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      Volume 127, Issue 1

      February 2018

    • The monsoon system: Land–sea breeze or the ITCZ?

      Sulochana Gadgil

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      For well over 300 years, the monsoon has been considered to be a gigantic land–sea breeze driven by the land–ocean contrast in surface temperature. In this paper, this hypothesis and its implications for the variability of the monsoon are discussed and it is shown that the observations of monsoon variability donot support this popular theory of the monsoon. An alternative hypothesis (whose origins can be traced to Blanford’s (1886) remarkably perceptive analysis) in which the basic system responsible for the Indian summer monsoon is considered to be the Intertropical Convergence Zone (ITCZ) or the equatorial trough, is then examined and shown to be consistent with the observations. The implications of considering the monsoon as a manifestation of the seasonal migration of the ITCZ for the variability of the Indian summer monsoon and for identification of the monsoonal regions of the world are briefly discussed.

    • Fossil wood flora from the Siwalik Group of Arunachal Pradesh, India and its climatic and phytogeographic significance

      Gaurav Srivastava R C Mehrotra C Srikarni

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      The plant fossil records from the Siwalik Group of Arunachal Pradesh, India are far from satisfactory due to remoteness and dense vegetation of the area. We report seven fossil woods of which three belong to the Middle Siwalik (Subansiri Formation), while the rest are from the Upper Siwalik (Kimin Formation). The modern analogues of the fossils from the Middle Siwalik are Lophopetalumlittorale (Celastraceae), Afzelia-Intsia and Sindora siamensis (Fabaceae) and from the Upper Siwalik are Miliusa velutina (Annonaceae), Calophyllum tomentosum and Kayea (Calophyllaceae) and Diospyros melanoxylon (Ebenaceae). The dominance of diffuse porosity in the fossil woods indicates a tropicalclimate with low seasonality (little variation) in temperature, while a high proportion of large vessels and simple perforation plates in the assemblage infer high precipitation during the deposition of the sediments. The aforesaid inference is in strong agreement with the previous quantitative reconstruction based on fossil leaves. Several modern analogues of the fossil taxa are now growing in low latitudes possibly due to an increase in seasonality (increased variation) in temperature caused by the rising Himalaya.

    • New paleomagnetic results on ~2367 Ma Dharwar giant dyke swarm, Dharwar craton, southern India: implications for Paleoproterozoic continental reconstruction

      N Ramesh Babu M Venkateshwarlu Ravi Shankar E Nagaraju V Parashuramulu

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      Here we report new paleomagnetic results and precise paleopole position of the extensional study on ~ 2367 Ma mafic giant radiating dyke swarm in the Dharwar craton, southern India. We have sampled 29 sites on 12 dykes from NE–SW Karimnagar–Hyderabad dykes and Dhone–Gooty sector dykes, eastern Dharwar craton to provide unambiguous paleomagnetism evidence on the spectacular radiating dyke swarm and thereby strengthening the presence of single magmatic event at ~ 2367 Ma. A total of 158 samples were subjected to detailed alternating field and thermal demagnetization techniques and the results are presented here along with previously reported data on the same dyke swarm. The remanent magnetic directions are showing two components, viz., seven sites representing four dykes show component (A) with mean declination of 94◦ and mean inclination of −70◦ (k = 87, α95 = 10◦) and corresponding paleopole at 16◦N, 41◦E (dp = 15◦ and dm = 17◦) and 22 sites representing 8 dykes yielded a component (B) with mean declination of 41◦ and mean inclination of −21◦ (k = 41, α95 = 9◦) with a paleopole at 41◦N, 200◦E (dp = 5◦ and dm = 10◦). Component (A) results are similar to the previously reported directions from the ~ 2367 Ma dyke swarm, which have been confirmed fairly reliably to be of primary origin. The component (B) directions appear to be strongly overprinted by the 2080 Ma event. The grand mean for the primary component (A) combined with earlier reported studies gives mean declination of 97◦ and mean inclination of −79◦ (k = 55, α95 = 3◦) with a paleopole at 15◦N, 57◦E (dp = 5◦, dm = 6◦). Paleogeographical position for the Dharwar craton at ~ 2367 Ma suggests that there may be a chance to possible spatial link between Dharwar dykes of Dharwar craton (India), Widgemooltha and Erayinia dykes of Yilgarn craton (Australia), Sebanga Poort Dykes of Zimbabwe craton (Africa) and Karelian dykes of Kola-Karelia craton (Baltica Shield).

