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In this paper the model outputs from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) are used to examine the climatology and interannual variability of the East Asian winter monsoon (EAWM). The multimodel ensemble (MME) is able to reproduce reasonably well the circulation features of the EAWM. The simulated surface air temperature still suffers from a cold bias over East Asia, but this bias is reduced compared with CMIP phase 3 models. The intermodel spread is relatively small for the large-scale circulations, but is large for the lower-tropospheric meridional wind and precipitation along the East Asian coast. The interannual variability of the EAWM-related circulations can be captured by most of the models. A general bias is that the simulated variability is slightly weaker than in the observations. Based on a selected dynamic EAWM index, the patterns of the EAWM-related anomalies are well reproduced in MME although the simulated anomalies are slightly weaker than the observations. One general bias is that the northeasterly anomalies over East Asia cannot be captured to the south of 30°N. This bias may arise both from the inadequacies of the EAWM index and from the ability of models to capture the EAWM-related tropical-extratropical interactions. The ENSO-EAWM relationship is then evaluated and about half of the models can successfully capture the observed ENSO-EAWM relationship, including the significant negative correlation between Niño-3.4 and EAWM indices and the anomalous anticyclone (or cyclone) over the northwestern Pacific. The success of these models is attributed to the reasonable simulation of both ENSO's spatial structure and its strength of interannual variability. [ABSTRACT FROM AUTHOR]

During glacial periods, the East Asian monsoon is typically thought to have been stronger in boreal winters and weaker in boreal summers. It is unclear, however, whether this view is true at larger scales and to what extent the East Asian monsoon responds to glacial conditions as a whole. Using all experiments conducted as part of the Paleoclimate Modeling Intercomparison Project (PMIP), this paper examines East Asian monsoon climatology during the Last Glacial Maximum (LGM), around 21 000 calendar years ago. In contrast to conclusions drawn from sparse proxy data, the intensity of the East Asian winter (December-February) monsoon (EAWM) during the LGM, as measured by regionally averaged meridional wind speed at 850 hPa, was found to vary both in sign and magnitude, with reference to baseline climate, across the PMIP simulations. It strengthened in 10 out of the 21 models but weakened in the remaining 11 models, with an average weakening of 4% for the 21-model ensemble mean (15% for the ensemble mean of the 14 models with computed sea surface temperatures). At the subregional scale, the LGM EAWM strengthened north of about 30°N but weakened south of this region in East Asia, which can be explained by changes in surface temperature. On the other hand, all of the 14 models chosen in this study consistently simulated a weaker than baseline East Asian summer (June-August) monsoon during the LGM, with an average weakening of 25%. [ABSTRACT FROM AUTHOR]

This study investigates the impact of boreal winter–peaked La Niña on the following-summer precipitation in East Asia through intermediate sea surface temperature (SST) anomalies playing the role of relay in observation and numerical models. There are widespread dry conditions in both North and South China and wet conditions in coastal areas of central and eastern China. Such a pattern is mainly attributed to an anomalous low pressure over the western tropical Pacific and an anomalous anticyclone over northeast Asia. It is found that the delayed impact of La Niña on the East Asian climate is operated through intermediate SST anomalies—the Z-shape cold SST anomalies in the tropical North Pacific. There might be three ways for the SST anomalies to operate. First, they produce tropical atmospheric perturbations that can penetrate into the subtropical jet through the westerly trough over the northeast subtropical Pacific, the wave train being then excited along the jet. Second, perturbations created through the monsoon trough over the western Pacific can directly stimulate northward-propagating Rossby waves along the East Asian coast, mainly at low level. And third, perturbations over the tropical Atlantic–northwest Africa can also trigger downstream propagating waves along the subtropical jet. The observation effects of the intermediate SST anomalies and their possible impact mechanisms on atmospheric circulation are largely reproduced within numerical simulations performed with the Community Earth System Model. [ABSTRACT FROM AUTHOR]

This study first investigates the interannual variations in spring precipitation intraseasonal variability over southern China (SC). The results show that SC spring precipitation exhibits distinct intraseasonal variations with a period of 7–25 days. The first mode of 7–25-day precipitation intraseasonal variability (PIV) displays a monopole pattern over SC, and the PIV magnitude is largely determined by the upward motion intensity during intraseasonal precipitation events. Further analysis suggests that two atmospheric wave trains are observed during intraseasonal precipitation events, which propagate eastward from the North Atlantic along the northern and southern paths. In strong PIV years, the two wave trains can propagate to East Asia and show coordinated influences. The resultant low pressure to the west of SC causes strong upward motion and PIV over SC by bringing strong zonal vorticity and meridional temperature advection. In weak PIV years, the southern wave train can only propagate to the Bay of Bengal; therefore, the northern wave train plays a major role. The resultant low pressure is now over the upper to middle reaches of the Yangtze River, which causes relatively weak upward motion and PIV over SC by bringing weak meridional vorticity and temperature advection. Further analysis indicates that the sea surface temperature (SST) condition over the tropical Indian Ocean and the South China Sea is essential for southern wave train propagation. The warming SST over the regions can intensify westerlies to its north and consequently favors the propagation of the southern wave train to SC, eventually contributing to strong PIV over SC. [ABSTRACT FROM AUTHOR]

