Madden–Julian Oscillation Events Research Articles

First results of the potential gradient variation in a tropical station in South America (Ica, Peru)

Measurements of the potential gradient (PG) under fair weather conditions at new locations are crucial for monitoring the global electric circuit. In this study, we analyzed the variations in PG recorded in Ica city, Peru, during the period from March 2018 to December 2022. Our analysis involved a detailed comparison of PG with various meteorological parameters such as rainfall, wind speed and direction, dust storms, dust devils and fog to establish the characteristic PG curve under fair weather conditions (referred to as the standard curve). We identified a significant threshold of 3.5 m/s for strong winds, which helps prevent the influence of sea breeze and dust lifting on PG. Our results showed the impact of 'Paracas' dust storms on PG, which aligns with patterns observed in other arid regions worldwide. Subsequently, we calculated monthly, seasonal, and annual averages of the standard curve which showed a response likely associated with local convective processes on the PG diurnal variation. Furthermore, the seasonal variation of PG reveals higher values during June, July, and August compared to December, January, and February. These differences are attributed to seasonal changes in aerosol concentrations, potentially influenced by biomass-burning activities in Peru. Additionally, we performed a wavelet transform analysis of PG hourly values. We found the periodicities of 1 day, ∼188 days, and 360 days which are related to the diurnal, semiannual and annual periods. During the months between January and March 2018 was found an intense period of ∼45-day likely associated with one of the strongest Madden-Julian Oscillation events. Through this comprehensive investigation, we deepen our understanding of the intricate relationships among meteorological conditions, sea breeze, dust storms, and the PG in arid regions like Ica.

MJO-Induced Warm Pool Eastward Extension Prior to the Onset of El Niño: Observations from 1998 to 2019

Abstract The Madden–Julian oscillation (MJO) and El Niño–Southern Oscillation (ENSO) are the two most important tropical phenomena that affect global weather and climate on intraseasonal and interannual time scales. Although they occur on different time scales, the MJO-induced sea surface temperature (SST) anomalies over the equatorial Pacific have spatial scales similar to SST anomalies prior to El Niño. This study aims to address the question of whether the MJO plays an important role in the warm pool eastward extension (WPEE) leading up to El Niño. We use over 20 years of satellite observations, including optimum interpolated SST, TRMM-GPM precipitation, and the cross-calibrated multiplatform (CCMP) surface winds from 1998 to 2019, to quantify the spatial structure and duration of the MJO-induced warm SST anomalies over the equatorial Pacific (10°S–10°N, 130°E–180°). The intensity of the MJO is measured by the total rain volume and average surface westerly wind speed throughout its convectively active phase. Results show that 1) 61% of the 98 MJO events induced a WPEE over 1000–3000 km along the equator, which can last beyond 15–30 days after the MJO precipitation ended; 2) the MJO events prior to El Niño are generally stronger and produce significant WPEE far beyond its annual cycle and increasing SST warming in the Niño-3.4 region; 3) consecutive MJO events can produce much stronger WPEE prior to El Niño, which are observed in all El Niño events from 1998 to 2019; and 4) more frequent and stronger MJO-induced WPEE occurs in March–May than other seasons. These results can help better understand the MJO–ENSO interaction and, ultimately, improve the prediction of El Niño onset.

Warm conveyor belt activity over the Pacific: modulation by the Madden–Julian Oscillation and impact on tropical–extratropical teleconnections

