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The onset of the South China Sea summer monsoon (SCSSM) heralds the establishment of the large-scale East Asian summer monsoon and the western North Pacific summer monsoon, as well as the beginning of the major rainy season. The occurrence of an early or late SCSSM onset is an important indicator for the summertime climate anomalies over East and Southeast Asia. Therefore, the onset of the SCSSM has received extensive research attention, and has been one of the key foci of monsoon research in recent decades. This paper reviews the multi-scale climate variations (from interdecadal to synoptic scales) and mechanisms of the SCSSM onset, with special attention paid to the progress in the past five years. On the interdecadal timescale, the SCSSM onset underwent a significant advancement in the mid-to-late 1990s, which may have been related to the background condition of the Pacific Ocean. On the interannual timescale, El Niño-Southern Oscillation (ENSO) is considered to be the most critical factor controlling the variability of the SCSSM onset. However, the linkage between ENSO and the SCSSM onset has become much weaker and insignificant in recent years. The intraseasonal oscillations (including the 30–60-day oscillation and quasi-biweekly oscillation) are important modulators of the SCSSM onset. The transition from an inactive phase to an active phase may be more worthy of attention than the phase itself. There appear to be close interactions between the SCSSM onset and synoptic-scale systems like tropical cyclones (TCs). TCs are important triggers for the SCSSM onset, while in return the SCSSM onset provides a favorable background condition for the formation and development of TCs. In addition, this paper also reviews a series of recent works on the withdrawal of the SCSSM. Finally, to close the paper, some important scientific issues worthy of further investigation are put forward. [ABSTRACT FROM AUTHOR]

The rainfall over the Indian region, governed majorly by the monsoonal flow, is a point of research in the perspective of climate change. In this paper, we compute the change points in the rainfall series at every grid of the India Meteorological Department (IMD) daily gridded rainfall data for a period of 120 years (1901 to 2020). The map shows clearly demarcated regions indicating different zones, where the rainfall statistics have altered at different periods. It is observed that in a major part of central India, the shift in rainfall intensity is mainly associated with the time frame 1955–1965; in the Indo-Gangetic plain, the changes are found to be more recent (1990), while the latest changes (post 2000) are observed particularly for North Eastern region and some parts along the East Indian coast. The changeover years are significant at a 95% confidence level for most part of the Indian landmass. The causes may be surmised due to moisture transport from the Arabian Sea (Central India), the presence of aerosol (Gangetic Plain), and the possible revival of monsoon due to land–ocean gradient (Eastern coast and North East India). This is the first-ever study which provides a comprehensive daily rainfall change point map over India using 120 years of gridded station data. [ABSTRACT FROM AUTHOR]

Projections of West African Monsoon (WAM) precipitation are uncertain. To address this, an improved understanding of the mechanisms driving WAM precipitation change is needed to shed light on inter-model differences and aid model development. The full forcing of increased CO2 can be decomposed into different components such as the impact of ocean warming, or the direct radiative effect of increased CO2. This paper investigates such a decomposition, analysing the effect of a uniform 4K ocean warming whilst keeping atmospheric CO2 concentrations constant. The analysis highlights several mechanisms acting to decrease WAM precipitation over a range of timescales, from days after the abrupt ocean warming, to the long-term equilibrium response. The initial decrease in WAM precipitation is caused by warming and enhanced convection over the ocean, stabilising the atmosphere inland and disrupting the monsoon inflow at low levels. Later in the response (after about 5 days), the WAM precipitation is reduced through a strengthening of the shallow circulation over West Africa, associated with changes in the large-scale temperature gradients and a local warming of the atmosphere related to a soil moisture feedback mechanism over the Sahel. Finally, from around 20 days after the SST increase, the WAM precipitation is also reduced through changes in specific humidity gradients that lead to increased potency of dry air advection into the monsoon rainband. The analysis concludes by demonstrating that the processes affecting precipitation in the early stages of the response are also relevant to the long-term equilibrium response. [ABSTRACT FROM AUTHOR]

Previous studies on the amplitude of East Asian summer monsoon (EASM) changes mainly focused on northern China (represented by the Loess Plateau). However, a rare investigation centered on the subtropical zone of southern China, where the important route for EASM moved northward or southward, especially addressing a lack of the research on mammals. The Ailuropoda-Stegodon fauna is a representative mammal fauna in southern China since the late Pleistocene. It indicates the southern mid-subtropical-tropical forest environment with tropical climate characteristics, and its southward or northward movements in the subtropical zone imply the changes of EASM intensity. Based on previous research, combined with the species characteristics and distribution range of the Ailuropoda-Stegodon fauna with tropical animals during the marine isotope stage 5 (MIS5), MIS3, MIS2, and MIS1 Megathermal periods, this paper mainly investigates its evolution and the fluctuations of EASM. The conclusions include: (1) The distribution geometric centers in the MIS5, MIS3, MIS2, and MIS1 Megathermal periods are (26°14′N, 111°22′E), (24°35′N, 107°30′E), (22°48′N, 112°01′E), and (26°19′N, 112°25′E), respectively. (2) Compared with the MIS5 period, the EASM of the MIS3 and MIS2 moved 180 km and 380 km southwards, and that of the MIS1 Megathermal period moved about 10 km northwards. The EASM movement indicated by the fauna migration happened synchronous with the climate records of stalagmites in subtropical China, the sporopollen from eastern China, and oxygen isotopes from Sulu Sea. They also correspond to the peaks and valleys of the total solar radiation at 35°N in the winter half-year. This suggests that the migrations of the Ailuropoda-Stegodon fauna are consistent with the changes of the global climate, and the driving force is mainly from the changes of total solar radiation at 35°N in the winter half-year. [ABSTRACT FROM AUTHOR]

This paper studies the long-term variability of frequency of atmospheric blockings over Western Siberia in 1948-2015 based on the data of three reanalysis projects. We revealed a decreasing blocking frequency for eight of twelve months. However, since the estimated trends of blocking frequency are small comparing to the significant amplitude of interannual variations, we proposed to divide the entire studied period into several quasi-decadal intervals that differ both in the amplitude of interannual fluctuations of blocking frequency and in trends. The effect of Western Siberian blockings imposed on synoptic and climatic variability of meteorological parameters in Asia was studied. The study demonstrated that in summer teleconnection patterns in temperature and precipitation fields are of the close sign-alternating structure; this indirectly indicates that in Western Siberia the blocking is a part of a large-scale wave mechanism. Like the Ural blockings, the blockings occurring over Western Siberia affect meteorological characteristics within the East Asian monsoon area. In winter time they contribute to lower surface temperature and decreased precipitation in Southeast Asia. In summer during blocking events over Western Siberia, precipitation increases in the East Asian monsoon area. [ABSTRACT FROM AUTHOR]

