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An editorial is presented on the outcomes of the 28th United Nations Climate Change Conference of the Parties (COP-28) held in Dubai, emphasizing the importance of international collaboration to address climate change. Topics include the conference's goals to limit global temperature increases, India's climate goals, and developments in climate finance, including the loss and damage fund.

The article offers information on the global acknowledgment of climate change as a reality caused by human intervention, with topics including the consequences of climate change, regional and global environmental concerns, and unique challenges faced by India, particularly the receding Sundarbans mangrove forest.

The article discusses the need for rural electrification using hybrid solar-wind energy systems to address the challenges of climate change and increasing energy demand in India. Topics include the rise in greenhouse gas concentrations; the importance of renewable energy sources like solar and wind; and the role of hybrid energy systems in providing a balanced solution for rural electrification while reducing the impact on climate.

The article focuses on the environmental impact and heritage preservation of Lonar Lake, a unique geological formation in India. It addresses the effects of climate change on heritage sites, particularly those vulnerable to rising sea levels and emphasizes the urgent need for mitigation measures. It also discusses the ecological damage and degradation faced by Lonar Lake due to shifting perimeters and other factors, highlighting the importance of immediate conservation efforts.

An editorial is presented on challenges faced by Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) to develop healthy ecosystems and biodiversity that are fundamental to life on Earth. Topics include threat to fishing cats is habitat destruction due to anthropogenic activities and climate change; and India's wetlands are at risk of destruction due to human settlement, drainage for agriculture, pollution and logging.

We examine long‐term trends in the near‐surface black carbon mass concentration, using multiyear primary data obtained from a dense network (ARFINET) of observatories over the Indian region. We report for the first time the statistically significant decreasing trend in black carbon mass concentration, based on primary data from this region, at an average rate of ~242 ± 53 ng · m−3 · year−1 during the period 2007–2016. This finding contrasts with the generally increasing trend in the columnar aerosol optical depth, reported earlier, and the steadily increasing trend in anthropogenic activities over this region. The roles of different possible mechanisms, including possible changes in the vertical redistribution of aerosols, are discussed. Over the period 2007–2015, a significant though weak, increasing trend is seen in the contribution from aerosols above 1 km to the columnar aerosol optical depth. These observations imply possible long‐term climate consequences. Key Points: We report the first time regional synthesis of black carbon aerosols over the Indian region using primary dataThe study revealed surprising observation of decreasing trend in the near surface black carbon aerosol concentrationWe found an increasing trend in contribution from free tropospheric aerosols to the columnar aerosol optical depth [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses several articles published within issue on topics related to climate change and health.

In order to understand the regional climate implications of aerosols over Indo-Gangetic Plains (IGP), a major Indo-US field experiment, Ganges Valley Aerosol Experiment (GVAX) was conducted during 2011-12. Atmospheric Radiation Measurement (ARM) mobile facility (AMF) was deployed at the northern Indo-Gangetic Plain over the high-altitude site, Manora Peak, Nainital (29°21'33.84"N, 79°27'29.27"E, 1980 m amsl) in Central Himalayas, for an year-round meas- urement of aerosols, clouds and other climate-relevant atmospheric parameters. One of the objectives of GVAX was examining the ability of models to simulate aerosols over Indian region and validate the simulations. In part-1 of this two-part paper, we examine use of the chemical transport model 'CHIMERE' to simulate aerosol fields over Indian region (4-37.5°N; 67-88.5°E) for multiple years (2006, 2007 and 2008) by simulating the spatial and temporal distribution of PM10, BC mass concentrations and OC/BC ratios. It is seen that the model successfully captures the broad features of the regional distribution of aerosols, including the most conspicuous IGP hotspot and its seasonality. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the performance of the chemical transport model 'CHIMERE' over large Indian region (4-37.5°N; 67-88.5°E) for multiple years (2006, 2007 and 2008) by comparing the model simulations with concurrent aerosol measurements from different locations. Model simulated near-surface black carbon mass concentrations agreed satisfactorily with measurements at various locations (oceanic, inland and island sites), in general, except during monsoon months, when the model under-predicted the measurements. Similar results were obtained when model simulated column integrated PM10 mass concentrations were correlated with MODIS-derived aerosol optical depth (AOD), using AOD as a proxy for aerosol loading. The under-performance of the model during monsoon arises, at least partly, due to the model-simulated rainfall being higher than the actual rainfall over the Indian domain, during the monsoon season. Notwithstanding these, the general performance of the CHIMERE model to simulate aerosol loading over Indian domain during dry months is, in general, found to be satisfactory. [ABSTRACT FROM AUTHOR]

Climate change has great significance in Asia in general, and India in particular; and atmospheric aerosols have a decisive role in this. The climate forcing potential of aerosols is closely linked to their optical, microphysical and chemical properties. Systematic efforts to characterize these properties over the Indian region started about 5 decades ago, and evolved over the years through concerted efforts in the form of long-term scientific programmes as well as concerted fields experiments. All these have resulted in this activity becoming one of the most vibrant fields of climate research in India and have brought several important issues in the national and international foci. The field experiment, RAWEX--GVAX (Regional Aerosol Warming Experiment--Ganges Valley Aerosol Experiment), conducted during 2011-12 jointly by the US Department of Energy, Indian Space Research Organization and Department of Science and Technology, has emerged as a direct outcome of the above efforts. This overview provides a comprehensive account of the development of aerosol--climate research in India and south Asia, and the accomplishment and newer issues that warranted the above field campaign. Details of RAWEX--GVAX, the major outcomes and the subsequent and more recent efforts are presented, followed by the way forward in this field for the next several years to come. [ABSTRACT FROM AUTHOR]