Abstract. Research in the last few decades has revealed that rapidly ascending airstreams in extratropical cyclones – so-called warm conveyor belts (WCBs) – play an important role in extratropical atmospheric dynamics. However on the subseasonal timescale, the modulation of their occurrence frequency, henceforth referred to as WCB activity, has so far received little attention. Also, it is not yet clear whether WCB activity may affect tropospheric teleconnection patterns, which constitute a source of predictability on this subseasonal timescale. Using reanalysis data, this study analyzes the modulation of WCB activity by the Madden–Julian Oscillation (MJO). A key finding is that WCB activity increases significantly over the western North Pacific when the convection of the MJO is located over the Indian Ocean. This increased WCB activity, which is stronger during La Niña conditions, is related to enhanced poleward moisture fluxes driven by the circulation of subtropical Rossby gyres associated with the MJO. In contrast, when the convection of the MJO is located over the western North Pacific, WCB activity increases significantly over the eastern North Pacific. This increase stems from a southward shift and eastward extension of the North Pacific jet stream. However, while these mean increases are significant, individual MJO events exhibit substantial variability, with some events even exhibiting anomalously low WCB activity. Individual events of the same MJO phase with anomalously low WCB activity over the North Pacific tend to be followed by the known canonical teleconnection patterns in the Atlantic–European region; i.e., the occurrence frequency of the positive phase of the North Atlantic Oscillation (NAO) is enhanced when convection of the MJO is located over the Indian Ocean and similarly for the negative phase of the NAO when MJO convection is over the western North Pacific. However, the canonical teleconnection patterns are modified when individual events of the same MJO phase are accompanied by anomalously high WCB activity over the North Pacific. In particular, the link between MJO and the negative phase of the NAO weakens considerably. Reanalysis data and experiments with an idealized general circulation model reveal that this is related to anomalous ridge building over western North America favored by enhanced WCB activity. Overall, our study highlights the potential role of WCBs in shaping tropical–extratropical teleconnection patterns and underlines the importance of representing them adequately in numerical weather prediction models in order to fully exploit the sources of predictability emerging from the tropics.

Analisis Korelasi Statistikal Fenomena Kejadian ENSO dan MJO terhadap Kondisi Klimatologis di Provinsi Riau

El Nino-Southern Oscillation (ENSO) and Madden-Julian Oscillation (MJO) events are significant factors in the global climate system. Riau Province, located on the island of Sumatra, is highly influenced by these phenomena. This study collects climate data from weather stations in Riau Province and reliable sources for ENSO and MJO indices. Statistical analyses, including correlation and regression, are employed to determine the relationship between climate variables in Riau Province and ENSO and MJO. Based on data from 2001-2019, the results reveal a medium category correlation value (r = 0.452) with coefficients a and b of 1.288 and 0.089, respectively. The increased MJO value contrasts with the rainfall during the 2001-2019 timeframe. This information serves as a reference for understanding the ENSO and MJO phenomena in the Riau region.

Observed Anomaly of Temperature and Mixed Layer Depth Associated with the Madden Julian Oscillation (MJO) Active Phase in the Banda Sea, Indonesia

The eastward propagation of atmospheric waves along the equatorial band from the central equatorial Indian Ocean to the western Pacific Ocean passing through the Indonesian Maritime Continent (IMC), known as the intraseasonal Madden Julian Oscillation (MJO) event, plays an important role on modulating both atmospheric and upper ocean dynamics along its path. This study aims to investigate the MJO active phase dynamics and its impact on changes in near-surface seawater temperature and mixed layer depth (MLD) anomaly in the Banda Sea Indonesia, using multi-datasets of atmospheric reanalysis, satellites derived sea surface temperature (SST), and Argo float between 2017 - 2018. This study revealed that the MJO waves propagate eastward along the southern equator-line over the IMC and pass through the Banda Sea, associated with significant decreased on Outgoing Longwave Radiation (OLR) and increased in zonal wind speed at 850hPa. The study result shows anomalous increased on surface wind speed and SST cooling during of MJO active phase. The amplitude peaks of filtered ocean-atmosphere variables range between 30 – 60 days. Argo float datasets in the Banda Sea for the first time captured upper ocean responses to the arrival of the MJO active phase, as characterized by a negative temperature anomaly of ~0.3°C in the surface mixed layer, large temperature anomaly of ~0.8°C in the thermocline layer and the deepening of the MLD of ~25 m. Hence, the MJO active phase impacts significantly on surface and vertical temperature cooling and regulate upper ocean mixing intensity in the Banda Sea.

The Indo‐Pacific Maritime Continent Barrier Effect on MJO Ensemble Prediction

AbstractThe barrier effect of the Indo‐Pacific Maritime Continent (MC) on the Austral summertime Madden‐Julian Oscillation (MJO) is explored using retrospective forecasts from subseasonal‐to‐seasonal (S2S) prediction models. The general MJO prediction skills in the S2S models are evaluated and the top‐performing models are identified. We select two sets of observed MJO events ‐ continuously propagating across the MC into the western Pacific (WP) and blocked by the MC. The continuously propagating MJO events are better predicted than the blocked MJO events for their systematic eastward propagating behavior, especially in the ocean‐atmosphere coupled models. Although the best four models and their ensemble consistently produce greater prediction skills of the continuously propagating MJOs, the all‐model ensemble is not better than the top‐performing models. Our analysis suggests that a realistic representation of air‐sea interaction over the WP is crucial for better MJO prediction.

