El Niño events typically bring heavy, drenching rain to South America, while Indonesia experiences drought conditions. And during La Niña this is reversed. But their impacts can be felt even further afield than this. Dr Mark Saunders from the University College of London's Department of Space and Climate Physics explains.
Analyses of historical climate data over 100 years shows that El Niño and La Niña are linked statistically to abnormal patterns of temperature, rainfall and storminess around the globe.
These influences are strongest in the tropics and in the pan-Pacific region, but weak impacts extend occasionally as far as Europe. For example, there is a link between strong ENSOs (El Niño Southern Oscillation) and heavier than normal spring rainfall over the central European and southern UK region.
The spring of 1998 saw rainfall which was 10-20% higher than usual, accompanied by flooding. This coincided with the strongest El Niño of recent times.
These remote linkages, or 'teleconnections', arise from the disruption ENSO causes to tropical atmospheric circulation. The warming and cooling of air above the central east Pacific leads to the formation of a wave-like set of stationary disturbances in the middle atmosphere. These change the strength and position of jet streams.
As extra-tropical storms and fronts generally track these jet streams, unusual temperatures and rain patterns may result at mid-latitudes remote to the Pacific. Such extra-tropical teleconnections are seen most clearly in northern hemisphere winter and spring.
One example of ENSO's global climate impact is its link to December-February rainfall in Mozambique and south east Africa. During La Niña periods, south east Africa experiences a higher likelihood of excess rainfall, and floods. And this is exactly what happened in this region from 1998-2001.
ENSO also has an influence on hurricane strikes on US and Caribbean shores. During La Niña periods, hurricane and tropical storm landfalls are twice as common over much of the Caribbean and Gulf of Mexico. Again the recent active Atlantic hurricane seasons of 1998-2001 illustrates this.
The ability to seasonally predict ENSO several months in advance would bring sound economic and social benefits in developing world countries. It would also help safeguard the revenue of 70% of business and industry in developed countries.
Efforts are underway at research centres worldwide to improve the long-range forecasting of ENSO. Steady progress is being made and scientists are now able to predict conditions up to six to nine months ahead. Having said that, models failed to predict the onset and intensity of the 1997/98 strong El Niño. Currently (Nov/Dec 2001), the consensus is for neutral ENSO conditions to persist through to April 2002.
Related Articles:
- What are El Niño and La Niña Events?
- More on La Niña
- More on hurricanes
- ENSO projections
- UCL's Department of Space and Climate Physics
