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