The Global Monsoon System

The following sections are included:

• Foreword
• Contents

The East Asian summer monsoon is characterized by strong, moist southwesterly flow over a broad expanse that includes the seas adjacent to China and the Pacific Ocean south of Japan. Relatively strong sea surface temperature (SST) gradients, particularly at the time of summer monsoon onset, exist over these waters as a result of the previous winter’s cold outbreaks. The flow of warm air over cooler water can lead to low-level convergence through the suppression of vertical momentum transport in the boundary layer as a result of increased stability. Given sufficient moisture and instability, deep convection can break out.

Much recent research has focused upon the marked intraseasonal variability of the summertime Australian monsoon system. There are significant synoptic scale phenomena embedded within the monsoon system, which have a clear impact on the total monsoon rainfall. In addition to tropical cyclones, there are many monsoon disturbances that resemble synoptic features found over India and Africa during boreal summer. Automated tracking of the Australian disturbances suggests that a significant proportion of these may develop in the subtropics in connection with the equatorward intrusion of extratropical features.

The multiscale nature of the South American Monsoon System is presented here in a review of the interannual to decadal variability, intraseasonal variability and regional and mesoscale features of the clouds systems associated with the break and active phases. Although the lack of long records in the Amazon and surrounding areas limits multidecadal analyses of the monsoon, associations of monsoon features with the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation have been found. There is evidence that El Niño/La Niña modulate the South Atlantic Convergence Zone and extreme daily rainfall events in the region. The onset/demise of the SAMS is variable throughout the region and associated to different features of convective activity, and the convective/ stratiform partition. Aerosols emitted by biomass burning have been shown to act as Could Condensation Nuclei whereby they may affect clouds although during the premonsoon phase not much sensitivity has been found to variations in aerosol concentration. During the wet season, however, aerosol concentration appears as a possible cause to explain convective intensity. Predictability of onset, amplitude, duration and demise of SAMS have shown increased skill through empirical relationships between bimonthly average precipitation and modes of interannual variability of upper level winds in South America.

This chapter provides a summary of the recent advances made on the understanding and simulation of the coupled atmosphere-ocean-land system of the West African Monsoon (WAM) and of its variability on a wide range of space and timescales. More specifically we highlight the interannual to climate scales, the intraseasonal variability, weather systems and their predictability, the surfaceatmosphere coupling and the coupling with dust.

The East Asian winter monsoon (EAWM) research of the past several years is briefly reviewed. On the interannual time scale, the EAWM variability features two major modes: the strength and pathway of the EAWM, which are linked to the changes in the amplitude and phase of atmospheric planetary waves, respectively. The blocking activity over Ural and Pacific regions exert significant impacts on the strength of the EAWM in the form of Eurasian and Western Pacific patterns. The former also contributes largely to the recent decadal amplification of the EAWM. El Niño-Southern Oscillation (ENSO) and Arctic sea ice are important external forcing for the EAWM variability, while the impacts of ENSO on the EAWM vary with decades. On the intraseasonal time scale, the Siberian high shows clear out-of-phase relationship between early and peak winter in recent thirty years. Both the stratospheric variability and the Madden-Julian Oscillation could influence the characteristics of cold surges over East Asia. All these provide intraseasonal prediction potentials for the EAWM.

Recent progress and achievements in the research on the Maritime Continent monsoon are reviewed by focusing on the studies reported in the last five years or so. The progress has been promoted by the advancement of computing facilities for data analysis and numerical simulations, technical innovations in observations, and well-designed numerical experimentations for better understanding. This review is divided into five subsections based on their time scales as follows: (a) annual cycle and seasonal transitions, (b) diurnal cycle of rainfall and its multiscale interactions, (c) subseasonal variability, (d) interannual variations and seasonal predictability, and (e) interdecadal variability, trends, and geological time-scale climate changes.