The relationship between the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM) across time scales has been an interesting topic for decades. In this study, we quantitatively investigate the EASM–EAWM relationship at the obliquity time scales using a set of accelerated transient simulations. By comparing different indices defined with different variables, we find that the EASM and EAWM intensities are positively correlated under obliquity forcing. High obliquity leads to warmer summertime and cooler wintertime surface temperatures, with a stronger response observed over land than over the oceans. The warmer summertime and cooler wintertime temperature responses are accompanied by a strengthened Asian low in summer and Siberian high in winter, with enhanced southerlies in summer and northerlies in winter, indicating an enhanced EASM and EAWM. Modulated by ice sheet forcing, however, the evolution of the simulated EAWM shifts toward the ice sheet maximum, such that the circulation-based EASM–EAWM relationship in the realistically forced simulation exhibits a phase shift of approximately 11 kyr, closer to the phase between the composite δ18O and loess grain size in observations. Our results may have implications for better understanding the distinct changes in the proxy-based EASM–EAWM relationship before and after the rapid growth of global ice volume at around 3 Ma. Significance Statement: Studying the relationship between the EASM and EAWM can help us understand the characteristics and mechanisms of the regional climate in response to external forcings at different time scales. By investigating the EASM–EAWM relationship over the past 300 000 years, we find that, forced by obliquity variations, the EASM and EAWM are positively correlated at the obliquity time scales. The ice sheet forcing, meanwhile, also influences the circulation over East Asia and modulates the evolutionary phases between the EASM and EAWM. Our results highlight the importance of the combined impacts of orbital parameters and ice sheets on past climate changes over Asia. [ABSTRACT FROM AUTHOR]

Both South Asia and East Asia are the most polluted regions of the world. Unlike East Asia, the aerosol optical depth (AOD) over South Asia keeps increasing for all recent years, which calls for more attention. This study investigates the impacts of anthropogenic emissions over South Asia on the downstream regional climate during spring with the Community Earth System Model 2 (CESM2). The model results suggest that South Asian pollutants have significant impacts on East Asian spring climate, and the impacts could be even larger than locally emitted aerosols. Two possible dynamical pathways (i.e., the northern and the southern pathways) bridging South Asian aerosol forcing and East Asian climate are proposed, and both ways are associated with the black carbon (BC)-induced climate feedbacks surrounding the Tibetan Plateau (TP). The northern pathway is mainly due to the TP warming induced by the BC snow darkening effect (SDE), which significantly reduces the surface air temperature (SAT) over northern East Asia. BC-induced TP warming increases the meridional thermal gradient and accelerates the midlatitude jet stream, which favors the cold-air advection over northern East Asia. The southern pathway is associated with the BC "elevated heat pump" hypothesis, which mainly affects the precipitation in southern East Asia. BC from South Asia accumulates near the south slope of TP, inducing an abnormal ascending motion near the Bay of Bengal. A compensating anomalous sinking motion is then forced in South China, which suppresses the precipitation there. A primary observational analysis is also performed to verify both dynamical pathways. [ABSTRACT FROM AUTHOR]

Coupled climate models project robust wintertime wetting trend over midlatitude East Asia under global warming scenarios, but the projected change in precipitation shows large intermodel uncertainty over subtropical East Asia from southern China to southwestern Japan. Based on an ensemble of climate models participating in CMIP6, this study shows that the weakened southern branch westerly jet (SWJ) on the southern side of Tibetan Plateau (TP) plays a key role in suppressing subtropical East Asian precipitation. The SWJ is deflected into southwesterly wind on the southeastern side of TP, bringing ascent and precipitation to subtropical East Asia primarily through isentropic gliding. As a result of the poleward and upward shift of the planetary-scale westerly jet under global warming, the SWJ becomes weaker and it acts to suppress subtropical East Asian precipitation by weakening the southwesterly wind and ascent. The SWJ-precipitation linkage also exists on interannual time scales, but the sensitivity of precipitation to interannual SWJ variability is systematically underestimated by the models compared with observation. The combined effects of the change in SWJ strength and the sensitivity of precipitation to SWJ explain about 40% of the intermodel spread of the projected precipitation changes. Observational constraint on the SWJ--precipitation relationship amplifies the projected drying trend and narrows the intermodel spread. It shows that the regional-averaged precipitation over subtropical East Asia decreases by 3.3% per degree of warming, and the amplitude of precipitation reduction over subtropical East Asia (southern China) is about 1.4 (3.4) times the raw projection. [ABSTRACT FROM AUTHOR]

During the winter and subsequent spring of an El Niño year, the East Asian marginal sea (EAMS) exhibits positive sea surface temperature anomalies (SSTAs) and fewer low clouds, while the western North Pacific experiences negative SSTAs. In this study, we suggest that the positive SSTAs in EAMS are maintained by a positive low cloud–SST feedback. In neutral winters and springs, the EAMS is covered by low clouds, which have a cooling effect on surface temperatures. During an El Niño year, a western North Pacific anomalous anticyclone is established, and along its northwestern flank, there are favorable conditions for convergence of moisture and weaker surface latent heat flux over the EAMS. Once a positive SSTA has been established, a further reduction of turbulent mixing results in less low cloud and enhanced solar heating of the ocean mixed layer; this reinforces and maintains both the positive SSTA and the lack of low cloud via a positive feedback mechanism. The concurrent increase of low cloud–SST feedback and anticyclone circulation strengths is evident in the coupled-model simulations from phase 6 of the Coupled Model Intercomparison Project. Furthermore, sensitivity experiments, performed with the atmospheric components of Community Earth System Model (CESM2), reveal that a positive SSTA helps to maintain the western North Pacific anomalous anticyclone. Four pacemaker-coupled experiments by CESM2, with sea surface temperature in the equatorial Pacific restored to the observational anomalies plus the model climatology and altered low cloud feedback over EAMS, suggest that the low cloud–SST feedback results in more than the maintenance of a positive SSTA over the EAMS: the positive feedback is also a previously overlooked mechanism for the maintenance of the western North Pacific anomalous anticyclone. Significance Statement: The East Asian marginal sea (EAMS) and western North Pacific are important areas that bridge El Niño and the climate of East Asia. Unlike the cold sea surface temperature anomaly (SSTA) over the western North Pacific during El Niño, the positive SSTA over EAMS, which is covered by winter low cloud, has received less attention. We suggest that a "low cloud–SST" feedback—namely, one in which decreasing low-level clouds allows more sunlight to strike the ocean surface and favors higher SST—maintains the positive SSTA over EAMS. We also configure a widely used atmospheric model with a set of preset SSTA patterns that mimic different climate patterns. Our experiments with different climate patterns and CMIP6 historical runs show that the low cloud–SST feedback (through the positive SSTA) is a possible supplementary mechanism for reinforcing the WNP anomalous anticyclone. [ABSTRACT FROM AUTHOR]

