Indian monsoon

Somali upwelling history has been reconstructed for the last 18.5 ka BP based on biogenic silica fluxes estimated from a sediment core retrieved from the western Ara-bian Sea. Surface winds along the east African coast during the southwest monsoon (SWM) cause the Somali up-welling; thus, the intensity of this upwelling has been related to the variability of the SWM. Biogenic silica flux variation suggests periodic weakening and strengthening of the Somali upwelling. Weakened upwelling during the 18.5–15 ka BP period and strengthened upwelling during the Bølling–Allerød (15–12.9 ka BP) suggest the onset of the SWM. The Younger Dryas (12.9–11.7 ka BP) is marked by reduced upwelling strength, with an intensification of the So-mali upwelling observed at the beginning of the Holocene and a further decline at 8 ka BP. The increase in the upwelling strength recorded since 8 ka BP suggests SWM strengthening during the latter part of the Holocene. A comparison of upwelling variations with the SWM precipitation record demonstrates a reversal in the relationship between the strength of the Somali upwelling and SWM rainfall at the beginning of the Holocene. This observed shift has been attributed to the variation in the SWM strength due to the latitudinal shift of the intertropical convergence zone (ITCZ) associated with changes in moisture sources.

Centralized system of production, distribution and consumption triggered nationalism and monoculture that inspired Fascism and also the root cause of global warming. Monsoon wisdom endgendred decentralized systems of production, distribution and consumption.

The aim of the present study is to find out the possible linkage between the North Atlantic Oscillation (NAO), a major ocean–atmosphere coupled phenomena believed to be responsible for the variability of Indian Summer Monsoon Rainfall (ISMR) and its relation with Quasi-Biennial Oscillation (QBO) using 60 years (1953–2012) period. Spring North Atlantic Oscillation Index (NAOI) has been found to be inversely correlated with the ISMR, which has been highly enhanced during the east years when the NAOI data have been stratified according to the phases of QBO. The effect of NAOI on the ISMR is shown to be strengthening significant in the later years of the study as compared to that of the initial years of the study. This interesting result provides an input to use it as a predictor of the ISMR.

Recent satellite observations show efficient vertical transport of Asian pollutants from the surface to the upper-level anticyclone by deep monsoon convection. In this paper, we examine the transport of carbonaceous aerosols, including black carbon (BC) and organic carbon (OC), into the monsoon anticyclone using of ECHAM6-HAM, a global aerosol climate model. Further, we investigate impacts of enhanced (doubled) carbonaceous aerosol emissions on the upper troposphere and lower stratosphere (UTLS), underneath monsoon circulation and precipitation from sensitivity simulations. The model simulation shows that boundary layer aerosols are transported into the monsoon anticyclone by the strong monsoon convection from the Bay of Bengal, southern slopes of the Himalayas and the South China Sea. Doubling of emissions of both BC and OC aerosols over Southeast Asia (10 • S-50 • N, 65-155 • E) shows that lofted aerosols produce significant warming (0.6-1 K) over the Tibetan Plateau (TP) near 400...

श्याम मनोहर- मौखिक आणि लिखित, या पुस्तकाचा हा परिचय आहे. एन्लायन्मेंट या युरोपातील सांस्कृतिक आंदोलनाचे हिरो म्हणजे न्यूटन, व्हॉल्तेयर आणि दिदेरो. निसर्गचे नियम असतात त्यांचं ज्ञान झालं तर प्रगत तंत्रज्ञान रचता येतं, त्यामुळे उपभोग्य वस्तुंचं उत्पादन वाढवून मानवी समाज सुखी होऊ शकतो, ही या आंदोलनाची प्रेरणा होती. निसर्गाप्रमाणेच समाजाचे म्हणून व्यक्तीचेही नियम असतात. त्यांचा शोध घेतला म्हणजे त्यांचं ज्ञान झालं तर अधिक चांगला समाज निर्माण करणं शक्य आहे हेही याच आंदोलना दरम्यान सुस्थापित झालं. त्यातून युरोपमध्ये आमूलाग्र बदल झाले. अज्ञाताचा शोध आणि ज्ञान, याला त्यामध्ये केंद्रस्थान होतं.
भारतातील समाजसुधारणा असोत की कला-साहित्य वा विज्ञान, यांच्याबाबतीत ज्ञानाचा मुद्दा अभावानेच दिसतो. श्याम मनोहर- मौखिक आणि लिखित, या पुस्तकाचा परिचय करून देताना मी या मुद्द्याकडे लक्ष वेधलं आहे.

