The Planetary-Scale Structure of the Madden-Julian Oscillation

Abstract Numerical experiments with a 2.5-layer and a 2-level model are conducted to examine the mechanism for the planetary scale selection of the Madden–Julian oscillation (MJO). The strategy here is to examine the evolution of an initial perturbation that has a form of the equatorial Kelvin wave at zonal wavenumbers of 1 to 15. In the presence of a frictional boundary layer, the most unstable mode prefers a short wavelength under a linear heating; but with a nonlinear heating, the zonal wavenumber 1 grows fastest. This differs significantly from a model without the boundary layer, in which neither linear nor nonlinear heating leads to the long wave selection. Thus, the numerical simulations point out the crucial importance of the combined effect of the nonlinear heating and the frictional boundary layer in the MJO planetary scale selection. The cause of this scale selection under the nonlinear heating is attributed to the distinctive phase speeds between the dry Kelvin wave and the wet Kelvin–Rossby wave couplet. The faster dry Kelvin wave triggered by a convective branch may catch up and suppress another convective branch, which travels ahead of it at the phase speed of the wet Kelvin–Rossby wave couplet if the distance between the two neighboring convective branches is smaller than a critical distance (about 16 000 km). The interference between the dry Kelvin wave and the wet Kelvin–Rossby wave couplet eventually dissipates and “filters out” shorter wavelength perturbations, leading to a longwave selection. The boundary layer plays an important role in destabilizing the MJO through frictional moisture convergences and in retaining the in-phase zonal wind–pressure structure.

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Prospects for Erratic and Intensifying Madden-Julian Oscillations

Climate ◽

10.3390/cli8020024 ◽

2020 ◽

Vol 8 (2) ◽

pp. 24

Author(s):

Patrick Haertel

Keyword(s):

Water Vapor ◽

Tropical Cyclones ◽

Radiative Forcing ◽

Coupled Model ◽

Equatorial Indian Ocean ◽

Madden Julian Oscillation ◽

Kelvin Wave ◽

Late 20Th Century ◽

Planetary Scale ◽

One Year

The Madden–Julian Oscillation (MJO) is a planetary-scale convective disturbance that typically forms in the equatorial Indian Ocean, propagates slowly eastward, and dissipates near the date line. This study examines how the MJO changes in response to a changing radiative forcing in a fully-Lagrangian coupled model (LCM) that is shown to simulate robust and realistic MJOs. After the LCM is spun up for 160 years to reproduce the late 20th century climate, non-water-vapor longwave optical depth is increased over 70 years to model the effects of increasing concentrations of greenhouse gases. The model is then run for another 30 years without additional changes to the radiative forcing. After the radiative forcing is modified, the MJO generally becomes more frequent and intense, but it is also more variable from one year to the next. Not only do composite MJO rainfall perturbations increase, but wind, temperature, and moisture perturbations also become stronger. The aspect of the MJO’s structure that changes the most is the largely dry equatorial Kelvin wave circulation that circumnavigates the globe between moist phases of the MJO. Potential impacts of these changes included alterations to the way in which the MJO modulates tropical cyclones, monsoon disturbances, and El Niño.

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A Modified Multivariate Madden–Julian Oscillation Index Using Velocity Potential

Monthly Weather Review ◽

10.1175/mwr-d-12-00327.1 ◽

2013 ◽

Vol 141 (12) ◽

pp. 4197-4210 ◽

Cited By ~ 66

Author(s):

Michael J. Ventrice ◽

Matthew C. Wheeler ◽

Harry H. Hendon ◽

Carl J. Schreck ◽

Chris D. Thorncroft ◽

...