The synoptic low pressure systems (LPSs) formed over the downwind side of the Tibetan Plateau explain a substantial portion of summer rainfall extremes along their paths. Recent studies have found that the total extreme rainfall trend over the East Asian landmass, which features the “south flood–north drought” pattern, can be understood to a great extent by the changes in terrestrial LPSs. Yet, the energy sources fueling these storms and the environmental drivers of their long-term trends remain unclear. Utilizing a probabilistic clustering method, three clusters of terrestrial LPS tracks for the period 1979–2018 are identified. Besides the differences in trajectories that distinguish the clusters into northeastward-migrating and quasi-stationary types, prominent intercluster differences are found in the LPS evolution, energetics, and trends. The Lorenz energetics suggest that while condensational heating is indispensable for all three clusters, the migratory type, which has greater intensity and faster development, is more closely tied to baroclinicity. Nonetheless, the summer baroclinicity alone is not enough to sustain these LPSs as these storms dissipate quickly after propagating out of the humid monsoon region and into the drier extratropics. Over time, occurrences of migratory LPSs decrease, and those of quasi-stationary LPSs increase. Using a Poisson model that links the LPS genesis to local environmental conditions, the decreasing occurrence of migratory LPSs is shown to result from the weakened baroclinicity, whereas the increasing occurrence of quasi-stationary LPSs is primarily driven by enhanced relative humidity and reduced steering flow in the mid-to-lower troposphere over East Asia. [ABSTRACT FROM AUTHOR]

Studies of the climate effects of black carbon (BC) in East Asia are not abundant and the effects remain uncertain. Using the Community Earth System Model version 1 (CESM1) with Peking University's emissions data, the fast response of the atmospheric water cycle to anthropogenic BC during summer in East Asia is investigated in this study. Results show that the CESM1-simulated BC concentration and its direct effective radiative forcing are comparable to observations. With the combination of aerosol–radiation interaction (ARI) and non-aerosol–radiation interaction (including aerosol–cloud interaction and surface albedo effects), anthropogenic BC induces a "wetter south and drier north" pattern over East Asia during summer. Also, anthropogenic BC affects the summer precipitation primarily through changing moisture transport rather than altering local evaporation over East Asia. Using the self-developed atmospheric water tracer method, the responses of dominant moisture sources [the tropical Indian Ocean (TIO) and northwest Pacific] to anthropogenic BC are investigated. Results show that the moisture originating from southwest monsoon-related sources (especially the TIO) is more responsive to anthropogenic BC effects over East Asia. In particular, differing from total precipitation, TIO-supplied precipitation shows a significant response to the ARI of anthropogenic BC over East Asia. Process analyses show that anthropogenic BC affects the southwest monsoon-related moisture supplies primarily via advection, deep convection, and cloud macrophysics. Interestingly, the anthropogenic BC-induced changes of TIO-supplied water vapor in these three processes are all dominated by the ARI over East Asia. [ABSTRACT FROM AUTHOR]

Because spring precipitation in East Asia is critical for recharging water resources after dry winters, its spatiotemporal variations and related mechanisms need in-depth research. This study analyzed a leading spatiotemporal variability of precipitation over East Asia for boreal spring (March-May) during 1979 to 2017. We found that a dipole mode dominates the anomalous spring precipitation between southern China and Southeast Asia with significant interannual and decadal variations. The interannual dipole mode is attributable to the eastern Pacific (EP)-type El Niño-Southern Oscillation (ENSO) while the decadal dipole mode is related to the decadal variation of the central Pacific (CP)-type ENSO. In the El Niño phases of both time scales, the anticyclonic anomaly over the South China Sea and Philippines causes moisture convergence (divergence) over southern China (Southeast Asia), resulting in positive (negative) precipitation anomalies therein; the opposite occurs in the La Niña phases. The ensemble experiments using the Community Atmosphere Model version 5.1 confirmed that the tropical sea surface temperature (SST) in the EP- and CP-type ENSO can be the major drivers of the interannual and decadal dipole modes, respectively. About half of 15 climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) showed that the El Niño phase of dipole mode will become dominant in the future. The individual models' future projections however considerably vary, implying that there is still large uncertainty. [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) play an important role in modulating the global water cycle and energy balance and frequently generate high-impact weather events. The majority of existing literature studying MCS activity over East Asia is based on specific case studies and more climatological investigations revealing the precipitation characteristics of MCSs over eastern China are keenly needed. In this study, we use an iterative rain cell tracking method to identify and track MCS precipitation during 2008-16 to investigate regional differences and seasonal variations of MCS precipitation characteristics. Our results show that the middle-to-lower reaches of the Yangtze River basin (YRB-ML) receive the largest amount and exhibit the most pronounced seasonal cycle of MCS precipitation in eastern China. MCS precipitation over YRB-ML can exceed 2.6mmday-1 in June, contributing over 30.0% of April-July total rainfall. Particularly long-lived MCSs occur over the eastern periphery of the Tibetan Plateau (ETP), with 25% of MCSs over the ETP persisting for more than 18 h in spring. In addition, spring MCSs feature larger rainfall areas, longer durations, and faster propagation speeds. Summer MCSs have a higher precipitation intensity and a more pronounced diurnal cycle except for southeastern China, where MCSs have similar precipitation intensity in spring and summer. There is less MCS precipitation in autumn, but an MCSprecipitation center over the ETP still persists. MCSs reach peak hourly rainfall intensities during the time of maximum growth (a few hours after genesis), reach their maximum size around 5 h after genesis, and start decaying thereafter. [ABSTRACT FROM AUTHOR]