Two sediment cores from the western (905; 10.46°90N, 51.56°40E, water depth 1586 m) and eastern (SK17; 15°150N, 72°580E, water depth 840 m) Arabian Sea were used to study past sea surface temperatures (SST) and seawater d18O (d18Ow) variations for the past 35 ka. We used coupled Mg/Ca-d18O calcite variability in two planktonic foraminiferal species: Globigerinoides ruber, which thrives throughout the year, and Globigerina bulloides, which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing. SSTs in both areas based on Mg/Ca in G. ruber were 􏱜3 to 4°C lower during the Last Glacial Maximum (LGM; 􏱜21 ka) than today and the Holocene period. The SST records based on G. bulloides also indicate general cooling, down to 18°C in both areas. SSTs in the western Arabian Sea based on G. bulloides were always lower than those based on G. ruber, indicating the presence of strong seasonal temperature contrast during the Holocene and LGM. We interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling (SW monsoon) and winter convective mixing (NE monsoon) in the western Arabian Sea. In the eastern Arabian Sea, G. bulloides-based SSTs were slightly lower (about 1°C) than G. ruber-based SSTs during the Holocene, indicating the almost absence of a seasonal temperature gradient, similar to today. However, a large seasonal temperature contrast occurred during the LGM which favors the assumption that strong NE monsoon winds forced winter upwelling or convective mixing offshore Goa. SST and d18Ow reconstructions reveal evidence of millennial-scale cycles, particularly in the eastern Arabian Sea. Here, the stadial periods (Northern Hemisphere cold periods such as Younger Dryas and Heinrich events) are marked by increasing SSTs and salty sea surface conditions relative to those during the interstadial periods. Indeed, the d18Ow record shows evidence of low-saline surface waters during interstadial periods, indicating increased freshwater runoff from the Western Ghats as a consequence of enhanced SW monsoon intensity.

The late early to middle Miocene sediments at Varkala cliff section (SW India) offer a great potential to study paleoenvironmental and paleoclimatic conditions. The succession consists of coastal marine sands alternating with fine grained, organic-rich siliciclastics. Based on several palyno-samples, a mangrove flora could be reconstructed, composed of Rhizophoraceae, Avicennia, Xylocarpus, and Sonneratia. These grew in front of backswamps, followed by evergreen forests in hinterland with many rainforest elements.

Despite these similarities between the Miocene and the modern vegetation, differences can be documented, e.g., the abundance of Nypa and the absence of gymnosperm in the Miocene vegetation. Based on the Coexistence Approach, a temperature is reconstructed, which is similar to today's (mean annual temperature 22.2–27.5 °C; coldest month temperature 20.6–23.6 °C; warmest month temperature 27.5–28.1 °C). However, in comparison to today, significantly lower values for the mean annual precipitation are reconstructed (1748–1958 mm), although a seasonality pattern was established (wettest month mean precipitation 225–358 mm; driest month mean precipitation 18–83 mm).

Comparison with other localities along the west coast of southern India hints at a similar vegetation and climate throughout the early and middle Miocene. Furthermore, the same results were obtained for SE India. This is in contrast to the strong west-east gradient in rainfall caused by the Indian Monsoon nowadays. Therefore, the paleovegetation of the early and middle Miocene of southern India appears to be more uniform than today. This outlines the complexity of describing the paleoclimatic evolution in the tropics based on plant fossils, but emphasizes the need for further study of this area to understand the early history of the Indian Monsoon.

The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

The Indus Delta is constructed of sediment eroded from the western Himalaya and since 20 ka has been subjected to strong variations in monsoon intensity. Provenance changes rapidly at 12–8 ka, although bulk and heavy mineral content remains relatively unchanged. Bulk sediment analyses shows more negative ε Nd and higher 87 Sr/86 Sr values, peaking around 8–9 ka. Apatite fission track ages and biotite Ar–Ar ages show younger grains ages at 8–9 ka compared to at the Last Glacial Maximum (LGM). At the ...

The Indus Delta is constructed of sediment eroded from the western Himalaya and since 20 ka has been subjected to strong variations in monsoon intensity. Provenance changes rapidly at 12–8 ka, although bulk and heavy mineral content remains relatively unchanged. Bulk sediment analyses shows more negative 1 Nd and higher 87 Sr/ 86 Sr values, peaking around 8 –9 ka. Apatite fission track ages and biotite Ar–Ar ages show younger grains ages at 8– 9 ka compared to at the Last Glacial Maximum (LGM). At the same time d 13 C climbs from – 23 to – 20‰, suggestive of a shift from terrestrial to more marine organic carbon as Early Holocene sea level rose. U–Pb zircon ages suggest enhanced erosion of the Lesser Himalaya and a relative reduction in erosion from the Transhimalaya and Karakoram since the LGM. The shift in erosion to the south correlates with those regions now affected by the heaviest summer monsoon rains. The focused erosion along the southern edge of Tibet required by current te...

