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Heatwaves are characterized by an increase in temperature to extreme levels, which adversely distress the living organisms. India ranks second in terms of disaster mortality among the world countries, preponderantly by heatwave—influenced by regional climatology. In this study, the Excess Heat Factor (EHF) index is used to detect the heatwave using the ERA-Interim reanalysis dataset over various states of India during the summer period (April–June of 2017–2019). EHF categorizes heatwaves based on the severity, which is an intensity measure created by combining the measures of excess heat, long-term temperatures anomaly characteristics by each location’s unique climatology of heat by various thresholds. The heatwave events are analysed by combining the means of excess heat and heat stress, which has a strong aspect of EHF measurements. Concerning the intensity of future heatwaves, EHF index helps to analyse the frequency and intensity of heatwave episodes and alert those community most exposed to heat related illness. One of the indices is derived from a climatological background to analyse the severity of heatwave over the Indian states. The analysis over India using the EHF index reflected a substantial rate of increase in the intensity and the frequency of heatwaves in the successive years with an average EHF intensity (mean EHF for the analysis period) of ~ 41 °C2, ~ 38 °C2 and ~ 39 °C2, especially over the north–western states, eastern coastal states and central and southern states, respectively. The results of this study serve as a drive in the risk and vulnerability planning and assessment.

This observational study mainly examines the impacts of short- and long-time fluctuations of surface wind fields over the Arabian Sea (AS), the Bay of Bengal (BoB), and the southern Indian Ocean (SIO) on Indian Summer Monsoon Rainfall (ISMR), with special reference to strong and weak Indian summer monsoons (ISM). Two datasets over 1991–2014 are used: (1) the daily gridded rainfall produced by India Meteorological Department (IMD), and (2) the Cross-Calibrated Multi-Platform (CCMP) wind product version 2.0 created by Remote Sensing Systems. Monthly mean surface wind speed, convergence, and curl in the AS, BoB, and SIO are overall not significantly different between strong and weak ISMRs except for wind speed in the AS in September. However, the probability density function (PDF) distribution of daily values over the AS, BoB, and SIO during strong ISMRs is different from during weak ISMs, suggesting that sub-monthly surface wind characteristics could be useful in diagnosing rainfall characteristics. Except for rainfall in the northeast part of India, Indian regional rainfalls are closely linked with surface wind speeds over the AS, and wind convergence and curl over the BoB on short timescales of up to 1 week. The daily area-averaged wind convergence over the BoB is better correlated with regional rainfall during strong ISMs than during weak ISMRs. Multiple linear regression analysis shows that the fluctuations of monthly wind fields in the AS and BoB can affect monthly rainfall in some regions but are not related to a significant change in rainfall over the whole India. It is the short-time fluctuations of wind speed over the AS as well as wind convergence and curl over the BoB rather than their long (monthly) timescale fluctuations that are related to the strength of ISMR. Surface winds over the SIO on weather timescales have little influence on ISMR.

We conducted literature searches of records from Illinois, Indiana, Iowa, Minnesota, Missouri, North Dakota, Ohio, and Wisconsin to create a source bibliography of wildland fire descriptions occurring between 1673 and 1905. A total of 795 landscape fire records were identified within or near the eastern tallgrass prairie–forest transition region, including 32 attributed to Native Americans, 194 to Europeans from spontaneous records in the nineteenth century, and 569 to Europeans from a systematic dataset collected during the late nineteenth and early twentieth centuries in Minnesota. From these historical accounts, we find overwhelming evidence that a two- to three-week period during October and November, known then as “Indian summer,” was the primary wildland fire season. Our records indicate that Native Americans used fire primarily for hunting, whereas Euro-American fires were set to reduce fire hazards near their habitations, to eliminate crop residues, and to facilitate plowing, or they were escapes due to mere carelessness. Only five lightning-caused fires were identified. Individual fires frequently burned thousands of hectares, creating dense smoke, damaging trees, personal property, and occasionally burning inhabitants fatally. South and southwest were the most frequent wind directions during wildfires. Drought years, including 1796, 1819, 1856, and 1871, were characterized by extensive fires, which ultimately resulted in legislation to protect property owners and public welfare. Fire events for the study period are certainly underestimated by this dataset because only large, spectacular, threatening fires were recorded, especially during European settlement. In addition, our estimate of Native American fire frequency and prevalence is less than their historical/expected frequency, due to their widespread population collapse and changed hunting methods following contact and dispossession by Europeans.

Nineteen thirty-eight was the last full season played by baseball slugger Lou Gehrig before amyotrophic lateral sclerosis (ALS) forced him to retire. He struggled to hit and field well for much of the season, and his final statistics -- a .295 batting average, 29 home runs, 114 runs batted in – were unusually low for him. But in mid-season, Gehrig enjoyed a streak in which he seemed to regain his previous power. This three-week stretch, not studied closely by neurologists or baseball historians until now, suggests that the “Iron Horse” may have experienced a temporary ALS reversal, which can be instructive for researchers and those coping with the disease.

Many of Ivo Petrić’s last works are orchestral. Some are related to his native Slovenia, while others are concertos for various solo instruments. They are normally in one movement, either showing some connection with traditional separate movements or multi-tempo works with numerous motivic interconnections.

