Synoptic I – ATMS 410 Tropical & Extratropical Oscillations (LP#3) –Intertropical convergence zone –Oscillations –Description of atmospheric oscillations.

Synoptic I – ATMS 410

• Tropical & Extratropical Oscillations (LP#3)– Intertropical convergence zone– Oscillations– Description of atmospheric oscillations


• Introduction– Up to now we have looked

at latitudinal averages• Assume changes across the

latitudes are more significant than changes across longitude

average

http://data2.collectionscanada.ca/ap/a/a051546.jpg


• Introduction– In this section of the

course, we’ll explore atmospheric changes across lines of longitude

http://www.photos.org.au/userimages/user756_1157947541.jpg


• Review: contributions of the different types of terms… (a) (b)

(c) (d)

(a) = undisturbed climatological flow

(b) = long term changes in the climatological flow

(c) = quasi-stationary long waves

(d) = shortwaves and cyclones


• In this lecture packet, we’ll be exploring contributions… (a) (b)

(c) (d)

(a) = undisturbed climatological flow

(b) = long term changes in the climatological flow

(c) = quasi-stationary long waves

(d) = shortwaves and cyclones


• Purpose– To begin to understand

how a better understanding of oscillations across the globe might improve our ability to forecast in the mid-latitudes

http://www.physics.pomona.edu/faculty/STAFF/HALEY/Lecture%20Demonstrations/TOC2.htm


• Dominant controls of tropical climates– Intertropical convergence

zone (ITCZ)– Subtropical high pressure

systems

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4028

http://earthobservatory.nasa.gov/Newsroom/NewImages/Images/itcz_goes11_lrg.jpg


• Intertropical convergence zone (ITCZ)– East-west oriented low pressure region at the surface

located near the equator– Position varies seasonally

• Migration over land is greater than that over the ocean


• Intertropical convergence zone (ITCZ)– East-west oriented low pressure region at the surface

located near the equator– Position varies seasonally

• Migration over land is greater than that over the ocean


• Intertropical convergence zone (ITCZ)– Seasonal migration is of high

significance to the amount of rainfall that occurs in the semiarid regions that bound the tropics

• Failure of the ITCZ to migrate to its “normal” position can lead to drought and to social disruptions


• Intertropical convergence zone (ITCZ)– Formation is thought to be tied to

the ascending branch between the Hadley Cells

– Oscillations can exert a significant influence on the strength and location of the ITCZ


• Intertropical convergence zone (ITCZ)– Formation is thought to be tied

to the ascending branch between the Hadley Cells

– Oscillations can exert a significant influence on the strength and location of the ITCZ


• Definition; oscillation– Any phenomenon that tends to vary above

or below a mean value in some sort of periodic way

• Occurs when a system is disturbed from a position of stable equilibrium

– If an oscillation has a recognized periodicity, then it may be called a cycle (occurs rarely in the atmosphere)

• Can exploit periodicity to make forecasts


• Types of oscillations– Damped

• Constantly decreasing amplitude

– Unstable• Growing amplitude, then breaking down

– Neutral, persistent or undamped• Maintains constant amplitude

– Forced oscillation• External forces initiates and maintains it

– Free oscillation• External force initiates it


• Examples of atmospheric oscillations– Southern Oscillation (SO)

– North Atlantic Oscillation (NAO)

– North Pacific Oscillation (NPO)/ Pacific Decadal Oscillation (PDO)

– Madden-Julian Oscillation (MJO)

– Quasi-biennial Oscillation (QBO)

– Pacific North American Oscillation (PNA)

– Arctic Oscillation (AO)

– Antarctic Oscillation (AAO)


• North Atlantic Oscillation (NAO)– The difference in sea level pressure between

a station in Iceland and a station near the Azores

http://www.lib.utexas.edu/maps/islands_oceans_poles/azores.jpg

http://www.findlocalguide.com/Maps/Iceland-Map-Big.jpg


• North Atlantic Oscillation (NAO)– Positive phase;

