Early In-orbit Performance of Scanning Sky Monitor Onboard AstroSat

We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ \(\times \) 2.5\(^\circ \) and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON.     

Thermodynamic structure of the monsoon boundary layer under the influence of a large-scale depression

Using data from the MONsoon Trough Boundary Layer EXperiment (MONTBLEX), the thermodynamic structure of the atmospheric boundary layer (ABL) under the influence of a monsoon depression has been studied. When the depression was in the vicinity of the observing station, the soundings showed an increase in potential temperature, the sub-cloud layer was well mixed, the wind speed increased to 35 m/s, and the monsoon boundary layer was convectively more unstable at night than in the daytime. Cloud-top processes, which lead to an apparent breakdown of the boundary layer, seem to explain this.     

Five dimensional universe model with variable cosmological term Λ and a big bounce

We assume the four dimensional induced matter of the 5D Ricci flat bouncing cosmological solution contains a perfect fluid. The big bounce singularity of simple 5D cosmological model is studied with the cosmological term Λ=α ρ and Λ=β H ² where α and β are constants and ρ and H are respectively energy density and Hubble parameter. This big bounce singularity is found to be an event horizon at which the scale factor and mass density of the universe are finite, while the pressure is infinite.      

Benthic foraminiferal response to changes in mining pattern: a case study from the Zuari estuary,Goa, India

Being sensitive to environmental changes, foraminifera have been extensively used to monitor pollution level in the marine environment, including the effect of mining in coastal areas. In the Goa state of India, the rejects from opencast mining on land largely find their way to the estuaries, as washout during monsoon. Additionally, the Mormugao Port at the mouth of the Zuari estuary is the hub of activities due to the transport of ore from hinterland areas by barges and its subsequent loading for export. On the directive of the Supreme Court of India, all the mining-related activities abruptly stopped throughout India, including that in Goa in 2012, and got reinstated in 2015. Therefore, it provided a fit case to test the effectiveness of benthic foraminifera as an indicator of environmental impact due to mining activities. A total of ten surface sediment samples from five locations in Zuari estuary were collected from a depth range of 4.5–8.5 m in the years of 2013 and 2016 and were analyzed for both the living (stained) and dead benthic foraminifera. The year 2013 represents a time interval immediately after the closure of extensive mining activity, and the sampling during 2016 represents minimal mining. The living benthic foraminiferal abundance was higher (19–54/g sediment) during 2013 and decreased substantially during 2016 (3–22/g sediment), suggesting an adverse effect of activities associated with mine closure on benthic foraminifera. Additionally, the relative abundance of Ammonia was also significantly low during the year 2016. The temporal variation in dead foraminifera was, however, different than that of the living foraminifera. The differential response was attributed to the terrigenous dilution as a result of change in sedimentation rate. Therefore, we conclude that living foraminifera correctly incorporate the changes in mining pattern and may be used as an effective tool to monitor the impact of mining. We further suggest that the potential counter effect of terrigenous dilution on total and living benthic foraminiferal population should be considered while interpreting temporal variations in foraminiferal abundance in marginal marine settings.     

Abundance and size variation of Globorotalia menardii in the Northeastern Indian Ocean during the late quaternary

Variation in absolute abundance, size and coiling direction ratio of the planktic foraminifera Globorotalia menardii during the late Quaternary have been studied in three cores, collected along a north-south transect from the northeastern Indian Ocean. Increased abundance and larger size is observed during the warm interglacial period, whereas, smaller and fewer G. menardii specimens are noted during the cold glacial periods. A comparatively better match between absolute abundance, size and oxygen isotopic composition of foraminifera as compared to carbon isotopic composition at all the locations indicates that the abundance and size of G. menardii is more affected by seawater temperature and salinity as compared to productivity changes. The amplitude and frequency of temporal changes in the abundance and size of G. menardii vary from core-to-core, indicating the influence of site-specific physico-chemical conditions. In comparison to the abundance and size, the coiling direction of G. menardii does not show any systematic change in any of the cores. The majority of the specimens coil sinistrally. We conclude that the absolute abundance and variation in the average size of G. menardii can be used to infer past climatic changes. However, the variation in coiling direction of G. menardii appears to be unaffected by late Quaternary paleoclimatic variations in the north-eastern Indian Ocean.     