The simulation of monsoons remains a challenging problem given the complexity of the multi-scale interactions and the modulating influences that operate on a broad range of time scales. Recent studies have demonstrated an improvement in the simulation of monsoons in CMIP5 relative to CMIP3, though many outstanding issues remain. For example, although mean state biases have been reduced in amplitude, the spatial error pattern remains virtually unchanged between the two vintages of experimentation. Systematic errors in the onset time of monsoons indicate that the simulated atmosphere-land-ocean interactions are not responding properly to the annual cycle of solar forcing. As such, the CMIP5 models have early monsoon onset over the Sahel and the North American domain, and late monsoon onset over India, the South American domain, and the Gulf of Guinea. This indicates that a regional process study approach is warranted for improving our understanding of atmosphere-land-ocean interactions inherent to monsoon development and onset. The simulation of intraseasonal variability remains a grand challenge problem, especially given its importance for initiating monsoon onset and being associated with precipitation extremes. Experimental prediction of intraseasonal variability suggests forecast skill to 3 weeks, with the potential for increased skill with the implementation of different projection basis function for boreal summer vs. boreal winter. Despite improvements in the simulation of the El Nino/Southern Oscillation, the interannual monsoon teleconnections are sensitive to biases in the regional rainfall that can compromise the response to the remote forcing. At best, interdecadal variations of Sahel rainfall are qualitatively captured in CMIP5, with the amplitude of the 1970’s-1980’s drought strongly underestimated. Conversely, mechanisms for observed interdecadal trends in rainfall over East Asia and northern Australia are yet to be understood, and these trends remain to be simulated. Higher horizontal resolution has been beneficial in the representation of orographic rainfall, as well as larger scale aspects of the circulation (e.g. Baiu front) though improvements to model physics are most essential for improving the simulation and prediction of monsoons.

This chapter summarizes the most salient features of the Madden Julian Oscillation’s (MJO) planetary wave structure. At upper tropospheric levels the MJO signature in wind (V) and geopotential height (Z) consists of equatorial Kelvin waves flanked by Rossby waves centered along 28°N/S, confined to the subtropics by the climatological-mean westerly jet streams and propagating all the way around the equatorial belt. At lower tropospheric levels the MJO resembles the response to a pulsating heat source over the Maritime Continent as in the solutions of Matsuno (1966) and Gill (1980). The contrasting upper and lower tropospheric structures can be interpreted as the superposition of a first internal baroclinic modal structure, which is dominant in the tropics and an equivalent barotropic field consisting mainly of extratropical wavetrains. The lower-tropospheric anomalies in wind and geopotential height induce a distinctive frictionally induced boundary layer convergence pattern, which is displaced to the east of the corresponding pattern in lower free tropospheric convergence. The contrasting divergence profiles in the boundary layer and free troposphere are responsible for the observed “bottom-up” evolution of the convection and the distinctive “swallowtail shaped” vertical velocity pattern.

In this chapter, we summarize our experiences with respect to the representation of the Madden- Julian oscillation (MJO) in general circulation models (GCMs). Specifically, we focus on diagnostics that have been used in evaluating GCM simulations, the empirical relationships that have been reported between GCM configurations and MJO simulation skill, and the theoretical frameworks that have been used to interpret the empirical relationships. Popular MJO simulation diagnostics that capture salient features of the MJO were recently standardized by the U.S. CLIVAR MJO Working Group, which make tracking of improvements possible across different models and model generations. Simulation of the MJO is sensitive in particular to the details of the cumulus parameterization used in GCMs. Inhibiting too-frequent activation of vigorous deep convection, which can be achieved a number of ways, generally leads to enhanced MJO variability. Recent MJO theoretical developments have led to new frameworks in which to interpret MJO modeling results. Different, but not mutually exclusive, theoretical frameworks have been applied in different studies, reflecting the lack of a single, satisfactory theory of the MJO. Possible future directions for further improvement of the MJO in GCMs are also discussed.

We review the progress of two related activities on real-time forecasting of modes of large-scale tropical intraseasonal variability. The modes are the Madden Julian Oscillation (MJO) and the Boreal Summer Intraseasonal Oscillation (BSISO). The MJO forecasting activity has reached a mature status and is judged a success based on: (a) the number of user hits its web page receives; (b) the application of the MJO forecasts for user-oriented forecast products; and (c) the number of research papers for which the forecasting and verification methods have been used. The BSISO forecasting activity is still developing and in 2013 had five different model contributions, with another to be added in 2014. Verification of the BSISO forecasts during 2013 show a similar level of skill for the main BSISO mode (BSISO1) compared to the MJO, but less for the 2nd mode (BSISO2). There are plans to analyze the relation of the BSISO modes to impacts in the East Asian monsoon, and also to provide a multi-model ensemble forecast.

