Rossby Wave Train Research Articles

Wave-Breaking Features of Blocking over Central Siberia and Its Impacts on the Precipitation Trend over Southeastern Lake Baikal

Precipitation over southeastern Lake Baikal features a significant decreasing trend in July and August over 1979-2018 and is closely related to blocking occurrence over central Siberia (45°–70°N, 75°–115°E). This study investigates the formation and maintenance of anticyclonic and cyclonic wave-breaking (AWB and CWB) blocking events and their climate impacts on precipitation in the southeastern Lake Baikal area. Both AWB and CWB blocking events are characterized by a cold trough deepening from the sub-Arctic region and a ridge amplifying toward its north over central Siberia, as well as an evident Rossby wave train over midlatitude Eurasia. For AWB blocking events, the ridge and trough pair tilts clockwise and the wave train exhibits a zonal distribution. In contrast, ridge and trough pair associated with CWB blocking events leans anticlockwise with larger-scale, meridional, and more anisotropic signatures. Moreover, the incoming Rossby wave energy associated with CWB blocking events is more evident than for AWB blocking events. Therefore, CWB blocking events are more persistent. AWB blocking events produce more extensive and persistent precipitation over the southeastern Lake Baikal area than CWB blocking events, in which moderate above-normal rainfall is seen in the decaying periods of blockings. A significant decreasing trend is found in terms of AWB blocking occurrence over central Siberia, which may contribute to the downward trend of precipitation over southeastern Lake Baikal.

Decadal Predictions of the Probability of Occurrence for Warm Summer Temperature Extremes

AbstractWe use a decadal prediction system with the Coupled Model Intercomparison Project Phase 6 version of the coupled Max Planck Institute Earth System Model to predict the probability of occurrence for extremely warm summers in the Northern Hemisphere. An assimilation run with Max Planck Institute Earth System Model shows a robust response of summer temperature extremes in northern Europe and northeast Asia to North Atlantic sea surface temperature via a circumglobal Rossby wavetrain. When the North Atlantic is warm, warm summer temperature extremes occur with a probability of 20% and 24% in northern Europe and northeast Asia, respectively. In a cold North Atlantic phase, these probabilities are 0% and 8%. A similar difference in probability of occurrence is found in the initialized climate predictions. Consequently, the likelihood of a warm summer temperature extreme occurring in the examined regions in the next 10 years can be inferred from predictions of North Atlantic temperature.

Wavelet isolation of meridionally moving geopotential height perturbations near the subtropics of eastern Africa and their relationship with the Madden–Julian Oscillation

AbstractPrior to the onset of convection over the western Indian Ocean for many Madden–Julian Oscillation (MJO) events, equatorward‐propagating upper tropospheric negative geopotential height anomalies are observed along the east coast of Africa. To identify these signals independently from the MJO, we calculate partial meridional‐temporal wavelet transforms averaged between 35 and 45°E and centred in the subtropics. During times when the amplitudes of MJO indices are strong and leading up to convective onset over the western Indian Ocean, increased wavelet power relative to the mean state is observed in the equatorward direction at intraseasonal time‐scales from both hemispheres. Regressions against groups of equatorward intraseasonal wavelet transform time series centred on negative anomalies in the subtropics show extratropical Rossby wave trains extending to the west across the Atlantic similar to signals previously observed leading up to the onset of Indian basin convection in composite MJO events. Compared to globally averaged mean‐state power spectra in the subtropics, increased equatorward propagation of upper tropospheric geopotential height anomalies occurs regionally near eastern Africa on intraseasonal time‐scales, which suggests that local mean‐state conditions, in addition to the MJO, may influence meridional wave propagation. Since these anomalies may in turn influence the onset of MJO convection over the western Indian Ocean and have higher local power, mean‐state conditions near the subtropics of eastern Africa may change the timing of the MJO.

