C. B. S. Dutt

Bio: C. B. S. Dutt is an academic researcher from National Remote Sensing Centre. The author has contributed to research in topics: Aerosol & Sea surface temperature. The author has an hindex of 14, co-authored 26 publications receiving 1065 citations. Previous affiliations of C. B. S. Dutt include Indian Space Research Organisation.

Wintertime aerosol characteristics over the Indo‐Gangetic Plain (IGP): Impacts of local boundary layer processes and long‐range transport

Abstract: [1] The Indo-Gangetic Plain (IGP) encompasses a vast area, (accounting for ∼21% of the land area of India), which is densely populated (accommodating ∼40% of the Indian population). Highly growing economy and population over this region results in a wide range of anthropogenic activities. A large number of thermal power plants (most of them coal fed) are clustered along this region. Despite its importance, detailed investigation of aerosols over this region is sparse. During an intense field campaign of winter 2004, extensive aerosol and atmospheric boundary layer measurements were made from three locations: Kharagpur (KGP), Allahabad (ALB), and Kanpur (KNP), within the IGP. These data are used (1) to understand the regional features of aerosols and BC over the IGP and their interdependencies, (2) to compare it with features at locations lying at far away from the IGP where the conditions are totally different, (3) to delineate the effects of mesoscale processes associated with changes in the local atmospheric boundary layer (ABL), (4) to investigate the effects of long-range transport or moving weather phenomena in modulating the aerosol properties as well as the ABL characteristics, and (5) to examine the changes as the season changes over to spring and summer. Our investigations have revealed very high concentrations of aerosols along the IGP, the average mass concentrations (MT) of total aerosols being in the range 260 to 300 μg m−3 and BC mass concentrations (MB) in the range 20 to 30 μg m−3 (both ∼5 to 8 times higher than the values observed at off-IGP stations) during December 2004. Despite, BC constituted about 10% to the total aerosol mass concentration, a value quite comparable to those observed elsewhere over India for this season. The dynamics of the local atmospheric boundary layer (ABL) as well as changes in local emissions strongly influence the diurnal variations of MT and MB, both being inversely correlated with the mixed layer height (Zi) and the ventilation coefficient (Vc). The share of BC to total aerosols is highest (∼12%) during early night and lowest (∼4%) in the early morning hours. While an increase in the Vc results in a reduction in the concentration almost simultaneously, an increase in Zimax has its most impact on the concentration after ∼1 day. Accumulation mode aerosols contributed ∼90% to the aerosol concentration at ALB, ∼77 % at KGP and 74% at KNP. The BC mass mixing ratio was ∼10% over all three locations and is comparable to the value reported for Trivandrum, a tropical coastal location in southern India. This indicates presence of submicron aerosols species other than BC (such as sulfate) over KGP and KNP. A cross-correlation analysis showed that the changes in MB at KGP is significantly correlated with those at KNP, located ∼850 km upwind, and ALB after a delay of ∼7 days, while no such delay was seen between ALB and KNP. Back trajectory analyses show an enhancement in MB associated with trajectories arriving from west, the farther from to the west they arrive, the more is the increase. This, along with the ABL characteristics, indicate two possibilities: (1) advection of aerosols from the west Asia and northwest India and (2) movement of a weather phenomena (such as cold air mass) conducive for build up of aerosols from the west to east. As the winter gives way to summer, the change in the wind direction and increased convective mixing lead to a rapid decrease in MB.

Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB): An overview

Abstract: During March–May 2006, an extensive, multi-institution, multi-instrument, and multi-platform integrated field experiment ‘Integrated Campaign for Aerosols, gases and Radiation Budget’ (ICARB) was carried out under the Geosphere Biosphere Programme of the Indian Space Research Organization (ISRO-GBP). The objective of this largest and most exhaustive field campaign, ever conducted in the Indian region, was to characterize the physico-chemical properties and radiative effects of atmospheric aerosols and trace gases over the Indian landmass and the adjoining oceanic regions of the Arabian Sea, northern Indian Ocean, and Bay of Bengal through intensive, simultaneous observations. A network of ground-based observatories (over the mainland and islands), a dedicated ship cruise over the oceanic regions using a fully equipped research vessel, the Sagar Kanya, and altitude profiling over selected regions using an instrumented aircraft and balloonsondes formed the three segments of this integrated experiment, which were carried out in tandem. This paper presents an overview of the ICARB field experiment, the database generated, and some of its interesting outcomes though these are preliminary in nature. The ICARB has revealed significant spatio-temporal heterogeneity in most of the aerosol characteristics both over land and ocean. Observed aerosol loading and optical depths were comparable to or in certain regions, a little lower than those reported in some of the earlier campaigns for these regions. The preliminary results indicate: • low (< 0.2) aerosol optical depths (AOD) over most part of the Arabian Sea, except two pockets; one off Mangalore and the other, less intense, in the central Arabian Sea at ∼ 18 ◦ N latitude;

