Tagged: El Nino/La Nina Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 1:05 pm on October 13, 2015 Permalink | Reply
    Tags: , , El Nino/La Nina,   

    From NASA Earth: “El Niño Strengthening” 

    NASA Earth Observatory

    NASA Earth Observatory

    1
    acquired October 5, 1997 – October 4, 2015

    The latest analyses from the National Oceanic and Atmospheric Administration and from NASA confirm that El Niño is strengthening and it looks a lot like the strong event that occurred in 1997–98. Observations of sea surface heights and temperatures, as well as wind patterns, show surface waters cooling off in the Western Pacific and warming significantly in the tropical Eastern Pacific.

    “Whether El Niño gets slightly stronger or a little weaker is not statistically significant now. This baby is too big to fail,” said Bill Patzert, a climatologist at NASA’s Jet Propulsion Laboratory. October sea level height anomalies show that 2015 is as big or bigger in heat content than 1997. “Over North America, this winter will definitely not be normal. However, the climatic events of the past decade make ‘normal’ difficult to define.”

    The maps above show a comparison of sea surface heights in the Pacific Ocean as observed at the beginning of October in 1997 and 2015. The measurements come from altimeters on the TOPEX/Poseidon mission (left) and Jason-2 (right); both show averaged sea surface height anomalies. Shades of red indicate where the ocean stood higher (in tens of millimeters) than the normal sea level because warmer water expands to fill more volume. Shades of blue show where sea level and temperatures were lower than average (contraction). Normal sea-level conditions appear in white.

    “The trade winds have been weakening again,” Patzert said. “This should strengthen this El Niño.” Weaker trade winds out of the eastern Pacific allow west wind bursts to push warm surface waters from the central and western Pacific toward the Americas. Click here [in the full article] to watch a video of Kelvin waves propagating across the ocean in the first seven months of 2015.

    In its October monthly update, scientists at NOAA’s Climate Prediction Center stated: “All multi-model averages predict a peak in late fall/early winter. The forecaster consensus unanimously favors a strong El Niño…Overall, there is an approximately 95 percent chance that El Niño will continue through Northern Hemisphere winter 2015–16.”

    2

    The July–September average of sea surface temperatures was 1.5°C above normal, NOAA reported, ranking third behind 1982 (1.6°C) and 1997 (1.7°C). The plot above shows sea surface temperatures in the tropical Pacific for all moderate to strong El Niño years since 1950.

    Both Patzert and NOAA forecasters believe the southern tier of North America, particularly southern California, is likely to see a cooler and wetter than normal winter, while the northern tier could be warmer and drier. But the sample of El Niños in the meteorological record are still too few and other elements of our changing climate are too new to say with certainty what the winter will bring.

    NASA Earth Observatory map by Jesse Allen, using Jason-2 and TOPEX/Posideon data provided by Akiko Kayashi and Bill Patzert, NASA/JPL Ocean Surface Topography Team. NASA Earth Observatory chart by Joshua Stevens, using data from NOAA. Caption by Mike Carlowicz.

    NASA Jason 2
    NASA/Jason-2

    NASA Topex Poseiden
    NASA TOPEX/Poseodon

    Instrument(s):
    TOPEX/Poseidon
    JASON-2

    See the original article for further reading references.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Earth Observatory’s mission is to share with the public the images, stories, and discoveries about climate and the environment that emerge from NASA research, including its satellite missions, in-the-field research, and climate models. The Earth Observatory staff is supported by the Climate and Radiation Laboratory, and the Hydrospheric and Biospheric Sciences Laboratory located at NASA Goddard Space Flight Center.

     
  • richardmitnick 12:51 pm on August 29, 2015 Permalink | Reply
    Tags: , , El Nino/La Nina,   

    From CSIRO: “Explainer: El Niño and La Niña” 

    CSIRO bloc

    Commonwealth Scientific and Industrial Research Organisation

    June 20, 2014
    Author: Carol Saab
    By Jaci Brown, CSIRO

    1
    Australia’s weather is influenced by warm water movements in the Pacific. Image: Flickr / Shayan USA, CC BY

    We wait in anticipation of droughts and floods when El Niño and La Niña are forecast but what are these climatic events?

