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East Asian summer monsoon precipitation is projected to increase under greenhouse warming with strong intraseasonal variation. Using a 35-member CESM Large Ensemble and 30 CMIP6 models, this study reveals that in July and August, maximum rainfall changes in East Asia take place in the midlatitudes, influencing regions encompassing North and Northeast China, the Korean Peninsula, and Japan. The intensified precipitation is attributed to the combined effect of the thermodynamic and dynamic components. The former stems from the enriched low-level moisture, which peaks in continental East Asia in July and August, under global warming. The dynamic effect is due to the enhanced upward motion, associated with the enhanced southerlies throughout the troposphere over midlatitude East Asia. The southerlies also act to intensify the low-level monsoonal circulation, strengthening moisture transport from the tropical ocean to the midlatitudes. In addition to the mean-state changes, the precipitation interannual variability in this region also intensifies, partly due to the enhanced low-level moisture and partly associated with enhanced large-scale circulation anomalies, such as the northwestern Pacific anticyclone. The enhanced background precipitation, along with the intensified interannual variability, may lead to more rainy summers in a warmer climate, with instances where historically extreme precipitation events become more frequent, posing challenges for water resource management and agriculture in the region. [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]

Reliable attribution of Asian summer monsoon variations to aerosol forcing is critical to reducing uncertainties in future projections of regional water availability, which is of utmost importance for risk management and adaptation planning in this densely populated region. Yet, simulating the monsoon remains a challenge for climate models that suffer from long-standing biases, undermining their reliability in attributing anthropogenically forced changes. We analyze a suite of climate model experiments to identify a link between model biases and monsoon responses to Asian aerosols and associated physical mechanisms, including the role of large-scale circulation changes. The aerosol impact on monsoon precipitation and circulation is strongly influenced by a model's ability to simulate the spatio-temporal variability in the climatological monsoon winds, clouds, and precipitation across Asia, which modulates the magnitude and efficacy of aerosol–cloud–precipitation interactions, an important component of the total aerosol response. There is a strong interplay between South Asia and East Asia monsoon precipitation biases and their relative predominance in driving the overall monsoon response. We found a striking contrast between the early- and late-summer aerosol-driven changes ascribable to opposite signs and seasonal evolution of the biases in the two regions. A realistic simulation of the evolution of the large-scale atmospheric circulation is crucial to realize the full extent of the aerosol impact over Asia. These findings provide important implications for better understanding and constraining the diversity and inconsistencies of model responses to aerosol changes over Asia in historical simulations and future projections. [ABSTRACT FROM AUTHOR]

• Lake evolution of Sumxi Co has been reconstructed from lacustrine carbonate isotopes. • Hydrological conditions were mainly dominated by regional precipitation on the northwestern QTP. • Millennial hydroclimate events were responding to globally cooling events and solar irradiance. Climatic and hydrological changes on the Qinghai-Tibetan Plateau (QTP) are controlled by the Asian summer monsoon and the mid-latitude westerlies, which directly affect a large population in Asia. However, the millennial temporal and spatial patterns of Holocene hydroclimate variations on the QTP remain unclear due to the lack of high-quality paleoclimatic records. This paper examines high-resolution stable oxygen and carbon isotopes of authigenic carbonate (δ18O carb and δ13C carb) covering the past 5,000 years taken from Sumxi Co, a hydrologically closed lake lies outside the direct influence of the large ice caps on the northwestern QTP. The hydrological environment of Sumxi Co inferred from the covariance between δ18O carb and δ13C carb values was unstable during the middle to late Holocene, with abrupt increases in lake-levels during the 5.0–4.0 cal ka BP, 3.2–3.1 cal ka BP, 1.8–1.3 cal ka BP, and 0.7 cal ka BP to present. Past millennial hydrological fluctuations coincide temporally with the occurrences of glacier advances on the northwestern QTP, implying increased regional moisture and precipitation during cold periods in the region. The 'cold and wet' hydroclimatic pattern is comparable in other records to the arid areas of central Asia dominated by westerlies before the current anthropogenic warming. The four millennial-scale humid events are synchronous with reduced solar irradiance within dating errors, supporting the hypotheses that the regional pattern of hydroclimatic evolution in arid central Asia responds dominantly and directly to changes in solar activity. This external forcing may be amplified by North Atlantic cooling events and southward shifts of the intertropical convergence, which have further modulated the position of mid-latitude westerlies and the strength of the Indian summer monsoon. [ABSTRACT FROM AUTHOR]

We describe the use of regional relaxation ("nudging") experiments carried out in initialised hindcasts to shed light on the contribution from particular regions to the errors developing in the Asian Summer Monsoon. Results so far confirm previous hypotheses that errors in the Maritime Continent region contribute substantially to the East Asia Summer Monsoon (EASM) circulation errors through their effects on the Western North Pacific Subtropical High. Locally forced errors over the Indian region also contribute to the EASM errors. Errors arising over the Maritime Continent region also affect the circulation and sea surface temperatures in the Equatorial Indian Ocean region, contributing to a persistent error pattern resembling a positive Indian Ocean Dipole phase. This is associated with circulation errors over India and the strengthening and extension of the westerly jet across southeast Asia and the South China Sea into the Western Pacific, thereby affecting the ASM circulation and rainfall patterns as a whole. However, errors developing rapidly in the deeper equatorial Indian Ocean, apparently independently of the atmosphere errors, are also contributing to this bias pattern. Preliminary analysis of nudging increments over the Maritime Continent region suggests that these errors may at least partly be related to deficiencies in the convection and boundary layer parametrisations. [ABSTRACT FROM AUTHOR]

Reconstruction and observational studies imply a potential linkage of moisture and precipitation change in arid central Asia and monsoonal East Asia, in which the evolution of moisture and precipitation in central Asia is out of phase with that in northern China but in phase with that in southern China. In order to ascertain whether there is a robust linkage between the changes in climate in Asian arid regions and monsoon regions and to elucidate the underlying dynamic mechanisms, we analyzed the Last Millennium Reanalysis dataset and outputs from the Community Earth System Model Last Millennium Ensemble (CESM-LME). The results indicate a significant decadal linkage between precipitation changes in central Asia's arid region and the Asian monsoon region during the last millennium, which is primarily driven by the Interdecadal Pacific Oscillation (IPO). In spring, the positive IPO could enhance westerlies over the Mediterranean Sea and to its east, which could transport more water vapor and cause increased precipitation over central Asia. In summer, the positive IPO is accompanied by a weakened Asian monsoon and southward Asian subtropical westerly jet, which can lead to increased (decreased) summer precipitation over southern China (over northern China and South Asia). The IPO plays a dominant role in connecting the decadal variations in precipitation between arid central Asia and monsoonal Asia by modulating the precipitation of their respective major rainy seasons. Model results suggest that this decadal linkage stems entirely from the internal variability present in the CESM-LME control and all single-forcing simulations. Changes in external forcing factors do not alter this inherent linkage caused by the IPO. Moreover, based on analyses of the aridity index and soil moisture content, this relationship of precipitation variation also causes a similar decadal linkage of moisture changes in central Asia and monsoonal Asia. The differences in the multi-centennial-scale moisture and precipitation variations in the Asian arid region and the monsoon region between the Medieval Climate Anomaly and Little Ice Age are also likely caused by IPO-like sea surface temperature anomalies. [ABSTRACT FROM AUTHOR]