• Stronger than usual subtropical high pressure and a deeper than normal Icelandic Low

– NAO Index defined in the winter season

http://www-paoc.mit.edu/paoc/research/NAO.gif


• North Atlantic Oscillation (NAO)– Driven by the atmosphere– Long time scale

• Changes in phase often take decades

http://www.cgd.ucar.edu/cas/jhurrell/nao.stat.winter.html


• North Pacific Oscillation (NPO)/ Pacific Decadal Oscillation (PDO) {a.k.a. PDV, IPO}– Index derived from monthly

SST anomalies north of 20oN in the Pacific Ocean

http://jisao.washington.edu/pdo/


• North Pacific Oscillation (NPO)/ Pacific Decadal Oscillation (PDO)– Study investigating the role of

sea surface temperature on salmon behavior in the North Pacific

http://www.cses.washington.edu/cig/outreach/workshopfiles/portland2004salmon/salmon_USFWS_cropped1.jpg


• North Pacific Oscillation (NPO)/ Pacific Decadal Oscillation (PDO)– Positive phase; warmer

than normal SSTs in the northeastern (along the west coast of North America) and Tropical Pacific Oean


• North Pacific Oscillation (NPO)/ Pacific Decadal Oscillation (PDO) {a.k.a. PDV, IPO}– Positive phase; northwest

SST anomalies are negative, eastern tropical Pacific Ocean anomalies are positive

http://www-pord.ucsd.edu/~ltalley/sio210/Decadal_variability/pdo_latest.png


• North Pacific Oscillation (NPO)/ Pacific Decadal Oscillation (PDO)– Represented by a shift of SST

that occurs on a 20 to 30 year cycle

– There have been just two full PDO cycles in the last 100 years

http://www-pord.ucsd.edu/~ltalley/sio210/Decadal_variability/pdo_latest.png


• Pacific North American Oscillation (PNA)– An alternating pattern of

pressures in the central Pacific Ocean and “centers of action” over western Canada and the southeastern United States

http://www.cdc.noaa.gov/Teleconnections/pna.html


• Pacific North American Oscillation (PNA)– Characterized by atmospheric

flow in which the west coast of North America is out of phase with the eastern Pacific and southeast United States



• Pacific North American Oscillation (PNA)– Positive phase

• Ridge over western N.A.– Similar anomaly signs; Hawaii and

intermountain region of Canada

• Troughs over central North Pacific and southeastern U.S.

– Similar anomaly signs; Aleutian Islands, southeastern U.S.



• Pacific North American Oscillation (PNA)– index

• Ridge over western N.A.– Similar anomaly signs; Hawaii and

intermountain region of Canada

• Troughs over central North Pacific and southeastern U.S.

– Similar anomaly signs; Aleutian Islands, southeastern U.S.

http://www.ecmwf.int/research/era/ERA-40_Atlas/images/full/G07_TS_YEA.gif


• Pacific North American Oscillation (PNA)– index

• Positive; strong Aleutian Low and a strong ridge over western Canada

• Derived at (20oN, 160oW), (45oN, 165oW), (55oN, 115oW), and (30oN, 85oW)


• Madden-Julian Oscillation (MJO)– 40-50 day oscillation– Eastward-propagating

• near the equator

– Found using tropical rawinsonde data at Canton Island (2.8oS, 171.7oW) over a ten year period

• Large coherence between surface pressure, zonal winds, and temperatures at various levels over a broad period range


• Madden-Julian Oscillation (MJO)– Characterized by anomalous

rainfall• Appears first over the Indian and

Pacific Ocean• Intensifies as it moves over the

very warm water of the western and central Pacific Ocean

• Becomes ill-defined over the cooler waters of the eastern Pacific


• Madden-Julian Oscillation (MJO)– Characterized by anomalous

rainfall• Identified by eastward

progression of a large region of either enhanced or suppressed rainfall

http://www-das.uwyo.edu/~geerts/cwx/notes/chap12/mjo.html


• Madden-Julian Oscillation (MJO)– Observed using

• outgoing long-wave radiation (OLR) from satellites

• global radiosonde network

– Both used to determine anomalies in

• OLR • Upper level divergence• Upper- and mid-level winds

http://www-das.uwyo.edu/~geerts/cwx/notes/chap12/mjo.html


• Quasi-biennial Oscillation (QBO)

HERE!!