This study examines the mechanisms by which the East Asian summer monsoon (EASM) changes in response to non–East Asian (NEA) anthropogenic aerosol forcing by distinguishing the fast direct atmospheric response and slow ocean-mediated response to forcing using a global aerosol–climate coupled model. The results show that NEA aerosol forcing significantly exacerbates the weakening of the EASM due to local aerosol forcing. The fast response is dominant in the weakening of the EASM and an anomalous precipitation pattern over eastern China resembling the "southern flood and northern drought" pattern in the total response to NEA aerosol forcing. Changes in upper-tropospheric temperature caused by the fast response play a major role in the impact of NEA aerosol forcing on the EASM. Anomalous cooling occurs during summer in the upper troposphere (at ~40°N) over East Asia caused by the fast response. This is due to the combined effects of strong eastward cold advection in the Northern Hemisphere midlatitudes caused by increased aerosol loading in Europe and the resulting change in local meridional heat transport in East Asia. Subsequently, the zonal wind speed changes on either side of the anomalous cooling, and the East Asian subtropical jet shifts equatorward, thereby weakening the EASM. The changes in atmospheric temperature and the local Hadley cell caused by the slow response to NEA aerosol forcing are conducive to strengthening the southwesterly winds over eastern China. Our study suggests the importance of NEA aerosol forcing in driving changes in the EASM on a fast time scale. [ABSTRACT FROM AUTHOR]

Given their high carbon uptake, the terrestrial ecosystems in the East Asia summer monsoon (EASM) region play an irreplaceable role in the global carbon cycle. Because the rich vegetation growth over East Asia benefits mainly from the sufficient water supply brought by the EASM, which is characterized by a strong intraseasonal oscillation (ISO), the intraseasonal spatiotemporal variations and underlying drivers of photosynthesis activity over East Asia have been comprehensively investigated using the daily gross primary productivity (GPP) and meteorological data. Strong intraseasonal fluctuations of GPP have been identified over the area between the Yangtze and Yellow Rivers (YYR) with a magnitude of 0.4 gC m−2 day−1. The mean power spectrum suggests that 20–50-day variation is the major component of the intraseasonal GPP anomalies over the YYR during the summers of 1980–2013. The 20–50-day ISO of YYR GPP anomalies is modulated by the local 20–50-day precipitation variation via soil moisture, with precipitation (soil moisture) leading GPP by 10 (7) days. The 20–50-day YYR precipitation anomalies are in turn controlled by tropical ISO signals, particularly the convective activity over the western North Pacific. This leading relationship between the 20–50-day atmospheric ISO and GPP suggests a potential for extended-range predictability of vegetation growth. [ABSTRACT FROM AUTHOR]

The heat wave in East Asia is examined by using empirical orthogonal function analysis to isolate dominant heat-wave patterns in the ground-based temperature observations over the Korean Peninsula and China and related large-scale atmospheric circulations obtained from the National Centers for Environmental Prediction–National Center for Atmospheric Research Reanalysis 1 during 1973–2012. This study focuses particularly on the interannual variability of heat waves and its decadal change. The analysis identifies two major atmospheric teleconnection patterns playing an important role in developing typical heat-wave patterns in East Asia—the Scandinavian (SCAND) and the circumglobal teleconnection (CGT) patterns, which exhibit a significant decadal change in the interannual variability in the mid-1990s. Before the mid-1990s, heat-wave occurrence was closely related to the CGT pattern, whereas the SCAND pattern is more crucial to explain heat-wave variability in the recent period. The stationary wave model experiments suggest an intensification of the SCAND pattern in the recent period driven by an increase in land–atmosphere interaction over Eurasia and decadal change in the dominant heat-wave patterns in East Asia. [ABSTRACT FROM AUTHOR]

Through extensive modeling efforts, it has been established that the ongoing global warming will increase the overall precipitation associated with the East Asian summer monsoon, but the future change of its spatial distribution has not reached a consensus. In this study, meridional shifts of the mei-yu–baiu rainband are studied in association with the subtropical jet by using outputs from atmosphere–ocean coupled climate models provided by CMIP5. The models reproduce observed associations between the jet and precipitation over wide time scales from synoptic to interannual. The same relation is found in intermodel differences in simulated climatology, so that the meridional locations of the jet and baiu precipitation are positively correlated. The multimodel-mean projection suggests that the both are shifted southward by the late twenty-first century. This shift is not inconsistent with the projected tropical expansion, not only because the change is local but also because the projected tropical expansion occurs mainly in the Southern Hemisphere. No significant future change in the continental mei-yu precipitation location is identified, which might be because the jet change is weak there. For comparison, the summertime Atlantic jet position, which shifts northward, is investigated briefly. This study suggests that the future change of the subtropical jet is an important aspect to investigate possible future changes of the baiu rainband, and it prompts further studies including the role of the ocean. [ABSTRACT FROM AUTHOR]

A quasi-stationary front, called the baiu front, often appears during the early-summer rainy season in East Asia (baiu in Japan). The present study examines how precipitation characteristics during the baiu season are determined by the large-scale environment, using satellite observation three-dimensional precipitation data. Emphasis is placed on the effect of subtropical jet (STJ) and lower-tropospheric convective instability (LCI). A rainband appears together with a deep moisture convergence to the south of the STJ. Two types of mesoscale rainfall events (REs; contiguous rainfall areas), which are grouped by the stratiform precipitation ratio (SPR; stratiform precipitation over total precipitation), are identified: moderately stratiform REs (SPR of 0%-80%) representing tropical organized precipitation systems and highly stratiform REs (SPR of 80%-100%) representing midlatitude precipitation systems associated with extratropical cyclones. As the STJ becomes strong, rainfall from both types of mesoscale precipitation systems increases, with a distinct eastward extension of a midtropospheric moist region. In contrast, small systems appear regardless of the STJ, with high dependency on the LCI. The results indicate that the STJ plays a role in moistening the midtroposphere owing to ascent associated with secondary circulation to the south of the STJ, producing environments favorable for organized precipitation systems in the southern part of the rainband. The horizontal moisture flux convergence may also contribute to precipitation just along the STJ. On the other hand, the LCI plays a role in generating shallow convection. In high-LCI conditions, deep convection can occur without the aid of mesoscale organization. [ABSTRACT FROM AUTHOR]