This paper appraises the association of lightning flash count (FC) with rainfall using the satellite-borne Lightning Imaging Sensor's (LIS) data along with gridded rainfall data (0.5 × 0.5) for Indian summer monsoon seasons over 10 years (2001-2010). During strong El Nino years, 2002 and 2009, FCs were greater in magnitude by about 26.5 % and 37 %, than the long-term average, respectively, while during weak El Nino year (2004), it was more by 8 %. During the same years, the rainfall was deficient by about 10 % than the long-term average. Similarly, a rise in aerosol optical depth (AOD) over its average value (by about 15 % and 20 %) reduces the ratio of rainfall to FC (RLR) by 41 % and 44 % for strong El Nino years 2002 and 2009, respectively, and for weak El Nino year (2004), a 6.5 % rise in AOD lowers the RLR by 20 %. Bowen ratio more by 11 % and 17 % of its average value reduces the RLR by 41 % and 44 % for strong El Nino years 2002 and 2009, respectively, and, also, Bowen ratio higher by 8 % for 2004 declines RLR by 20 %. On the other hand, Bowen ratio less by 9 % and 6 % raises the RLR by 19 % and 56 % for moderate La Nina year (2007) and strong La Nina year (2010), respectively. Results for the daily rainfall, AOD and Bowen ratio over Indian regions, are discussed for strong El Nino and La Nina years. Correlations of FC with AOD and Bowen ratio of 0.66 and 0.71, respectively, while, that of FC with ONI of 0.56 indicates numerous (fewer) break days during El Nino (La Nina) years. [ABSTRACT FROM AUTHOR]

Most of the annual rainfall over India occurs during the Southwest (June-September) and Northeast (October-December) monsoon periods. In March 2008, however, Southern peninsular India and Sri Lanka received the largest rainfall anomaly on record since 1979, with amplitude comparable to summer-monsoon interannual anomalies. This anomalous rainfall appeared to be modulated at intraseasonal timescale by the Madden Julian Oscillation, and was synchronous with a decaying La Niña event in the Pacific Ocean. Was this a coincidence or indicative of a teleconnection pattern? In this paper, we explore factors controlling rainfall over southern India and Sri Lanka between January and April, i.e. outside of the southwest and northeast monsoons. This period accounts for 20% of annual precipitation over Sri Lanka and 10% over the southern Indian states of Kerala and Tamil Nadu. Interannual variability is strong (about 40% of the January-April climatology). Intraseasonal rainfall anomalies over southern India and Sri Lanka are significantly associated with equatorial eastward propagation, characteristic of the Madden Julian Oscillation. At the interannual timescale, we find a clear connection with El Niño-Southern Oscillation (ENSO); with El Niños being associated with decreased rainfall (correlation of −0.46 significant at the 98% level). There is also a significant link with local SST anomalies over the Indian Ocean, and in particular with the inter-hemispheric sea surface temperature (SST) gradient over the Indian Ocean (with colder SST south of the equator being conducive to more rainfall, correlation of 0.55 significant at the 99% level). La Niñas/cold SSTs south of the equator tend to have a larger impact than El Niños. We discuss two possible mechanisms that could explain these statistical relationships: (1) subsidence over southern India remotely forced by Pacific SST anomalies; (2) impact of ENSO-forced regional Indian Ocean SST anomalies on convection. However, the length of the observational record does not allow distinguishing between these two mechanisms in a statistically significant manner. [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 inner shelf sediments of the East China Sea (ECS) preserve valuable information regarding climatic changes on land through detrital material discharged from large rivers, particularly the Yangtze River. In this paper, we examine the provenance changes of fine-grained detrital quartz preserved in the sediment of the MD06-3040 core retrieved from the mud belt on the inner shelf of the ECS during the last 6 kyrs. The provenance of the fine silt fraction (4–16 μm) of the sediments, which is considered to represent the suspended particulate matter (SPM) from the Yangtze River, is estimated based on the electron spin resonance (ESR) signal intensity and crystallinity index (CI) of quartz. By comparing the ESR signal intensity and CI of quartz in the fine silt fraction of sediments to those from different parts of tributaries in the modern Yangtze River drainage, we can discriminate the SPM sourced from the northwestern and southeastern tributaries of the Yangtze River. Shifts in the East Asian summer monsoon (EASM) front are monitored by changes in the main precipitation areas which are manifested as changes in source rock ages and types implied from the ESR signal intensity and CI of quartz in the fine silt fraction of the studied sediments discharged from the Yangtze River. Temporal changes in provenance of the fine silt fraction through time suggest that shifts in the main location of EASM precipitation (most likely representing the EASM front) occurred at a multi-centennial-to-millennial scale with the deepest northwestward penetration of the EASM precipitation front (an enhanced EASM) occurring during the period 3.5–2.0 kyr BP and a southeastward retreat (a weak EASM) occurring during the periods 6.0–4.1 and 2.0–0 kyr BP. [ABSTRACT FROM AUTHOR]

This paper contributes to an enhanced understanding of present climatic conditions, observed climate trends and regional climate vulnerability of the Bhutan Himalayas. Bhutan's complex, often high-altitude terrain and the severe impact of the Indian summer monsoon leads to a strong exposure of the countries' key economic sectors (agriculture, forestry, hydropower generation and tourism) to climatic changes. Climate change also threatens Bhutan's vast biodiversity and increases the likelihood of natural hazards (e.g. glacier lake outburst floods, flash floods, droughts and forest fires). A better understanding of Bhutan's climate and its variability, as well as observed and possible climate impacts, will help in improving the handling of regional social, economic and ecologic challenges not limited to the Himalayas. Only a few climatological studies exist for the eastern Himalayas. They mainly focus on adaptation to immediate threats by glacier lake outbursts. In contrast, this paper (1) investigates the average spatial and inner-annual diversity of the air temperature regime of Bhutan, based on local meteorological observations, (2) discusses past temperature variability, based on global datasets, and (3) relates effects of observed warming to water availability, hydropower development, natural hazards, forests, biodiversity, agriculture, human health and tourism in the Bhutan Himalayas. Results indicate a large spatial and temporal temperature variability within Bhutan and considerably increasing temperatures especially over recent decades. Implications of regional climatic changes on various socio-economic sectors and possible adaptation efforts are discussed. [ABSTRACT FROM AUTHOR]

