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More Ocean Indices
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Transcript of More Ocean Indices
More Ocean Indices More Ocean Indices
Paul Knight, Richard Grumm and Paul Roundy
PSU Meteorology and NWS
State College
Pacific Decadal OscillationPacific Decadal OscillationPDA/NPO Oceanic IndexPDA/NPO Oceanic Index
The Pacific Decadal Oscillation (PDO) is an index of long-term variability of the sea-surface temperatures of the North Pacific Ocean. – reflects the dominant mode of SST over the North Pacific
Ocean.
– The PDO can impact the climate.
– A characteristic that distinguishes the PDO from ENSO is that 20th century PDO events have tended to persist for 20-to-30 years, while ENSO events have typically persisted for 6 to 18 months.
– also known as the North Pacific Oscillation (NPO) and the terms can be used interchangeably.
Phases of the PDO/NPOPhases of the PDO/NPO
– the high phase of the NPO is the term used to describe a warm PDO and the low phase of the NPO is the term used to describe the cold PDO.
– Recent research indicates a clear link of the PDO to the ENSO. The Climate Prediction Center thinks that the sign of the PDO may be a composite of a longer term ENSO cycle.
PDO SST ExamplesPDO SST Examples
Figure 2 The warm phase (left) and cold phase (right) of the PDO. The warm phase is also known asa high NPO while the cold phase is also known as a low NPO. Similar to an El Nino event, note thewarm water in the eastern Pacific.
The cold phaseThe cold phase
Cold PDO regimes prevailed from 1890-1950– cold phase index is positive– the PDO was higher then average from 1920 to 1950. – cold phase may behave like a weak La Nina
note colder water in tropical Pacific dominates may enhance impacts of La Nina when they are in phase
– The cold phase occurs when there is warmer water over the western and central Pacific associated with a deepened Aleutian low.
– Colder water over eastern and tropical Pacific
The warm phaseThe warm phase
Warm PDO regimes dominated from 1950 into the 1990’s.
During the warm phase, the PDO is negative. On a 30 year time scale, the PDO was lower
than average from 1950 to 1980. A negative PDO may act like an El Nino. The warm phase occurs when there is colder
water over the western and central Pacific.
The warm phaseThe warm phase
Warmer and drier winters in the northern regions of the nation and wetter and cooler winters observed in the southern areas of the United States.
El Nino is associated with a negative SOI, weak tropical easterlies and warm Nino3.4 SST’s.
PDO PDO SST/wind vectors/MSLP anomaliesSST/wind vectors/MSLP anomalies
Figure 2 The warm phase (left) and cold phase (right) of the PDO. The warm phase is also known asa high/positive NPO while the cold phase is also known as a low/negative NPO. Similar to an El Ninoevent, note the warm water in the eastern Pacific.
PDO-ENSO Similarities PDO-ENSO Similarities SST/wind vectors/MSLP anomaliesSST/wind vectors/MSLP anomalies
PDO values 1900-2000PDO values 1900-2000
PDO SummaryPDO Summary Relates to ENSO cycles
– Frequency of El Nino can be related to PDO phase during the past 30-40 years.
– PDO can interfere both constructively and destructively with ENSO.– PDO may not be independent of ENSO
High NPO (warm phase) – Cold water in north/central Pacific– Warm water along west coast NOAM (fishing industry named
phases!)– May enhance El Nino effects in eastern US
Low NPO (cold phase)– Warm water in north/central Pacific– La Nina like impact connect with weaker storm tracks, farther north
[dry-nation]
ReferemcesReferemces
Rogers, J.C., 1997: North Atlantic storm track variability and its association to the North Atlantic Oscillation and climate variability of Northern Europe. Journal of Climate 10(7), 1635-1647.
Hurrell, J.W., 1995: Decadal trends in the North Atlantic Oscillation and
relationships to regional temperature and precipitation. Science 269, 676-679. Wallace, J.M. and David S. Gutzler, 1981:"Teleconnections in the Geopotential
Height Field during the Northern Hemisphere Winter" Mon. Wea. Review,109,784-812.
Teleconnections Linking Wolrdwide Climate Anomalies. ed. M.H. Glantz, R.W. Katz and N. Nicholls, Cambridge University Press, 1991.
Rogers, J.C. and H. Van Loon, 1979: "The Sea-Saw in winter temperatures between Greenland and Northern Europe. Part II. Some atmospheric and oceanic effectes in middle and high latitudes." Mon Wea. Rev. ,107, 509-519.
The Large-Scale ConvectiveThe Large-Scale ConvectiveDisturbanceDisturbance
Tropical Intraseasonal or
Madden-Julian Oscillation
What is the MJO?What is the MJO?
