Current Science

Nizy Mathew ¹, Viju Oommen John ², C. Suresh Raju ¹, K. Krishna Moorthy ³

Affiliations
1 Space Physics Laboratory, Vikram Sarabhai Space Centre, Indian Space Research Organization, Thiruvananthapuram 695 022, IN
2 Hadley Centre, Met Office, Exeter, GB
3 ISRO Headquarters, Antariksh Bhavan, New BEL Road, Bengaluru 560 231, IN

Abstract

Upper tropospheric humidity (UTH) has been derived using a 'brightness temperature (T_b) transformation' method from the humidity sounder channels of SAPHIR payload on-board Megha-Tropiques (MT). These channels are very close to the water vapour absorption peak at 183.31 GHz. The channel at 183.31 ± 0.2 GHz enables retrieval of humidity up to the highest altitude possible with the present nadir-looking microwave humidity sounders. Megha-Tropi-ques satellite has an equatorially inclined orbit, which ensures frequent spatial and temporal coverage of the global tropical belt. Transformation coefficients for the first three channels for all the incidence angles have been derived and are used to convert brightness temperatures to weighted average upper tropospheric humidity having weighting function peaks at different pressure levels. The methodology has been validated by comparing the SAPHIR-derived UTH with that de-rived from radiosonde observations. Inter-comparison of the derived UTH has been done with layer averaged humidity product from SAPHIR measurements and with UTH product using infrared measurements from Kalpana satellite (MOSDAC). UTH over the tropical belt for six months has been studied taking the ad-vantage of the humidity product with high spatial and temporal resolution. The transformation coefficients and methodology to identify the cloud-free pixels to derive UTH from the three channels for all the possi-ble incidence angles are presented here, so that the users can directly derive UTH from the brightness temperature data.

Keywords

Brightness Temperature, Radiosonde Observations, Sounder Channels, Upper Tropospheric Humidity.

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K. Krishna Moorthy , S. K. Satheesh , V. R. Kotamarthi

Abstract

Climate change has great significance in Asia in general, and India in particular due to its diverse geographical features and high population density. It is now well known that atmospheric aerosols have a decisive role in perturbing regional and global climate. Ground-based and satellite-borne measurements have shown that the Indo-Gangetic Plains (IGP), which extends from western desert, across the plains and over to the Bay of Bengal and one of the densely populated and rapidly developing regions of the subcontinent, has some of the highest and persistent aerosol optical depths (AOD)/loading, especially during the dry winter and pre-monsoon seasons.

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K. Krishna Moorthy ¹, S. K. Satheesh ¹, V. R. Kotamarthi ²

Affiliations
1 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
2 Environmental Science Division, Argonne National Laboratory, Argonne, IL, US

Abstract

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.

Keywords

Aerosols, Climate Change, ICARB, RAWEX–GVAX.

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N. Srivastava ¹, S. K. Satheesh ², Nadege Blond ³, K. Krishna Moorthy ⁴

Affiliations
1 Department of Physics, Birla Institute of Technology, Mesra, Ranchi 835 215, IN
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 Laboratoire Image Ville Environnement, UMR7362 CNRS, Université de Strasbourg, Strasbourg, FR
4 ISRO HQ, Antariksh Bhavan, Bengaluru 560 231, IN

Abstract

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 measurement 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.

Keywords

Aerosols, Black Carbon, Chemistry Transport Model, CHIMERE, GVAX.

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N. Srivastava ¹, S. K. Satheesh ², Nadege Blond ³, K. Krishna Moorthy ⁴

Affiliations
1 Department of Physics, Birla Institute of Technology, Mesra, Ranchi 835 215, IN
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 Laboratoire Image Ville Environnement, UMR7362 CNRS, Université de Strasbourg, Strasbourg, FR
4 ISRO HQ, Antariksh Bhavan, Bengaluru 560 231, IN

Abstract

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 underpredicted 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 underperformance 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.

Keywords

Aerosols, Black Carbon, Chemistry Transport Model.

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Narendra Singh ¹, Raman Solanki ¹, N. Ojha ², M. Naja ¹, U. C. Dumka ¹, D. V. Phanikumar ¹, Ram Sagar ¹, S. K. Satheesh ³, K. Krishna Moorthy ⁴, V. R. Kotamarthi ⁵, S. K. Dhaka ⁶

Affiliations
1 Aryabhatta Research Institute of Observational Sciences, Nainital 263 002, IN
2 Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, Mainz, DE
3 Center for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
4 ISRO Head Quarters, Bengaluru 560 231, IN
5 Environmental Science Division, Argonne National Laboratory, Illinois, US
6 Radio and Atmospheric Physics Lab., Rajdhani College, University of Delhi, Delhi 110 015, IN

Abstract

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.