Recent studies, over regions influenced by biomass burning aerosol, have shown that it is possible to define a 'critical cloud fraction' ( CCF) at which the aerosol direct radiative forcing switch from a cooling to a warming effect. Using 4 years of multi-satellite data analysis, we show that CCF varies with aerosol composition and changed from 0.28 to 0.13 from postmonsoon to winter as a result of shift from less absorbing to moderately absorbing aerosol. Our results indicate that we can estimate aerosol absorption from space using independently measured top of the atmosphere ( TOA) fluxes [Cloud Aerosol Lidar with Orthogonal Polarization-Moderate resolution Imaging Spectroradiometer-Clouds and the Earth's Radiant Energy System ( CALIPSO-MODIS- CERES)] combined algorithms for example. [ABSTRACT FROM AUTHOR]

Aerosol absorption is poorly quantified because of the lack of adequate measurements. It has been shown that the Ozone Monitoring Instrument (OMI) aboard EOS-Aura and the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard EOS-Aqua, which fly in formation as part of the A-train, provide an excellent opportunity to improve the accuracy of aerosol retrievals. Here, we follow a multi-satellite approach to estimate the regional distribution of aerosol absorption over continental India for the first time. Annually and regionally averaged aerosol single-scattering albedo over the Indian landmass is estimated as 0.94±0.03. Our study demonstrates the potential of multisatellite data analysis to improve the accuracy of retrieval of aerosol absorption over land. [ABSTRACT FROM AUTHOR]

Even though satellite observations are the most effective means to gather global information in a short span of time, the challenges in this field still remain over continental landmass, despite most of the aerosol sources being land-based. This is a hurdle in global and regional aerosol climate forcing assessment. Retrieval of aerosol properties over land is complicated due to irregular terrain characteristics and the high and largely uncertain surface reflection which acts as 'noise' to the much smaller amount of radiation scattered by aerosols, which is the 'signal'. In this paper, we describe a satellite sensor - the 'Aerosol Satellite (AEROSAT)', which is capable of retrieving aerosols over land with much more accuracy and reduced dependence on models. The sensor, utilizing a set of multi-spectral and multi-angle measurements of polarized components of radiation reflected from the Earth's surface, along with measurements of thermal infrared broadband radiance, results in a large reduction of the 'noise' component (compared to the 'signal'). A conceptual engineering model of AEROSAT has been designed, developed and used to measure the landsurface features in the visible spectral band. Analysing the received signals using a polarization radiative transfer approach, we demonstrate the superiority of this method. It is expected that satellites carrying sensors following the AEROSAT concept would be 'self-sufficient', to obtain all the relevant information required for aerosol retrieval from its own measurements. [ABSTRACT FROM AUTHOR]

During a series of measurements, simultaneous measurements were made of spectral aerosol optical depths (AOD), black carbon (BC) mass concentration, total and size segregated composite aerosol mass concentrations at the second campus of Indian Institute of Science (IISc), Challakere, Karnataka. Surprisingly, most of the aerosol mass is found in the submicron size range, which is unusual for a dry region. Unexpectedly large enhancement in BC aerosol concentration was observed during the morning hours (6-8 a.m.), both during summer and winter, which is mysterious and hence requires further study. However, BC mass fraction, which is one of the most important climaterelevant parameters was 3.3% of total aerosol mass, implying a significantly low aerosol-induced absorption of solar radiation and hence consequent atmospheric warming. Based on our initial measurements as well as 11 years of satellite data analysis, we conclude that this location is best suited for establishing a climate observatory. [ABSTRACT FROM AUTHOR]

Atmospheric chemistry is a branch of atmospheric science where major focus is the composition of the Earth's atmosphere. Knowledge of atmospheric composition is essential due to its interaction with (solar and terrestrial) radiation and interactions of atmospheric species (gaseous and particulate matter) with living organisms. Since atmospheric chemistry covers a vast range of topics, in this article the focus is on the chemistry of atmospheric aerosols with special emphasis on the Indian region. I present a review of the current state of knowledge of aerosol chemistry in India and propose future directions. [ABSTRACT FROM AUTHOR]

Mineral dust constitutes the single largest contributor of natural aerosols over continents. The first step towards separating natural aerosol radiative impact from its anthropogenic counterparts over continents is to gather information on dust aerosols. The infrared (IR) radiance (10.5-12.5 μm) acquired from the Kalpana-I satellite (∼8-km resolution) was used to retrieve regional characteristics of dust aerosols over the Afro-Asian region during the winter of 2004, coinciding with a national aerosol campaign. Here, we used aerosol-induced IR radiance depression as an index of dust load. The regional distribution of dust over various arid and semi-arid regions of India and adjacent continents has been estimated, and these data in conjunction with regional maps of column aerosol optical depth (AOD) are used to infer anthropogenic aerosol fraction. Surprisingly, even over desert locations in India and Saudi Arabia, the anthropogenic fraction was relatively high (∼0.3 to 0.4) and the regionally averaged anthropogenic fraction over India was 0.62 ± 0.06. [ABSTRACT FROM AUTHOR]