    • Crystallochemical studies on davidite from Bichun, Jaipur District, Rajasthan, India

      Yamuna Singh Anubhooti Saxena A K Bhatt R Viswanathan T S Shaji L K Nanda

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      Crystallochemical data on metamict davidite from albitites and albitised rocks from the Bichun area (Jaipur district, Rajasthan, India) of Banded Gneissic Complex (BGC) are provided. Davidite occurs as euhedral, subhedral to anhedral crystals in the form of disseminated grains and also as fracture filled veins. The crystals of davidite are up to 8 cm in length and 6 cm in width. The powder X-ray diffraction (XRD) pattern of the heat-treated davidite (at 900◦C) reveals well-defined reflections of crystallographic planes. The calculated unit-cell parameters of the heat treated davidite are: a0 = b0 = 10.3556˚A and c0 = 20.9067˚A, with unit-cell volume (V) = 1941.6385˚A³; and α = β = 90◦ and γ = 120◦, which are in agreement with the values of davidite standard. Geochemical data reveals that the investigated davidite contains 51.5–52.6% TiO₂, 14.8–15.1% Fe₂O₃, 9.8–10.2% FeO, 6.97–7.12% U₃O₈, 6.72–6.92% RE₂O₃, 3.85–3.61% K₂O, 0.9–1.4% Al₂O₃, and 0.8–1.2% SiO₂. The calculated structural formulae of the two davidite crystals are: D-1: K0.0044/0.004Ba0.0044/0.005Ca0.20/0.20Na0.012/0.012Mn0.053/0.053Mg0.14/0.14Pb0.0076/0.008Fe2.675/2.675Fe1.59/1.59Y0.1175/0.118P0.053/0.053Nb0.008/0.008Sn0.001/0.001Zr0.033/0.033U0.468/0.468Th0.009/0.009REE0.6829/0.683)6.05/6.05(Ti12.15/12.15 Fe1.9022/1.903Si0.372/0.372 Al0.517/0.517 Cr0.018/0.018Co0.009/0.009Ni0.027/0.027)15/15O36/36(OH0.319/0.319[]1.681/1.681)2/2 and D-2: (K0.004/0.004Ba0.005/0.005Ca0.20/0.20Na0.012/0.012Mn0.05/0.05Mg0.094/0.094Pb0.007/0.007Fe2.58/2.58Fe1.71/1.71Y0.112/0.112P0.106/0.106Nb0.006/0.006Sn0.001/0.001Zr0.03/0.03U0.48/0.48Th0.009/0.009REE0.665/0.665)6.088/6.088(Ti12.48/12.48Fe1.87/1.87Si0.249/0.249Al0.334/0.334Cr0.019/0.019Co0.008/0.008Ni0.04/0.04)15/15O36/36(OH0.098/0.098[]1.90/1.90)2/2.The calculated structural formulae are not fully stoichiometric, which could be due to metamict nature of davidite. The characteristic feature of distribution pattern of REE in davidite is unusually high concentration of LREE and HREE and substantially low content of MREE. It may be due to the occupation of REEs in two distinct crystallographic sites in davidite structure, i.e., M(1) and M(O) sites. Chondrite-normalised plot of davidite reveals a pronounced negative Eu-anomaly (Eu/Eu∗ = 0.30−0.39), which suggests extremely fractionated nature of the metasomatising fluids from which davidite had crystallized. Metamict davidite-bearing U ores not only from Rajasthan, but also from other parts of India are likely to yield very high U leachability, thereby making them attractive sources of U, which otherwise are ignored by mineral engineers as uneconomic U ores.

