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This paper provides an updated analysis of observed changes in extreme precipitation using high-quality station data up to 2018. We examine changes in extreme precipitation represented by annual maxima of 1-day (Rx1day) and 5-day (Rx5day) precipitation accumulations at different spatial scales and attempt to address whether the signal in extreme precipitation has strengthened with several years of additional observations. Extreme precipitation has increased at about two-thirds of stations and the percentage of stations with significantly increasing trends is significantly larger than that can be expected by chance for the globe, continents including Asia, Europe, and North America, and regions including central North America, eastern North America, northern Central America, northern Europe, the Russian Far East, eastern central Asia, and East Asia. The percentage of stations with significantly decreasing trends is not different from that expected by chance. Fitting extreme precipitation to generalized extreme value distributions with global mean surface temperature (GMST) as a covariate reaffirms the statistically significant connections between extreme precipitation and temperature. The global median sensitivity, percentage change in extreme precipitation per 1 K increase in GMST is 6.6% (5.1% to 8.2%; 5%–95% confidence interval) for Rx1day and is slightly smaller at 5.7% (5.0% to 8.0%) for Rx5day. The comparison of results based on observations ending in 2018 with those from data ending in 2000–09 shows a consistent median rate of increase, but a larger percentage of stations with statistically significant increasing trends, indicating an increase in the detectability of extreme precipitation intensification, likely due to the use of longer records. [ABSTRACT FROM AUTHOR]

In the context of global climate change, recent studies indicate a poleward migration trend of tropical cyclones (TCs) in the western North Pacific (WNP), while little attention has been paid to the TC cyclolysis (hereafter Lysis). With respect to two different datasets, this study identifies the poleward migration of the annual-mean latitude of TC Lysis during 1979-2018, being more significant for the intensified TCs, although this trend is suppressed by the reduction in the TC frequency over the sea. It is found that the TC migration is more like a poleward translation of the overall movement rather than the expansion of a specific phase's distance span. Subsequently, the trends of several environmental parameters related to TC development are also analyzed. The large-scale sea surface temperature warming leads to the increase of potential intensity and enhances the possibility of TC poleward migration. Through controlling the TC formation in the eastern WNP tropics, the variations of vertical wind shear and horizontal winds affect TC Lysis latitude, facilitate the TC development environment around East Asia offshore and island chain areas, and steer TCs poleward migration through the southerly wind anomalies in the area north of 308N. Regarding the cyclonic vorticity in the lower troposphere and the divergence in the upper troposphere, their influence on TC Lysis latitude is mainly by adjusting the numbers of TCs rather than directly interfering with the TC movement process. The present results indicate that the northern WNP coastal region will also become a TC-prone area in the future, which needs to be treated with caution. [ABSTRACT FROM AUTHOR]

The present study examines variations in summertime (July–September) tropical cyclone (TC) activity over East Asia during the period 1951–2003. To represent TC activity, a total of 853 TC best tracks for the period were converted to TC passage frequencies (TPFs) within 5° × 5° latitude–longitude grids; TPFs are defined as the percentage values obtained by dividing the number of TC appearances in each grid box by the total number of TCs each year. Empirical orthogonal function analysis of the TPF showed three leading modes: two tropical modes that represent the long-term trend and the relationship with ENSO and one midlatitude mode that oscillates between south of Korea and southeast of Japan with an interannual time scale. The latter proved to be the most remarkable climatic fluctuation of summertime TC activity in the midlatitudes and is referred to as the East Asian dipole pattern (EADP) in this paper. Anomalous atmospheric flows directly connected to the EADP are an enhanced anticyclonic (cyclonic) circulation centering around Japan when the TPF is high south of Korea (southeast of Japan), thereby showing an equivalent barotropic structure in the entire troposphere. This regional circulation anomaly varies in conjunction with the zonally oriented quasi-stationary Rossby wave train in the upper troposphere. This wave train is meridionally trapped in the vicinity of the summer-mean jet stream; therefore, the mean jet stream alters its internal meandering structure according to the phase of the wave train. [ABSTRACT FROM AUTHOR]