Previous studies have shown that the Indo-Pacific atmospheric response to ENSO comprises two dominant modes of variability: a meridionally quasi-symmetric response (independent of the annual cycle) and an antisymmetric response (arising from the nonlinear atmospheric interaction between ENSO variability and the annual cycle), referred to as the combination mode (C-mode). This study demonstrates that the direct El Niño signal over the tropics is confined to the equatorial region and has no significant impact on the atmospheric response over East Asia. The El Niño-associated equatorial anomalies can be expanded toward off-equatorial regions by the C-mode through ENSO's interaction with the annual cycle. The C-mode is the prime driver for the development of an anomalous low-level anticyclone over the western North Pacific (WNP) during the El Niño decay phase, which usually transports more moisture to East Asia and thereby causes more precipitation over southern China. An atmospheric general circulation model is used that reproduces well the WNP anticyclonic anomalies when both El Niño sea surface temperature (SST) anomalies as well as the SST annual cycle are prescribed as boundary conditions. However, no significant WNP anticyclonic circulation anomaly appears during the El Niño decay phase when excluding the SST annual cycle. The analyses herein of observational data and model experiments suggest that the annual cycle plays a key role in the East Asian climate anomalies associated with El Niño through their nonlinear atmospheric interaction. Hence, a realistic simulation of the annual cycle is crucial in order to correctly capture the ENSO-associated climate anomalies over East Asia. [ABSTRACT FROM AUTHOR]

Numerical experiments are conducted to investigate the differences between summer precipitation over continental East Asia simulated by the Community Atmosphere Model, version 5 (CAM5), and superparameterized CAM5 (SPCAM5, a multiscale modeling framework). The results show that SPCAM5 effectively alleviates several original biases. Overestimates of precipitation on the eastern periphery of the Tibetan Plateau are reduced from CAM5 to SPCAM5 as a result of decreases in both the average hourly precipitation frequency and mean hourly intensity. Underestimates along the coastal regions in southern China are improved following a corresponding increase in mean hourly intensity and a decrease in average hourly precipitation frequency. The frequency-intesnsity relationship is also more realistic in SPCAM5. For western China, overestimated frequency values (in CAM5) of both weak-to-moderate (0-20 mm day−1) and heavy (20-50 mm day−1) intensity ranges are reduced in SPCAM5. For southern China, overestimates of frequency values (in CAM5) in the weak-to-moderate range are also reduced, whereas underestimates in the intense ranges are enhanced. In terms of diurnal variability, SPCAM5 generally exhibits a delay in the afternoon peak time and greater diurnal amplitude. The possible physical reasons for the variations in the precipitation between the models are further investigated. It is found that the change in deep convection intensity is a primary factor governing the shift in the precipitation simulations. SPCAM5 better simulates an intermediate transition stage from shallow to deep convection, which helps the deep convection to grow more fully to a greater magnitude, thus delaying the peak time and increasing the precipitation maxima. [ABSTRACT FROM AUTHOR]

This study assesses the ability of the 25 GCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to simulate Ural blocking (UB) and its linkage with the East Asian winter climate [December-February (DJF)] in a historical run (1950/51-2004/05). A Ural blocking index (UBI) is defined as the DJF-mean blocking frequency over 45°-90°E for each winter. Regression analyses suggest that the long-term mean bias of UBI is caused by the long-term mean circulation bias over the North Atlantic. On seasonal time scales, the GCMs simulating a positive bias of UBI are associated with a stronger Atlantic jet stream, as well as stronger westerly momentum fluxes from the North Atlantic to Europe. On synoptic time scales, however, these GCMs tend to be associated with a weaker Siberian high and East Asian trough during the evolution of a UB event. Altogether, there is no apparent linkage between the long-term mean bias of UB and the East Asian winter climate. Further studies are needed to explore the teleconnection between UB and the East Asian winter climate in the GCMs. [ABSTRACT FROM AUTHOR]

The simulations of summertime diurnal cycle of precipitation and low-level winds by the Community Atmosphere Model, version 5, are evaluated over subtropical East Asia. The evaluation reveals the physical cause of the observed diurnal rainfall variation in East Asia and points to the source of model strengths and weaknesses. Two model versions with horizontal resolutions of 2.8° and 0.5° are used. The models can reproduce the diurnal phase of large-scale winds over East Asia, with an enhanced low-level southwesterly in early morning. Correspondingly, models successfully simulated the diurnal variation of stratiform rainfall with a maximum in early morning. However, the simulated convective rainfall occurs at local noontime, earlier than observations and with larger amplitude (normalized by the daily mean). As a result, models simulated a weaker diurnal cycle in total rainfall over the western plain of China due to an out-of-phase cancellation between convective and stratiform rainfalls and a noontime maximum of total rainfall over the eastern plain of China. Over the East China Sea, models simulated the early-morning maximum of convective precipitation and, together with the correct phase of the stratiform rainfall, they captured the diurnal cycle of total precipitation. The superposition of the stratiform and convective rainfalls also explains the observed diurnal cycle in total rainfall in East Asia. Relative to the coarse-resolution model, the high-resolution model simulated slight improvement in diurnal rainfall amplitudes, due to the larger amplitude of stratiform rainfall. The two models, however, suffer from the same major biases in rainfall diurnal cycles due to the convection parameterization. [ABSTRACT FROM AUTHOR]