40% of global population, who resides in Asian monsoon region is at high risk from extreme hot summer events, which is expected to increase by 25%/30 years under RCP8.5 scenario. Using Community Earth System Model (CESM) Large-ensemble simulations we assess the relative contribution of external forcings and internal variability on hot extremes over South and East Asia. Climate change projects surface mean temperature to reach 2.0 °C and 5.0 °C by ~2050 and ~2100, respectively, making the region uninhabitable under exposed conditions. Internal variability will partly obscure anthropogenic warming over South and Southeast Asia; however, East Asia will experience a 4–6 fold rise in record breaking hot events in later periods. Nevertheless, beyond 2.35 °C warming internal variability will decrease over South Asia due to weaker albedo feedback on unforced internal variability. Our results contradict the existing hypothesis that warming will increase volatility in weather patterns everywhere, particularly the Asian monsoon regions. [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 present paper examined the teleconnections between two huge Asian summer monsoon components (South and East Asia) during three time slices in future: near-(2010–2039), mid-(2040–2069) and far-(2070–2100) futures under the RCP4.5 and RCP8.5 scenarios. For this purpose, a high-resolution atmospheric general circulation model is used and integrated at 40 km horizontal resolution. To get more insight into the relationships between the two Asian monsoon components, we have studied the spatial displaying correlation coefficients (CCs) pattern of precipitation over the entire Asian monsoon region with that of South Asia and three regions of East Asia (North China, Korea–Japan and Southern China) separately during the same three time slices. The possible factors responsible for these teleconnections are explored by using mean sea level pressure (MSLP) and wind fields at 850 hPa. The CC pattern of precipitation over South Asia shows an in-phase relationship with North China and an out-of-phase relationship with Korea–Japan, while precipitation variations over Korea–Japan and Southern China exhibit an out-of-phase relationship with South Asia. The CCs analysis between the two Asian blocks during different time slices shows the strongest CCs during the near and far future with the RCP8.5 scenario. The CC pattern of precipitation over Korea–Japan and Southern China with the wind (at 850 hPa) and MSLP fields indicate that the major parts of the moisture over Korea–Japan gets transported from the west Pacific along the western limb of NPSH, while the moisture over Southern China comes from the Bay of Bengal and South China Seas for good monsoon activity. [ABSTRACT FROM AUTHOR]

Based on our previous study (Yu et al., Clim Dyn 49:1139-1156, 2017), this paper further investigates the interdecadal change in the relationship between the Kuroshio Extension (KE; 27°-37°N, 140°-158°E) and the East Asian summer monsoon (EASM) in the late 1980s. The summer KE sea surface temperature anomalies (SSTAs) show a significant positive relationship with the EASM over the period 1968-1987 (P1), but a significant negative connection with the EASM between 1991 and 2010 (P2). This interdecadal change in the KE-EASM relationship can be interpreted by considering the difference in the relationships of summer KE SSTAs with the East Asian subtropical westerly jet (EASWJ) and western North Pacific subtropical high (WNPSH) during the two periods. During P1, summertime KE SST warming is significantly related to the strengthened EASWJ and WNPSH, but it has close relationships with the weakened and northward-moving EASWJ and WNPSH during P2. These anomalous EASWJ and WNPSH associated with the summertime KE SST warming in P1 (P2) then favors increased (reduced) rainfall over the Yangtze River Valley that corresponds to a strong (weak) EASM, thereby leading to the significant positive (negative) KE-EASM relationship during this period. This change in the relationships of summer KE SSTAs with the EASWJ and WNPSH may be attributed to the increased KE SST variability associated with an enhanced Pacific Decadal Oscillation (PDO) in summer during P2, which is most probably induced by the stronger North Pacific Oscillation (NPO)-like atmospheric forcing, especially its southern pole (SP), in the preceding spring during this period. The spring NPO-like SP forces the KE SSTAs and PDO more directly during the following summer and can thus have been a better precursor for the following EASM than the full NPO-like dipole after the late 1980s. [ABSTRACT FROM AUTHOR]

We analyze a mini ensemble of regional climate projections over the CORDEX Africa domain carried out with RegCM4 model as part of the Phase I CREMA experiment (Giorgi ). RegCM4 is driven by the HadGEM2-ES and MPI-ESM global models for the RCP8.5 and RCP4.5 greenhouse gas and aerosol concentration scenarios. The focus of the analysis is on seasonal and intraseasonal monsoon characteristics. We find two prominent change signals. Over West Africa and the Sahel MPI produces a forward shift in the monsoon season in line with previous findings, and this shift is also simulated by the RegCM4. Furthermore, the regional model produces a widespread decrease of monsoon precipitation (when driven by both MPI and HadGEM) associated with decreased easterly wave activity in the 6-9 days regime and with soil moisture-precipitation interactions. South of the equator we find an extension of the dry season with delayed onset and anticipated recession of the monsoon and a narrowing and strengthening of the ITCZ precipitation band. This signal is consistent in all global and regional model projections, although with different spatial detail. We plan to enlarge this mini-ensemble as a further contribution to the CORDEX project to better assess the robustness of the signals found in this paper. [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]

In this paper, the regional climate model REMO is used to investigate the added value of downscaling low resolutions global climate models (GCMs) and the climate change projections over Central Africa. REMO was forced by two GCMs (EC-Earth and MPI-ESM), for the period from 1950 to 2100 under the Representative Concentration Pathway 8.5 scenario. The performance of the REMO simulations for current climate is compared first with REMO simulation driven by ERA-Interim reanalysis, then by the corresponding GCMs in order to determine whether REMO outputs are able to effectively lead to added value at local scale. We found that REMO is generally able to better represent some aspects of the rainfall inter-annual variability, the daily rainfall intensity distribution as well as the intra-seasonal variability of the Central African monsoon, though few biases are still evident. It is also found that the boundary conditions strongly influences the spatial distribution of seasonal 2-m temperature and rainfall. From the analysis of the climate change signal from the present period 1976-2005 to the future 2066-2095, we found that all models project a warming at the end of the twenty-first century although the details of the climate change differ between REMO and the driving GCMs, specifically in REMO where we observe a general decrease in rainfall. This rainfall decrease is associated with delayed onset and anticipated recession of the Central African monsoon and a shortening of the rainy season. Small-scales variability of the climate change signal for 2-m temperature are usually smaller than that of the large-scales climate change part. For rainfall however, small-scales induce change of about 70% compared to the present climate statistics. [ABSTRACT FROM AUTHOR]