East African Monsoon as a Drawbridge for the Circumnavigation of Madden–Julian Oscillation Events

AbstractThe seasonality of circumnavigation of Madden–Julian Oscillation (MJO) events is examined using 42 years of observations, reanalysis, and global model simulations. MJO events are most likely to propagate across the Atlantic Ocean, Africa and back to the equatorial Indian Ocean relatively unweakened during March–April–May and to a lesser extent during September–October–November. During these seasons, referred to as the “long‐rain” and “short‐rain” periods of East African Monsoon (EAM), precipitation is near the equator and extends farthest east toward the Indian Ocean. Moisture budget analysis of a circumnavigating MJO event under real and hypothetical seasonally varying background conditions indicates that the seasonal zonal movement of the zonal component of the background circulation regulates the moistening of MJO crossing from Eastern Africa to the Indian Ocean. Ensembles of Energy Exascale Earth System Model simulations of the MJO event under idealized seasonally varying background state confirm the observed drawbridge‐like role of the EAM in the propagation of MJO.

Surface‐driven amplification of Madden–Julian oscillation circulation anomalies across East Africa and its influence on the Turkana jet

AbstractIn semi‐arid environments, rainfall‐driven soil moisture fluctuations exert a strong influence on surface turbulent fluxes. Intraseasonal rainfall variability can therefore impact low‐level atmospheric temperatures and influence regional circulations. Using satellite observations and an atmospheric reanalysis, we investigate whether rainfall variability induced by the Madden–Julian oscillation (MJO) triggers land–atmosphere feedbacks across East Africa.We identify that surface fluxes during the East African wet seasons (March–May and October–December) are sensitive to MJO‐induced precipitation variations across low‐lying regions of South Sudan and highland regions of Uganda and southwest Kenya. For example, during MJO phases 6 to 8, when rainfall is suppressed, surface temperatures and sensible heat fluxes increase, whilst evapotranspiration decreases. Spatial variations in the surface flux response to rainfall variability feed back onto the atmosphere through amplifying MJO‐associated pressure anomalies. During dry MJO events for instance, surface warming across the exit region of the Turkana channel increases the low‐tropospheric along‐channel pressure gradient and intensifies the Turkana jet. We conclude that average surface‐driven temperature fluctuations during a single day are responsible for approximately 12% of MJO‐associated variability of the Turkana jet speed. However, we expect that the accumulation of heat over multiple days to the west of the East African Highlands further amplifies anomalies in the pressure gradient and jet intensity. Modelling experiments are required to quantify the accumulated impact of the surface forcing. Surface‐driven Turkana jet variations influence the East African moisture budget and affect the intensity and inland propagation of coastal convection. Not only is this the first study to investigate the importance of intraseasonal land–atmosphere feedbacks across East Africa, but it is also the first to show that Turkana jet characteristics are partly driven by surface conditions. This work motivates an investigation into whether subseasonal forecast models fully harness the predictability from surface‐induced jet variations.

Influences of Oceanic Processes Between the Indian and Pacific Basins on the Eastward Propagation of MJO Events Crossing the Maritime Continent

AbstractTropical intraseasonal Madden‐Julian oscillation (MJO) is one of the dominant products of ocean‐atmosphere interactions. The relationship between its eastward propagation and atmospheric boundary layer processes has been emphasized. Using the Climate Forecast System Reanalysis (CFSR) daily data, the eastward propagating MJO events are divided into the MJO_C events which pass through the Maritime Continent (MC) and MJO_N that cannot. In further research, the path from Lombok Strait to Timor Sea across the south of MC is identified as the critical movement path of MJO (MJO_SC) events. The differences in the oceanic processes and lower atmospheric fields are then revealed between the MJO_SC and MJO_N events along this critical path. The MJO_SC (MJO_N) events triggered in the eastern (western) side of the tropical Indian Ocean lead to the thermocline deepening (shallowing) and warm (cold) upper ocean in the Lombok Strait‐Timor sea. Subsequently, MJO_N events propagate northeastward over the land of MC and die out. However, MJO_SC events are pulled toward the Timor Sea. During the eastward propagation of the MJO_SC events, an eastward anomalous subsurface warm current is discovered in the Timor Sea, which is prior to the atmospheric convection center. This advective heat transport in the upper ocean dominates the sea surface warming under the MJO atmospheric convection center and its eastern flank. The followed outward turbulent heat flux and vapor cause an increase in moisture and instability in the lower atmosphere east of the MJO convection center, which promotes the growth and continued eastward propagation of the MJO.

