• R P 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.

• 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.

• 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.

• Space-based long-term observation of shrinking grassland habitat: A case-study from central India

Grassland ecosystem is critical for survival of herbivores and plays an important role in conservation and management of wildlife. These habitats are widely studied for various issues, including biodiversity, biomass assessment, carrying capacity, etc. Woody species ingression in grasslands is one such important aspect that needs critical attention in protected area as this leads to shrinking of grasslands habitat. This study presents a case of Ronda grassland in Kanha National Park – a well-known protected area in India, known for its herbivore diversity and hard-ground Barasingha (Rucervus duvaceli branderi), in particular. Long-term satellite observation for five decades was carried out to understand spatio-temporal changes. Declassified Corona satellite data, aerial photographs along with satellite datasets in the subsequent period were utilised for this study. The study revealed that 88 ha (16% of Ronda and surrounding) have been ingressed during 1962–2011, in and around Ronda grassland of Kanha National Park. Rates of ingression on linear transects were found to be 60–120 m per decade. Field studies and NDVI analysis along the edge of grassland pixels as well as inside region using 1972 as baseline data, indicated woody vegetation replacing area of grassland. It was noted that Butea monosperma is invading more than other species in Ronda grassland, particularly along the stream where moisture availability is higher. Grassland habitats in Kanha are thus shrinking and thus leading to reduction in the area available for herbivore population which has increased in recent years. This can lead to severe impact on carrying capacity of these grasslands.

• # Journal of Earth System Science

Current Issue
Volume 128 | Issue 5
July 2019