Using data from Ozone Monitoring Instrument (OMI) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, we have retrieved regional distribution of aerosol column single scattering albedo (parameter indicative of the relative dominance of aerosol absorption and scattering effects), a most important, but least understood aerosol property in assessing its climate impact. Consequently we provide improved assessment of short wave aerosol radiative forcing (ARF) (on both regional and seasonal scales) estimates over this region. Large gradients in north-south ARF were observed as a consequence of gradients in single scattering albedo as well as aerosol optical depth. The highest ARF (-37Wm-2 at the surface) was observed over the northern Arabian Sea during June to August period (JJA). In general, ARF was higher over northern Bay of Bengal (NBoB) during winter and premonsoon period, whereas the ARF was higher over northern Arabian Sea (NAS) during the monsoon and postmonsoon period. The largest forcing observed over NAS during JJA is the consequence of large amounts of desert dust transported from the west Asian dust sources. High as well as seasonally invariant aerosol single scattering albedos (0.98) were observed over the southern Indian Ocean region far from continents. The ARF estimates based on direct measurements made at a remote island location,Minicoy (8.3°?N, 73°?E) in the southern Arabian Sea are in good agreement with the estimatesmade followingmultisatellite analysis. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the measurements of spectral surface reflectance (ρlambda;8) in the wavelength range 350-2500 nm measured using a spectroradiometer onboard a low-flying aircraft over Bangalore (12.95° N, 77.65° E), an urban site in southern India. The large discrepancies in the retrieval of aerosol properties over land by the Moderate-Resolution Imaging Spectroradiometer (MODIS), which could be attributed to the inaccurate estimation of surface reflectance at many sites in India and elsewhere, provided motivation for this paper. The aim of this paper was to verify the surface reflectance relationships assumed by the MODIS aerosol algorithm for the estimation of surface reflectance in the visible channels (470 and 660 nm) from the surface reflectance at 2100 nm for aerosol retrieval over land. The variety of surfaces observed in this paper includes green and dry vegetations, bare land, and urban surfaces. The measuredreflectance data were first corrected for the radiative effects of atmosphere lying between the ground and aircraft using the Second Simulation of Satellite Signal in the Solar Spectrum (6S) radiative transfer code. The corrected surface reflectance in the MODIS's blue (ρ4708), red (ρ6608), and shortwave-infrared (SWIR) channel (ρ21008)) was linearly correlated. We found that the slope of reflectance relationship between 660 and 2100 nm derived from the forward scattering data was 0.53 with an intercept of 0.07, whereas the slope for the relationship between the reflectance at 470 and 660 nm was 0.85. These values are much higher than the slope (~0.49) for either wavelengths assumed by the MODIS aerosol algorithm over this region. The reflectance relationship for the backward scattering data has a slope of 0.39, with an intercept of 0.08 for 660 nm, and 0.65, with an intercept of 0.08 for 470 nm. The large values of the intercept (which is very small in the MODIS reflectance relationships) result in larger values of absolute surface reflectance in the visible channels. The discrepancy between the measured and assumed surface reflectances could lead to error in the aerosol retrieval. The reflectance ratio (ρ6608)/(ρ21008) showed a clear dependence on the NDVIswia where the ratio increased from 0.5 to 1 with an increase in NDVISWIR from 0 to 0.5. The high correlation between the reflectance at SWIR wavelengths (2100, 1640, and 1240 nm) indicated an opportunity to derive the surface reflectance and, possibly, aerosol properties at these wavelengths. We need more experiments to characterize the surface reflectance and associated inhomogeneity of land surfaces, which play a critical role in the remote sensing of aerosols over land. [ABSTRACT FROM AUTHOR]

Extensive measurements of aerosol optical and microphysical properties made at a remote island, Minicoy in southern Arabian Sea for the period (February 2006-March 2007) are used to characterize their temporal variability and Black Carbon (BC) mass mixing ratio. Large decrease in aerosol BC (from ∼800 ng m-3 to ∼100 ng m-3) was observed associated with change in airmass characteristics and monsoon rains. The total aerosol mass varied between ∼80 and 20 μg m-3. Though the total mass fell drastically, a slight increase in super micron mass was observed during the June-August period associated with high winds. The mass fraction of Black Carbon aerosols during the prevalence of continental airmass is found to be ∼1.2% of the composite aerosols, which is much lower than the values reported earlier for this region. [ABSTRACT FROM AUTHOR]