Using nine model simulations from the PMIP3, we study simulated mean Indian summer (June–September) climate and its variability during the Last Millennium (LM; CE0850-1849) with emphasis on the Medieval Warm Period (MWP; CE1000-1199) and Little Ice Age (LIA; CE1550-1749), after validation of the simulated ‘current day (CE1850-2005)’ climate and trends. We find that the simulated above (below) mean-LM summer temperatures during the MWP (LIA) are associated with relatively higher (lower) moisture, and relatively higher (lower) number of concurrent El Ninos (La Ninas). Importantly, the models simulate higher (lower) Indian summer monsoon rainfall (ISMR) during the MWP (LIA) compared to the LM-mean, notwithstanding a strong simulated negative correlation between NINO3.4 index and the area-averaged ISMR. Interestingly, the percentage of the simulated strong El Ninos (La Ninas) associated with negative (positive) ISMR anomalies is higher (lower) in the LIA (MWP). This nonlinearity is explained by the simulated background climate changes, as follows. Distribution of simulated anomalous 850 hPa boreal summer velocity potential during MWP in models indicates, relative to the mean LM conditions, a zone of anomalous convergence in the central tropical Pacific flanked by two zones of divergence, i.e. a westward shift in the Walker circulation. The anomalous divergence centre in the west during the MWP also extends into the equatorial eastern Indian Ocean, triggering in an anomalous convergence zone over India and relatively higher moisture transport therein and therefore excess rainfall during the MWP as compared to the LM-mean, and hence an apparent weakening in the El Nino impact.

The sedimentology, geochemistry, and plant microfossils of volcanic lake sediments from Cambodia were analysed to reconstruct a 4700 year record of change in moisture availability. This site sits at the heart of the intersection zone of the East Asian and Indian summer monsoons – a climatic system that is socio-ecologically important but poorly understood. Proxies for lake deepening and shallowing indicate a stepwise weakening of the summer monsoon from c. 4700 to 1700 cal. years BP, after which it appears to gradually strengthen. This trend is punctuated by seven dry events between 4300 and 1540 cal. years BP. The results present one of the longest, continuous records of palaeo-hydrological change in the Asian monsoon intersection zone. In doing so, they suggest that the climate of the region was broadly comparable to the East Asian summer monsoon (EASM) province to approximately 2240 cal. years BP, and the Indian summer monsoon (ISM) province between 2240 and 1700 cal. years BP. The subsequent, late Holocene hydroclimate appears to reflect a combination of both subsystems. These findings highlight dynamism in EASM and ISM dominance over mainland southeast Asia over the past five thousand years, but overall demonstrate regional vs. local scale influence on the hydroclimate of the region. The multi-decadal periods of strong drying that punctuate longer-term monsoon patterns demonstrate the natural variability of the mid- to late- Holocene climate of the intersection zone. This is of consequence given that apparently less severe drought events of the last millennium have had dramatic socio-economic consequences. Resultantly, planning for the resilience of socio-ecological systems within the region needs to account for the real potential of similar scale events occurring in the future, particularly given the increased extremes predicted for Asian summer monsoon region over the 21st century.

India experienced two extreme summer monsoons, 2007 (active monsoon) and 2009 (weak monsoon) in the recent past decade. The characteristic features of these two contrasting Indian summer monsoons have been presented. The country received 11.8% excess and 17.1% deficit rainfall during 2007 and 2009 monsoon seasons, respectively. These large deviations in rainfall encourage us to study the influence of meteorological factors on rainfall activity. The distributions of rainfall over India, latent heat flux, wind, Vertically Integrated Moisture Transport (VIMT), and Vertically Integrated Moisture Divergence (VIMD) values in the layer 1000–300 hPa for the domain, 0°–40°N, 40°–120°E in the two contrasting monsoon seasons are evaluated. In active monsoon, (i) predominant low level southwesterly flow over the Arabian sea and deflection of winds over the Bay of Bengal, strengthening of the tropical easterly jet stream, wide area extent of easterlies in the upper troposphere, the maximum strength of easterlies in the upper troposphere (150 hPa) is observed over the area around 10°–15°N and 70°–75°E; (ii) position of subtropical ridge is more northward, i.e., 32°N; (iii) a predominant moisture transport in the layer 1000–300 hPa from Southern Hemisphere, Arabian Sea and the Bay of Bengal to the Indian mainland, westward/northward transport of moisture and area coverage of larger quantum of moisture flux is seen; and (iv) India experienced more number of mesoscale systems. The reverse is true for weak monsoon. Positive (neutral) Indian Ocean Dipole (IOD) and La-Nina (El-Nino) conditions lead to active (poor) summer monsoon conditions over India in 2007 (2009) year.

Corroboration of El Nino and Southern Oscillation (ENSO) events on the climatic variability in the Indian subcontinent is mentioned in various studies. In the Indian context, if we observe the rising number of dengue cases, it could be treated as a major cause of health concern for the government of this country. Nowadays, an increasing number of dengue incidences are reported from different Indian states which are leading to unfortunate hospitalization and fatal death of the people. Keeping the context in mind, we have examined the relationship between the ENSO events, inter-annual variability in dengue cases in major states of India and Indian summer monsoonal rainfall (ISMR). In this study, we use Pearson’s product-moment correlation (hereafter PPMC) to find out the interconnections between ‘+ winter ONI’ (OND, NDJ, DJF, and JFM seasons) events, rainfall index for the JJAS season (June, July, August, September) and annual 10 major state-level data of dengue cases index for the past 14 years. It has been observed through the study that the PPMC result between the ‘rainfall index’ and ‘dengue index’ is showing greater variation among different states of the country. Interestingly, we have observed that the correlation result between the ‘+ winter ONI’ and dengue incidence index have (r) value ranging from highly (−) to very high (+) value −0.53 to + 0.83 across the different states.

Indian Summer and Winter monsoon winds are major drivers of the mixed layer processes in the Arabian Sea. Our study shows that the Arabian Sea &lsq...

