Madden–Julian Oscillation Activity Research Articles

Volcanically forced Madden–Julian oscillation triggers the immediate onset of El Niño

A process-level understanding of the volcanically forced climate response is an urgent challenge due to its similarities to the potential effects of geoengineering techniques. Although the influence of volcanic forcing on El Niño events has been studied extensively, the mechanisms driving the volcanically-induced immediate onset of El Niño remain uncertain, with many climate models producing a delayed El Niño response compared to observations. In this study, using large ensemble simulations that allow us to isolate the impacts of volcanic forcing on the El Niño response, we demonstrate a mechanism that highlights the central triggering role of the Madden–Julian oscillation (MJO), which has been overlooked in existing literature. Because the land areas surrounding the Indo-Pacific warm pool dry more quickly after a volcanic eruption, the background moisture distribution becomes more favorable for the MJO to propagate eastward from the Indian Ocean into the Pacific. This increases the likelihood of ensemble members having stronger MJO activity in the western Pacific by about 35% compared to non-volcanic years, which subsequently increases the frequency of westerly wind bursts by about 76%, ultimately enhancing the probability of the onset of an El Niño by about 98% following major volcanic eruptions.

Vertical structure and occurrence patterns of the cross-equatorial northerly surge under different ENSO and MJO phases

This study investigated the vertical structure of 6 cross-equatorial northerly surge (CENS) events during the Year of Maritime Continent–Cold Surge Observation in 2021 (YMC-CSO2021) campaign. These events, named CENS1 (Jan. 18–20), CENS2 (Jan. 29–30), CENS3 (Feb. 2–5), CENS4 (Feb. 5–9), CENS5 (Feb. 18–20), and CENS6 (Feb. 25–26), occurred under different environmental conditions associated with cold surges (CSs) and the Madden–Julian Oscillation (MJO). Using radiosonde observations, we identified distinct characteristics in the northerly wind layer thickness, westerly wind bursts, and potential temperature anomalies among the events. Notably, CENS6 featured a deep northerly wind layer reaching 400 hPa, influenced by a southward pressure gradient linked to a cyclone in the Southern Hemisphere. Statistical analysis of past CENS events using reanalysis dataset showed that 80% occurred in January and February, with higher frequencies during La Niña years and active MJO phases over the western Pacific, aligning with YMC-CSO2021 observations. Composite analysis showed that CENS events induced significant ascending motion and localized potential temperature gradients, leading to positive precipitation anomalies around the Maritime Continent. These findings enhance our understanding of CENS dynamics and their impact on regional climate variability.

Comparing MJO Intensity over the Tropical Western Pacific during Mega and Equatorial La Niña Winters

Abstract This study investigated variations in the Madden–Julian oscillation (MJO) behavior between two types of La Niña winters: mega and equatorial La Niñas. Results of this work show that in contrast to mega conditions, accompanied by more abundant intraseasonal column-integrated moisture anomalies over the planetary boundary layer, intensities of intraseasonal outgoing longwave radiation anomalies are stronger over the tropical western Pacific (WP) at MJO phases 5–6 under equatorial conditions. The occurrence of the moisture anomaly change averaged over the tropical WP is supported by a distinct moisture tendency difference. Moisture budget and multiscale interaction diagnoses underscore the pivotal effect of an area-averaged vertical gradient change in low-frequency background moisture in driving such tendency change. Considering notable MJO convection variations, the teleconnections associated with MJO phases 5–6 over East Asia (EA) were also explored, including warmer surface air temperature anomalies and stronger positive geopotential height anomalies at 200 hPa on the intraseasonal time scale under equatorial conditions. Results from a linear baroclinic model demonstrate that such teleconnection changes could be effectively explained by the linear response to the MJO’s diabatic heating anomaly. Roles of mean state and MJO itself variations in the linear response change are also discussed. These findings provide novel insights into MJO activity and offer potential improvements for subseasonal forecasting in EA. Significance Statement The relationship between El Niño–Southern Oscillation (ENSO) and MJO has been extensively explored recently. However, variations in the MJO behavior and its climate effects under mega and equatorial La Niña winters have not been thoroughly investigated. In this work, we utilized reanalysis datasets and an idealized linear baroclinic model to address these questions. We observed more robust and abundant intraseasonal convection activity and planetary boundary layer–integrated moisture anomaly averaged over the tropical WP at MJO phases 5–6 under equatorial conditions than mega conditions, which is closely linked with the vertical gradient change in low-frequency background moisture. Additionally, MJO-related teleconnections also exhibit some changes. This work may provide a new perspective on understanding the relationship between the MJO and ENSO and offer potential improvements for the subseasonal forecast.

