Monitoring ENSO

1
Monitoring ENSO
2
El Niño alert system

• The purpose of the El Niño Alert System is to
  forewarn the Australian community of any
  potential or growing threat from El Niño, using a
  staged or graduated approach.
• The three steps or stages in the system are
  designed to reflect the level of confidence that
  meteorologists and oceanographers have in
  detecting a developing El Niño event.
• A Stage 1 Alert or WATCH will be issued when the
  Pacific Ocean is becoming, or has become, primed
  for an event. In percentage terms, the chance of
  an event developing would most likely be in the
  vicinity of 50. Stage 1 would normally be
  reached in late summer or autumn, i.e. between
  about February and May.
• A Stage 2 Alert or WARNING will be issued when
  observational evidence indicates the probable
  early phase of an El Niño event. However, there
  is still the risk of a false alarm. In percentage
  terms, the chance of an event developing would be
  over 70. Stage 2 would normally be reached in
  late autumn or winter, i.e. between about May and
  August.
• A Stage 3 Alert or DECLARATION will be issued
  when conditions in the Pacific have developed to
  such an extent that an El Niño event can be
  confidently declared to be in progress. Stage 3
  would normally be reached in winter or early
  spring, i.e. between about June and October.
• NB THIS IS AN INTERNAL UNOFFICIAL DOCCUMENT USED
  FOR GUIDANCE ONLY!

3
El Niño alert system

• Stage 1 (WATCH) has been satisfied
• Climate system in neutral or declining La Niña
  state (climate system in a neutral state)
• At least one of the following applies
• Four or more of the first ten SOI analogues
  having EITHER falling SOI (Southern Oscillation
  Index) during the next four months (specifically
  a fall of 3 points or more in the 3-month average
  value), OR the 3-month average SOI reaching -5.0
  or lower (satisfied 4 satisfy both 1986, 1877,
  1891, 1932 and another three 2002, 1965, 1946
  satisfy the final value criterion) OR
• Significant sub-surface warming has been observed
  in the western or central equatorial Pacific
  (not satisfied - subsurface temps generally
  close to average with little trend)
• About one-third or more in a survey of
  internationally recognised ocean forecast models
  show warming to at least a 1 standard deviation
  temperature anomaly (about 0.8C warmer than
  average) in the NINO3 or NINO3.4 regions of the
  Pacific by the late winter or spring (i.e. about
  August to November) (satisfied 6 of 11 are warm
  by December)
• NB THIS IS AN INTERNAL UNOFFICIAL DOCCUMENT USED
  FOR GUIDANCE ONLY!

4
El Niño alert system

• Stage 2 (WARNING) has been satisfied
• Clear warming trend in the NINO3 or NINO3.4
  regions of the Pacific during previous three to
  six months (satisfied NINO3.4 index has been
  0.39, 0.66 and 0.84 for June, July and August
  to date respectively)
• A majority in a survey of internationally
  recognised ocean forecast models show warming to
  at least a 1 standard deviation temperature
  anomaly (about 0.8C warmer than average) in the
  NINO3 or NINO3.4 regions of the Pacific by the
  late winter or spring (i.e. about August to
  November) (satisfied majority warm by December)
• Observed SOI below 7 for two consecutive months,
  OR observed average SOI below 7 over two months
  (satisfied 7 in July and 14 in June)
• Low-level westerly wind anomalies (i.e. weakened
  or reversed trade winds) analysed over the
  western equatorial Pacific during any two of the
  last three months (satisfied CPC western
  Pacific 850 hPa wind index will almost certainly
  be negative for August, following values of 0.1
  and 0.9 in July and June respectively)
• NB THIS IS AN INTERNAL UNOFFICIAL DOCCUMENT USED
  FOR GUIDANCE ONLY!

5
El Niño alert system

• Stage 3 (DECLARATION) (NB all conditions must be
  achieved)
• Temperature anomaly in the NINO3 or NINO3.4
  regions of the Pacific has reached 1 standard
  deviation (about 0.8C warmer than average)
• A majority in a survey of internationally
  recognised ocean forecast models show anomalies
  of at least a 1 standard deviation (about 0.8C
  warmer than average) in the NINO3 or NINO3.4
  regions of the Pacific until the end of the year
• Observed SOI below 7 for at least three
  consecutive months, OR observed average SOI below
  7 over at least three consecutive months
• Low-level westerly wind anomalies analysed over
  the western equatorial Pacific during any three
  of the last four months
• NB THIS IS AN INTERNAL UNOFFICIAL DOCCUMENT USED
  FOR GUIDANCE ONLY!

6
Monitoring sea surface temperatures
7
Monitoring sub surface temperatures
8
Monitoring surface winds
9
Monitoring OLR and MJO activity
Outgoing Longwave Radiation (OLR) Satellites
measure the amount of radiation being emitted to
space from the Earth. High levels of radiation
are emitted from warm areas and low levels from
cool areas such as the poles. Clouds emit
radiation the high cirrus clouds that form over
giant tropical convective clusters are very cold
and so have lower OLR values than the surrounding
clear areas.
10
Monitoring OLR and MJO activity
11
Monitoring SOI activity
12
Monitoring Niño 3 forecasts
13
Subjective wrap-up