Lecture 8 el nino, la nina, and their connection with hong kong climate
-
Upload
polylsgiedx -
Category
Science
-
view
290 -
download
5
Transcript of Lecture 8 el nino, la nina, and their connection with hong kong climate
Lecture 8
El Nino/La Nina, and their connection with
Hong Kong’s climate
LSGI1B02 Climate Change and Society
LEUNG Wing-mo
Climate variabilityVariability ranges over many time and space scales such as localized thunderstorms and tornadoes, to larger-scale storms, to droughts, to multi-year, multi-decade and even multi-century time scales.
Some examples of this longer time-scale variability might include a series of abnormally mild or exceptionally severe winters, and even a mild winter followed by a severe winter.
Such year-to-year variations in the weather patterns are often associated with changes in the wind, air pressure, storm tracks, and jet streams that encompass areas far larger than that of your particular region.
At times, the year-to-year changes in weather patterns are linked to specific weather, temperature and rainfall patterns occurring throughout the world due to the naturally occurring phenomena known as El Niño and La Niña – a teleconnection phenomenon –changes occurring in places far away affect the weather/climate in other parts of the world.
Climate Variability and Climate Change
Normals
Climate Change
Climate Oscillations
Climate VariabilityNormals
Short term: (years to decadal) rises and falls about the trend line (El Nino Southern Oscillation, ENSO)
Long Term Trends or major shifts in climate: (centuries, significant and persistent change from mean state)
Multi-decadal oscillations in regional climate: (e.g. Pacific Decadal Oscillation, PDO, North Atlantic Oscillation, NAO)
Drought in Queensland, Australia, 2014
https://www.youtube.com/watch?v=dzat16LMtQk
Understanding El Nino, Bureau of Meteorology, Australia
El Nino
(Boy Child):
Sea Surface
temperature
(SST) changes
in the Pacific
Jan
DecEquatorial “cold tongue”
Major ocean currents -
result of winds, continental land masses, and Coriolis effect
Gulf stream
Calif. current
Kuroshio current
Walker Circulation
Walker Circulation & Southern Oscillation
Tahiti
Darwin
Southern Oscillation: fluctuations in the surface air pressure between Tahiti (east) and Darwin (west) – an indication of
the strength of Walker Circulation
Walker Circulation
Relationship between El Nino (SST) and Southern
Oscillation (pressure)
El Nino, SSTchanges
Southern Oscillation, surface pressure changes
Discovery of the “El Niño- Southern Oscillation (ENSO)”
• In 1960’s , Bjerknes found a link between the two phenomena, and that the anomalous warming of the waters during El Niño extended over a large portion of the equatorial Pacific.
• SOI (Southern Oscillation index) = Tahiti pressure anomaly –Darwin pressure anomaly
• Mean cycle of 4 years (2 – 7)
ONI - 3-month running means of SST anomalies in the Niño 3.4 region [5N-5S, 120-170W]. The anomalies are derived from the 1971-2000 SST climatology.
Equatorial
cold
tongue is
weaker
than
average or
absent
during El
Niño,
resulting
in positive
SST
anomalies
Equatorial
cold
tongue is
stronger
than
average
during La
Niña,
resulting
in negative
SST
anomalies
Equatorial cold tongue is weaker than average or absent during El Niño, resulting in positive SST anomalies
Equatorial cold tongue is strongerthan average during La Niña, resulting in negative SST anomalies
Effects on fishery (upwelling affects phytoplankton concentration)
(Weak upwelling)
“El Niño”
WarmCold
Warm
Cold
Warm
Convection shifts eastward
over the central and/or
eastern Pacific Ocean.
Convection becomes
suppressed over the far
western Pacific/Indonesia.
Easterly trade winds
weaken.
Thermocline deepens and
the cold water upwelling
decreases in the eastern
Pacific.
“La Niña”
ColdWarm
WarmCold
Stronger
Stronger
Upwelling
Enhanced
More
Convection
becomes more shallow
Convection becomes
stronger over the far
western Pacific Ocean/
Indonesia and more
suppressed in the central
Pacific.