• Quasi-biennial Oscillation (QBO)– Alternating bands of easterly and

westerly winds that originate above 30 km and move downward in the stratosphere at 1 km per month

– Discovered using rawinsonde data at Canton Island

• R.J. Reed (1961)• R.A. Ebdon (1960)


• Quasi-biennial Oscillation (QBO)– Alternating bands of easterly and

westerly winds that originate above 30 km and move downward in the stratosphere at 1 km per month

– Discovered using rawinsonde data at Canton Island

• R.J. Reed (1961)• R.A. Ebdon (1960)


• Quasi-biennial Oscillation (QBO)– Alternating bands of stratospheric

easterlies and westerlies over the equator were observed during the famous eruption of Krakatoa, August 1883

• Krakatoa Easterlies

• Berson Westerlies


• Quasi-biennial Oscillation (QBO)– Wind fluctuations vary with a period of 25-27 months

(quasi-biennial periodicity)– Wind regimes (equatorial easterlies and westerlies) take

about a year to descend from 10 to 60 hPa– No loss of amplitude during descent


• Quasi-biennial Oscillation (QBO)– Initiation and maintenance of

QBO still the subject of research, involves

• Gravity wave

• Rossby wave

interaction in a rotating stratified atmosphere (similar phenomena identified on other planets, Jupiter) http://www.jisao.washington.edu/data_sets/qbo/qbo.jpg


• Quasi-biennial Oscillation (QBO)– Initiation and maintenance of QBO still

the subject of research, involves• Simulation of QBO remains a great challenge

for general circulation models (GCMs)– Gravity waves generated by equatorial convection

are essential

– Better modeling of dynamics of mesoscale convective systems, and the synoptic-scale tropical waves in which these systems are embedded

http://www.theoldcomputer.com/Misc%20Artwork/Calendar_Past%20Computers_2005.jpg


• Quasi-biennial Oscillation (QBO)– Linkage between QBO and

sunspot activity• Solar ultraviolet irradiance

can serve as pacemakers to the period and phase of the QBO

http://astronomy.neatherd.org/Sunspots.htm


• Arctic Oscillation (AO) &Antarctic Oscillation (AAO)– The AO and NAO are different ways of

describing the same phenomenon

– AO is computed as an index by comparing pressure in the polar region with pressure at 45oN

– Positive phase occurs when higher than normal pressure is found at 45oN and lower than normal pressure in the polar region

http://www.washington.edu/newsroom/news/2001archive/07-01archive/k070501a.html


• Arctic Oscillation (AO) &Antarctic Oscillation (AAO)– AO recently has been

mostly in a positive phase– AAO is a “dynamical

twin” of the AO; has much in common with the AO pattern, just at the south pole

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/season.JFM.ao.gif


http://www.aoml.noaa.gov/graphics/elnino.gif

• Southern Oscillation (SO) {a.k.a. ENSO}– Results from large-scale

interactions between the tropical-subtropical atmosphere and the Pacific to Indian Ocean basins

– Irregular/ aperiodic phenomenon that has

• quasi-biennial (2-2.5 year) • LF interannual (2.5-7 year)

components


• Southern Oscillation (SO)– What happens?

• In normal, non-El Niño conditions, the trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador.