The plains of northwest South Asia receive rainfall during both the Indian summer (June–September) and winter (December–March) monsoon. Researchers have long attempted to deconstruct the influence of these precipitation regimes in paleoclimate records, in order to better understand regional climatic drivers and their potential impact on human populations. The mid–late Holocene transition between 5.3 and 3.3 ka is of particular interest in this region because it spans the period of the Indus Civilization from its early development, through its urbanization, and onto eventual transformation into a rural society. An oxygen isotope record of the surface-dwelling planktonic foraminifer Globigerinoides ruber from the northeast Arabian Sea provided evidence for an abrupt decrease in rainfall and reduction in Indus River discharge at 4.2 ka, which the authors linked to the decline in the urban phase of the Indus Civilization (Staubwasser et al., 2003). Given the importance of this study, we used the same core (63KA) to measure the oxygen isotope profiles of two other foraminifer species at decadal resolution over the interval from 5.4 to 3.0 ka and to replicate a larger size fraction of G. ruber than measured previously. By selecting both thermocline-dwelling (Neogloboquadrina dutertrei) and shallow-dwelling (Globigerinoides sacculifer) species, we provide enhanced detail of the climatic changes that occurred over this crucial time interval. We found evidence for a period of increased surface water mixing, which we suggest was related to a strengthened winter monsoon with a peak intensity over 200 years from 4.5 to 4.3 ka. The time of greatest change occurred at 4.1 ka when both the summer and winter monsoon weakened, resulting in a reduction in rainfall in the Indus region. The earliest phase of the urban Mature Harappan period coincided with the period of inferred stronger winter monsoon between 4.5 and 4.3 ka, whereas the end of the urbanized phase occurred some time after the decrease in both the summer and winter monsoon strength by 4.1 ka. Our findings provide evidence that the initial growth of large Indus urban centers coincided with increased winter rainfall, whereas the contraction of urbanism and change in subsistence strategies followed a reduction in rainfall of both seasons.

Loess and stalagmite records in China show different responses of Asian monsoon to the astronomical insolation during Marine Isotope Stage (MIS) 5c and 5e, raising the question whether the amplitudes of the whole Asian monsoon are linearly controlled by the astronomical summer insolation changes and whether the regional differences exist. In this study, a set of numerical experiments are conducted for these stages to examine the sensitivity of Asian summer monsoon to changes in the astronomical parameters. The results highlight a complicated response changing with regions and signals. The East Asian monsoon is remarkably stronger during MIS-5e, which is characterized by southerly winds, primarily due to the anomalous anticyclone over northwestern Pacific. The intensified East Asian monsoon leads to less precipitation in the eastern China and Japan but more in the further north and northwest. However, the Indian monsoon circulation does not vary significantly while the precipitation over Arabian Sea is significantly promoted by the upward air motion. Change in water vapor sources of Indian and Pacific Oceans qualitatively explains the observed differences in stalagmite δ18O records, implying that these proxy changes are primarily controlled by the water vapor delivery from oceans, at least on the astronomical timescale.

The Himalayas in the north part of Indian sub-continent is characterized by variable topography, heterogeneous landuse and climate variations. It acts as a barrier to atmospheric circulation for Indian summer and winter monsoon, thus modulating the associated precipitation over these regions. Western disturbances embedded in Indian winter monsoon (IWM) arriving from Mediterranean region result in one-third of annual precipitation over Himalayas. In the recent decade, studies have shown increased forcings associated with Arctic Oscillations (AOs). In the present study, impact of AO on IWM (December, January, February—DJF) is analyzed. During positive AO years, Polar region is having low surface pressure and colder conditions in comparison with higher pressure with cold surges to midlatitudes during negative AO years. For detailed analysis, National Center of Environmental Prediction/National Center for Atmospheric Research, US reanalysis data is used. Analysis of positive and negative AO year composites shows stronger westerlies over Arabian Sea and neighboring Indian region. Stronger north–south temperature gradient due to warmer Indian Ocean and colder Tibetan region is seen during positive AO years. In addition, weakening of Hadley circulation is seen during positive AO years. This weakening helps in Polar and/or extratropical mass to move southwards having mid-latitude interactions leading to enhanced precipitation over Indian regions. Extensive and intense wave train seen during positive AO years indicates Rossby wave response. Such forcings associated with AOs led to increased precipitation over the northern Indian region.

This study undertakes a comprehensive assessment of dynamical downscaling of summer monsoon (June–September; JJAS) rainfall over heterogeneous regions namely the Western Ghats (WG), Central India (CI) and North-Eastern Region (NER) for long term mean, excess and deficit episodes for the historical period from 1951 to 2005. This downscaling assessment is based on six Coordinated Regional Climate Downscaling Experiments (CORDEX) for South Asia (SAS) region, their five driving Global Climate Models (GCM) simulations along with observations from India Meteorological Department (IMD) and Asian Precipitation Highly Resolved Observational Integrated Towards Evaluation for Water Resources (APHRODITE). The analysis reveals an overall reduction of dry bias in rainfall across the regions of Indian sub-continent in most of the downscaled CORDEX-SAS models and in their ensemble mean as compared to that of driving GCMs. The interannual variabilities during historical period are reasonably captured by the ensemble means of CORDEX-SAS simulations with an underestimation of 0.43%, 38% and 52% for the WG, CI and NER, respectively. Upon careful examination of the CORDEX-SAS models and their driving GCMs revealed considerable improvement in the regionally downscaled rainfall. The value addition of dynamical downscaling is apparent over the WG in Regional Climate Model (RCM) simulations with an improvement of more than 30% for the long term mean, excess and deficit episodes from their driving GCMs. In the case of NER, the improvement in the downscaled rainfall product is more than 10% for all the episodes. However, the value addition in the CORDEX-SAS simulations for CI region, dominantly influenced by synoptic scale processes, is not clear. Nevertheless, the reduction of dry bias in the complex topographical regions is remarkable. The relative performance of dynamical downscaling of rainfall over complex topography in response to local forcing and orographic lifting depict the value addition (30% over WG and 10% over NER, with a statistical significance of more than 5% level), when compared with the synoptic scale system induced rainfall over the plains of central-India.

The Indian and East Asian summer monsoons are two active components of the global monsoon system and are closely related. However, their relationship is weakened after the late 1970s. This study revisited the possible mechanism for the weakening relationship between Indian and central East Asian summer rainfall, focusing on the influence from the middle-to-high-latitude climate system. The results show that variability in the summer North Atlantic Oscillation since the late 1970s induces a zonal atmospheric teleconnection pattern, resulting in anomalous upper level atmospheric circulation south of the Baikal Lake, which is further closely related to central East Asian summer rainfall over the period after the late 1970s. When the signal of the atmospheric circulation variability south of the Baikal Lake is removed, the relationship between the Indian and central East summer rainfall becomes significant again over the period after the late 1970s. The summer North Atlantic Oscillation thus opposes the influence of the Indian summer rainfall on central East Asian summer rainfall, consequently contributing to the breakdown of the Indian–central East Asian summer rainfall relationship after the late 1970s.

