scholarly journals Zonal‐Scale of the Madden‐Julian Oscillation and Its Propagation Speed on the Interannual Time‐Scale

2021 ◽  
Vol 48 (6) ◽  
Author(s):  
Mengxia Lyu ◽  
Xianan Jiang ◽  
Zhiwei Wu ◽  
Daehyun Kim ◽  
Ángel F. Adames
Keyword(s):  
Time Scale ◽  
Propagation Speed ◽  
Madden Julian Oscillation ◽  
Interannual Time Scale ◽  
Zonal Scale

scholarly journals Circulation Factors Determining the Propagation Speed of the Madden–Julian Oscillation

2020 ◽  
Vol 33 (8) ◽  
pp. 3367-3380 ◽  
Author(s):  
Guosen Chen ◽  
Bin Wang
Keyword(s):  
Deep Convection ◽  
Propagation Speed ◽  
Warm Pool ◽  
Propagation Mechanism ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Central Pacific ◽  
Zonal Scale ◽  
Pacific Warm Pool ◽  
Shed Light

ABSTRACTThe eastward propagating Madden–Julian oscillation (MJO) events exhibit various speeds ranging from 1 to 9 m s−1, but what controls the propagation speed remains elusive. This study attempts to address this issue. It reveals that the Kelvin wave response (KWR) induced by the MJO convection is a major circulation factor controlling the observed propagation speed of the MJO, with a stronger KWR corresponding to faster eastward propagation. A stronger KWR can accelerate the MJO eastward propagation by enhancing the low-level premoistening and preconditioning to the east of the MJO deep convection. The strength of the KWR is affected by the background sea surface temperature (SST). When the equatorial central Pacific SST warms, the zonal scale of the Indo-Pacific warm pool expands, which increases the zonal scale of the MJO, favoring enhancing the KWR. This effect of warm-pool zonal scale has been verified by idealized experiments using a theoretical model. The findings here shed light on the propagation mechanism of the MJO and provide a set of potential predictors for forecasting the MJO propagation.

scholarly journals Relationships between the Antarctic Oscillation, the Madden–Julian Oscillation, and ENSO, and Consequences for Rainfall Analysis

2010 ◽  
Vol 23 (2) ◽  
pp. 238-254 ◽  
Author(s):  
B. Pohl ◽  
N. Fauchereau ◽  
C. J. C. Reason ◽  
M. Rouault
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Rainfall Variability ◽  
Austral Summer ◽  
La Niña ◽  
Madden Julian Oscillation ◽  
Antarctic Oscillation ◽  
Interannual Time Scale ◽  
La Nina ◽  
The Antarctic

Abstract The Antarctic Oscillation (AAO) is the leading mode of atmospheric variability in the Southern Hemisphere mid- and high latitudes (south of 20°S). In this paper, the authors examine its statistical relationships with the major tropical climate signals at the intraseasonal and interannual time scales and their consequences on its potential influence on rainfall variability at regional scales. At the intraseasonal time scale, although the AAO shows its most energetic fluctuations in the 30–60-day range, it is not unambiguously related to the global-scale Madden–Julian oscillation (MJO) activity, with in particular no coherent phase relationship with the MJO index. Moreover, in the high southern latitudes, the MJO-associated anomaly fields do not appear to project coherently on the well-known AAO patterns and are never of an annular nature. At the interannual time scale, a strong teleconnection with ENSO is found during the peak of the austral summer season, corroborating previous studies. El Niño (La Niña) tends to correspond to a negative (positive) AAO phase. The results are statistically significant only when the seasonal mean fields averaged for the November through February season are considered. Based on these results, the authors then isolate the specific influence of the AAO on rainfall variability at both intraseasonal and interannual time scales. The example taken here is southern Africa, a region under the influence of both the MJO and ENSO, experiencing its main rainy season in austral summer and containing a relatively dense network of rain gauge measurements. At the interannual time scale, the significance of the teleconnections between southern African rainfall and the AAO reveals itself to be a statistical artifact and becomes very weak once the influence of ENSO is removed. At the intraseasonal time scale, the AAO is seen to significantly affect the rainfall amounts over much of the country, without interference with other modes of variability. Its influence in modulating the rain appears to be strongest during La Niña years.

