Cool Phase -
-
Or "cool event")
refers to a La Niņa with its anomalously
cool water.
El Niņo -
-
Comes from the
Spanish term for "the Christ Child" because of the occurrence
of warmer than normal waters that disrupted fishing along the coast of Ecuador
and Peru around Christmas. Common usage of the term has expanded
to refer to the large scale warming of the tropical Pacific Ocean at
irregular intervals of between about 2 and 7 years and lasting for 1 to
3 years.
- El Niņo is one of the two phases of the
El Niņo-Southern Oscillation (ENSO) climate pattern that occurs in the
tropical Pacific Ocean. During an El Niņo event, the surface waters of
the central and eastern Pacific Ocean become unusually warm, which can
cause changes in weather patterns around the world.
Normally, trade
winds blow from east to west across the Pacific Ocean, pushing warm
surface water towards the western Pacific. This causes cooler water to
rise to the surface in the eastern Pacific, which helps to maintain a
stable climate in the region. However, during an El Niņo event, the
trade winds weaken, or even reverse, allowing the warm water to spread
eastward across the Pacific, leading to a warming of the surface
waters in the eastern Pacific.
ENSO -
-
El
Niņo/Southern
Oscillation. ENSO is a general term used to describe both
warm (El Niņo) and cool (La Niņa) ocean-atmosphere events in the tropical
Pacific as well as the Southern Oscillation the atmospheric component of
these phenomena.
Intertropical Convergence Zone
(ITCZ) -
-
The region of cloudiness near the Equator caused by the
convergence of the Trade Winds. [Image of
ITCZ]
La Niņa -
-
"Infant
Girl" in Spanish and is so named because in many ways it is the
opposite of El Niņo. La Niņa is characterized by large scale
cooling of the tropical Pacific Ocean and often begins during the summer
at irregular intervals of between about 2 and 7 years and lasting for 1
to 3 years.
Modoki (or Central Pacific) El Niņo -
- Modoki El Niņo is a type of El Niņo
event that occurs when warm sea surface temperatures develop in the
central tropical Pacific Ocean, rather than in the eastern Pacific as
in a typical El Niņo. "Modoki" is a Japanese word meaning "similar but
different," which reflects the fact that Modoki El Niņo events are
similar in some ways to traditional El Niņo events, but different in
their patterns of warming.
During a
Modoki El Niņo, the central Pacific experiences a warming of the ocean
surface, while the eastern and western Pacific remain relatively cool.
This warming can affect weather patterns around the world, causing
changes in rainfall, temperature, and storm activity.
Modoki El
Niņo events were first identified in the early 2000s, although some
researchers suggest that they may have occurred in the past but were
not recognized at the time. The frequency of Modoki El Niņo events
appears to be increasing in recent decades, possibly due to climate
change.
Multivariate ENSO Index (MEI)
-
-
(MEI) is a composite index using a number
of variables to measure ENSO events. The MEI uses sea surface
temperatures, surface air temperatures, sea-level pressure, zonal (i.e.,
east-west) surface wind, meridional (i.e., north-south) surface wind and
total amount of cloudiness. Positive MEI values are related to
warm phase or El Niņo events and negative values with to cool
phase or La Niņa events. [More
on MEI]
Niņo Regions -
- The Niņo regions, also known as the
Niņo indices, are areas of the tropical Pacific Ocean that are used to
monitor and measure the El Niņo-Southern Oscillation (ENSO) climate
pattern. There are three Niņo regions, named Niņo 1+2, Niņo 3, and
Niņo 4, each covering a different area of the Pacific Ocean.
Niņo 1+2
covers a small area along the equator off the coast of South America,
from 0° to 10°S latitude and 90°W to 80°W longitude. Niņo 3 covers a
larger area along the equator, from 5°N to 5°S latitude and 150°W to
90°W longitude. Niņo 4 covers a wider area in the western and central
tropical Pacific, from 5°N to 5°S latitude and 160°E to 150°W
longitude.