Foraminifers as indicators of marine pollution: a culture experiment with Rosalina leei

In order to develop a viable foraminiferal proxy for heavy metal pollutants, juvenile specimens of Rosalina leei were subjected to different mercury concentrations (0-180 ng/l). Initially considerable growth was observed in specimens kept in saline water having a mercury concentration up to 100 ng/l. But with the gradual increase in concentration of mercury the growth rate started decreasing. Total growth achieved was significantly lower in case of specimens kept at relatively higher mercury concentrations then those maintained in normal saline water. The most significant result of this experiment was the addition of abnormal chambers in the specimens kept at higher mercury concentration. Later the specimens kept at highest concentration (180 ng/l) were subjected to progressively increasing concentration of mercury to see the further effects and it was found that the specimens were still living at as high a mercury concentration as 260 ng/l although there was no growth.     

Numerical study of the effects of urban heat island on the characteristic features of the sea breeze circulation

A two-dimensional numerical model is employed to study the effect of the coastal urban heat island on the sea breeze front and the thermal internal boundary layer height. The temperature at the land surface is determined by solving an energy budget equation. The effect of the urban heat island is studied by varying the width of the region and its intensity. During the early afternoon, the presence of the urban heat island enhances the strength of convergence of the sea breeze front and also reduces its inland penetration. The presence of the urban heat island causes increased thermal internal boundary layer height. Larger urban width causes larger vertical velocity and higher thermal internal boundary layer. Stronger convergence and higher thermal internal boundary layer are also obtained in case of larger heat island intensity.     

Scanning sky monitor (SSM) onboard AstroSat

Scanning Sky Monitor (SSM) onboard AstroSat is an Xray sky monitor in the soft X-ray band designed with a large field of view to detect and locate transient X-ray sources and alert the astronomical community about interesting phenomena in the X-ray sky. SSM comprises position sensitive proportional counters with 1D coded mask for imaging. There are three detector units mounted on a platform capable of rotation which helps covering about 50% of the sky in one full rotation. This paper discusses the elaborate details of the instrument and few immediate results from the instrument after launch.     

Oxygen isotope records of Globigerina bulloides across a north-south transect in the south-western Indian Ocean

Along a north-south transect (9.69°N to 55.01°S) in the southwestern Indian Ocean during the Indian Pilot Expedition to Southern Ocean (PESO), the oxygen isotopic analysis of planktic foraminifera (Globigerina bulloides) from 23 surface sediment samples was carried out to assess the relationship between isotopic composition of G. bulloides and the prevailing physical (seawater temperature and salinity) conditions of the ambient seawater. An increasing trend in the δ¹⁸O value is noticed towards higher latitude. Apparently such an increase in δ¹⁸O values is inversely related to the temperature changes along the transect. However, slight mismatch is observed at a few stations due to calcification out of optimum conditions or due to the salinity changes. The preliminary results of the present study, if extended to the subsurface sediments coupled with other parameters, may contribute to the reconstruction of the paleohydrography of the region, especially the position of various seawater fronts during the geologic past albeit with areal limitation.     

Relationship between abundance and morphology of benthic foraminifera <Emphasis Type="Italic">Epistominella exigua</Emphasis>: Paleoclimatic implications

The relationship between abundance (relative as well as absolute abundance) and morphology (size of the shell, number of chambers and proloculus size) of benthic foraminifera Epistominella exigua has been studied in a core to understand the influence of changing environmental conditions on its morphology and distribution. A total of 50 samples from the top 100 cm section of a gravity core collected from the southern Bay of Bengal Fan were used. The changes in abundance of E. exigua match well with variation in average proloculus size of E. exigua. An opposite relationship however, is observed between the abundance and size of E. exigua shells. The higher abundance corresponds with smaller E. exigua shells. Similarly, the increased E. exigua abundance matches with a decrease in the number of chambers. The increased abundance of E. exigua shows favourable conditions for its growth and survival. Thus the study indicates that during favourable conditions, while the number of chambers in the shells and the size of the shells of E. exigua decreases, more number of specimens have a larger proloculus. Since asexual reproduction results in megalospheric specimens with larger proloculus, smaller size and less number of chambers, it is inferred that E. exigua prefers an asexual mode of reproduction during favorable conditions. The findings can be used to apply morphological characteristics of E. exigua as a proxy to infer past climatic conditions.