Monitoring_ENSO

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					Monitoring ENSO




                  1
                             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!


                                                                                                      2
                             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 0.8°C 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!
                                                                                                       3
                             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 0.8°C 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!



                                                                                                     4
                         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 0.8°C warmer than average)
• A majority in a survey of internationally recognised ocean forecast models show
  anomalies of at least a +1 standard deviation (about 0.8°C 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!




                                                                                       5
Monitoring sea surface temperatures




                                      6
Monitoring sub surface temperatures




                                      7
Monitoring surface winds




                           8
     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.
                                                    9
Monitoring OLR and MJO activity




                          Typical situation
                          Current La Niño
                          Typical El Niña




                                          10
                 Monitoring SOI activity

30


20



10


 0



-10



-20



-30


-40
   1996   1997    1998   1999   2000   2001   2002   2003   2004
                                                                   11
Monitoring Niño 3 forecasts




                              12
Subjective wrap-up




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posted:3/31/2012
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