Large-scale atmospheric circulations significantly affect regional precipitation patterns. However, it is not well known whether and how these phenomena affect regional precipitation distribution in northern China. This paper reported the individual and coupled effects of El Niño-Southern Oscillation (ENSO), Indian summer monsoon (ISM), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) on annual precipitation for the Ordos Basin, an arid and semi-arid basin, currently with major industries of coal, fossil oil, natural gas, and halite in north central China. Our results showed that ENSO and ISM exerted substantial impact on annual precipitation while the impact of PDO and AMO was relatively limited. There were 24 and 15 out of 33 stations showing significant differences ( p < 0.1) in annual precipitation (from 1950 to 2013) for ENSO and ISM, respectively. The median precipitation across the basin during El Niño years was 21.49 % higher than that during La Niña years and 17.28 % higher during the positive phase of ISM years compared to the negative phase of the ISM years. The impacts of ENSO and ISM on precipitation were enhanced during a PDO cold phase but weakened in a PDO warm phase. The impact of ENSO was still enhanced by an AMO warm phase. The effects of climatic phenomena on precipitation showed a strong spatial difference in the Ordos Basin. The impact of ENSO was mostly evident around the edges of the basin while the impact of ISM decreases from south to north. The deserts (i.e., Hobq Desert and Mu Us Sandy Land) in the center of the basin were less affected by these large-scale climatic phenomena. An improved understanding of such relationships would be helpful in water resource planning and disaster management for the Ordos Basin. [ABSTRACT FROM AUTHOR]

Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon (EAM) system are reviewed in this paper. The understanding of the EAM system has improved in many aspects: the basic characteristics of horizontal and vertical structures, the annual cycle of the East Asian summer monsoon (EASM) system and the East Asian winter monsoon (EAWM) system, the characteristics of the spatio-temporal variabilities of the EASM system and the EAWM system, and especially the multiple modes of the EAM system and their spatio-temporal variabilities. Some new results have also been achieved in understanding the atmosphere-ocean interaction and atmosphere-land interaction processes that affect the variability of the EAM system. Based on recent studies, the EAM system can be seen as more than a circulation system, it can be viewed as an atmosphere-ocean-land coupled system, namely, the EAM climate system. In addition, further progress has been made in diagnosing the internal physical mechanisms of EAM climate system variability, especially regarding the characteristics and properties of the East Asia-Pacific (EAP) teleconnection over East Asia and the North Pacific, the “Silk Road” teleconnection along the westerly jet stream in the upper troposphere over the Asian continent, and the dynamical effects of quasi-stationary planetary wave activity on EAM system variability. At the end of the paper, some scientific problems regarding understanding the EAM system variability are proposed for further study. [ABSTRACT FROM AUTHOR]

In this paper, changes in the long and short spells of different rain intensities are statistically analyzed using daily gridded rainfall data prepared by the India Meteorological Department for the period 1951-2008. In order to study regional changes, analyses have been conducted over nine selected agro-meteorological (agro-met) divisions, five homogeneous zones, and also over the whole of India. Rain events of different intensities with continuous rainfall of more than or equal to 4 days are classified here as long spells. Those with less than 4 days are termed as short spells. Those results which are statistically significant at 95% confidence level are discussed in this paper. Trend analysis shows that during the summer monsoon months of June to September, short spell rain events with heavy intensity have increased over India as a whole. On the other hand, long spell rain events with moderate and low intensities have decreased in numbers. Results further show that the contributions of long spell moderate and short spell low-intensity rain events to the total rainfall have decreased whereas the contributions of short spell heavy and moderate-intensity rain events to the total seasonal rainfall have increased. Percentage changes in various categories of long and short spells in the decade 1991-2000 compared with the earlier decade 1951-1960, highlight the maximum increase in heavy-intensity short spell category and decrease in moderate-intensity long spell category in India as a whole and in most of the homogeneous zones and agro-met divisions. The changes in different types of rain events differ in the six homogeneous zones and nine selected agro-met divisions. However, in three homogeneous zones and three agro-met divisions, the short spell heavy-intensity rain events dominate as in the entire country. There are also changes observed in the monthly occurrences of above categories of rain events during the 4 months of summer monsoon. Such results with details of changes in rain categories in different parts of India have important implications in agriculture sector in the country. [ABSTRACT FROM AUTHOR]

On 21-22 July 2012, torrential rains hit North China, with the daily precipitation record at Beijing station reaching 160.6 mm; this event is named the Beijing 7-21 case. This paper assesses the likelihood of the occurrence of local torrential rains, such as the Beijing 7-21 case, from the perspective of climate variability. In particular, the influence of the Pacific Decadal Oscillation (PDO) is assessed. There were five extreme events, with daily precipitation records equal to or larger than 160.6 mm, at Beijing station during the period 1951-2012; all of these events happened during negative phases of the PDO. The present analysis indicates that precipitation events more extreme than the Beijing 7-21 case should happen more than once per decade during negative phases of the PDO, but only about once every four decades during positive PDO phases. The negative phase of the PDO is found to be associated with a much greater probability of daily records of southerly winds in North China during summer. Strong southerly summer monsoons are deemed favorable for increasing the occurrence of local extreme rainfall over North China. [ABSTRACT FROM AUTHOR]

This paper presents results of a study of long term trends in the characteristics of the within-season temporal profile of southwest monsoon rainfall over western India during the last five decades in relation to global warming induced regional climate change. In contrast to recent climate change analyses and projections, no significant long-term trends have been observed in this study. Slow decadal scale variations observed are analysed in relation to Pacific Decadal Oscillations (PDO). Daily variations in rainfall anomaly show opposite characteristics during negative and positive phases of PDO. The above-normal rainfall (>25%) is found during the starting phase of monsoon in negative PDO. Over the last decade, i.e., during 2000-2007, the seasonal rainfall amount, as well as seasonal span of southwest monsoon over western India is indicative of a gradual increase. [ABSTRACT FROM AUTHOR]

The paper assesses the damage caused by 2010 flash flood and its underlying causes in the upper zone of Panjkora River within district Dir Upper, Khyber Pakhtunkhwa (KP) Province in Pakistan. Floods in general and flash floods in particular are very common in the area, and the phenomenon has intensified in the wake of observed climatic changes in the region. Anticipating an increase in the multiplicity of causes and a rise in the human, livelihood, and property losses attributed to flash floods calls for a detailed study of affected communities in the region. Within the study area of District Dir Upper-within the band of 200 m on both sides of Panjkora River, three most affected communities, namely Barikot, Kalkot, and Sharingal, were picked on random basis to have detailed analysis of underlying causes and the quantification of damage assessment in the area. Questionnaire-based household survey and structured interviews were conducted to investigate physical and economic damages in the sample sites. Global positioning system (GPS) survey is also conducted to acquire absolute location of damages, and geographic information system is used to visualize land use, land cover, physical features, and GPS data. Monsoon winds interacted with the westerlies abnormally caused unprecedented high intensity rainfall in the valley. The steep topography of the area caused rainwater to accumulate rapidly in the Panjkora River channel, overpowering the withholding capacity of the river. The flash flood inflected heavy losses to life and properties of the local population. The infrastructure such as houses, roads, retaining walls, bridges, water supply schemes, and irrigation channels were destroyed severely in the whole area particularly in Kalkot. Three explored underlying causes of flash floods and the degree of damage due to 2010 flash floods in the region call for an enhanced realization for climatic change adaptability, flood risk management, and mitigation measures, better flood response through early warning systems, and improved rehabilitation and recovery efforts within flood prone areas such as district Dir Upper, KP, Pakistan. [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]