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; • High Ångström exponent in the southern Arabian Sea signifying steep AOD spectra and higher abundance of accumulation mode particles in the southern Arabian Sea and off Mangalore; • Remarkably low Ångström exponents signifying increased concentration of coarse mode aerosols and high columnar abundance in the northern Arabian Sea; • Altitude profiles from aircraft showed a steady BC level up to 3 km altitude with structures which were associated with inversions in the atmospheric boundary layer (ABL); • A surprisingly large increase in the BC mass fraction with altitude; • Presence of a convectively mixed layer extending up to about 1 km over the Arabian Sea and Bay of Bengal; • A spatial off shore extent of <100 km for the anthropogenic impact at the coast; and • Advection of aerosols, through airmass trajectories, from west Asia and NW arid regions of India leading to formation of elevated aerosol layers extending as far as 400 km off the east coast. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Satellite‐ (MODIS onboard TERRA satellite) measured regional dust distribution has been used in this paper to examine the effect of dust aerosols on top of the atmosphere (TOA) albedo and it was found they have significant impact, especially over deserts, where surface reflection is high. With increasing dust load, TOA albedo was found to decrease significantly and it was observed that over deserts, TOA albedo becomes less than that at the surface (as much as 15% in near infrared) due to absorption by dust. The temporal variations of aerosol properties were examined at three representative locations: northern Africa (10° N–20° N; 20° E–30° E) and Saudi Arabia (19° N–24° N; 53° E–58° E) (both of which are influenced heavily by dust); and southern Africa (10° S–20° S; 20° E–30° E) (where the influence of dust is seasonal). Over northern Africa, optical depth was maximum (&nvsim;0.6) during the June–August period and lower (0.3–0.6) during the rest of the year. The aerosol fine mode fraction (AFMF) was, in general, low (&nvsim;0.05), except in the June–August period, when the AFMF shot up to 0.4. Over southern Africa, optical depth was maximum (&nvsim;0.5) during the September–October period, lower (&nvsim;0.3) in December–March, with the minimum (&nvsim;0.1) during April–June. The AFMF was, in general, high (&nvsim;0.9) throughout the year, and minimum (&nvsim;0.6) during the May–July period. Over Saudi Arabia, optical depths and AFMF showed opposite trends, which is typical of regions influenced heavily by dust. Optical depths as high as &nvsim;0.8 (AFMF &nvsim;0.3) were observed during June–July. The regional average aerosol radiative forcing at these locations was estimated by integrating the measured (column) aerosol properties (from AERONET) into satellite (MODIS) data and then incorporating them into a radiation model. The radiative forcing at the TOA over northern Africa and Saudi Arabia was in the range of +2 to +4 W m -2 , whereas that estimated over southern Africa was in the range of -1 to +2 W m -2 . While TOA forcing was nearly zero (due to large surface reflectance), the radiative forcing at the surface was large. The radiative forcing at the surface over northern and southern Africa was in the range of -15 to -45 W m -2 , whereas that over Saudi Arabia was in the range of -30 to -70 W m -2 . The atmospheric absorption estimated for northern and southern Africa translates into a lower atmospheric heating rate of 0.4 to 1.2 K day -1 , and the same for Saudi Arabia was in the range of 0.8 to 2.2 K day -1 . [ABSTRACT FROM AUTHOR]

Radiative forcing of aerosols is much more difficult to estimate than that of well-mixed gases due to the large spatial variability of aerosols and the lack of an adequate database on their radiative properties. Estimation of aerosol radiative forcing generally requires knowledge of its chemical composition, which is sparse. Ground-based sky radiance measurements [e.g., aerosol robotic network (AERONET)] can provide key parameters such as the single-scattering albedo, but in shipborne experiments over the ocean it is difficult to make sky radiance measurements and hence these experiments cannot provide parameters such as the single-scattering albedo. However, aerosol spectral optical depth data (cruise based as well as satellite retrieved) are available quite extensively over the ocean. Spectral optical depth measurements have been available since the 1970s, and spectral turbidity measurements (carried out at meteorological departments all over the world) have been available for several decades, while long-term continuous chemical composition information is not available. A new method to differentiate between scattering and absorbing aerosols is proposed here. This can be used to derive simple aerosol models that are optically equivalent and can simulate the observed aerosol optical properties and radiative fluxes, from spectral optical depth measurements. Thus, aerosol single-scattering albedo and, hence, aerosol radiative forcing can be estimated. Note that the proposed method is to estimate clear-sky aerosol radiative forcing (over regions where chemical composition data or sky radiance data are not available) and not to infer its exact chemical composition. Using several independent datasets from field experiments, it is demonstrated that the proposed method can be used to estimate aerosol radiative forcing (from spectral optical depths) with an accuracy of ±2 W m-2. [ABSTRACT FROM AUTHOR]

The author offers insights on environmental concerns associated with carbon dioxide emissions associated with the airline industry. Topics discussed include the contribution of greenhouse gases (GHG) to global warming according to the United Nations (UN) Intergovernmental Panel on Climate Change (IPPCC), the smoke produced by the burning of aviation fuel, and the carbon footprints linked to long-distance air travel.

Knowledge of aerosol radiative forcing over land is essential to answer crucial questions related to climate change. Retrieval of aerosol properties over land is complicated due to irregular terrain characteristics and high surface reflection. The retrieval of algorithms used in conventional satellite sensors for continental regions is not completely free from the high reflectance effect and hence leads to large uncertainties in the retrieved parameters. We propose a dedicated satellite sensor namely multi-angle polarization imager (MAPI). The main characteristic of MAPI is multi-spectral and multi-angle measurements of polarized components of reflected radiation from the Earth. The proposed sensor has capability of aerosol retrieval over land. The sensor also has the ability to discriminate dust aerosols (which is the major natural aerosol over land) from other aerosols (using infrared radiance). This is the first step towards separating natural and anthropogenic aerosols, which is needed for the scientific community at large. [ABSTRACT FROM AUTHOR]

In the shortwave solar spectrum ( 0.25 - 5 μ m ), radiation is affected by the change in various aerosol properties and also by water vapour and other gas molecules. The presence of a variety of aerosols over the Bay of Bengal (BoB) during different seasons results in a change in aerosol properties, including the aerosol layer height. The BoB is an integral part of the Indian monsoon, and hence it is essential to understand the radiation budget over the BoB. The sensitivity of the aerosol forcing due to the changes in aerosol properties and other parameters has been studied using the Santa Barbara discrete ordinates radiative transfer model. The aerosol forcing at the top of the atmosphere was found to depend on the aerosol loading (aerosol optical depth), aerosol type (single scattering albedo) and the angular distribution of the scattered radiation (asymmetry parameter). The analysis also shows the presence of a relationship between aerosol layer height and the total amount of water vapour present in the atmosphere. The present study highlights the need for better retrievals of vertical aerosol distribution and water vapour profiles for a better understanding of the role of aerosols in the climate. [ABSTRACT FROM AUTHOR]

The article presents author's comments on the issues related to Earth. It focuses on the climate change and increasing global temperature. It mentions that the anthropogenic emission of greenhouse gases is the major contributor to the risk. It states that there is an increasing demand for actions to control the emissions that are effecting the climate.