WAVETRISK-1.0: an adaptive wavelet hydrostatic dynamical core

Abstract. This paper presents the new adaptive dynamical core wavetrisk. The fundamental features of the wavelet-based adaptivity were developed for the shallow water equation on the β plane and extended to the icosahedral grid on the sphere in previous work by the authors. The three-dimensional dynamical core solves the compressible hydrostatic multilayer rotating shallow water equations on a multiscale dynamically adapted grid. The equations are discretized using a Lagrangian vertical coordinate version of the dynamico model. The horizontal computational grid is adapted at each time step to ensure a user-specified relative error in either the tendencies or the solution. The Lagrangian vertical grid is remapped using an arbitrary Lagrangian–Eulerian (ALE) algorithm onto the initial hybrid σ-pressure-based coordinates as necessary. The resulting grid is adapted horizontally but uniform over all vertical layers. Thus, the three-dimensional grid is a set of columns of varying sizes. The code is parallelized by domain decomposition using mpi, and the variables are stored in a hybrid data structure of dyadic quad trees and patches. A low-storage explicit fourth-order Runge–Kutta scheme is used for time integration. Validation results are presented for three standard dynamical core test cases: mountain-induced Rossby wave train, baroclinic instability of a jet stream and the Held and Suarez simplified general circulation model. The results confirm good strong parallel scaling and demonstrate that wavetrisk can achieve grid compression ratios of several hundred times compared with an equivalent static grid model.

How Tropical Pacific Surface Cooling Contributed to Accelerated Sea Ice Melt from 2007 to 2012 as Ice Is Thinned by Anthropogenic Forcing

Abstract Over the past 40 years, the Arctic sea ice minimum in September has declined. The period between 2007 and 2012 showed accelerated melt contributed to the record minima of 2007 and 2012. Here, observational and model evidence shows that the changes in summer sea ice since the 2000s reflect a continuous anthropogenically forced melting masked by interdecadal variability of Arctic atmospheric circulation. This variation is partially driven by teleconnections originating from sea surface temperature (SST) changes in the east-central tropical Pacific via a Rossby wave train propagating into the Arctic [herein referred to as the Pacific–Arctic teleconnection (PARC)], which represents the leading internal mode connecting the pole to lower latitudes. This mode has contributed to accelerated warming and Arctic sea ice loss from 2007 to 2012, followed by slower declines in recent years, resulting in the appearance of a slowdown over the past 11 years. A pacemaker model simulation, in which we specify observed SST in the tropical eastern Pacific, demonstrates a physically plausible mechanism for the PARC mode. However, the model-based PARC mechanism is considerably weaker and only partially accounts for the observed acceleration of sea ice loss from 2007 to 2012. We also explore features of large-scale circulation patterns associated with extreme melting periods in a long (1800 yr) CESM preindustrial simulation. These results further support that remote SST forcing originating from the tropical Pacific can excite significant warm episodes in the Arctic. However, further research is needed to identify the reasons for model limitations in reproducing the observed PARC mode featuring a cold Pacific–warm Arctic connection.

Effects of western Pacific intraseasonal convection on surface air temperature anomalies over North America

AbstractUsing the daily outgoing longwave radiation and 850‐hPa zonal wind over (10°S–30°N, 105°–150°E) during the extended boreal summer (May to October), the lifecycle of the western Pacific intraseasonal oscillation (WPISO) is divided into eight phases based on the first two principle components of multivariate empirical orthogonal function decomposition. Because of the pronounced northward propagation feature, the meridional location of the convection anomaly centre in each WPISO phase is quite different, leading to distinct surface air temperature (SAT) anomaly responses over the Northern Hemisphere, in which North America shows the most significant SAT anomalies, and the SAT anomalies vary significantly with WPISO phase. Under different WPISO phases, convection can induce different mid‐to‐high latitude Rossby wave trains emanating from East Asia to North America, resulting in different SAT anomaly patterns over North America. Four numerical experiments are conducted and demonstrate that the convection at different meridional locations in each WPISO phase could shape the pattern of the Rossby wave train and in turn lead to different SAT anomalies over North America. The results in this study are expected to provide predictability sources for the sub‐seasonal‐to‐seasonal (S2S) prediction of North American SAT anomalies.

Tropical Cyclone as a Possible Remote Controller of Air Quality over South Korea through Poleward-Propagating Rossby Waves

AbstractAir quality depends as much on large-scale tropospheric circulation as on the amount of pollutant emissions. Many studies have found a relationship between air quality and midlatitude synoptic weather systems. A stable low-level troposphere and airflow from polluted areas are conditions that favor air pollution in a region. However, few studies have focused on the possible remote effect of tropical cyclone (TC) activity in the tropics on air quality in the midlatitude East Asian countries. Here, we found that TCs in the South China Sea (SCS) can increase the concentration of particulate matter with aerodynamic diameters less than 10 μm (PM10) over South Korea through poleward-propagating Rossby waves. According to our analyses, intense divergence due to a TC causes a barotropic Rossby wave train from the SCS to the North Pacific Ocean. Anomalous highs over the Korean Peninsula (part of the Rossby wave train) result in stable air conditions and cause polluted air inflow to increase the PM10 concentration up to 65 μg m−3. Our finding suggests that TC activity in the tropics should be considered for more accurate forecasts of air quality in South Korea.