Predictability of summer climate anomalies over East Asia and the northwestern Pacific is investigated using observations and a multimodel hindcast ensemble initialized on 1 May for the recent 20-30 yr. Summertime East Asia is under the influence of the northwestern Pacific subtropical high (PASH). The Pacific-Japan (PJ) teleconnection pattern, a meridional dipole of sea level pressure variability, affects the northwestern PASH. The forecast models generally capture the association of the PJ pattern with the El Niño-Southern Oscillation (ENSO). The Silk Road pattern, a wave train along the summer Asian jet, is another dominant teleconnection that influences the northwestern PASH and East Asia. In contrast to the PJ pattern, observational analysis reveals a lack of correlations between the Silk Road pattern and ENSO. Coupled models cannot predict the temporal phase of the Silk Road pattern, despite their ability to reproduce its spatial structure as the leading mode of atmospheric internal variability. Thus, the pattern is rather unpredictable at monthly to seasonal lead, limiting the seasonal predictability for summer in East Asia. The anomalous summer of 2010 in East Asia is a case in point, illustrating the interference by the Silk Road pattern. Canonical anomalies associated with a decayed El Niño and developing La Niña would have the PJ pattern bring a cold summer to East Asia in 2010. In reality, the Silk Road pattern overwhelmed this tendency, bringing a record-breaking hot summer instead. A dynamical model experiment indicates that European blocking was instrumental in triggering the Silk Road pattern in the 2010 summer. [ABSTRACT FROM AUTHOR]

Using hourly rain gauge records and Tropical Rainfall Measuring Mission 3B42 from 1998 to 2006, the authors present an analysis of the diurnal characteristics of summer rainfall over subtropical East Asia. The study shows that there are four different regimes of distinct diurnal variation of rainfall in both the rain gauge and the satellite data. They are located over the Tibetan Plateau with late-afternoon and midnight peaks, in the western China plain with midnight to early-morning peaks, in the eastern China plain with double peaks in late afternoon and early morning, and over the East China Sea with an early-morning peak. No propagation of diurnal phases is found from the land to the ocean across the coastlines. The different diurnal regimes are highly correlated with the inhomogeneous underlying surface, such as the plateau, plain, and ocean, with physical mechanisms consistent with the large-scale 'mountain-valley' and 'land-sea' breezes and convective instability. These diurnal characteristics over subtropical East Asia can be used as diagnostic metrics to evaluate the physical parameterization and hydrological cycle of climate models over East Asia. [ABSTRACT FROM AUTHOR]

The summertime mei-yu-baiu rainband over East Asia displays considerable interannual variability. A singular value decomposition (SVD) analysis for interannual variability reveals that precipitation anomalies over the mei-yu-baiu region are accompanied by in situ anomalies of midtropospheric horizontal temperature advection. Anomalous warm (cool) advection causes increased (decreased) mei-yu-baiu precipitation locally by inducing adiabatic ascent (descent). The anomalous precipitation acts to reinforce the vertical motion, forming a feedback system. By this mechanism, the remotely forced anomalous atmospheric circulation can induce changes in mei-yu-baiu precipitation. The quasi-stationary precipitation anomalies induced by this mechanism are partially offset by transient eddies. The SVD analysis also reveals the association of mei-yu-baiu precipitation anomalies with several teleconnection patterns, suggesting remote induction mechanisms. The Pacific-Japan (PJ) teleconnection pattern, which is associated with anomalous convection over the tropical western North Pacific, contributes to mei-yu-baiu precipitation variability throughout the boreal summer. The PJ pattern mediates influences of the El Niño-Southern Oscillation in preceding boreal winter on mei-yu-baiu precipitation. In early summer, the leading covariability pattern between precipitation and temperature advection also features the Silk Road pattern-a wave train along the summertime Asian jet-and another wave train pattern to the north along the polar-front jet that often leads to the development of the surface Okhotsk high. [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted on the impact of soil moisture on the climate, but few studies have attempted to diagnose the linkage between soil moisture and climate variability using observational data. Here, using both observed and reanalysis data, the spring (April--May) soil moisture is found to have a significant impact on the summer (June--August) monsoon circulation over East Asia and precipitation in east China by changing surface thermal conditions. In particular, the spring soil moisture over a vast region from the lower and middle reaches of the Yangtze River valley to north China (the YRNC region) is significantly correlated to the summer precipitation in east China. When the YRNC region has a wetter soil in spring, northeast China and the lower and middle reaches of the Yangtze River valley would have abnormally higher precipitation in summer, while the region south of the Yangtze River valley would have abnormally lower precipitation. An analysis of the physical processes linking the spring soil moisture to the summer precipitation indicates that the soil moisture anomaly across the YRNC region has a major impact on the surface energy balance. Abnormally wet soil would increase surface evaporation and hence decrease surface air temperature ( Ta). The reduced Ta in late spring would narrow the land--sea temperature difference, resulting in the weakened East Asian monsoon in an abnormally strengthened western Pacific subtropical high that is also located farther south than its normal position. This would then enhance precipitation in the Yangtze River valley. Conversely, the abnormally weakened East Asian summer monsoon allows the western Pacific subtropical high to wander to south of the Yangtze River Valley, resulting in an abnormally reduced precipitation in the southern part of the country in east China. [ABSTRACT FROM AUTHOR]

Satellite observations are analyzed to examine the correlations between aerosols and the tropical tropopause layer (TTL) temperature and water vapor. This study focuses on two regions, both of which are important pathways for the mass transport from the troposphere to the stratosphere and over which Asian pollution prevails: South and East Asia during boreal summer and the Maritime Continent during boreal winter. Using the upper-tropospheric carbon monoxide measurements from the Aura Microwave Limb Sounder as a proxy of aerosols to classify ice clouds as polluted or clean, the authors find that polluted clouds have a smaller ice effective radius and a higher temperature and specific humidity near the tropopause than clean clouds. The increase in water vapor appears to be related to the increase in temperature, as a result of increased aerosols. Meteorological differences between the clouds cannot explain the differences in temperature and water vapor for the polluted and clean clouds. The authors hypothesize that aerosol semidirect radiative heating and/or changes in cirrus radiative heating, resulting from aerosol microphysical effects on clouds, may contribute to the increased TTL temperature and thus increased water vapor in the polluted clouds. [ABSTRACT FROM AUTHOR]