Long-term and continuous measurements of aerosol concentration and optical properties from the Challakere Climate Observatory, located in a remote rural semi-arid region northwest of Bengaluru, are examined for the impact of the prolonged and phased national lockdown during the COVID-19 pandemic. The analyses revealed that the lockdown, which almost brought all the anthropogenic activities (particularly associated with fossil fuel use such as in transport and industrial sectors) to a standstill and then slowly relaxed in phases, had very little impact on the aerosol properties at this remote site, in sharp contrast to the impacts seen in the major urban conglomerate, Bengaluru, located about 230 km southeast to Challakere. Rather than impacts from anthropogenic sources associated with fossil fuel combustion, the aerosol characteristics at Challakere are strongly influenced by regional and synoptic meteorology. The findings re-emphasize that the emissions from fossil fuel combustion in industrial and automobile sector are the major source of aerosols (especially absorbing type) over urban and semi-urban environments. [ABSTRACT FROM AUTHOR]

Continuous analytical measurements of the loading and optical properties of near-surface aerosols over the megacity Bengaluru, in south India, are examined for the impact of the national lockdown (LD) associated with COVID-19 pandemic. The near total shutdown of rail, road, and air traffic as well as total closure of most of the business establishments and IT industry, especially during the first phase of the LD, is found to dramatically reduce black carbon (BC) abundance. Within one week of the first week of the LD phase 1 (LD1), the ambient BC concentration at the urban centre came down to levels comparable to those reported for remote rural locations, primarily due to >60% reduction in BC from fossil fuel (BCff) emissions. On the other hand, BC from biomass burning (BCwb) did not show any conspicuous impact. Consequently, the fraction of BCwb to BC more than doubled and the spectral absorption coefficient increased from ~1.15 to ~1.4. The single scattering albedo increased from its prevailing mean value 0.66 before LD to 0.74 during LD1 and then gradually decreased to 0.68 with increasing relaxations on vehicular traffic. The results reveal the unequivocal role of vehicular emissions in impacting the aerosol loading and their optical properties over Bengaluru. The study also shows how the environment responded to the gradual relaxations in the subsequent phases of LD. It is interesting to note that a few spells of strong rainfall towards the fourth phase of the LD impacted the aerosols non-selectively leading to sharp decrease in all the quantities. However, owing to the non-selective nature of the washout this large reduction in loading did not impact the single scattering albedo, unlike the case with the LD. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented in which the guest editor discusses the Mars Orbiter Mission (MOM) of the Indian Space Research Organization for the launch of an elliptical orbit in Mars.

An introduction is presented in which the editor discusses articles in the issue including field observations to understand temperature and precipitation changes in the Himalayas, mass balance and ice thickness in assessing the effect of changing climate, and mass loss analysis by geodetic method.

The author comments on the United Nations (UN) Climate Change Conference held in Lima, Peru in December 2014, the 20th yearly session of the Conference of the Parties (COP 20) of the UN Framework Convention on Climate Change (UNFCCC). Participants reached a consensus to plan their national contributions to reduce emissions, or Intended Nationally Determined Contributions (INDC), which may determine future mitigation strategies. Issues raised by the event include the feasibility of INDC.

An introduction to a series of articles about the regional aerosol warming experiment - Ganges Valley aerosol experiment (RAWEX-GVAX) published within the issue is presented.

Synergizing satellite remote sensing data with vertical profiles of atmospheric thermodynamics and regional climate model simulations, we investigate the relative importance, transport pathways, and seasonality of contribution of dust from regional (Thar Desert and adjoining arid regions) and remote (southwest Asia and northeast Africa) sources over the northeast Indian Ocean [i.e., the Bay of Bengal (BOB)]. We show that while over the northern BOB dust from the regional sources contribute more than 50% to the total dust load during the southwest monsoon period (June–September), interestingly; the remote dust sources dominate rest of the year. On the other hand, over the southern BOB, dust transported from the remote-source regions dominate throughout the year. During June, the dry elevated layer (at altitudes between 850 and 700 hPa) of dust, transported across the Indo-Gangetic Plain to the northern BOB, arises primarily from the Thar Desert. Dust from remote sources in the far west reaches the southern BOB after traversing over and around the southern Indian Peninsula. Since dust from these distinct source regions have different mineral composition (hence optical properties) and undergo distinct changes during atmospheric transport, it is important to understand source-specific dust contribution and transport pathways to address dust–climate feedback. [ABSTRACT FROM AUTHOR]

A response to a letter to the editor on the article on the mechanisms of mammatus formation in the previous issue is presented.

