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Introduction to Global Climate and the Climate of the South Pacific Stakeholder Workshop Enhanced Application of Climate Predictions in Pacific Island Countries Vanuatu, Solomon Islands , Fiji, Tonga, Samoa, Niue, Cook Islands, Tuvalu, Kiribati 2005. Overview.

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Introduction to Global Climate and the Climate of the South PacificStakeholder Workshop Enhanced Application of Climate Predictions in Pacific Island Countries Vanuatu, Solomon Islands, Fiji, Tonga, Samoa, Niue, Cook Islands, Tuvalu, Kiribati2005

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  • Introduction to Global and Pacific weather and climate

    • Intertropical Convergence Zone, South Pacific Convergence Zone

  • Climate variability in the South Pacific

  • Climate change in the South Pacific

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The Driver for Weather and Climate is Heating from the Sun

Heat lost to space

  • Highly simplified (assumes earth is not rotating)

  • Result:

    Low pressure at the equator

    High pressure at poles

    All weather and climate is driven by this energy imbalance – this is essentially a global “sea breeze effect”

Heat from sun

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Focus on the tropical belt

The Global Circulation – The Effect of the Earth’s Rotation

  • Rising motion triggering rain and cloud in the tropics (same as in the no-rotation case)

  • Sinking motion in the subtropics – deserts.

  • Mid latitude cyclones around 60º.

Heating from sun

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West Pacific is usually warmer than the east

The warmest waters tend to follow the sun – so does the rain

Climate of the Tropics and South Pacific

Tropical weather is driven by where cloud and rainfall is favored. Generally, this is where the land or ocean is warmest => rainfall patterns are driven by changes in ocean temperatures.

January ocean temperatures

July ocean temperatures

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Rainfall in the Tropics(mm/day)

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Climate of the South Pacific

Intertropical Convergence Zone

Dry east Pacific

South Pacific Convergence Zone

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The Inter Tropical Convergence Zone

(also called the Equatorial trough)

  • A zone of high rainfall and much cloudiness

  • A zone of convergence of the trade winds

  • Moves north and south with the seasons

  • Can have ragged edges or “spurs”

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The Climate of Suva – Fiji

More rainfall in summer when the ITCZ

is closest.

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The South Pacific Convergence Zone (SPCZ)

  • The largest and most persistent “spur” of the ITCZ; a belt of high rainfall and cloudiness

  • Stretches from the Solomon Islands to Fiji, Samoa and Tonga

  • Associated with a sea surface temperature maxima

  • Is present year round but most active in the Southern Hemisphere summer

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ITCZ tends to move

N to S

SPCZ tends to move

SW to NE

Focus of tropical convection can shift from west to east

Climate Variability in the South Pacific

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Climate Variability Short and Long Term

  • Climate variability affecting the South Pacific

  • Seasonal variations (ITCZ and SPCZ)

  • Interannual variations (El Niño/La Niña)

  • Long-term Climate Change

    • Climate change and Climate Variability are not the same.

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The El Niño – Southern Oscillation (ENSO)

We are interested in El Niño because it is the dominant driver of natural climate variability.

El Niño refers to a broad scale warming of water in the central and eastern tropical Pacific Ocean (remember rain tends to occur over the warmest waters).

They tend to occur every 3 to 7 years – e.g., 1994, 1997, 2002.

La Niña is the reverse of El Niño.

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“Typical” SST pattern during an El Niño

Increasing sea surface temperatures (SSTs) across

the central and eastern Pacific

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The Impact of El Nino and La Nina

The changes in ocean temperatures associated with El Niño and La Niña, cause large changes in rainfall.

Also, El Niño and La Niña can be predicted, and so their impacts can also be predicted.

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Periods of rapid change

lower predictability

The typical cycle of El Nino

Period of slow change

higher predictability

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Paths of Tropical Cyclones

El Niño years

La Niña years

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Queensland Centre for Climate Applications

Source: Peter Hastings, University of Queensland

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1997 an El Nino - 2000 a La Nina (mm/day)

Central Pacific: 350mm in 2000 versus 1000mm in 1997

Severe western Pacific drought in 1997

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Tracking El Niño

  • Indicators for an El Niño include:

  • The Walker Circulation and trade winds weaken.

  • The warm pool region moves east towards the central Pacific - ocean temperatures become warmer than average in the central and eastern Pacific.

  • The SOI remains negative for several consecutive months.

  • Cloud and rainfall increase over the central and east Pacific. Decreases in the west - over Australia, Indonesia, Solomon Islands etc.

  • La Niña is largely the opposite.

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Tracking ENSO – The SOI

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Global Climate Change

  • Global observations show that the climate is changing:

    Temperatures are generally warming.

    Rainfall patterns have changed. Some places are wetter, some drier.

    Climate extremes have change. More hot days and hot nights.

    These changes are very likely to continue.

  • The major cause for many of these changes are human influences.

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Global Temperature Increase

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Local Climate Change

  • South Pacific Sea Level Monitoring Project:

  • Aim is to "Provide an accurate long term record of sea levels in the South Pacific”

  • Initiated in 1991

  • 14 countries involved

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South Pacific Convergence Zone

Has shifted northeast in recent decades.

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Climate Change in Your Country?

  • Are there signs of change in your country?

    Possible signs include:

    Hotter days and nights

    Different rainfall patterns

    Different timing of crops/flowers

    Coral Bleaching

    Erosion of beaches and atolls

    Different fish being caught

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Future Climate – Local Changes

  • Climate Change Projections from a single model:

  • Short lead: 2025-2034 minus model 1961-1990

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Further Information

  • Your local Meteorological Service

  • The internet





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Thank You

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Tracking La Niña

  • Indicators for a La Niña include:

  • The Walker Circulation and trade winds strengthen.

  • The warm pool moves west towards Indonesia - ocean temperatures become cooler than average in the central and eastern Pacific.

  • The SOI remains positive for several consecutive months.

  • Cloud and rainfall decrease over the central and east Pacific. Increase in the west - over Australia, Indonesia, Solomon Islands etc.

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Model Forecasts of El Niño/La Niña

El Niño

La Niña

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Climate Processes

Global climate is highly complex.

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Local Climate Change

Day Time Temperatures

From: Griffiths et al (submitted to

International Journal of Climatology).

Night Time Temperatures

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NOAA Image

Thermocline: Layer of water between the warmer surface zone and the colder deep zone. In the thermocline, temperature decreases rapidly with depth.

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NOAA Image

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NOAA Image

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Spac winter

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Spac summer

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Courtesy Neville Nicholls, BMRC

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Ocean Currents of the World

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Climate of Kampala, Uganda, Africa

ITCZ crosses twice – hence two rainfall peaks

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The Madden Julian Oscillation?

A progression of large regions of both enhanced

and suppressed rainfall that moves from

west to east mainly over the Tropical Indian and Pacific Oceans.

It is the dominant influence on weather variations in the tropics.

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Gives rise to rainy spells – an active monsoon

Can trigger cyclone development

Can influence the development of El Niño

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