Previous studies have found a link between north China and Indian rainfall during summer, with significantly increased rainfall in north China related to a stronger Indian summer monsoon. This link is weakened after the late 1970s, generally attributed to the reduced magnitude of interannual variability in the Indian summer rainfall. This study reveals a similar change in this rainfall link in early summer after the late 1970s. Related to a heavier Indian early summer rainfall, rainfall in north China enhances significantly before the late 1970s but not thereafter. The change in rainfall teleconnection is caused by the weakened impact on north China rainfall of a midlatitude wave train along the Asian jet in the upper troposphere. After the late 1970s, the portion of the wave train over East Asia displaces eastward, leading to an eastward shift in the associated ascending motion and, subsequently, enhanced rainfall from north China to the Yellow Sea. Moreover, the change in the midlatitude wave train is attributed to the change in the basic state over East Asia (i.e., a northward shift of the East Asian upper-tropospheric westerly jet after the late 1970s). The latter reduces stationary Rossby wavenumber and increases wavelength of the midlatitude wave train, leading to an eastward shift of the wave train over East Asia. Therefore, in this study a mechanism is proposed for the change in early summer, different from the previous mechanism for the entire summer period.

Previous studies have indicated a connection between interannual variations of the Indian and North China summer rainfall. An atmospheric circulation wave pattern over the mid-latitude Asia plays an important role in the connection. The present study compares the influence of the above-normal and below-normal Indian summer rainfall on the North China summer rainfall variations. Composite analysis shows that the mid-latitude Asian atmospheric circulation and the North China rainfall anomalies during summer tend to be anti-symmetric in above-normal and below-normal Indian rainfall years. Analysis indicates that the Indian-North China summer rainfall relation tends to be stronger when larger Indian rainfall anomaly occurs during a higher mean rainfall period. The observed long-term change in the Indian-North China summer rainfall relationship cannot be explained by the impact of the El Nino-Southern Oscillation (ENSO). The present study evaluates the Indian-North China summer rainfall relationship in climate models. Analysis shows that the Indian-North China summer rainfall relationship differs largely among different climate models and among different simulations of a specific model. The relationship also displays obvious temporal variations in both individual and ensemble mean model simulations. This suggests an important role of the atmospheric internal variability in the change of the Indian-North China summer rainfall relationship.

In 1977, Jean Rouch visited New York to show his films at the first Margaret Mead Film Festival. Later, he returned to the United States to make his cine-portrait of Mead, and he was invited to teach film workshops in the Boston area. He coined the term “Indian Summer School” for these programs. I taught visual anthropology with Rouch at Harvard Summer School from 1980 to 1986. America fascinated Rouch; he, meanwhile, bewildered his students. In the 1980s, Africa was remote from the consciousness of most Americans, and filmmakers of color were not empowered. Rouch’s films and cinematic inventions opened the students up to new fields, and to the possibility of seeing and representing African societies.

Hydroclimatic variations during the summer monsoon season (June–September) across the Himalaya are examined over the past several hundred years using tree-ring oxygen isotope records. Owing to their strong associations with hydroclimatic variables including precipitation, relative humidity, and the Palmer Drought Severity Index, tree-ring δ18O chronologies from the Himalaya can be used to reconstruct summer monsoon intensity precisely. A regional chronology derived from five local chronologies across the Himalaya shows a significant correlation with Indian summer rainfall data. One of the most noteworthy features of the regional chronology is a drying trend over the past 180 years, indicating that summer monsoon intensity in the Himalayan region has weakened. A declining land–ocean thermal gradient over South Asia seems to be responsible for the weakened summer monsoon. By analyzing spatio-temporal correlations between zonally distributed tree-ring data over the Himalaya, we also explore possible changes in the relative contributions of source water originating in the Arabian Sea and the Bay of Bengal.

The Indian subcontinent receives most of its annual precipitation due to Indian summer (June, July, August and September) monsoon. Southeastern coastal region of the India receives significant amount of precipitation due to the northeast monsoon (October and November). Over northern Indian region almost one-third of annual precipitation is received during winter (December, January and February) by eastward moving extratropical cyclone called ‘western disturbances (WDs)’ in Indian meteorological parlance. Various studies are conducted to understand the Indian summer and northeast monsoons. However, the dynamics and characterization of winter precipitation is not well understood except with reference to the western disturbances (WDs). In this study, wintertime dynamics associated with large-scale flows and WDs influencing winter precipitation is proposed and termed ‘Indian winter monsoon’. In addition, winter precipitation – the Indian winter monsoon – is proposed as eastward traveling WDs embedded in the large-scale subtropical westerlies over the Indian sub-continent. During winter (December, January and February) upper level subtropical westerly jet moves southwards and passes over the Indian sub-continent and provides associated precipitation over the northern Indian region. With concurrent research and changing global context, increased understanding of the Indian winter monsoon is imperative. Equally important is the behavior of WDs showing different patterns in the Peninsular India and the Himalaya particularly during the Holocene. During the Little Ice Age (LIA), it appears that high frequency of El Nino events was responsible for drier conditions in the core monsoon zone but generated more monsoon “breaks” over the Himalaya and thus the climatic conditions in the core Indian summer monsoon area were generally opposite to those in the foothills of the Himalaya during the Holocene period. During this period, a higher frequency of El Nino events might have restricted transport of warm water to the North Atlantic Ocean and brought about a cooling of adjacent continents including Central Asia and this may have amplified the extent of snow over Asia during the winter, and may even have been accounted for early snow in the region at the expanse of reduction in the Indian summer monsoon strength. Thus, this study delineates the Indian winter monsoon at intraseasonal-sub seasonal-interannual-paleoclimate scale and provides comprehensive details on defining the Indian winter monsoon and makes an attempt to understand the WDs particularly from mid-Holocene onwards as well.

