On the stability and evolution of stationary whistler turbulence

It is shown that stationary turbulence consisting of an ensemble of small amplitude whistler wave packets becomes unstable against adiabatic perturbations. The rate of increase of the purely growing instability is presented. A stationary non-linear BGK solution for the whistler electric fields is obtained.     

Observations of wind and waves in the central Bay of Bengal during BOBMEX-99 and their effect on mixed layer depth variability due to forced mixing

Time-series wind and wave measurements were carried out onboard INS Sagardhwani in the central Bay of Bengal during BOBMEX-99. Various other marine meteorological and oceanographic measurements relevant to monsoon studies were also collected simultaneously. The observed variations of wind and waves and the associated mixed layer depth (MLD) variability based on both temperature and density criteria at 3 hourly intervals are presented in this paper as a case study. At the time-series location (13‡N, 87‡E) wind varied between 6 and 16m/s and the predominant direction was southwesterly. The significant wave height and period varied from 1.9 to 3.7m and 8 to 13 s respectively. Some of the available statistical predictive methods for the determination of MLD by forced mixing are utilized to test the extent of mechanical mixing within the top layer of water by the local wind and wave activity. The same is extended to formulate a new empirical relation for gross estimation of effective depth within which the sound energy is generally trapped during its transmission in the surface duct. The present analysis aiming for estimation of observed MLD variability (35 to 75 m) using the suggested simple empirical relation reveals that, the mixed layer variability observed during the experiment depends on both local ocean variability as well as remote forcing as reported earlier.     

Debye shielding in a dusty plasma

The phenomenon of Debye shielding is investigated in a dusty plasma consisting of Boltzmann electrons and ions, and negatively charged, massive dust grains. Both small and large amplitude electrostatic potentials are considered and a parameter study conducted.     

Excitation of ULF and VLF waves in the ionosphere

It is shown that a two-dimensional lower-hybrid wave structure can parametrically trigger the growth of VLF and ULF noises in a plasma. Analytical expressions for the increment and threshold of the instability are obtained. Application of our work to the auroral zones of the topside ionosphere is discussed.     

Itawa Bhopji (L3–5) chondrite regolith breccia: Fall,classification, and cosmogenic records

Abstract— A stony meteorite fell at Itawa Bhopji, Rajasthan, India on 2000 May 30. This is the fifth recorded fall in a small area of Rajasthan during the past decade. The meteorite is an ordinary chondrite with light clasts in a dark matrix, consisting of a mixture of equilibrated (mainly type 5) and unequilibrated components. Olivine is Fa_24–26 and pyroxene Fs_20–22 but, within the unequilibrated components, olivine (Fa_5–29) and low calcium pyroxene (Fs_5–37) are highly variable. Based on petrographic studies and chemical analyses, it is classified as L(3–5) regolith breccia. Studies of various cosmogenic records, including several gamma‐emitting radionuclides varying in half‐life from 5.6 day ⁵²Mn to 0.73 Ma ²⁶Al, tracks and rare gases have been carried out. The exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19.6 Ma. The track density varies by a factor of ?3 (from 4 to 12 times 10⁶/cm²) within the meteorite, indicating a preatmospheric body of ?9 cm radius (corresponding to a meteoroid mass of ?11 kg) and small ablation (1.5 to 3.6 cm). Trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite. Large excess of neutron‐produced ⁸²Kr and ¹²⁸Xe in both the light and the dark lithology but very low ⁶⁰Co, indicating low neutron fluxes received by the meteoroid in the interplanetary space, are clear signatures of an additional irradiation on the parent body.     

Agricultural management impacts on groundwater: simulations of existing and alternative management options in Peninsular India

Understanding the principal causes and possible solutions for groundwater depletion in India is important for its water security, especially as it relates to agriculture. A study was conducted in an agricultural watershed in Andhra Pradesh, India to assess the impacts on groundwater of current and alternative agricultural management. Hydrological simulations were used as follows: (1) to evaluate the recharge benefits of water‐harvesting tillage through a modified Soil and Water Assessment Tool (SWAT) model and (2) to predict the groundwater response to changing extent and irrigation management of rice growing areas. The Green–Ampt infiltration routine was modified in SWAT was modified to represent water‐harvesting tillage using maximum depression storage parameter. Water‐harvesting tillage in rainfed croplands was shown to increase basin‐scale groundwater recharge by 3% and decrease run‐off by 43% compared with existing conventional tillage. The groundwater balance (recharge minus irrigation withdrawals), negative 11 mm/year under existing management changed to positive (18–45 mm/year) when rice growing areas or irrigation depths were reduced. Groundwater balance was sensitive to changes in rice cropland management, meaning even small changes in rice cropland management had large impacts on groundwater availability. The modified SWAT was capable of representing tillage management of varying maximum depression storage, and tillage for water‐harvesting was shown to be a potentially important strategy for producers to enhance infiltration and groundwater recharge, especially in semi‐arid regions where rainfall may be becoming increasingly variable. This enhanced SWAT could be used to evaluate the landscape‐scale impacts of alternative tillage management in other regions that are working to develop strategies for reducing groundwater depletion. Copyright © 2013 John Wiley & Sons, Ltd.     

Stability analysis of multi-directional anchored rock slope subjected to surcharge and seismic loads

More than one set of anchors with different orientations can be an economical solution to completely stabilize the rock slope. In this note, a general analytical expression for the factor of safety of a multi-directional anchored rock slope (MDARS) against plane failure is derived, incorporating most of the practically occurring destabilizing forces under surcharge and seismic loading conditions. Several special cases of this expression are found to be similar to those reported in the literature. A graphical presentation shows that for any specific inclination of one set of anchors to the normal at failure plane, the variation in the inclination of the second set of anchors to the normal at failure plane, when greater than approximately 60°, does not cause a significant change in the factor of safety of the MDARS.