The frequency of large-scale anomalous precipitation events over China has increased during 1961–2018. However, it remains challenging to understand the mechanisms associated with these anomalous events showing different spatial patterns. Here, we applied an autoencoder technique to identify large-scale anomalous precipitation events for both observations and model simulations, which were then classified into several patterns through a self-organizing map method. The synoptic behavior and atmospheric circulation background of different anomalous patterns were also analyzed using simultaneous composite analyses. Results show that occurrences of different anomalous precipitation patterns have increased significantly, except those centered in North China, Northeast China, and the Yangtze River basin. The anomalous precipitation patterns manifest various intraseasonal distributions, which are linked to zonal oscillations of the western North Pacific subtropical high (WNPSH) and meridional displacements of East Asia westerly jet (EAJ). Accompanied by the westward movement of WNPSH, anticyclonic systems transport warm moist air from the Indian Ocean and the South China Sea to converge with the cold air caused by anomalous cyclones over the northwest flank of the WNPSH, leading to large-scale anomalous precipitation in these regions. Besides WNPSH, the northward and southward displacements of EAJ also favor the occurrence of anomalous precipitation events in northern and southern China, respectively. Our study also illustrates that the occurrence frequency of anomalous precipitation events is projected to increase remarkably under the Shared Socioeconomic Pathway 5–8.5 (SSP585) scenario by rates of twofold to fourfold. [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]

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]

Sea surface temperature anomalies (SSTAs) in the Kuroshio Extension (KE) region play a key role in influencing midlatitude climate variations. This study investigates the impacts of SSTAs in the KE region (KE-SSTA) on East Asian climate during boreal autumn. The results reveal that positive KE-SSTA, changing the meridional temperature gradient in the lower troposphere, contributes to the formation of an anomalous quasi-barotropic anticyclonic circulation (AC) over the KE region. Such a configuration tends to be affected by wind through thermal wind adjustment. Simultaneously, it is also impacted by eddy activity related to the strengthened atmospheric baroclinicity through transient eddy feedback. By both means, obvious descending motion and warm advection are generated, which increases tropospheric temperature through adiabatic heating and further maintains the abnormal AC over the KE region. This anomalous circulation changes wind in the east of the East Asian trough, which favors the transportation of warm and wet air from the midlatitude northwest Pacific and further causes the increase of temperature in northeastern East Asia. Moreover, it also leads to the convergence and divergence of water vapor fluxes in Northeast Asia and eastern North China, favoring the increase and decrease of precipitation in the two regions, respectively. The above responsive characteristics of the midlatitude atmospheric circulation to positive KE-SSTA can be confirmed by numerical experiments. These results suggest that anomalous SST in the KE region can be used as a potentially effective predictability source for autumn climate variations in the mid- to high latitudes of East Asia. Significance Statement: Anomalous variations of sea surface temperature (SST) in the Kuroshio Extension (KE) region play an essential role in influencing midlatitude climate variations. Considering the importance of autumn climate in East Asia to agricultural production, this study aims to explore the relationship between the East Asian climate and autumn SST anomaly in the KE region (KE-SSTA), and to understand how KE-SSTA effects East Asian climate during boreal autumn. Our results suggest that KE-SSTA can be used as one of the effective predictors of East Asian climate, which will contribute to the improvement of short-term climate prediction levels over East Asia. [ABSTRACT FROM AUTHOR]

Even though winter land–sea thermal contrast (LSC) is expected to undergo a strong weakening in the future warmer climate, its effects have been poorly investigated. Here we run a set of idealized winter simulations featuring reduced LSC in the Northern Hemisphere (NH) extratropics, or in individual extratropical sectors of the NH (Atlantic and Pacific), using an intermediate-complexity atmospheric general circulation model. Reduced LSC is obtained by imposing a warming of surface land temperatures in East Asia and North America. For similar warming intensities over the two regions, the response of the model to East Asia forcing is significantly stronger and dominates the response to the sum of the two forcing patterns. We find that the LSC reduction causes a weakening and poleward shift of the midlatitude jet streams, and a strong interference with zonal wavenumbers 1 and 2. In particular, East Asian warming reduces the amplitude of waves 1 and 2, producing a strengthening of the stratospheric vortex, while a weaker vortex due to a moderate amplification of wave 1 is detected when warming North America. Eventually, stratospheric signals propagate downward in the troposphere affecting the midlatitude winter NH even remotely from the forcing. In this work we pinpoint some mechanisms by which weakened winter LSC influences the NH extratropical circulation: the results may become useful to interpret the response to long-term projections displaying reduced LSC along with other climate change forcing patterns. [ABSTRACT FROM AUTHOR]