Hydroclimatic process in the Yarlung Tsangpo River (YTR) basin, a sensitive area to climate change, is obviously changing during recent years, but there has limited understanding about it. In this study, we investigated the spatiotemporal variation of precipitation over last four decades in the basin and the impact thereon of the changing Indian summer monsoon at interannual and decadal time scales. All the precipitation series have similar scaling behavior, reflecting similar climatic regime throughout the basin. However, the effect of the Indian monsoon strengthens from the downstream to upstream, causing spatial variability in the seasonal distribution of precipitation, and on this basis, the YTR basin is roughly divided into three regions: east, middle, and west. Both the occurrence times and magnitude of precipitation extremes, ranging 25-50mm/d, are exhibiting downward trends over the last four decades, which bodes well for water disaster controls in the basin. The Indian summer monsoon index, as an intensity indicator for the Indian summer monsoon, shows a positive relationship with the summer precipitation in the YTR basin. Periodic variability of the Indian monsoon determines the interannual nonstationary fluctuations of precipitation. Especially, the weakening effect of the Indian summer monsoon has caused an obvious decrease in precipitation over the rainy season after 1998. If the Indian summer monsoon keeps weakening, the precipitation would decrease and potentially water shortage would become more severe in the basin. Effective adaptation strategy should therefore be developed proactively to handle the unfavorable water situation, which is likely to occur in the future.

The El Nino–Southern Oscillation (ENSO) is a main driving force of the northern hemisphere summer monsoon rainfall, including the Indian Summer Rainfall (ISR). The impacts of typical ENSO and atypical ENSO events on the ISR remain unclear during their developing summers. This study examines the different linkages between a typical ENSO and the ISR and between an a typical ENSO and the ISR. During the developing summer of a typical El Nino, negative rainfall anomalies are seen over the northeastern Indian subcontinent, while the anomalous rainfall pattern is almost the opposite for a typical La Nina; as for an atypical ENSO, the approximate “linear opposite” phenomenon vanishes. Furthermore, an anomalous global zonal wave train is found at mid-latitudes, with a local tripole circulation pattern over central–eastern Eurasia during the developing summer of a typical ENSO, which might explain the corresponding rainfall response over the Indian Peninsula. By contrast, such features are not obvious duri...

Prediction of Indian summer (June–September) rainfall on regional scales remains an open issue. The operational predictions of West Central Indian summer rainfall (WCI-R) and Peninsular Indian summer rainfall (PI-R) made by the Indian Meteorological Department (IMD) had no skills during 2004–2012. This motivates the present study aiming at better understanding the predictability sources and physical processes governing summer rainfall variability over these two regions. Analysis of 133 year data reveal that although the lower boundary forcing that associated with enhanced WCI-R and PI-R featured a similar developing La-Nina and “east high west low” sea-level pressure (SLP) dipole pattern across the Indo-Pacific, the anomalous high sea surface temperature (SST) over the northern Indian Ocean and weak low pressure over northern Asia tended to enhance PI-R but reduce WCI-R. Based on our understanding of physical linkages with the predictands, we selected four and two causative predictors for predictions of the WCI-R and PI-R, respectively. The intensified summer WCI-R is preceded by (a) Indian Ocean zonal dipole-like SST tendency (west-warming and east-cooling), (b) tropical Pacific zonal dipole SST tendency (west-warming and east-cooling), (c) central Pacific meridional dipole SST tendency (north-cooling and south-warming), and (d) decreasing SLP tendency over northern Asia in the previous season. The enhanced PI-R was lead by the central-eastern Pacific cooling and 2-m temperature cooling tendency east of Lake Balkhash in the previous seasons. These causative processes linking the predictors and WCI-R and PI-R are supported by ensemble numerical experiments using a coupled climate model. For the period of 1871–2012, the physics-based empirical (P-E) prediction models built on these predictors result in cross-validated forecast temporal correlation coefficient skills of 0.55 and 0.47 for WCI-R and PI-R, respectively. The independent forecast skill is significantly higher than the skill of operational seasonal forecast made by the IMD for the period of 2004–2012. These prediction models offer a tool for seasonal prediction and their retrospective forecast skills provide an estimation of the lower bound of the predictability for WCI-R and PI-R.

Monthly correlation of Indian monsoon rainfall (IMR) index with various monsoon indices changes predominantly and peaks within summer season (Ailikun and Yasunari, 2001). There is transition in this lead and lagged correlation during spring (March, April and May). This spring transition could not be captured in many general circulation models (GCMs) and is termed as “predictability barrier” (Latif and Graham, 1991). It has been less investigated and hence reasons for dampening/reversal of associated large scale fields during spring are intriguing. Present study illustrates dynamics of spring predictability barrier with Indian summer (June, July, August and September) monsoon (ISM). In this study, based on data from 1979 to 2008, an internal dynamics between various monsoon indices and corresponding IMR anomaly is diagnosed. It is found that secular behaviour of El Nino– Southern Oscillation (ENSO) during preceding spring of monsoon months (June, July, August and September) gets reversed in succeeding spring. Though correlation between various monsoon indices and ISM index remains similar during preceding and succeeding springs with peaks during monsoon (June, July, August and September), corresponding large scale fields show that strong significant convection dominates over the southern equatorial eastern Pacific Ocean, northern equatorial western Pacific Ocean, Indonesian throughflow and weaker significant convection dominates over the Head Bay of Arabian Sea and western to central Indian sub-continent during preceding spring. Such patterns reverse during succeeding spring.

