vietnam lecture5 tropics

8/14/2019 Vietnam Lecture5 Tropics

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Jacek Piskozub

Institute of Oceanology PAS

Sopot, Poland

Ho Chi Minh City, December 2007

Lecture 5:

Climate change threats,(Part I: Changes in the climate of the tropic)


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Jacek Piskozub Klimat a ocean: wczoraj, dzi i jutro,kurs wykadw dla doktorantw 19.02-14.05.2007

Maszyna klimatyczna Ziemia (zmienno w skali geologicznej)

Epoka lodowa w ktrej yjemy (zmienno w skali astronomicznej) Gwatowne zmiany klimatu (deglacjacja, zmienno suborbitalna)

Holocen: klimat, ocean a cywilizacja, (staa soneczna i wulkanizm)

Pnocny Atlantyk kunia klimatu (cyrkulacja termohalinowa, NAO)

Tropiki a zmienno klimatu (ENSO, huragany, monsuny)

Aerozol: wielka niewiadoma klimatyczna Gazy o znaczeniu klimatycznym (cykl wgla, CO2, metan, DMS)

Globalne ocieplenie a ocean (zmienno antropogeniczna)

Zmiany klimatyczne w rejonach polarnych


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A reminder: Earth atmospheric circulation

Climate of the tropics is ruled by the Intertropical Convergence Zone (ITCZ)

between two Hadley cells, which you can feel on the surface as the trade winds.


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Inny widok tej samej cyrkulacji.


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Walker circulation cell over the equatorial Pacific

The general circulation pattern is more complicated over the Pacific wherea convection cell exists also along the equator between a low in the West(close to South-East Asia) and a high in the East (close to South America).

Sir Gilbert Thomas

Walker (1868 - 1958)


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Two phases of Walker circulation:El Nio-Southern Oscillation (ENSO)

The traditional view of ENSO:

after a period of normalWalker circulation, a warmanomaly appears in the EastPacific . Because the date itwas ofter detected off-Perushores was close to Christmas,

it was named The [boy] baby(El Nio).

At present most researcherstreat ENSO as a cycle of twometastable phases: : El Nio

and La Nia, of which one is nomore normal than the other.

The ENSO cycle of 3-7 yearperiod is the largest source of

climate variability in themultiannual time scale.


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La Nia

El Nio

Two phasesof ENSO


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ENSO-3 Index

Positive anomalies of equatorial East Pacific from the averageare called El Nio, the negative ones La Nia. Variability with

periods shorter than one year has been filtered out.McPhaden 1999 (Science)


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ENSO index in the 20th century

An alternative way of defining the ENSO phases, comparing theindex to its multiannual sliding average of equatorial EastPacific temperatures. Using this approach both phases (La Niaoraz El Nio) are equally frequent almost by definition.

Fedorov & Philander 2000 (Science)


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How do we know?

The array of instruments monitor oceanic conditions: blue lines are thetracks of commercial ships of opportunity, arrows show drifting buoys, yellowdots represent tide gauges measuring sea level, red diamonds and squaresare buoys moored to the ocean floor.

Fedorov & Philander 2000 (Science)

O


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Beginning of El Nio: October 1997

Sea surface temperature (SST) in October 1997 and its anomalyfrom a long term average for the month. The characteristic warmwedge close to South America is almost 5 deg warmer than theaverage.

Webster & Palmer 1997 (Nature)


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Pocztki El Nio: 11.1996 - 10.1997

Anomaly from multiannualPacific SST during thedevelopment of El Nio

1997/1998.

Webster & Palmer 1997 (Nature)

D l i El Ni th i


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Developing El Nio:another view

Time evolution of wind anomaly (red means more Western), SST and20 C isotherm depth (reds mean deeper).

McPhaden 1999 (Science)

P f th t ENSO i ll li l


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Proof that ENSO is really cyclical

Time trajectory of potential energy caused by thermocline tilt (E) and powertransferred by wind to ocean (W) shows the periodicity od ENSO(counterclockwise). The grayed out fragments are periods of westerly winds.