Keywords

Ceilometer, Central Himalaya, Cloud-Base, GVAX, Monsoon.

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Sobhan Kumar Kompalli ¹, S. Suresh Babu ¹, Lakshmi N. Bharatan ², K. Krishna Moorthy ³

Affiliations
1 Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695 022, IN
2 Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuinram 695 022, IN
3 ISRO Head Quarters, Bengaluru 560 231, IN

Abstract

Long-term measurements (from August 2009 to December 2014) of aerosol black carbon mass concentration (M_BC) and spectral aerosol optical depth (AOD) were carried out from a high-altitude location, Hanle in western trans-Himalaya as part of the Regional Aerosol Warming Experiment. Both MBC and AOD showed distinct annual pattern with a clear spring-time enhancement (April-June) with significant inter-annual variability associated with the changes in source processes. The potential source regions contributing to the spring-time enhancement in aerosol loading are the dust-dominated west Asian region as well as biomass burning from NW India. The overall annual mean value of M_BC over Hanle is extremely low compared to many other Himalayan locations, including the Ganges Valley Aerosol Experiment campaign site at Nainital, which also showed spring-time (pre-monsoon) enhancement. The vertical extents of elevated aerosol layers, which contribute to the spring-time enhancement, are found to be in the range 5-7 km amsl from the analysis of vertical profiles of extinction coefficients from CALIPSO data.

Keywords

Aerosol Optical Depth, Black Carbon, Spring-Time Enhancement, High-Altitude Locations.

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Manish Naja ¹, Piyush Bhardwaj ¹, Narendra Singh ¹, Phani Kumar ¹, Rajesh Kumar ², N. Ojha ¹, Ram Sagar ³, S. K. Satheesh ⁴, K. Krishna Moorthy ⁵, V. R. Kotamarthi ⁶

Affiliations
1 Aryabhatta Research Institute of Observational Sciences, Nainital 263 002, IN
2 National Center for Atmospheric Research, Boulder, Colorado, US
3 Indian Institute of Astrophysics, Bengaluru 560 034, IN
4 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
5 Indian Space Research Organization, Head Quarters, Bengaluru 560 231, IN
6 Argonne National Laboratory, Argonne, IL, US

Abstract

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.

Keywords

Aerosols, Radiosonde, Subtropical Jet, Tropopause Folding, Vertical Profiling.

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C. Suresh Raju ¹, Tinu Antony ¹, Nizy Mathew ¹, K. N. Uma ¹, K. Krishna Moorthy ¹

Affiliations
1 Space Physics Laboratory, Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram 695 022, IN

Abstract

This article reports the potential of the 'MADRAS' payload on-board the Megha-Tropiques satellite for land surface studies. The analysis has been divided into two parts as application of MADRAS data for studying the land surface properties and estimation of microwave emissivity directly from MADRAS brightness temperature (TB) data by applying an in-house developed Microwave Radiative Transfer Computation Code. The derived emissivity is further used to characterize the microwave emissivity of different land surface classes. The polarization difference (PD) parameters, the difference between horizontal (H-) and vertical (V-) polarization of TBs at 18 and 36 GHz clearly discern surface features of different surface classes such as deserts, arid/semi-arid and vegetated regions. Land surface microwave emissivity for MADRAS channels is derived on a global basis. These are inter-compared with the emissivity derived from the operational TRMM Microwave Imager and are in reasonably good agreement. The analysis based on emissivity shows spectral variation for different surface classes.

Keywords

Land-Surface Microwave Emissivity, MADRAS Payload, Megha-Tropiques Mission, Microwave Radiometry.

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K. Krishna Moorthy , S. Suresh Babu , B. V. Krishna Murthy , J. Srinivasan

Abstract

No Abstract.

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A. Ajay ¹, K. Krishna Moorthy ², S. K. Satheesh ³, G. Ilavazhagan ¹

Affiliations
1 Hindustan Institute of Technology and Science, Chennai 603 103, IN
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru 560 012, IN

Abstract

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.

Keywords

Black Carbon, COVID-19 Lockdown, Scattering Coefficients, Single Scattering Albedo.

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A. Ajay ¹, K. Krishna Moorthy ², S. K. Satheesh ³, G. Ilavazhagan ¹

Affiliations
1 Hindustan Institute of Technology and Science, Chennai 603 103, IN
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru 560 012, IN

Abstract

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.