This paper is aimed to summarize the previous findings on various propagation characteristics of intraseasonal variations (ISV) over the Asian Monsoon region during boreal summer and reviews and suggests major mechanisms associated with the propagation characteristics. The ISV consists of various components whose characteristics are different in terms of propagation direction and its time scale. Three major components include the eastward propagating component with time scales of 30–60 days, which propagates mainly along the tropical belt, the westward propagating component with shorter time scales of a week to a month in the subtropical Western Pacific and Indochina, and the northward propagating component with time scales of about 40 days in the Indian Ocean and Western Pacific region. It is demonstrated that the essential mechanism for the eastward and westward propagations is rooted in the convectively coupled Kelvin-Rossby waves with frictional moisture convergence. The propagation direction and time scales are shown to be determined by the horizontal structures of surface boundary conditions, particularly the sea surface temperature. The northward propagation, on the other hand, appears to be related to the strong vertical wind shear in the South Asian Monsoon region, as appears only during boreal summer. The wind shear mechanisms include the vorticity titling mechanism and the cumulus momentum mixing (CMT) and the CMT is discussed as a major mechanism in this paper.

The progress and current status of prediction activities on the Madden-Julian Oscillation (MJO) are reviewed. We have witnessed the significant progress in dynamical MJO prediction from 7-day limit using the (NCEP)-1 reanalysis vintage model during 1990s to about 30-day limit using the latest version of European Centre for Medium-Range Weather Forecasts (ECMWF) model during 2010s. Motivated by significant societal demands for reliable subseasonal prediction, several international efforts have been coordinated including real-time MJO and boreal summer intraseasonal oscillation (BSISO) prediction intercomparison by MJO Task Force and Working Group on Numerical Experimentation (WGNE), and Intraseasonal Variability Hindcast Experiment (ISVHE). Analysis of 12 climate models’ hindcast participated in ISVHE showed that the MJO can be potentially predictable up to 35∼45 days and the multi-model ensemble has a useful skill for the Realtime Multivariate MJO (RMM) index up to 26∼28 days for 1989.2008 during boreal winter, demonstrating capability of current models for seamless weather-intraseasonal-seasonal prediction. It is also noted that the current MJO prediction depends on initial and target MJO phase and El Ni.no and Southern Oscillation (ENSO) phase. The dynamical models’ common biases in simulating the MJO are slower eastward propagation, underestimation of MJO amplitude, and the Maritime Continent barrier. Key factors to further improve the MJO prediction include improvement of models’ intrinsic MJO mode, better initialization, and proper representation of air-sea coupling.

The “Vertical Structure of Diabatic Processes of the Madden-Julian Oscillation” global-model evaluation project developed a novel experimental framework, which produces a complete characterization of models’ abilities to simulate the Madden-Julian oscillation (MJO). The three components of the project comprise 2-day and 20-day hindcasts and 20-year simulations; each obtained heating, moistening and momentum tendencies from the models’ sub-grid parameterizations. Thirty-five centers provided output for at least one component; nine centers provided data for all three. The models vary greatly in MJO fidelity in climate and hindcast experiments, yet fidelity in one was not correlated with fidelity in the other. In 20-year simulations, strong MJO models demonstrated heating, vertical-velocity and zonal-wind profiles that tilted westward with height, as in reanalysis data. The 20-day hindcasts showed no correspondence between the shape of the heating profile and hindcast skill. Low-to-mid-level moistening at moderate rain rates was a consistent feature of highskill models and absent from low-skill models, suggesting a role for boundary-layer and congestus clouds in the MJO transition, which was confirmed by timestep data from the 2-day hindcasts. These hindcasts revealed a poor simulation of the MJO transition phase, even at short leads, with large mid-tropospheric dry biases and discrepancies in radiative-heating profiles.

In this chapter, we provide an overview of Madden-Julian oscillation (MJO) simulations with global high-resolution models that require large amounts of computational resources. After introducing the recent activities regarding such models, we focus on the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), in which we are involved, and summarize our experiences with respect to the representation of the MJO in NICAM. State-of-the-art supercomputers have carried us to a point where global sub-kilometer grid systems are applicable for short simulations of several days, and sub- 10-km grid systems can be applied for simulations that are several years long. The high resolution and the more explicit physics compared to those of conventional general circulation models allow a higher degree of freedom in the modeled state of the atmosphere. The increased degree of freedom not only provides the model a higher potential to closely represent the real atmosphere but it also provides more reasons for the model to be different from reality. Use of a highly complex model requires a great amount of effort to determine numerous parameters in physics schemes. Although simulation of MJO events by NICAM today is successful overall, the question remains whether it can maintain realistic climatology and intra-seasonal variability in climate simulations. The development of an efficient procedure to appropriately confine the range of these parameters is one of the main issues for the future. Moreover, it is important to keep in mind that higher complexity could increase the difficulty of interpreting the results and improving scientific understanding.

