El Nino-Southern Oscillations (ENSO)
El Nino-Southern Oscillations (ENSO) is a periodical phenomenon of climatic interannual variability. It can cause floods and droughts and has impact on the ecosystem and on economic activities like fishing. ENSO is of worldwide concern because it affects many countries (Southern America, Australia, India, Africa, etc.). ENSO events occurred during the past centuries and - there is also evidence - over the past thousand years. In the years 1982-1983 a severe event has been reported; successively in 1991 an anomalously long period started. Climatic indicators, early in 1997, detected the development of another event.
ENSO is a coupled ocean (El Nino) - atmosphere (Southern Oscillations) phenomenon although the two components are not always linked. It can be detected, among others, as a warming of the sea surface temperature over the tropical Eastern Pacific.
A present issue about this phenomenon is the investigation about its variation in intensity and frequency as related to global climate change (e.g. global warming) as well as its influence on climate change. The understanding of ENSO has increased since - in the late 1980s - it became possible to reproduce some features associated to such events, with the advent of coupled atmosphere-ocean Global Circulation Models (GCMs) for weather prediction.
In Peru a service for El Nino forecasting started in 1983: a forecast is issued every year in November, when the El Nino event could begin (actually its name is related to Christmas). The appearance and the disappearance of the event are both economically important: during ENSO years floods are reported; during non-ENSO years drought can occur.
An overview of global El Nino impacts and benefits as well as El Nino prediction and forecast are accessible from the NOAA El Nino theme page.
ENSO global continuous monitoring is carried on internationally, in the framework of World Climate and Oceanography Programs. To this aim satellite data are routinely used. Sea Surface Temperature (SST) and Sea Surface Height (SSH) are considered as ENSO indicators: the latter - as measured by altimeter - is an indicator of ocean heat content.
A monthly updated ENSO forecast is available in the Integrated Global Ocean Services System (IGOSS) Product Bulletin. An ENSO indicator is defined as the SST averaged (SSTA) over an Eastern Equatorial Pacific area (NINO3).
Among the IGOSS products there is the monthly Pacific ERS-1 sea level anomaly (1994-1995), as derived from ERS-1 Altimeter measurements.
Global maps of the Sea Surface Temperature (SST) detecting the latest El Nino events have been produced. Pictures of 1992 and 1997 are available.
Several institutes are carrying out research about the ENSO on the basis of ERS Altimeter data, in the framework of ESA ERS supported projects.
Some links are provided below:
Institute of Oceanography - University of Hamburg
Delft Institute for Earth-Oriented Space Research at the Delft University of Technology
At a recent ERS Symposium (Florence, 1997) some studies related to the El Nino were presented. Links to papers are given below.
Use of ATSR data and in situ observations to study ocean
Dynamics near the Kuroshio boundary
...The results suggest that SST anomaly near the Kuroshio boundary is associated with El Nino event. Analysis of wind data shows that El Nino event may affect the Kuroshio path via wind stress....
ERS Satellite Microwave Radar Observations of Antarctic
...interannual variability is observed in the sea-ice drift dynamics. Coupled model simulations reproduce this variability and indicate that there is significant interannual variability in Weddell Sea ice formation, drift and extent on the ENSO time scale, with a period of ~ 8 years. ...
(Data from ERS-1 and ERS-2 scatterometer and SAR)