Influence of Western Pacific Madden–Julian Oscillation on New York City's Record‐Breaking Air Pollution in Early June 2023

AbstractIn early June 2023, New York City (NYC) and other cities in the northeastern US experienced a severe air pollution event. Although reports associated this hazardous pollution event with the smoke from Canadian wildfires, the factors triggering the southward waft of the smoke remain unclear. We found the northerly anomaly that transported the smoke was linked to the Rossby wave train excited by the Madden–Julian Oscillation (MJO) over the Philippine Sea, which led to the formation of an enhanced northerly at the western edge of the cyclonic anomaly over the East Coast–North Atlantic. When the MJO convection left the western Pacific, the disorganized teleconnection caused the pollution to dissipate. Observational findings were further supported by model simulations and predictions. These results suggest that monitoring and predictions of MJO activity may help mitigate air pollution events over the northeastern US during Canadian wildfire seasons.

Factors influencing subseasonal predictability of northern Eurasian cold spells

AbstractCold‐air outbreaks have significant impacts on human health, energy consumption, agriculture, and overall well‐being. This study aims to evaluate the effectiveness of Subseasonal‐to‐Seasonal (S2S) models in predicting cold conditions over northern Eurasia, defined here as the lower tercile of weekly mean 2‐metre temperature anomalies. To assess the predictability of these events we use ensemble hindcasts from five prediction systems from the S2S database. Our analysis focuses on identifying the conditions under which the models confidently predict cold temperatures with a high (>0.5) probability 3–4 weeks ahead, which potentially can represent windows of forecast opportunity. We compare the group of forecasts that correctly predicted the events to the group that forecasted events that did not occur in practice (false alarms). Most of the confident forecasts of cold spells, both correct and false alarms, have cold anomalies already in the initial conditions, often in conjunction with either a negative phase of the North Atlantic Oscillation, or Scandinavian Blocking. We find that S2S models tend to overpredict cold temperatures, with false alarms occurring more likely when the forecasts are initialized during a weak polar vortex. Furthermore, most of the confident false alarms receive the signal from the stratosphere rather than following internal tropospheric dynamics. False alarms initialized during the weak polar vortex conditions are more common when the vortex is in a recovery stage and, subsequently, the downward ‐propagating signal is short‐lived in the troposphere. The analysis of forecasts during different Madden–Julian Oscillation (MJO) phases shows that nearly half of all confident correct cold‐temperature forecasts are initialized during an active MJO in phases 6–8. On the other hand, most false alarms occur during phase 3, which we suggest is due to the presence of the Scandinavian Blocking regime in the initial conditions for this phase.

Untangling the dynamics of heavy rainfall events (HRE) in the Northeast monsoon season and exploring its connection to the Indian Ocean warming and the Madden Julian Oscillation

Untangling the dynamics of heavy rainfall events (HRE) in the Northeast monsoon season and exploring its connection to the Indian Ocean warming and the Madden Julian Oscillation

Impact of the Madden–Julian oscillation and equatorial waves on tracked mesoscale convective systems over southeast Asia