Indian monsoon depressions are synoptic-scale storms that form primarily over the Bay of Bengal and propagate westward over the subcontinent, producing a large fraction of India’s total summer precipitation. We recently showed that, contrary to long-standing ideas, the westward propagation of Indian monsoon depressions is accomplished primarily by horizontal adiabatic advection of potential vorticity (PV), not by vortex stretching or diabatic PV generation that occurs in the region of quasi-geostrophic ascent southwest of the vortex center. This chapter extends that work by using several reanalysis products to examine case studies of Indian monsoon depressions. In all reanalyses examined, monsoon depressions have maximum PV in the middle troposphere, at higher altitudes than the level of maximum relative vorticity. The horizontal structure of mid-tropospheric PV suggests that the axial asymmetry of the vortex that produces the nonlinear westward advection may result at least partly from diabatic heating. Thus, although storm motion is produced primarily by horizontal adiabatic advection, diabatic heating can play an indirect role by shaping the PV field that produces this advection.

This chapter reviewed the main results of four recent published papers on squall lines in east China covering the radar characteristics, structure and predictability of squall lines under different environmental flow systems including tropical cyclone, westerly trough, and cold vortex. The general features of squall lines in east China was first examined based on two-year’s mosaic of radar reflectivity in 2008 and 2009 in comparison to the U.S. squall lines. In particular, the general features of squall lines preceding landfall tropical cyclones were documented in details. Following that, the structure and predictability of squall lines associated with a westerly trough and a cold vortex were further examined. Results showed that the rear inflow that formed through the consolidation of three pairs of bookend vortices played an essential role in the formation of a large bowing structure within a squall line that formed in front of a westerly trough. Through a detailed damage survey, radar and radiosonde analyses, the radar features and formation environment of a tornadic supercell developing in a cold-vortex-associated squall line was examined. This chapter also examined the predictability of a squall line associated with a westerly trough. It was found that squall-line simulation could be very sensitive to model error from horizontal resolution and uncertainties in physical parameterization schemes. A linear improvement in the performance of squall line simulation was observed when the initial error was decreased gradually, with the largest contribution from initial moisture field.

In South China (SC), the annual precipitation commonly exceeds 2000mm and about 40%–50% of the amount falls during April–June, which is called the pre-summer rainy season over SC. Frequent occurrences of extreme rainfall in the pre-summer rainy season often lead to severe flooding and inundations. In this paper, previous research and field programs aiming at better understanding of the heavy rainfall formation are reviewed. Current scientific issues of relevance to the heavy rainfall events are then presented followed by an introduction to SCMREX, which has been approved by World Meteorological Organization as a World Weather Research Program research and development project, including its background, scientific objectives, field experiment design, and preliminary scientific results.

Heavy rainfalls associated with summer monsoon in East Asia are closely related to the local frontal activities: Meiyu, Baiu and Changma. Recent studies utilizing Doppler radar data on heavy rain weather systems related to East Asian summer monsoon are reviewed. Field experiments on heavy rainfalls with Doppler radar in East Asia are highlighted.

The synoptic behavior of present-day heat waves (HW) over East Asia is studied using a global high-resolution atmospheric model (HiRAM) with 50-km grid-spacing. The simulated HW characteristics are compared with those derived from Climate Forecast System Reanalysis products. Additional runs of HiRAM are conducted for the “time slice” of 2086–2095 in the climate scenario corresponding to Representative Concentration Pathway (RCP) 4.5. By the end of the 21st century, the averaged duration and frequency of HW in selected East Asian sites are projected to increase by a factor of 1.4–2.1 and 2.0–2.3, respectively, from the present-day values. The output from a continuous integration of a coupled general circulation model with a lower resolution through the 1901–2100 period indicates a notable increase in severity, duration and HW days during the 21st century.