The upper part of each graph is La Nia while the lower is El Nio.Philander & Fedorov 2003 Annu. Rev. Earth Planet. Sci.

World wide El Nio effects (old & simple view)


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World wide El Nio effects (old & simple view)

The El Nio phase causes measurable changes of precipitation in mostEarth areas: drought in Indonesia, Australia, Middle America (hence lesshurricanes hurricanes in El Nio years), Eastern Africa and India (weakmonsoon), while parts of the United States and Argentina have increased

precipitation. Rosenzweig 1994 (Nature) after Nicholls 1993

A more modern view of ENSO climate influence


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A more modern view of ENSO climate influence

The influence of the cold (La Nia) and warm (El Nio) phase of ENSO on theclimate in winter DJF(upper) and summer JJA (lower).

en.wikipedia.org after NOAA

Mechanism of world wide spreading of ENSO climate


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Mechanism of world wide spreading of ENSO climateeffects: atmospheric circulation

Changes of atmospheric circulations as a function of lime and latitude. Themomentum transfer by changing westerly winds towards the poles after eachEl Nio is clearly visible.

Dickey, Marcus & Hide 1992 (Nature)

Wppp


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Wppp

Wpp

Forchhammer et al. 1998 (Nature)

Influence of El Nio on maize crop in Zimbabwe


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Influence of El Nio on maize crop in Zimbabwe

ENSO-3 index (dashed lines) is highly correlated with precipitation andmaize crop in Zimbabwe. It is noteworthy ENSO correlates better withmaize crop than with precipitation (which may mean that ENSO influencesalso Zimbabwe temperature and/or other factors).

Cane, Eshel & Buckland 1994 (Nature)


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ENSO w holocenie

Pozycja ITCZ (na podstawie siymonsunu), temperatury Zachodniego iWschodniego Pacyfiku orazczstotliwo zjawisk ENSO w ciguostatnich 14ka.

Widoczne jest minimum aktywnociENSO w okresie optimumklimatycznego holocenu.

Uwaga: Niska aktywno w epocelodowej nie jest zgodna zprzedstawionymi wynikami Tudhope etal 2001. Autorzy mimo przedstawienia

jej na rysunku w artykule nie wycigajwnioskw co do epoki lodowej

Koutavas et al. 2006 (Geology)

ENSO in the past millennium


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ENSO in the past millennium

Seasonal changes of temperature (18O) from Palmyra fossil corals showthat ENSO was practically independent from temperature and irradiance

variability in the last millennium. Cobb et al. 2003 (Nature)

Tropical atmospheric circulation changes


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Tropical atmospheric circulation changes

During last 100+ years the pressure gradients which power the Walkercirculation decreased by 2.5 3 % (a). This change can be modeled (b). Itis important that natural forcing cannot explain the change (c) butanthropogenic change can (d) explain the changes of tropospheric

circulation. Vecchi et al. 2006 (Nature)

How will ENSO change in the greenhouse world?


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How will ENSO change in the greenhouse world?

SST variability (upper) and ENSO period (lower) does not change in theworld of doubled CO2 concentration: an averaged results of 15 generalcirculation models. But how much can we trust them?

Merryfield 2006 (Journal of Climate)

ENSO forecasting: an example


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ENSO forecasting: an example

ENSO forecasting for 2007 by 20 models I showed to my students in

March. How accurate it was? McPhaden, Zebiak & Glantz 2006 (Science)


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The outcome: not one model predicted the Nino 3.4 value of 0.0

which was recorded in the month I presented this for the first time.

Podsumowanie 1/3


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Podsumowanie 1/3

ENSO (El Nio Southern Oscillation) is an oscillation of the ocean-atmosphere system in the tropical Pacific with a period of 2-7 years.

Its warm phase (El Nio) means decreasing: Walker circulation, tradewinds, cold water upwelling at South American coast, South Asia &Eastern Africa monsoons, hurricanes in the Atlantic & typhoons in thePacific; the cold phase (La Nia) restores a state previously deemednormal.