The spatial patterns of rainfall and rain systems during El Niño and La Niña episodes are distinctly different due to the longitudinal variations in the Walker circulation ascent/decent branches over India and adjoining Oceans. In order to examine these differences, 16 years (1998-2013) of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data have been utilized. TRMM-PR delineated precipitating systems (convective, stratiform and shallow) show distinctly different spatial structures over India and adjoining Oceans during El Niño and La Niña episodes. During the El Niño episode, the occurrence of deep systems is high over north of 20°N latitude, and shallow systems are plentiful over south of 20°N latitude. On the other hand, during the La Niña episodes, the occurrence of shallow systems is in excess over Pakistan, central India, northwest Arabian Sea, southwest Indian Ocean and northern Bay of Bengal while the deep systems are abundant over west coast of India, Ganges basin, eastern Indian Ocean and Arabian Sea. The excess convective rain pixels observed during El Niño years are from deep and deep and wide convective core systems due to increase in the CAPE, nevertheless the broad stratiform rain systems are prevalent during La Niña years due to the high convergence of moisture flux and mid-tropospheric upward motion. Though the convective occurrence is more, their intensity is weaker during El Niño years than during La Niña years, indicating the intense nature of convective storms during La Niña episodes. [ABSTRACT FROM AUTHOR]

Effects of aerosols such as black carbon (BC) on climate and buildup of the monsoon over the Indian Ocean are insufficiently quantified. Uncertain contributions from various natural and anthropogenic sources impede our understanding. Here, we use observations over 5 y of BC and its isotopes at a remote island observatory in northern Indian Ocean to constrain loadings and sources during little-studied monsoon season. Carbon-14 data show a highly variable yet largely fossil (65 ± 15%) source mixture. Combining carbon-14 with carbon-13 reveals the impact of African savanna burning, which occasionally approach 50% (48 ± 9%) of the total BC loadings. The BC mass-absorption cross-section for this regime is 7.6 ± 2.6 m²/g, with higher values during savanna fire input. Taken together, the combustion sources, longevity, and optical properties of BC aerosols over summertime Indian Ocean are different than the more-studied winter aerosol, with implications for chemical transport and climate model simulations of the Indian monsoon. [ABSTRACT FROM AUTHOR]

The aerosol mass concentrations over several Indian regions have been simulated using the online chemistry transport model, WRF-Chem, for two distinct seasons of 2011, representing the pre-monsoon (May) and post-monsoon (October) periods during the Indo-US joint experiment 'Ganges Valley Aerosol Experiment (GVAX)'. The simulated values were compared with concurrent measurements. It is found that the model systematically underestimates near-surface BC mass concentrations as well as columnar Aerosol Optical Depths (AODs) from the measurements. Examining this in the light of the modelsimulated meteorological parameters, we notice the model overestimates both planetary boundary layer height (PBLH) and surface wind speeds, leading to deeper mixing and dispersion and hence lower surface concentrations of aerosols. Shortcoming in simulating rainfall pattern also has an impact through the scavenging effect. It also appears that the columnar AODs are influenced by the unrealistic emission scenarios in the model. Comparison with vertical profiles of BC obtained from aircraft-based measurements also shows a systematic underestimation by the model at all levels. It is seen that concentration of other aerosols, viz., dust and sea-salt are closely linked with meteorological conditions prevailing over the region. Dust is higher during pre-monsoon periods due to the prevalence of north-westerly winds that advect dust from deserts of west Asia into the Indo-Gangetic plain. Winds and rainfall influence sea-salt concentrations. Thus, the unrealistic simulation of wind and rainfall leads to model simulated dust and sea-salt also to deviate from the real values; which together with BC also causes underperformance of the model with regard to columnar AOD. It appears that for better simulations of aerosols over Indian region, the model needs an improvement in the simulation of the meteorology. [ABSTRACT FROM AUTHOR]

Realizing the importance of aerosol characterization and addressing its spatio-temporal heterogeneities over Bay of Bengal (BoB), campaign mode observations of aerosol parameters were carried out using simultaneous cruise, aircraft and land-based measurements during the Winter Integrated Campaign for Aerosols gases and Radiation Budget (W ICARB). Under this, airborne measurements of total and hemispheric backscatter coefficients were made over several regions of coastal India and eastern BoB using a three wavelength integrating nephelometer. The measurements include high resolution multi-level (ML) sorties for altitude profiles and bi-level (BL) sorties for spatial gradients within and above the Marine Atmospheric Boundary Layer (MABL) over BoB. The vertical profiles of the scattering coefficients are investigated in light of the information on the vertical structure of the atmospheric stability, which was derived from the collocated GPS (Global Positioning System) aided radiosonde ascents. In general, the altitude profiles revealed that the scattering coefficient remained steady in the convectively well-mixed regions and dropped off above the MABL. This decrease was quite rapid off the Indian mainland, while it was more gradual in the eastern BoB. Investigation on horizontal gradients revealed that the scattering coefficients over northern BoB are 3 to 4 times higher compared to that of central BoB within and above the MABL. A north-south gradient in scattering coefficients is observed over Port Blair in the eastern BoB, with values decreasing from south to north, which is attributed to the similar gradient in the surface wind speed, which can be replicated in the sea salt abundance. The gradients are parameterized using best-fit analytical functions. [ABSTRACT FROM AUTHOR]

Extensive measurements of columnar aerosol optical depth (AOD), composite (MT) and black carbon aerosol mass (MB) concentrations were made over the tropical Indian and Southern Oceans as a part of the Pilot Expedition to the Southern Ocean during the boreal winter. The AOD, MT and MB show large latitudinal gradient towards south up to ITCZ. Beyond ITCZ, up to 56°S, AOD and MB show very low and steady values. However MT shows large variations in the Southern Ocean due to the enhanced production of sea salt aerosols associated with high sea surface winds. The short wave aerosol radiative forcing at the surface over north of equator is in the range - 10 to - 23 W m-2, whereas that over the Southern Ocean was in the range - 4 to - 5 W m-2. The corresponding atmospheric forcing was in the range of 6-13 W m-2 and 0.8-1.4 W m-2. This large north-south change in the aerosol radiative forcing has important implications to the meridional circulation and hence to climate. [ABSTRACT FROM AUTHOR]