scholarly journals Comparison of Moisture Transport between Siberia and Northeast Asia on Annual and Interannual Time Scales

2018 ◽  
Vol 31 (18) ◽  
pp. 7645-7660 ◽  
Author(s):  
Jinling Piao ◽  
Wen Chen ◽  
Qiong Zhang ◽  
Peng Hu
Keyword(s):  
Annual Cycle ◽  
Time Scale ◽  
Moisture Transport ◽  
Precipitation Amount ◽  
Northeast Asia ◽  
Empirical Orthogonal Functions ◽  
Moisture Convergence ◽  
Interannual Time Scale ◽  
Orthogonal Functions ◽  
Moisture Supply

The moisture supplies over Siberia and Northeast Asia are investigated by comparing their similarities and differences, enlightened by the seesaw pattern in their summer precipitation. Based on the rotated empirical orthogonal functions in the 3-month standardized precipitation evapotranspiration index (SPEI_03), Siberia and Northeast Asia are defined as the regions within 55°–70°N, 80°–115°E and 40°–55°N, 90°–115°E, respectively. Our results show that over both regions, evaporation contributes the most to the precipitation amount at the annual time scale, and moisture convergence contributes the most on the interannual time scale. For moisture convergence, both the stationary and transient terms are subject to impacts of the midlatitude westerlies. For the annual cycle, the net moisture supply over both Siberia and Northeast Asia is closely associated with both stationary and transient moisture transport. However, on the interannual time scale, the net moisture convergence is closely related to the stationary term only. The examination of the boundary moisture transport shows that in addition to the zonal component, the meridional stationary moisture transport plays a key role in the net moisture convergence. The transient moisture transport mainly depends on moisture transport through the western and southern boundaries, with a comparable magnitude to that of the stationary one, further confirming the importance of the stationary and transient terms on the moisture supply for the annual cycle. In addition, the circulations responsible for moisture transport anomalies indicate that the stationary moisture circulation is the key factor for the moisture supply anomalies over both Siberia and Northeast Asia, with limited impacts from the transient moisture circulation.

scholarly journals Moist Thermodynamics of the Madden–Julian Oscillation in a Cloud-Resolving Simulation

2011 ◽  
Vol 24 (21) ◽  
pp. 5571-5583 ◽  
Author(s):  
Samson Hagos ◽  
L. Ruby Leung
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Active Phase ◽  
Vertical Transport ◽  
Madden Julian Oscillation ◽  
Boundary Layer Diffusion ◽  
Inactive Phase ◽  
Thermodynamic Processes

Abstract The moist thermodynamic processes that determine the time scale and energy of the Madden–Julian oscillation (MJO) are investigated using moisture and eddy available potential energy budget analyses on a cloud-resolving simulation. Two MJO episodes observed during the winter of 2007/08 are realistically simulated. During the inactive phase, moisture supplied by meridional moisture convergence and boundary layer diffusion generates shallow and congestus clouds that moisten the lower troposphere while horizontal mixing tends to dry it. As the lower troposphere is moistened, it becomes a source of moisture for the subsequent deep convection during the MJO active phase. As the active phase ends, the lower troposphere dries out primarily by condensation and horizontal divergence that dominates over the moisture supply by vertical transport. In the simulation, the characteristic time scales of convective vertical transport, mixing, and condensation of moisture in the midtroposphere are estimated to be about 2 days, 4 days, and 20 h respectively. The small differences among these time scales result in an effective time scale of MJO moistening of about 25 days, half the period of the simulated MJO. Furthermore, various cloud types have a destabilizing or damping effect on the amplitude of MJO temperature signals, depending on their characteristic latent heating profile and its temporal covariance with the temperature. The results are used to identify possible sources of the difficulties in simulating MJO in low-resolution models that rely on cumulus parameterizations.