A key component of the East Asian climate system is seasonally varying monsoon wind. Its interannual and interdecadal variability, as well as underlying oceanic processes, is the subject of a recent project completed by the Chinese Academy of Sciences. A series of research progress in the areas of monsoon winds, ocean responses, upwelling and productivity has been made and reviewed by this paper. [ABSTRACT FROM AUTHOR]

The aim of this paper was to characterize the southwest monsoon onset over Myanmar based on the model. The Regional Climate Model (RegCM3) was run for a period of 10 years (2000-2009) to simulate the meteorological fields which focused on April to July season. The model input data were obtained from the reanalyzed datasets of the National Center for Environmental Prediction (NCEP) and National Centre for Atmospheric Research (NCAR). Grell scheme with Arakawa closure for cumulus parameterization assumption was used for simulation with 45 km horizontal resolution. The results revealed that southwest monsoon onset was confirmed when the prevailing wind direction up to 600 hPa level had shifted from northeasterly to westerly or southwesterly. The southwest monsoon first arrived at southernmost Kawthoung station of Myanmar and progressed through the Deltaic and Central parts until it reached at northernmost Putao station. Over the simulation periods, the southwest monsoon onset progressed from the southernmost to northernmost parts of the country in 19 ± 10 days. The position of Intertropical Convergence Zone (ITCZ) appeared (23°N-28°N) over the Northern part of the country before the onset. Furthermore, 500 hPa ridge appeared consistently over the Deltaic area of Myanmar from 6 to 10 days before the monsoon onset. Its position is about 6° to the south of the ITCZ. [ABSTRACT FROM AUTHOR]

Deserts and sandylands that are located in the semi-arid and arid regions in the middle latitudes of the Northern Hemisphere are usually regarded as environmentally sensitive change belts which respond to global climatic change. In northern China, activation or immobilization of sand dunes is mainly influenced by humid and dry variation and is related to stronger or weaker Asian monsoons. In this paper, the history of Holocene millennial-scale climatic and environmental change is reconstructed by the systematic analysis of the geochemical element contents and parameters, along with the OSL and C chronologies, from the different lithologies of the palaeosol-aeolian sand sequence in the south-eastern Mu Us Desert, northern China. Our results indicate that the region was dominated by a dry climate with intensive aeolian activity before 7.2 ka BP, and there was an optimal humid climate and fixed desert in 7.2-4.6 ka. Afterwards, the dune fields became mobile again as the effective humidity declined. Additionally, six dry events were discovered with times of ~7.2, 7.0-6.8, 6.6-5.7, 4.6-4.1, 3.7-3.5, and 3.3-2.5 ka, which were not only coincident with the intervals of millennial-scale weaker Asian summer monsoons, but also accordant with the cold events evidenced in the ice cores and deep-sea deposits of the high latitudes in the Northern Hemisphere. In general, the Holocene climatic and environmental changes had the characteristics of the 'monsoonal mode' and 'abrupt millennial-scale oscillation' in the Mu Us Desert. [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]

In this study, using the NCAR Community Earth System Model (CESM1.2.2), we investigate the changes in the characteristics of the summer monsoon low pressure systems (LPS) over India in a twenty-first century climate change simulation corresponding to the RCP8.5 scenario. A slight weakening in monsoon circulation and an increase in mean summer monsoon precipitation over India are simulated in a warmer climate, consistent with several previous studies. The weakening of the monsoon circulation is associated with a pair of anticyclonic anomalies straddling the equator in the low level, weakening the cross-equatorial monsoonal flow from the southern hemisphere. These low-level circulation anomalies appear to be robust features in the equatorial Indian Ocean under climate change. An increase in moisture flux is also simulated over the Indian subcontinent. However, we find no significant change in the number of LPS or their spatial distribution under the RCP8.5 scenario. This is attributed to a small but non-significant decrease in the low-level meridional cyclonic shear in zonal winds. An increase in the intensity and frequency of extreme precipitation over India in a warmer world is simulated and is likely associated with an increase in moisture content. Our study shows that the fractional contribution of LPS to mean and extreme precipitation over India in a warmer world is likely unchanged, but the frequency and intensity of extreme events are larger. Because of the diversity in the results from single model studies on LPS characteristics in a warmer world, a future study that uses CMIP6 multi-model data would be valuable to assess the robustness and the uncertainty in changes in LPS activities under climate change. [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]

Investigations into the climatic forcings that affect the long-term variability of the Indian summer monsoon are constrained by a lack of reliable rainfall data prior to the late nineteenth century. Extensive qualitative and quantitative meteorological information for the pre-instrumental period exists within historical documents, although these materials have been largely unexplored. This paper presents the first reconstruction of monsoon variability using documentary sources, focussing on western India for the period 1781-1860. Three separate reconstructions are generated, for (1) Mumbai, (2) Pune and (3) the area of Gujarat bordering the Gulf of Khambat. A composite chronology is then produced from the three reconstructions, termed the Western India Monsoon Rainfall reconstruction (WIMR). The WIMR exhibits four periods of generally deficient monsoon rainfall (1780-1785, 1799-1806, 1830-1838 and 1845-1857) and three of above-normal rainfall (1788-1794, 1813-1828 and 1839-1844). The WIMR shows good correspondence with a dendroclimatic drought reconstruction for Kerala, although agreement with the western Indian portion of the tree-ring derived Monsoon Asia Drought Atlas is less strong. The reconstruction is used to examine the long-term relationship between the El Nino-Southern Oscillation (ENSO) and monsoon rainfall over western India. This exhibits peaks and troughs in correlation over time, suggesting a regular long-term fluctuation. This may be an internal oscillation in the ENSO-monsoon system or may be related to volcanic aerosol forcings. Further reconstructions of monsoon rainfall are necessary to validate this. The study highlights uncertainties in existing published rainfall records for 1817-1846 for western India. [ABSTRACT FROM AUTHOR]