The spatial and temporal variations of aerosol loading over eastern Asia specified in terms of the aerosol optical depth (AOD) at the 550-nm wavelength during July are examined in conjunction with the intensity of the Indian summer monsoon. AOD derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, gridded reanalyses, and ground-based measurements are used in the analysis. Two contrasting years, 2002 and 2003, which represent weak and active Indian summer monsoon events, respectively, are selected for the study, with a focus on an eastern Asian southern subregion (SR; 23°°--32°°N, 105°°--120°°E) and an eastern Asian northern subregion (NR; 35°°--44°°N, 115°°--130°°E). It is shown that the interannual variation of July mean wind intensity is a major factor in regulating the midsummer spatial pattern of aerosols over eastern Asia when the Indian monsoon index is anomalously large. The AOD anomalies in the NR and SR are positive and negative, respectively, during an active monsoon year, whereas the opposite is observed during a weak monsoon year. The variation patterns of less cloudy-day visibility, observed at four meteorological stations in the SR and NR subregions, also show spatial--temporal aerosol variability evident in the MODIS AOD data. Relative to the case of a weak monsoon year, meridional winds and convection are stronger and more clouds and precipitation are observed in the NR subregion during the active monsoon year. The opposite pattern is observed in the SR subregion. The spatial--temporal variation pattern of aerosols over eastern Asia illustrates the nonnegligible role of transport and dispersal mechanisms associated with the Indian summer monsoon in the region. [ABSTRACT FROM AUTHOR]

The Indian summer monsoon (ISM) tends to be intensified in a global-warming scenario, with a weakened linkage with El Niño--Southern Oscillation (ENSO), but how the East Asian summer monsoon (EASM) responds is still an open question. This study investigates the responses of the EASM from observations, theoretical, and modeling perspectives. Observational and theoretical evidence demonstrates that, in contrast to the dramatic global-warming trend within the past 50 years, the regional-mean EASM rainfall is basically dominated by considerable interannual-to-decadal fluctuations, concurrent with enhanced precipitation over the middle and lower reaches of the Yangtze River and over southern Japan and suppressed rainfall amount over the South China and Philippine Seas. From 1958 through 2008, the EASM circulation exhibits a southward shift in its major components (the subtropical westerly jet stream, the western Pacific Ocean subtropical high, the subtropical mei-yu--baiu--changma front, and the tropical monsoon trough). Such a southward shift is very likely or in part due to the meridional asymmetric warming with the most prominent surface warming in the midhigh latitudes (45°°--60°°N), which induces a weakened meridional thermal contrast over eastern Asia. Another notable feature is the enhanced ENSO--EASM relationship within the past 50 years, which is opposite to the ISM. Fourteen state-of-the-art coupled models from the Intergovernmental Panel on Climate Change show that the EASM strength does not respond with any pronounced trend to the global-warming ''A1B'' forcing scenario (with an atmospheric CO2 concentration of 720 ppm) but shows interannual-to-decadal variations in the twenty-first century (2000--99). These results indicate that the primary response of the EASM to a warming climate may be a position change instead of an intensity change, and such position change may lead to spatial coexistence of floods and droughts over eastern Asia as has been observed in the past 50 years. [ABSTRACT FROM AUTHOR]

Previous studies on the predictability of East Asian summer monsoon circulation based on SST-constrained Atmospheric Model Intercomparison Project (AMIP)-type simulations show that this phenomenon is reproduced with lower skill than other monsoon patterns. The authors examine the reason in terms of the predictability of land--sea thermal contrast change. In the observation, a stronger monsoon circulation is dominated by a tropospheric warming over East Asian continent and a cooling over the tropical western Pacific and North Pacific, indicating an enhancement of the summertime ''warmer land--colder ocean'' mean state. The tropospheric cooling over the tropical western Pacific and North Pacific, and the tropospheric warming over East Asian continent are reproducible in AMIP-type simulations, although there are biases over both the North Pacific and East Asia. The tropospheric temperature responses in the model indicate a reasonable predictability of the meridional land--sea thermal contrast; the zonal land--sea thermal contrast change is also predictable but shows bias over the region north to 25°°N in North Pacific. The reproducibility of the meridional thermal contrast is higher than that of the zonal thermal contrast. An examination of the predictability of two commonly used monsoon indices reveals far different skills. The index defined as zonal wind shear between 850 and 200 hPa averaged over East Asia is highly predictable. The skill comes from the predictability of the meridional land--sea thermal contrast. Although the zonal thermal contrast change is mostly predictable except for the biases over the North Pacific, the monsoon index defined as zonal sea level pressure (SLP) difference across the East Asian continent and the North Pacific is unpredictable. The low skill is related to the index definition, which attaches more importance to the land SLP change. The limitation of the index in measuring the land SLP change reduces the model skill. Although regional features of monsoon precipitation changes remain a challenge for current climate models, the predictable land--sea thermal contrast change sheds light on monsoon circulation prediction. [ABSTRACT FROM AUTHOR]

This study investigates a decadal climate shift over East Asia in winter, focusing on the changes in hydrological cycle as well as large-scale circulation using the National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM). The RSM is forced by perfect boundary conditions for winter (December-February) from 1979 to 2007. Analyses for two separate periods (1979-87 and 1999-2007) are performed to investigate the regional climate model's ability to simulate climate change in precipitation as well as large-scale circulation. The RSM reproduces differences in large-scale features associated with winter climate change over East Asia when the winter monsoon is modulated on decadal time scales with its weakening pattern observed since the late 1980s. The model adequately reproduces a weakening of the Siberian high and shallowness of the Aleutian low in the lower troposphere and a weakened East Asian coastal trough and East Asian jet in the upper troposphere during 1999-2007, as compared to the first nine winters of 1979-87. Conversely, the decadal shift in precipitation is not well reproduced by the model. The model is capable of reproducing the power spectrum of daily precipitation with maxima at 8.5 days and 45 days in 1979-87, whereas widely spread peaks in 1999-2007 are not captured. The increase of precipitation due to parameterized convection is prominent. This study shows that the dynamical numerical model has a limited capability to reproduce the wintertime hydrological climate over East Asia associated with global warming in recent years. [ABSTRACT FROM AUTHOR]