    • Morphodynamics of the Kulsi River Basin in the northern front of Shillong Plateau: Exhibiting episodic inundation and channel migration

      Watinaro Imsong Swapnamita Choudhury Sarat Phukan Bhagawat Pran Duarah

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      The present study is undertaken in the Kulsi River valley, a tributary of the Brahmaputra River that drains through the tectonically active Shillong Plateau in northeast India. Based on the fluvial geomorphic parameters and Landsat satellite images, it has been observed that the Kulsi River migrated 0.7–2 km westward in its middle course in the past 30 years. Geomorphic parameters such as longitudinal profile analysis, stream length gradient index (SL), ratio of valley floor width to valley height (Vf), steepness index (k/s) indicate that the upstream segment of the Kulsi River is tectonically more active than the downstream segment which is ascribed to the tectonic activities along the Guwahati Fault. 14C ages obtained from the submerged tree trunks of the Chandubi Lake, which is located in the central part of the Kulsi River catchment suggests inundation (high lake levels) during 160 ± 50 AD, 970 ± 50 AD, 1190 ± 80 AD and 1520 ± 30 AD, respectively. These periods broadly coincide with the late Holocene strengthened Indian Summer Monsoon (ISM), Medieval Warm Period (MWP) and the early part of the Little Ice Age (LIA). The debris which clogged the course of the river in the vicinity of the Chandubi Lake is attributed to tectonically induced increase in sediment supply during high magnitude flooding events.

    • Application of Persistent Scatterer Interferometry (PSI) in monitoring slope movements in Nainital, Uttarakhand Lesser Himalaya, India

      Akano Yhokha Pradeep K Goswami Chung-Pai Chang Jiun-Yee Yen Kuo-En Ching K Manini Aruche

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      Orogenic movements and sub-tropical climate have rendered the slopes of the Himalayan region intensely deformed and weathered. As a result, the incidences of slope failure are quite common all along the Himalayan region. The Lesser Himalayan terrane is particularly vulnerable to mass-movements owing togeological fragility, and many parts of it are bearing a high-risk of associated disaster owing to the high population density. An important step towards mitigation of such disasters is the monitoring of slope movement. Towards this, the Persistent Scatterer Interferometry (PSI) technique can be applied. In the present study, the PSI technique is employed in Lesser Himalayan town of Nainital in Uttarakhandstate of India to decipher and monitor slope movements. A total of 15 multi-date ENVISAT ASAR satellite images, acquired during August 2008 to August 2010 period, were subjected to PSI, which revealed a continuous creep movement along the hillslopes located towards the eastern side of the Nainital lake. The higher reaches of the hill seem to be experiencing accelerated creep of ~21mm/year, which decreases downslope to ~5mm/year. Based on spatial pattern of varying PSI Mean LOS Velocity (MLV) values, high (H), moderate (M), low (L) and very low (S) creeping zones have been delineated in thehillslopes. Given the long history of mass movements and continuously increasing anthropogenic activities in Nainital, these results call for immediate measures to avert any future disaster in the town.

    • Surface waves in a cylindrical borehole through partially-saturated porous solid

      M D Sharma

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      Propagation of surface waves is discussed in a cylindrical borehole through a liquid-saturated porous solid of infinite extent. The porous medium is assumed to be a continuum consisting of a solid skeletal with connected void space occupied by a mixture of two immiscible inviscid fluids. This model also representsthe partial saturation when liquid fills only a part of the pore space and gas bubbles span the remaining void space. In this isotropic medium, potential functions identify the existence of three dilatational waves coupled with a shear wave. For propagation of plane harmonic waves along the axially-symmetricborehole, these potentials decay into the porous medium. Boundary conditions are chosen to disallow the discharge of liquid into the borehole through its impervious porous walls. A dispersion equation is derived for the propagation of surface waves along the curved walls of no-liquid (all gas) borehole. A numerical example is studied to explore the existence of cylindrical waves in a particular model of theporous sandstone. True surface waves do not propagate along the walls of borehole when the supporting medium is partially saturated. Such waves propagate only beyond a certain frequency when the medium is fully-saturated porous or an elastic one. Dispersion in the velocity of pseudo surface waves is analysed through the changes in consolidation, saturation degree, capillary pressure or porosity.

