Current Science

Ram Sagar ¹, U. C. Dumka ¹, Manish Naja ¹, Narendra Singh ¹, D. V. Phanikumar ¹

Affiliations
1 Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 002, IN

Abstract

ARIES, acronym for Aryabhatta Research Institute of Observational Sciences, located in the Central Gangetic Himalayan (CGH) region is emerging as one of the unique sites for climate change studies. The long-term, in situ, precise measurements of aerosols and trace gases obtained from this region provide valuable inputs for climate studies. Atmospheric scientists from ARIES are actively involved in nearsurface measurements for meteorology, aerosols and trace gases as well as vertical profiling. The Institute is also providing the observational infrastructure and research support to three major projects of the Indian Space Research Organization, Geosphere Biosphere Programme, which basically deals with the measurement of aerosols, trace gases and boundary-layer experiments. The upcoming stratosphere-troposphere radar and high-power micro-pulse lidar observational facilities will be utilized for the continuous vertical profiling of winds, aerosol and cloud properties at a very fine resolution in time and space. Apart from this, atmospheric scientists of ARIES also have active national and international research collaborations. The important results obtained from these research activities are highlighted and upcoming major observational facilities in the field of atmospheric sciences are discussed. They clearly demonstrate the importance of the unique geographical location of ARIES for climate change studies in the CGH region. These measurements and routine meteorological observations provide the necessary atmospheric corrections to the astrophysical observations taken using optical telescopes located at the site.

Keywords

Aerosols, Air Pollution, Climate Change, Trace Gases, Wind Profiler.

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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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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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Amitesh Omar ¹, Brijesh Kumar ¹, Maheswar Gopinathan ¹, Ram Sagar ¹

Affiliations
1 Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 002, IN

Abstract

India's largest 3.6 m aperture optical telescope has been successfully installed in the central Himalayan region at Devasthal, Nainital district, Uttarakhand. The primary mirror of the telescope uses the active optics technology. The back-end instruments, enabling spectroscopic and photometric imaging of the celestial sky are designed and developed by ARIES along with other Indian institutes. The Devasthal optical telescope in synergy with two other highly sensitive telescopes in the country, namely GMRT operating in the radio wavebands and AstroSat operating in the high-energy X-ray, ultraviolet and visual wavebands, will enable Indian astronomers to carry out scientific studies in several challenging areas of astronomy and astrophysics.

Keywords

Active Optics Technology, Celestial Sky, Instrumentation, Optical Astronomy.

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Ram Sagar ¹, Brijesh Kumar ², Amitesh Omar ²

Affiliations
1 Indian Institute of Astrophysics, Sarajapur Road, Koramangala, Bengaluru 560 034, IN
2 Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 001, IN

Abstract

India’s largest 3.6 metre Devasthal Optical Telescope (DOT) was commissioned in 2016, though the idea of building it germinated way back in 1976. This article provides research accounts as well as glimpses of its nearly four decades of journey. After a decade of site surveys, Devasthal in the central Himalayan region of Kumaon, Uttarkhand was identified. Thereafter, a detailed site characterization was conducted and project approvals were obtained. The telescope is designed to be a technologically advanced optical astronomy instrument. It has been demonstrated to resolve a binary star having angular separation of 0.4 arc-sec. After technical activation of the telescope on 30 March 2016, it has been in regular use for testing various back-end instruments as well as for optical and near-infrared observations of celestial objects. Back-end instruments used for these observations are 4K × 4K CCD IMAGER, faint object imager-cum-spectrograph and TIFR nearinfrared camera-II. A few published science results based on the observations made with the telescope are also presented. Furthermore, routine observations show that for a good fraction of observing time the telescope provides sky images of sub-arc second resolution at optical and nearinfrared wavelengths. This indicates that the extreme care taken in the design and construction of the telescope dome building has been rewarding, since the as-built thermal mass contributes minimally so as not to degrade the natural atmospheric seeing measured at Devasthal about two decades ago during 1997–99 using differential image motion monitor. The overall on-site performance of the telescope is found to be excellent and at par with the performance of other similar telescopes located over the globe.

Keywords

History, Optical Telescope, Optical Observatory, Site Characterization, Sky Performance.

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