SO 442 the MaddenJulian Oscillation Lesson 6 What

SO 442 – the Madden-Julian Oscillation Lesson 6

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 • Now known to be a major propagator of weather systems

Atmospheric Scales of Motion Climate: PDO Years: ENSO Seasons: Monsoons Months/Weeks: MJO Space and time-scales of dynamical atmospheric processes. SOURCE: UCAR

The Madden-Julian Oscillation (MJO) Univ of Munich Physics Dept • Important features: – Convectively coupled disturbance that propagates eastward across the Tropics – 5 -10 m s-1 propagation speed in the Indian and west Pacific, where MJO convective variability is strongly coupled to the large-scale flow. – Simple baroclinic wind structure, with 850 h. Pa and 200 h. Pa wind perturbations 180 o out of phase – Characteristic timescales of 30 -90 days. Madden and Julian 1972

MJO- 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 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

MJO Structure in Outgoing Longwave Radiation (OLR): Indian Ocean and Western Pacific, Phases 1 -8 subsidence component 1 5 convective component 2 6 3 7 4 8 convective anomaly subsidence anomaly

Note: in this graphic, the MJO is not one thunderstorm that covers an entire ocean. Such a thing doesn’t exist! Rather, in the region represented by the cloud, MJO favors the development of more thunderstorms than normal • MJO is a very large scale oscillation (approximately 15, 000 km east-west distance) • Centered on the equator climate. gov • Features: one region of upward motion (favoring convection) and one region of downward motion (favoring drier conditions)

• MJO couplet (one region of upward motion and one region of downward motion) moves eastward along the equator • Why does it move along the equator, and not off the equator? • MJO really is an “equatorally trapped” Kelvin wave • Coriolis force acts to trap the MJO wave along the equator • Over a 3 -5 week period, the MJO convective couplet can transit the tropical eastern hemisphere

More views of the MJO convective couplet – not just thunderstorms but also specific humidity and wind anomalies, too! NOAA Pacific Northwest Laboratory (PNL) Univ of Washington Atmos Sci dept The passage of the MJO across the tropical oceans also shows up in SST anomalies US Dept of Energy

Jon Gottschalck, NOAA Climate Prediction Center MJO Cluster Structure

Jon Gottschalck, NOAA Climate Prediction Center MJO Forecasting

MJO Forecasting NOAA Climate Prediction Center

How MJO was discovered In the 1960 s and 1970 s, new computer power created the ability to look for patterns in meteorological observations. Could only look for patterns in TIME (at a location), not SPACE (at a given time). Tended to detect OSCILLATIONS.

What They Found • Surface pressure oscillates with a period of 40 -50 days. • ZONAL winds in the lower and upper troposphere also oscillate at this frequency, but 180° out-of-phase. • The signal was limited to the deep tropics. • They found little signal in the meridional wind, or in zonal winds in the midtroposphere.

Evidence of MJOs Sea Level Pressure, Equator and 180 E, May – Oct 1979 45 days Figure from R. Madden, 31 Aug 2005

Evidence of MJOs Temperature, Upper Ocean, Equator and 155 W, Aug 1991 – Jul 1992 T 125 m T 150 m 45 days

Their Interpretation MJO is a region of low-level convergence and convection. Propagating eastward only. Circumnavigates the globe in 4050 days.

Their Interpretation Pressure is LOW in the region of strongest convection. Upper-level outflow is only in the zonal direction.

Circumnavigating the Globe? • Madden and Julian originally believed that this area of convection propagated all the way around the world every 40 -50 days. • But this isn’t exactly right.

Circumnavigating the Globe? • Rather, the convection is TRIGGERED in the eastern Indian Ocean (typically by intruding midlatitude systems). • Convection dies out in the eastern Pacific due to cold SSTs

Circumnavigating the Globe? • However, the region of upper-level divergence WILL generally travel all the way around the world as a Kelvin Wave.

El Nino and the MJO • MJO events can TRIGGER El Nino events by weakening the trade winds (or even having a WESTERLY WIND BURST).

El Nino and the MJO • Why doesn’t EVERY MJO trigger an El Nino event? – CHARGE/DISCHARGE THEORY: – MJO is the TRIGGER—it happens much more often than the El Nino event itself. – Not every trigger is exactly right. – Even when the trigger is right, maybe ocean conditions are not yet right. – A partial explanation for the timing of ENSO.

Triggering MJO Events An MJO event in the Indian Ocean upsets the SSTs. It takes time for the SSTs to recover. Any intruding midlatitude systems during this period will FAIL to trigger an MJO event. Only when the environment is ready (another 40 -50 days) will the next midlatitude system be able to trigger a new MJO!

What are MJO events? • Described by “Nakazawa’s Hierarchy of Convection”

What are MJO events? • Each MJO event is actually composed of a small number of “super cloud clusters”-SCCs

What are MJO events? • SCCs: – Move EASTWARD – Last a day or two

What are MJO events? • What are SCCs? – Made of Cloud Clusters (CCs)

What are MJO events? • What are CCs? – Small groups of thunderstorms – Last less than a day – Move WESTWARD

1 MJO

4 SCCs

Many CCs

OBSERVATIONS OF KELVIN WAVES AND THE MJO Time–longitude diagram of CLAUS Tb (2. 5 S– 7. 5 N), January–April 1987 MJO event from Feb-Mar 1987 seen as cluster of Kelvin waves. Other Kelvin waves were also seen in March & April that were not really part of MJO (5 m s-1) Kelvin waves (15 m s-1)

OLR power spectrum, 1979– 2001 (Symmetric) How did we know that the cloud clusters in the previous slide were MJO and Kelvin waves? We could calculate their periods and zonal wavenumbers and identify them in this power spectrum diagram from Wheeler and Kiladis, 1999

