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High-resolution time-depth view of dimethylsulphide cycling in the surface sea
Get PDFEmission of the trace gas dimethylsulphide (DMS) from the ocean influences the chemical and optical properties of the atmosphere, and the olfactory landscape for foraging marine birds, turtles and mammals. DMS concentration has been seen to vary across seasons and latitudes with plankton taxonomy and activity, and following the seascape of ocean’s physics. However, whether and how does it vary at the time scales of meteorology and day-night cycles is largely unknown. Here we used high-resolution measurements over time and depth within coherent water patches in the open sea to show that DMS concentration responded rapidly but resiliently to mesoscale meteorological perturbation. Further, it varied over diel cycles in conjunction with rhythmic photobiological indicators in phytoplankton. Combining data and modelling, we show that sunlight switches and tunes the balance between net biological production and abiotic losses. This is an outstanding example of how biological diel rhythms affect biogeochemical processes
Atmospheric heating due to black carbon aerosol during the summer monsoon period over Ballia: A rural environment over Indo-Gangetic Plain
No full textBlack carbon (BC) aerosols are one of the most uncertain drivers of global climate change. The prevailing view is that BC mass concentrations are low in rural areas where industrialization and vehicular emissions are at a minimum. As part of a national research program called the “Ganga Basin Ground Based Experiment-2014 under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Phase-III” of Ministry of Earth Sciences, Government of India, the continuous measurements of BC and particulate matter (PM) mass concentrations, were conducted in a rural environment in the highly-polluted Indo-Gangetic Plain region during 16th June to 15th August (monsoon period), 2014. The mean mass concentration of BC was 4.03 (± 0.85) μg m− 3 with a daily variability between 2.4 and 5.64 μg m− 3, however, the mean mass PM concentrations [near ultrafine (PM1.0), fine (PM2.5) and inhalable (PM10)] were 29.1(± 16.2), 34.7 (± 19.9) and 43.7 (± 28.3) μg m− 3, respectively. The contribution of BC in PM1.0 was approximately 13%, which is one of the highest being recorded. Diurnally, the BC mass concentrations were highest (mean: 5.89 μg m− 3) between 20:00 to 22:00 local time (LT) due to the burning of biofuels/biomass such as wood, dung, straw and crop residue mixed with dung by the local residents for cooking purposes. The atmospheric direct radiative forcing values due to the composite and BC aerosols were determined to be + 78.3, + 44.9, and + 45.0 W m− 2 and + 42.2, + 35.4 and + 34.3 W m− 2 during the months of June, July and August, respectively. The corresponding atmospheric heating rates (AHR) for composite and BC aerosols were 2.21, 1.26 and 1.26; and 1.19, 0.99 and 0.96 K day− 1 for the month of June, July and August, respectively, with a mean of 1.57 and 1.05 K day− 1 which was 33% lower AHR (BC) than for the composite particles during the study period. This high AHR underscores the importance of absorbing aerosols such as BC contributed by residential cooking using biofuels in India. Our study demonstrates the need for immediate, effective regulations and policies that mitigate the emission of BC particles from domestic cooking in rural areas of India
Role of long-range transport and local meteorology in seasonal variation of surface ozone and its precursors at an urban site in India
No full textThis study is based on the continuous measurements of ozone (O3), carbon monoxide (CO) and nitrogen oxides (NOx) at a semi-arid urban site in Udaipur, India during the years 2011–2012. The mixing ratios of trace gases show strong and weak diurnal variations during the winter and monsoon seasons, respectively. The temporal changes in local emission and PBL depth play an important role in the diurnal variation of trace gases. The daily means of O3, CO and NOx were in the ranges of 5–53 ppbv, 121–842 ppbv and 3–29 ppbv, respectively. The mixing ratios of trace gases were highest and lowest during the winter/pre-monsoon and monsoon seasons, respectively. In the winter season, the lowest of O3 during night–morning hours was caused by the efficient loss due to titration and deposition compared to other seasons. During the winter to the pre-monsoon period, higher levels of trace gases were due to regional biomass burning and long-range transport of continental pollutants. However, strong convection, rainfall and transport of oceanic