Land‐Locked Convection as a Barrier to MJO Propagation Across the Maritime Continent

AbstractLarge‐scale convection associated with the Madden‐Julian Oscillation (MJO) initiates over the Indian Ocean and propagates eastward across the Maritime Continent (MC). Over the MC, MJO events are generally weakened due to complex interactions between the large‐scale MJO and the MC landmass. The MC barrier effect is responsible for the dissipation of 40%–50% of observed MJO events and is often exaggerated in weather and climate models. We examine how MJO propagation over the MC is affected by two aspects of the MC—its land‐sea contrast and its terrain. To isolate the effects of mountains and land‐sea contrast on MJO propagation, we conduct three high‐resolution coupled atmosphere‐ocean model experiments: (a) control simulation (CTRL) of the 2011 November–December MJO event, (b) flattened terrain without MC mountains (FLAT), and (c) no‐land simulation (WATER) in which the MC islands are replaced with 50 m deep ocean. CTRL captures the general properties of the diurnal cycle of precipitation and MJO propagation across the MC. The WATER simulation produces a more intense and smoother‐propagating MJO compared with that of CTRL. In contrast, the convergence of sea breezes in the FLAT simulation produces much more organized convection and precipitation far inland than in CTRL, which results in a stronger barrier effect to MJO propagation. The land‐sea contrast induced land‐locked convection weakens the MJO's convective organization. The land‐locked convective systems over land in FLAT are more intense, grow larger, and last longer, which is more detrimental to MJO propagation over the MC, than the mountains that are present in CTRL.

A Multimodel Real-Time System for Global Probabilistic Subseasonal Forecasts of Precipitation and Temperature

Abstract A global multimodel probabilistic subseasonal forecast system for precipitation and near-surface temperature is developed based on three NOAA ensemble prediction systems that make their forecasts available publicly in real time as part of the Subseasonal Experiment (SubX). The weekly and biweekly ensemble means of precipitation and temperature of each model are individually calibrated at each grid point using extended logistic regression, prior to forming equal-weighted multimodel ensemble (MME) probabilistic forecasts. Reforecast skill of week-3–4 precipitation and temperature is assessed in terms of the cross-validated ranked probability skill score (RPSS) and reliability diagram. The multimodel reforecasts are shown to be well calibrated for both variables. Precipitation is moderately skillful over many tropical land regions, including Latin America, sub-Saharan Africa and Southeast Asia, and over subtropical South America, Africa, and Australia. Near-surface temperature skill is considerably higher than for precipitation and extends into the extratropics as well. The multimodel RPSS skill of both precipitation and temperature is shown to exceed that of any of the constituent models over Indonesia, South Asia, South America, and East Africa in all seasons. An example real-time week-3–4 global forecast for 13–26 November 2021 is illustrated and shown to bear the hallmarks of the combined influences of a moderate Madden–Julian oscillation event as well as weak–moderate ongoing La Niña event. Significance Statement This paper develops a system for forecasting of precipitation and temperatures globally over land, several weeks in advance, with a focus on biweekly averaged conditions between three and four weeks ahead. The system provides the likelihood of biweekly and weekly conditions being below, near, or above their long-term averages, as well the probability of exceeding (or not exceeding) any threshold value. Using historical data, the precipitation forecasts are demonstrated to have skill in many tropical regions, and the temperature forecasts are more widely skillful. While weather and seasonal range forecasts have become quite generally available, this is one of the first examples of a publicly available, calibrated multimodel probabilistic real-time forecasting system for the subseasonal range.