    • The development and evolution of landform based on neotectonic movement: The Sancha river catchment in the southwestern China

      Lingmin Zhong Mo Xu Yanna Yang Xingbing Wang

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      Neotectonics has changed the coupled process of endogenic and exogenic geological dynamics, which mold the modern landform. Geomorphologic analysis is essential for identifying and understanding the tectonic activity and indicates the responsive mechanism of the landform to tectonic activity. At first, this research reconstructed the twisted Shanpen period planation surface, computed the valley floor width-to-height ratio of Sancha river and extracted the cross sections marking the river terraces to analyze the characteristics of the neotectonics. And then, the relation between neotectonic movement and landform development was analyzed by dividing the landform types. At last, the spatial variation of landform evolution was analyzed by extracting the Hypsometric Integral of sub-catchments. The Sancha river catchment’s neotectonic movement presents the tilt-lift of earth’s crust from NW to SE, which is characterized by the posthumous activity of Yanshan tectonic deformation. The spatial distribution of river terraces indicates that Sancha river catchment has experienced at least four intermittent upliftsand the fault blocks at both the sides of Liuzhi–Zhijin basement fault have differentially uplifted since the late Pleistocene. As the resurgence of Liuzhi–Zhijin basement fault, the Sancha river catchment was broken into two relative independent landform units. The spatial variations of the landform types nearthe Sancha river and the sub-catchments’ landform evolution are characterized by periodic replacement. The styles of geological structure have controlled the development of landform far away from the Sancha River and influenced the landform evolution. The posthumous activities of the secondary structurehave resulted in the spatial variation of sub-catchments’ landform evolution, which presents periodic replacement with local exceptions. The present study suggests that spatial variations of the development and evolution of modern landform of Sancha River catchment owe their genesis to the interplay betweenthe hydrodynamic force and tectonic activity in the neotectonic period. Likewise, the application of geomorphic indicators also provides a new way to assess the regional crustal stability.

    • Geomorphic investigation of the Late-Quaternary landforms in the southern Zanskar Valley, NW Himalaya

      Shubhra Sharma Aadil Hussain Amit K Mishra Aasif Lone Tarun Solanki Mohammad Khatib Khan

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      The Suru, Doda and Zanskar river valleys in the semi-arid region of Southern Zanskar Ranges (SZR) preserve a rich repository of the glacial and fluvial landforms, alluvial fans, and lacustrine deposits. Based on detailed field observations, geomorphic mapping and limited optical ages, we suggest four glaciations of decreasing magnitude in the SZR. The oldest Southern Zanskar Glaciation Stage (SZS-4) is inferred from glacially polished bedrock and tillite pinnacles. The SZS-4 is ascribed to the Marine Isotopic Stage (MIS)-4/3. The subsequent SZS-3 is represented by obliterated and dissected moraines, and is assigned to MIS-2/Last Glacial Maximum. The multiple recessional moraines of SZS-2 glaciation are assigned the early to mid Holocene age whereas, the youngest SZS-1 moraines were deposited during the Little Ice Age. We suggest that during the SZS-2 glaciation, the Drang-Drung glacier shifted its course from Suru Valley (west) to the Doda Valley (east). The study area has preserved three generations of outwash gravel terraces, which broadly correlate with the phases of deglaciation associated with SZS-3, 2, and 1. The alluvial fan aggradation, lacustrine sedimentation, and loess deposition occurred during the mid-to-lateHolocene. We suggest that glaciation was driven by a combination of the mid-latitude westerlies and the Indian Summer Monsoon during periods of cooler temperature, while phases of deglaciation occurred during enhanced temperature.