Keywords

Anthropogenic Emissions, Black Carbon, COVID-19 Lockdown, Rural Aerosols, Scattering Coefficients, Single Scattering Albedo.

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Mukunda M. Gogoi ¹, S. Suresh Babu ¹, B. S. Arun ¹, K. Krishna Moorthy ², A. Ajay ³, P. Ajay ⁴, Arun Suryavanshi ⁵, Arup Borgohain ⁶, Anirban Guha ⁷, Atiba Shaikh ⁸, Binita Pathak ⁴, Biswadip Gharai ⁹, Boopathy Ramasamy ¹⁰, G. Balakrishnaiah ¹¹, Harilal B. Menon ⁸, Jagdish Chandra Kuniyal ¹², Jayabala Krishnan ¹³, K. Rama Gopal ¹¹, M. Maheswari ¹³, Manish Naja ¹⁴, Parminder Kaur ⁷, Pradip K. Bhuyan ⁴, Pratima Gupta ¹⁵, Prayagraj Singh ¹⁶, Priyanka Srivastava ¹⁴, R. S. Singh ¹⁷, Ranjit Kumar ¹⁵, Shantanu Rastogi ¹⁶, Shyam Sundar Kundu ⁶, Sobhan Kumar Kompalli ¹, Subhasmita Panda ¹⁰, Tandule Chakradhar Rao ¹¹, Trupti Das ¹⁰, Yogesh Kant ¹⁸

Affiliations
1 Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695 022, IN
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru 560 012, IN
4 Centre for Atmospheric Studies, Dibrugarh University, Dibrugarh 786 004, IN
5 Regional Remote Sensing Centre, Indian Space Research Organisation, Nagpur 440 033, IN
6 North Eastern – Space Application Centres, Shillong 793 103, IN
7 Department of Physics, Tripura University, Suryamaninagar, Agartala 799 022, IN
8 Department of Marine Sciences, Goa University, Goa 403 206, IN
9 National Remote Sensing Centre, Indian Space Research Organisation, Hyderabad 500 037, IN
10 Indian Institute of Mineral and Materials Technology, Bhubaneswar 751 013, IN
11 Sri Krishna Devaraya University, Anantapur 515 003, IN
12 G. B. Pant Institute of Himalayan Environment and Development, Kullu 175 126, IN
13 Tamil Nadu Agricultural University, Coimbatore 641 003, IN
14 Aryabhatta Research Institute of Observational Sciences, Nainital 263 002, IN
15 Department of Chemistry, Dayalbagh Educational Institute, Agra 282 005, IN
16 Department of Physics, D.D.U. Gorakhpur University, Gorakhpur 273 009, IN
17 Department of Chemical Engineering, IIT-BHU, Varanasi 221 005, IN
18 Indian Institute of Remote Sensing, Indian Space Research Organisation, Dehradun 248 001, IN

Abstract

In this study, we assess the response of ambient aero-sol black carbon (BC) mass concentrations and spec-tral absorption properties across Indian mainland during the nation-wide lockdown (LD) in connection with the Coronavirus Disease 19 (COVID-19) pan-demic. The LD had brought near to total cut-off of emissions from industrial, traffic (road, railways, ma-rine and air) and energy sectors, though the domestic emissions remained fairly unaltered. This provided a unique opportunity to delineate the impact of fossil fuel combustion sources on atmospheric BC characte-ristics. In this context, the primary data of BC meas-ured at the national network of aerosol observatories (ARFINET) under ISRO-GBP are examined to assess the response to the seizure of emissions over distinct geographic parts of the country. Results indicate that average BC concentrations over the Indian mainland are curbed down significantly (10–40%) from pre-lockdown observations during the first and most in-tense phase of lockdown. This decline is significant with respect to the long-term (2015–2019) averaged (climatological mean) values. The drop in BC is most pronounced over the Indo-Gangetic Plain (>60%) and north-eastern India (>30%) during the second phase of lockdown, while significant reduction is seen during LD1 (16–60%) over central and peninsular Indian as well as Himalayan and sub-Himalayan regions. De-spite such a large reduction, the absolute magnitude of BC remained higher over the IGP and north-eastern sites compared to other parts of India. Notably, the spectral absorption index of aerosols changed very little over most of the locations, indicating the still persisting contribution of fossil-fuel emissions over most of the locations.

Keywords

ARFINET, Black Carbon, COVID-19.

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