Effect of Teleconnected Land–Atmosphere Coupling on Northeast China Persistent Drought in Spring–Summer of 2017

Northeast China (NEC) suffered a severe drought that persisted from March to July of 2017 with profound impacts on agriculture and society, raising an urgent need to understand the mechanism for persistent droughts over midlatitudes. Previous drought mechanism studies focused on either large-scale teleconnections or local land–atmosphere coupling, while less attention was paid to their synergistic effects on drought persistence. Here we show that the 2017 NEC drought was triggered by a strong positive phase of the Arctic Oscillation in March, and maintained by the anticyclone over the area south to Lake Baikal (ASLB) through a quasi-stationary Rossby wave in April–July, accompanied by sinking motion and north wind anomaly. By using a land–atmosphere coupling index based on the persistence of positive feedbacks between the boundary layer and land surface, we find that the coupling states over NEC and ASLB shifted from a wet coupling in March to a persistently strengthened dry coupling in April–July. Over ASLB, the dry coupling and sinking motion increased surface sensible heat, decreased cloud cover, and weakened longwave absorption, resulting in a diabatic heating anomaly in the lower atmosphere and a diabatic cooling anomaly in the upper atmosphere. This anomalous vertical heating profile led to a negative anomaly of potential vorticity at low levels, indicating that the land–atmosphere coupling had a phase-lock effect on the Rossby wave train originating from upstream areas, and therefore maintained the NEC drought over downstream regions. Our study suggests that an upstream quasi-stationary wave pattern strengthened by land–atmosphere coupling should be considered in diagnosing persistent droughts, especially over northern midlatitudes.

Large-scale dynamics of western disturbances caused extreme precipitation on 24–27 January 2017 over Jammu and Kashmir, India

Western Himalaya receives heavy precipitation due to western disturbances embedded in the eastward moving upper tropospheric Rossby wave train, especially in the winter months. The interaction of intricate topography and large-scale atmospheric dynamics plays an essential role in determining the amount of precipitation over this region. The cold air intrusion causes the middle troposphere to be baroclinically unstable and develop a sharp gradient of potential temperature which in turn is responsible for non-conservation of Ertel potential vorticity. Baroclinic instability provided energy of the disturbance (latent heating) by strengthening the influence of baroclinicity on the vertical component of relative vorticity causing intense convection. The increase in the baroclinic influence on the vertical component of relative vorticity in the moist middle and upper troposphere led to extreme precipitation over Jammu and Kashmir region during 24–27 January 2017 and can be considered as one of the prognostic parameters for predictions of such event. Extreme precipitation over western Himalayan regions in the winter months is generally attributed to the passage of western disturbance. In this paper, we investigated large-scale atmospheric influences which are responsible for the occurrence of such extreme precipitation. Our results indicated that the cold air intrusion from the northern latitudes into the core of western disturbances causes modulation of the density field, which in turn causes middle troposphere of this region to become baroclinically unstable. The influence of baroclinicity on the vertical component of relative vorticity and non-convergence of Ertel potential vorticity led to the development of intense convection and heavy precipitation over Jammu and Kashmir region of India.

Relationship between the sharp decrease in dust storm frequency over East Asia and the abrupt loss of Arctic sea ice in the early 1980s

AbstractBased on dust storm frequency (DSF) data from the China Meteorological Administration, Arctic sea-ice concentration (SIC) data from the Hadley Centre, and atmospheric reanalysis data from the National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR), temporal variations and regime shifts of East Asian DSF and Arctic SIC during 1961–2015 are revealed, and the possible relationship between them is explored. The results show that East Asian DSF in spring is closely associated with the preceding winter SIC from the northern Greenland Sea to the Barents Sea (20° W–60° E, 74.5° N–78.5° N). In the past half-century, both East Asian DSF and Arctic SIC have shown significant declining trends, with consistent regime shifts in the early 1980s. Further statistical analyses indicate that the abrupt decrease of East Asian DSF in spring may be attributed to the concurrent sharp loss of Arctic SIC in the preceding winter. It is the loss of Arctic SIC that causes the atmospheric circulation anomalies downstream by stimulating a Rossby wave train, resulting in decelerated wind speed, dampened vertical wind shear and restrained synoptic-scale disturbances over the dust source region, eventually leading to the decline in East Asian DSF over decadal timescales.