Climate implications of large warming by elevated aerosol over India

Abstract: Wide-ranging multi-platform data from a major field campaign conducted over Indian region was used to estimate the energy absorbed in ten layers of the atmosphere. We found that during pre-monsoon season, most of Indian region is characterized by elevated aerosol layers.Three-fold increase in aerosol extinction coefficient was observed at higher atmospheric layers (>2 km) compared to that near the surface and a substantial fraction (as much as 50 to 70%) of aerosol optical depth was found contributed by aerosols above (reflecting) clouds. Consequent absorption and hence strong warming above clouds was found larger by several degrees (K) compared to that near the surface. The aerosol-induced elevated warming was mostly confined below 2 km over northern Indian Ocean while found up to 4 km over central India, thus exhibiting strong meridional gradients (similar to 4 K) at atmospheric levels above 2 km. Climate implications of the large elevated warming are discussed.

Dust absorption over the “Great Indian Desert” inferred using ground‐based and satellite remote sensing

Abstract: Mineral dust is the single largest contributor of natural aerosols over land. Dust aerosols exhibit high variability in their radiative effects because their composition varies locally. This arises because of the regional distinctiveness of the soil characteristics as well as the accumulation of other aerosol species, such as black carbon, on dust while airborne. To accurately estimate the climate impact of dust, spatial and temporal distribution of its radiative properties are essential. However, this is poorly understood over many regions of the world, including the Indian region. In this paper, infrared (IR) radiance $(10.5–12.5 \hspace{2mm} \mu m)$ acquired from METEOSAT-5 satellite (∼5-km resolution) is used to retrieve dust aerosol characteristics over the “Great Indian Desert” and adjacent regions. The infrared radiance depression on account of the presence of dust in the atmosphere has been used as an index of dust load, called the Infrared Difference Dust Index (IDDI). Simultaneous, ground-based spectral optical depths estimated at visible and near-infrared wavelengths (using a multiwavelength solar radiometer) are used along with the IDDI to infer the dust absorption. The inferred single scattering albedo of dust was in the range of 0.88–0.94. We infer that dust over the Indian desert is of more absorbing nature (compared with African dust). Seasonally, the absorption is least in summer and most in winter. The large dust absorption leads to lower atmospheric warming of 0.7–1.2 K $day^{-1}$.

Aircraft measurements of aerosol black carbon from a coastal location in the north-east part of peninsular India during ICARB

Abstract: During the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) over India, high-resolution airborne measurements of the altitude profiles of the mass concentrations (MB) of aerosol black carbon (BC) were made off Bhubaneswar (BBR, 85.82°E, 20.25°N), over northwest Bay of Bengal, in the altitude region upto 3 km. Such high-resolution measurements of altitude profiles of aerosols are done for the first time over India. The profiles showed a near-steady vertical distribution of MB modulated with two small peaks, one at 800m and the other at ∼2000m. High resolution GPS (Global Positioning System) sonde (Vaisala) measurements around the same region onboard the research vessel Sagar Kanya (around the same time of the aircraft sortie) revealed two convectively well mixed layers, one from ground to ∼700m with an inversion at the top and the other extends from 1200m to ∼2000m with a second inversion at ∼2200m and a convectively stable region in the altitude range 700–1200m. The observed peaks in the MB profile are found to be associated with these temperature inversions. In addition, long-range transport from the Indo-Gangetic Plain (IGP) and deserts lying further to the west also influence the vertical profile of BC. Latitudinal variation of MB showed a remarkable land ocean contrast at the 500m altitude (within the well mixed region) with remarkably lower values over oceans, suggesting the impact of strong sources over the mainland. However, above the ABL (at 1500m), the latitudinal variations were quite weak, and this appears to be resulting from the impact of long-range transport. Comparison of the altitude profiles of MB over BoB off BBR with those obtained during the earlier occasion over the inland stations of Hyderabad and Kanpur showed similarities above ∼500m, with MB remaining around a steady value of ∼1 μg m−3. However, large differences are seen within the ABL. Even though the observed MB values are not unusually high, their near constancy in the vertical column will have important implications to radiative forcing.

‘Breathing’ of the terrestrial biosphere: lessons learned from a global network of carbon dioxide flux measurement systems

Abstract: Published eddy covariance measurements of carbon dioxide (CO2) exchange between vegetation and the atmosphere from a global network are distilled, synthesised and reviewed according to time scale, climate and plant functional types, disturbance and land use. Other topics discussed include history of the network, errors and issues associated with the eddy covariance method, and a synopsis of how these data are being used by ecosystem and climate modellers and the remote-sensing community. Spatial and temporal differences in net annual exchange, FN, result from imbalances in canopy photosynthesis (FA) and ecosystem respiration (FR), which scale closely with one another on annual time scales. Key findings reported include the following: (1) ecosystems with the greatest net carbon uptake have the longest growing season, not the greatest FA; (2) ecosystems losing carbon were recently disturbed; (3) many old-growth forests act as carbon sinks; and (4) year-to-year decreases in FN are attributed to a suite of stresses that decrease FA and FR in tandem. Short-term flux measurements revealed emergent-scale processes including (1) the enhancement of light use efficiency by diffuse light, (2) dynamic pulses in FR following rain and (3) the acclimation FA and FR to temperature. They also quantify how FA and FR respond to droughts and heat spells.