Climate in Eastern Asia is composed of monsoon climate in the east, arid and semi-arid climate in the north and west, and the cold and dry climate of Qinghai-Tibetan Plateau in the southwest. The underlying causes for the evolution of East Asian climate during late Cenozoic have long been investigated and debated, particularly with regards to the role played by the Qinghai-Tibetan Plateau uplift and the global cooling. In this paper, we reviewed major research developments in this area, and summarized the important results. Based on a synthesis of data, we propose that the Qinghai-Tibetan Plateau uplift alone cannot fully explain the formation of monsoon and arid climates in Eastern Asia during the past 22-25 Ma. Other factors such as the global ice volume and high-latitude temperature changes have also played a vital role. Moreover, atmospheric CO changes may have modulated the monsoon and dry climate changes by affecting the location of the inter-tropical convergence zone (ITCZ), which controls the monsoon precipitation zone and the track of the East Asian winter monsoon during late Cenozoic. The integration of high-resolution geological record and numerical paleoclimate modeling could make new contributions to understanding the climate evolution and variation in eastern Asia in future studies. It could facilitate the investigation of the regional differences in East Asian environmental changes and the asynchronous nature between the uplift of Qinghai-Tibetan Plateau and their climatic effects. These would be the keys to understanding underlying driving forces for the evolution of the East Asian climate. [ABSTRACT FROM AUTHOR]

The Indian Ocean Dipole (IOD) can affect the El Niño-Southern Oscillation (ENSO) state of the following year, in addition to the well-known preconditioning by equatorial Pacific Warm Water Volume (WWV), as suggested by a study based on observations over the recent satellite era (1981-2009). The present paper explores the interdecadal robustness of this result over the 1872-2008 period. To this end, we develop a robust IOD index, which well exploits sparse historical observations in the tropical Indian Ocean, and an efficient proxy of WWV interannual variations based on the temporal integral of Pacific zonal wind stress (of a historical atmospheric reanalysis). A linear regression hindcast model based on these two indices in boreal fall explains 50 % of ENSO peak variance 14 months later, with significant contributions from both the IOD and WWV over most of the historical period and a similar skill for El Niño and La Niña events. Our results further reveal that, when combined with WWV, the IOD index provides a larger ENSO hindcast skill improvement than the Indian Ocean basin-wide mode, the Indian Monsoon or ENSO itself. Based on these results, we propose a revised scheme of Indo-Pacific interactions. In this scheme, the IOD-ENSO interactions favour a biennial timescale and interact with the slower recharge-discharge cycle intrinsic to the Pacific Ocean. [ABSTRACT FROM AUTHOR]

As one of the most important geological events in Cenozoic era, the uplift of the Tibetan Plateau (TP) has had profound influences on the Asian and global climate and environment evolution. During the past four decades, many scholars from China and abroad have studied climatic and environmental effects of the TP uplift by using a variety of geological records and paleoclimate numerical simulations. The existing research results enrich our understanding of the mechanisms of Asian monsoon changes and interior aridification, but so far there are still a lot of issues that need to be thought deeply and investigated further. This paper attempts to review the research on the influence of the TP uplift on the Asian monsoon-arid environment, summarize three types of numerical simulations including bulk-plateau uplift, phased uplift and sub-regional uplift, and especially to analyze regional differences in responses of climate and environment to different forms of tectonic uplifts. From previous modeling results, the land-sea distribution and the Himalayan uplift may have a large effect in the establishment and development of the South Asian monsoon. However, the formation and evolution of the monsoon in northern East Asia, the intensified dryness north of the TP and enhanced Asian dust cycle may be more closely related to the uplift of the main body, especially the northern part of the TP. In this review, we also discuss relative roles of the TP uplift and other impact factors, origins of the South Asian monsoon and East Asian monsoon, feedback effects and nonlinear responses of climatic and environmental changes to the plateau uplift. Finally, we make comparisons between numerical simulations and geological records, discuss their uncertainties, and highlight some problems worthy of further studying. [ABSTRACT FROM AUTHOR]

This paper analyzes the evolution of the South Asian High (SAH) during and after the development of tropical cyclone Neoguri over the South China Sea (SCS) in mid-April 2008, the formation of tropical storm Nargis over the Bay of Bengal (BOB) in late April, and the Asian summer monsoon onset, as well as their interrelationships. Numerical sensitivity experiments are conducted to explore the underlying mechanism responsible for these seasonal transitions in 2008. It is demonstrated that strong latent heating related with tropical cyclone activities over the SCS can enhance the development of the SAH aloft and generate zonal asymmetric potential vorticity (PV) forcing, with positive vorticity advection to its east and negative advection to its west. Following the decay of the tropical cyclone, this asymmetric forcing leads to instability development of the SAH, presenting as a slowly westward-propagating Rossby wave accompanied by a westward shift of the high PV advection. A strong upper tropospheric divergence on the southwest of the SAH also shifts westward, while positive PV eddies are shed from the high PV advection and eventually arrives in the southern BOB. Such synoptic patterns provide favorable pumping conditions for local cyclonic vorticity to develop. The latent heating release from the cyclogenesis further intensifies the upper-layer divergence, and the lower and upper circulations become phase locked, leading to the explosive development of the tropical cyclone over the southern BOB. Consequently, a tropical storm is generated and the BOB summer monsoon commences. [ABSTRACT FROM AUTHOR]

The southeastern Chinese Loess Plateau is the terminal deposition area of dusts transported by the East Asian winter monsoon and the frontal area penetrated by the East Asian summer monsoon, and thus a climate sensitive region. This paper reports a rock magnetic study of a Quaternary loess-paleosol section in such a region. We tried to reconstruct the paleoclimate evolution history in the region during 1.95-0.40 Ma with magnetic parameters. The results show a general up-section decreasing trend of the ratio of HIRM/(SIRM-IRM), indicating a long-term decreasing trend of hematite coercivities in the deposits, which can be mainly related to the cooling and aridification trend of the environment in interglacial depositional area and glacial dust source region. The ratio, χ/ χ, widely used to reflect the variations of magnetic mineral grain size, manifests a long-term increasing trend of the magnetic mineral grain size and tends to indicate an overall weakening trend of the East Asian summer monsoon that controlled the pedogenic intensity. Although the regional multi-segmented paleoclimatic records revealed by several magnetic parameters in our study, the long-term Asian cooling and aridification trend inferred here is of global correlation significance. [ABSTRACT FROM AUTHOR]