AbstractSoutheast Asia is a region dominated by high‐impact weather, but numerical weather prediction here is a challenge owing to the complex orography and interactions between small‐ and large‐scale phenomena. Localised mesoscale convective systems (MCSs) can produce intense precipitation. Here, we track MCSs over a 5‐year period in Himawari satellite data, characterise the distribution of MCSs in the region, and investigate how they are modulated by the Madden–Julian oscillation (MJO) and equatorial waves. Between 10°S and 10°N in southeast Asia, MCSs account for 45–70% of the precipitation during boreal extended winter (November–April). Over most of the region, the fractional MCS contribution to rainfall is higher than average on days with extreme rainfall (>55%). Long‐lived (>12 hr) MCSs contribute disproportionately, providing 85% of the rainfall despite comprising only 34% of all MCSs. Variability in MCS rainfall accounts for >50% of the total rainfall variability during an MJO cycle, mostly due to larger numbers of MCSs in convectively active MJO phases. Variations in MCS size and mean rain rate due to shifts in the stratiform proportion provide compensating effects. In the west of the region, a shift to faster moving MCSs in active MJO phases and slower moving MCSs in inactive phases resulted in fast‐moving MCSs having the greatest impact on the MJO‐associated variability. Variability is larger in the west than in the east. Equatorial Kelvin waves modulate MCS rainfall, with MCSs accounting for 20–50% of local rainfall anomalies. This variability is again enhanced in the west. By contrast, rainfall anomalies due to westward‐propagating mixed Rossby–gravity waves and Rossby‐1 waves are dominated by tropical‐cyclone‐related rainfall. Skill at local scales may be extracted from forecasts of subseasonal drivers such as the MJO and Kelvin waves, by understanding how these modulate the number and characteristics of MCSs.

The impact of the Madden-Julian oscillation on spring and autumn afternoon diurnal convection in Sri Lanka

This study examines the impact of strong Madden-Julian Oscillation (MJO) phases (P1–P8) on diurnal rainfall patterns focusing on Afternoon Diurnal Convection (ADC) events in Sri Lanka during 2001–2020 spring and autumn. Daily mean rainfall increases (decreases) during the P2-to-P3 (P6-to-P7) MJO phases in both seasons, while the diurnal rainfall amplitude peaks during the P2-to-P3 (P8-to-P1) MJO phases in spring (autumn). ADC events also occur more frequently and intensely during MJO P2-to-P3 (P8-to-P1) in spring (autumn). The MJO’s modulation of diurnal rainfall amplitude and ADC events is more apparent in autumn than in spring. Active MJO phases enhance the westward propagation of diurnal rainfall associated with ADC events, sustained by moisture flux convergence and enhanced upward motion. The prevailing mid-to-upper level easterly wind, combined with deep convection over Sri Lanka, contributes to a more pronounced westward propagation during the P2-to-P3 (P8-to-P1) phases for ADC events in spring (autumn).

How Can We Improve the Seamless Representation of Climatological Statistics and Weather Toward Reliable Global K‐Scale Climate Simulations?

AbstractToward the achievement of reliable global kilometer‐scale (k‐scale) climate simulations, we improve the Nonhydrostatic ICosahedral Atmospheric Model (NICAM) by focusing on moist physical processes. A goal of the model improvement is to establish a configuration that can simulate realistic fields seamlessly from the daily‐scale variability to the climatological statistics. Referring to the two representative configurations of the present NICAM, each of which has been used for climate‐scale and sub‐seasonal‐scale experiments, we try to find the appropriate partitioning of fast/local and slow/global‐scale circulations. In a series of sensitivity experiments at 14‐km horizontal resolution, we test (a) the tuning of terminal velocities of rain, snow, and cloud ice, (b) the implementation of turbulent diffusion by the Leonard term, and (c) enhanced vertical resolution. These tests yield reasonable convection triggering and convection‐induced tropospheric moistening, and result in better performance than in previous NICAM climate simulations. In the mean state, double Intertropical Convergence Zone bias disappears, and the zonal contrast of equatorial precipitation, top‐of‐atmosphere radiation balance, vertical temperature profile, and position/strength of subtropical jet are reproduced dramatically better. Variability such as equatorial waves and the Madden–Julian oscillation (MJO) is spontaneously realized with appropriate spectral power balance, and the Asian summer monsoon, boreal‐summer MJO, and tropical cyclone (TC) activities are more realistically simulated especially around the western Pacific. Meanwhile, biases still exist in the representation of low‐cloud fraction, TC intensity, and precipitation diurnal cycle, suggesting that both higher spatial resolutions and further model development are warranted.

