photo taken by a QANTAS navigator above Sydney Oct 2009

PNG Ecuador We had progress of the cool counter current above the thermocline westwards. Rapid breakdown from warm to neutral at the surface. Thermocline now tilting. Large cold anomalies at depth

cloudy clear Decreasing cloud around the International Date Line = la Nina The Coral seas is still less cloudy. Indonesia has remained cloudy for the last 3 months Victoria is normal

The SOI has ants in its pants el Niño warning November fry up Cyclone Oli Southern Oscillation Index = SOI = difference in air pressure (Tahiti – Darwin)

November 16th 2009 El Niño In early November the Coral and Arafura sea cooled off as a result of the plunging SOI in Oct. The long awaited el Niño was finally fully coupled. This led to the much maligned fry up.

December 31st 2009 El Niño El Niño peaks. At Nino 3 and 3.4 areas of the Pacific were 1.5 and 1.9oC warmer. Much of the ocean to the north was warm. There was a lack of gradient in the Indian Ocean.

June 24th 2010 x x Currently the Nino 3, 3.4 and 4 areas of the Pacific are -0.35, -0.42 and -0.02oC warmer, near the -0.8 threshold. The DMI measurement of the IOD is +0.12 which is neutral.

Harvest time, North Dakota Oct 2009

Southern Annular Mode, SAM or AAO The SAM index is calculated by the differences in pressure between 40o and 65o degrees latitude Southern Annular Mode, SAM or AAO Measures the strength of polar westerlies in the Southern Ocean.

The Southern Annular Mode (AAO) was more negative for the 2009 winter spring year. Negative SAM Polar winds weaker Westerlies closer to Southern Aus Pushes fronts more northward. But changes weekly and isn’t the absolute cause of rain in the south

SAM has been positive for the last 6 weeks There is more usefulness in the SAM during winter. Its more positive Autumn in the last 25 years has been partially blamed for poor Autumns. +SAM can significant lead to a wetter summer in E Gippsland. The up and downs over summer in 2009-10 haven’t really affected Victorian rainfall.

Most of the upward trend is over Summer and Autumn

10 years +SAM 1957-2010 13 years -SAM

10 years +SAM 1957-2010 13 years -SAM

Sub-tropical ridge The Sub tropical ridges originate as a result of the Hadley Cells emanating from the Equator. One in each hemisphere, dry descending air causing high pressure. Mediterranean climates and deserts occur in these regions of the world.

Sub Tropical Ridge July 2009 Winter pattern, centre of highs over the top of the Bight Jan 2009 Sub Tropical Ridge The High pressure belt lying over Australia and at all mid latitudes of the world. Summer pattern, centre of highs over Melbourne

The Sub Tropical Ridge for the month of May was normally positioned and pressure was lower than normal, the ridge down to Tasmania wasn’t helpful

For most of the month of June the STR has been in a favourable position but the strength of the high pressures has been greater.

Increased high pressure systems in the last 50 years

30 years 27 years 28 years 27 years

30 years 24 years 1901-2010 20 years 24 years

A January 2010 day at Metung

The latest “Fast Break” analysis for the next three months Pacific cool (La nina) Indian slightly warm Rainfall Average-slightly wetter Slightly warmer temps

The “Fast Break” analysis for four to six months Pacific cool (La nina) Indian slightly warm Rainfall Slightly wetter Average- slightly warmer temps

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