• A K Singh

Articles written in Journal of Earth System Science

• Features of discrete VLF emissions observed at Gulmarg, India during the magnetic storm of 6–7 March, 1986

During the analysis of archived VLF data from Indian low latitude ground stations, some discrete VLF emissions recorded at the low latitude ground station Gulmarg (geomagnetic latitude 24°26′N; geomagnetic longitude 147° 09′E, L = 1.28) during moderate magnetic storm activity (𝛴 $K^{−}_{P}} = 32$, $K_P$ index varies from 4 to 6 during the observation period) on 6/7 March, 1986 are presented in this paper. The dynamic spectra of these discrete VLF emissions were observed along with tweeks and its harmonics, which is interesting and complex to explain. In most of the events the harmonic frequency of tweeks correlates with the starting frequency of harmonics of discrete emissions. In order to explain the observed features of discrete VLF emissions, we propose cyclotron resonance interaction between whistler mode wave and energetic electrons of inner radiation belt as possible generation mechanism. An attempt is also made to determine parallel energy, anisotropy and wave growth relevant to the generation process of VLF emissions.

• Observations of unusual whistlers during daytime at Jammu

In this paper,we report observations of unusual whistlers recorded at Jammu (geomag.lat.= 22° 26′N; 𝐿 =1.17), India on March 8, 1999 during the daytime. They are interpreted as one-hop ducted whistlers having propagated along higher 𝐿 -values in closely spaced narrow ducts from the opposite hemispheres. After leakage from the duct, the waves might have propagated in the earthionosphere waveguide towards the equator in surface mode.Tentative explanation of the dynamic spectra of these events is brieﬂy presented.

• Dependence of thermal conductivity of snow on microstructure

A geometrical model,including different geometrical shapes in ﬂuencing thermal conductivity of snow is proposed.The geometrical model has been assumed to comprise of unit cells having solid (ice)inclusion as an aggregation of spherical,cylindrical or cubical shapes with vertical connection, arranged in a cubic packing.From the geometrical model and one-dimensional heat transfer theory, the effective thermal conductivity has been computed.For this purpose,coupled one-dimensional heat transfer equations have been solved for steady-state condition to account for conduction in ice, conduction in air and latent heat transfer due to water vapour sublimation through air.The model demonstrates the dependency of thermal conductivity on density,grain-spacing,grain contact ratio and temperature.Spherical inclusions give highest conductivity while cubical inclusion estimates lowest value for the same density.Thermal conductivity has been found increasing sharply near to the packing density for all three shapes.Empirical model results and results obtained from existing microstructure based models have also been compared with the present model.

• Quasi-periodic VLF emissions observed during daytime at a low latitude Indian ground station Jammu

This paper reports quasi-periodic pulsing hiss emissions recorded during daytime in the frequency range of 50 Hz –15 kHz at low latitude station Jammu (geomag.lat.=22° 26′N; 𝐿 =1.17). It is noted that pulsing VLF emissions are a rare phenomena at low latitudes.The various spectrograms of pulsing VLF hiss emissions presented in this paper clearly show band limited spectrums regularly pulsing with almost equal period of the order of few seconds in the frequency range of ∼3-8 kHz. Generation and propagation mechanism of these emissions are brieﬂy discussed.

• Characteristics of low latitude ionospheric E-region irregularities linked with daytime VHF scintillations measured from Varanasi

VHF amplitude scintillations recorded during the daytime period from January 1991 to December 1993, April 1998 to December 1999 and January 2008 to December 2008 at low latitude station Varanasi (geographic lat. = 25° 15′N; long. = 82° 59′E; geomagnetic lat. = 14° 55′N, long. = 154°E, dip angle = 37.3°, sub-ionospheric dip = 34°) have been analyzed to study the behaviour of ionospheric E-region irregularities during the active solar and magnetic periods. The autocorrelation functions, power spectral densities, signal de-correlation times are computed to study the temporal features of ionospheric E-region irregularities linked with daytime scintillations. Derived spectral index ranges between −2 and −9. Assuming velocity of irregularities, the characteristic lengths of the E-region irregularities are estimated. We have estimated the minimum and maximum range of scale length of sporadic-E ($E_s$) irregularities to be observed over Varanasi. These results are in close agreement with those reported from this latitude region.

• Water quality of the Chhoti Gandak River using principal component analysis, Ganga Plain, India

Chhoti Gandak is a meandering river which originates in the terai area of the Ganga Plain and serves as a lifeline for the people of Deoria district, Uttar Pradesh. It travels a distance of about 250 km and drains into Ghaghara near Gothani, Siwan district of Bihar. It has been observed that people of this region suffer from water-borne health problems; therefore water samples were collected to analyse its quality along the entire length of Chhoti Gandak River.

The principal components of water quality are controlled by lithology, gentle slope gradient, poor drainage, long residence of water, ion exchange, weathering of minerals, heavy use of fertilizers, and domestic wastes. At some stations water is hard with an excess alkalinity and is not suitable for drinking and irrigation purposes. The variation in the local and regional hydrogeochemical processes distinguished the geogenic sources from the anthropogenic one.

• Characteristic of plasma bubbles observed by DMSP in the topside ionosphere during the year 2005

To study the characteristic of plasma bubbles in the topside ionosphere during the solar minima, we have analyzed a large database of post-sunset plasma density measurement acquired during ∼5104 equatorial crossings made by Defense Meteorological Satellite Program (DMSP) F14 in 2005. On 675 of these crossings, equatorial plasma bubbles (EPBs) events were observed as intervals of depleted and irregular plasma densities that degrade communication and navigation signals. We have analyzed these EPB events to study their distributions with month, season and longitude. To test for possible dependence of EPB occurrence at topside altitudes on the level of magnetic activity, we compared the distributions of one year database with those of Kp index at the time of equatorial crossings by the DMSP satellites. We also examined the response of the evening sector, low-latitude ionosphere during eight magnetic storms with minimum Dst ≤ −100nT. We observed that EPBs occurred regularly during geomagnetic storms, especially in the initial and main phases but can be suppressed sometimes for days, after prolonged activity during recovery phases. These results are discussed according to the other reported results.

• Tidal and gravity waves study from the airglow measurements at Kolhapur (India)

Simultaneous photometric measurements of the OI 557.7 nm and OH (7, 2) band from a low latitude station, Kolhapur (16.8°N, 74.2°E) during the period 2004–2007 are analyzed to study the dominant waves present in the 80–100 km altitude region of the atmosphere. The nocturnal intensity variations of different airglow emissions are observed using scanning temperature controlled filter photometers. Waves having period lying between 2 and 12 hours have been recorded. Some of these waves having subharmonic tidal oscillation periods 4, 6, 8 and 12 hours propagate upward with velocity lying in the range 1.6–11.3 m/s and the vertical wave length lying between 28.6 and 163 kms. The other waves may be the upward propagating gravity waves or waves resulting from the interaction of inter-mode tidal oscillations, interaction of tidal waves with planetary waves and gravity waves. Some times, the second harmonic wave has higher vertical velocity than the corresponding fundamental wave. Application of these waves in studying the thermal structure of the region is discussed.

• # Journal of Earth System Science

Volume 131, 2022
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019