    The simplest way to understand El Niño and La Niña is through the sloshing around of warm water in the ocean.

    The top layer of the tropical Pacific Ocean (about the first 200 metres) is warm, with water temperatures between 20C and 30C. Underneath, the ocean is colder and far more static. Between these two water masses there is a sharp temperature change known as the thermocline.

    Winds over the tropical Pacific, known as the trade winds, blow from east to west piling the warm top layer water against the east coast of Australia and Indonesia. Indeed, the sea level near Australia can be one metre higher than at South America.

    Warm water and converging winds near Australia contribute to convection, and hence rainfall for eastern Australia.

    2
    La Niña. Image: US National Weather Service

    In a La Niña event, the trade winds strengthen bringing more warm water to Australia and increasing our rainfall totals.

    3
    El Niño. Image: US National Weather Service

    In an El Niño the trade winds weaken, so some of the warm water flows back toward the east towards the Americas. The relocating warm water takes some of the rainfall with it which is why on average Australia will have a dry year.

    In the Americas El Niño means increased rainfall, but it reduces the abundance of marine life. Typically the water in the eastern Pacific is cool but high in nutrients that flow up from the deep ocean. The warm waters that return with El Niño smother this upwelling.

    Have El Niño and La Niña always been around?

    El Niño and La Niña are a natural climate cycle. Records of El Niño and La Niña go back millions of years with evidence found in ice cores, deep sea cores, coral and tree rings.

    El Niño events were first recognised by Peruvian fisherman in the 19th century who noticed that warm water would sometimes arrive off the coast of South America around Christmas time.

    Because of the Christmas timing they called this phenomenon El Niño, meaning “boy child”, after Jesus. La Niña, being the opposite, is the “girl child”.

    Predicting El Niño and La Niña

    Being able to predict an El Niño event is a multi-million, possibly billion dollar question.

    4
    The drought hit Wagga Wagga, NSW, in 2006. Image: Flickr / John Schilling, CC BY-NC-ND

    Reliably predicting an impending drought would allow for primary industries to take drought protective action and Australia to prepare for increased risk of dry, hot conditions and associated bushfires.

    Unfortunately each autumn we hit a “predictability barrier” which hinders our ability to predict if an El Niño might occur.

    In autumn the Pacific Ocean can sit in a state ready for an El Niño to occur, but there is no guarantee it will kick it off that year, or even the next.

    Nearly all El Niños are followed by a La Niña though, so we can have much more confidence in understanding the occurrence of these wet events.

    A variety of events

    Predictability would be even easier if all El Niños and La Niñas were the same, but of course they are not.

    Not only are the events different in the way they manifest in the ocean, but they also differ in the way they affect rainfall over Australia – and it’s not straightforward.

    The exceptionally strong El Niños of 1997 and 1982 have now been termed Super El Niños. In these events the trade winds weaken dramatically with the warm surface water heading right back over to South America.

    Recently a new type of El Niño has been recognised and is becoming more frequent.

    This new type of El Niño is often called an El Niño Modoki – Modoki being Japanese for “similar, but different”.

    In these events the warm water that is usually piled up near Australia heads eastward but only makes it as far as the central Pacific. El Niño Modoki occurred in 2002, 2004 and 2009.

    5
    (a) Australian rainfall in 1998 La Niña (May 1998 to March 1999), (b) the 1997 Super El Niño (April 1997 to March 1998), © the 1982 Super El Niño (April 1982 to February 1983) and (d) the 2002 El Niño Modoki (March 2002 to January 2003). Image: (c) Bureau of Meteorology

    Australian rainfall is affected by all its surrounding oceans. El Niño in the Pacific is only one factor.

    As a general rule though, the average rainfall in eastern and southern Australia will be lower in an El Niño year and higher in a La Niña. The regions that will experience these changes and the strength are harder to pinpoint.

    El Niño and climate change

    It is not yet clear how climate change will affect El Niño and La Niña. The events may get stronger, they may get weaker or they may change their behaviour in different ways.

    Some research is suggesting that Super El Niños might become more frequent with climate change, while others are hypothesising that the recent increase in El Niño Modoki is due to climate change effects already having an impact.

    Because climate change in general may decrease rainfall over southern Australia and increase potential evaporation (due to higher temperatures) then it would be reasonable to expect that the drought induced by El Niño events will be exacerbated by climate change.

