Search

Monsoon onset over the South China Sea occurs in April–May, marking the start of the wet season over East Asia. Skillful prediction of onset timing remains an open challenge. Recently, theoretical studies using idealized models have revealed feedbacks at work during the seasonal transitions of the Hadley cells and have shown that these are relevant to monsoon onset over Asia. Here, I hypothesize that monsoon onset occurs earlier in years when the atmosphere over the South China Sea is already in a state where these feedbacks are more easily triggered. I find that local anomalies in lower‐level moist static energy in the preceding January–March are well correlated with South China Sea Monsoon onset timing. This relationship remains relatively consistent on decadal timescales, while correlations with other teleconnections vary, and is used to develop a simple forecast model for onset timing that shows skill competitive with that of more complex models. Plain Language Summary: Arable land in China is estimated to feed 20% of the world's population on 7% of the world's farmlands, with much of this region watered by rainfall from the East Asian Summer Monsoon. Forecasting the arrival of the monsoon, which occurs first over the South China Sea in April–May, is therefore helpful for agricultural planning. However, producing a reliable forecast remains an open challenge. Recently, simple climate models, for example, models including seasons but with no land, have been used along with observations to investigate the most basic processes controlling climatological monsoon onset over Asia. In this paper, I suggest that year‐to‐year variations in monsoon onset timing are controlled by the same processes and, based on these, I suggest climate variables that may help in predicting when the monsoon will begin. By using this approach, I find that the "Moist Static Energy" (a quantity that combines temperature and humidity) over the South China Sea in January–March is strongly correlated with monsoon onset timing. This insight can be used to predict future onset timing competitively compared with more complex forecast models. Key Points: Recent theoretical studies have revealed feedbacks at work during monsoon onsetIf the spring atmosphere is in a state where these feedbacks are easily triggered, onset is earlierThis insight is used to produce a simple forecast of South China Sea Monsoon onset timing [ABSTRACT FROM AUTHOR]

Mila Zinkova begins this issue weather of Weather with the second in a fascinating series of papers investigating the 'mirage theory' of the Titanic disaster with an examination of the haze reported by lookouts in 'Titanic's mirage, part 2: Did a mysterious mirage‐associated haze camouflage the iceberg?' on p. 151. On 24 April 2017 there was a significant remobilisation of ash deposits in southern Iceland left over from the huge eruptions of Eyjafjallajökull in 2010 and Grímsvötn in 2011. Krista Hammond and Frances Beckett investigate the specific meteorological conditions that led up to the event on p. 167 in 'Forecasting resuspended ash clouds in Iceland at the London VAAC'. The Sumatra squall is a common and yet highly disruptive weather system that affects part of the south‐east Asia region. On p. 176, Man Yau Chan, Jeff Chun‐Fung Lo and Thomas Orton examine the structure of one event in detail with a view to understanding the dynamics in order to improve forecasting of these features in 'The structure of tropical Sumatra squalls'. Staying in the tropics, on p. 181 in 'Monsoon tropical cyclones: Part 3', David Membery looks into the meteorology and impact of five destructive tropical cyclones that have affected the Arabian sea and considers the long‐term trends in their occurrence. The application of satellite technology has been a rapidly expanding field in recent years. In our final paper this month on p. 186, C. Purna Chand, M. V. Rao, K. V. S. R. Prasad and K. H. Rao bring us some important research on the use satellite sensing to estimate low‐level circulations in 'Validation of global sea‐level pressure fields calculated from Oceansat‐2 scatterometer wind data using the UWPBL model'. [ABSTRACT FROM AUTHOR]

A growing body of research has underscored the radiative impact of mineral dust in influencing Indian summer monsoon rainfall variability. However, the various aerosol‐cloud‐precipitation interaction mechanisms remain poorly understood. Here we analyze multisatellite observations to examine dust‐induced modification in ice clouds and precipitation susceptibility. We show contrasting dust‐induced changes in ice cloud regimes wherein despite a 25% reduction in ice particle radius in thin ice clouds, we find ~40% increase in ice particle radius and ice water path in thick ice clouds resulting in the cloud deepening and subsequently strengthened precipitation susceptibility, under strong updraft regimes. The observed dust‐ice cloud‐precipitation interactions are supported by a strong correlation between the interannual monsoon rainfall variability and dust frequency. This microphysical‐dynamical coupling appears to provide negative feedback to aerosol‐cloud interactions, which acts to buffer enhanced aerosol wet scavenging. Our results underscore the importance of incorporating meteorological regime‐dependent dust‐ice cloud‐precipitation interactions in climate simulations. Plain Language Summary: The Indian summer monsoon is the central source of freshwater availability to the densely populated regions of southern Asia. The monsoon circulation and rainfall variability are widely known to be governed by large‐scale atmosphere‐land‐ocean dynamics, meteorological processes, and air‐sea interactions. In the past two decades, the role of atmospheric aerosols has emerged as a source of modulating monsoon rainfall, as suggested by a host of climate modeling studies. In this paper, we have investigated a new aspect of aerosols in possibly influencing monsoon clouds and rainfall by specifically examining interaction between mineral dust aerosols and ice clouds, as part of the monsoon system. Using state‐of‐the‐art information derived for aerosols and clouds from multisensor and disparate satellite observations spanning 11 years, we find characteristic signature of dust aerosol‐induced modification of thick ice clouds (so‐called cloud invigoration effect) toward strengthened susceptibility of monsoon precipitation. Overall, our results shed new light on the potential role of dust and ice cloud interactions in modulating the Indian summer monsoon. Key Points: Elevated dust‐induced microphysical‐dynamical coupling in thick ice clouds amplifies ice cloud formation under favorable meteorologyStrengthened summer monsoon precipitation susceptibility is linked to dust‐induced changes in ice clouds under strong updraft regimesMicrophysical‐dynamical coupling provides negative feedback to aerosol‐cloud interaction and buffers the enhanced aerosol wet scavenging [ABSTRACT FROM AUTHOR]