Intensity duration and frequency of Heat wave in different phases of MJO over India

Intensity duration and frequency of Heat wave in different phases of MJO over India

The tropical influence on sub‐seasonal predictability of wintertime stratosphere and stratosphere–troposphere coupling

AbstractA unique set of relaxation experiments with a forecast model initialized during December–January 1999–2019 is used to explore tropical influence on the Northern Hemisphere polar stratosphere and stratosphere–troposphere coupling, to quantify predictability benefits due to the perfect knowledge of the tropical variability. On average, predictability of the polar stratosphere, as represented by the 50 hPa geopotential height anomalies north of 50°N (Z50), increases from 17 days in freely running (control) forecasts to 21 days in the tropical relaxation experiments. At sub‐seasonal time‐scales, a statistically significant improvement in weekly mean skill scores can be demonstrated in 14%–20% of individual forecast ensembles, mostly in cases when the skill of the corresponding control forecast is worse than average. In these forecasts, root‐mean‐square errors and forecast spread of Z50 during forecast weeks 3–5 are decreased by 10%–15%. Stratospheric improvements are detected during periods of both vortex strengthening and vortex weakening, including most major Sudden Stratospheric Warmings that occurred during the study period, via modulation of the upward wave activity fluxes. An active Madden–Julian Oscillation (MJO) is found in most of these events with MJO phase 5–7 preceding vortex weakening and MJO phase 3–4 preceding vortex strengthening. Forecasts with improved stratospheric circulation also have improved tropospheric circulation during and after the periods when improvements are detected in the stratosphere. We attribute these improvements to both stratosphere–troposphere coupling and tropospheric tropical teleconnections.

QBO modulation of MJO teleconnections in the North Pacific: impact of preceding MJO phases

This study examines the influence of the Quasi-Biennial Oscillation (QBO) on the Madden-Julian Oscillation (MJO) teleconnections in the North Pacific using ERA5 data. It is found that the Rossby wave trains induced by MJO phase 6–7 exhibit greater strength and robustness during the westerly QBO winter (WQBO) than during the easterly QBO winter (EQBO), although the MJO itself is weaker during the former. This counter-intuitive dependency of MJO teleconnections on the QBO is attributed to the preexisting MJO teleconnections prior to the MJO phase 6–7. The MJO phase 6–7 is more frequently preceded by stronger MJO phase 3–4 during the EQBO than during the WQBO. The preceding MJO phase 3–4 teleconnections, which have opposed signs to the MJO phase 6–7 teleconnections, result in a considerable attenuation of the MJO phase 6–7 teleconnections by destructive interference. This result is supported by linear model experiments. The subseasonal-to-seasonal prediction models also indicate improved prediction skills of MJO phase 6–7 teleconnections during the WQBO compared to the EQBO. These results suggest that enhanced MJO activities during the EQBO do not necessarily result in stronger and more robust MJO teleconnections in the North Pacific.

The effect of diurnal warming of sea‐surface temperatures on the propagation speed of the Madden–Julian oscillation

AbstractThe diurnal warm layer in the upper ocean develops during low surface winds and high incoming solar radiation conditions, often increasing sea‐surface temperatures (SSTs) by up to 1°C. The suppressed phase of the Madden–Julian Oscillation (MJO) favours the formation of such a layer. Here, we analyse the coupled ocean–atmosphere and atmosphere‐only numerical weather prediction systems of the UK Met Office to reveal that important differences arise from the representation of the diurnal warm layer in the coupled model. Though both models are skilful in predicting the MJO to at least a 7‐day lead time, the coupled model predicts approximately 12% faster MJO RMM phase speed propagation than the atmosphere‐only model due to the ability to resolve diurnal warming in the upper ocean that rectifies onto MJO‐associated SST anomalies. The diurnal warming of SST (dSST) in the coupled model leads to an increase in daily mean SST compared with the atmosphere‐only model persisted foundation SST. The strength of the dSST in the coupled model is modulated by MJO conditions. During suppressed MJO conditions on lead day 1, the dSST is enhanced, leading to 0.2°C warmer daily mean MJO‐associated SST anomalies and increased convection in the coupled model by lead day 7. During active MJO convection, the dSST is suppressed, leading to 0.1°C colder MJO‐associated SST anomalies in the coupled model and reduced convection by lead day 7. This variability in dSST further amplifies the MJO propagation speed, underlining the importance of the two‐way feedback between the MJO and the diurnal cycle of SST and the need to accurately represent this process in coupled models.