Since the beginning of the 21st century Taiwan has experienced a dramatic increase in typhoonrelated rainfall. Some investigators suggested that they are the manifestation of global warming effects. However, an analysis of typhoon rainfall intensity with respect to typhoon tracks in different landfall phases relative to the Central Mountain Range indicates this is unlikely the cause. Rather, most of the recently observed large increase in typhoon rainfall in the pre-landing and overland phases is the result of slower moving tropical cyclones (TCs) and their tracks relative to the high mountains. A positive feedback mechanism in which the convective heating pattern forced by topography acts to slow down the TC motion, which is most efficient for the slowly-moving northern-track storms. Another factor contributing to increased TC-related rainfall is the interaction between the typhoon circulation and southwest monsoon wind surges. This factor is most important after the typhoon center exits Taiwan and led to the increase of both typhoon rainfall intensity and rainfall amount in the new century. Both the slower TC motion and the increased monsoon interaction are consistent with the recently observed multidecadal trend of intensifying subtropical monsoon and tropical circulations, which is contrary to some theoretical and model projections of global warming. There is also no evidence of a positive feedback between global warming-related water vapor supply and TC intensity in the typhoon rainfall increase, as the number of strong landfalling TCs has decreased significantly since 1960 and the recent heavy rainfall typhoons are all of weak to medium intensity.

In this study, the uncertainties of (1) the sudden recurvature of Typhoon Megi (2010), and (2) precipitation over Taiwan under the joint influence of the outer circulation of Megi and the northeasterly monsoon are examined with ensemble simulations based on an ensemble Kalman filter data assimilation system and the Weather Research and Forecasting (WRF) Model. Our analysis shows that the overall movement of Megi well aligned with the direction of steering flow associated with the monsoon trough. After Megi headed north, the approaching upper-level trough helped enhance Megi’s northward movement.

The global monsoon (GM) is an evolving concept that has not yet been fully recognized, especially whether its interannual-multidecadal climate variability can be viewed as one of the major modes of the global climate system. In this chapter we focus on reviewing the common variability and linkages among all regional monsoons. We begin with a brief review of the concept of the GM and elaborate what the essence of the GM is and why it is a defining feature of the Earth’s climatology. The GM variability and change are driven by two sets of factors. One is external forcing, both natural (solar orbital change, volcanic aerosols) and man-made (greenhouse gases concentration, anthropogenic aerosols, land use, etc.). The other is internal feedback processes within the coupled Earth’s climate system. Evidence is reviewed to show that on the interannual-to-multidecadal time scale, the monsoon variations are not merely of isolated regional characters; rather, the monsoon can be driven by common internal feedback processes on global scale such as El Nino-Southern Oscillation (ENSO), mega-ENSO, and Atlantic Multidecadal Oscillation (AMO). The changes in solar radiation flux and volcanic forcing is shown to generate a coherent variability of all regional monsoons; thus the GM represents a leading mode of variability on centennial or longer time scales in response to changing solar forcing. In addition, we review how anthropogenic forcing affects future change of GM precipitation. It is important to understand the difference in GM responses to anthropogenic and natural forcings. In summary, it is argued that the GM is not only a defining feature of the Earth’s climatology but also a major mode of Earth’s climate variability across time scales ranging from interannual to centennial.

The Asian monsoon represents one of the major modes of the seasonal cycle on the planet and undergoes variations on intraseasonal through interannual time scales that affect the water supply for more than half the global population. But the monsoon also undergoes appreciable variability on decadal time scales, noted both in the Asian monsoon and also as part of more coherent variations in the global monsoon. In the observed data, large variations on multi-decadal time scales are present but are confounded by external drivers including anthropogenic aerosols and greenhouse gas emissions. This review examines some of the mechanisms linking internal multi-decadal ocean modes with Asian monsoon decadal variability, including from the Pacific and Atlantic. Since much focus is still being given to seasonal monsoon prediction, we also examine perturbations caused by long time-scale oceanic modes to the monsoon-ENSO teleconnection, affecting seasonal monsoon predictability. Finally, we examine new prospects for decadal monsoon prediction in research considering the CMIP5 decadal hindcasts and forecasts, which are particularly encouraging for Atlantic multi-decadal variation modes. If future work can establish links between synoptic or intraseasonal monsoon variability and longer-term variations in the mean state, then there is potential for a cascade of predictability, improving our forecasts of the monsoon.

We provide a latest view of the current understanding of future changes in global as well as regional monsoon precipitation as projected by the state-of-the-art CMIP5 model simulations under RCP2.6 and RCP8.5 scenarios. The amount and intensity of the Asian summer monsoon rainfall is projected to increase under global warming, with the rate of increase being higher than that in other monsoon regions.