    Given that we are locked into at least a few degrees of warming over the coming century, it’s hard not to fear more drought and bushfires for Australia.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    CSIRO campus

    CSIRO, the Commonwealth Scientific and Industrial Research Organisation, is Australia’s national science agency and one of the largest and most diverse research agencies in the world.

     
  • richardmitnick 11:00 am on August 18, 2015 Permalink | Reply
    Tags: , , El Nino/La Nina,   

    From UNSW: “2015-16 is shaping up to deliver a rollercoaster from strong El Niño to La Niña” 

    U NSW bloc

    University of New South Wales

    18 Aug 2015
    Wenju Cai, Agus Santoso and Guojian Wang

    1
    Warming seas suggest El Niño is on the horizon. dmytrok/Flickr

    The coming El Niño and La Niña double bill could be the strongest since 1998, affecting a vast swathe of the planet from Africa, through Australasia and all the way to the Americas, write Wenju Cai, Agus Santoso and Guojian Wang.

    OPINION: The anticipation is growing that this year’s newly formed will turn out to be very big. All climate models surveyed by the Australian Bureau of Meteorology are currently predicting a strong event later this year.

    5
    The 1997–98 El Niño observed by TOPEX/Poseidon. The white areas off the Tropical Western coasts of northern South and all Central America as well as along the Central-eastern equatorial and Southeastern Pacific Ocean indicate the pool of warm water.

    We’ve been here before – last year, in fact, when fears of a 2014 “super El Niño” proved anticlimactic. But it’s not over yet. The El Niño – Spanish for “the little boy”, which refers to a particular pattern of ocean and atmospheric temperatures across the Pacific – has resumed its growth this year and this time it is not showing any signs of slowing down.

    It’s easy to see why this little boy gets so much attention. First, we are talking about a climate phenomenon that brings drought, rains, floods, heatwaves and other extreme weather events to many parts of the world.

    Second, it is almost 20 years since the previous extreme El Niño. The 1997-98 event was the biggest in modern records and its worldwide catastrophic impacts earned it the infamous description of “the climate event of the 20th century”. A comparable but slightly weaker El Niño occurred in the summer of 1982-83, which was marked by severe drought in eastern Australia and the tragic Ash Wednesday bushfires.

    Third, the latest climate model projections – reviewed by us in a study published today in Nature Climate Change – have shown that Earth will probably experience more super El Niños as the global climate warms. The projections also suggest that the extreme version of La Niña – the sister and “opposite” of El Niño – will also increase in frequency, as will the positive phase of the siblings’ “cousin”, a related phenomenon called the Indian Ocean Dipole. This also includes more successive occurrences of the trio.

    3
    Sea surface skin temperature anomalies in November 2007 showing La Niña conditions

    6
    Water temperatures around the Mentawai Islands dropped about 4° Celsius during the height of the Indian Ocean Dipole in November of 1997. During these events unusually strong winds from the east push warm surface water towards Africa, allowing cold water to upwell along the Sumatran coast. In this image blue areas are colder than normal, while red areas are warmer than normal.

    A family gathering

    This atypical “family gathering” has happened before. A positive Indian Ocean Dipole occurred in the southern spring of 1997, before the El Niño peaked the following summer. A La Niña then followed in the summer of 1998-99. For western Pacific rim countries, the overall result was drier-than-normal conditions in 1997, followed by unusually wet conditions in 1998. A similar series of events also occurred in 1982-83.

    To understand this and to see how global warming spurs such events, we need to understand the physics of El Niño, taking the most recent unfolding events as a start.

    The 2014-2016 chain of events would be interesting in its own right. While the failed 2014 super El Niño left many experts scrabbling for an explanation, its warming remnants in the central Pacific have now transformed into the official 2015 El Niño.

    It is not common that two El Niño events would occur consecutively. The heat accumulated in the equatorial Pacific Ocean that fuels an El Niño is usually discharged, and some of this heat goes into the atmosphere, where it helps to accelerate warming in global surface temperature.