A new index measuring the East Asian winter monsoon is defined using the mean wind shears of upper-tropospheric zonal wind based on the belief that the physical processes of both higher and lower latitudes, and at both lower and upper troposphere, should be considered to depict the variability of monsoon. When the index is high (low), the westerly jet is strong (weak), the East Asian trough is deep (shallow), the Siberian high is strong (weak), and anomalous low-level northerlies (southerlies) prevail over East Asia. As a result, the surface and lower-tropospheric temperature over East Asia decreases (increases) and the cold surges over Southeast Asia and tropical western Pacific are more (less) active. The index, which exhibits distinct interannual variations, is also strongly correlated with the Arctic Oscillation and Niño-3.4 sea surface temperature (SST) index. Compared to previous indexes, this index takes into account more influencing factors and better elucidates the physical processes associated with monsoon, enhancing interpretations of the variability of monsoon and its effects on regional weather and climate. Furthermore, the monsoon index is significantly linked to antecedent tropical Pacific SST and is highly predictable in the NCEP Climate Forecast System, indicating the advantage of the index for operational predictions of monsoon. [ABSTRACT FROM AUTHOR]

The performance of an interim version of the NCAR Community Atmospheric Model (CAM3.5) in simulating the East Asian summer monsoon (EASM) is assessed by comparing model results against observations and reanalyses. Both the climate mean states and seasonal cycle of major EASM components are evaluated. Special attention is paid to the sensitivity of model performance to changes in the convection scheme. This is done by analyzing four CAM3.5 runs with identical dynamical core and physical packages but different modifications to their convection scheme, that is, the original Zhang–McFarlane (ZM) scheme, Neale et al.’s modification (NZM), Wu et al.’s modification (WZM), and Zhang’s modification (ZZM). The results show that CAM3.5 can capture the major climate mean states and seasonal features of the EASM circulation system, including reasonable simulations of the Tibetan high in the upper troposphere and the western Pacific subtropical high (WPSH) in the middle and lower troposphere. The main deficiencies are found in monsoon rainfall and the meridional monsoon cell. The weak meridional land–sea thermal contrasts in the model contribute to the weaker monsoon circulation and to insufficient rainfall in both tropical and subtropical regions of EASM. The seasonal migration of rainfall, as well as the northward jump of the WPSH from late spring to summer, is reasonably simulated, except that the northward jump of the monsoon rain belt still needs improvement. Three runs using modified schemes generally improve the model performance in EASM simulation compared to the control run. The monsoon rainfall distribution and its seasonal variation are sensitive to modifications of the ZM convection scheme, which is most likely due to differences in closure assumptions. NZM, which uses a convective available potential energy (CAPE)-based closure assumption, performs better in tropical regions where the rainfall is closely related to CAPE. However, WZM and ZZM, which use quasi-equilibrium (QE) closure, have more realistic subtropical rainfall in the mei-yu/baiu/changma front region, mainly because the rainfall in the subtropics is more sensitive to the rate of destabilization by the large-scale flow. [ABSTRACT FROM AUTHOR]

The authors examine the projected change in interannual variability of East Asian summer precipitation and of dominant monsoonal circulation components in the twenty-first century under scenarios A1B and A2 by analyzing the simulated results of 12 Coupled Model Intercomparison Project phase 3 (CMIP3) coupled models. Interannual standard deviation is used to depict the intensity of interannual variability. An evaluation indicates that these models can reasonably reproduce the essential features of the present-day interannual variability in both East Asian rainfall and the rainfall-related circulations. The models project an enhanced interannual variability of summer rainfall over East Asia in the twenty-first century, under both scenarios A1B and A2. Over the East Asian summer rain belt, 10 of the 12 models under scenario A1B and 9 of the 10 models under scenario A2 show enhanced variability in the twenty-first century relative to the twentieth century. The multimodel ensemble (MME) results in increased ratios of interannual standard deviation of precipitation averaged over this region of about 12% and 19% under scenarios A1B and A2, respectively. Furthermore, it is found that the interannual variability is intensified much more remarkably in comparison with mean precipitation. Two circulation factors, the western North Pacific subtropical high (WNPSH) and East Asian upper-tropospheric jet (EAJ), which are closely related to the interannual variability of East Asian summer rainfall, are also projected by the models to exhibit enhanced interannual variability in the twenty-first century. This provides more evidence for the enhancement of interannual variability in East Asian summer rainfall and implies intensified interannual variability of the whole East Asian summer monsoon system. On the other hand, the relationships of East Asian rainfall with the WNPSH and EAJ do not exhibit clear changes in the twenty-first century under scenarios A1B and A2, and there are great discrepancies in the changes of the relationships among the individual models. [ABSTRACT FROM AUTHOR]

Seasonal variations of the synoptic-scale transient eddy activity (STEA) and the jet streams over East Asia are examined through analysis of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data. Extracted from the 6-hourly upper-level wind fields, the distribution of the jet core numbers exhibits a distinct geographical border for the East Asian subtropical jet (EASJ) and the East Asian polar front jet (EAPJ) at the latitudes of the northern Tibetan Plateau (TP). In the cool seasons, two branches of the STEA and low-level baroclinicity exist over the East Asian landmass, accompanied by the two-jet state of the EASJ and EAPJ. In the warm seasons, a single jet pattern of the EASJ along the north flank of the TP is accompanied by the weakened STEA over the mid- to high latitudes of East Asia. Further analysis shows two distinct features of the seasonal variations of the STEA over East Asia, compared with that over the North Pacific. First, during the transitional period of April–June, the main STEA band over East Asia migrates northward dramatically, in conjunction with the EAPJ shifting in the same direction. Second, both the upper-level STEA and the lower-level baroclinicity poleward of the TP are prosperous in spring. The relationship between the STEA, baroclinicity, vertical wind shear, and static stability in the EAPJ region in different seasons is further investigated. It is found that in addition to the time-mean wind fields, the rapid increase in the sensible heat flux poleward side of the TP region in spring and the associated boundary layer processes are partially responsible for the spring prosperity of the local baroclinicity and the STEA. [ABSTRACT FROM AUTHOR]