Whether the South Asian summer monsoon (SASM) is controlled by local or remote insolation at the orbital band remains uncertain. Here, we perform a transient simulation forced by Earth's orbital parameters between 400 and 350 ka BP, a period characterized by significant contrast between local and remote insolation, to identify the SASM's response to insolation forcing. Simulation results suggest that the primary driver of orbital‐scale SASM variability is the Northern Hemisphere high‐latitude June insolation, as opposed to local insolation. High June insolation in the Southern Hemisphere might reduce the SASM intensity. Remote insolation influences the SASM by altering the latitudinal thermal gradient and, consequently, the meridional position of the South Asian high (SAH). The SAH is associated with intense convection and hence drives the meridional shift of the intertropical convergence zone and the SASM rain belt. Thus, orbital‐scale SASM variability is strongly related to remote insolation forcing. Plain Language Summary: Because the monsoon is directly related to the movement of the subsolar point, insolation changes are important in regulating the South Asian summer monsoon (SASM) intensity at an orbital timescale. However, it remains unclear whether the SASM is driven by local insolation that directly strikes southern Asia, or remote insolation in the high‐latitude Northern Hemisphere or the Southern Hemisphere at the precession band. We find a time window between 400 and 350 ka BP (ka = thousand years, BP = before present) when local and remote insolations differ significantly, allowing us to determine which insolation dominates the SASM at orbital timescales. We use an Earth system model with orbital forcing to run a transient simulation between 400 and 350 ka BP. Simulations suggest that the SASM is primarily influenced by Northern Hemisphere high‐latitude summer insolation rather than local insolation. Additionally, Southern Hemisphere insolation has a negative impact on orbital‐scale SASM variability. Remote insolation influences the SASM by inducing an anomalous meridional thermal gradient, which moves the South Asian high and thus the Intertropical Convergence Zone. Our findings are significant for future SASM projections because the obvious difference between remote and local insolation will reappear in the next 50 ka. Key Points: Local insolation is not the direct driver for orbital‐scale variability of the South Asian summer monsoon (SASM)The meridional shift of the South Asian high (SAH) affects orbital‐scale SASM variabilityRemote insolation influences the meridional shift in the SAH through altering the latitudinal thermal contrast [ABSTRACT FROM AUTHOR]

Water isotopes‐climate correlations are used to reconstruct paleoclimate from various natural archives. Intra‐seasonal oscillation is one of the major atmospheric patterns that modulate the ratio of precipitation isotope in low latitudes, yet their spatial and temporal distribution patterns are unclear. Here we presented a detailed analysis of how the intra‐seasonal oscillations (MJO, Madden‐Julian Oscillation, and BSISO, Boreal Summer Intra‐seasonal Oscillation) modulate precipitation δ18O and vapor δ18O over the Asian monsoon region and the equatorial region. This analysis found consistent intra‐seasonal variations between the ISO and rain δ18O. We interpret it as the ISO regulating the active and inactive convective systems on the regional scale, leading to the intra‐seasonal oscillations in precipitation δ18O, with amplitudes from 4‰ up to 15‰. The MJO (BSISO) leads to eastward (northeastward) propagation of δ18O intra‐seasonal oscillations in the Asian equatorial (monsoon) region, coinciding with the spatial patterns of OLR oscillations, reflecting the response of precipitation/vapor δ18O to the oscillation of large‐scale convective activity or accumulated depletion of regional precipitation. We proved that the amplitudes of intra‐seasonal variation of precipitation δ18O are comparable to seasonal variations, and both of them are the main patterns for precipitation δ18O in study regions. Our results are conducive to the accurate interpretation of δ18O in climate proxies such as precipitation, ice cores, tree cellulose, cave stalagmites, et al. on the intra‐seasonal scale in this region. Plain Language Summary: Periodicity is a phenomenon in which similar characteristics or states of things reappear steadily and continuously. The Tropical Intra‐seasonal Oscillation (Andersen et al., 2004, https://doi.org/10.1038/nature02805) is the reappearance of a large‐scale envelope of more abundant convective rain systems moving eastward in the tropical regions with a typical oscillatory period of 30–60 days. The ratios of H218O and HDO vary during the cycle of continuous circulation of water in the atmosphere, and therefore are widely used as proxies for climate records. We used the measured data of precipitation or vapor isotopes to reveal that the propagation of ISO can be recorded by the ratio of H218O covering Asian tropical and monsoon regions. Furthermore, the increased (decreased) ISO intensity leads to the increased (decreased) amplitude of convection intensity, which results in the increased (decreased) amplitude of the H218O ratio in precipitation or vapor. Key Points: The intra‐seasonal oscillations are one of the main patterns of precipitation δ18O covering the Asian monsoon and equatorial regionsThe stronger δ18O intra‐seasonal oscillation corresponds to the season with active convective activities, more rainfall, and low‐level δ18OThe stronger regional convective intensity leads to the cumulative effect in the depletion of rain δ18O during the convective phases of ISO [ABSTRACT FROM AUTHOR]