• In normal, non-El Niño conditions, the sea surface temperature is about 8 degrees C higher in the west, with cool temperatures off South America, due to an upwelling of cold water from deeper levels. This cold water is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. Rainfall is found in rising air over the warmest water, and the east Pacific is relatively dry. The observations at 110 W (left diagram of 110 W conditions) show that the cool water (below about 17 degrees C, the black band in these plots) is within 50m of the surface.

http://www.pmel.noaa.gov/tao/elnino/images/elnino.gif



• In El Niño conditions, the trade winds relax in the central and western Pacific leading to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west.



• In El Niño conditions, the observations at 110W show, for example, that during 1982-1983, the 17-degree isotherm dropped to about 150m depth. This reduced the efficiency of upwelling to cool the suface and cut off the supply of nutrient rich thermocline water to the euphotic zone. The result was a rise in sea surface temperature and a drastic decline in primary productivity, the latter of which adversely affected higher trophic levels of the food chain, including commercial fisheries in this region. The weakening of easterly tradewinds during El Niño is evident in this figure as well. Rainfall follows the warm water eastward, with associated flooding in Peru and drought in Indonesia and Australia. The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific. http://www.pmel.noaa.gov/tao/elnino/images/elnino.gif


• Southern Oscillation (SO)– Locked to a seasonal

cycle…weakest in boreal spring (austral autumn)

• Time of the predictability barrier (spring frailty)

• New events are likely to develop

• Existing conditions are likely to collapse

http://www.pmel.noaa.gov/pubs/docs/mcph1401/front.jpg


• Southern Oscillation (SO)– Index

• Derived from the normalized difference in monthly atmospheric pressure between Tahiti and Darwin

http://www.bom.gov.au/climate/enso/


• Southern Oscillation (SO)– ENSO-like fluctuations


• Southern Oscillation (SO)– A more objective way to

analyse the nature of ENSO is through the use of spectral and signal detection techniques (e.g. MTM-SVD)


• Southern Oscillation (SO)– QB (2-2.5 yr) and LF (2.5-8 yr) signals– Fluctuations with “ENSO like” characteristics

• Quasi-decadal signal (9-13 yr)

• Multidecadal signal (15-20 yr)– Indicative of the PDO phenomenon


• Perspective– Note the differences in time scales…MJO PDO

20-30 years40-50 days

v.

Synoptic-scale cyclones 3 – 5 days


• Perspective– Note the differences in time scales…MJO PDO

20-30 years40-50 days

Synoptic-scale cyclones 3 – 5 days

Although weather in the tropics is generally less predictable than in the extratropics, the tropical oscillations tend to be long-lived and, if their interactions with the extratropics can be understood, observations of tropical oscillations can aid in our extratropical weather forecasts


• In other words, why do we care about tropical oscillations in a course focusing on the extratropics (mid-latitudes)?– Example…the relatives who visit for an

extended stay• Aunt Matilda and Uncle Billy visit your house

for four weeks, what do you predict will happen in your household after the first week of their visit?


• References– Baldwin, M.P., L.J. Gray, T.J. Dunkerton, K. Hamilton, P.H. Haynes, W.J.

Randel, J.R. Holton, M.J. Alexander, I. Hirota, T. Horinouchi, D.B.A. Jones, J.S. Kinnersley, C. Marquardt, K. Sato, and M. Takahashi, 2001: The Quasi-Biennial Oscillation, Reviews of Geophysics, 39, 179-229.

– Bridgman and Oliver, 2006: The Global Climate System; Patterns, Processes and Teleconnections. Cambridge University Press, 331 pp.

– Diaz, H .F., and V. Markgraf (Eds.), 2000: El Niño and the Southern Oscillation: Multiscale Variability and Global and Regional Impacts, Cambridge University Press, 496 pp.

– Madden, R. A., and P. R. Julian, 1994: Observations of the 40-50 day tropical oscillation: A review. Mon. Wea. Rev., 122, 814-837.

Synoptic I – ATMS 410 Tropical & Extratropical Oscillations (LP#3) –Intertropical convergence zone –Oscillations –Description of atmospheric oscillations.

Documents

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itcz slide

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long term changes

hadley cells oscillations

atmospheric changes

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