Large-scale disturbance of deep convection and winds that controls up to half of the variance of tropical convection in some regions
Brief history
MJO- an intraseasonal eventMJO- an intraseasonal event
Prior to 1971, it was thought that virtually all variability in the weather conditions within a given season in the Tropics was random.
There were indications of interseasonal variations, such as the Southern Oscillation
Studies of Tropical rainfall and pressure changes showed additional oscillations
The MJO - A DescriptionThe MJO - A Description
A 30-60 day oscillation in the coupled Tropical ocean-atmosphere system
An eastward progression of enhanced and suppressed convection
Low level and upper level wind patterns show distinct anomalies
Strong year to year variability in MJO that is related to ENSO cycle
Wave CooperationWave Cooperation
Kelvin and Rossby waves linked by convection, land, and air-sea interaction combine to produce the observed disturbance.
Schematic of Mature MJOSchematic of Mature MJO
The 3D view of MJOThe 3D view of MJO
Axis of coupled convection/suppressed convection usually between 5S-5N
SST feedback could be sensitive enough to either trigger or help propagate the wave
Kelvin Waves in the OceanKelvin Waves in the Ocean
Convective Kelvin WaveConvective Kelvin Wave
H L
Convection removesSome of the accumulating mass, slows propagation
Propagation speed: less than 20 ms-1
z
x
MJO StatisticsMJO Statistics
Eastward propagation, 4 +/- 2 ms-1. Also has standing wave behavior
30-60 day periodWavenumber 1-4 (planetary scale)Interacts with midlatitudes, but some
of this is nonlinear and hard to quantify
Finding the MJOFinding the MJO
S ate lli tesO u tg o ing Lo ng W a ve
V e lo c ity P o te n tia ld ive rge n t w in d com po ne n t
W ind an om aliesU pp e r a nd lo w le ve ls
M JO D e tec tion
The Satellite View of MJOThe Satellite View of MJO
The MJO is noted by a cluster of thunderstorms drifting eastward along the equatorial Indian and Pacific oceans.
Simplified Madden-Julian Oscillation Composite OLR from A.J. Matthews, 2000.
The Velocity Potential ViewThe Velocity Potential View
The 200 mb velocity potential illustrates yet another way of detecting both the presence and movement of the MJO. This is noted by a couplet of anomalies.
Disturbances in the 500mb Disturbances in the 500mb FlowFlow
Another method of detecting the presence of the MJO is following height and wind perturbations in the 500 mb flow over the equatorial Pacific ocean.
How Does It Propagate?How Does It Propagate?
Is a matter of debate, but, probably involves – interactions with equatorial waves
Kelvin wave Equatorial Rossby wave
– Feedbacks from convection– Sea surface temperatures—air-sea interaction– Land interactions
MJO - Probable CauseMJO - Probable Cause
Wave-CISK Theory (Chang, Lau, Lim)– slow moving wave with conditional instability
of the second kind (see Tropical Meteo)
Evaporation-wind feedback Theory (Emanuel, Neelin, Wang)– diabatic heating due to cumulus convection
nearly balanced by adiabatic cooling
Relationship of MJO to Relationship of MJO to North American WeatherNorth American Weather
Most prominent connection to phase of ENSO
Winter weather along the West Coast (see figure)
Secondary downstream effects in USAModulation of tropical storm development
in Atlantic basin during the summer
The MJO and West Coast WxThe MJO and West Coast Wx
FormationRegion
Decay Region
Active Convection
Active Convection
EnhancedEasterlies
Active Convection
Energy Build-up
Deflected Jet Stream
Active Convection
Cold air outbreak enhancement
MJO - A Modeler’s NightmareMJO - A Modeler’s Nightmare
GCM simulation of convection (CPS)
SST variations not well simulated
Change of phase speed from eastern to western hemispheres
Handling of very low wave number
Recent modifications-– increased vertical
resolution– better parameterization
of: radiation convection cloud formation precipitation surface convergence
Prediction of MJOPrediction of MJO
Global weather models predict it with some skill to about 7 or 8 days
Filtering methods allow prediction up to 20 days (Wheeler and Weikmann, 2001)
Statistical schemes may allow prediction for more than 40 or 50 day lead times
MJO ResearchMJO Research
Chang, Lim, 1988: Kelvin wave-CISK
Chen, Murakami, 1988: Development and life-cycle of the Indian monsoon
Crum, Dunkerton, 1994: CISK and evaporational-wind feedback
Ferranti, Palmer, Molteni and Klinker,1990: Tropical and extra-tropical interactions associated with 30-60 day oscillation
Gray,1988: Seasonal frequency variations in the 40-50 day cycle