Aerosol light absorption and its measurement: A review

Abstract: Light absorption by aerosols contributes to solar radiative forcing through absorption of solar radiation and heating of the absorbing aerosol layer. Besides the direct radiative effect, the heating can evaporate clouds and change the atmospheric dynamics. Aerosol light absorption in the atmosphere is dominated by black carbon (BC) with additional, significant contributions from the still poorly understood brown carbon and from mineral dust. Sources of these absorbing aerosols include biomass burning and other combustion processes and dust entrainment. For particles much smaller than the wavelength of incident light, absorption is proportional to the particle volume and mass. Absorption can be calculated with Mie theory for spherical particles and with more complicated numerical methods for other particle shapes. The quantitative measurement of aerosol light absorption is still a challenge. Simple, commonly used filter measurements are prone to measurement artifacts due to particle concentration and modification of particle and filter morphology upon particle deposition, optical interaction of deposited particles and filter medium, and poor angular integration of light scattered by deposited particles. In situ methods measure particle absorption with the particles in their natural suspended state and therefore are not prone to effects related to particle deposition and concentration on filters. Photoacoustic and refractive index-based measurements rely on the heating of particles during light absorption, which, for power-modulated light sources, causes an acoustic signal and modulation of the refractive index in the air surrounding the particles that can be quantified with a microphone and an interferometer, respectively. These methods may suffer from some interference due to light-induced particle evaporation. Laser-induced incandescence also monitors particle heating upon absorption, but heats absorbing particles to much higher temperatures to quantify BC mass from the thermal radiation emitted by the heated particles. Extinction-minus-scattering techniques have limited sensitivity for measuring aerosol light absorption unless the very long absorption paths of cavity ring-down techniques are used. Systematic errors can be dominated by truncation errors in the scattering measurement for large particles or by subtraction errors for high single scattering albedo particles. Remote sensing techniques are essential for global monitoring of aerosol light absorption. While local column-integrated measurements of aerosol light absorption with sun and sky radiometers are routinely done, global satellite measurements are so far largely limited to determining a semi-quantitative UV absorption index.

Aerosol and monsoon climate interactions over Asia

Abstract: The increasing severity of droughts/floods and worsening air quality from increasing aerosols in Asia monsoon regions are the two gravest threats facing over 60% of the world population living in Asian monsoon regions. These dual threats have fueled a large body of research in the last decade on the roles of aerosols in impacting Asian monsoon weather and climate. This paper provides a comprehensive review of studies on Asian aerosols, monsoons, and their interactions. The Asian monsoon region is a primary source of emissions of diverse species of aerosols from both anthropogenic and natural origins. The distributions of aerosol loading are strongly influenced by distinct weather and climatic regimes, which are, in turn, modulated by aerosol effects. On a continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulations. The atmospheric thermodynamic state, which determines the formation of clouds, convection, and precipitation, may also be altered by aerosols serving as cloud condensation nuclei or ice nuclei. Absorbing aerosols such as black carbon and desert dust in Asian monsoon regions may also induce dynamical feedback processes, leading to a strengthening of the early monsoon and affecting the subsequent evolution of the monsoon. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of different monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol-monsoon climate system, subject to external forcing of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol-monsoon interactions calls for an integrated approach and international collaborations based on long-term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.

Carbon footprint: current methods of estimation

Abstract: Increasing greenhouse gaseous concentration in the atmosphere is perturbing the environment to cause grievous global warming and associated consequences. Following the rule that only measurable is manageable, mensuration of greenhouse gas intensiveness of different products, bodies, and processes is going on worldwide, expressed as their carbon footprints. The methodologies for carbon footprint calculations are still evolving and it is emerging as an important tool for greenhouse gas management. The concept of carbon footprinting has permeated and is being commercialized in all the areas of life and economy, but there is little coherence in definitions and calculations of carbon footprints among the studies. There are disagreements in the selection of gases, and the order of emissions to be covered in footprint calculations. Standards of greenhouse gas accounting are the common resources used in footprint calculations, although there is no mandatory provision of footprint verification. Carbon footprinting is intended to be a tool to guide the relevant emission cuts and verifications, its standardization at international level are therefore necessary. Present review describes the prevailing carbon footprinting methods and raises the related issues.