La Niña

Sea surface skin temperature anomalies in November

2007, showing La Niña conditions

La Niña (/lɑːˈniːnjə/, Spanish

pronunciation: [la ˈniɲa]) is a coupled
ocean-atmosphere phenomenon that is
the colder counterpart of El Niño, as part
of the broader El Niño–Southern
Oscillation climate pattern. The name La
Niña originates from Spanish, meaning
"the little girl", analogous to El Niño
meaning "the little boy". It has also in the
past been called anti-El Niño,[1] and El Viejo
(meaning "the old man").[2] During a period
of La Niña, the sea surface temperature
across the equatorial Eastern Central
Pacific Ocean will be lower than normal by
3 to 5°C (5.4 to 9°F). An appearance of La
Niña persists for at least five months. It
has extensive effects on the weather
across the globe, particularly in North
America, even affecting the Atlantic and
Pacific hurricane seasons.

Definition
La Niña is the positive and cold phase of
the El Niño–Southern Oscillation, and is
associated with cooler-than-average sea
surface temperatures in the central and
eastern tropical Pacific Ocean.[3] However,
each country and island nation has a
different threshold for what constitutes a
La Niña event, which is tailored to their
specific interests.[4] For example, the
Australian Bureau of Meteorology looks at
the trade winds, SOI, weather models and
sea surface temperatures in the Niño 3
and 3.4 regions before declaring that a La
Niña event has started.[5] However, the
Japan Meteorological Agency declares
that a La Niña event has started when the
average five-month sea surface
temperature deviation for the NINO.3
region is more than 0.5 °C (0.90 °F) cooler
for six consecutive months or longer.[6]

Occurrences

A timeline of all La Niña episodes between

1900 and 2019.[7][8]
There was a relatively strong La Niña
episode during 1988–1989. La Niña also
formed in late 1983,[9] in 1995, and a
protracted La Niña event that lasted from
mid-1998 through early 2001. This was
followed by a neutral period between 2001
and 2002. The La Niña which developed in
mid-2007, and lasted until almost 2009,
was a moderate one. The strength of La
Niña made the 2008 Atlantic hurricane
season one of the five most active since
1944; sixteen named storms had winds of
at least 39 miles per hour (63 km/h), eight
of which became 74-mile-per-hour
(119 km/h) or greater hurricanes.[10]
A new La Niña episode developed quite
quickly in the eastern and central tropical
Pacific in mid-2010,[11] and lasted until
early 2011.[12] It intensified again in mid-
2011 and lasted until early 2012.[13] This
La Niña, combined with record-high ocean
temperatures in the north-eastern Indian
Ocean, was a large factor in the 2010–
2011 Queensland floods,[14] and the
quartet of recent heavy snowstorms in
North America starting with the December
2010 North American blizzard. The same
La Niña event was also a likely cause of a
series of tornadoes of above-average
severity that struck the Midwestern and
Southern United States in the spring of
2011, and drought conditions in the South
Central states including Texas, Oklahoma
and Arkansas.[15] Meanwhile, a series of
major storms caused extensive flooding in
California in December 2010, with seven
consecutive days of non-stop rainfall,
leading to one of the wettest Decembers
in over 120 years of records. This is in
contrast to the drier-than-normal
conditions typically associated with La
Niña in California, especially in the
south.[16]

In 2011, on a global scale, La Niña events

helped keep the average global
temperature below recent trends. As a
result, 2011 tied with 1997 for the
eleventh-warmest year on record. It was
the second-coolest year of the 21st
century to date, and tied with the second-
warmest year of the 20th century. A
relatively strong phase of La Niña opened
the year, dissipated in the spring before re-
emerging in October and lasted through
the end of the year. When compared to
previous La Niña years, the 2011 global
surface temperature was the warmest
observed. The 2011 globally-averaged
precipitation over land was the second-
wettest year on record, behind 2010.
Precipitation varied greatly across the
globe. This La Niña contributed to severe
drought in East Africa and to Australia's
third-wettest year in its 112-year period of
records.[17]

La Niñas occurred in 1904, 1908, 1910,

1916, 1924, 1928, 1938, 1949–51,[18]
1954–56, 1964, 1970–72, 1973–76,
1983–85,[9] 1988–89, 1995–96, 1998–
2001, 2007–08, 2008–09, 2010–12,
2016–17, and 2017–18.[11][19][20]

Impacts on the global climate

La Niña impacts the global climate and
disrupts normal weather patterns, which
as a result can lead to intense storms in
some places and droughts in others.[21]
Regional impacts
Observations of La Niña events since
1950, show that impacts associated with
La Niña events depend on what season it
is.[22] However, while certain events and
impacts are expected to occur during
events, it is not certain or guaranteed that
they will occur.[22]

Africa

Between 50,000 and 100,000 people died during the

[ ]
2011 Horn of Africa drought.[23]

La Niña results in wetter-than-normal

conditions in Southern Africa from
December to February, and drier-than-
normal conditions over equatorial East
Africa over the same period.[24]

Asia

During La Niña years, the formation of

tropical cyclones, along with the
subtropical ridge position, shifts westward
across the western Pacific Ocean, which
increases the landfall threat in China.[25] In
March 2008, La Niña caused a drop in sea
surface temperatures over Southeast Asia
by 2 °C (36 °F). It also caused heavy rains
over Malaysia, the Philippines, and
Indonesia.[26]

North America

Regional impacts of La Niña.