Diversity of the Madden-Julian Oscillation

2020 ◽  
Author(s):  
Guosen Chen ◽  
Bin Wang ◽  
Fei Liu
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Dominant Mode ◽  
Sea Surface ◽  
Extreme Weather Events ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Tight Coupling ◽  
Zonal Scale ◽  
Wave Response

<p>Madden-Julian Oscillation (MJO) is the dominant mode of atmospheric intraseasonal variability and the cornerstone for subseasonal prediction of extreme weather events. Climate modeling and prediction of MJO remain a big challenge, partially due to lack of understanding the MJO diversity. Here, we delineate observed MJO diversity by cluster analysis of propagation patterns of MJO events, which reveals four archetypes: standing, jumping, slow eastward propagation, and fast eastward propagation. Each type of MJO exhibits distinctive east-west asymmetric circulation and thermodynamic structures. Tight coupling between the Kelvin wave response and major convection is unique for the propagating events (slow and fast propagations), while the strength and length of Kelvin wave response distinguish slow and fast propagations. The Pacific sea surface temperature anomalies can affect MJO diversity by modifying the Kelvin wave response and its coupling to MJO convection. An El Niño state tends to increase the zonal scale of Kelvin wave response, to amplify it, and to enhance its coupling to the convection, while a La Niña state tends to decrease the zonal scale of Kelvin wave response, to suppress it, and to weaken its coupling to the major convection. This effect of background sea surface temperature on the MJO diversity has been verified by using a theoretical model. The results shed light on the mechanisms responsible for MJO diversity and provide potential precursors for foreseeing MJO propagation.</p>

scholarly journals Machine learning prediction of the Madden-Julian oscillation

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Riccardo Silini ◽  
Marcelo Barreiro ◽  
Cristina Masoller
Keyword(s):  
Neural Network ◽  
Extreme Events ◽  
Time Scale ◽  
Climate Models ◽  
Dominant Mode ◽  
Prediction Skill ◽  
Madden Julian Oscillation ◽  
Weather Extremes ◽  
Feed Forward Neural Network ◽  
Good Ability

AbstractThe socioeconomic impact of weather extremes draws the attention of researchers to the development of novel methodologies to make more accurate weather predictions. The Madden–Julian oscillation (MJO) is the dominant mode of variability in the tropical atmosphere on sub-seasonal time scales, and can promote or enhance extreme events in both, the tropics and the extratropics. Forecasting extreme events on the sub-seasonal time scale (from 10 days to about 3 months) is very challenging due to a poor understanding of the phenomena that can increase predictability on this time scale. Here we show that two artificial neural networks (ANNs), a feed-forward neural network and a recurrent neural network, allow a very competitive MJO prediction. While our average prediction skill is about 26–27 days (which competes with that obtained with most computationally demanding state-of-the-art climate models), for some initial phases and seasons the ANNs have a prediction skill of 60 days or longer. Furthermore, we show that the ANNs have a good ability to predict the MJO phase, but the amplitude is underestimated.

Multiplicative MJO Forcing of ENSO

2012 ◽  
Vol 25 (23) ◽  
pp. 8132-8147 ◽  
Author(s):  
Atul Kapur ◽  
Chidong Zhang
Keyword(s):  
Southern Oscillation ◽  
Propagation Speed ◽  
Madden Julian Oscillation ◽  
Ensemble Spread ◽  
Coupled Models ◽  
Stable Regime ◽  
Basic Parameters ◽  
Evolving Model ◽  
Zonal Propagation

Abstract The Madden–Julian oscillation (MJO) is parameterized to study the role of the feedback it receives from sea surface temperature (SST) in its influence on El Niño–Southern Oscillation (ENSO). The parameterization describes MJO surface westerlies in terms of a few basic parameters that include amplitude, zonal propagation extent, propagation speed, and the interval between adjacent events. It is used to drive a coupled ocean–atmosphere model of intermediate complexity tuned to a marginally stable regime. The MJO parameters acquire values either additively (i.e., based on observed estimates of most probable value and stochasticity) or multiplicatively (i.e., modulated by an evolving model ENSO SST, albeit with some stochasticity). Simulations reveal that ENSO variance increases with the stochasticity of MJO amplitude but is insensitive to the stochasticity of zonal extent and speed, except that ENSO vanishes completely when the propagation speed is zero. Likewise, ENSO strengthens linearly with the SST modulation of MJO amplitude, but not of speed and zonal extent—even though the two are known to be significantly influenced by SST. Ensemble comparisons between simulations with and without SST feedback demonstrate that SST feedback to the MJO acting in a stable regime can be responsible for the observed ENSO variance. The multiplicative case has a larger ensemble spread than the additive case, which manifests in a larger interdecadal variability of ENSO. The results emphasize that ENSO reproduction in coupled models depends on correctly representing the MJO, especially its amplitude and SST feedback.