    The discharge is proportional to the intensity of an El Niño. So the stronger the El Niño, the stronger the discharge. Also, the stronger the El Niño, the more dramatic the weakening of the Walker Circulation, with slackened trade winds and equatorial currents. This weakening Walker Circulation extends into the Indian Ocean which tends to induce a positive Indian Ocean Dipole during the southern spring.

    Following the peak of an El Niño in the southern summer, the equatorial Pacific Ocean is depleted of heat and needs to be recharged. Winds associated with La Niña are effective in this recharge, and so an El Niño tends to be followed immediately by a La Niña.

    Clearly the 2014 El Niño conditions were not strong enough for this to happen. Another similar exception occurred during 1986-1988. The 1986-87 El Niño was weak, the Pacific Ocean heat was not completely depleted, allowing for another somewhat stronger El Niño in 1987-88. These two events are considered weak to moderate.

    The impact was mild and confined to northeastern Australia, in part because there were no concurrent positive Indian Ocean Dipole events which also act to channel El Niño’s impact to southern Australia.

    However, after the two consecutive events, the equatorial Pacific was finally depleted of heat. The subsurface ocean was colder, facilitating surface cooling in the central Pacific through a suite of atmosphere-ocean positive feedback processes, leading to the extreme La Niña of 1988-89.
    What is in store?

    In terms of intensity and the growth rate up to July, the 2015 El Niño is second only to corresponding time of the 1997 event, and looks set to outpower the 1982 event. However, the eventual intensity of the 2015 El Niño is still hard to predict. What seems more certain is a La Niña in 2016.

    For Australia, the extent and strength of the impact of the 2015 El Niño to a large extent depends on whether there is a concurrent positive Indian Ocean Dipole. In 2014, there was no positive Indian Ocean Dipole. To date, most models are predicting a positive dipole this year, raising the prospect of a strong El Niño preceded by a positive Indian Ocean Dipole and followed by a La Niña event – exactly as occurred in 1982-84 and 1997-99.

    2
    The pattern of Pacific Ocean temperatures during the last strong El Nino event in 1997. NOAA

    For Australia, the impacts of this sequence could be significant, as attested by the devastating Ash Wednesday bushfire in 1983 over southern Australia and the floods that hit the country’s northeast in early 1984.

    This swing between opposite extremes from one year to the next could have globally damaging consequences too. On the far side of the Pacific, California may get a break from its a prolonged drought, although this hopefully won’t be in the form of intense storms and flooding.
    Climate change bringing extremes

    We cannot be sure if climate change plays a role in an individual event, and climate models are certainly not perfect. Observations need to be sustained to gather and compare robust statistics. But due to recent research we can now say that stronger El Ninos, La Ninas, and positive Indian Ocean Dipoles are all to be expected on a warming planet.

    Climate models project an overall weakening of the Walker Circulation over the 21st century, underpinned by faster warming in the eastern equatorial Pacific (which is favourable for extreme El Niños, and in turn conducive to extreme La Niña). There will also be faster warming in the western than the eastern Indian Ocean, which would tend to promote positive Indian Ocean Dipole events. As a consequence, the sequence of an El Niño preceded by a positive Indian Ocean Dipole and followed by a La Niña event is projected to occur more frequently.

    These sequences of events are likely to affect a vast swathe of the planet, extending from Africa, right through to South Asia and Australasia, and all the way across to the coastlines of the eastern Pacific.

    Guojian Wang is a Postdoctoral fellow at CSIRO.

    Agus Santoso is a Senior Research Associate at UNSW.

    Wenju Cai is a Principal Research Scientist, Wealth from Oceans Flagship at CSIRO.

    This opinion piece was first published in The Conversation.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    U NSW Campus

    Welcome to UNSW Australia (The University of New South Wales), one of Australia’s leading research and teaching universities. At UNSW, we take pride in the broad range and high quality of our teaching programs. Our teaching gains strength and currency from our research activities, strong industry links and our international nature; UNSW has a strong regional and global engagement.

    In developing new ideas and promoting lasting knowledge we are creating an academic environment where outstanding students and scholars from around the world can be inspired to excel in their programs of study and research. Partnerships with both local and global communities allow UNSW to share knowledge, debate and research outcomes. UNSW’s public events include concert performances, open days and public forums on issues such as the environment, healthcare and global politics. We encourage you to explore the UNSW website so you can find out more about what we do.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: