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The Western Ghats (WG) is one of the important biodiversity hotspots and rainfall intense regions in south Asia. In this paper, the long-term trend analysis is carried out during southwest monsoon rainfall over different latitudinal regions of the WG. Further, the gridded daily rainfall data (0.25 × 0.25 spatial grid resolution) is classified into six intensity bins: dry, low, moderate, heavy, very heavy, and extreme, from 1951 to 2015. A detailed trend and variability analysis of rainfall and its frequency in different intensity bins along with their relative contribution were carried out. The results of different rainfall intensity bins depict that the moderate and low intensity bins contribute a maximum share in seasonal rainfall with 45% and 20%, respectively, from the 30% and 50% rainy days in all the regions. Heavy and very heavy intensity bins together contribute about 30% of the seasonal rainfall from about 9% rainy days. Extreme intensity bin recorded an alarming share of 6% with only 1% rainy day occurrences. In general, the relative contribution shows an ascending pattern of moderate, low, very heavy, heavy, extreme, and dry intensity bins. A decreasing trend in rainfall was observed in heavy and very heavy intensity bins, while other intensity bins illustrated mixed trends in different study regions. Extreme rainfall events marked a major shift upward in the WG region during the study period. Overall, our result portrays a negative trend in rainfall during the southwest monsoon season over all the study regions during the study period. [ABSTRACT FROM AUTHOR]

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The tropical easterly jet (TEJ) is a prominent atmospheric circulation feature observed during the Asian summer monsoon. It is generally assumed that sensible heating over the Tibetan Plateau directly influences the location of the TEJ. However, other studies have suggested the importance of latent heating in determining the jet location. In this paper, the relative importance of latent heating on the maintenance of the TEJ is explored through simulations with a general circulation model. The simulation of the TEJ by the Community Atmosphere Model, version 3.1 is discussed in detail. These simulations showed that the location of the TEJ is well correlated with the location of the precipitation. Significant zonal shifts in the location of the precipitation resulted in similar shifts in the zonal location of the TEJ. These zonal shifts had minimal effect on the large-scale structure of the jet. Further, provided that precipitation patterns were relatively unchanged, orography did not directly impact the location of the TEJ. These changes were robust even with changes in the cumulus parameterization. This suggests the potential important role of latent heating in determining the location and structure of the TEJ. These results were used to explain the significant differences in the zonal location of the TEJ in the years 1988 and 2002. To understand the contribution of the latitudinal location of latent heating on the strength of the TEJ, aqua-planet simulations were carried out. It has been shown that for similar amounts of net latent heating, the jet is stronger when heating is in the higher tropical latitudes. This may partly explain the reason for the jet to be very strong during the JJA monsoon season. [ABSTRACT FROM AUTHOR]

Afro-Asian summer monsoon precipitation (AfroASMP) is the life blood of billions of people living in many developing countries covering West Africa and Asia. Its complex variabilities are always accompanied by natural disasters like floods, landslides and droughts. Reliable AfroASMP prediction several months in advance is valuable for not only decision-makers but also regional socioeconomic sustainability. To address the current predicament of the AfroASMP seasonal prediction, this study provides an effective machine-learning model (Y-model). Y-model uses the monsoon related big climate data for searching the potential predictors, encompassing atmospheric internal factors and external forcings. Only the predictors associated with significant anomalies in summer horizonal winds at 850 hPa over the monsoon domain are retained. These selected predictors are then reorganized into a large ensemble based upon different thresholds of four fundamental principles. These principles include the focused sample sizes, the relationships between predictors and predictand, the independence among predictors, and the extremities of predictors in the forecast year. Real-time predictions can be generated based on the ensemble mean of skillful members during an independent hindcast period. Y-model skillfully predicts four monsoon precipitation indices of AfroASMP during 2011–2022 at lead 4–12 months, correlation skills range from 0.58 to 0.90 and root mean square error skills are reduced by 11–53% compared to CFS v2 model at lead 1 month. This study offers an effective method for preprocessing predictors in seasonal climate prediction. [ABSTRACT FROM AUTHOR]

Large-scale climate models (LCM) have been used to understand climate change and its effects, but there remains a concern about their inability fully to reflect local contexts and about a high degree of their uncertainty. Through a case study that involved residents of a coastal community in Central Vietnam, this paper presents how local people perceive climate change and characterize climate impacts on their life. Findings of the study show that local people perceive a variety of important manifestations of climate change, especially temperature, rainfall, sea level rise and monsoons, although they have limited ideas about future climate change. In addition, local people unpack the complexity of climate impacts through interactions among climatic events, livelihoods and the five capitals (physical, natural, financial, human and social resources). Findings of the research suggest that it will be necessary to move away from viewing coastal villages in Vietnam as homogenous units with shared climate experiences, and to combine both local experience and scientific evidence based on LCMs to promote the synergies and address the limitations of the two sources of information for climate interventions at the local level. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Stable isotope paleoaltimetry has provided unprecedented insights into the topographic histories of many of the world's highest mountain ranges. However, on the Tibetan Plateau (TP), stable isotopes from paleosols generally yield much higher paleoaltitudes than those based on fossils. It is therefore essential when attempting to interpret accurately this region's paleoaltitudes that the empirical calibrations of local stable isotopes and the relations between them are established. Additionally, it is vital that careful estimations be made when estimate how different isotopes sourced from different areas may have been influenced by different controls. We present here 29 hydrogen isotopic values for leaf wax-derived n-alkanes (i.e., D values, and abundance-weighted average δD values of C and C) in surface soils, as well as the δD values of soil water ( δD) samples (totaling 22) from Mount Longmen (LM), on the eastern TP (altitude ~0.8-4.0 km above sea level (asl), a region climatically affected by the East Asian Monsoon (EAM). We compared our results with published data from Mount Gongga (GG). In addition, 47 river water samples, 55 spring water samples, and the daily and monthly summer precipitation records (from May to October, 2015) from two precipitation observation stations were collected along the GG transect for δD analysis. LM soil D values showed regional differences and responded strongly to altitude, varying from-160‰ to-219‰, with an altitudinal lapse rate (ALR) of-18‰ km ( R =0.83; p<0.0001; n=29). These D values appeared more enriched than those from the GG transect by ~40‰. We found that both the climate and moisture sources led to the differences observed in soil D values between the LM and GG transects. We found that, as a general rule, ε , ε and ε values (i.e., the isotopic fractionation of D corresponding to δD, δD and δD) increased with increasing altitude along both the LM and GG transects (up to 34‰and 50‰, respectively). Basing its research on a comparative study of D, δD, δD( δD) and δD, this paper discusses the effects of moisture recycling, glacier-fed meltwater, relative humidity ( RH), evapotranspiration ( ET), vegetation cover, latitude, topography and/or other factors on ε values. Clearly, if ε values at higher altitudes are calculated using smaller ε values from lower altitudes, the calculated paleowater δD values are going to be more depleted than the actual δD values, and any paleoaltitude would therefore be overestimated. [ABSTRACT FROM AUTHOR]

This paper investigates the processes and mechanisms by which the East Asian winter monsoon (EAWM) affects the Madden-Julian oscillation (MJO) over the equatorial western Pacific in boreal winter (November-April). The results show that both the EAWM and MJO over the equatorial western Pacific have prominent interannual and interdecadal variabilities, and they are closely related, especially on the interannual timescales. The EAWM influences MJO via the feedback effect of convective heating, because the strong northerlies of EAWM can enhance the ascending motion and lead the convection to be strengthened over the equatorial western Pacific by reinforcing the convergence in the lower troposphere. Daily composite analysis in the phase 4 of MJO (i.e., strong MJO convection over the Maritime Continent and equatorial western Pacific) shows that the kinetic energy, outgoing longwave radiation (OLR), moisture flux, vertical velocity, zonal wind, moist static energy, and atmospheric stability differ greatly between strong and weak EAWM processes over the western Pacific. The strong EAWM causes the intensity of MJO to increase, and the eastward propagation of MJO to become more persistent. MJO activities over the equatorial western Pacific have different modes. Furthermore, these modes have differing relationships with the EAWM, and other factors can also affect the activities of MJO; consequently, the relationship between the MJO and EAWM shows both interannual and interdecadal variabilities. [ABSTRACT FROM AUTHOR]

Reliable prediction of the South Asian monsoon rainfall and its variability is crucial for various hydrological applications and early warning systems. The National Centers for Environmental Prediction-Global Forecast System (NCEP-GFS) is one of the popular global deterministic numerical weather prediction models, which is recently upgraded from T574 to T1534. In this paper, medium range monsoon precipitation forecasts from both the T1534 and T574 models are critically evaluated over the South Asia for the peak monsoon months (July and August) of 2015. Although both the versions of GFS model show similar large-scale monsoon rainfall patterns, the dry bias over the northwest India and equatorial Indian Ocean is noticeably improved in day-1 through day-5 forecasts in the new high-resolution T1534 model. The error decomposition analysis shows similar error characteristics in the monsoon rainfall prediction from both the versions of GFS model, in general. However, forecast improvement factor shows 10-30 % improvement in precipitation forecast from the latest T1534 model over most parts of the South Asia. These preliminary analyses suggest that a suitable bias-correction to the GFS model precipitation forecasts will be useful for any specific application. [ABSTRACT FROM AUTHOR]

Seasonal prediction of the East Asian summer monsoon (EASM) strength is probably one of the most challenging and crucial issues for climate prediction over East Asia. In this paper, a statistical method called partial-least square (PLS) regression is utilized to uncover principal sea surface temperature (SST) modes in the winter preceding the EASM. Results show that the SST pattern of the first PLS mode is associated with the turnabout of warming (or cooling) phase of a mega-El Niño/Southern Oscillation (mega-ENSO) (a leading mode of interannual-to-interdecadal variations of global SST), whereas that of the second PLS mode leads the warming/cooling mega-ENSO by about 1 year, signaling precursory conditions for mega-ENSO. These indicate that mega-ENSO may provide a critical predictability source for the EASM strength. Based on a 40-year training period (1958-1997), a PLS prediction model is constructed using the two leading PLS modes and 3-month-lead hindcasts are performed for the validation period of 1998-2013. A promising skill is obtained, which is comparable to the ensemble mean of versions 3 and 4 of the Canadian Community Atmosphere Model (CanCM3/4) hindcasts from the newly developed North American Multi-model Ensemble Prediction System regarding the interannual variations of the EASM strength. How to improve dynamical model simulation of the EASM is also examined through comparing the CanCM3/4 hindcast (1982-2010) with the 106-year historical run (1900-2005) by the Second Generation Canadian Earth System Model (CanESM2). CanCM3/4 exhibits a high skill in the EASM hindcast period 1982-2010 during which it also has a better performance in capturing the relationship between the EASM and mega-ENSO. By contrast, the simulation skill of CanESM2 is quite low and it is unable to reproduce the linkage between the EASM and mega-ENSO. All these results emphasize importance of mega-ENSO in seasonal prediction and dynamical model simulation of the EASM. [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of 29 state-of-art CMIP5-coupled atmosphere-ocean general circulation models (AOGCM) in their representation of regional characteristics of monsoon simulation over South Asia. The AOGCMs, despite their relatively coarse resolution, have shown some reasonable skill in simulating the mean monsoon and precipitation variability over the South Asian monsoon region. However, considerable biases do exist with reference to the observed precipitation and also inter-model differences. The monsoon rainfall and surface flux bias with respect to the observations from the historical run for the period nominally from 1850 to 2005 are discussed in detail. Our results show that the coupled model simulations over South Asia exhibit large uncertainties from one model to the other. The analysis clearly brings out the presence of large systematic biases in coupled simulation of boreal summer precipitation, evaporation, and sea surface temperature (SST) in the Indian Ocean, often exceeding 50 % of the climatological values. Many of the biases are common to many models. Overall, the coupled models need further improvement in realistically portraying boreal summer monsoon over the South Asian monsoon region. [ABSTRACT FROM AUTHOR]

Scientific issues relevant to interactions between aerosols and the Asian monsoon climate were discussed and evaluated at the 33rd 'Forum of Science and Technology Frontiers' sponsored by the Department of Earth Sciences at the Chinese Academy of Sciences. Major results are summarized in this paper. The East Asian monsoon directly affects aerosol transport and provides a favorable background circulation for the occurrence and development of persistent fog-haze weather. Spatial features of aerosol transport and distribution are also influenced by the East Asian monsoon on seasonal, inter-annual, and decadal scales. High moisture levels in monsoon regions also affect aerosol optical and radiative properties. Observation analyses indicate that cloud physical properties and precipitation are significantly affected by aerosols in China with aerosols likely suppressing local light and moderate rainfall, and intensifying heavy rainfall in southeast coastal regions. However, the detailed mechanisms behind this pattern still need further exploration. The decadal variation in the East Asian monsoon strongly affects aerosol concentrations and their spatial patterns. The weakening monsoon circulation in recent decades has likely helped to increase regional aerosol concentrations. The substantial increase in Chinese air pollutants has likely decreased the temperature difference between land and sea, which favors intensification of the weakening monsoon circulation. Constructive suggestions regarding future studies on aerosols and monsoons were proposed in this forum and key uncertain issues were also discussed. [ABSTRACT FROM AUTHOR]

The East Asian winter monsoon (EAWM) exhibits significant variability on intraseasonal, interannual, and interdecadal time scales and the variability can be extended to Holocene centennial and millennial scales. Previous Holocene EAWM proxy data records, which were mostly located in Central, Eastern and Southern China, did not show a consistent Holocene EAWM history. Therefore, it is difficult to provide insights into mechanisms of the long-term winter monsoon variability on the basis of the records. Eolian sediments at the southern edge of the Gobi Desert, Western China, are sensitive to the EAWM changes and less affected by the East Asian summer monsoon due to an obstruction of the Qinghai-Tibet Plateau. This paper presents a comparison between a well-dated Holocene EAWM record and coupled climate model simulations, so as to explore physical processes and influencing factors of the Holocene EAWM. Sediment samples from two Holocene eolian sedimentary sections [Huangyanghe (a) and Huangyanghe (b)] were acquired at the southern edge of the Gobi Desert. Chronologies were established based on twenty bulk organic matter AMS C ages and five pollen concentrates AMS C ages. Proxy data, including grain-size, total organic carbon, magnetic susceptibility and carbonate content were obtained from the two eolian sections. The grain-size standard deviation model was applied to determine components sensitive to variability of the Holocene EAWM. After a comparison of environmentally-sensitive grain-size components and proxy data, the 20-200 μm component at the Huangyanghe (a) and the 20-159 μm component at the Huangyanghe (b) section were selected as indicators of the Holocene EAWM, which show a strong early Holocene winter monsoon and a decline of the winter monsoon since the mid-Holocene. We also present equilibrium and transient simulations of the climate evolution for the Holocene using a state-of-art coupled climate model: the Community Climate System Model version 3 (CCSM3). Indices for the Holocene EAWM were calculated and are consistent with the reconstructed Holocene EAWM intensity. The simulations indicate that orbital forcing effects on the land-sea temperature and sea level pressure contrast can account for the observed EAWM trends. Other forcings that were present in the early Holocene, including the remnant Laurentide ice sheet and meltwater forcing in the North Atlantic, were not responsible for the Holocene trends. [ABSTRACT FROM AUTHOR]

The mid-Pliocene warm period was the most recent geological period in Earth's history that featured long-term warming. Both geological evidence and model results indicate that East Asian summer winds (EASWs) strengthened in monsoonal China, and that East Asian winter winds (EAWWs) weakened in northern monsoonal China during this period, as compared to the pre-industrial period. However, the corresponding mechanisms are still unclear. In this paper, the results of a set of numerical simulations are reported to analyze the effects of changed boundary conditions on the mid-Pliocene East Asian monsoon climate, based on PRISM3 (Pliocene Research Interpretation and Synoptic Mapping) palaeoenvironmental reconstruction. The model results showed that the combined changes of sea surface temperatures, atmospheric CO concentration, and ice sheet extent were necessary to generate an overall warm climate on a large scale, and that these factors exerted the greatest effects on the strengthening of EASWs in monsoonal China. The orographic change produced significant local warming and had the greatest effect on the weakening of EAWWs in northern monsoonal China in the mid-Pliocene. Thus, these two factors both had important but different effects on the monsoon change. In comparison, the effects of vegetational change on the strengthened EASWs and weakened EAWWs were relatively weak. The changed monsoon winds can be explained by a reorganization of the meridional temperature gradient and zonal thermal contrast. Moreover, the effect of orbital parameters cannot be ignored. Results showed that changes in orbital parameters could have markedly affected the EASWs and EAWWs, and caused significant short-term oscillations in the mid-Pliocene monsoon climate in East Asia. [ABSTRACT FROM AUTHOR]

Steep slope, heavy rainfall and forested cover have unique soil erosion and sediment transport in South Korea. Sediment transport pattern in the monsoon region (from June to September) is complex and sediment transport modeling in these areas is often difficult as sediment load in the river varies largely from year to year. This paper describes a GIS-based soil erosion model and then developed a sediment transport model to estimate sediment yield (SY) at different basin scales. The model for estimating suspended sediment is based on Revised Universal Soil Loss Equation and suspended delivery ratio (SDR) models. For applying SDR model, basin-specific parameter was validated on the basis of field data, which ranged from 0.6 to 1.2 based on observed SY. In the study region, the high flow rates lasted for 4 months (from July to September) and over 90 % of total SY discharged during that time. At that time, it was found that annual bed loads in this area are 56-84 % of total sediment loads. [ABSTRACT FROM AUTHOR]

China's Loess Plateau is located at the edge of the Asian summer monsoon in a transition zone of climate and ecology. In the Loess Plateau, climate and environments change along with space, which has an obvious impact on the spatial distribution of surface energy fluxes. Because of scarce land-surface observation sites and short observation time in this area, previous studies have failed to fully understand the land-surface energy balance characteristics over the entire the Loess Plateau and their effect mechanisms. In this paper, we first test the simulation ability of the Community Land Model (CLM) model by comparing its simulated data with observed data. Based on the simulation data for the Loess Plateau over the past thirty years, we then analyze the spatial distribution of surface energy fluxes and compare the pattern differences between the area averages for the driest year and wettest year. Furthermore, we analyze the relationship between the spatial distribution of the components of the surface energy balance with longitude, latitude, altitude, precipitation and temperature. The main results are as follows: the spatial distribution of surface energy fluxes are significantly different, with the surface net radiation and sensible heat flux increasing from south to north and latent heat flux and soil heat flux decreasing from southeast to northwest. The sensible heat flux at the driest point is nearly twice as high as that at the wettest point, whereas the latent heat flux and soil heat flux at the driest point are half as much as that at the wettest point. The impact of variations of annual precipitation on the components of the surface energy balance is also obvious, and the maximum magnitude of the changes to the sensible heat flux and latent heat flux is nearly 30%. To a certain extent, geographical factors (including longitude, latitude, and altitude) and climate factors (including temperature and precipitation) affect the surface energy fluxes. However, the surface net radiation is more closely related to latitude and altitude, sensible heat flux is more closely related to the monsoon rainfall and latitude, and latent heat flux and soil heat flux are more closely related to the monsoon rainfall. [ABSTRACT FROM AUTHOR]

Interannual variability of the Indian summer monsoon rainfall (ISMR) is explained through the total column water vapor in the atmosphere, primarily controlled by the incoming zonal moisture flux over the Arabian Sea ( F W ) and outgoing flux over the Bay of Bengal ( F E ). In this study, we discern the underlying mechanisms driving F W and F E leading to ISMR droughts in the observations and seasonal hindcasts by the Climate Forecast System version 2 (CFSv2) model. In observations, a reduction in F W is essential for droughts to occur. In addition, an increase in F E results in a severe drought. On the contrary, droughts in CFSv2 primarily occur due to an enhancement in F E , seldom accompanied by a decrease in F W . This hypersensitivity of the CFSv2 ISMR to F E is further explained using Matsuno–Gill response to moist convection. During El Nino droughts, precipitation decreases over the equatorial western Pacific and eastern Indian Oceans. The resulting anomalous diabatic cooling increases local surface pressure ( SP ), intensifying meridional SP gradient, and thus, F E . The reduction in F W , however, is associated with a cooling of the central north Pacific Ocean in tandem with El Nino. During non-El Nino droughts, frequent occurrences of cold sea surface temperature over the western north Pacific Ocean are noticed. This cooling decreases SP over east Asia, resulting in an increase in F E . To summarize, droughts in CFSv2 are controlled by the pan-Pacific climate, significantly increasing F E but weakly decreasing F W . But in observations, a strong decrease in F W and a moderate increase in F E together lead to droughts. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) is a unique regional monsoon in the extratropics involving not only tropical but midlatitude processes. Most of the previous studies identified the role of condensational heating which is largely relevant to the tropical moisture transport in determining the dynamical structure of EASM. However, how midlatitude synoptic eddy activities can affect the EASM structure has not been well recognized. With dynamical diagnoses, this study revisits the EASM structure by emphasizing the roles of feedbacks of condensational heating versus synoptic eddy activities. As EASM is characterized by a grand low-level low with strong humid southerly flows extending from the tropics to the northeastern Asia, its vertical structure is found to have a dramatic meridional difference bounded at around 35.5°N. In the southern domain, EASM features a meridional overturning cell and a baroclinic structure with an upper-level high versus a lower-level low in geopotential height, which are primarily controlled by substantial condensational heating due to abundant monsoon precipitation. However, in the northern domain, EASM exhibits an equivalent barotropic structure with an upper-level low versus a lower-level low. Such a unique structure results from a combined effect of feedbacks of condensational heating and synoptic eddy activities, in which the upper-level low is dominated by the synoptic eddy dynamical feedback while the lower-level low is induced by the both feedbacks. The role of the midlatitude synoptic eddy activities in shaping the EASM structure proposed in this study provides a new perspective for understanding the formation and variation of EASM. [ABSTRACT FROM AUTHOR]

A large intraseasonal variation in geopotential height over the Central Asia region, where the Asian subtropical jet is located, occurs between May and June, and the most dominant variation has a wave-like distribution. This variation in geopotential height influences precipitation across South and Southeast Asia. In this paper, we use composite analysis to determine the causes of this intraseasonal variation over Central Asia. The wave train propagates from the northern Atlantic Ocean to Central Asia over a period of a week, and generates an anomaly in geopotential height over the region. The tropical disturbance, which is similar to the Madden-Julian oscillation, appears a few days before the maximum of the anticyclonic anomaly over Central Asia, and is accompanied by active convection over the Indian Ocean and suppressed convection over Central America. Results of numerical experiments using a linear baroclinic model show that the active convection over the northern Indian Ocean causes the anticyclonic anomaly over Central Asia. The wave train that extends from the northern Atlantic Ocean to Central Asia is generated by negative thermal forcing over Central America, and the phase distribution of this wave train is similar to that observed in the composite analysis. Central Asia is the region where the effects of the tropics and middle latitudes overlap, and it is an important connection point between the Asian monsoon and middle latitudes. [ABSTRACT FROM AUTHOR]

Long-term highly accurate surface soil moisture data of TP (Tibetan Plateau) are important to the research of Asian monsoon and global atmospheric circulation. However, due to the sparse in-situ networks, the lack of soil moisture observations has seriously hindered the progress of climate change researches of TP. Based on the Dual-Channel soil moisture retrieval algorithm and the satellite observation data of AMSR-E (Advanced Microwave Scanning Radiometer for EOS), we have produced the surface soil moisture data of TP from 2003 to 2010 and analyzed the seasonal characteristic of the soil moisture spatial distribution and its multi-year changing trend in area of TP. Compared to the in-situ observations, the accuracy of the soil moisture retrieved by the proposed algorithm is evaluated. The evaluation result shows that the new soil moisture product has a better accuracy in the TP region than the official product of AMSR-E. The spatial distribution of the annual mean values of soil moisture and the seasonal variations of the monthly-averaged soil moisture are analyzed. The results show that the soil moisture variations in space and time are consistent with the precipitation distribution and the water vapor transmission path in TP. Based on the new soil moisture product, we also analyzed the spatial distribution of the changing trend of multi-year soil moisture in TP. From the comparisons with the precipitation changing trend obtained from the meteorological observation sites in TP, we found that the spatial pattern of the changing trend of soil moisture coincides with the precipitation as a whole. [ABSTRACT FROM AUTHOR]

In arid regions, because of spatial variability, using single climate records is difficult to reconstruct the past climate change for the drainage basins. Holocene environmental records were collected from the upper, middle and lower regions of the Shiyang River drainage basin in the marginal area of the Asian monsoon (northwest China). The main objective of this paper was to compare the records from the terminal lake and the middle and upper reaches of the basin to study the basin-wide environmental changes. During the early Holocene the vegetation was sparse, and the effective moisture was relatively low in the basin. The Holocene Climatic Optimum started between 7.0 and 8.0 cal ka BP, during which the lake level reached the highest level in the terminal lake; the vegetation density and the effective moisture reached the highest level during the Holocene in the drainage basin. From 4.7 cal ka BP the terminal lake began to shrink, while the vegetation density decreased dramatically. In the middle and upper regions of the drainage, the effective moisture began to decrease since 3.5 cal ka BP, and the arid tendency was earlier in the terminal lake than it was in the middle and upper regions of the drainage basin. During the early Holocene the relatively arid environment was affected by the gradually intensifying East Asian monsoon and the dry westerly winds. The mid-Holocene Optimum benefited from the intensive East Asian monsoon and the humid westerly winds. Then, the East Asian monsoon retreated since the late-Holocene. In the basin the arid tendency may be related to the retracting of the East Asian monsoon. However, the intensifying acidification after 1.5 cal ka BP may be correlated to the increasing dryness of the westerly winds. [ABSTRACT FROM AUTHOR]

Geological climatic records and model simulations on the Asian summer monsoon climate change induced by insolation forcing of the Earth's precession are systematically reviewed in this paper. The presentation of the questions on the mechanism of the Asian monsoon evolution at the precession band, currently existing debates and future research directions are discussed. Since the early 1980s, more and more observed evidence and simulated results, especially the absolute-dated stalagmite records and orbital-scale transient model runs in the last few years, have indicated that the quasi-20ka period in the Quaternary monsoon climate change is caused by precession. However, debates still exist on the dynamic mechanism how precession affects the Asian monsoon. The "zero phase" hypothesis says that the Asian monsoon is merely controlled by summer insolation in the Northern Hemisphere (NH) while the "latent heat" hypothesis emphasizes the dominant effect of latent heat transport from the Southern Hemisphere (SH) besides the role of the northern insolation. The two hypotheses have separately been supported by some evidence. Although we are cognizant of the importance of northern solar radiation and the remote effect of southern insolation, it has still a long way to go before comprehensively understanding the evolutionary mechanism of the Asian monsoon. In view of the problems existing in present researches of monsoon-dominated climate change at the precession scale, we propose that studies on the environmental significance of geological monsoon proxies, feedback processes in the long-term transient simulations and intercomparisons between observations and modeling results should be strengthened in the future. [ABSTRACT FROM AUTHOR]

This paper is to promote a further understanding of the interdecadal variations of the summer monsoon rainfall over South China (SCMR). With this focus, we will specifically aim at better understanding possible mechanism responsible for such an interdecadal variation relationship between the SCMR and El Niño/Southern Oscillation (ENSO). In many of the previous studies on precipitation, the datasets used are satellite observations or gridded reanalyzed data due to the lack of long-term reliable observations over the marginal seas of the Asian continent. Such an approach could lead to possible errors in the results. In this work, several representative stations with long-term rain-gauge observations are chosen to reduce such uncertainty. The study of the interdecadal variabilities of SCMR indicates that there is a strong linkage between SCMR and ENSO on the interdecadal variations. These results agree well with those from previous studies that the Pacific Decadal Oscillation (PDO) and ENSO are not independent of each other, the interannual and interdecadal variations of tropical Pacific Sea Surface temperatures (SSTs) could affect the interdecadal variations of the SCMR, and the incorporating information on the PDO/ENSO could improve the long-term prediction of the SCMR. [ABSTRACT FROM AUTHOR]

In this paper, the maintenance of Asian summer monsoon circulation is compared in the National Centres for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis and National Centre for Medium Range Weather Forecasting (NCMRWF), India operational analysis. The time mean summer monsoon circulation is bifurcated into stable mean and transient eddy components. The mean component of the summer monsoon circulation is elucidated through the study of large-scale balances of kinetic energy, heat and moisture. Although the balance requirements are fairly satisfied by both NCEP/NCAR and NCMRWF fields, a major difference is noticed. Strong monsoon circulation is evinced by NCEP/NCAR over the Oceanic regions and NCMRWF over the landmass. The various mean budgets under consideration indicated this feature invariably. [ABSTRACT FROM AUTHOR]

Summary The monsoon is a global climate phenomenon. This paper addresses the seasonal reversal of atmospheric circulation and the transition of dry/wet spells in the monsoon regions worldwide. The NCEP/NCAR 850 hPa wind reanalysis data for 1950–1999 and the upper-tropospheric water vapour (UTWV) band brightness temperature (BT) data observed by NOAA polar orbiting satellites for 1980–1995 are used. In the tropics, there are three large wet-UTWV centres. The summer monsoon in the subtropics can be defined as the expansion of these centres associated with the influence of cross-equatorial flows. Specifically, the dry/wet spell transition is determined by the BT values that are smaller than 244 K. The regions of the South and North African monsoons, the Asian-northwest Pacific and Australian-Southwest Pacific monsoons, and the North and South American monsoons are examined with a focus on the dry/wet spell transition and stream field features. Findings suggest that the summer monsoons over many subtropical regions can be defined by both cross-equatorial flows and dry/wet spell transitions. In the mid- and low-latitudes, there exist six major dry/wet spell transition regions with a dry or wet period lasting more than one month. The region of most significant change is located over the subtropical North Africa–Asia–northwest Pacific. The others appear over subtropical South Africa, Indonesia–Australia, southwest Pacific, the Mexico-Caribbean Sea, and subtropical South America. In addition, three regions exist where only one of the two indicators (cross-equatorial flow and dry/wet transition) is satisfied. The first is near the Equator where the directions of cross-equatorial flows alternate but a dry/wet spell transition is never experienced. The second is over North Africa where only the dry/wet spell transition can be found but not the cross-equatorial flows. The third is over the mid-latitude regions in North China, South Africa, and northern North America. These regions are influenced by cross-equatorial flows but the upper-tropospheric water vapour content is not as high as that in tropical regions. [ABSTRACT FROM AUTHOR]

Long-term multi-decadal scale variability of South Asian Summer Monsoon (SASM) is known to be associated with the Atlantic Multidecadal Oscillation (AMO) with positive phase associated with above-normal rainfall and vice-versa over SASM region. Analysis of the 120-year historical record suggests that the relationship between the AMO and the SASM has weakened in recent decades. Two possible reasons emerge from the analyses of observational datasets and model experiments. Enhanced Indian Ocean warming and weakened North Atlantic Subtropical High (NASH) are the prime factors weakening AMO-SASM association in the recent decades. Indian Ocean warming co-occurred during the recent AMO warm phase weakens the meridional temperature gradient, weakening the regional Hadley cell, large-scale monsoon circulation and precipitation. The suppressed convection triggers a Rossby wave which manifests as a cyclonic circulation over west central Asia weakening the Tibetan anticyclone. In addition, weakening of NASH weakens the Circum-Global Teleconnection (CGT) connecting AMO to the SASM, leading to weakening of AMO-SASM association. Projected warming of the Indian Ocean and Atlantic demands better understanding of the AMO-SASM teleconnection and their projected changes for assessing future changes in SASM in a warming world. [ABSTRACT FROM AUTHOR]

Global warming has increased the spatio-temporal variations of Extreme Precipitation (EP), causing floods, in turn leading to losses of life and economic damage across the globe. It is found that EP variability strongly correlates with large-scale climate teleconnection resulting from ocean–atmosphere oscillations. In this study, the Non-Stationary Generalized Extreme Value (NSGEV) framework is used to model EP for high resolution daily gridded (0.5° latitude × 0.5° longitude) APHRODITE dataset over Monsoon Asian Region (MAR) using climate indices as covariates. The proposed framework has three major components (i) Selection of non-uniform time-lag climate indices as covariates, (ii) Regionalization of NSGEV model parameters, and (iii) Estimation of zone-wise EP changes. According to Akaike Information Criterion (AICc), results reveal that the NSGEV model is prevalent in 92% of the grid locations across MAR compared to Stationary(S) GEV models. The Gaussian Mixture Model (GMM) clustering algorithm has identified six zones for MAR. It is observed that the derived zonal parameters of NSGEV model is able to mimic the EP characteristics. Further, zone-wise estimation of EP changes for selected return periods shows that the relative percentage change in intensity ranges between 4 and 11% across the six zones. The change in EP is significantly higher in the monsoonal windward and coastal regions when compared to the other parts of MAR. Overall, the intensities of the EP across MAR are increasing, and return periods are decreasing, which can majorly impact on planning, design and operations of the water infrastructure in the region. [ABSTRACT FROM AUTHOR]

Northern Hemisphere planetary waves exhibit an abrupt change in early summer and a significant impact on East Asian summer monsoon rainfall. Although great achievements have been made toward understanding the characteristics and maintenance of planetary waves during winter and summer, the transition of planetary waves during the abrupt-change period is less well understood. This study aims to assess the relative contribution of harmonic waves to the planetary wave transition and mechanism from the perspective of full nonlinear responses to the mountains of Asia (above 500 m) during May and June, with a primary focus on the largest positive geopotential height anomaly over northeastern Asia. The largest positive geopotential height anomaly over northeastern Asia is primarily contributed by wavelengths of around 7000 km, which corresponds to zonal wavenumber 3. The mid–high latitudes planetary waves mainly consist of wavelengths of around 10,000 km (zonal wavenumber 2, roughly) and 7000 km, which are in-phase (out-of-phase) with each other over the Western (Eastern) Hemisphere. Wavelengths of around 10,000 km weaken and displace eastward, while those of 7000 km magnify and hence contribute to the largest positive geopotential height anomaly over northeastern Asia. The full nonlinear response to the forcing by the mountains of Asia provides a considerable contribution to the largest geopotential height anomaly over northeastern Asia. Such a positive contribution comes mainly from the full nonlinear response to sensible heating associated with the mountains over Asia, which is partially offset by the full nonlinear response to dynamical forcing of the Asian mountains. [ABSTRACT FROM AUTHOR]

Eastern Asia is a major source of global air pollution. The distribution and intensity of these emissions are becoming well characterized, but their impact on the earth surface considering regional hydroclimatological settings has yet to be quantified. Here we show high-resolution spatiotemporal trace metal distributions of precipitation samples collected throughout the Japanese archipelago in 2013, when the world's coal consumption was the greatest, to depict the mass transportation and deposition of pollution. The results show that metals emitted through coal combustion transported from the continent via prevailing wind were intensively deposited along the western coast of the archipelago during winter due to heavy snowing, resulting in lead (Pb) concentration of precipitations exceed the critical level (> 10 μg l−1). About 1497 tons of Pb of continental origin loaded through wet deposition accounted for over ca. 87% of the total annual flux in 2013, which constituted ca. 18.5% of the total emissions from China in 2012. This study presents the first detailed picture of monsoon climate-controlled atmospheric metal transportation and loading in the hotspot region after the phase-out of leaded gasoline in the twentieth century. The dataset can serve as a base for evaluating the effect of countermeasures implemented recent year. [ABSTRACT FROM AUTHOR]

Our confidence in future climate projection depends on the ability of climate models to simulate the current climate, and model performance in simulating atmospheric circulation affects its ability of simulating extreme events. In this study, the self-organizing map (SOM) method is used to evaluate the frequency, persistence, and transition characteristics of models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) for different ensembles of daily 500 hPa geopotential height (Z500) in Asia, and then all ensembles are ranked according to a comprehensive ranking metric (MR). Our results show that the SOM method is a powerful tool for assessing the daily-scale circulation simulation skills in Asia, and the results will not be significantly affected by different map sizes. Positive associations between each two of the performance in frequency, persistence and transition were found, indicating that a good ensemble of simulation for one metric is good for the others. The r10i1p1f1 ensemble of CanESM5 best simulates Z500 in Asia comprehensively, and it is also the best of simulating frequency characteristics. The MR simulation of the highest 10 ensembles for the Western North Pacific Subtropical High (WNPSH) and the South Asia High (SAH) are far better than those of the lowest 10. Such differences may lead to errors in the simulation of extreme events. This study will help future studies in the choice of ensembles with better circulation simulation skills to improve the credibility of their conclusions. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Across the Miocene–Pliocene boundary (MPB; 5.3 million years ago, Ma), late Miocene cooling gave way to the early-to-middle Pliocene Warm Period. This transition, across which atmospheric CO2 concentrations increased to levels similar to present, holds potential for deciphering regional climate responses in Asia—currently home to more than half of the world's population— to global climate change. Here we find that CO2-induced MPB warming both increased summer monsoon moisture transport over East Asia, and enhanced aridification over large parts of Central Asia by increasing evaporation, based on integration of our ~1–2-thousand-year (kyr) resolution summer monsoon records from the Chinese Loess Plateau aeolian red clay with existing terrestrial records, land-sea correlations, and climate model simulations. Our results offer palaeoclimate-based support for 'wet-gets-wetter and dry-gets-drier' projections of future regional hydroclimate responses to sustained anthropogenic forcing. Moreover, our high-resolution monsoon records reveal a dynamic response to eccentricity modulation of solar insolation, with predominant 405-kyr and ~100-kyr periodicities between 8.1 and 3.4 Ma. Global warming drove 'wet gets wetter and dry gets drier' climate shifts in Asia ~5.3 million years ago with monsoon pacing by ~400,000 and ~ 100,000 year cycles. This could be a template for future Asian climate response to anthropogenic warming. [ABSTRACT FROM AUTHOR]

Analysis of observational precipitation indicates that in last few decades, the precipitation in boreal summer (June–August) over the South China Sea (SCS) exhibited an interdecadal variation, characterized by a decrease of 0.59 mm/day from the period 1964–1981 to the period 1994–2011. Accompanied this decrease in precipitation is weakened monsoon circulation featured by an anti-cyclonic circulation anomaly over the SCS in the later period relative to the early period. This work investigates impacts of anthropogenic forcing changes on this interdecadal change in observations, quantify the relative roles of greenhouse gases (GHG) forcing and anthropogenic aerosol (AA) forcing. A set of experiments is designed using the atmospheric component of a state-of-the-art climate model coupled to a multi-level mixed-layer ocean model forced with GHG concentrations and AA emissions in two periods. Modeling results indicate a dominant role of anthropogenic forcing on the observed interdecadal precipitation decrease and weakened monsoon circulation over the SCS in the late twentieth century in which AA forcing plays a more important role compared with GHG forcing. The mechanisms of GHG influences and AA induced changes are revealed by individual forcing experiments. Increasing GHG concentrations can suppress convection over the SCS summer monsoon region by warming the tropical Pacific with an El-Niño like sea surface temperature (SST) pattern, which is associated with a weakened Walker circulation. The changes in AA emissions, mainly through increases in emissions over Asia, lead to cool SST in the north Indian Ocean and the western North Pacific (WNP), and result in changes in meridional SST gradient over the tropical Indian Ocean and the WNP in pre-monsoon seasons. This anomalous meridional SST gradient leads to anomalous local Hadley circulation, characterized by anomalous ascents around the equator and descents over monsoon region, which suppresses convection over the SCS and reduces local precipitation. [ABSTRACT FROM AUTHOR]

Agriculture (e.g., rice paddies) has been considered one of the main emission sources responsible for the sudden rise of atmospheric methane concentration (XCH4) since 2007, but remains debated. Here we use satellite-based rice paddy and XCH4 data to investigate the spatial–temporal relationships between rice paddy area, rice plant growth, and XCH4 in monsoon Asia, which accounts for ~87% of the global rice area. We find strong spatial consistencies between rice paddy area and XCH4 and seasonal consistencies between rice plant growth and XCH4. Our results also show a decreasing trend in rice paddy area in monsoon Asia since 2007, which suggests that the change in rice paddy area could not be one of the major drivers for the renewed XCH4 growth, thus other sources and sinks should be further investigated. Our findings highlight the importance of satellite-based paddy rice datasets in understanding the spatial–temporal dynamics of XCH4 in monsoon Asia. The role of paddy rice agriculture in the spatial and temporal dynamics of atmospheric methane concentration remains unclear. Here, Zhang et al. show that regions with dense rice paddies have high satellite-based column averaged CH4 concentrations (XCH4), and that seasonal dynamics of XCH4 mirror those of paddy rice growth. [ABSTRACT FROM AUTHOR]

In this study, the parameterization of sea surface turbulent heat flux in National Center for Atmospheric Research Community Atmosphere Model version 5 (CAM5) is improved by including the contribution of mesoscale convective motion (i.e., mesoscale enhancement). The effect of mesoscale enhancement on the simulation of the East Asian summer monsoon circulation is further explored with SST-forced experiments that are conducted for the period of January 1979 to December 2015. Experiments suggest that the standard CAM5 exhibits evident biases in simulating the East Asian summer monsoon system. For example, the simulated westerlies at 850 hPa in low latitude of East Asia are too weak, the precipitations in the Bay of Bengal, the South China Sea, and the tropical western Pacific are underestimated, the simulated south Asia and western Pacific subtropical highs are too weak, and the upper and middle troposphere in the low latitudes of East Asia is too cold. By including the mesoscale enhancement in CAM5, these biases are clearly reduced. For example, the simulated summer mean precipitation in the Bay of Bengal is increased from 9.85 to 11.76 mm/day, which is closer to the observed value of 13.80 mm/day. Further analyses show that the improvements in the East Asian summer monsoon precipitations and circulations can be attributed to the enhancement of convections and the increase in water evaporation in the tropical western Pacific Ocean induced by mesoscale enhancement. Correspondingly, the latent heat due to vapor condensation in the atmosphere also increases, which reduces the cold bias in the mid-upper troposphere. Meanwhile, the geopotential height of the upper-middle-level atmosphere is elevated, which makes the simulated intensity of the south Asian and the western Pacific subtropical highs, two important components of the East Asian summer monsoon circulation, closer to the reality. [ABSTRACT FROM AUTHOR]

Monsoon and arid regions in the Asia-Africa-Australia (A-A-A) realm occupy more than 60% of the total area of these continents. Geological evidence showed that significant changes occurred to the A-A-A environments of the monsoon and arid regions, the land-ocean configuration in the Eastern Hemisphere, and the topography of the Tibetan Plateau (TP) in the Cenozoic. Motivated by this background, numerical experiments for 5 typical geological periods during the Cenozoic were conducted using a coupled ocean-atmosphere general circulation model to systemically explore the formations and evolutionary histories of the Cenozoic A-A-A monsoon and arid regions under the influences of continental drift and plateau uplift. Results of the numerical experiments indicate that the timings and causes of the formations of monsoon and arid regions in the A-A-A realm were very different. The northern and southern African monsoons existed during the mid-Paleocene, while the South Asian monsoon appeared in the Eocene after the Indian Subcontinent moved into the tropical Northern Hemisphere. In contrast, the East Asian monsoon and northern Australian monsoon were established much later in the Miocene. The establishment of the tropical monsoons in northern and southern Africa, South Asia, and Australia were determined by both the continental drift and seasonal migration of the Inter-Tropical Convergence Zone (ITCZ), while the position and height of the TP were the key factor for the establishment of the East Asian monsoon. The presence of the subtropical arid regions in northern and southern Africa, Asia, and Australia depended on the positions of the continents and the control of the planetary scale subtropical high pressure zones, while the arid regions in the Arabian Peninsula and West Asia were closely related to the retreat of the Paratethys Sea. The formation of the mid-latitude arid region in the Asian interior, on the other hand, was the consequence of the uplift of the TP. These results from this study provide insight to the important roles played by the earth's tectonic boundary conditions in the formations and evolutions of regional climates during geological times. [ABSTRACT FROM AUTHOR]

Urban land use in East China has undergone considerable change since the 1990s. How such change affects both in situ and remote climate conditions is investigated through numerical modelling experiments with the Community Atmosphere Model Version 5.1. The results show that urbanization causes an increase in surface temperature due to reduced surface albedo but a decrease in specific humidity due to locally reduced surface evaporation. The change in specific humidity overwhelms the surface temperature change effect, leading to locally reduced precipitation. It is noted that urbanization causes changes in climate conditions not only locally but also remotely. Anomalous low-level divergence associated with the reduced precipitation in situ prevents the northward progression of the East Asian summer monsoon. As a result, the major monsoon rain band is strengthened and confined over South China and the tropical Asian monsoon zone along 12°–25°N. The increase of rainfall in the tropical zone, on one hand, induces the local overturning cell, leading to anomalous subsidence over mid-latitude Asia and the equatorial zone, and, on the other hand, perturbs the Subtropical Jet, generating a Rossby wave train disseminating along the Jet. Both of these processes cause anomalous dry and hot conditions over mid-latitude Asia. [ABSTRACT FROM AUTHOR]

The boreal-summer MJOs exhibit three distinctive downstream evolutions on their passages over the Maritime Continent (MC): (i) smoothly transitioning from Indian Ocean (IO) to western Pacific (type-I); (ii) rapidly decayed over the MC (type-II); and (iii) significantly intensified over the MC (type-III). During the life cycles of type-I and -III MJOs, basin-wide overturning circulations connect the convective dipoles between western and eastern north Pacific. For type-II MJO, regional overturning circulations connect the convective dipoles between the IO and Western North Pacific (WNP). For type-I and -III MJOs, the associated convection over eastern IO is able to generate strong Kevin-wave responses and significant positive SST anomalies over the MC and western Pacific. On the other hand, for type-II MJO in the IO, a persistent convection lingers around the WNP. It intensifies westerly monsoon flows, thus preventing the generation of coherent positive SST anomalies ahead of the IO MJO convection. It also blocks the formation of a robust Kelvin-wave response over the MC and western Pacific by delaying the northeastward migrations of the dry phase. The convection of type-I and -III MJOs at eastern IO is able to generate positive boundary-layer moisture anomalies along with positive column-integrated moisture tendencies over the MC and western Pacific, thus allowing them to propagate eastward smoothly. On the other hand, the type-II MJO convection in eastern IO is associated with a very dry troposphere and negative column-integrated moisture tendency over western Pacific, which result in the rapid decay of convection over the MC. These results emphasize the important roles of robust Kelvin-wave responses and positive SST anomalies on the eastward propagation of boreal-summer MJOs over the MC through moistening the troposphere ahead of the convection. [ABSTRACT FROM AUTHOR]

This study investigates the multidecadal variations of the interannual relationship between the East Asian summer monsoon (EASM) and El Niño-Southern Oscillation (ENSO) in 1000-year simulation of a coupled climate model. The interannual relationship between ENSO and EASM has experienced pronounced changes throughout the 1000-year simulation. During the periods with significant ENSO-EASM relationship, the ENSO-related circulation anomalies show a Pacific-Japan (PJ)-like pattern with significant wave-activity flux propagating from the tropics to the north in lower troposphere and from the mid-latitudes to the south in upper troposphere. The resultant ENSO-related precipitation anomalies are more (less) than normal over the East Asia (western North Pacific) in the decaying summers of El Niño events. In contrast, the circulation and precipitation anomalies are weak over East Asia-western North Pacific during the periods with weak ENSO-EASM relationship. Based on the energy conversion analysis, the related anomalies achieve barotropic and baroclinic energy from the mean flow during the periods with strong ENSO-EASM relationship. On the contrary, during the low-correlation periods, the energy conversion is too weak to form the link between the tropics and mid-latitudes. The main reason for the multidecadal variations of ENSO-EASM relationship is the amplitude discrepancy of SST anomalies over the Indo-western Pacific Ocean which, in turn, leads to the intensity difference of the western North Pacific anomalous anticyclone (WPAC) and related climate anomalies. [ABSTRACT FROM AUTHOR]

The Year-to-year variability of the western Pacific subtropical high (WPSH) is primarily controlled by atmosphere-ocean interaction (AOI) between the WPSH and the Indo-Pacific warm pool dipole SST anomalies (AOI mode) and the anomalous SST forcing from the equatorial central Pacific (the CP forcing mode). In this study, we show that the impacts of the WPSH variability on Asian summer monsoon rainfall have changed after the late 1990s. Before the late 1990s (the PRE epoch), the WPSH primarily affects East Asian summer monsoon (EASM) and had little influence on Indian summer monsoon (ISM), whereas after the late 1990s (the POST epoch), the WPSH has strengthened its linkage to the ISM while weakened its relationship with the EASM. This epochal change is associated with a change in the leading circulation mode in the Asia-WP region. During the PRE (POST) epoch the WPSH variation is mainly controlled by the AOI (CP forcing) that mainly affects EASM (ISM). The epochal change of the leading mode may be attributed to the change of the ENSO properties in late 1990s: the CP types of El Nino become a leading ENSO mode in the POST epoch. This work provides a new perspective for understanding decadal changes of the ENSO-monsoon relationship through subtropical dynamics. [ABSTRACT FROM AUTHOR]

It is well recognized that El Niño-Southern Oscillation (ENSO) may exert a direct impact on the East Asian summer monsoon rainfall through modulating the Philippine Sea anticyclone variability. Such ENSO associated influence is evident in the monsoon region, i.e., Southeast China, the Yangtze River, Korean Peninsula and Japan. It remains unclear whether and how this ENSO related effect can reach the Yellow River region, a monsoon/arid transition region. In this study, results show that the year-to-year variations of the Yellow River summer rainfall can be indirectly influenced by ENSO, during its developing phase. The western Tibetan Plateau snow cover (WTPSC) may act as a “capacitor”, helping ENSO signal to reach the Yellow River region. During the El Niño developing spring, the associated diabatic heating in Pacific region can excite an anomalous cyclone over the plateau and anomalous upward flows over the western plateau. Such circulation configuration favors an excessive WTPSC anomaly in spring. The more WTPSC may increase the surface albedo, decrease the absorbed net shortwave radiation and in turn intensify the WTPSC. Through such snow-albedo feedback process, the excessive WTPSC anomaly may strengthen and persist through summer, which may induce two noticeable wave trains in the upper and lower troposphere propagating northeastward to the Yellow River region. Associated with the wave trains, a low pressure anomaly prevails over northeast China. To the southwest side of the anomalous low pressure, the abnormal northerly wind may bring large volumes of dry cold air with little moisture to the Yellow River region, leading to the anomalous drought there. During the La Niña developing summer, the situation tends to be opposite. As such, the ENSO associated influence is tied to the interannual variations of the following summer Yellow River precipitation, with the development of ENSO from spring. [ABSTRACT FROM AUTHOR]

The daily rainfall data at 13 stations over the Central Highlands (CH) Vietnam were collected for the period 1981-2014. Two different sets of criteria using daily observed rainfall and 850 hPa daily reanalysis wind data were applied to determine the onset (retreat) dates of the summer rainy season (RS) and summer monsoon (SM) season, respectively. Over the study period, the mean RS and SM onset dates were April 20 and May 13 with standard deviations of 17.4 and 17.8 days, respectively. The mean RS and SM retreat dates were November 1 and September 30 with standard deviations of 17.9 and 10.2 days, respectively. The year-to-year variations of the onset dates and the rainfall amount within the RS and SM season were closely linked with the preceding winter and spring sea surface temperature in the central-eastern and western Pacific. It was also found that the onset dates were significantly correlated with the RS and SM rainfall amount. [ABSTRACT FROM AUTHOR]

The subseasonal migrations of the East Asian summer monsoon are nearly identical to that of the South Asian summer monsoon. In mid-May to mid-June (Phase 1), the South Asian westerly strengthens, the center of the South Asian high moves northwestward, and the East Asian frontal system coupled to and located north of the Western North Pacific (WNP) high moves northward, with all of these actions occurring rapidly. In mid-June to late July (Phase 2), the strength of the South Asian westerly reaches a maximum, the center of the South Asian high remains at approximately 30°N, and the northward propagation of the WNP high becomes stagnant. The speed of the northward movement of the WNP high in Phase 2 is only half the speed of that in Phase 1. By late June, the South Asian monsoon has reached northern India and been blocked by the Himalayas. This indicates that the Himalayas have an effect of constraining the speed of the northward movement of the South Asian high and, in turn, the WNP high. Climate model experiments further reveal that the near-stationary nature of the East Asian frontal system in Phase 2 is related to the blocking of the South Asian summer monsoon by the Himalayas. We suggest that the evolution of the WNP high is constrained by the evolution of the South Asian high, and the Meiyu–Baiu is connected to the South Asian summer monsoon through the impact of the South Asian monsoon heating on the upper tropospheric circulation. [ABSTRACT FROM AUTHOR]

Greenland Sea ice area (GRESIA) in boreal autumn and its association with the subsequent summer monsoon rainfall over India and South Korea is assessed for the period 1983–2013. It is found that GRESIA in the month of October has a significant positive relation (correlation coefficient (cc) = 0.45) with the subsequent Indian monsoon rainfall (IMR) while having a significant negative relation (cc = −0.40) with the ensuing Korean monsoon rainfall (KMR). GRESIA episodes in the preceding autumn impact the ensuing summer monsoon rainfall over India (South Korea) adversely (favourably). While central Pacific sea surface temperatures (SSTs) play a mediating role in transmitting the GRESIA signal towards the Indian subcontinent, snow over eastern Eurasia, just north of the Korea–Japan peninsula, plays a mediating role in transmitting the GRESIA signal towards the Korean peninsula. Although, the anomalies of equatorial central Pacific SSTs and eastern Eurasian snow play a crucial role in modulating IMR and KMR respectively, the GRESIA variability also plays a dominant role in modulating the monsoon variability over both the regions. Thus, a combination of autumn GRESIA along with SSTs over the central Pacific and snow over the eastern Eurasia, may possibly serve as a unique precursor to presage Asia’s two diverse regional subsystems. [ABSTRACT FROM AUTHOR]

A long-term perspective on the spatial variation of the northern boundary of the East Asian summer monsoon (EASM) and the related physical mechanisms is important for understanding past climate change in Asia and for predicting future changes. However, most of the meteorological definitions of the EASM northern boundary do not correspond well to the actual geographical environment, which is problematic for paleoclimatic research. Here, we use monthly CMAP and GPCP precipitation data to define a new EASM northern boundary index by using the concept of the global monsoon, which is readily applicable to paleoclimatic research. The results show that the distribution of the 2 mm day precipitation isoline (i.e., 300 mm precipitation) has a good relationship with the spatial distribution of modern land cover types, the transitional climate zone and the potential natural vegetation types, in China. The locations of the precipitation isolines also correspond well to the locations of major shifts in wind direction. These results suggest that the 2 mm day isoline has a clear physical significance since the climatic, ecological, and geographical boundary can be used as the northern boundary index of the EASM (which we call the climatological northern boundary index). The index depicts the northeast-southwest orientation of the climatological (1981−2010) EASM northern boundary, along the eastern part of the Qilian Mountains-southern foothills of the Helan Mountains-Daqing Mountains-western margin of the Greater Khingan Range, from west to east across Northwest and Northeast China. The interannual change of the EASM northern boundary from 1980 to 2015 covers the central part of Gansu, the northern part of Ningxia, the eastern part of Inner Mongolia and the northeastern region in China. It can extend northward to the border between China and Mongolia and retreat southward to Shangdong-central Henan. There is a 200−700 km fluctuation range of the interannual EASM northern boundaries around the locations of the climatological northern boundary. In addition, the spatial variation of the interannual EASM northern boundaries gradually increases from west to east, whereas the trend of north-south fluctuations maintains a roughly consistent location in different regions. [ABSTRACT FROM AUTHOR]

In this study, we compare the resolution sensitivity of the Asian Summer Monsoon (ASM) in two Atmospheric General Circulation Models (AGCMs): the MRI-AGCM and the MetUM. We analyze the MetUM at three different resolutions, N96 (approximately 200-km mesh on the equator), N216 (90-km mesh) and N512 (40-km mesh), and the MRI-AGCM at TL95 (approximately 180-km mesh on the equator), TL319 (60-km mesh), and TL959 (20-km mesh). The MRI-AGCM and the MetUM both show decreasing precipitation over the western Pacific with increasing resolution, but their precipitation responses differ over the Indian Ocean. In MRI-AGCM, a large precipitation increase appears off the equator (5-20°N). In MetUM, this off-equatorial precipitation increase is less significant and precipitation decreases over the equator. Moisture budget analysis demonstrates that a changing in moisture flux convergence at higher resolution is related to the precipitation response. Orographic effects, intra-seasonal variability and the representation of the meridional thermal gradient are explored as possible causes of the resolution sensitivity. Both high-resolution AGCMs (TL959 and N512) can represent steep topography, which anchors the rainfall pattern over south Asia and the Maritime Continent. In MRI-AGCM, representation of low pressure systems in TL959 also contributes to the rainfall pattern. Furthermore, the seasonal evolution of the meridional thermal gradient appears to be more accurate at higher resolution, particularly in the MRI-AGCM. These findings emphasize that the impact of resolution is only robust across the two AGCMs for some features of the ASM, and highlights the importance of multi-model studies of GCM resolution sensitivity. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Asian summer monsoon (ASM) anticyclone isolates upper-tropospheric air within the interior of the anticyclone from the outside. Forward trajectory simulations in previous studies have shown that much of the air within the ASM anticyclone can be trapped for up to two or three weeks, not only laterally but also vertically. Here, we investigate the locations of exit points for upper-tropospheric air trapped within the ASM anticyclone, especially the preferred tropopause-crossing locations, using a 3-dimensional trajectory model. Forward trajectory calculations show two-thirds of the air crosses the tropopause at the southern part of the anticyclone via upward diabatic transport. Furthermore, some air crosses at northern and eastern parts via isentropic shedding, but air crosses rarely through the center of the anticyclone. However, calculations also show that many stratospheric parcels within the anticyclone are traceable from the upper-tropospheric anticyclone. This implies they cannot break through the tropopause directly overhead but instead enter the stratosphere via other entry points. [ABSTRACT FROM AUTHOR]

Land-atmosphere coupling over the south Asian monsoon region is examined using a regional climate model. For this purpose, the Weather Research and Forecasting (WRF) model with a resolution of 45 km was used. In the control experiment (CTL), the model was integrated from the year 2000 to 2011 and allowed the soil moisture interaction with the atmosphere using a coupled land surface model. In the second experiment (CSM), the soil moisture evolution at each time step was replaced with the climatology of soil moisture taken from the control run. The results reveal that land-atmosphere coupling plays a critical role in influencing the south Asian monsoon climate variability. Soil moisture is found to have stronger impacts on daily maximum temperature compared to minimum temperature. Soil moisture also makes a significant contribution to monsoon rainfall variability over the monsoon region. The coupling strength for large-scale rainfall is found to be higher compared to that of cumulus rainfall. Soil moisture is found more strongly coupled to sensible heat flux over most of the monsoon region. [ABSTRACT FROM AUTHOR]