Keyword(s):

Zonal Wind ◽

Velocity Potential ◽

Longwave Radiation ◽

Warm Pool ◽

Boreal Summer ◽

Madden Julian Oscillation ◽

Systematic Analysis ◽

Planetary Scale ◽

Daily Data ◽

The Indian Ocean

Abstract A new Madden–Julian oscillation (MJO) index is developed from a combined empirical orthogonal function (EOF) analysis of meridionally averaged 200-hPa velocity potential (VP200), 200-hPa zonal wind (U200), and 850-hPa zonal wind (U850). Like the Wheeler–Hendon Real-time Multivariate MJO (RMM) index, which was developed in the same way except using outgoing longwave radiation (OLR) data instead of VP200, daily data are projected onto the leading pair of EOFs to produce the two-component index. This new index is called the velocity potential MJO (VPM) indices and its properties are quantitatively compared to RMM. Compared to the RMM index, the VPM index detects larger-amplitude MJO-associated signals during boreal summer. This includes a slightly stronger and more coherent modulation of Atlantic tropical cyclones. This result is attributed to the fact that velocity potential preferentially emphasizes the planetary-scale aspects of the divergent circulation, thereby spreading the convectively driven component of the MJO’s signal across the entire globe. VP200 thus deemphasizes the convective signal of the MJO over the Indian Ocean warm pool, where the OLR variability associated with the MJO is concentrated, and enhances the signal over the relatively drier longitudes of the equatorial Pacific and Atlantic. This work provides a useful framework for systematic analysis of the strengths and weaknesses of different MJO indices.

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A Frictional Skeleton Model for the Madden–Julian Oscillation*

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-020.1 ◽

2012 ◽

Vol 69 (9) ◽

pp. 2749-2758 ◽

Cited By ~ 24

Author(s):

Fei Liu ◽

Bin Wang

Keyword(s):

General Circulation ◽

Large Scale ◽

General Circulation Models ◽

Madden Julian Oscillation ◽

Ekman Pumping ◽

Convective Envelope ◽

Skeleton Model ◽

Planetary Scale ◽

System A ◽

Frictional Convergence

Abstract The Madden–Julian oscillation (MJO) is a multiscale system. A skeleton model, developed by Majda and Stechmann, can capture some of planetary-scale aspects of observed features such as slow eastward propagation, nondispersive behavior, and quadrupole-vortex structure. However, the Majda–Stechmann model cannot explain the source of instability and the preferred planetary scale of the MJO. Since the MJO major convection region is leaded by its planetary boundary layer (PBL) moisture convergence, here a frictional skeleton model is built by implementing a slab PBL into the neutral skeleton model. As a skeleton model allowing the scale interaction, this model is only valid for large-scale waves. This study shows that the PBL frictional convergence provides a strong instability source for the long eastward modes, although it also destabilizes very short westward modes. For the long waves (wavenumber less than 5), the PBL Ekman pumping moistens the low troposphere to the east of the MJO convective envelope, and sets up favorable moist conditions to destabilize the MJO and favor only eastward modes. Sensitivity experiments show that a weak PBL friction will enhance the instability slightly. The sea surface temperature (SST) with a maximum at the equator also prefers the long eastward modes. These theoretical analysis results encourage further observations on the PBL regulation of mesosynoptic-scale motions, and exploration of the interaction between PBL and multiscale motions, associated with the MJO to improve the MJO simulation in general circulation models (GCMs).

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Tropical Atmospheric Madden–Julian Oscillation: A Strongly Nonlinear Free Solitary Rossby Wave?

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0319.1 ◽

2017 ◽

Vol 74 (10) ◽

pp. 3473-3489 ◽

Cited By ~ 10

Author(s):

Jun-Ichi Yano ◽

Joseph J. Tribbia

Keyword(s):

Rossby Wave ◽

Order Approximation ◽

Intraseasonal Variability ◽

Analytic Solutions ◽

Water Model ◽

Small Scale ◽

Madden Julian Oscillation ◽

Strongly Nonlinear ◽

Planetary Scale ◽

Theoretical Considerations

Abstract The Madden–Julian oscillation (MJO), a planetary-scale eastward-propagating coherent structure with periods of 30–60 days, is a prominent manifestation of intraseasonal variability in the tropical atmosphere. It is widely presumed that small-scale moist cumulus convection is a critical part of its dynamics. However, the recent results from high-resolution modeling as well as data analysis suggest that the MJO may be understood by dry dynamics to a leading-order approximation. Simple, further theoretical considerations presented herein suggest that if it is to be understood by dry dynamics, the MJO is most likely a strongly nonlinear solitary Rossby wave. Under a global quasigeostrophic equivalent-barotropic formulation, modon theory provides such analytic solutions. Stability and the longevity of the modon solutions are investigated with a global shallow-water model. The preferred modon solutions with the greatest longevities compare well overall with the observed MJO in scale and phase velocity within the factors.