Overview of Madden-Julian Oscillations (MJOs) 1. major and complex disturbances of the global tropical atmosphereocean system 2. propagating intraseasonal (~ 1 -2 months) oscillations 3. usually start in tropical Indian - W Pacific region 4. have largest amplitude in tropical Indian - Pacific region 5. propagate E-ward through the tropics 6. may propagate around globe, especially as UL disturbance 7. period 30 -60 days 45 days 8. zonal wave length Earth’s circumference 9. occur throughout the year 10. may have large impacts on global tropics and extratropics 11. have impacts on midlatitude climate 12. strong atmosphere-ocean coupling makes them difficult to analyze and model

MJOs and Teleconnections Modeled Tropospheric Response to Western Tropical Pacific Positive Heating Anomaly in Northern Winter H H = positive heating anomaly = energy propagation through wave train L L H = dry air advection = moist air advection

MJOs and Teleconnections Relationships Between Propagating Tropical Positive Convection Anomaly and North Pacific – North American Circulation and Precipitation Anomalies cf. Higgins and Mo, J Clim, 1997 Figure from: http: //www. cpc. ncep. noaa. gov/products/intraseasonal_faq. html#what

MJOs and Teleconnections Z 200 Anomalies, Dec 1996 – Jan 1997 During Dec 96 - Jan 97: 1. Weak La Nina conditions in tropical Pacific 2. Intense MJO activity in Indian Ocean – western tropical Pacific 3. Anomalously heavy precipitation and flooding in N CA, OR, WA 4. Anomalously low precipitation in SW US 5. Extratropical wave train similar to expected for MJO convection in tropical E IO – W Pacific Other examples of MJO impacts on west coast precipitation? Jan 92, Feb 93, Jan 95, Oct–Nov 03, Dec 04 – Jan 05, Dec 05 - Jan 06

Composites for: Phase 3, All Amplitudes, and all Background States, by Season ONDJFM OND JFM NPNA response to MJO affected by season. Effects can be dramatic. Likely causes: seasonal changes in location of convection and subsidence, and in strength, location, shear of east Asia - North Pacific jet.

Favorable and Unfavorable Factors for Wet and Dry Conditions in California Favorable / Unfavorable Conditions for MJO-Associated Anomalously Wet Conditions in CA Favorable 1. Early or late phases of the MJO 2. OND or JFM 3. El Niño or neutral background state 4. Wave train from Asia with anomalous low north and west of CA 5. Southwest to northeast tilt to the anomalous low off CA Unfavorable 1. La Niña background state 2. Middle phases of the MJO Favorable / Unfavorable Conditions for MJO-Associated Anomalously Dry Conditions in CA Favorable 1. Middle or late phases of the MJO 2. JFM 3. La Niña background state 4. Anomalous high over northeastern Pacific Unfavorable 1. Early phases of the MJO 2. El Nino background state Corresponding results for PNW, BC, and AK regions (not shown)

The 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.

Decay Region Formation Region

Active Convection

Active Convection Enhanced Easterlies

Cold air outbreak enhancement Active Convection

Deflected Jet Stream Active Convection Energy Build-up

MJO - 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

Theory: Moisture Modes and the MSE Budget • A moisture mode instability can result if large-scale divergent motions associated with convection import MSE into the column (e. g. Raymond et al. 2009, negative gross moist stability) • Alternatively, export by divergent motions can be positive, but MSE sources such as latent heat flux and cloud-radiative feedbacks overcompensate to produce MSE increases as a result of convection. • Such instability is manifest for WTG as strong positive moistureconvection feedbacks Peters and Bretherton (2006)

Madden-Julian Oscillation (a. k. a. Intraseasonal, 40 -50, 30 -60 Day Oscillation) • Intraseasonal Time Scale: ~40 -60 days • Planetary-Scale: Zonal Wavenumbers 1 -3 • Typical Baroclinic. Variables Wind Structure • Eastward Propagation Used for MJO Analysis üE. Hem: ~5 m/s, Surf. +Conv. +Circ. Interactions üW. Hem: ~ > 10 m/s, ~Free Tropospheric Wave • Tendency. Cloudy to be Equatorially Trapped Clear 1987/88 Low OLR Dependence: • Strong Seasonal High OLR ü NH Winter: Eastward Propagation ü NH Summer: ~Northeast Propagation U 200 • Significant Interannual Variability • Potential Role of Ocean/SST Feedback • Convection Has Multi-Scale Rainfall U 850 Structure • Significant Remote and Extra-Tropical Impacts Madden & Julian, 1972

A Typical MJO in N. H. Winter • Composite rainfall maps derived from merged satellite and in-situ measurements are separated by 10 days. • Rainfall anomalies propagate in a eastward fashion and mainly affect the Tropical eastern hemisphere. • These anomalies are accompanied by anomalies in wind, solar radiation, sea surface temperature, etc.

3 A Typical MJO in N. H. Summer 4 5 1 2 • Composite rainfall maps derived from merged satellite and in-situ measurements are separated by 10 days. • Rainfall anomalies propagate in a northeast fashion and mainly affect the Tropical eastern hemisphere. • These anomalies are accompanied by anomalies in wind, solar radiation, sea surface temperature, etc.

Boreal Summer Complex Propagation & Multi. Scale Organization Eastward Propagating Convective Envelope ~40 -50 days 3 4 5 Kemball-Cook & Wang, 2001 1 Westward Propagating Rossby-Waves ~ 10 -20 day; Modulated by 40 -50 day Northward Propagation Of Rossby-Wave Convection (twisting, SST, moisture feedback) 2