Application of CHIRPS dataset in the selection of rain-based indices for drought assessments in Johor River Basin, Malaysia

This paper aims to select the most appropriate rain-based meteorological drought index for detecting drought characteristics and identifying tropical drought events in the Johor River Basin (JRB). Based on a multi-step approach, the study evaluated seven drought indices, including the Rainfall Anomaly Index (RAI), Standardized Precipitation Index (SPI), China-Z Index (CZI), Modified China-Z Index (MCZI), Percent of Normal (PN), Deciles Index (DI), and Z-Score Index (ZSI), based on the CHIRPS rainfall gridded-based datasets from 1981 to 2020. Results showed that CZI, MCZI, SPI, and ZSI outperformed the other indices based on their correlation and linearity (R2 = 0.96–0.99) along with their ranking based on the Compromise Programming Index (CPI). The historical drought evaluation revealed that MCZI, SPI, and ZSI performed similarly in detecting drought events, but SPI was more effective in detecting spatial coverage and the occurrence of ‘very dry’ and ‘extremely dry’ drought events. Based on SPI, the study found that the downstream area, north-easternmost area, and eastern boundary of the basin were more prone to higher frequency and longer duration droughts. Furthermore, the study found that prolonged droughts are characterized by episodic drought events, which occur with one to three months of ‘relief period’ before another drought event occurs. The study revealed that most drought events that coincide with El Niño, positive Indian Ocean Dipole (IOD), and negative Madden-Julian Oscillation (MJO) events, or a combination of these events, may worsen drought conditions. The application of CHIRPS datasets enables better spatiotemporal mapping and prediction of drought for JRB, and the output is pertinent for improving water management strategies and adaptation measures. Understanding spatiotemporal drought conditions is crucial to ensuring sustainable development and policies through better regulation of human activities. The framework of this research can be applied to other river basins in Malaysia and other parts of Southeast Asia.

The Use of Regional Data Assimilation to Improve Numerical Simulations of Diurnal Characteristics of Precipitation during an Active Madden–Julian Oscillation Event over the Maritime Continent

This study examines the impact of regional data assimilation on diurnal characteristics of precipitation and winds over the Maritime Continent (MC) using a set of cloud-permitting-scale (~3 km) numerical simulations with the mesoscale community Weather Research and Forecasting (WRF) model and the NCEP Gridpoint Statistical Interpolation (GSI)-based ensemble-3DVAR hybrid data assimilation system. Numerical experiments focus on January 2018, when a well-defined, active Madden–Julian Oscillation (MJO) propagated through the MC region. Available conventional and satellite data are assimilated. Results show that simulated precipitation with data assimilation generally agrees better with satellite-derived rainfall than the control simulation without data assimilation. Simulations with data assimilation also reproduce the diurnal cycle of precipitation better, especially for the timing of the precipitation peak. Data assimilation modulates the overstrong (overweak) diurnal forcing over the land (ocean) in the control simulation. The vertical phase shift of the thermodynamic environment, associated with the timing of vertical motion transition along with low-level water vapor supplies, results in maximum precipitation occurring later, especially over land. To further demonstrate the impact of data assimilation, an additional experiment assimilates NASA Cyclone Global Navigation Satellite System (CYGNSS)-derived ocean surface winds. The results indicate that the assimilation of CYGNSS data exhibits an evident impact on the diurnal variation of surface variables and a similar shift in the diurnal cycle of precipitation. Overall, this study highlights the importance of regional data assimilation in improving the representation of precipitation over the MC, paving the way for a better understanding of the interactions of local diurnal convective precipitation cycles with MJO.