In a climate change scenario, the present work deals with the possibility of the changes in the rainfall pattern during the principal monsoon season (June 1-September 30) of the Indian summer monsoon. For this purpose three attributes are defined as DTMR, DHMR and DNMR representing the day when 10, 50 and 90 % of the accumulated summer monsoon rainfall is achieved respectively. Using a high resolution (1° × 1°) gridded rainfall data set for the last 50 years prepared by India Meteorological Department (Rajeevan et al. , in Curr Sci 91:296-306, ), the analysis has been carried out over the different parts of the Indian subcontinent. Using statistically robust significance tests, it is observed that the distribution of the three variables have changed significantly at 1 % (or 5 %) significance level in the last 50-year of period. The DTMR and DNMR arrive 2 days early over central India, whereas DHMR appears to arrive 6 days early over west India in the recent decades. The results presented in this paper are supported by the statistically robust significance tests; suggest an apparent change in terms of the arrival of the rainfall attributes during the last half century. [ABSTRACT FROM AUTHOR]

This paper is a review of studies of abrupt climate changes (ACCs) during the Holocene published during the past ten years. North Atlantic cold events are indicators of ACCs. As indicated by North Atlantic ice-rafted debris (IRD), there were nine confirmed cold events during the Holocene, occurring at 11.1 kyr, 10.3 kyr, 9.4 kyr, 8.1 kyr, 5.9 kyr, 4.2 kyr, 2.8 kyr, 1.4 kyr, and 0.4 kyr respectively according to most representative results from Bond et al. (1997). However, the identification of chronology has been made with some uncertainties. Considerable climatic proxy data have shown that, during the cold events, substantial climate abnormalities have occurred widely across the globe, particularly in the areas surrounding the North Atlantic. These abnormalities were in the form of high-latitude cold in the both hemispheres, expansion of the Westerlies to low latitudes, drought in the monsoon regions, recession of summer monsoons, and intensification of the winter monsoons. Studies have indicated that the four ACCs occurring in the early Holocene may be related to freshwater pulses from ice melting in the northern part of the North Atlantic, and the other five ACCs that occurred during the middle and late Holocene may be related to the decreased solar activity. [ABSTRACT FROM AUTHOR]

Marine Isotope Stage (MIS) 13, an interglacial about 500,000 years ago, is unique due to an exceptionally strong East Asia summer monsoon (EASM) occurring in a relatively cool climate with low greenhouse gas concentrations (GHG). This paper attempts to find one of the possible mechanisms for this seeming paradox. Simulations with an Earth System model LOVECLIM show that the presence of ice sheets over North America and Eurasia during MIS-13 induces a positive phase of the winter North Atlantic Oscillation (NAO) like feature. The ocean having a longer memory than the atmosphere, the oceanic anomalies associated with NAO persists until summer. The signals of summer NAO are transmitted to East Asia to reinforce the monsoon there through the stationary waves excited at the Asian Jet entrance. The geopotential height shows clearly a mid-latitude wave train with positive anomalies over the eastern Mediterranean/Caspian Sea and the Okhotsk Sea and a negative anomaly over Lake Baikal. This reinforces the effect of the high-latitude wave train induced independently by the Eurasian ice sheet topography as shown in previous study. These features reinforce the Meiyu front and enhance the precipitation over East Asia. The results obtained from LOVECLIM are further confirmed by an atmospheric general circulation model, ARPEGE. [ABSTRACT FROM AUTHOR]

This paper provides a synoptic view of extreme monsoon floods on all the nine large rivers of South Asia and their association with the excess (above-normal) monsoon rainfall periods. Annual maximum flood series for 18 gauging stations spread over four countries (India, Pakistan, Bangladesh and Nepal) and long-term monsoon rainfall data were analyzed to ascertain whether the extreme floods were clustered in time and whether they coincided with multi-decade excess monsoon rainfall epochs at the basin level. Simple techniques, such as the Cramer's t-test, regression and Mann-Kendall (MK) tests and Hurst method were used to evaluate the trends and patterns of the flood and rainfall series. MK test reveals absence of any long-term tendency in all the series. However, the Cramer's t test and Hurst-Mandelbrot rescaled range statistic provide evidence that both rainfall and flood time series are persistent. Using the Cramer's t-test the excess monsoon epochs for each basin were identified. The excess monsoon periods for different basins were found to be highly asynchronous with respect to duration as well as the beginning and end. Three main conclusions readily emerge from the analyses. Extreme floods (>90th percentile) in South Asia show a tendency to cluster in time. About three-fourth of the extreme floods have occurred during the excess monsoon periods between ~1840 and 2000 AD, implying a noteworthy link between the two. The frequency of large floods was higher during the post-1940 period in general and during three decades (1940s, 1950s and 1980s) in particular. [ABSTRACT FROM AUTHOR]

A series of recent papers showed that sea surface temperature (SST) anomalies in the south equatorial tropical Atlantic modulate the interannual variability of the African and Indian monsoon rainfall. Physically this teleconnection can be explained by a simple Gill-Matsuno mechanism. In this work, the output from five different models chosen within the CMIP3 (Coupled Model Intercomparison Project version 3) ensemble of coupled general circulation models (CGCMs) are analyzed to investigate how state-of-the-art CGCMs represent the impact of the South Tropical Atlantic (STA) SSTs on the Indian and African region. Using a correlation-regression technique, it is found that four out of the five models display a teleconnection between STA and Indian region which is generally weaker than in the observations but in agreement in the rainfall field pattern. This teleconnection is also noticeable in the ensemble mean of the five models. Over Africa, however, the significant changes in rainfall displayed in the observation are properly caught by only one of the CGCMs. Additionally, none of the models reproduces the symmetric upper-level wind response around the Equator seen over the Indian Ocean in the observations and all have significant biases also in the surface pressure field response to the tropical Atlantic SSTs. Nonetheless the STA response, particularly over the southern hemisphere, is indicative of the Gill-Matsuno-type mechanism identified in previous studies using idealized experiments with atmospheric GCMs and observational data. With a suite of atmospheric-only GCM integrations it is shown that the differences in amplitude and pattern are not only due to the strong biases and reduced variabilities of the CGCMs over the tropical Atlantic but they are also caused by the different physical parameterizations used in models. [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]