San Diego River flooding duringthe 2005 El Nio

ENSO influence reaches most o the planetans is the greatest source of climateinterannual variability.

Although there is evidence ENSO periodlengthened since 1980s, generally in the

last millennium it did not change much. Our models show no significant change in

the coming greenhouse world but wecannot yet be sure we are able to predictthis when our models cannot reliable

model even the present ENSO cycles.

Monsuny: bryza o cyklu rocznym


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y y y y

Monsoons work in yearly scale as a breeze in the daily one: they blow windstowards the hot continent in the summer and from a cold one in the winter.

They are one of the only two climate connections between the hemispheres(thermohaline circulation being the other one) .

Intertropical Convergence Zone


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Intertropical Convergence Zone

Kump et al. 2004

During the year ITCZ movestowards the more sunwardhemisphere(which is visible in the graph- though not very well)

What controls the monsoon strength in the long time?


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Oxygen isotopes from Hulu Cave (China) show how over 70 ka the monsoon

strength depended both on THC and North Hemisphere summer insolation.Wang et al. 2001 (Science)

THC and sun...


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A little longer time scaleand the same result:

Monsoon intensitydepends both on thesummer insolation of theNorth Hemisphere andon the intensity ofthermohaline circulation(THC).

Henderson 2006 (Science)

Monsoon (and ENSO) in the Holocene


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Intensity of the monsoons and the ENSO cycle have anticorrelated in theHolocene Lower graphs: reconstructed SST and salinity 6000 years ago(compared to the present average values). Abram et al. 2007 (Nature)

Climate teleconnections


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The influence of THC on the monsoon is

easy to explain (THC influences theEurasian temperatures).

Other teleconnections (up) are not soobvious: usually we do not fullyunderstand what influences what.

Zahn 2003 (Nature); Sirocko et al. 1996 (Nature)

Monsoon and ENSO


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Intensity of monsoon rains in India as a function of the ENSO-3 index: astrong anticorrelation. Large droughts (


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Correlation between India monsoon intensity and Nino-3 index (thin line

and the lower dotted one when two atypical years 1983 and 1997 areomitted), winter temperature of Western Europe air (thick solid) andCentral Europe (dotted line). One can see the strong ENSO monsoonanticorrelation. Winter temperature of Europe correlates significantly(horizontal lines) only when NAO index is positive. The positive NAOmeans strong westerly circulation making European climate influence the

central Euroasia. Chang, Harr & Ju 2001 (Journal of Climate)

A reminder: Winter values of NAO since 1950


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e de te a ues o O s ce 950

NAO was consistently low on the 1960s and high in the 1990s.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/season.JFM.nao.gif

S 2/3


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Summary 2/3

During the Holocene, monsoon strength anticorrelatedwith ENSO variability.

Asia monsoon intensity depends on the NorthernHemisphere summer insolation and (with a shortertimescale) on THC intensity (both correlations are

positive). The probable reason fr both is their influence onsummer temperature of Eurasia.

In still shorter timescale, monsoon anticorrelates with theENSO index (drought during El Nio and strong rainsduring La Nia).

The reason for this (and others) climate teleconnections(remote influences) are not yet fully explained andunderstood. Even the strongest correlation does notexplain causality

Stalagmite from Dongge Cave

(Southern China) - a record of9000 years of monsoon history

Hurricanes / cyclones / typhoons


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Hurricanes / cyclones / typhoons

Hurricanes (cyclones, typhoons) are defined as tropical lows with windspeed consistently over 33 m/s commence over tropical ocean areas ofSST greater than 28 C. Over land, they quickly lose their power. InAtlantic the hurricane season is defined as June 1 November 30.