Rainfall in the Asia summer monsoon (ASM) domain has a complex spatial pattern with the temporal variability at different timescales and their long‐term change has not been fully characterized. An updated 320 multiple proxies network is used to reconstruct the May–October precipitation during the past millennium for eight regions in the ASM domain. The spatial consistency of summer monsoon precipitation variability and the possible links to the internal climate oscillations are investigated. The results show that the regional precipitations over the last millennium in the ASM regions are dominated by the interannual cycle of 2–2.5a and 3.5‐5a, the decadal cycle of ~11a and 15–25a and the multidecadal cycle of ~30a and 40–80a. Coherent dry decades in different regions appear in 1100–1250, 1600–1650 and 1960–2000, while the wet decades appear in 970–990, 1330–1350, 1380–1430, 1550–1580, 1700–1780 and 1810–1910. On interannual scale, the relationships between precipitation for each region and El Niño–Southern Oscillation (ENSO) in both developing and decaying stages are unstable over the entire millennium, but they have opposite‐sign correlations most of the time, which implies that the summer precipitation anomaly for a region tends to reverse in the next summer when a strong ENSO event occurs in the winter. For the long‐term change from multidecadal to centennial scales, the longest dry period of the 12th to 13th centuries in eastern Asia coincides with the period with the lowest ENSO variability due to the in phase change of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation, which could result in the neutral interbasin east–west cell in Tropics and low frequency of ENSO events. [ABSTRACT FROM AUTHOR]

In the East Asian monsoon region, eolian deposits widely distributed in the middle-lower reaches of the Yantgze River are among the best materials available for studies on Quaternary climate change in the subtropical zone of Southern China. Typical eolian deposits in this region include upper Xiashu Loess (XL) and underlying Vermiculated Red Soil (VRS) layers. In this paper, chronological and paleoclimatic studies are conducted on an eolian deposit sequence near Jiujiang (JJ) city in northern Jiangxi province. A magnetostratigraphic study, combined with optically stimulated luminescence (OSL) dating, is conducted on the JJ section and provides further evidence that eolian deposits in the middle-lower reaches of the Yangtze River have been formed since the late Early Pleistocene, and that the boundary age between the XL and VRS layers is about 300-400 kaBP. In grain-size records of the JJ section, the median grain-size and content of the >30 μm size fraction increase sharply after 300-400 kaBP, representing an East Asian winter monsoon intensification event. Further pollen analysis reveals differing pollen assemblages before and after 300-400 kaBP: there is an evident increase in plants adapted to grow in a warm humid environment after 300-400 kaBP, implying an increase in precipitation caused by intensification of the East Asian summer monsoon. Global ice volume and uplift of the Tibet Plateau (TP) are regarded as crucial factors influencing variations of the East Asian monsoon on a long-term scale. The deep-sea δ18O record, which reflects variations in global ice volume, shows no obvious change after 300-400 kaBP. Moreover, the influence of global ice volume changes on the East Asian summer and winter monsoons is inverse; the global ice volume increase (decrease) implies a strengthened (weakened) winter monsoon and weakened (strengthened) summer monsoon. We therefore interpret the coupled intensifications of the East Asian summer and winter monsoons at about 300-400 kaBP to the uplift of the TP in the Middle Pleistocene. This climate event is also documented in eolian deposits from the southern margin of the Chinese Loess Plateau (CLP) and from the desert-loess transitional belt. However, it is not recorded in the loess-paleosol sequences from the central part of the CLP, thereby indicating differing climate responses to TP uplift in different regions, which requires further study. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, interannual variations of convective and stratiform precipitations in summer East Asian monsoon ( SEAM) dominion are analysed using 16-year (1998-2013) Tropical Rainfall Measuring Mission ( TRMM) precipitation radar ( PR) rain products ( 2A25 and 3A25). It is found that the climatological mean patterns of convective and stratiform rain rates ( RRs) are generally similar to each other, but the area fraction ( AF) of stratiform precipitation can always reach about 80% and dominates in summer East Asia. Nonetheless, convective precipitation produces similar rainfall quantity with stratiform rainfall. For the RR, AF and contribution fraction ( CF), their interannual standard deviation and coefficient of variation ( CV) spatial patterns are similar between summer convective and stratiform precipitations in East Asia, because of the fact that they are all maybe influenced by SEAM. Differently, only the intensity of interannual variability (i.e. CV) for convective precipitation AF is much greater than that for stratiform precipitation, while CV for both convective and stratiform precipitations RR/ CF are similar in most areas. Moreover, the interannual variability of SEAM is more highly correlated with that of RR for convective precipitation than that for stratiform precipitation in most land regions. While the opposite conclusion is found in ocean regions. Generally, the SEAM intensity in the lower troposphere mainly controls interannual variability of the atmospheric stability and both stratiform and convective precipitations RR. Then, atmospheric stability variation further modulates the AF and CF variations of both stratiform and convective precipitations on the interannual scale. This work mainly provides possible evidence of linkage between large-scale circulation and convective and stratiform precipitations on the interannual scale. It suggests that the possible dominant mechanism should be explored using more observations and together with model simulations in the future work. [ABSTRACT FROM AUTHOR]