The onset/progression phase of theIndian summer monsoon (ISM) is very crucial for the agricultural sector of the country as it has strong bearing on the sowing of kharif crops, which in turn affects overall food grain production and hence food security. The recent ISMs of 2013 and 2014 exhibited quite distinct progression phases. While 2013 had one of the fastest advancement in the last 70 years, 2014 witnessed a comparatively lethargic progression phase. The major difference was felt in the early monsoon month of June, with 2013 (2014) monthly rainfall being +34% (−43%) of its long period average. Observational investigations reveal that, during June 2013, the monsoon trough was very active in its normal position favouring low-level positive vorticity generation and moisture convergence, whereas the absence of monsoon trough during June 2014 facilitated the prevalence of a strong low-level anticyclonic circulation over central India hampering the northward progression of the ISM. It is found that June 2013 (2014) was associated with (i) stronger (weaker) north-south tropospheric temperature (TT) gradient with positive (negative) TT anomalies over Eurasia and north of 60°N; (ii) negative (positive) SST anomalies over the equatorial Indian Ocean, northwestern Arabian Sea and equatorial eastern Pacific; (iii) stronger (weaker) monsoonal Hadley circulation; and (iv) stronger (weaker) Walker circulation in response to the negative (positive) SST anomalies over the equatorial Pacific. The study also examines the skill of an Ensemble Prediction System (EPS) in predicting the observed contrasting behaviour during June 2013/2014 on extended range (∼15–20 days in advance) in real time. The EPS not only forecasted the observed discrepancy, but also predicted the influential role of the large-scale meteorological conditions prevalent during June 2013 (2014), thus demonstrating the remarkable skill of the EPS in predicting June extremes.

The plains of northwest South Asia receive rainfall during both the Indian Summer (June–September) and Winter (December–March) Monsoon. Researchers have long attempted to deconstruct the influence of both precipitation regimes in paleoclimate records, in order to better understand regional climatic drivers and their potential impact on human populations. The Mid–Late Holocene transition between 5.3–3.3 ka BP is of particular interest in this region because it spans the period of the Indus Civilization from its early development to eventual transformation. The oxygen isotope record of the surface-dwelling planktonic foraminifer Globigerinoides ruber from the northeast Arabian Sea provided evidence for an abrupt decrease in rainfall and reduction in Indus River discharge at 4.2 ka BP, which the authors linked to the decline of the urban phase of the Indus Civilization (Staubwasser et al., 2003). Given the importance of this study, we used the same core (63KA) to replicate the oxygen isotope profiles of a larger size fraction of G. ruber than measured previously and, in addition, we measured two other foraminifer species at decadal resolution over the interval from 5.4 to 3.0 ka BP. By selecting both thermocline-dwelling (Neogloboquadrina dutertrei) and shallow-dwelling (Globigerinoides sacculifer) species, we provide enhanced detail of the climatic changes that occurred over this crucial time interval. We found evidence for a period of increased surface water mixing, which we suggest was related to a strengthened winter monsoon with a peak intensity over 200 years from 4.5 to 4.3 ka BP. The time of greatest change occurred at 4.1 ka BP when both the summer and winter monsoon weakened, resulting in a reduction in rainfall in the Indus region. The earliest phase of the Mature Harappan period coincided with the period of inferred stronger winter monsoon between 4.5–4.3 ka BP, whereas the end of the urbanized phase followed the decrease in both the summer and winter monsoon strength by 4.1 ka BP. Our findings provide evidence that the initial growth of large Indus urban centers was coincident with increased winter rainfall, whereas the contraction of urbanism and change in subsistence strategies followed a reduction in rainfall of both seasons.

In this paper, the impact of the SST drifts in the ECMWF system 3 forecasting system on the simulated monsoon climatology is investigated. It is shown that hindcasts initialized in February show paradoxically better climatological rainfall in the early monsoon season compared to the hindcasts initialized in the May. The differences in rainfall and SST evolution in the two hindcast sets point to the SST differences as the crucial factor that improves the February initialized hindcasts. Further experiments with the atmospheric component of the ECMWF system 3 forecasting system confirm this by showing similar rainfall biases in the early monsoon season as the hindcasts initialized in the May. This study points to the potential beneficial impacts of reducing systematic biases in the atmospheric components forecasting systems, and of an anomaly initialization technique to improve Indian Monsoon forecasts.

The Indian summer (JJAS) shows high variability in both space and timescales. Changes in precipitation extremes play an important role on the regional scale due to their serious socio-economic consequences. This study, therefore, is mainly focused on understanding the variation of precipitation extremes during summer monsoon season in the presence of cyclonic disturbances forming over the Bay of Bengal (BOB), Arabian Sea, Land Area (LA) and Total. For this, several indices of observed precipitation extremes, in terms of frequencies, intensities and spell duration have been computed for the period 1951–2007 using daily APHRODITE data of 0.5° latitude × 0.5° longitude resolution. Correlation analysis reveals that a large part of the country exhibits positive relationship between the indices of precipitation extremes and frequency of cyclonic disturbances. Correlations with the indices of frequencies defined as seasonal count of days when rainfall exceeds 30, 20 and 10 mm show that spatial extent and strength of the positive relationship decreases with increase in threshold values. Disturbances forming over BOB play dominant role in precipitation during Indian summer monsoon.

We present a shoreline-based, millennial-scale record of lake-level changes spanning 12.8–2.3 ka for a large closed-basin lake system on the southwestern Tibetan Plateau. Fifty-three radiocarbon and eight U–Th series ages of tufa and beach cement provide age control on paleoshorelines ringing the basin, supplemented by nineteen ages from shell and aquatic plant material from natural exposures generally recording lake regressions. Our results show that paleo-Ngangla Ring Tso exceeded modern lake level (4727 m asl) continuously between ~ 12.8 and 2.3 ka. The lake was at its highstand 135 m (4862 m asl) above the modern lake from 10.3 ka to 8.6 ka. This is similar to other closed-basin lakes in western Tibet, and coincides with peak Northern Hemisphere summer insolation and peak Indian Summer Monsoon intensity. The lake experienced a series of millennial-scale oscillations centered on 11.5, 10.8, 8.3, 5.9 and 3.6 ka, consistent with weak monsoon events in proxy records of the Indian Summer Monsoon. It is unclear whether these events were forced by North Atlantic or Indian Ocean conditions, but based on the abrupt lake-level regressions recorded for Ngangla Ring Tso, they resulted in significant periodic reductions in rainfall over the western Tibetan Plateau throughout the Holocene.