During the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) experiment of ISRO-GBP, altitude profiles of mass concentrations of aerosol black carbon (MB) and total (composite) aerosols (MT) in the lower troposphere were made onboard an aircraft from an urban location, Chennai (13.04 °N, 80.17 °E). The profiling was carried out up to 3 km (AGL) in eight levels to obtain higher resolution in altitude. Besides, to explore the horizontal gradient in the vertical profiles, measurements were made at two levels [500m (within ABL) and 1500m (above ABL)] from 10 °N to 16 °N and 80 °E to 84 °E. The profiles showed a significant vertical extent of aerosols over coastal and offshore regions around Chennai with BC concentrations (2 μg m-3) and its contribution to composite aerosols remaining at the same level (between 8 to 10% for FBC) as at the surface. Even though the values are not unusually high as far as an urban location is concerned, but their constancy throughout the vertical column will have important implications to climate impact of aerosols [ABSTRACT FROM AUTHOR]

Multiyear measurements of spectral aerosol optical depths (AODs) were made at Manora Peak in the central Himalaya Range (29°22′N, 79°27′E, ∼1950 m above mean sea level), using a 10-channel multiwavelength solar radiometer for 605 days during January 2002–December 2004. The AODs at 0.5 μm were very low (≤0.1) in winter and increased steeply to reach high values (∼0.5) in summer. It was observed that monthly mean AODs vary significantly (by more than a factor of 6) from January to June. Strong short-period fluctuations (within a daytime) were observed in the AODs. Further investigations of this aspect have revealed that boundary layer dynamics plays a key role in transporting aerosols from the polluted valley region to higher altitudes, causing large contrast in AODs between forenoon and afternoon. The seasonal variations in AODs, while examined in conjunction with synoptic-scale wind fields, have revealed that the transport of dust aerosols from arid regions to the valley regions adjacent to the observational site and their subsequent transport upward by boundary layer dynamics are responsible for the summer increases. [ABSTRACT FROM AUTHOR]

During the second phase of the Arabian Sea Monsoon Experiment (ARMEX-II), extensive measurements of spectral aerosol optical depth, mass concentration, and mass size distribution of ambient aerosols as well as mass concentration of aerosol black carbon (BC) were made onboard a research vessel during the intermonsoon period (i.e., when the monsoon winds are in transition from northeasterlies to westerlies/southwesterlies) over the Arabian Sea (AS) adjoining the Indian Peninsula. Simultaneous measurements of spectral aerosol optical depths (AODs) were made at different regions over the adjoining Indian landmass. Mean AODs (at 500-nm wavelength) over the ocean (∼0.44) were comparable to those over the coastal land (∼0.47), but were lower than the values observed over the plateau regions of central Indian Peninsula (∼0.61). The aerosol properties were found to respond distinctly with respect to change in the trajectories, with higher optical depths and flatter AOD spectra associated with trajectories indicating advection from west Asia, and northwest and west-coastal India. On average, BC constituted only ∼2.2% to total aerosol mass compared to the climatological values of ∼6% over the coastal land during the same season. These data are used to characterize the physical properties of aerosols and to assess the resulting short-wave direct aerosol forcing. The mean values were –27 W m-2 at the surface and -12 W m-2 at the top of the atmosphere (TOA), resulting in a net atmospheric forcing of +15 W m-2. The forcing also depended on the region from where the advection predominates. The surface and atmospheric forcing were in the range -40 to -57 W m-2 and +27 to +39 W m-2, respectively, corresponding to advection from the west Asian and western coastal India where they were as low as -19 and +10 W m-2, respectively, when the advection was mainly from the Bay of Bengal and from central/peninsular India. In all these cases, the net atmospheric forcing (heating) efficiency was lower than the values reported for northern Indian Ocean during northern winter, which is attributed to the reduced BC mass fraction. [ABSTRACT FROM AUTHOR]

This study presents and evaluates the most comprehensive set to date of chemical, physical and optical properties of aerosols in the outflow from South Asia covering a full winter (Nov. 2014 - March 2015), here intercepted at the Indian Ocean receptor site of the Maldives Climate Observatory in Hanimaadhoo (MCOH). Cluster analysis of air-mass back trajectories for MCOH, combined with AOD and meteorological data, demonstrate that the wintertime northern Indian Ocean is strongly influenced by aerosols transported from source regions with three major wind regimes, originating from the Indo-Gangetic Plain (IGP), the Bay of Bengal (BoB) and the Arabian Sea (AS). As much as 97 ± 3% of elemental carbon (EC) in the PM10 was also found in the fine mode (PM2.5). Other mainly anthropogenic constituents such as organic carbon (OC), non-sea-salt (nss) -K+, nss-SO42− and NH4+ were also predominantly in the fine mode (70-95%), particularly in the air masses from IGP. The combination at this large-footprint receptor observatory of consistently low OC/EC ratio (2.0 ± 0.5), strong linear relationships between EC and OC as well as between nss-K+ and both OC and EC, suggest a predominance of primary sources, with a large biomass burning contribution. The particle number-size distributions for the air masses from IGP and BoB exhibited clear bimodal shapes within the fine fraction with distinct accumulation (0.1 μm < d < 1 μm) and Aitken (0.025 μm < d < 0.10 μm) modes. This study also supports that IGP is a key source region for the wider South Asia and nearby oceans, as defined by the criteria that anthropogenic AODs exceed 0.3 and absorption AOD > 0.03. Taken together, the aerosol pollution over the northern Indian Ocean in the dry season is dominated by a well-mixed long-range transported regime of the fine-mode aerosols largely from primary combustion origin. [ABSTRACT FROM AUTHOR]