The long‐term evolution of the East Asian Monsoon and the processes controlling its variability under changing climate boundary conditions remain enigmatic. Here, we integrate new and published high‐resolution planktic and benthic foraminiferal isotope data with proxy records for chemical weathering derived from diffuse reflectance spectroscopy at Ocean Drilling Program Site 1146 (South China Sea) to reconstruct the evolution of the summer monsoon between ∼17 and 5 Ma. Our records show that an overall warm and humid tropical climate prevailed over southeastern Asia during the Miocene Climatic Optimum, suggesting northward expansion of the tropical rain belt in response to greenhouse gas forcing. By contrast, monsoon seasonality increased during the middle Miocene Climatic Transition in tandem with Antarctic glacial expansion and global cooling. Substantial weakening of the summer monsoon between ∼12.7 and 10.9 Ma supports that decreased weathering and riverine input of nutrients and alkalinity contributed to carbonate depletion in the deep ocean during the Carbonate Crash. Intensification of monsoonal circulation and strengthening of the biological pump through the late Miocene promoted carbon burial, drawdown of atmospheric CO2, and climate cooling during the Biogenic Bloom. These results underscore the dynamic evolution of the East Asian Monsoon throughout the middle to late Miocene. Variations in local insolation forcing and in Southern Hemisphere ice volume, influencing the latitudinal thermal gradient, evaporation‐moisture budgets, and the strength of the tropical convection, exerted major controls on the development of the monsoon. Key Points: Equable, warm, and humid climate over Southeast Asia during Miocene Climatic Optimum due to latitudinal expansion of tropical convectionIntensification of seasonal monsoonal regime linked to stepwise climate cooling during middle Miocene Climatic TransitionDecreased riverine input of alkalinity to ocean due to summer monsoon decline contributed to middle to late Miocene Carbonate Crash [ABSTRACT FROM AUTHOR]

Despite the well‐known biogeographic pattern in the Northern Hemisphere of disjunct distributions in plants between eastern Asia and North America, many details regarding the evolution of the disjunction between lineages of tropical Asia and tropical America remain poorly understood. Berchemia (Rhamnaceae), comprising ca. 32 species, is distributed predominantly in tropical regions of east to southeast Asia and North America. However, the phylogeny and biogeography of this genus are still not clear. Furthermore, fossils of the genus have been found in Europe, making it an ideal group to understand the biogeographical story of tropical disjunction in the Northern Hemisphere. With two nuclear (ETS, ITS) and three plastid (petA‐psbJ, psbA‐trnH, trnL‐F) DNA regions, we first reconstructed the phylogeny of Berchemia with Bayesian inference and maximum likelihood approaches. Our results indicated that Berchemia, excluding the African species B. discolor and B. zeyheri, which were placed into the reinstated Phyllogeiton, was well‐supported as monophyletic. Divergence times and ancestral areas were inferred using a Bayesian uncorrelated lognormal relaxed molecular clock model and Bayesian binary MCMC method, respectively. The core Berchemia likely originated in the Western Tethys during the middle Eocene, then formed the tropical Asia and tropical America disjunction during the Oligocene and further diversified in Asia from the early Miocene on. The formation and diversification of the core Berchemia likely resulted from a mixture of geologic events, such as the close of the Tethys Ocean, disappearance of the North Atlantic Land Bridges, uplift of the Qinghai‐Tibetan Plateau, and climatic events, such as the establishment and enhancement of Asian monsoons. [ABSTRACT FROM AUTHOR]