MJO Influence on Subseasonal-to-Seasonal Prediction in the Northern Hemisphere Extratropics

Abstract The impacts of the Madden–Julian oscillation (MJO) on the subseasonal-to-seasonal (S2S) prediction in the Northern Hemisphere extratropics are examined using the reforecasts from the S2S Project and Subseasonal Experiment Project (SubX). When forecasts are initialized during an active MJO, extratropical prediction skill becomes significantly higher at 3–4-week windows compared to inactive MJO. Such prediction skill improvement is evident in the 500-hPa geopotential height over the Pacific–North America region and the North Atlantic and in surface temperature over North America, especially when the model is initialized during the MJO phases 6–7 and 8–1. However, the extratropical prediction skill is not modulated by the MJO phases 2–3 and 4–5. This phase dependency is likely determined by the arrival time of the MJO at the Maritime Continent (MC) barrier that substantially enhances the MJO amplitude error. This result suggests that only MJO phases whose convection lies east of the MC are a source of wintertime S2S predictability in the extratropics.

Increased extinction probability of the Madden-Julian oscillation after about 27 days.

The Madden-Julian oscillation (MJO) is a tropical weather system that has an important influence in the tropics and beyond; however, many of its characteristics are poorly understood, including their initiation and termination. Here we define Madden-Julian events as contiguous time periods with an active MJO, and we show that both the durations and the sizes of these events are well described by a double power-law distribution. Thus, small events have no characteristic scale, and the same for large events; nevertheless, both types of events are separated by a characteristic duration of about 27 days (this corresponds to half a cycle, roughly). Thus, after 27 days, there is a sharp increase in the probability that an event becomes extinct. We find that this effect is independent of the starting and ending phases of the events, which seems to point to an internal mechanism of exhaustion rather than to the effect of an external barrier. Our results would imply an important limitation of the MJO as a driver of subseasonal predictability.

Rainfall Variation on the West Coast of Sumatra during Each Phase of the Madden-Julian Oscillation from GPM Satellite Observation

The West Coast of Sumatra has a significantly higher annual rainfall than its surrounding areas, making this region crucial in controlling precipitation in Sumatra. The Madden-Julian Oscillation (MJO) heavily influences the West Coast of Sumatra. MJO is an intraseasonal activity that occurs in tropical regions and can be recognized by the eastward movement of convective activity from the Indian Ocean towards the Pacific Ocean for 30-60 days. Using Global Precipitation Measurement (GPM) satellite data from 2014 to 2020, this study investigates the influence of MJO on rainfall on the West Coast of Sumatra. The data used in this study is the attenuation-corrected reflectivity (dBZ) of Ku PR (Z-Ku) and Ka PR (Z-Ka) from GPM DPR Level 2 data. For convective rainfall, the Z-Ku and Z-Ka reflectivity values are higher during the inactive MJO phase than the active MJO phase, consistent with previous research in Sumatra. Thus, during the inactive MJO phase, strong convection occurs, leading to updrafts and increased formation of larger raindrops through coalescence processes. During the active MJO phase, there is a significant decrease in raindrop size, indicating dominant break-up processes.

The Lack of a QBO‐MJO Connection in Climate Models With a Nudged Stratosphere

AbstractThe observed stratospheric quasi‐biennial oscillation (QBO) and the tropospheric Madden‐Julian oscillation (MJO) are strongly connected in boreal winter, with stronger MJO activity when lower‐stratospheric winds are easterly. However, the current generation of climate models with internally generated representations of the QBO and MJO do not simulate the observed QBO‐MJO connection, for reasons that remain unclear. This study builds on prior work exploring the QBO‐MJO link in climate models whose stratospheric winds are relaxed toward reanalysis, reducing stratospheric biases in the model and imposing a realistic QBO. A series of ensemble experiments are performed using four state‐of‐the‐art climate models capable of representing the MJO over the period 1980–2015, each with similar nudging in the stratosphere. In these four models, nudging leads to a good representation of QBO wind and temperature signals, however no model simulates the observed QBO‐MJO relationship. Biases in MJO vertical structure and cloud‐radiative feedbacks are investigated, but no conclusive model bias or mechanism is identified that explains the lack of a QBO‐MJO connection.