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A Multiscale Model for the Intraseasonal Impact of the Diurnal Cycle over the Maritime Continent on the Madden–Julian Oscillation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0158.1 ◽

2016 ◽

Vol 73 (2) ◽

pp. 579-604 ◽

Cited By ~ 27

Author(s):

Andrew J. Majda ◽

Qiu Yang

Keyword(s):

Diurnal Cycle ◽

Numerical Models ◽

Multiscale Model ◽

Boreal Winter ◽

Madden Julian Oscillation ◽

Maritime Continent ◽

Upper Troposphere ◽

Planetary Scale ◽

Baroclinic Modes ◽

Huge Challenge

Abstract The eastward-propagating Madden–Julian oscillation (MJO) typically exhibits complex behavior during its passage over the Maritime Continent, sometimes slowly propagating eastward and other times stalling and even terminating there with large amounts of rainfall. This is a huge challenge for present-day numerical models to simulate. One possible reason is the inadequate treatment of the diurnal cycle and its scale interaction with the MJO. Here these two components are incorporated into a simple self-consistent multiscale model that includes one model for the intraseasonal impact of the diurnal cycle and another one for the planetary/intraseasonal circulation. The latter model is forced self-consistently by eddy flux divergences of momentum and temperature from a model for the diurnal cycle with two baroclinic modes, which capture the intraseasonal impact of the diurnal cycle. The MJO is modeled as the planetary-scale circulation response to a moving heat source on the synoptic and planetary scales. The results show that the intraseasonal impact of the diurnal cycle during boreal winter tends to strengthen the westerlies (easterlies) in the lower (upper) troposphere in agreement with the observations. In addition, the temperature anomaly induced by the intraseasonal impact of the diurnal cycle can cancel that from the symmetric–asymmetric MJO with convective momentum transfer, yielding stalled or suppressed propagation of the MJO across the Maritime Continent. The simple multiscale model should be useful for the MJO in observations or more complex numerical models.

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The role of large-scale moistening by adiabatic lifting in the Madden-Julian Oscillation convective onset

Journal of Climate ◽

10.1175/jcli-d-21-0322.1 ◽

2021 ◽

pp. 1-49

Author(s):

Chelsea E. Snide ◽

Ángel F. Adames ◽

Scott W. Powell ◽

Víctor C. Mayta

Keyword(s):

Large Scale ◽

Heat Fluxes ◽

Data Sets ◽

Madden Julian Oscillation ◽

Onset Of Convection ◽

Surface Heat Fluxes ◽

Planetary Scale ◽

Moisture Advection ◽

The Indian Ocean

AbstractThe initiation of the Madden-Julian Oscillation over the Indian Ocean is examined through the use of a moisture budget that applies a version of the weak temperature gradient (WTG) approximation that does not neglect dry adiabatic vertical motions. Examination of this budget in ERA-Interim reveals that horizontal moisture advection and vertical advection by adiabatic lifting govern the moistening of the troposphere for both primary and successive MJO initiation events. For both types of initiation events, horizontal moisture advection peaks prior to the maximum moisture tendency, while adiabatic lifting peaks after the maximum moisture tendency. Once convection initiates, moisture is maintained by anomalous radiative and adiabatic lifting. Adiabatic lifting during successive MJO initiation is attributed to the return of the circumnavigating circulation from a previous MJO event, while in primary events the planetary-scale circulation appears to originate over South America. Examination of the same budget with data from the DYNAMO northern sounding array shows that adiabatic lifting contributes significantly to MJO maintenance, with a contribution that is comparable to that of surface heat fluxes. However, results from the DYNAMO data disagree with those from ERA-Interim over the importance of adiabatic lifting to the moistening of the troposphere prior to the onset of convection. In spite of these differences, the results from the two data sets show that small departures from WTG balance in the form of dry adiabatic motions cannot be neglected when considering MJO convective onset.