air resulted in the lowest concentrations of trace gases during the monsoon season. The O3min values tend to increase slightly with increasing values of Tmin while COmax and NOxmax decrease rapidly with increasing values of Tmin. The levels of CO and NOx decreased with increasing wind speed, while O3 tends to increase with wind speed. The rates of change of O3 (dO3/dt) were about 3.7 ppbv h− 1 and − 4.5 ppbv h− 1 during the morning and evening hours, respectively. Exceptionally high levels of trace gases during the Diwali (festival) period were due to extensive use of firecrackers from evening till morning hours. The enhancements of O3, CO and NOx compared to normal days were about 61%, 62% and 23%, respectively
Android App for Argo Floats
Get PDFINCOIS has deployed more than 400 Argo floats till now and soon reaching a special milestone of 500 Indian Argo floats. In this context there is a necessity to have a unique application by which scientists can effectively and efficiently track all the information of these floats and also monitor the active floats among them regularly. The present work describes about an Android application or app which eases the work of researchers to track the information of these Argo floats as well as monitor them regularly. This app is designed and developed to give all the information related to Argo floats like its various types, its deployed positions, its current positions, its functionality, search option, etc., in the form of maps and charts in turn uses real time data to give latest status of Argo floats. In addition to it, this app is also useful in advising the scientists involved in Argo program about the floats in danger of getting grounded or beached that need immediate attention. This app is a very useful tool for the scientists to check the current status of Argo floats from anywhere or anytime using a smart phone
Optical characterization and assessment of ocean colour algorithms in Chilika Lagoon
No full textAsia's largest brackish water ecosystem, Chilika lagoon, supports livelihood of millions of inhabitants and also known to be bio-geo-chemically dynamic. This demands continuous monitoring of lagoon for which optical remote sensing may be crucial. The in situ bio-optical parameters were analyzed in two sectors (Outer Channel: OC and Southern Sector: SS) of Asia's largest brackish water ecosystem, Chilika lagoon. The spectral Remote Sensing Reflectance (Rrs) ranged from 0.003 to 0.02sr-1 in OC whereas in SS it was between 0.003 and 0.028sr-1. The minimum Rrs was at 400nm that gradually increased with a peak at 580nm and subsequently decreased towards longer wavelength. Rrs exhibited similar pattern in both the sectors from 400 to 600nm. Beyond this wavelength, Rrs was relatively higher in SS. The shifting of peak towards longer wavelength could be attributed to high absorption due to chlorophyll-a (chl-a) and chromophoric dissolved organic matter (CDOM) that varied largely between sectors with relatively higher concentration of chl-a in OC and CDOM in SS. Further, we modelled chl-a by seven ocean colour algorithms (OC4, OC4E, OC4O, OC3M, OC3V, OC3C and OCMO2) using in situ Rrs. The modelled chl-a was overestimating in situ at all stations due to high concentration of CDOM contaminating chl-a signals. However in OC, in situ and modelled chl-a followed the same trend (R2=0.88 to 0.90) probably due to strong co-variance of chl-a with CDOM. The analysis of this study points out towards the requirement for sector specific bio-optical algorithm for accurate chl-a retrieval for synoptic monitoring of lagoon health
Diurnal cycle of convection during the CAIPEEX 2011 experiment
No full textThe diurnal cycle of convective storm events is investigated in the study with the help of C-band radar reflectivity data during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX 2011) in combination with other ground-based observations. A threshold reflectivity of 25 dBZ is used to identify the initiation of storms. Observations from collocated sensors such as a microwave radiometer profiler, water vapor measurement from eddy covariance system, and wind lidar measurements are used to investigate the characteristic features and diurnal cycle of convectively initiated storms from 21st September to 5th November 2011. The maximum reflectivity follows a normal distribution with a mean value of 40 dBZ. The cloud depth over the domain varied between 5 and 15 km corresponding to a range of reflectivity of 30–50 dBZ values. In the diurnal cycle, double maximum in the precipitation flux is noted—one during the afternoon hours associated with the diurnal heating and the other in