Diverse MJO Genesis and Predictability

Abstract The Madden–Julian oscillation (MJO) is the dominant intraseasonal wave phenomenon influencing extreme weather and climate worldwide. Realistic simulations and accurate predictions of MJO genesis are the cornerstones for successfully monitoring, forecasting, and managing meteorological disasters 3–4 weeks in advance. Nevertheless, the genesis processes and emerging precursor signals of an eastward-propagating MJO event remain largely uncertain. Here, we find that the MJO genesis processes observed in the past four decades exhibit remarkable diversity with different seasonality and can be classified objectively into four types, namely, a novel downstream origin from the westward-propagating intraseasonal oscillation (WPISO; 20.4%), localized breeding from the Indian Ocean suppressed convection (IOSC; 15.4%), an upstream succession of the preceding weakly dispersive (WD; 25.9%), and strongly dispersive (SD; 38.3%) MJO. These four types are associated with different oceanic background states, characterized by central Pacific cooling, southern Maritime Continent warming, eastern Pacific cooling, and central Pacific warming for the WPISO, IOSC, WD, and SD types, respectively. The SD type is also favored during the easterly phase of the stratospheric quasi-biennial oscillation. Diverse convective initiations possibly imply various kinds of propagations of MJO. The subseasonal reforecasts indicate robustly distinct prediction skills for the diverse MJO genesis. A window of opportunity for skillful week 3–4 prediction probably opens with the aid of the WPISO-type MJO precursor, which has increased the predictability of primary MJO onset by 1 week. These findings suggest that the diversified MJO genesis can be skillfully foreseen by monitoring unique precursor signals and can also serve as benchmarks for evaluating contemporary models’ modeling and predicting capabilities.

The Role of Surface Fluxes in MJO Propagation through the Maritime Continent

Abstract The “barrier effect” of the Maritime Continent (MC) is a known hurdle in understanding the propagation of the Madden–Julian oscillation (MJO). To understand the differing dynamics of MJO events that propagate versus stall over the MC, a new tracking algorithm utilizing 30–96-day-filtered NOAA Interpolated OLR anomalies is presented. Using this algorithm, MJO events can be identified, tracked, and described in terms of their propagation characteristics. Latent heat flux from OAFlux and CYGNSS surface winds and fluxes are compared for MJO events that do and do not propagate through the MC. Events that successfully propagate through the MC demonstrate regional surface flux anomalies that are stronger, more spatially coherent, and have a larger fetch. The spatial scale of convective anomalies for events that successfully propagate through the MC region is also larger than for terminating events. Large-scale enhancement of latent heat fluxes near and to the east of the date line, equally driven by dynamic and thermodynamic effects, also accompanies MJO events that successfully propagate through the MC. These findings are placed in the context of recent theoretical models of the MJO in which latent heat fluxes are important for propagation and destabilization.

Contrasting the energy recharge-discharge cycle between propagating and eastward-decaying Madden–Julian Oscillation events

Contrasting the energy recharge-discharge cycle between propagating and eastward-decaying Madden–Julian Oscillation events

The Indo-Pacific Maritime Continent Barrier Effect on MJO Prediction

Abstract The Madden–Julian oscillation (MJO) is often observed to weaken or sometimes completely decay as its convective anomaly moves from the Indian Ocean over to the Maritime Continent (MC), which is known as the MC barrier effect on the MJO. This barrier effect is often exaggerated in numerical models. Using 23 years of the retrospective intraseasonal forecast from two coupled model systems with useful MJO prediction skills, we show that the predictive skill of the real-time multivariate MJO (RMM) index for the continuously propagating MJO events across the MC region is higher than for the blocked MJO events. The greater prediction skill is not related to the higher initial RMM amplitude for the continuous MJO events. Rather the higher skill arises from the more persistent behavior of the propagating MJO events as the convective anomaly moves through the MC region into the western Pacific. The potential predictability is similar for both types of MJO events, suggesting the forecast models hardly differentiate the two types of MJO events in prediction; they only maintain higher RMM magnitudes of the continuously propagating events. The global reanalysis dataset indicates that the blocked events are often associated with persistent higher surface pressures over colder sea surface temperatures in the central Pacific, suggesting the large-scale environment plays a role in promoting or inhibiting the MJO propagation across the MC region. Caveats in the models to reproduce the observed MJO events are also discussed.

