Midterm Flashcards
What is Enso
El Nino- Southern Oscillation (ENSO)
is a reoccurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean. The entire phenomenon is reffered to as ENSO
La Nina
Positive ENSO Conditions
the opposite of el nino
strengthening of the trade winds and warm water conditions in the western tropical Pacific.
El Nino
the warming of equatorial currents off the western coast of S.America associated with weakend trade winds
Southern Oscillation
seesaw effect in the surface atmospheric pressure between the eastern and western Pacific Oceans
Explain Walker Circulation
“ENSO neutral Conditions”
- high atm pressure in the east, LOW in the west
-pressure gradient forms in an E-W direction
-atm winds flow from E-W
-frictional dragging of sea surface by the trade winds causes a current to occur at the equator pushing warm waters westward
-accumulate near Australia
-sea level rises (~40cm),
-avg surface temp 4-8° higher.
-reduced temperature in the east b/c of upwelling
Weather results of Walker Circulation
Lower SST in the east: chill overlaying air –> high atm pressure –> no rising air= limited rain
Walker Circulation Weather in West
Wam water –> density of air to decrease –> leads to lower atm pressure –> cloudy and rainy
El Nino conditions (West)
Cold and DRY
Lower SST chills overlaying air–> increases air density–>causes high atm pressure–> no rising air =limited rain
El Nino conditions (EAST)
WARM and RAINY in the east
warm water –> density of air decreases–> lower atm pressure –> cloudy and rainy
Consequences of El Nino conditions (Eastern Pacific)
more rain than usual in South and Central America and US
Fish stock die due to warmer waters.
Consequences of El nino (western Pacific)
less rain over australia
droughts and wild fires common
Global Impacts of ENSO
-subtropical jet stream is shifted by the changing pressure systems
-changes polar jet stream
-climate anomolies being related over large distances
-causes the biggest changes in semi-permanent pressure cells
Southern Oscillation Index
Way to quantify ENSO.
La Nina is POSITIVE phase of ENSO - above +1
El Nino is NEGATIVE phase. below -1
0 value= ENSO neutral
Prolonged periods of negative SOI values coincide with…
abornmally warm ocean waters across the eastern tropical Pacific typicalal of EL Nino episods
Prolonged periods of POSITIVE SOI values coincide with…
abnormally cold ocean waters across the easter tropical Pacific typical of La Nina
Nino 3.4 index
another way to identify enso events:
- measures SST in regions of the equatorial Pacific Ocean.
+/-1 degree from long-term avg conditions for 3 months
region bounded by 120°W-170°W
positive values indicate warmer SSTs(EL nino) and negative = la nina
Multivariable Enso Index
combines multiples variables into a single index: sea level pressure, surface wind vectors, SSTs, surface air temp, cloud cover.
positve= El Nino
negative = La nina
-often identifeis events earier
-can be adapted w changing climate conditions
Socio-Ecological Impacts of ENSO
strong el nino (1789-1793) –> poor crop yields in europe, start of French Revolution
(1876-77) El Nino extreme storms casued extreme faminie
(1998) intense El nino killed 16% of worlds reef systems due to1.5 incease SST
Earliest observation of ENSO
1500s by Spanish Explorers
Enso in the Last 30 years
At least 30 el nino events since 1900
strongest:
1982-83
1997-98
2014-16
How do we measure Enso?
Space based observations
in-situ Observations
Space Based Observations: Ocean ecology
from satellite images can measure the colour of the ocean from chlorophyll
lower chlorophyll amounts occur during EL Nino events
Ozone Space based observations
during strong el nino: redistribution of ozone due to change in E-W tropical circulation.
see higher ozone levels over indonesia
lower levels over tropical cntral and eastern pacific ocean.
Aura Satellite measures concentration in troposphere.
space based observations : fires
during la nina: Central America experienced more fire activty then normal:
MODIS instruments on AURA gives a global picture of fire activites
ARGO
an international program that uses floats to observe temp, salinity, and currents
since early 2000’s
floats- have ability to rise and fall in the water column by changing its own density.
In Situ Observations
ARGO
coastal tide gauge network
drifting arrays
moored arrays
Long term records of ENSO
displayed in stacked proxy diagrams
is essential to anticipate response to past and furture climate scenarios
Sedimentary Cores
terrestrial cores often from closed lake systems
organic material carbon isotope ratios can tell us about precipitation vs evaporation determinates on lake level
Climate models
try to replicate changes observed in long term recoreds to determine causes in enso trends
from the Holocene
SST from foraminifera
single celled organisms that live in PHOTIC zone of marine enviro
have specific habitat conditions which details of are preserved in their fossils.
oxygen 18 isotopes
SST from Coral records
oxygen 18 and 16 isotopes from cores of coral skeletons
Speleotherm Records
cave stalagmites allow for reconstruction of past rainfall variabilty.
isotopic composition of rainwater is preserved as water travels through cave bedrock to feed cave drips that form stalagmites
oxygen 18 isotope = thinner/thicker annual layer indicates decrease/increase in growth rate
How enso has changed with climate warming
increased in extremes sinces 1970s
extreme events every 2.8 years compared to 4.7 years
Hypothesis 1: Permanent El nino
el nono/ la nina alterations will disappear and only have el nino