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The Tropical Madden–Julian Oscillation and the Global Wind Oscillation

Monthly Weather Review ◽

10.1175/2008mwr2686.1 ◽

2009 ◽

Vol 137 (5) ◽

pp. 1601-1614 ◽

Cited By ~ 31

Author(s):

Klaus Weickmann ◽

Edward Berry

Keyword(s):

Phase Space ◽

Winter Season ◽

Oscillatory Behavior ◽

Madden Julian Oscillation ◽

Physical Processes ◽

Similar Frequency ◽

Planetary Scale ◽

The Pacific ◽

The Pacific Ocean

Abstract The global wind oscillation (GWO) is a subseasonal phenomenon encompassing the tropical Madden–Julian oscillation (MJO) and midlatitude processes like meridional momentum transports and mountain torques. A phase space is defined for the GWO following the approach of Wheeler and Hendon for the MJO. In contrast to the oscillatory behavior of the MJO, two red noise processes define the GWO. The red noise spectra have variance at periods that bracket 30–60 or 30–80 days, which are bands used to define the MJO. The correlation between the MJO and GWO is ∼0.5 and cross spectra show well-defined, coherent phase relations in similar frequency bands. However, considerable independent variance exists in the GWO. A basic dynamical distinction occurs in the direction of midlatitude wave energy dispersion, being predominantly meridional during a MJO and zonal during the GWO. This is primarily a winter season feature centered over the Pacific Ocean. A case study during April–May 2007 focuses on the GWO and two ∼30-day duration orbits with extreme anomalies in GWO phase space. The MJO phase space projections for the same time were irregular and, it is argued, partially driven by mountain torques and meridional transports. The case study reveals that multiple physical processes and time scales act to create slowly evolving planetary-scale circulation and tropical convection anomalies.

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An Air–Sea Coupled Skeleton Model for the Madden–Julian Oscillation*

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0348.1 ◽

2013 ◽

Vol 70 (10) ◽

pp. 3147-3156 ◽

Cited By ~ 21

Author(s):

Fei Liu ◽

Bin Wang

Keyword(s):

Boundary Layer ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Western Hemisphere ◽

Sea Surface ◽

Longitudinal Variation ◽

Madden Julian Oscillation ◽

Skeleton Model ◽

Planetary Scale ◽

The Mean

Abstract This work is an extension and improvement of the minimal Madden–Julian oscillation (MJO) “skeleton” model developed by Majda and Stechmann, which can capture some important features of the MJO—slow eastward propagation, quadrupole-vortex structure, and independence of frequency on wavelength—but is unable to produce unstable growth and selection of eastward-propagating planetary waves. With the addition of planetary boundary layer frictional moisture convergence, these deficiencies can be remedied. The frictional boundary layer “selects” the planetary-scale eastward propagation as the most unstable mode, but the dynamics remains confined to atmospheric processes only. Here the authors study the role of air–sea interaction by implementing an oceanic mixed-layer (ML) model of Wang and Xie into the MJO skeleton model. In this new air–sea coupled skeleton model, the features of the original skeleton model remain; additionally, the air–sea interaction under mean westerly winds is shown to produce a strong instability that selectively destabilizes the eastward-propagating planetary-scale waves. Although the cloud–shortwave radiation–sea surface temperature (CRS) feedback destabilizes both eastward and westward modes, the air–sea feedback associated with the evaporation and oceanic entrainment favors planetary-scale eastward modes. Over the Western Hemisphere where easterly background winds prevail, the evaporation and entrainment feedbacks yield damped modes, indicating that longitudinal variation of the mean surface winds plays an important role in regulation of the MJO intensity in addition to the longitudinal variation of the mean sea surface temperature or mean moist static stability. This theoretical analysis suggests that accurate simulation of the climatological mean state is critical for capturing the realistic air–sea interaction and thus the MJO.

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