| |
CX2SA > CLIMAT 02.01.10 18:01l 179 Lines 10124 Bytes #999 (0) @ WW
BID : 29870_CX2SA
Read: GUEST
Subj: EL NI¥O/LA NI¥A UPDATE
Path: ON0AR<DB0RES<DK0WUE<7M3TJZ<XE1FH<F4BWT<VK4FY<WU3V<CX2SA
Sent: 100102/1658Z @:CX2SA.LAV.URY.SA #:29870 [Minas] FBB7.00e $:29870_CX2SA
From: CX2SA@CX2SA.LAV.URY.SA
To : CLIMAT@WW
EL NI¥O/LA NI¥A UPDATE
======================
Current Situation and Outlook
An El Ni¤o event, which started in June 2009, is well established across the
tropical Pacific. El Ni¤o conditions are very likely to continue at least
through the remainder of 2009 and into the first quarter of 2010. Some
climate patterns typical of El Ni¤o have been observed over the last several
months. The expected continued presence of El Ni¤o into early 2010 has
implications for many climate patterns around the world over the next
several months, keeping in view the fact that, in some regions, impacts
typically continue during the decay phase. Decay of the El Ni¤o event to
near-neutral conditions across the tropical Pacific during the approximate
March-May 2010 period is considered the most likely further development. The
possibilities of a second year of El Ni¤o conditions or rapid transition to
a La Ni¤a situation are considered unlikely at this time.
Across the central and eastern Equatorial Pacific, sea surface temperatures
were generally about 1 Degree Celsius warmer than normal during
June-September 2009. This period formed the early phase of the developing El
Ni¤o event, although the magnitude of the warming through September was
relatively small in comparison to several previous El Ni¤o events.
During October, a further pulse of warming occurred in the central and
eastern Equatorial Pacific Ocean, both at the surface, and in sub-surface
waters. Atmospheric climate patterns across the tropical Pacific also took
on characteristics typical of an El Ni¤o event, including weaker surface
trade winds and stronger displacement of convection and cloudiness from the
western Equatorial Pacific to the central Equatorial Pacific. Surface
temperature conditions in the western Equatorial Pacific have become widely
and substantially below normal. Taken together, these developments indicate
enhanced ocean-atmosphere coupling during this El Ni¤o event across the
tropical Pacific.
Most dynamical and statistical forecast models anticipate the continuation
of El Ni¤o conditions at least into early 2010. Weekly average surface
temperatures in the latter half of October in the central and eastern
Equatorial Pacific were around 1.5 Degree Celsius warmer than normal and
this is around the level anticipated by most models for the
November-February period. The observed developments during October may not
yet be fully represented in the model forecasts. Therefore some modest
additional warming cannot be ruled out, but substantial intensification
remains unlikely at this time.
The expectation therefore continues to be for El Ni¤o conditions to prevail
through the remainder of 2009 and into the first quarter of 2010. This
expectation is based on model forecasts, and the typical life-cycle of El
Ni¤o events, which once established in the early-middle part of a year,
usually persist through into the first quarter of the following year. Beyond
the first quarter of 2010, there is no information of substance on the
likelihood of whether El Ni¤o, near-neutral or La Ni¤a will prevail in the
tropical Pacific, and users are advised to assume the long-term
climatological probability of occurrence, which is 50% for neutral and 25%
each for El Ni¤o and La Ni¤a. There are a few rare examples in the
historical record of situations like the current one leading to a second
year of El Ni¤o conditions, or rapid transition to La Ni¤a conditions. These
two possibilities are considered unlikely at this time, but they are the
ones that forecasters will be watching for in their models over the next few
months.
In considering risk-management responses, it should be recalled that no two
El Ni¤o events are identical. Furthermore, the timing of impacts typically
varies by region, and can continue during the decay phase of an event.
Even in regions that are typically strongly impacted by El Ni¤o,
climate-risk assessments should not rely solely on El Ni¤o/La Ni¤a
indications. Many climate extremes develop independently of El Ni¤o and La
Ni¤a, and users should consult tailored regional and national climate
outlooks. Such outlooks integrate region-specific climate assessments with
those for the major global systems of El Ni¤o and La Ni¤a. Users should
therefore consult their respective National Meteorological and Hydrological
Services and regional climate institutions for more specific climate
outlooks and follow-up updates.