This study explores how the Indian Summer Monsoon rainfall simulations are affected by the mathematical representations of the planetary boundary and microphysics parameterizations at a gray zone resolution. The monsoon is simulated with the Weather Research and Forecast model at a 9 km horizontal resolution over South–East Asia for three different years, chosen to represent early, normal, and delayed monsoon onset. Changing the boundary layer from a hybrid to a local scheme dramatically impacts the monsoon simulation, reducing around 40% in total rainfall. In contrast, changing the microphysics scheme has a less pronounced impact (5%) on the precipitation but still induces regional variations. To assess how physical parameterization changes affect South Asia's rainfall, we evaluate their impact on both the energy and moisture budgets over the subcontinent. It is revealed that local changes in evaporation do not directly drive changes in precipitation. Instead, changes in the regional distribution of the energy sources and sinks modify the atmospheric circulation, which affects the distribution of rainfall. In particular, the boundary layer changes can substantially increase the latent heat flux, strengthening the monsoon. In the tropics, overturning circulation that exports energy is tied to a net inflow of water. Thus, the intensification of the monsoonal circulation results in an enhanced water inflow and increased rainfall. Plain Language Summary: The high resolution atmospheric model can produce realistic monsoon simulations, and such simulations are highly sensitive to the physical parameterizations used in the model. Current research reveals how cloud microphysics and planetary boundary layer can severely affect the precipitation patterns over India. In this study, a monsoon is simulated using the Weather Research and Forecast model at a 9 km horizontal resolution over south Asia during 2007, 2008, and 2015, representing an early, normal, and delayed monsoon onset. It has been found that changing the boundary layer scheme from hybrid to local scheme has a dramatic impact on simulation, with a reduction of around 40% in total rainfall. Simulations with a hybrid scheme capture most of the circulations and precipitations patterns, but the local scheme leads to an overall weaker monsoonal strength. Different microphysics parameterizations show similar total rainfall distributions (5% variations) but exhibit regional variabilities. Key Points: Weather Research Forecast (WRF) can accurately reproduce the monsoon precipitation distribution but exhibit sensitivity to physical processesChanges to planetary boundary layer parameterizations cause around 40% change in seasonal precipitationIncreased heating intensifies the overturning circulation, exports more energy, and thus import more rainfall [ABSTRACT FROM AUTHOR]

The projected monsoon hydrological sensitivity, namely, the precipitation change rate per kelvin of global warming, shows substantial intermodel spread among 40 Coupled Model Intercomparison Project phase 5 models. The hydrological sensitivity of the Northern Hemisphere summer monsoon is negatively correlated with that of the Southern Hemisphere summer monsoon. The intermodel spread of the Northern Hemisphere summer monsoon hydrological sensitivity is mainly attributed to the projected interhemispheric temperature gradients and the associated low‐level cross‐equatorial flows. The intermodel spread of the Afro‐Asia summer monsoon sensitivity is rooted in the projected continent‐ocean thermal gradients, while the spread of the North American monsoon sensitivity is related to the projected sea surface temperature pattern in the tropical eastern Pacific and Atlantic. These findings suggest that further constraining monsoon hydrological sensitivity requires a better projection of the warming rate between the Northern and Southern Hemispheres and between the land and ocean, and the sea surface warming pattern in the tropical eastern Pacific and Atlantic. Plain Language Summary: Global monsoon precipitation has far‐reaching impacts on agriculture planning and social‐economic sustainable development. Previous studies suggested that the increasing of global monsoon precipitation is sensitive to global warming rate, but the precipitation sensitivities, i.e., the precipitation change rate per kelvin of global warming, are also different among state‐of‐the‐art coupled models. The causes of uncertainty in the monsoon precipitation sensitivity and the associated dominant physical mechanism remain elusive. Based on 40 state‐of‐the‐art coupled climate models, we reveal that the greenhouse gas‐induced interhemispheric temperature gradient causes the uncertainty of global monsoon precipitation sensitivity by changing the strengths of monsoon circulation and Hadley circulation and altering the Intertropical Convergence Zone position. Our results highlight the importance of a reliable projection of interhemispheric differential warming to the future change of global monsoon precipitation. Key Points: Substantial intermodel spread of GM hydrological sensitivity in the CMIP5 models is foundThe intermodel spread of projected GM hydrological sensitivity could be attributed to the projected interhemispheric temperature gradientThe intermodel spread of regional monsoon hydrological sensitivity is attributed to the projected land‐ocean temperature gradient and SST pattern [ABSTRACT FROM AUTHOR]

This study investigates changes in the East Asian winter monsoon (EAWM) under 1.5 and 2.0°C global warming (1.5 and 2.0GW) targets using multi‐model results from the Coupled Model Intercomparison Project phase 5 (CMIP5). It is found that the surface air temperature increases over the Asian continent and Pacific, and the precipitation increases over the northern Asian continent in winter during the 1.5 and 2.0GW periods. For the 1.5GW period, large uncertainties can be found in the projection of EAWM system members (i.e., Siberian high, Aleutian low, low‐level winds over eastern Asia, East Asian trough [EAT] and East Asian jet stream [EAJS]). For the 2.0GW period, more than two‐thirds of the models show that the Siberian high, the EAT and the meridional shear of the EAJS are weakened, but the Aleutian low is intensified. In addition, the intensified Aleutian low enhances low‐level northwesterly wind along the coast of northeastern Asia. Compared to those in the 1.5GW period, the EAWM system members show more robust changes during the 2.0GW period, except for the low‐level winds at mid‐latitude eastern Asia. These conclusions are suitable for both the RCP4.5 and RCP8.5 scenarios. [ABSTRACT FROM AUTHOR]