These
regions are important for monitoring ENSO because they are areas where
changes in ocean temperature can indicate the onset or end of an El
Niņo or La Niņa event. For example, during an El Niņo event, the
surface waters in the Niņo 3 and Niņo 4 regions become significantly
warmer than normal, while during a La Niņa event, these regions become
significantly cooler than normal. The Niņo indices are widely used by
scientists and meteorologists to track and forecast ENSO events, and
to predict their potential impacts on weather patterns and climate
around the world. [Map of
Niņo
Regions]
Oceanic
Niņo Index (ONI)-
-
has
become the de-facto standard that NOAA uses for identifying El Niņo
(warm) and La Niņa
(cool) events in the tropical Pacific. It is
the running 3-month mean SST
anomaly for the Niņo
3.4 region (i.e.,
5oN-5oS, 120o-170oW).
Events are defined as 5 consecutive months at or above the +0.5o
anomaly for warm (El Niņo)
events and at or below the -0.5 anomaly for cold (La Niņa)
events. The threshold is further broken down into Weak (with a 0.5 to
0.9 SST anomaly), Moderate (1.0 to 1.4), Strong (1.5
to 1.9), and Very Strong (≥ 2.0) events. For the purpose of this report for an event to be
categorized as weak, moderate or strong it much have equaled or exceeded
the threshold for at least 3 months. [Data
and Plot]
Sea Surface Temperature (SST) -
-
A key characteristic of El and La
Niņa events.
SSTs are monitored from ship reports, buoys and satellite imagery.
[Current
SST chart]
Sea Surface Temperature Anomaly
(SSTA)-
-
The departure of a given SST from the long term average
temperature. Positive anomalies are related to warm phase or El
Niņo
events and negative anomalies are related to cool phase or La
Niņa
events. [Current
SST Anomaly chart]
Southern Oscillation
(SOI) -
-
Is the difference between the seasonally
normalized sea level pressures of
Darwin, Australia
and Tahiti. A negative SOI (also called "low index") usually
relates to a weakening of the Trade Winds and a resulting warm event.
Conversely a positive SOI ("high index") usually relates to an
increase in the Trades and a resulting cool event.
First
recognized by British scientist Sir Gilbert Walker in the 1920s by
observing pressure differences between Darwin, Australia and Tahiti
while stationed in India and studying the monsoon.
[Current
SOI Table]
TAO Array -
- Tropical-Ocean-Atmosphere
Array (renamed the TAO/TRITON array ) consists of approximately 70
moored buoys in the tropical Pacific Ocean that telemeter oceanographic
and meteorological data in real-time. [Project
Page]
Teleconnections -
Thermocline -
- The boundary layer between the warmer well-mixed surface water and
colder deep ocean water. The depth of the thermocline is another
indicator of an El Niņo events when it deepens in the eastern Pacific.
[Current]
TOPEX/Poseidon -
-
(TOPography
EXperiment for Ocean Circulation) is a
joint US/French satellite launched in 1992 to map ocean surface
topography. [Mission
page]
Trade Winds - (also Trades or
Tropical Easterlies)
-
The steady winds resulting from the circulation
of air from the Subtropical High pressure regions toward the Equator and
deflected to the west by the Coriolis Force. The convergence
of these winds along the Equator is the Intertropical Convergence Zone
(ITCZ). Because of the dependability of these winds they
were used by sailing ships of the 17th and 18th centuries to establish
"trade" with the New World. [Image of Trade
Winds]
Upwelling -
-
The
upward motion of sub-surface water toward the surface of the ocean which
is often a source of cold, nutrient-rich water. Significant upwelling
occurs along the equator under the influence of persistent trade winds
and also along coastlines. The disruption of upwelling by
the warmer than normal
waters during El Niņo events disrupts fishing along the coast of
Ecuador and Peru.
Walker Circulation -
- Named for
Sir Gilbert Walker by Jacob Bjerknes in 1969, it describes the three-dimensional
circulation across the tropical Pacific and the displacement of this
circulation by
El
Niņo
and La Niņa events.
See
Walker Circulation.
Warm Phase -
-
Or "warm
event", refers to an El Niņo with its anomalously warm
water.
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