Precipitation samples were collected across the Himalayas from Kashmir (western Himalaya) to Assam (eastern Himalaya) to understand the variation of the stable isotopic content ( $$\updelta ^{18}$$ O and $$\updelta $$ D) in precipitation associated with two dominant weather systems of the region: western disturbances (WDs) and Indian summer monsoon (ISM). Large spatial and temporal variations in isotopic values were noted with $$\updelta ^{18}$$ O and $$\updelta $$ D values ranging from $$-30.3$$ to and $$-228$$ to , respectively. The d-excess values also exhibit a large range of variation from $$-30$$ to . In general, heavier isotopic values are observed in most of the samples in Jammu, whereas lighter values are observed in majority of the samples in Uttarakhand. Precipitation at Jammu seems to have undergone intense evaporation while that from Uttarakhand suggest normal Rayleigh fractionation/distillation of the air mass as it moves from the source region to the precipitation site and/or orographic lifting. The d-excess of rainfall in Kashmir has a distinctly higher median value of compared to other precipitation sites with a median of . Using distinct isotopic signatures, the regions receiving precipitation from two different weather systems have been identified.

Spring snow cover variations over Eurasia consist of a same-sign component and a west-east dipole component. The same-sign component is dominant during late 1970s through 1980s, and the two components are equally important during 1990s and 2000s. Present study contrasted Eurasian spring and summer climate anomalies associated with western and eastern Eurasian spring snow cover variations and between 1975–1989 and 1993–2007 and found notable differences and obvious interdecadal changes in Eurasian climate anomalies. After 1990, spring surface temperature anomalies display an obvious west-east contrast pattern, consistent with a prominent atmospheric wave pattern over Eurasia. The temperature anomalies are larger corresponding to western than eastern Eurasian snow cover change. Snow-albedo effect plays a main role in temperature change during 1975–1989, whereas atmospheric processes also contribute largely to temperature change during 1993–2007. Large soil moisture anomalies occur corresponding to western Eurasian snow cover and during 1975–1989. The snow-hydrological effect on summer precipitation is mainly detected over the West Siberian Plain where soil moisture anomalies persist over 3 months. Over most of other Eurasian regions, atmospheric circulation pattern plays a dominant role in summer surface temperature and precipitation variations. The relationship of Indian summer rainfall to western Eurasian spring snow cover was weakened since the mid-1990s, and the correlation of Northeast China summer rainfall with local spring snow cover changed from positive to negative around 1990.

Using observational and reanalyses data, we investigated the impact of dust aerosols over the Middle East and the Arabian Sea (AS) on the Indian summer monsoon (ISM) rainfall. Satellite and aerosol reanalysis data show extremely heavy aerosol loading, mainly mineral dust, over the Middle East and AS during the ISM season. Multivariate empirical orthogonal function analyses suggest an aerosol-monsoon connection. This connection may be attributed to dust-induced atmospheric heating centered over the Iranian Plateau (IP), which enhances the meridional thermal contrast and strengthens the ISM circulation and rainfall. The enhanced circulation further transports more dust to the AS and IP, heating the atmosphere (positive feedback). The aerosols over the AS and the Arabian Peninsula have a significant correlation with rainfall over central and eastern India about 2 weeks later. This finding highlights the nonlocal radiative effect of dust on the ISM circulation and rainfall and may improve ISM rainfall forecasts.

A large spread exists in both Indian and Australian average monsoon rainfall and in their interannual variations diagnosed from various observational and reanalysis products. While the multi model mean monsoon rainfall from 59 models taking part in the Coupled Model Intercomparison Project (CMIP3 and CMIP5) fall within the observational uncertainty, considerable model spread exists. Rainfall seasonality is consistent across observations and reanalyses, but most CMIP models produce either a too peaked or a too flat seasonal cycle, with CMIP5 models generally performing better than CMIP3. Considering all North-Australia rainfall, most models reproduce the observed Australian monsoon-El Nino Southern Oscillation (ENSO) teleconnection, with the strength of the relationship dependent on the strength of the simulated ENSO. However, over the Maritime Continent, the simulated monsoon-ENSO connection is generally weaker than observed, depending on the ability of each model to realistically reproduce the ENSO signature in the Warm Pool region. A large part of this bias comes from the contribution of Papua, where moisture convergence seems to be particularly affected by this SST bias. The Indian summer monsoon-ENSO relationship is affected by overly persistent ENSO events in many CMIP models. Despite significant wind anomalies in the Indian Ocean related to Indian Ocean Dipole (IOD) events, the monsoon-IOD relationship remains relatively weak both in the observations and in the CMIP models. Based on model fidelity in reproducing realistic monsoon characteristics and ENSO teleconnections, we objectively select 12 “best” models to analyze projections in the rcp8.5 scenario. Eleven of these models are from the CMIP5 ensemble. In India and Australia, most of these models produce 5–20 % more monsoon rainfall over the second half of the twentieth century than during the late nineteenth century. By contrast, there is no clear model consensus over the Maritime Continent.

Heat wave is a hazardous weather-related extreme event that affects living beings. The 2015 summer heat wave affected many regions in India and caused the death of 2248 people across the country. An attempt has been made to quantify the intensity and duration of heat wave that resulted in high mortality across the country. Half hourly Physiologically Equivalent Temperature (PET), based on a complete heat budget of human body, was estimated using automatic weather station (AWS) data of four locations in Andhra Pradesh state, where the maximum number of deaths was reported. The heat wave characterization using PET revealed that extreme heat load conditions (PET >41) existed in all the four locations throughout May during 2012-2015, with varying intensity. The intensity and duration of heat waves characterized by "area under the curve" method showed good results for Srikakulam and Undi locations. Variations in PET during each half an hour were estimated. Such studies will help in fixing thresholds for defining heat waves, designing early warning systems, etc.