Speleothem δ18O is widely used to reconstruct past hydroclimate variability, particularly over Asia. However, the interpretation of this proxy is still in debate. While this proxy is originally interpreted as regional rainfall amount of the Asian monsoon, other studies have interpreted it as upstream monsoon rainfall or atmospheric circulation changes. To better understand the signal preserved in speleothems over various time scales, this study employs a state‐of‐the‐art isotope‐enabled climate model to quantify contributions to the oxygen isotope composition of precipitation (δ18OP) over China. Results suggest that orbital‐scale speleothem δ18O variations at Chinese sites mainly record the meridional migration of the Asian monsoon circulation, accompanied by an early northward movement of the East Asian rain belt. At interannual scales, Chinese speleothem δ18O is also tied to the intensity of monsoonal circulation, via a change in moisture source locations: Enhanced moisture delivery from remote source regions leads to more negative δ18OP, particularly in late summer and early autumn. Our results have implications for the hydroclimatic interpretation of speleothem δ18O from Chinese caves and suggest that this interpretation is time scale dependent. Key Points: At orbital scales, Chinese speleothem oxygen isotopes mainly represent the meridional migration of the East Asian monsoon circulationAt orbital scales, low values of Chinese speleothem oxygen isotopes are associated with early northward movement of the East Asian rainbeltAt interannual scales, Chinese speleothem oxygen isotope ratios are mainly controlled by the change of moisture source locations [ABSTRACT FROM AUTHOR]

The Japan Sea is directly influenced by the Asian monsoon, a system that transports moisture and heat across southeast Asia during the boreal summer, and is a major driver of the Earth's ocean‐atmospheric circulation. Foraminiferal and facies analyses of a 460‐kyr record from Integrated Ocean Drilling Program Expedition 346 Site U1427 in the Japan Sea reveal a record of nutrient flux and oxygenation that varied due to sea level and East Asian monsoon intensity. The East Asian summer monsoon (EASM) was most intense during marine isotope stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c when the Tsushima Warm Current flowed into an unrestricted well‐mixed normal salinity Japan Sea, whereas East Asian winter monsoon (EAWM) conditions dominated MIS 2, MIS 4, MIS 6, and MIS 8 when sea level minima restricted the Japan Sea resulting in low‐salinity and oxygen conditions in the absence of Tsushima flow. Reduced oxygen stratified, low‐salinity, and higher productivity oceanic conditions characterize Terminations TV, TIII, TII, and TI when East China Sea coastal waters breached the Tsushima Strait. Chinese loess, cave, and Lake Biwa (Japan) and U1427 proxy records suggest EASM intensification during low to high insolation transitions, whereas the strongest EAWM prevailed during lowest insolation periods or high to low insolation transitions. Ice sheet/CO2 forcing leads to the strongest EAWM events in glacials and enhanced EASM in interglacials. Mismatches between proxy patterns suggest that latitudinal and land/sea thermal contrasts played a role in East Asian monsoon variability, suggesting that a complex interplay between ice sheet dynamics, insolation, and thermal gradients controls monsoonal intensity. Key Points: East Asian summer monsoon intensified in MIS 5, MIS 7, MIS 9, and MIS 11 when the Tsushima Current flowed into an unrestricted normal marine Japan SeaEast Asian winter monsoon dominated MIS 2, MIS 4, MIS 6, and MIS 8 when sea level lows restricted the Japan Sea causing low‐salinity and oxygen conditionsReduced oxygen stratified, low‐salinity, and higher productivity oceanic conditions characterize Terminations TV, TIII, TII, and TI [ABSTRACT FROM AUTHOR]

We investigate the daily variability of the East Asian summer monsoon (EASM) by projecting daily wind anomaly data onto the two major modes of an interannual multivariate Empirical Orthogonal Functions analysis. Mode 1, closely resembling the Pacific–Japan (PJ) pattern and referred to as PJ‐mode, transits from positive to negative phase around mid‐summer consistent with the Meiyu rains predominantly being an early summer phenomenon. Mode 2, which is influenced by the Indian summer monsoon (ISM) and referred to as ISM‐mode, peaks in late July and early August and is associated with rainfall farther north over China. We then analyze the relation between the intraseasonal variation of the EASM and the Madden–Julian Oscillation (MJO) by analyzing circulation anomalies following MJO events. In the lower troposphere, the circulation anomalies associated with the MJO most strongly project on the PJ‐mode. MJO phases 1–4 (5–8) favor the positive (negative) phase of the PJ‐mode by favoring the anticyclonic (cyclonic) anomalies over the subtropical western North Pacific. In the upper troposphere, the circulation anomalies associated with the MJO project mainly on the ISM‐mode. [ABSTRACT FROM AUTHOR]

The genesis of tropical disturbances in strong and weak monsoon trough (MT) patterns is examined in an idealized model. The initial MT patterns in the model simulations are obtained from a global reanalysis dataset that encompasses a 29‐year period. The simulations show that a tropical disturbance tends to develop over the eastern part of western North Pacific (WNP) near 150°–160°E when the MT extends eastward, whereas a tropical disturbance tends to occur over the western part of the WNP near 120°–130°E when the MT retreats westward. In addition, there is a faster development of tropical disturbance with a greater intensity in the strong MT pattern than that in the weak MT pattern. The tropical disturbances are triggered in the most convectively unstable region through the local dynamic and thermodynamic processes in the strong and weak MT patterns. [ABSTRACT FROM AUTHOR]