We present the measurements of cloud-base height variations over Aryabhatta Research Institute of Observational Science, Nainital (79.45°E, 29.37°N, 1958 m amsl) obtained from Vaisala Ceilometer, during the nearly year-long Ganges Valley Aerosol Experiment (GVAX). The cloud-base measurements are analysed in conjunction with collocated measurements of rainfall, to study the possible contributions from different cloud types to the observed monsoonal rainfall during June to September 2011. The summer monsoon of 2011 was a normal monsoon year with total accumulated rainfall of 1035.8 mm during June-September with a maximum during July (367.0 mm) and minimum during September (222.3 mm). The annual mean monsoon rainfall over Nainital is 1440 ± 430 mm. The total rainfall measured during other months (October 2011-March 2012) was only 9% of that observed during the summer monsoon. The first cloud-base height varied from about 31 m above ground level (AGL) to a maximum of 7.6 km AGL during the summer monsoon period of 2011. It is found that about 70% of the total rain is observed only when the first cloud-base height varies between surface and 2 km AGL, indicating that most of the rainfall at high altitude stations such as Nainital is associated with stratiform low-level clouds. However, about 25% of the total rainfall is being contributed by clouds between 2 and 6 km. The occurrences of high-altitude cumulus clouds are observed to be only 2-4%. This study is an attempt to fill a major gap of measurements over the topographically complex and observationally sparse northern Indian region providing the evaluation data for atmospheric models and therefore, have implications towards the better predictions of monsoon rainfall and the weather components over this region. [ABSTRACT FROM AUTHOR]

An extensive field study, RAWEX--GVAX, was carried out during a 10-month (June 2011-March 2012) campaign at ARIES, Nainital and observations on a wide range of parameters like physical and optical properties of aerosols, meteorological parameters and boundary layer evolution were made. This work presents results obtained from high-frequency (four launches per day), balloon-borne observations of meteorological parameters (pressure, temperature, relative humidity, wind speed and wind direction). These observations show wind speed as high as 84 m/s near the subtropical jet. It is shown that reanalysis wind speeds are in better agreement at 250 hPa (altitude of subtropical jet) than those above or below this value (100 hPa or 500 hPa). These observations also demonstrate that AIRS-derived temperature profiles are negatively biased in the lower altitude region, whereas they are positively biased near the tropopause. WRF simulated results are able to capture variations in temperature, humidity and wind speed profile reasonable well. WRF and AIRS-derived tropopause height, tropopause pressure and tropopause temperature also show agreement with radiosonde estimates. [ABSTRACT FROM AUTHOR]

The RAWEX-GVAX field campaign has been carried out from June 2011 to March 2012 over a high altitude site Manora Peak, Nainital (29.4°N; 79.2°E; 1958 m amsl) in the central Himalayas to assess the impacts of absorbing aerosols on atmospheric thermodynamics and clouds. This paper presents the preliminary results of the observations and data analysis of the Doppler Lidar, installed at Nainital. Strong updrafts with vertical winds in the range of ~2-4 ms-1 occurred during the daytime and throughout the season indicating thermally driven convection. On the other hand during nighttime, weak downdrafts persisted during stable conditions. Plan Position Indicator scan of Doppler Lidar showed north-northwesterly winds in the boundary layer. The mixing layer height, derived from the vertical velocity variance, showed diurnal variations, in the range ~0.7-1 km above ground level during daytime and very shallow during nighttime. [ABSTRACT FROM AUTHOR]

Simultaneous and collocated measurements of total and hemispherical backscattering coefficients (σ and β, respectively) at three wavelengths, mass size distributions, and columnar spectral aerosol optical depth (AOD) were made onboard an extensive cruise experiment covering, for the first time, the entire Bay of Bengal (BoB) and northern Indian Ocean. The results are synthesized to understand the optical properties of aerosols in the marine atmospheric boundary layer and their dependence on the size distribution. The observations revealed distinct spatial and spectral variations of all the aerosol parameters over the BoB and the presence of strong latitudinal gradients. The size distributions varied spatially, with the majority of accumulation modes decreasing from north to south. The scattering coefficient decreased from very high values (resembling those reported for continental/urban locations) in the northern BoB to very low values seen over near-pristine environments in the southeastern BoB. The average mass scattering efficiency of BoB aerosols was found to be 2.66 ± 0.1 m2 g-1 at 550 nm. The spectral dependence of columnar AOD deviated significantly from that of the scattering coefficients in the northern BoB, implying vertical heterogeneity in the aerosol type in that region. However, a more homogeneous scenario was observed in the southern BoB. Simultaneous lidar and in situ measurements onboard an aircraft over the ocean revealed the presence of elevated aerosol layers of enhanced extinction at altitudes of 1 to 3 km with an offshore extent of a few hundred kilometers. Back-trajectory analyses showed these layers to be associated with advection from west Asia and western India. The large spatial variations and vertical heterogeneity in aerosol properties, revealed by the present study, need to be included in the regional radiative forcing over the Bay of Bengal. [ABSTRACT FROM AUTHOR]

Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Ångström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Ångström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from the adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Ångström exponent (α) remained significantly lower (∼1) over the Arabian Sea compared to Bay of Bengal (BoB) (∼1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of α, showing dominance of accumulation mode aerosols, over BoB are associated well with the advection, above the boundary layer, of fine particles from the east Asian region during March and April. The change in the airmass to marine in May results in a rapid decrease in α over the BoB. [ABSTRACT FROM AUTHOR]