Summer mean (June, July, and August) surface air temperature (SSAT) in East Asia during the period from 1958 to 2001 has shown a warming. However, the relative contributions of external forcing (EF) and internal climate variability (ICV) to the SSAT changes over East Asia remain unclear. In this study, a new approach is applied to estimate the changes in the SSAT determined by the effects of EF and ICV over East Asia during the period from 1958 to 2001. Reanalysis data as well as simulated results from both global atmosphere–ocean coupled model outputs and a regional climate model (RCM) are used for this approach. The observed SSATs over East Asia have undergone a decreasing trend from 1958 to 1972 (20.148C decade-1, p<0.01) and an increasing trend after 1972 (0.248C decade-1, p<0.01). While these features are not captured by the reanalysis studied here, they are reproduced when the reanalysis output is downscaled using an RCM. The effects of the EF and the ICV on the SSAT can be separated based on the RCM downscaling simulation. The results show that the SSAT with EF displayed significant warming over most regions of East Asia, whereas the SSAT with ICV mainly exhibited cooling over East Asia. Furthermore, EF mainly influenced the decadal changes of the SSAT, whereas the ICV mainly influenced the interannual changes in the SSAT over East Asia. The interannual changes of the SSAT over East Asia that were influenced by the ICV are mainly manifested as the combined effects of the large-scale ocean–atmosphere circulations, which expressed 79% explanatory power on the SSAT changes. [ABSTRACT FROM AUTHOR]

The western Pacific pattern (WP) is one of the most important atmospheric teleconnections over the Northern Hemisphere (NH) in boreal winter and plays key roles in regulating weather and climate variations over many parts of the NH. This study evaluates the ability of the coupled models participating in CMIP5 and CMIP6 to capture the spatial pattern, dominant frequency, and associated climate anomalies of the winter WP. Ensemble means of the CMIP5 and CMIP6 models well capture spatial structures of the WP, with slightly higher skills for the CMIP6. However, the northern (southern) center of the WP is shifted westward (eastward) relative to the observations, and the strength of the northern center is overestimated in most CMIP5 and CMIP6 models. CMIP6 shows an improvement in simulating the dominant periodicity of the WP. WP-related climatic anomalies in most parts of the NH can be well simulated. However, there exists a large spread across the models in simulating surface air temperature (SAT) anomalies in the Russian Far East and northwest North America, which is attributable to the diversity of the intensity of the WP's northern lobe. Most CMIP5 and CMIP6 models largely overestimate the WP-related precipitation anomalies over Siberia, which is partly due to the overestimation of mean precipitation there. Furthermore, most models simulate a close relation of the WP and Arctic Oscillation (AO), which does not exist in observation. The CMIP5 and CMIP6 models with weak WP–AO relations have better ability than the models with strong WP–AO relations in capturing the WP-related SAT and precipitation anomalies over the NH, especially over Eurasia. [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]