    • Earth fissures in Qinglong Graben in Yuncheng Basin, China

      Jianwei Qiao Jianbing Peng Yahong Deng Yanqiu Leng Zhenjiang Meng

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      Qinglong Graben is located in southeastern Yuncheng Basin, China flanked by two north-east trending normal faults, where the geological condition is favourable for generating earth fissures. Since 1978, five earth fissures have formed in Qinglong Gaben. In the present work, a series of geological investigation consisting of site investigation, geological drilling and trench excavation was used to characterise and determine the reasons for the formation of the earth fissures. The site investigation indicated that the trend of the five earth fissures are parallel to the general strike of the normal fault, i.e., geological drilling and trench studies revealed that syn-sedimentary fault is the key reason for the formation of theearth fissures. Additionally, over-exploitation of groundwater and erosion process are important factors in the development and expansion of the earth fissures in Qinglong Graben. The earth fissures forming process in Qinglong Graben can be divided into three stages: the regional extension first caused normal faults under the surface, and then the pumping action of excessive groundwater induced the normal faults propagate to the surface, and finally the erosion promoted the formation of the current earth fissure.

    • Rainfall characteristics and thresholds for periglacial debris flows in the Parlung Zangbo Basin, southeast Tibetan Plateau

      Mingfeng Deng Ningsheng Chen Haitao Ding

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      The Parlung Zangbo Basin in the southeastern Tibet Plateau is affected by the summer monsoon from the Indian Ocean, which produces large rainfall gradients in the basin. Rainfall data during 2012–2015 from five new meteorological stations are used to analyse the rainfall characteristics. The daily rainfall, rainfallduration, mean rainfall intensity, and peak rainfall intensity are consistent, but sometimes contrasting. For example, these values decrease with increasing altitude, and the gradient is large downstream and small upstream, respectively. Moreover, the rainfall intensity peaks between 01:00 and 06:00 and increasesduring the afternoon. Based on the analysis of 14 debris flow cases in the basin, differences in the rainfall threshold differ depending on the location as sediment varieties. The sediment in the middle portions of the basin is wet and well structured; thus, long-duration, high-intensity rainfall is required to generatedebris flows. Ravels in the upstream area are arid and not well structured, and short-duration rainfall is required to trigger debris flows. Between the above two locations, either long-duration, low-intensity rainfall or short-duration, high-intensity rainfall could provoke debris flows. Clearly, differences in rainfall characteristics and rainfall thresholds that are associated with the location must be considered in debris flow monitoring and warnings.

    • Fission-track evidence of tectonic evolution in the northwestern Qaidam Basin, China

      Guo-Qiang Sun Wei-Ming Liu Jia-Jia Guo Ye-Tong Wang

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      Fission-track dating was conducted on zircons and apatites from 11 cores of the upper Xiaganchaigou Formation and lower Shangganchaigou Formation (northwestern Qaidam Basin). The obtained apatite fission-track age is 3.1–61.9 Ma, and the zircon fission-track age is 49.2–123.5 Ma. Although the averageapatite age is consistent with ages predicted from the stratigraphy, nine of the 11 apatite fission-track ages have P(χ ²) < 5%, indicating that the grains experienced heterogeneous annealing after sedimentation. The average zircon age is greater than that indicated by stratigraphy, and all eight zircon fission ageshave P(χ ²) > 5%, exhibiting consistent characteristics and indicating that zircons retain provenance age information after burial. From the zircon and apatite ages, the fission-track length distribution, and the geological setting, the northwestern Qaidam Basin has experienced two tectonothermal events sincethe Late Mesozoic, at 39.1 ± 9.3 to 133.7 ± 6.6 Ma and 1.2 ± 0.6 to 32.0 ± 3.0 Ma. The earlier (39.1–133.7 Ma) tectonothermal event resulted from the initial collision of the Indian and Eurasian plates. As a consequence of the collision, the Altyn Tagh fault, which forms the northwestern boundary of the Qaidam Basin, began to develop. Subsequently, uplift of the Altyn Tagh mountains began and the northwestern depression of the Qaidam Basin started to form. The later (1.2–32.0 Ma) tectonothermal event resulted from further collision of the Indian and Eurasian plates along the Yarlung Tsangpo suture zone. Strata in the Qaidam Basin were further deformed by transpression in this period and this period played a crucial role in petroleum accumulation.