Easterly trade winds
strengthen
Thermocline becomes
more shallow and the
cold water upwelling
increases in the eastern
Pacific.
Thermocline
Global El Niño Impacts
Global La Niña Impacts
Mid-latitude impacts generally occur during the winter season (NH –DJF; SH- JJA).
Atlantic
Hurricanes
Specific ImpactsHistorical:• Disease outbreaks (1918-1919 influenza
pandemic /Spanish flu)?• Loss of civilizations, civil wars?
Current:• Damages from floods and landslides in Peru
and southern California; • Forest fires in Indonesia - serious air pollution
problems • Crop failures - famine from droughts in
southern Africa • Collapse of the Peruvian anchoveta fisheries
because of warmer coastal waters. • Low and high agricultural yields - price
fluctuations;• Water resources;• Energy demand - disruption to hydropower;
1997 southeast Asian haze
Nazca civilization: 100BC-800AD
Spring rainfall (Mar – May) in HK
30 June 1997
Stronger SW winds at 850 hPa (around 1000m) following El Nino onset
Cyclonic vortex near HK in strong El Nino summers
Wind anomalies following La Nina onset – anomalous anticyclone
Number of tropical cyclones within 500 km of Hong
Kong
Aug - Oct
Tropical Cyclone
Track
Density
Relationship between the mean Nino-3.4 SSTA and the mean no. of landfalling TCs during the late season for(a) area 2 – China; (b) area 3 –Indochina and (c) area 4 - The Philippines
La Nina years
El Nino years
Composite
circulation, late
season:
(i) Genesis
near Asia
in La Nina
(ii) Stronger
Pacific
ridge steers
typhoons
towards
land
Winter temperature in HK
La Nino, 2008 China snowstorm
The current situation - SST anomalies 25 Feb 2015 ( in degree C), NOAA
What Next?
Forecast of Sea Surface Temperature (SST) anomalies in Nino 3.4 International Research Institute for Climate and Society:
http://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/
Climate Change and ENSO
• IPCC-AR4: “No consistent indication at this time of discernible changes in projected ENSO amplitude or frequency in the 21st
century.”
• A weak shift towards average background conditions which may be described as ‘El Niño-like’, with sea surface temperatures in the central and east equatorial Pacific warming more than those in the west.
• Weakened tropical circulations, shifting rainfall eastward.
• ENSO projections differ from model to model.
• The sign of the sensitivity of ENSO amplitude and frequency to increased greenhouse gases remains highly uncertain.
• Continued ENSO variability in the future even with changes to the background state
ENSO linksIRI: http://iri.columbia.edu/climate/ENSO/background/basics.htmlNOAA: http://www.pmel.noaa.gov/tao/elnino/faq.htmlhttp://www.oar.noaa.gov/k12/html/elnino2.htmlhttp://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtmlhttp://www.pmel.noaa.gov/tao/elnino/nino-home.htmlhttp://www.cdc.noaa.gov/map/clim/sst_olr/el_nino_anim.shtmlhttp://faculty.washington.edu/kessler/occasionally-asked-questions.html#q1Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/enso/http://www.bom.gov.au/climate/current/soi2.shtmlhttp://www.bom.gov.au/climate/enso/australia_detail.shtmlhttp://www.longpaddock.qld.gov.au/Chinahttp://bcc.cma.gov.cn/en/International Research Institute for Climate and Society:http://iri.columbia.edu/climate/ENSO/index.htmlMet Office, UK:http://www.metoffice.gov.uk/research/hadleycentre/obsdata/climateindicators.htmlhttp://www.metoffice.gov.uk/research/seasonal/elnino/index.htmlhttp://www.metoffice.gov.uk/research/seasonal/regional/index.htmlHKO:http://www.hko.gov.hk/lrf/enso/enso-front.htmhttp://www.weather.gov.hk/education/edu01met/wxphe/article/46-nclau.pdf