The relationship between the tropical west Pacific (TWP) and East Asian summer monsoon/precipitation has been documented in previous studies. However, the stability for the signals of midsummer precipitation in the TWP sea surface temperature (SST_TWP), which is important for climate variation, has drawn little attention. This study identifies a strengthened relationship between the leading empirical orthogonal function mode (EOF1) of midsummer precipitation over Northeast China (NEC) and the SST_TWP after the mid-1990s. The EOF1 mode shows a significant positive correlation with the SST_TWP for 1996–2016, whereas the relationship is statistically insignificant for 1961–90. Further results indicate that the North Pacific multidecadal oscillation (NPMO) shifts to a positive phase after the 1990s. In the positive NPMO phase, the anomalous circulation over the northeast Pacific expands westward over the central North Pacific–Aleutian Islands region. Concurrently, the SST_TWP-associated wavelike pattern propagates northeastward from the west Pacific to the northwest Pacific and farther to the North Pacific, facilitating the poleward expansion and intensification of the SST_TWP-related circulation anomalies over the North Pacific. Therefore, the SST_TWP has an enhanced influence on NEC precipitation through the modulation of the circulation anomalies over the central North Pacific–Aleutian Islands region after the mid-1990s. Additionally, the tropical anticyclone/cyclone associated with the SST_TWP expands westward to South China, exerting an intensified impact on meridional wind anomalies along eastern China and on moisture transport over NEC. These conditions jointly contribute to the strengthened relationship between the SST_TWP and the EOF1 mode of NEC midsummer precipitation after the mid-1990s. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) intensified during the early to mid-Holocene relative to the present primarily due to orbital forcing. However, on the regional scale, changes in the monsoonal precipitation exhibit considerable spatial disparity, and the underlying mechanisms remain unresolved. In this study, the dynamic processes responsible for the difference of the EASM precipitation between the mid-Holocene and preindustrial period are systematically examined using the CMIP5 multimodel simulations. The moisture budget diagnostic identifies vertical motion as the key factor determining the cross-like precipitation pattern in East Asia. Relative to the preindustrial period, the mid-Holocene anomalous ascending motion corresponds well with the excessive precipitation over northern and southern China, and vice versa for west-central China, the Korean peninsula, Japan, and its marginal seas. In the framework of the moist static energy budget, the increased insolation and the attendant intensification of land–sea thermal contrast give rise to anomalous ascending motions, while descending motions are fundamentally forced by the decreased latitudinal insolation gradient. In particular, thermodynamic changes, namely, the reduced pole–equator temperature and humidity gradients, account for the downward motions over the northwestern Pacific. Dynamic changes, namely, the weakened westerlies, play a leading role in suppressing updrafts in west-central China. This study highlights that the orbital-scale monsoonal precipitation changes are not solely determined by local radiative forcing as repeatedly emphasized before. The latitudinal uneven distribution of insolation is crucial to explain the spatial inhomogeneity in the EASM precipitation changes during the Holocene. [ABSTRACT FROM AUTHOR]

An integrated picture of the future changes in the water cycle is provided focusing on the global land monsoon (GLM) region, based on multimodel projections under the representative concentration pathway 8.5 (RCP8.5) from phase 5 of the Coupled Model Intercomparison Project (CMIP5). We investigate the reservoirs (e.g., precipitable water, soil moisture) and water fluxes (e.g., precipitation P, evaporation E, precipitation minus evaporation P − E, and total runoff) of the water cycle. The projected intensification of the water cycle with global warming in the GLM region is reflected in robust increases in annual-mean P (multimodel median response of 0.81% K−1), E (0.57% K−1), P − E (1.58% K−1), and total runoff (2.08% K−1). Both surface (−0.83% K−1) and total soil moisture (−0.26% K−1) decrease as a result of increasing evaporative demand. Regionally, the Northern Hemispheric (NH) African, South Asian, and East Asian monsoon regions would experience an intensified water cycle, as measured by the coherent increases in P, P − E, and runoff, while the NH American monsoon region would experience a weakened water cycle. Changes in the monthly fields are more remarkable and robust than in the annual mean. An enhanced annual cycle (by ~3%–5% K−1) with a phase delay from the current climate in P, P − E, and runoff is projected, featuring an intensified water cycle in the wet season while little changes or slight weakening in the dry season. The increased seasonality and drier soils throughout the year imply increasing flood and drought risks and agricultural yields reduction. Limiting global warming to 1.5°C, the low warming target set by the Paris Agreement, could robustly reduce additional hydrological risks from increased seasonality as compared to higher warming thresholds. [ABSTRACT FROM AUTHOR]

A winter Eurasian cooling trend and a large decline of winter sea ice concentration (SIC) in the Barents–Kara Seas (BKS) are striking features of recent climate changes. The question arises as to what extent these phenomena are related. A mechanism is presented that establishes a link between recent winter SIC decline and midlatitude cold extremes. Such potential weather linkages are mediated by whether there is a weak north–south gradient of background tropospheric potential vorticity (PV). A strong background PV gradient, which usually occurs in North Atlantic and Pacific Ocean midlatitudes, acts as a barrier that inhibits atmospheric blocking and southward cold air intrusion. Conversely, atmospheric blocking is more persistent in weakened PV gradient regions over Eurasia, Greenland, and northwestern North America because of weakened energy dispersion and intensified nonlinearity. The small climatological PV gradients over mid- to high-latitude Eurasia have become weaker in recent decades as BKS air temperatures show positive trends due to SIC loss, and this has led to more persistent high-latitude Ural-region blocking. These factors contribute to increased cold winter trend in East Asia. It is found, however, that in years when the winter PV gradient is small the East Asian cold extremes can even occur in the absence of large negative SIC anomalies. Thus, the magnitude of background PV gradient is an important controller of Arctic–midlatitude weather linkages, but it plays no role if Ural blocking is not present. Thus, the "PV barrier" concept presents a critical insight into the mechanism producing cold Eurasian extremes and is hypothesized to set up such Arctic–midlatitude linkages in other locations. [ABSTRACT FROM AUTHOR]