The CNRM atmospheric general circulation model Arpege-Climat is relaxed towards atmospheric reanalyses outside the 10°S-32°N 30°W-50°E domain in order to disentangle the regional versus large-scale sources of climatological biases and interannual variability of the West African monsoon (WAM). On the one hand, the main climatological features of the monsoon, including the spatial distribution of summer precipitation, are only weakly improved by the nudging, thereby suggesting the regional origin of the Arpege-Climat biases. On the other hand, the nudging technique is relatively efficient to control the interannual variability of the WAM dynamics, though the impact on rainfall variability is less clear. Additional sensitivity experiments focusing on the strong 1994 summer monsoon suggest that the weak sensitivity of the model biases is not an artifact of the nudging design, but the evidence that regional physical processes are the main limiting factors for a realistic simulation of monsoon circulation and precipitation in the Arpege-Climat model. Sensitivity experiments to soil moisture boundary conditions are also conducted and highlight the relevance of land-atmosphere coupling for the amplification of precipitation biases. Nevertheless, the land surface hydrology is not the main explanation for the model errors that are rather due to deficiencies in the atmospheric physics. The intraseasonal timescale and the model internal variability are discussed in a companion paper. [ABSTRACT FROM AUTHOR]

study of the variability of the extreme rainfall events in Bangladesh during the time period 1958-2007 has been carried out in this paper. Quality-controlled homogeneous daily precipitation records of nine stations distributed over Bangladesh are used for the study. A total of 15 annual and seasonal indices of rainfall are examined. Variability of annual and seasonal rainfall trends is also assessed. The Mann-Kendall statistic and Sen's Slope model are used to reveal the trends and estimate the magnitude of change, respectively. A significant increase of annual and pre-monsoon rainfall in Bangladesh is observed. In general, an increasing trend in heavy precipitation days and decreasing trends in consecutive dry days are observed. Significant change in most of the extreme rainfall indices are observed in Northwest Bangladesh. [ABSTRACT FROM AUTHOR]

Climate change has the potential ability to alter the occurrence and severity of extreme events. Though predicting changes of such extreme events is difficult, understanding them is important to determine the impacts of climate change in various sectors. This paper presents the change in rainfall extremes in the monsoon season in south-west Indian peninsula. Daily rainfall data were analysed for the entire Kerala state in India to determine if the extreme rainfall had changed over the 50-year period. Several indices were derived from the data to identify the extreme rainfalls. The trends of all the extreme indices were assessed by parametric ordinary least square regression technique, which were tested for significance at 95% level. Results showed significant decrease in monsoon rainfall extremes in Kerala that would affect the tendency of change in seasonal total rainfall. This study provides a comprehensive knowledge on extreme monsoon precipitation in Kerala, which could also be employed to study changing climate at local scale in other regions. [ABSTRACT FROM AUTHOR]

The Shiyang River drainage basin is located in the northwest margin of the Asian monsoon region. Previous studies reached different conclusions about Holocene climatic changes in the basin. Some studies suggested the Holocene climatic changes were mainly controlled by the Asian monsoon and that the climate was relatively humid during the early Holocene (11.6--7.1 cal ka BP). Other studies found the mid-Holocene Climatic Optimum (7.0--5.0 cal ka BP), and this climate condition was similar to the Holocene westerly wind pattern in arid Central Asia. The modern climate is affected by the Asian monsoon and westerly wind in the drainage basin, and the Holocene climatic records showed two different Holocene climatic patterns--a westerly wind pattern and monsoonal pattern. However, it remains unclear what caused the two different Holocene climatic patterns to co-exist in the region. The palynological records are the main evidence for the Holocene climatic changes in the basin. This paper focuses on palynological records for different parts of the drainage basin. Among them, QTH02, QTL-03 and Sanjiaocheng records are located in the terminal lake, and the Hongshuihe record is located in the middle reaches of the basin. In the terminal lake, the palynological records of QTH02 and QTL-03 are similar, but the Sanjiaocheng record differs. The difference is mainly affected by the variable pollen assemblages in the different locations of the lake basin. From comparison and synthesis of the four palynological records, we concluded that the millennial-scale Holocene climatic changes were affected by the combined effects of the Asian monsoon and westerly wind in the drainage basin, which show the complicated Holocene climatic pattern in the northwest margin of the Asian monsoon. [ABSTRACT FROM AUTHOR]

The Indian summer monsoon season of 2009 commenced with a massive deficit in all-India rainfall of 48% of the average rainfall in June. The all-India rainfall in July was close to the normal but that in August was deficit by 27%. In this paper, we first focus on June 2009, elucidating the special features and attempting to identify the factors that could have led to the large deficit in rainfall. In June 2009, the phase of the two important modes, viz., El Niño and Southern Oscillation (ENSO) and the equatorial Indian Ocean Oscillation (EQUINOO) was unfavourable. Also, the eastern equatorial Indian Ocean (EEIO) was warmer than in other years and much warmer than the Bay. In almost all the years, the opposite is true, i.e., the Bay is warmer than EEIO in June. It appears that this SST gradient gave an edge to the tropical convergence zone over the eastern equatorial Indian Ocean, in competition with the organized convection over the Bay. Thus, convection was not sustained for more than three or four days over the Bay and no northward propagations occurred. We suggest that the reversal of the sea surface temperature (SST) gradient between the Bay of Bengal and EEIO, played a critical role in the rainfall deficit over the Bay and hence the Indian region. We also suggest that suppression of convection over EEIO in association with the El Niño led to a positive phase of EQUINOO in July and hence revival of the monsoon despite the El Niño. It appears that the transition to a negative phase of EQUINOO in August and the associated large deficit in monsoon rainfall can also be attributed to the El Niño. [ABSTRACT FROM AUTHOR]

Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season (March–May) is the hottest part of the year over almost the entire South Asian region, in which hot weather extremes including heat waves are recurring natural hazards having serious societal impacts, particularly on human health. In the present paper, recent trends in extreme temperature events for the pre-monsoon season have been studied using daily data on maximum and minimum temperatures over a well-distributed network of 121 stations for the period 1970–2005. For this purpose, time series of extreme temperature events have been constructed for India as a whole and seven homogeneous regions, viz., Western Himalaya (WH), Northwest (NW), Northeast (NE), North Central (NC), East coast (EC), West coast (WC) and Interior Peninsula (IP). In general, the frequency of occurrence of hot days and hot nights showed widespread increasing trend, while that of cold days and cold nights has shown widespread decreasing trend. The frequency of the occurrence of hot days is found to have significantly increased over EC, WC and IP, while that of cold days showed significant decreasing trend over WH and WC. The three regions EC, WC and NW showed significant increasing trend in the frequency of hot nights. For India as whole, the frequency of hot days and nights showed increasing trend while cold days and nights showed decreasing trends. Day-to-day fluctuations of pre-monsoon daily maximum and minimum temperatures have also been studied for the above regions. The results show that there is no significant change in day-to-day magnitude of fluctuations of pre-monsoon maximum and minimum temperatures. However, the results generally indicate that the daily maximum and minimum temperatures are becoming less variable within the season. [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]