The relationship between air pollution and climate change in Monsoon Asia has long been studied, but most of these studies were conducted for a one-directional focus on the impact of air pollution on climate or the influence of Asian monsoon on air pollution. In this review, we give a summary on both directions with focus on their two-way interactions in Monsoon Asia. The main characteristics of air pollution and monsoon climate in Asia and the basic processes of air pollution-monsoon climate interaction are introduced. From the perspectives of observation analysis and numerical modeling, the main studies and findings on the impact of air pollution, mainly aerosols, on monsoon climate and the impact of monsoon climate change on air pollution at different temporal scales are reviewed. Typical cases are also illustrated to explain the main mechanisms of two-way interactions in regions with intensive and complex pollution, and their implications are also discussed. This review highlights the importance of long-term observations and two-way coupled numerical modeling on improving the current understanding of air pollution and climate change issues in the Monsoon Asia region.

The East Asian Summer Monsoon (EASM) has exhibited robust inter-decadal changes. In this paper, the authors present a review on our current understanding of the observed changes. The weakening phase of the EASM in the 2^nd half of the 20^th century is demonstrated to be primarily forced by the positive phase of IPO (Inter-decadal Pacific Oscillation) /PDO (Pacific Decadal Oscillation), and secondarily driven by the increased aerosol emission. The dominance of IPO/PDO to EASM is also evidenced by the recent recovery of EASM since the 1990s, associated with the transition of IPO/PDO from positive to negative phases. Both data diagnosis and numerical model experiments indicate that the decadal change of EASM is dominated by internal variability mode of IPO/PDO and also partly driven by anthropogenic external forcings. The IPO/PDO is traditionally regarded as internal climate variability mode at decadal time scale, but recent studies suggested that external forcings may also trigger the phase transition of IPO/PDO, this has posed a new issue calling for further study. In addition to long-term changes, the EASM also exhibits inter-decadal shift of interannual variability mode. The suggested mechanisms are reviewed, including changes in mean circulation, interannual variability and its ENSO relationship, and the climatological intraseasonal oscillation.

An international field campaign CINDY/DYNAMO took place in the Indian Ocean and its surrounding regions during October 2011–March 2012. The main goal of the field campaign was to collect observations that are needed for advancing our understanding and forecast of MJO initiation over the Indian Ocean. Three scientific hypotheses on interaction between convection and its environmental moisture, evolution in cloud population, and air-sea interaction were proposed to guide the design and operation of the field campaign. Unprecedented data were collected by numerous instruments of advanced technology from ground, airplanes, ships, moorings and other platform. These data cover detailed processes through all stages of convective initiation of three very different MJO events. Field observations were released for public use one year after the completion of the field campaign. Studies using these observations have increasingly emerged. These studies confirmed some existing knowledge, challenge some well-accepted paradigms, and reveal new phenomena that motivate novel thinking and approaches to solve the puzzle of MJO initiation.

Intraseasonal (30–90 day) variations of surface wind speed and solar radiation associated with the Madden-Julian Oscillation (MJO) induce intraseasonal variations of net surface heat flux of ±30 Wm⁻² in phase with atmospheric convective anomalies, and sea surface temperature (SST) variation of ±0.1°C in quadrature with wind speed and convective anomalies. The DYNAMO (2011) and TOGA COARE (1992) experiments observed local processes and MJO events with stronger than average intraseasonal amplitude. Calm periods between intraseasonal convection permit diurnal warm layers to raise the SST, increasing the minimum value of the sensible and latent heat flux. The number of atmospheric cold pools increases during the convective phase, increasing the sensible heat flux by lowering air temperature, and increasing sensible and latent heat flux by wind gusts.

The Asian Monsoon Years 2007–2012 (AMY) program, is a cross-cutting coordinated observation and modeling initiative that is part of the International Monsoon Study under the World Climate Research Programme (WCRP). From 2008 to 2010, the AMY program coordinated an Intensive Observing Period (IOP). More than twenty international and national projects joined in this IOP. In particular, multi-scale interactions in the extreme rainfall events that characterize the Asian monsoon region were explored. Here, we briefly review multi-scale interactions on intra-seasonal, synoptic, and diurnal time-scales on the Indonesian Maritime Continent, particularly the role of the Asian winter cold-surge and the Madden-Julian Oscillation (MJO) in heavy rainfall events on Jawa Island.