The wintertime Arctic temperature (T; surface-400 hPa) decreased from 1979 to 1997 and increased rapidly from 1998 to 2012, in contrast to the global mean surface air temperature. Here aspects of circulation variability that are associated with these temperature changes are examined using the NCEP-NCAR reanalysis and ERA-Interim products. It is found that the Nordic-Siberia seesaw of meridional winds near 70°N is associated with two-thirds of the variance of the Arctic winter mean T, possibly contributing to the cooling and warming trends. It is suggested here that the seesaw accounts for much of the difference in Arctic amplification between observations and climate models. Growth of sea ice in winter is hindered by southerly winds over the Nordic region (0°-60°E). Through modulation of the wind seesaw, the eastern Atlantic (EA) pattern is found to be significantly associated with Arctic and East Asia winter climate variations. In one phase of the EA pattern, a midlatitude North Atlantic ridge anomaly is associated with a poleward shift of the mean storm track, a weakened eddy-driven jet over Eurasia, and above-normal sea level pressure (SLP) over Siberia, most significantly in the region to the northwest of Lake Baikal. The EA pattern is associated with two-thirds of the variance of winter-average SLP over Siberia. [ABSTRACT FROM AUTHOR]

Arctic sea ice (ASI) and its potential climatic impacts have received increasing attention during the past decades, yet the relevant mechanisms are far from being understood, particularly how anomalous ASI affects climate in midlatitudes. The spring precipitation takes up as much as 30% of the annual total and significantly influences agriculture in East Asia. Here, observed evidence and numerical experiment results show that the ASI variability in the Norwegian Sea and the Barents Sea in the preceding winter is intimately connected with interannual variations of the East Asian spring precipitation (EAP). The former can explain about 14% of the total variance of the latter. The ASI anomalies persist from winter through the ensuing spring and excite downstream teleconnections of a distinct Rossby wave train prevailing over the Eurasian continent. For the reduced ASI, such a wave train pattern is usually associated with an anomalous low pressure center over the Mongolian plateau, which accelerates the East Asian subtropical westerly jet. The intensified subtropical westerly jet, concurrent with lower-level convergence and upper-level divergence, enhances the local convection and consequently favors rich spring precipitation over East Asia. For the excessive ASI, the situation tends to be opposite. Given that seasonal prediction of the EAP remains a challenging issue, the winter ASI variability may provide another potential predictability source besides El Niño-Southern Oscillation. [ABSTRACT FROM AUTHOR]

The summer precipitation anomalies over the tropical western North Pacific (WNP), which greatly affect East Asian climate, are closely related to Indian Ocean (IO) SST anomalies, and this WNP-IO relationship is widely assumed to be linear. This study indicates that the IO SST-WNP precipitation relationship is generally linear only when the IO SST anomalies are positive and not when the IO SST anomalies are negative, that is, a strongly cooler IO, in comparison with a moderately cooler IO, does not correspond to stronger precipitation enhancement over the WNP. Further analysis suggests that the phases of ENSO play a crucial role in modifying the impacts of IO SSTs on WNP anomalies. The reverse IO SST-WNP precipitation relationship, which exists without apparent ENSO development/decay, is intensified by El Niño decay through the enhancement of IO SST anomalies, but weakened by El Niño development and La Niña decay through the concurrence of SST anomalies in the tropical central and eastern Pacific. After removing El Niño developing and La Niña decaying cases, the IO SST and WNP precipitation anomalies show a clear linear relationship. Because of the effects of the phases of ENSO, the years of negative precipitation or anticyclonic anomalies over the WNP are highly concentrated over strongly warmer IO and El Niño decaying years, which is consistent with previous studies. However, the years of positive precipitation anomalies are scattered over cooler IO and moderately warmer IO years, implying a complexity of tropical SST forcing on positive WNP precipitation anomalies. [ABSTRACT FROM AUTHOR]