Robust Solar Signature in Late Winter Precipitation Over Southern China

AbstractThe 11‐year solar cycle (SC) has been widely recognized as a potential source of regional climate variability in the Northern Hemisphere winter. However, whether an SC signal exists in the southern China winter precipitation remains unclear. By analyzing land surface precipitation and sunspot number data from 1901 to 2010 in this study, evidence of a robust positive precipitation response that is synchronous with the SC in late winter (January–March) over southern China is provided, and the most statistically significant signals (p < 0.01) are detected over the middle Yangtze River basin. In early winter (October–December), there are only nonsignificant negative responses. The late winter SC‐precipitation relationship persists over time and appears to largely result from a solar‐associated Rossby wave train originating from the North Atlantic/European region. Our results indicate an enhanced predictability of late winter precipitation over southern China.

Different Sources of 10‐ to 30‐day Intraseasonal Variations of Autumn Snow over Western and Eastern Tibetan Plateau

AbstractUsing the latest daily Moderate Resolution Imaging Spectroradiometer satellite snow cover data, the present study reveals distinctly different sources of 10‐ to 30‐day intraseasonal snow cover variations over the western and eastern Tibetan Plateau (TP) during September–December. The intraseasonal snow variation over the western TP is related to a midlatitude wave train associated with the Arctic Oscillation and that over the eastern TP is related to a subtropical wave train triggered by the North Atlantic Oscillation. The Rossby wave train in both cases leads to anomalous water vapor convergence and ascending motion, which contributes to snow accumulation and positive snow cover anomalies. For the western TP snow events, the moisture comes from the Caspian Sea. During the eastern TP snow events, the moisture originates from the Bay of Bengal.

Influence of December snow cover over North America on January surface air temperature over the midlatitude Asia

AbstractThe impact of North American (NA) snow cover on the Northern Hemisphere climate has drawn increasing attention in recent years. This study reveals a negative relationship between NA snow cover in December and surface air temperature (SAT) over the midlatitude Asia in the following January. The results show that, in December, the extensive snow cover decreases SAT over NA via local diabatic cooling, which further intensifies the Atlantic jet stream by enlarging the meridional gradient of the 1,000‐ to 300‐hPa layer thickness, especially along 40°N. Meanwhile, we found negative sea surface temperature (SST) anomalies over the Western North Atlantic and enhanced transient eddy activity over the Eastern North Atlantic due to anomalous net energy conversion from the mean flow. In January, a zonally oriented dipole of transient eddy anomalies straddles the North Atlantic, with the negative–positive (west–east) anomaly centres attributing to local oceanic cooling and the persistence of the eddy–mean flow interaction, respectively. Such dipole of transient eddy activity in turn favours the downstream development of the Atlantic jet stream. Besides, the changes in surface turbulent heat flux over the North Atlantic trigger a Rossby wave train that propagates across Europe and towards the Far East. Coincident with the strengthened Siberian High and the accelerated East Asian jet stream in January, SAT decreases over the midlatitude Asia. Hence, our analysis indicates that December NA snow cover could potentially be exploited for subseasonal predictability over Asia.

Arctic\u2013Eurasian climate linkage induced by tropical ocean variability

Eurasian continent has experienced cold winters over the past two decades in contrast with Arctic warming. Previous studies have suggested that the cold Eurasian winters are associated with Arctic sea-ice loss, while others attributed them to atmospheric internal variability. However, here we show that the Arctic and Eurasian climate linkage is driven by the combination between atmospheric teleconnection originating in the tropical oceans and Arctic sea ice. Like a battery charges a capacitor, El Niño heats the tropical Atlantic, and the warmer Atlantic condition persists until early winter of El Niño-decay year. We find that the persisting tropical Atlantic warming induces anomalous Rossby wave train arching to Eurasia, leading to Arctic sea-ice increase and Eurasian warming. In La Niña phase these changes are reversed. Our results therefore suggest that the combination of recent tropical Pacific cooling and Arctic sea-ice loss have contributed to the frequent Eurasian cold winters.