    • Seismic stratigraphy and depositional history of the BüyükÇekmece Bay since Latest Pleistocene, Marmara Sea, Turkey

      Denizhan Vardar Hakan Alp Bedri Alpar

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      High-resolution seismic data shed light on latest Pleistocene and Holocene sedimentation beneath the BüyükÇekmece Bay, northern shelf area of the Marmara Sea, Turkey. Discontinuous fluvio-marine and marine deposits overlying the erosional truncation surface of Oligocene–Lower Miocene deposits are as thick as 30 m and preserved preferentially within the incised valleys that were controlled by some old faults. A series of prograding shoreline, laterally passing to the latest Pleistocene–Holocene valley-fill deposits, are thought to have accumulated mainly during times of shoreline transgression and sealevelrise. The overall morphology and stratigraphic setting observed in the BüyükÇekmece Bay and at the southern outlet of the Bosphorus Strait have nearly same characteristics, implying that similar hydrodynamic conditions, erosional and depositional processes were mainly under the control of strong northerly flows during the Late Quaternary. These flows were less powerful in the BüyükÇekmece region with decreased sediment input and smaller accommodation space.

    • Comparison of AMSR-2 wind speed and sea surface temperature with moored buoy observations over the Northern Indian Ocean

      B Nanda Kishore Reddy R Venkatesan Krishna K Osuri Simi Mathew Jagadeesh Kadiyam K Jossia Joseph

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      The Northern Indian Ocean (NIO) is unique due to seasonal reversal of wind patterns, the formation of vortices and eddies which make satellite observations arduous. The veracity of sea surface wind (SSW) and sea surface temperature (SST) products of sun-synchronous AMSR-2 satellite are compared with high-temporal moored buoy observations over the NIO. The two year-long (2013–2014) comparisons reveal that the root-mean-square-error (RMSE) of AMSR-2 SST and SSW is <0.4◦C and <1.5 ms⁻¹, respectively, which are within the error range prescribed for the AMSR-2 satellite (±0.8◦C, ±1.5 ms⁻¹). The SST–wind relation is analyzed using data both from the buoy and satellite. As a result, the low- SST is associated with low-wind condition (positive slope) in the northern part of the Bay of Bengal (BoB), while low SST values are associated with high wind conditions (negative slope) over the southern BoB. Moreover, the AMSR-2 displayed larger slope for SST–wind relation and could be mainly due to overestimation of SST and underestimation of wind as compared to the buoy. The AMSR-2 SSW exhibited higher error during post-monsoon followed by monsoon season and could be attributed to the high wind conditions associated with intense oceanic vortices. The study suggests that the AMSR-2 products are reliable and can be used in tropical air–sea interactions, meso-scale features, and weather and climate studies.

    • Variations of trace gases over the Bay of Bengal during the summer monsoon

      I A Girach Narendra Ojha Prabha R Nair Yogesh K Tiwari K Ravi Kumar

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      In situ measurements of near-surface ozone (O₃), carbon monoxide (CO), and methane (CH₄) were carried out over the Bay of Bengal (BoB) as a part of the Continental Tropical Convergence Zone (CTCZ) campaign during the summer monsoon season of 2009. O₃, CO and CH₄ mixing ratios varied in the ranges of 8–54 ppbv, 50–200 ppbv and 1.57–2.15 ppmv, respectively during 16 July–17 August 2009. The spatial distribution of mean tropospheric O₃ from satellite retrievals is found to be similar to that in surfaceO₃ observations, with higher levels over coastal and northern BoB as compared to central BoB. The comparison of in situ measurements with the Monitoring Atmospheric Composition & Climate (MACC) global reanalysis shows that MACC simulations reproduce the observations with small mean biases of1.6 ppbv, –2.6 ppbv and 0.07 ppmv for O₃, CO and CH4, respectively. The analysis of diurnal variation of O₃ based on observations and the simulations from Weather Research and Forecasting coupled with Chemistry (WRF-Chem) at a stationary point over the BoB did not show a net photochemical build up during daytime. Satellite retrievals show limitations in capturing CH₄ variations as measured by in situ sample analysis highlighting the need of more shipborne in situ measurements of trace gases over thisregion during monsoon.

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