Wind Variability and its Impact on IOD and MJO Phenomena in Western Waters


 
 
 
 
 
 This study investigates the interplay between wind variability and the Indian Ocean Dipole (IOD) and Madden-Julian Oscillation (MJO) phenomena in the western waters of Sumatra during the period 1982-2021. Utilizing monthly average wind data from satellite images, the research employs a comprehensive approach involving GrADS, Microsoft Excel, Surfer, Matlab, and Panoply software for data processing. The analysis reveals distinct wind patterns and varying IOD and MJO phases, with notable instances such as a positive IOD in October 1982 and a negative IOD in March 1983, coupled with strong MJO activity in February 1982 and weak activity in October 1983. This research underscores the significant influence of wind conditions on the dynamics of IOD and MJO phenomena in the studied region, contributing to a deeper understanding of ocean-atmosphere interactions.
 Highlight:
 
 
 
 
 
 
 
 
 
 
 
 Temporal Analysis: This study examines wind variability's interplay with IOD and MJO phenomena over three decades, revealing distinct patterns and phases in the western waters of Sumatra.
 Comprehensive Approach: Utilizing advanced software tools, the research processes satellite-derived wind data, shedding light on the complex dynamics of ocean-atmosphere interactions.
 Phenomena Dynamics: Notable occurrences, including positive and negative IOD events and varying MJO strengths, emphasize the profound impact of wind conditions on shaping the behavior of these critical climate phenomena, contributing to enhanced understanding and prediction.
 
 
 
 
 
 
 
 
 Keyword: Wind Variability, Indian Ocean Dipole (IOD), Madden-Julian Oscillation (MJO), Ocean-Atmosphere Interactions, Western Sumatra
 
 
 
 
 
 
 
 

QBO deepens MJO convection

The underlying mechanism that couples the Quasi-Biennial Oscillation (QBO) and the Madden-Julian oscillation (MJO) has remained elusive, challenging our understanding of both phenomena. A popular hypothesis about the QBO-MJO connection is that the vertical extent of MJO convection is strongly modulated by the QBO. However, this hypothesis has not been verified observationally. Here we show that the cloud-top pressure and brightness temperature of deep convection and anvil clouds are systematically lower in the easterly QBO (EQBO) winters than in the westerly QBO (WQBO) winters, indicating that the vertical growth of deep convective systems within MJO envelopes is facilitated by the EQBO mean state. Moreover, the deeper clouds during EQBO winters are more effective at reducing longwave radiation escaping to space and thereby enhancing longwave cloud-radiative feedback within MJO envelopes. Our results provide robust observational evidence of the enhanced MJO activity during EQBO winters by mean state changes induced by the QBO.

Analysis of Madden-Julian Oscillation (MJO) on extreme rainfall event in the west coastal south Sulawesi for mitigation disaster

Madden Julian Oscillation (MJO) is one of the global phenomena that affects weather and climate conditions in Indonesia. MJO increases the rainfall rate and causes a plethora of extreme rainfall occurrences in areas along its trajectory. Those extreme rainfall events could trigger hydrometeorological hazards that endanger the surrounding environment. As the first step to analyse this extreme weather event, this research tries to determine the threshold of the extreme rainfall rate. The method used for determining the threshold is the statistical method 98th percentile. The next step is to identify the frequency trend of the extreme rainfall in the period of 1991 to 2020, by measuring the rainfall rate and comparing it with the normal value. If the rainfall rate is above the normal condition in a certain threshold, then it is considered an extreme rainfall event. After that, these extreme rainfall occurrences are compared to the active MJO phase to find out the influence of MJO to the rainfall in the west coast of South Sulawesi. Then, the dynamical atmospheric conditions are to be analysed during those extreme rainfall events. The result shows that the frequency trend of extreme rainfall events are generally negative in 5 (five) regions, which means an insignificant correlation between MJO and rainfall rate. In contrast, 3 (three) other regions show a positive trend. The influence of an active MJO on the extreme rainfall rate is about 34,1%. Meanwhile, the rest for about 65,9% is influenced by other factors. The use of MJO indices for generating early warning hydrometeorological disasters is by utilising the MJO monitoring data, supported with the analysis of dynamical atmospheric condition in the west coast of South Sulawesi.