Summertime midlatitude weather and climate extremes induced by moisture intrusions to the west of Greenland

AbstractThe summer of 2010 was characterized by weather and climate extremes such as the western Russia heatwave and the Pakistan floods. A recent study found that summer was dominated by a particular 200 hPa geopotential height pattern featuring an anomalous Rossby wave train with ridges centred over Greenland, Europe and Russia. The daily frequency of this pattern has dramatically increased recently and closely resembles the mean‐state difference in 200 hPa geopotential height fields between 1998–2014 (P2) and 1979–1997 (P1). Because anomalous wave trains are often driven by localized diabatic heating, it is tested in this study whether the P2 minus P1 pattern is caused by diabatic heating anomalies near Greenland. While it is found that sea ice concentrations declined and sea‐surface temperatures rose over Baffin Bay to the west of Greenland during P2, surface latent heat fluxes actually increased downward, indicating that surface processes were likely not the source of diabatic heating. Rather, an increase in vertically integrated horizontal latent‐heat flux convergence over Baffin Bay was observed in P2, which led to the condensation of water vapour and latent heating. Thus, the mid‐tropospheric circulation established the diabatic heating. A set of initial‐value calculations with idealized heating over Baffin Bay show solutions that remarkably resemble the P2 minus P1 pattern and provide a plausible explanation as to why the pattern has been occurring more frequently. This study demonstrates that changes in the Arctic can arise from moisture transport from the midlatitudes, and, in turn, these changes can induce weather and climate extremes in distant midlatitude regions.

Two Distinct Types of Extratropical Circulation Anomalies Associated with Cold Surges over the South China Sea

Abstract This study investigated the extratropical circulation anomalies responsible for cold surges over the South China Sea in winter. The surge events were identified by the intensity of northerly winds over 110°–117.5°E along 15°N at 925 hPa. Two distinct patterns of sea level pressure (SLP) anomalies in East Asia were found to have a crucial role in inducing cold surges over the South China Sea. Accordingly, the cold surge events were classified into two types. The first type of cold surge is characterized by a pair of SLP anomalies with positive and negative ones centered over China and Japan, respectively, whereas the second type of cold surge is characterized by widespread and persistent positive SLP anomalies over East Asia. Furthermore, the first type of cold surge is accompanied by a deepened East Asian trough and precursory Rossby wave trains across the Eurasian continent in the mid- and upper troposphere, but the latter is not. Prior to both types of the cold surges, the Siberian high is significantly intensified. However, diagnosis of the SLP tendency indicates that the intensification is related to different physical processes. In the first type of cold surge, the Rossby wave trains favor negative vorticity advection and cold advection, inducing intensification of the Siberian high. By contrast, in the second type of cold surge, vorticity advection can be ignored due to the lack of Rossby wave trains, and only the lower-tropospheric cold advection induced by anomalous northerly winds, resulting from the anomalous Siberian high, contributes to the further intensification of the Siberian high.

Possible impact of North Atlantic warming on the decadal change in the dominant modes of winter Eurasian snow water equivalent during 1979–2015

An east–west dipole mode of winter Eurasian snow water equivalent (SWE) is found during the period of 1979–2015. It accounts for about 23.4% of the total variance, and displayed a significant decadal change in the early-2000s. The basin warming footprint of the North Atlantic likely exerted an influence on this decadal change, and the observation-based evidence is reproduced by numerical experiments using the Community Atmosphere Model (CAM3.1). A basin-wide warming of North Atlantic sea surface temperature induced atmospheric anomalies by exciting a stationary Rossby wave train, which prorogates from the subtropical North Atlantic to the mid-to-high latitudes of the Eurasian continent. Along with the Rossby wave train, an enhanced upper-level ridge occurs over the Ural Mountain, and a deepened upper-level trough appears over the eastern Siberian Plateau, which promotes heavy snowfall over the eastern Siberian Plateau and light snowfall to its west. Thus, it is plausible that the North Atlantic warming plays a role in exciting the Rossby wave train to modulate the decadal change in the east–west dipole SWE mode of the extratropical Eurasian continent. The possible moisture transport paths associated with the decadal change in the east–west dipole SWE mode are also discussed.