Climatological diagnostics and subseasonal‐to‐seasonal predictions of Madden–Julian Oscillation events

AbstractThe Madden–Julian Oscillation (MJO) is the dominant mode of tropical intraseasonal variability, which serves as a primary source of subseasonal‐to‐seasonal (S2S) predictability. Noticeably, MJO is not always a regularly recurring cycle but is characterized by discrete episodes. In this study, considering the quasi‐consecutive actives and eastward propagating features, a standard metric is proposed to identify MJO events based on the real‐time multivariate MJO (RMM) index. The re‐identification of historical MJO events reveals that there were 5.4 MJO events each year since 1981, and the average duration of each event is about 31.5 days. More MJO events tend to occur in the boreal winter and spring, with stronger intensity, longer duration and faster propagating speed than those in the boreal summer. Furthermore, MJO events are more likely to initiate in Phases 2 and 5, with a longer lifetime than those initiating in other phases. The amplitude and propagation characteristics of MJO events are strongly modulated by the dominant modes of sea surface temperature interannual variability with a strong regional dependence. Based on hindcast datasets of six S2S models, the prediction skill for the MJO is evaluated in the perspective of individual events. The longest leading time of the skilful prediction for individual MJO events ranges from 11 to 17 days, far below the traditional recognition. This result could be attributed to the apparent prediction barrier of MJO initiation, that is, a rapid decrease in prediction skill when predictions are carried out before the initiation of MJO events. In addition, the prediction skills of MJO events depends on interannual variabilities, with relatively higher skills under the conditions of the El Niño and Indian Ocean basin warming. These findings may shed light on the complexity and challenges of profoundly understanding and skilfully predicting MJO events.

Hydrometeor Storage and Advection Effects in DYNAMO Budget Analyses

Abstract The Dynamics of the Madden–Julian Oscillation (MJO) (DYNAMO) field campaign over the central Indian Ocean captured three strong MJO events during October–December 2011. Using the conventional budget approach of Yanai et al. surface rainfall P0 is computed as a residual from the vertically integrated form of the moisture budget equation. This budget-derived P0 is spatially averaged over the Gan Island NCAR S-PolKa radar domain and compared with rainfall estimates from the radar itself. To isolate the MJO signal, these rainfall time series are low-pass (LP) filtered and a three-MJO composite is created based on the time of maximum LP-filtered S-PolKa rainfall for each event. A comparison of the two composite rainfall estimates shows that the budget rainfall overestimates the radar rainfall by ∼15% in the MJO buildup stage and underestimates radar rainfall by ∼8% in the MJO decay stage. These rainfall differences suggest that hydrometeor (clouds and rain) storage and advection effects, which are neglected in the budget approach, are likely significant. Satellite and ground-based observations are used to investigate these hydrometeor storage and advection effects. While the findings are qualitatively consistent with expectations from theory, they fall short of explaining their full magnitude, suggesting even more refined experimental designs and measurements will be needed to adequately address this issue.

Tropical‐wave activity and Madden–Julian oscillation termination

AbstractThe Madden–Julian oscillation (MJO) is the dominant mode of intraseasonal variability in the tropics and generates large‐scale precipitation, cloud, and circulation anomalies. Interactions between the MJO and dry and convectively coupled equatorial waves (CCEWs) have been identified in previous works; however, these studies have not focused on MJO events that maintain themselves versus those that decay. Knowledge on how pre‐existing MJO events interact with CCEWs is important for producing more realistic and reliable representations of MJO events in weather forecast and global climate models. This study presents an analysis of intraseasonally varying outgoing longwave radiation (OLR) and zonal wind anomalies at 200 and 850 hPa from National Oceanic and Atmospheric Administration (NOAA) observations and ERA‐Interim reanalysis data respectively, throughout the lifetime of observed MJO events. A climatology of continuing and terminating MJO events is created from an event identification algorithm using common tracking indices including the OLR‐based MJO Index (OMI), filtered OMI (FMO), real‐time multivariate MJO (RMM), and velocity potential MJO (VPM) index. Wheeler–Kiladis power spectra are calculated for each event type to identify predominant wave modes. Symmetric and anti‐symmetric wave spectra are composited and results include the sensitivity of the variables used to define the waves and index choice for identifying the MJO. Our results show fractional differences between continuing and terminating MJO events that are statistically significant at the 95% level. Statistical significance is most prominent within the MJO band where continuing events have higher power, as well as global mixed Rossby–gravity (MRG) waves and tropical depression (TD) waves where terminating events have higher power. These results are mostly robust to meteorological variable and index although the importance of Kelvin waves is amplified in the VPM. A regional analysis including phase separation contains results that are sensitive to variable and domain although westward traveling waves are commonly associated with MJO termination regardless of location.