It has been demonstrated in climate models that both the Indian and East Asian summer monsoons (ISM and EASM) are strengthened by the uplift of the entire Asian orography or Tibetan Plateau (TP) (i.e. bulk mountain uplift). Such an effect is widely perceived as the major mechanism contributing to the evolution of Asian summer monsoons in the Neogene. However, geological evidence suggests more diachronous growth of the Asian orography (i.e. regional mountain uplift) than bulk mountain uplift. This demands a re-evaluation of the relation between mountain uplift and the Asian monsoon in the geological periods. In this study, sensitivity experiments considering the diachronous growth of different parts of the Asian orography are performed using the regional climate model COSMO-CLM to investigate their effects on the Asian summer monsoons. The results show that, different from the bulk mountain uplift, the regional mountain uplift can lead to an asynchronous development of the ISM and EASM. While the ISM is primarily intensified by the thermal insulation (mechanical blocking) effect of the southern TP (Zagros Mountains), the EASM is mainly enhanced by the surface sensible heating of the central, northern and eastern TP. Such elevated surface heating can induce a low-level cyclonic anomaly around the TP that reduces the ISM by suppressing the lower tropospheric monsoon vorticity, but promotes the EASM by strengthening the warm advection from the south of the TP that sustains the monsoon convection. Our findings provide new insights to the evolution of the Asian summer monsoons and their interaction with the tectonic changes in the Neogene.

A multi-millennial run of the CSIRO Mark2 coupled climatic model has been used to investigate megadroughts and megafloods during the Indian summer monsoon (June–September). These extreme events were defined as having rainfall anomalies at least two standard deviations from normal. More than ten megafloods and more than twenty megadroughts, so-defined, were found to occur in a 5,000-year period of the simulation. The simulation replicated most of the major features of the observed summer monsoon, but a comparison of observed and simulated probability density functions suggests that the limited observed rainfall time series to date does not adequately sample the possible range of Indian monsoonal rainfall. An investigation of causal mechanisms of Indian rainfall variability reproduced the observed negative correlation with ENSO events, but it was found that neither extreme ENSO events or extremes of a range of other climatic phenomena coincided with the simulated, extreme megadroughts and megafloods. This disconnect between these events is succinctly illustrated with examples related to ENSO events in particular. Autoregressive and FFT analysis of observed and simulated Indian summer monsoon rainfall time series revealed them to consist of white noise. Since these time series therefore consist of random outcomes, it is apparent that these Indian megadroughts and megafloods are the consequence of stochastic influences. Thus, it is concluded that the interannual variability of Indian summer monsoonal rainfall cannot be predicted in general, nor can megadroughts and megafloods in particular.

The Anglo-Indian composer Kaikhosru Shapurji Sorabji (1892–1988) is best known for his virtuosic, highly decorative and complex style of piano music and vast post-Romantic scale, as typified by his magnum opus, Opus Clavicembalisticum. In his last creative period (post-1973), however, he composed a number of more concise works which depart from the idiom of the piano. This article examines two of these works, Il tessuto d'arabeschi (1979) for flute and string quartet, and Fantasiettina Atematica (1981) for wind trio. It looks primarily at the place of these two works in Sorabji's oeuvre as a whole, but also the wider issues of Sorabji's compositional approach and musical attitudes in later life.

A few studies from the western Arabian Sea indicate that the Indian summer (or southwest) monsoon (ISM), after attaining its maximum intensity at ca. 9 ka, declined during the Holocene, as did insolation. In contrast, earlier and later observations from both the eastern and the western Arabian Sea do not support this inference. Analysis of multiple proxies of productivity in a new sediment core from the western Arabian Sea fails to confirm the earlier, single-proxy (e.g. abundance of Globigerina bulloides) based, inference of the Holocene weakening of ISM, following insolation. The reason for the observed decreasing trend in foraminiferal abundance – the basis for the earlier inference – could be the favouring of silicate rather than carbonate productivity by the increased ISM wind strength. Although ISM exhibits several multi-millennial scale fluctuations, there is no evidence from several multi-proxy data to conclude that it declined during the Holocene; this is consistent with the phase lag analysis of longer time series of monsoon proxies. Thus, on sub-Milankovitch timescales, ISM did not follow insolation, highlighting the importance of internal feedbacks. A comparison with East Asian summer monsoon (EASM) records suggests that both ISM and EASM varied in unison, implying common forcing factors on such longer timescales. Copyright © 2010 John Wiley & Sons, Ltd.

This paper examines an issue concerning the simulation of anomalously wet Indian summer monsoons like 1994 which co-occurred with strong positive Indian Ocean Dipole (IOD) conditions in the tropical Indian Ocean. Contrary to observations it has been noticed that standalone atmospheric general circulation models (AGCM) forced with observed SST boundary condition, consistently depicted a decrease of the summer monsoon rainfall during 1994 over the Indian region. Given the ocean–atmosphere coupling during IOD events, we have examined whether the failure of standalone AGCM simulations in capturing wet Indian monsoons like 1994 can be remedied by including a simple form of coupling that allows the monsoon circulation to dynamically interact with the IOD anomalies. With this view, we have performed a suite of simulations by coupling an AGCM to a slab-ocean model with spatially varying mixed-layer-depth (MLD) specified from observations for the 1994 IOD; as well as four other cases (1983, 1997, 2006, 2007). The specification of spatially varying MLD from observations allows us to constrain the model to observed IOD conditions. It is seen that the inclusion of coupling significantly improves the large-scale circulation response by strengthening the monsoon cross-equatorial flow; leading to precipitation enhancement over the subcontinent and rainfall decrease over south-eastern tropical Indian Ocean—in a manner broadly consistent with observations. A plausible physical mechanism is suggested to explain the monsoonal response in the coupled frame-work. These results warrant the need for improved monsoon simulations with fully coupled models to be able to better capture the observed monsoon interannual variability.