Huragan Isabel, 2003, International Space Station

Saffir-Simpson scale: Tropical storm: 17.5 -32 m/s

Category 1: 3342 m/s Category 2: 4349 m/s Category 3: 5058 m/s Category 4: 5969 m/s Category 5: 70 m/s

A hurricane cross-section


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Left cross-section presents horizontal velocities (scaled up to 50m/s), right panel presents vertical velocities (red means upwards

blue is downwards) Emmanuel 2003 (Ann. Rev. Earth Planet Sci.)

Wppp


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Wpp

Forchhammer et al. 1998 (Nature)


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Hurricanesand SST

Because hurricanes

start only in waters ofSST > 28 C, does theirnumber depend onocean averagetemperature?

Number of Atlantichurricanes andaverage temperatureof the NorthernHemisphere.

Goldenberg et al. 2001 (Science)

Hurricanes and SST: direct proof


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Total dissipation energy (power dissipation index) ofhurricanes/typhoons over the whole season strongly correlates theaverage SST of their generation area for Atlantic (left) and Pacific(right) (respectively r2=0.65 i r2=0.67).

Emanuel 2005 (Nature)

More and more strong hurricanes


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Contrary to what the models show, the maximum wind velocity in ahurricane does not increase. On the other hand, we have more and morehurricanes close to the upper limit (categories 4 and 5).

Webster et al. 2005 (Science)

Hurricanes correlate with SST and... nothing else


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Analysis of datafrom various tropicalocean areas showsthat the number of

hurricanes in class 4& 5 correlate onlywith SST (A), whilethere is nosignificantcorrelation with air

humidity (B), windshear (C) i andNorth-South windspeed gradients (D).

Hoyos et al. 2006 (Science)

Caveat: data series is of uneven quality


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Analysis of old satellite photographs of 1968-1989 using modern methodsmade it possible to discover hurricanes of categories 4 & 5 that were notrecognized as such when they happened. Above: four examples from

northern Indian Ocean. Landsea et al. 2006 (Science)


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Studying hurricane statisticsolder than meteorology itself?

Study of oxygen isotope ratios in thesummer-autumn part of yearly tree-

rings in Georgia, USA shows (afterfiltering out the interannualvariability) whether a hurricanepassed nearby (index value < -1).

In the period which has good

meteorological data (since 1940),this method gave only one falsepositive event (1943).

Miller et al. 2006 (PNAS)


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Three hurricane regimes inthe Atlantic?

However, Atlantic SST andhurricane numbers havebeen comparatively wellknown for a long time.

It seems that the last 100years had three distinctclimate regimes of thetropical Atlantic with a non-linear increase of hurricanenumber with increasing SST.

Holland 2006(Komisja Senatu)

2005: a record breaking year in the Atlantic


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In 2005 Atlantic had a record number (26) of named hurricanes and tropicalstorms beating the 1933 by five. The season lasted for a record time period(until January 6, 2006). A named storm reached Europe for the first time ever.

NOAA

Few Atlantic hurricanes 2006: El Nio or Sahara?


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2005: 12 tropical storms (1 not named) and 15 hurricanes2006: 4 tropical storms and 5 hurricanes

The reason for that is lower SST values of the tropical Atlantic. Possiblereason for that may be El Nio. There is also another possibility: dust stormsfrom Sahara brought dust to tropical Atlantic in June and July cooling down

the sea beneath. Or maybe both phenomena are linked? Lau & Kim 2007 re rint

Summary 3/3


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Hurricanes (cyclones and typhoons) formexclusively over the ocean of SST of at least

28 C. A large correlation exists between theirtotal energy over a season and the SST of theirgeneration area (especially strong for theAtlantic, the ocean with the longest series ofreliable tropical storm data)

Hurricane power does not correlate with othermeteorological parameters (even where theorypredicts such correlations).

There is more and more strong hurricanesinstead of the expected increase of hurricane

maximal wind speed. After the record 2005 season, there was a

relatively quiet 2006. The reason for lowertropical Atlantic SST in 2006 could be El Nioor Sahara dust storms (or is one dependent on

the other?)

Hurricane evacuation route

(Miami, Florida)

vietnam lecture5 tropics

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