scholarly journals Extratropical Impacts of the Madden–Julian Oscillation over New Zealand from a Weather Regime Perspective

2016 ◽  
Vol 29 (6) ◽  
pp. 2161-2175 ◽  
Author(s):  
N. Fauchereau ◽  
B. Pohl ◽  
A. Lorrey
Keyword(s):  
New Zealand ◽  
Austral Summer ◽  
Daily Rainfall ◽  
Propagation Speed ◽  
Southern Annular Mode ◽  
Madden Julian Oscillation ◽  
Orographic Effects ◽  
Regional Circulation ◽  
Circulation Anomalies ◽  
The Impact

Abstract The Madden–Julian oscillation (MJO) signal in the Southern Hemisphere (SH) extratropics during the austral summer (November–March) is investigated over the New Zealand (NZ) sector, using the paradigm of atmospheric weather regimes (WRs), following a classification initially established by Kidson. The MJO is first demonstrated to have significant impacts on daily rainfall anomalies in NZ. It is suggested that orographic effects arising from the interaction between regional atmospheric circulation anomalies and NZ’s topography can explain the spatially heterogeneous precipitation anomalies that are related to MJO activity. These local impacts and circulation anomalies are shown to be better understood as resulting from changes in the occupation statistics of regional WRs (the Kidson types) through the MJO life cycle, although both constructive and destructive effects are demonstrated. The hypothesis of a significant forcing of the MJO over the NZ sector is further supported by lagged composite analyses, which reveal timing characteristics of the delayed regional circulation response compatible with the average propagation speed of the MJO. While the southern annular mode (SAM) has been previously shown to be statistically related to the MJO and is known to be a significant driver of NZ’s climate, no evidence is found that the impact of the MJO over the NZ sector is mediated by the SAM. It is therefore suggested that the MJO directly impacts regional circulation and climate in the NZ region, potentially through extratropical Rossby wave response to tropical diabatic heating. These findings suggest a new potential for predictability for some aspects of NZ’s weather and climate deriving from the MJO beyond the meteorological time scales.

scholarly journals Interannual Shift of the Tropical Upper-Tropospheric Trough and Its Influence on Tropical Cyclone Formation over the Western North Pacific

2016 ◽  
Vol 29 (11) ◽  
pp. 4203-4211 ◽  
Author(s):  
Chao Wang ◽  
Liguang Wu
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Time Scale ◽  
Western North Pacific ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Physical Factors ◽  
Interannual Time Scale ◽  
Core System ◽  
East West

Abstract The east–west migration of the tropical upper-tropospheric trough (TUTT) on the interannual time scale and its influence on tropical cyclone (TC) formation over the western North Pacific (WNP) is investigated in this study. Climatologically, the TUTT can be identified from 100 to 400 hPa with a relative vorticity maximum between 150 and 200 hPa. In addition to the strong westerly vertical wind shear in the south flank of the TUTT, this study shows that the cold-core system is associated with low relative humidity and subsidence to the east of the trough axis. As a result, the TC formation is enhanced (suppressed) in the eastern portion of the WNP when the TUTT shifts eastward (westward) on the interannual time scale. The interannual TUTT shift is closely associated with the SST anomalies in the central and eastern tropical Pacific or ENSO phases. The warm (cold) phase of ENSO corresponds to the eastward (westward) shift of the TUTT. The physical factors found to be responsible for the influence of ENSO on TC formation can be associated with the east–west shift of the TUTT. It is shown that the interannual variations of TC formation in the eastern part of the WNP basin are closely associated with the east–west shift of the TUTT due to the associated environmental conditions that are generally not favorable for TC formation.

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