Previous studies suggested that the boreal spring Arctic Oscillation (AO) exerts a pronounced influence on the following East Asian summer monsoon (EASM) variability. This study reveals that the relationship of spring AO with the following EASM experienced a significant interdecadal change in the early 1970s. The influence of spring AO on the following EASM is weak during the 1950s and 1960s but strong and significant during the mid-1970s through the mid-1990s. The spring AO-related sea surface temperature (SST), atmospheric circulation, and heating anomalies are compared between 1949-71 and 1975-97. Results show that the spring AO-related cyclonic circulation anomaly over the tropical western North Pacific is weaker and located more northward in the former epoch than in the latter epoch. Correspondingly, SST, atmospheric circulation, and heating anomalies over the tropical North Pacific are located more northeastward in the former than latter epoch from spring to summer. In the following summer, the spring AO-related cyclonic circulation anomalies over the tropical North Pacific are located farther away from East Asia in the former epoch. This interdecadal change in the AO-EASM connection may be attributed to a significant change in the intensity of spring North Pacific synoptic-scale eddy activity around the early 1970s from a weak regime to a strong regime, which induces a stronger eddy feedback to the low-frequency mean flow after the early 1970s. This may explain a stronger spring AO-related cyclonic circulation over the tropical western North Pacific and thus a closer relationship between the spring AO and the following EASM in the latter than former epoch. [ABSTRACT FROM AUTHOR]

This study provides evidence of the robust response of the East Asian monsoon rainband to the 11-yr solar cycle and first identify the exact time period within the summer half-year (1958-2012) with the strongest correlation between the mean latitude of the rainband (MLRB) over China and the sunspot number (SSN). This period just corresponds to the climatological-mean East Asian mei-yu season, characterized by a large-scale quasi-zonal monsoon rainband (i.e., 22 May-13 July). Both the statistically significant correlation and the temporal coincidence indicate a robust response of the mei-yu rainband to solar variability during the last five solar cycles. During the high SSN years, the mei-yu MLRB lies 1.2° farther north, and the amplitude of its interannual variations increases when compared with low SSN years. The robust response of monsoon rainband to solar forcing is related to an anomalous general atmospheric pattern with an up-down seesaw and a north-south seesaw over East Asia. [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]

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 current seasonal prediction of East Asia (EA) summer monsoon deals with June–July–August (JJA) mean anomalies. This study shows that the EA summer monsoon may be divided into early summer [May–June (MJ)] and late summer [July–August (JA)] and exhibits remarkable differences in mean state between MJ and JA. This study reveals that the principal modes of interannual precipitation variability have distinct spatial and temporal structures during the early and late summer. These principal modes can be categorized as either El Niño–Southern Oscillation (ENSO) related or non-ENSO related. During the period of 1979–2007, ENSO-related modes explain 35% of MJ variance and 45% of JA variance, and non-ENSO-related modes account for 25% of MJ variance and 20% of JA variance. For ENSO-related variance, about two-thirds are associated with ENSO decaying phases, and one-third is associated with ENSO developing phases. The ENSO-related MJ modes generally concur with rapid decay or early development of ENSO episodes, and the opposite tends to apply to ENSO-related JA modes. The non-ENSO MJ mode is preceded by anomalous land surface temperatures over southern China during the previous March and April. The non-ENSO JA mode is preceded by lasting equatorial western Pacific (the Niño-4 region) warming from the previous winter through late summer. The results suggest that 1) prediction of bimonthly (MJ) and (JA) anomalies may be useful, 2) accurate prediction of the detailed evolution of ENSO is critical for prediction of ENSO-related bimonthly rainfall anomalies over East Asia, and 3) non-ENSO-related modes are of paramount importance during ENSO neutral years. Further establishment of the physical linkages between the non-ENSO modes and their corresponding precursors may provide additional sources for EA summer monsoon prediction. [ABSTRACT FROM AUTHOR]