ABSTRACT This study investigates surface winds blowing through the Taiwan Strait using scatterometer wind measurements and atmospheric reanalysis data to present climatological features specific to northeasterly and southwesterly along-strait winds. For both the northeasterly and southwesterly along-strait winds, strong winds occur within the strait and originate from the southern tip of Taiwan Island. Between these strong wind regions, weak winds are formed in the lee of Taiwan Island. This contrastive wind structure extends downwind. While fluctuating winds are aligned with the strait throughout the year, the northeasterly and southwesterly along-strait winds exhibit contrastive seasonal variations. The northeasterly along-strait winds predominantly occur in the cool season and are induced by the East Asian winter monsoon when the developed Siberian high with cold air moves southward to cover the Asian continent and a cyclone develops to the southeast of Japan. The monthly mean speeds of the northeasterly along-strait winds rapidly increase, coincident with the onset of the winter monsoon, and gradually weaken with seasonal advance. The southwesterly along-strait winds often occur in the warm season. Although the speeds reach a maximum in the warm season, they are less than the seasonal minimum speeds for the northeasterly along-strait winds. In the warm season, tropical cyclones approaching Taiwan Island from the southeast create a large pressure gradient across the strait and induce the strong northeasterly along-strait winds. The southwesterly along-strait winds blow along the western periphery of the Pacific high developing westward. Tropical cyclones after making landfall on the Asian continent also contribute to the southwesterly along-strait winds. [ABSTRACT FROM AUTHOR]

ABSTRACT Drought is a recurrent natural disaster in northwestern China and it can have a substantial impact on the affected region; therefore, knowledge of drought variability is very important for drought adaptation and mitigation. However, the observed climate data are generally limited in length, which may hamper our understanding the full range of drought variability. Using tree-ring width measurements of 155 series from 81 Pinus tabulaeformis trees at three sites in the northern Min Mountains of northwestern China, the standardized precipitation evapotranspiration index ( SPEI) for May-August from 1804 to 2011 were reconstructed, which account for 64.8% of the variance in the instrumental record over 1954-2011. The new reconstruction is generally consistent with other moisture reconstructions nearby. Two notable features of the SPEI reconstruction is the severe drought starting in the late 1990s and the gradual drying trend since 1954. These features are also apparent in areas located in the north boundaries of Eastern Asian Summer Monsoon ( EASM), which indicates that the study area may be affected by the EASM. [ABSTRACT FROM AUTHOR]

Qinghai Lake is of significance for paleoclimate research because it lies in a pivotal region that is influenced by both the mid-latitude Westerlies and the low-latitude Asian summer monsoon (ASM). Most published lake level histories of Qinghai Lake are interpreted from drill-core proxies. Here we combine geomorphic shoreline investigations with optically stimulated luminescence dating to constrain lake level variations since the last deglacial. The results indicate that two periods of highstands occurred during the last deglacial (∼16-14.9 and ∼12.6-12.2 ka), and that lake levels were 6-7.4 m higher than at present. Lake levels dropped abruptly during the Younger Dryas, and were generally low with frequent fluctuations during the early Holocene. Qinghai Lake reached its highest Holocene level, 9.1 m higher than modern, at ∼5 ka, and has regressed during the past 2 ka. We propose that high lake levels during the last deglacial were due mainly to melting glacial and permafrost waters, supplemented by enhanced Westerlies precipitation and decreased evaporation during Heinrich Event 1 (∼16-14.9 ka) and increased ASM rainfall during the Bølling-Alleröd warm period (∼14-12 ka). Lake level fluctuations during the Holocene were generally in accordance with moisture variations in the marginal monsoon zones of inland China. [ABSTRACT FROM AUTHOR]

We present a new reconstruction of summer sea-surface salinity ( SSS) over the past 15 000 years based on a diatom record from piston core 17940, located on the northern slope of the South China Sea ( SCS). The reconstructed diatom-based summer SSS values for the modern period are in accord with instrumental observations of summer SSS in the area. Here, the modern summer SSS is primarily controlled by river runoff, in particular from the Pearl River. The reconstruction presented in this study shows that the summer SSS varied between 33.3 and 34.2 psu over the past 15 000 years. The long-term summer SSS trend closely followed the trend of the orbitally controlled solar insolation at 20° N, suggesting that orbital forcing was the dominant driver of changes in summer SSS in this area. Comparisons to speleothem δ 18O data and studies of surface hydrography in the region suggest that changes in solar insolation affected the summer SSS through changes in the East Asian Monsoon and sea-level changes associated with the last deglaciation. Univariate spectral analyses indicate that centennial-scale oscillatory variations in summer SSS were superimposed on the long-term trend. During the deglacial period ( c. 12 000-9000 cal. a BP), the dominant periodicity was centred around 230-250 years, whereas a ∼350-year oscillation dominated in the period 2200-4500 cal. a BP. The balance of evidence suggests that these centennial-scale changes in summer SSS may have been driven by solar-induced changes in the East Asian Monsoon, but further evidence is needed to firmly establish this relationship. [ABSTRACT FROM AUTHOR]