the nocturnal periods. The nocturnal precipitation maximum is attributed to initiation of several single-cell storms (of congestus type) with a duration that is larger than the storms initiated during the daytime. The convective available potential energy (CAPE) showed a diurnal variation and was directly linked with the surface level water vapor content. The high CAPE favored single storms with a reflectivity >40 dBZ and higher echo top heights. In the evening or late night hours, a nocturnal low-level jet present over the location together with the reduced stability above the cloud base favored enhancement of low-level moisture, CAPE, and further initiation of new convection. The study illustrated how collocated observations could be used to study storm initiation and associated thermodynamic features
The interplay between submesoscale instabilities and turbulence in the surface layer of the Bay of Bengal
Get PDFThe Air-Sea Interactions Regional Initiative (ASIRI) aims to understand vertical fluxes of momentum and heat across the surface layer in the Bay of Bengal. As the mesoscale and submesoscale eddies redistribute freshwater input over saline water of the bay, they influence the vertical distribution of salinity and thus impact air-sea fluxes. This study reports on numerical simulations performed to investigate processes that can lead to the observed vertical structure of stratification near the ocean surface. Processes are explored at multiple lateral scales, ranging from a few meters to tens of kilometers, to elucidate how the interplay among large-scale motion, submesoscale instabilities, and small-scale turbulent motion affects the surface layer
Technological advancements in observing the upper ocean in the Bay of Bengal: Education and capacity building
Get PDFBecause the monsoon strongly affects India, there is a clear need for indigenous expertise in advancing the science that underlies monsoon prediction. The safety of marine transport in the tropics relies on accurate atmospheric and ocean environment predictions on weekly and longer time scales in the Indian Ocean. This need to better forecast the monsoon motivates the United States to advance basic research and support training of early career US scientists in tropical oceanography. Earlier Indian field campaigns and modeling studies indicated that an improved understanding of the interactions between the upper ocean and the atmosphere in the Bay of Bengal at finer spatial and temporal scales could lead to improved intraseasonal monsoon forecasts. The joint US Air-Sea Interactions Regional Initiative (ASIRI) and the Indian Ocean Mixing and Monsoon (OMM) program studied these interactions, resulting in scientific advances described by articles in this special issue of Oceanography. In addition to these scientific advances, and while also developing long-lasting collaborations and building indigenous Indian capability, a key component of these programs is training early career scientists from India and the United States. Training has been focusing on finescale and mixing studies of the upper ocean, air-sea interactions, and marine mammal research. Advanced methods in instrumentation, autonomous robotic platforms, experimental design, data analysis, and modeling have been emphasized. Students and scientists from India and the United States at all levels have been participating in joint cruises on Indian and US research vessels and in training participants in modern tools and methods at summer schools, at focused research workshops, and during research visits. Such activities are building new indigenous capability in India, training a new cadre of US scientists well versed in monsoon air-sea interaction, and forging strong links between Indian and US oceanographic institutions
Possible shift in the ENSO-Indian monsoon rainfall relationship under future global warming
No full textEI Nino-Southern Oscillation (ENSO) and Indian monsoon rainfall are known to have an inverse relationship, which we have observed in the rainfall spectrum exhibiting a spectral dip in 3–5 y period band. It is well documented that El Nino events are known to be associated with deficit rainfall. Our analysis reveals that this spectral dip (3–5 y) is likely to shift to shorter periods (2.5–3 y) in future, suggesting a possible shift in the relationship between ENSO and monsoon rainfall. Spectral analysis of future climate projections by 20 Coupled Model Intercomparison project 5 (CMIP5) models are employed in order to corroborate our findings. Change in spectral dip speculates early occurrence of drought events in future due to multiple factors of global warming