Interannual variations of the East Asian trough (EAT) axis at 500 hPa are studied with the European Centre for Medium-Range Weather Forecasts 40-yr reanalysis data. The associated circulation pattern and pathway of the East Asian winter monsoon (EAWM) with the EAT axis tilt are specially investigated with a trough axis index, which is closely related to the midlatitude baroclinic process and mainly represents the intensity of the eddy-driven jet over the East Asia–North Pacific sector. When the tilt of EAT is smaller than normal, the EAWM prefers to take the southern pathway and less cold air moves to the central North Pacific. However, the EAWM prefers the eastern pathway and brings more cold air to the North Pacific when the tilt of EAT is larger than normal. These differences induce pronounced changes in both the precipitation and the surface air temperature over East and Southeast Asia. Furthermore, the tilt status of the EAT has a significant modulation effect on the regional climate anomalies related to the intensity of the EAWM. The findings suggest an increase in the temperature anomaly associated with the EAWM intensity and a clear northward–southward shift in its pattern in anomalous tilt phase of the EAT. In addition, the modulation tends to be confined mainly to East Asia and expanded to a larger area during the weak and the strong EAWM winters, respectively. The possible reasons for interannual variations of the EAT tilt are discussed, and it is speculated that the midlatitude air–sea interaction in the North Pacific plays a dominant role. This study on the EAT tilt may enrich knowledge of the East Asian winter monsoon beyond the conventional intensity index and may be helpful to improve regional climate prediction in East Asia. [ABSTRACT FROM AUTHOR]

A basin-scale warming is the leading mode of tropical Indian Ocean sea surface temperature (SST) variability on interannual time scales, and it is also the prominent feature of the interdecadal SST trend in recent decades. The influence of the warming on the East Asian summer monsoon (EASM) is investigated through ensemble experiments of several atmospheric general circulation models (AGCMs). The results from five AGCMs consistently suggest that near the surface, the Indian Ocean warming forces an anticyclonic anomaly over the subtropical western Pacific, intensifying the southwesterly winds to East China; and in the upper troposphere, it forces a Gill-type response with the intensified South Asian high, both favoring the enhancement of the EASM. These processes are argued to contribute to the stronger EASM during the summer following the peak of El Niño than monsoons in other years. These model results also suggest that tropical Indian Ocean warming may not have a causal relationship to the synchronous weakening of EASM on interdecadal time scales. [ABSTRACT FROM AUTHOR]

Numerous modeling studies have shown that soil moisture anomalies in later spring have a significant effect on the summer rainfall anomalies in North America. On the other hand, the role of soil moisture in forming monsoonal precipitation in East Asia has not been identified. This study attempts to clarify the importance of soil moisture on the summer rainfall in late spring in East Asia. The National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) is utilized for 3-month (June–August) simulations in 1998 (above-normal precipitation year) and 1997 (below-normal precipitation year). Initial and boundary conditions are derived from the NCEP–Department of Energy (DOE) reanalysis. The control run uses the initial soil moisture from the reanalysis, whereas it is set as a saturation and wilting point for “wet” and “dry” experiments, respectively. The impact of soil moisture anomalies on the simulated summer rainfall in East Asia is not significant. The change in precipitation between the wet and dry experiments is about 10%. A conflict between the local feedback of soil moisture and a change in large-scale circulations associated with the summertime monsoonal circulation in East Asia can be attributed as a reason for this anomaly. It is found that enhanced (suppressed) evaporation from the soil to the atmosphere in wet (dry) initial soil moisture reduces (increases) the land–sea contrast between East Asia and the Pacific Ocean, leading to a weakened sensitivity of the monsoonal circulations to the initial soil moisture. It can be concluded that the impact of the initial soil moisture is significant on the dynamic circulation in East Asia. [ABSTRACT FROM AUTHOR]

The occurrence frequency of the east Asian cold surge exhibits an interannual variation in concert with the El Niño–Southern Oscillation (ENSO) cycle. That is, the cold surge occurs more (less) frequently during warm (cold) ENSO winters. Because the cold surge high–low dipoles are coupled with the upper-level synoptic short waves, any mechanism modulating the activity of these waves would affect the cold surge activity. The streamfunction budget analysis in the short-wave regime indicates that the development of the cold surge short-wave train over east Asia and the northwest Pacific is modulated by the North Pacific ENSO short-wave train. Due to the coupling between the upper-level cold surge short-wave train and the surface cold surge dipole, it is inferred from this streamfunction budget analysis that the interannual variation of the cold surge occurrence frequency is a result of this modulation. [ABSTRACT FROM AUTHOR]