Seasonal persistence of soil moisture anomalies related to freeze\u2013thaw over the Tibetan Plateau and prediction signal of summer precipitation in eastern China

Soil moisture can be an effective climate prediction signal due to its long memory. This study investigated seasonal persistence of soil moisture anomalies from the preceding autumn to spring dominated by the soil freeze–thaw (FT) process over the Tibetan Plateau (TP), and their relationship with summer precipitation in eastern China. Results demonstrated that soil moisture anomalies from the preceding autumn can persist until spring by water storage effect of the soil FT process. Soil moisture in the TP during the preceding autumn and winter had similar climatic effects as spring soil moisture. Positive soil moisture anomalies in the eastern TP during the spring led to less summer precipitation in south China and the Yellow River basin, and more summer precipitation in the Yangtze River basin and northeast China. A possible mechanism for this was that wetter soil moisture anomalies from the preceding autumn were stored in the soil by soil freezing, and were released with soil thawing in the spring, inducing surface diabatic heating anomalies over the TP. These anomalies then persisted into summer and enhanced the TP’s thermal forcing to the subtropical westerlies and affected stationary Rossby wave train propagation in middle latitudes, particularly on the northwest and northeast sides of the TP. This study suggests that most of spring soil moisture anomalies signal contains the preceding two seasons’ soil moisture anomalies information; therefore, summer precipitation predicting signals can be obtained from soil moisture anomalies from the preceding autumn, which could lengthen the seasonal climate prediction period.

The Atmospheric Response to Positive IPV, Positive AMV, and Their Combination in Boreal Winter

AbstractThe interdecadal Pacific oscillation (hereafter termed IPV, using “variability” in lieu of “oscillation”) and the Atlantic multidecadal oscillation (hereafter AMV, similar to IPV) are regulators of global mean temperature, large-scale atmospheric circulation, regional temperature and precipitation, and related extreme events. Despite a growing recognition of their importance, the combined influence of these modes of low-frequency sea surface temperature (SST) variability remains elusive given the short instrumental record and the difficulty of coupled climate models to simulate them satisfactorily. In this study, idealized simulations with two atmospheric global climate models (AGCMs) are used to show a partial cancellation of the North Pacific atmospheric response to positive IPV (i.e., deeper Aleutian low) by the concurrent positive phase of the AMV. This effect arises from a modulation of the interbasin Walker circulation that weakens deep convection in the western Pacific and the associated Rossby wave train into the northern extratropics. The weaker Aleutian low response is associated with less upward wave activity flux in the North Pacific; however, the associated stratospheric jet weakening is similar to when the +IPV alone forces the vortex, as additional upward wave activity flux over Siberia makes up the difference. While comparable warming of the polar stratosphere is found when the positive AMV is included with the positive IPV, the downward propagation of the stratospheric response is significantly reduced, which has implications for the associated surface temperature extremes. The robust anticorrelation between the positive IPV and positive AMV signals over the North Pacific and their lack of additivity highlight the need to consider the IPV–AMV interplay for anticipating decadal changes in mean climate and extreme events in the Northern Hemisphere.

Impact of air\u2013sea coupling on Northern Hemisphere summer climate and the monsoon\u2013desert teleconnection

Previous studies have established the existence of a large-scale teleconnection between ascent in the South Asian Summer Monsoon and subsidence over the Mediterranean (known as “the monsoon–desert mechanism”). Improving the representation of this mechanism could potentially improve the skill of seasonal forecasts for European summer weather patterns. In this study, the impact of air–sea coupling on the NH summer climate and the representation of the monsoon–desert mechanism is analysed in two 45-year experiments with the Met-Office Unified Model. In the first coupled experiment, the atmosphere is allowed to freely interact with a high-vertical-resolution mixed-layer ocean model. The diagnosed daily SSTs from this experiment are then used to force an atmosphere-only uncoupled experiment. The two experiments have a similar mean state, but the coupled experiment has a substantially more realistic representation of interannual precipitation variability over the Indian Summer Monsoon region. The coupled experiment can capture the observed westward propagating Rossby-wave trains excited by the Indian Summer Monsoon, while in the uncoupled experiment the Rossby-wave response is more local. It is shown that in the coupled experiment more moisture is transported inland and monsoon precipitation reaches further north, which favours westward Rossby wave propagation. Finally, evidence is shown that the coupled experiment can capture the observed interannual relationship between the Indian Summer Monsoon precipitation and precipitation over the Balkans/Black Sea region.