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Archive for the ‘Australian drought’ Category

Impact of El Niño and La Niña on Rainfall

Posted by feww on October 24, 2009

How El Niño and La Niña affect Rainfall

El Niño 1997
ENSO_sst_rainfall_anomalies_198812

La Niña, 1988
ENSO_sst_rainfall_anomalies_199712

El Niño and its counterpart La Niña alter weather patterns across the world. These images show the strongest El Niño and La Niña events of the past twenty years and their impact on rainfall over North and South America.

The top image pair shows the El Niño event of 1997, and the direct correlation between warm surface waters and rainfall. The 1997 El Niño was unusually strong and brought heavy rain to northwest South America and the southern United States. Cooler ocean temperatures caused drought in Australia and Indonesia, as shown in the 1997 rainfall anomaly image.

The lower image pair shows La Niña in 1988 . La Niña occurs when the eastern Pacific off the coast of South America cools. The unusually cold ocean cools the atmosphere above it. The cool, dense air means less  rain falls over the cold waters in the eastern equatorial Pacific. Image reveals that the drought reached Peru and Ecuador in northwest South America. Globally, La Niña causes unusually heavy rain in India, Southeast Asia, Australia, and southeastern Africa.

NASA Earth Observatory images by Rob Simmon and Jesse Allen, based on data from the National Oceanic and Atmospheric Administration’s Advanced Very High Resolution Radiometer and the Global Precipitation Climatology Project at NASA Goddard Space Flight Center. Caption by Holli Riebeek. [Edited for brevity by FEWW]

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Posted in Australian drought, rain in India, South America weather, Southeast Asia rain, southeastern Africa | Tagged: , , , , , , | Leave a Comment »

El Niño event almost certain: BOM

Posted by feww on July 1, 2009

El Niño event likely, says Australia’s Bureau of Meteorology

More evidence of a developing El Niño event has emerged during the past fortnight, and computer forecasts show there’s very little chance of the development stalling or reversing. —BOM

Equatorial sea-surface temperatures are currently more than 1°C above normal in the eastern Pacific, while the Southern Oscillation Index (SOI) remains below zero at around −2, says BOM.

A sustained negative SOI is often associated with El Nino conditions.

BOM hopes to provide a clear picture of the situation in the Pacific by next week when their final June data are analyzed.

El Niño events are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia.

Another adverse sign for southeastern Australian rainfall is the recent trend to positive values in the Indian Ocean Dipole (IOD), as measured by the Dipole Mode Index (DMI).

The next BOM update is available on July 8, 2009.

Last month FEWW reported US Climate Prediction Center as saying that conditions were favorable for a transition from ENSO-neutral to El Niño conditions during June – August 2009.

sst_wind_home_5day
Click image to update and enlarge.


Images from Tropical Atmospheric Ocean project: NOAA

Summary of BOM Weekly Update:

  • The Pacific Ocean sea surface is currently significantly warmer than the long-term average across most of the tropical Pacific, especially central to eastern areas.
  • A large amount of the sub-surface water of the tropical Pacific is also warmer than the long-term average, particularly in the east.
  • The latest 30-day SOI value is −2, while the monthly value for May was −5.
  • Trade winds remain weaker than normal across the central equatorial Pacific.
  • Cloudiness near the date-line is near-normal, and is yet to show a consistent trend towards El Niño conditions.
  • All international climate models predict the tropical Pacific to continue to warm and to be above El Niño thresholds throughout most of the second half of 2009.

“Australia is the world’s fourth-largest wheat exporter and its grain production is still recovering from the worst drought in more than 100 years that reduced the 2006/07 crop to just 10.6 million tonnes and the 2007/08 crop to 13.0 million tonnes.” Reuters reported.

FEWW Moderators estimate that a new episode of El Niño, which would have devastating impact globally, could cause up to $500 billion in damages.

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See also comments section for latest updates.


Posted in Australian drought, Australian rainfall, drought and deluge, Indian Ocean Dipole, Southern Oscillation Index | Tagged: , , , , | 2 Comments »