Eocene palynological samples from 37 widely distributed sites across China were analysed using co-existence approach to determine trends in space and time for seven palaeoclimate variables: Mean annual temperature, mean annual precipitation, mean temperature of the warmest month, mean temperature of the coldest month, mean annual range of temperature, mean maximum monthly precipitation and mean minimum monthly precipitation. Present day distributions and observed climates within China of the nearest living relatives of the fossil forms were used to find the range of a given variable in which a maximum number of taxa can coexist. Isotherm and isohyet maps for the early, middle and late Eocene were constructed. These illustrate regional changing patterns in thermal and precipitational gradients that may be interpreted as the beginnings of the modern Asian Monsoon system, and suggest that the uplift of parts of the Tibetan Plateau appear to have taken place by the middle to late Eocene. [ABSTRACT FROM AUTHOR]

A high-resolution palaeorecord (06SD) from Lake Shudu, Yunnan Province, southwestern China indicates a broad trend towards catchment stability, enhanced organic productivity and regional forest-cover expansion during the early to mid Holocene. These changes are congruent with a shift to warm, wet climatic conditions, probably driven by orbitally forced Asian summer monsoon strengthening. Intriguingly, however, during the very early Holocene ( c. 10.7 to 10.1 cal. ka BP), there is a prominent reversal in this trend, suggesting a weakening Asian summer monsoon. The precise cause and extent of this event remain unclear but demonstrate the urgent need for more comprehensive dating of records from across the region to test for synchroneity and examine climatic forcing mechanisms. [ABSTRACT FROM AUTHOR]

Considering the complex spatial and vertical structure of the South Asian summer monsoon (SASM), the validation of a regional climate model (RCM) dealing with only a few surface variables is considered insufficient. Therefore, we have proposed an evaluation framework for the better assessment of the capability of an RCM in capturing the fundamental structure of SASM. This framework has been applied to the regional climate model REMO using ERA40 lateral boundary conditions for the period 1961-2000. The application of framework yielded satisfactory performance of REMO in capturing the lower, middle, and upper component of the SASM circulation. REMO has higher correlation between different SASM indices as compared to ERA40, showing its ability in capturing the dynamical link between these indices better than ERA40. We have employed different criteria for the assessment of the monsoon onset, and the movement of the Intertropical Convergence Zone (ITCZ) during the boreal summer and REMO has captured these phenomena reasonably well. The model has also shown the association of the meridional temperature gradient with the easterly shear of zonal winds. These results lead us to the conclusion that REMO is well suited for long-term climate change simulations to examine projected future changes in the complex SASM system. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Previous observational studies have found a persistent maximum in stratospheric water vapor (SWV) in the upper troposphere lower stratosphere (UTLS) confined by the upper‐level anticyclone over the Asian summer monsoon region. This study investigates the simulation of SWV in the Community Earth System Model, version 1 with the Whole Atmosphere Community Climate Model as its atmospheric component [CESM1(WACCM)]. CESM1(WACCM) generally tends to simulate a SWV maximum over the central Pacific Ocean, but this bias is largely improved in the high vertical resolution version. The high vertical resolution model with increased vertical layers in the UTLS is found to have a less stratified UTLS over the central Pacific Ocean compared with the low vertical resolution model. It therefore simulates a steepened potential vorticity gradient over the central Pacific Ocean that better closes the upper‐level anticyclone and confines the SWV within the enhanced transport barrier. Key Points: The discrepancies in simulating SWV over the Asian summer monsoon region are commonly found in WACCM experimentsThe UTLS temperature over the central Pacific Ocean is crucial in confining the SWV within the Asian summer monsoon anticycloneModel with high vertical resolution resolves the UTLS temperature more accurately which better confines the SWV within the transport barrier [ABSTRACT FROM AUTHOR]

This study presents the first algal thallus (skeleton) archive of Asian monsoon strength and Red Sea influence in the Gulf of Aden. Mg/Ca, Li/Ca, and Ba/Ca were measured in Lithophyllum yemenense from Balhaf (Gulf of Aden) using laser ablation inductively coupled plasma mass spectrometry, and Mg/Ca ratio oscillation was used to reconstruct the chronology (34 y). Oscillations of element rates corresponding to the algal growth between 1974 and 2008 were compared with recorded climate and oceanographic variability. During this period, sea surface temperatures ( SST) in Balhaf recorded a warming trend of 0.55°C, corresponding to an increase in Mg and Li content in the algal thallus of 2.1 mol-% and 1.87 μmol-%, respectively. Lithophyllum yemenense recorded decadal SST variability by Li/Ca, and the influence of the Pacific El-Niño Southern Oscillation on the NW Indian Ocean climate system by Ba/Ca. Additionally, algal Mg/Ca, Li/Ca, and Ba/Ca showed strong and significant correlations with All Indian Rainfall in the decadal range indicating that these proxies can be useful for tracking variability in the Indian monsoon system, possibly due to changes of the surface wind system, with deep water upwelling in summer, and a distinct seasonality. [ABSTRACT FROM AUTHOR]