The Kazakhstan orocline, a pair of concentric horseshoe-shaped volcanic arcs of Devonian (external) and late Paleozoic (internal) age, is thought to have formed during the amalgamation of Eurasia. Paleomagnetic investigations of several volcanic complexes ranging in age from Silurian to Permian are described in Chapters 2, 3 and 4 of this thesis. These studies have resulted in the construction of a tectonic model for the formation of the Kazakhstan orocline. Our results suggest that in the Middle Devonian, a nearly straight, northwest-southeast trending volcanic arc delineated the northeastern margin of the Kazakhstania landmass. In the Late Devonian, an initial collision with Tarim pinned Kazakhstania's southern corner, while dextral shear motion and the considerable clockwise rotation of Siberia dragged its northern end. Relative convergence between Siberia and Tarim caused initial buckling of the Kazakhstania continent trapped between them, subdividing the volcanic arc into three (southwestern, middle, and northeastern) segments. Continued subduction under the established limbs of the orocline, with an estimated outward-directed subduction velocity of ˜6mm/yr, gradually led to the closure of the intervening Junggar-Balkhash Ocean and tightening of the orocline. By the Late Permian, the Junggar-Balkhash Ocean no longer existed and the Kazakhstan orocline had obtained its present-day strongly curved shape. The ratio of two pedogenic iron oxides, goethite and hematite, has been demonstrated to be a good proxy for precipitation in soil-forming (terrestrial) environments. A similar interpretation of the mineral ratio has been increasingly applied to studies of marine sediments, in which variation in the goethite to hematite ratio is thought to reflect variation in the precipitation regime at the source area of the sediments. The rock magnetic study of Bengal Fan sediments described in Chapter 5 of this thesis suggests that in some intervals of the studied sedimentary section, variation in the ratio reflects a change in the degree of diagenetic alteration of the initial detrital assemblage rather than a climatic signal. Therefore, when assigning climatic interpretation to changes in the relative abundance of goethite and hematite in marine sediments, the possibility of diagenetic modification should be evaluated.

Simulations with climate models is a computationally challenging problem. It is even more challenging when a coupled model of ocean and atmosphere is used. In this article, we report the implementation of a coupled ocean–atmospheric model on the PARAM Padma, a high-performance ...

The transition phase of Indian monsoon has strong impacts on the agriculture, societal, and economic conditions of India. The present study addresses the role of South Asian High (SAH) and subtropical westerly jet (STJ) on the transition period (onset and withdrawal) of the Indian summer monsoon. For this purpose, we have utilized the output of the Regional Climate Model (RegCM v4.6) and reanalysis ERA5 pressure level data for 24 years (1982 - 2005) of study. We begin our analysis with the evaluation of Tibetan Plateau (TP) heating and its connection with different atmospheric factors during the seasonal transition of monsoon is perused. We have further tried to decipher the link between SAH and inter-annual variability of monsoon. Our analysis shows the efficiency of the model in simulating inter-annual variability of monsoon onset and withdrawal features. The days of onset and withdrawal simulated by the model have a similar mid-latitude connection as that obtained from the reanalysis data. The vertical structure of the Hadley cell and the horizontal position of SAH have been produced realistically during the transition of the monsoon. We found that the change in meridional position of STJ has a significant impact on phase-shifting of arrival and departure of monsoon. This repositioning of STJ in a meridional direction is strongly correlated to the upper-level high developed over the eastern periphery of the western pacific which is an important component of monsoon flow over the Bay of Bengal. Thus the zonal position of SAH is observed to have direct implications on the onset and withdrawal dates of India.

A 4.9-m-thick lake sequence, formed due to the landslide damming of a stream in the semiarid Garhwal Himalaya, was studied to understand past monsoonal variations in the region. The Optically Stimulated Luminescence (OSL) chronology indicates that the lake existed between ~ 12 and ~ 7 ka ago. Chronologically constrained trends of sand percent, organic phosphorus (OP), apatite inorganic phosphorus (AIP) and parameters of environmental magnetism were measured in the paleolake profile. Measured proxies indicate that the Indian summer monsoon ameliorated in the early Holocene after 12 ka cooling, and it appears that all the proxies from the lake have captured this globally recognized early Holocene warming. Four phases of wet conditions (intensified monsoon) are recognized at ~ 11.5 ka, ~ 11–10.5 ka, ~ 10–9 ka and ~ 8–7 ka with maximum uncertainties of ~ 1000 years. The wet phases are characterized by high magnetic susceptibility, increased OP and reduced AIP. In an attempt to understan...