In summary:
An El Ni¤o event is underway, with the early phase of the event holding
steady at weak-to-moderate levels through July-September;
During October, almost all indicators of El Ni¤o became noticeably stronger;
Large-scale conditions in the tropical Pacific, as captured by dynamical
and statistical forecast models, suggest further substantial intensification
of El Ni¤o conditions is unlikely. Expert interpretations do not alter this
expectation, despite the observed developments in October;
Forecasts into 2010 from dynamical and statistical models generally
anticipate the most typical El Ni¤o event evolution that is found in the
historical record, with a return to near-neutral conditions the most likely
outcome for around the March-May 2010 period;
This assessment has important implications for climate patterns around the
world, continuing at least into the second quarter of 2010. During this
time, climate patterns typical of an El Ni¤o event may have increased
likelihood of occurrence; however, this information should be combined with
that on other relevant regional systems to estimate the net impacts.
The situation in the tropical Pacific will continue to be carefully
monitored. More detailed interpretations of regional climate fluctuations
will be generated routinely by the climate forecasting community over the
coming months and will be made available through the National Meteorological
and Hydrological Services. For web links of the National Meteorological
Services, please visit:
http://www.wmo.int/pages/members/members_en.html
El Ni¤o/La Ni¤a Background
Climate Patterns in the Pacific
Research conducted over recent decades has shed considerable light on the
important role played by interactions between the atmosphere and ocean in
the tropical belt of the Pacific Ocean in altering global weather and
climate patterns. During El Ni¤o events, for example, sea temperatures at
the surface in the central and eastern tropical Pacific Ocean become
substantially higher than normal. In contrast, during La Ni¤a events, the
sea surface temperatures in these regions become lower than normal. These
temperature changes are strongly linked to major climate fluctuations around
the globe and, once initiated, such events can last for 12 months or more.
The strong El Ni¤o event of 1997-1998 was followed by a prolonged La Ni¤a
phase that extended from mid-1998 to early 2001. El Ni¤o/La Ni¤a events
change the likelihood of particular climate patterns around the globe, but
the outcomes of each event are never exactly the same. Furthermore, while
there is generally a relationship between the global impacts of an El
Ni¤o/La Ni¤a event and its intensity, there is always potential for an event
to generate serious impacts in some regions irrespective of its intensity.
Forecasting and Monitoring the El Ni¤o/La Ni¤a Phenomenon
The forecasting of Pacific Ocean developments is undertaken in a number of
ways. Complex dynamical models project the evolution of the tropical Pacific
Ocean from its currently observed state. Statistical forecast models can
also capture some of the precursors of such developments. Expert analysis of
the current situation adds further value, especially in interpreting the
implications of the evolving situation below the ocean surface. All forecast
methods try to incorporate the effects of ocean-atmosphere interactions
within the climate system.
The meteorological and oceanographic data that allow El Ni¤o and La Ni¤a
episodes to be monitored and forecast are drawn from national and
international observing systems. The exchange and processing of the data are
carried out under programmes coordinated by the World Meteorological
Organization.
Acknowledgements
This El Ni¤o/La Ni¤a Update has been prepared through a collaborative effort
between the World Meteorological Organization (WMO) and the International
Research Institute for Climate and Society (IRI) as a contribution to the
United Nations Inter-Agency Task Force on Natural Disaster Reduction. It has
been prepared based on contributions from the African Centre of
Meteorological Applications for Development (ACMAD), Asia-Pacific Economic
Cooperation (APEC) Climate Centre (APCC), Australian Bureau of Meteorology
(BoM), Australian Centre for Sustainable Catchments of the University of
Southern Queensland, Centro Internacional para la Investigaci¢n del Fen¢meno
El Ni¤o (CIIFEN), China Meteorological Administration (CMA), Climate
Prediction Center (CPC) of the National Oceanic and Atmospheric
Administration (NOAA) of the United States of America (USA), Climate
Variability and Predictability (CLIVAR) project of the World Climate
Research Programme (WCRP), Comisi¢n Permanente del Pac¡fico Sur (CPPS), El
Comit‚ Multisectorial encargado del Estudio Nacional del Fen¢meno El Ni¤o
(ENFEN) of Peru, European Centre for Medium Range Weather Forecasts (ECMWF),
Fiji Meteorological Service, M‚t‚o-France, IGAD (Inter-Governmental
Authority on Development) Climate Prediction and Applications Centre
(ICPAC), Instituto Nacional de Meteorologia e Hidrologia (INAMHI) of
Ecuador, International Research Institute for Climate and Society (IRI),
Japan Meteorological Agency (JMA), Korea Meteorological Administration
(KMA), Mauritius Meteorological Services (MMS), Met Office in the United
Kingdom (UKMO), National Center for Atmospheric Research (NCAR) of the USA,
National Institute of Water and Atmospheric Research (NIWA) of New Zealand,
University of Colorado of USA, and Wageningen University of The Netherlands.
Source: WMO
Read previous mail | Read next mail
| |