La Niña causes mostly the opposite
effects of El Niño, above-average
precipitation across the northern Midwest,
the northern Rockies, Northern California,
and the Pacific Northwest's southern and
eastern regions. Meanwhile, precipitation
in the southwestern and southeastern
states, as well as Southern California, is
below average.[27] This also allows for the
development of many stronger-than-
average hurricanes in the Atlantic and
fewer in the Pacific.

The synoptic condition for Tehuantepecer

winds is associated with high-pressure
system forming in Sierra Madre of Mexico
in the wake of an advancing cold front,
which causes winds to accelerate through
the Isthmus of Tehuantepec.
Tehuantepecers primarily occur during the
cold season months for the region in the
wake of cold fronts, between October and
February, with a summer maximum in July
caused by the westward extension of the
Azores-Bermuda high pressure system.
Wind magnitude is weaker during La Niña
years than El Niño years, due to the less
frequent cold frontal incursions during La
Niña winters,[28] with its effects can last
from a few hours to six days.[29] Between
1942 and 1957, La Niña had an impact
that caused isotope changes in the plants
of Baja California.[30]

In Canada, La Niña will, in general, cause a

cooler, snowier winter, such as the near-
record-breaking amounts of snow
recorded in La Niña winter of 2007/2008 in
Eastern Canada.[31][32]

South America

During a time of La Niña, drought plagues

the coastal regions of Peru and Chile.[33]
From December to February, northern
Brazil is wetter than normal.[33] La Niña
causes higher than normal rainfall in the
central Andes, which in turn causes
catastrophic flooding on the Llanos de
Mojos of Beni Department, Bolivia. Such
flooding is documented from 1853, 1865,
1872, 1873, 1886, 1895, 1896, 1907, 1921,
1928, 1929 and 1931.[34]

Diversity

Map showing Niño3.4 and other index regions

The traditional La Niña, also called Eastern

Pacific (EP) La Niña,[35] involves
temperature anomalies in the Eastern
Pacific. However, in the last two decades,
nontraditional La Niña were observed, in
which the usual place of the temperature
anomaly (Niño 1 and 2) is not affected, but
an anomaly arises in the central Pacific
(Niño 3.4).[36] The phenomenon is called
Central Pacific (CP) La Niña,[35] "dateline"
La Niña (because the anomaly arises near
the dateline), or La Niña "Modoki" (Modoki
is Japanese for "similar, but
different").[37][38] There are flavors of ENSO
additional to EP and CP types and some
scientists argue that ENSO exists as a
continuum often with hybrid types.[39]
The effects of the CP La Niña are different
from those of the traditional EP La Niña—
e.g., the recently discovered La Niña leads
to a rainfall increase over northwestern
Australia and northern Murray-Darling
basin, rather than over the east as in a
conventional La Niña.[38] Also, La Niña
Modoki increases the frequency of
cyclonic storms over Bay of Bengal, but
decreases the occurrence of severe
storms in the Indian Ocean overall, with
the Arabian Sea becoming severely non-
conductive to tropical cyclone
formation.[40][41]
The recent discovery of ENSO Modoki has
some scientists believing it to be linked to
global warming.[42] However,
comprehensive satellite data go back only
to 1979. Generally, there is no scientific
consensus on how/if climate change may
affect ENSO.[43]

There is also a scientific debate on the

very existence of this "new" ENSO. A
number of studies dispute the reality of
this statistical distinction or its increasing
occurrence, or both, either arguing the
reliable record is too short to detect such a
distinction,[44][45] finding no distinction or
trend using other statistical
approaches,[46][47][48][49][50] or that other
types should be distinguished, such as
standard and extreme ENSO.[51][52]

Recent years when La Niña Modoki events

occurred include 1973–74, 1975–76,
1983–84, 1988–89, 1998–99, 2000–01,
2008–09, 2010–11 and 2016–
17.[37][53][54][55][56][57]

See also
2010 Pakistan floods (attributed to La
Niña)
2010–11 Queensland floods (attributed
to La Niña)
 2010–12 La Niña event
2010–13 Southern United States and
Mexico drought (attributed to La Niña)
2011 East Africa drought (attributed to
La Niña)
El Niño–Southern Oscillation, the
atmospheric component of La Niña–El
Niño cycle
Walker circulation

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External links
What is La Niña? at NOAA Pacific
Marine Environmental Laboratory
 La Niña FAQs at NOAA Pacific Marine
Environmental Laboratory
La Niña episodes in the Tropical Pacific
at CPC
El Niño–Southern Oscillation (ENSO) at
CPC
List of El Niño and La Niña events since
1950 at CPC

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