Defence Science Journal |
Albedo Variations and Surface Energy Balance in Different Snow-Ice
The present study is aimed at investigating the radiation budget in different snow-ice media (shelf ice, continental ice and natural snow) at three different elevated sites in the general area of Prince Astrid Coast of EastAntarctica. Measurements of the dependence of albedo in different snow and ice media on solar elevation angle, cloud cover, liquid water content, grain size, etc. can be interpreted in terms of single and multiple scattering radiative transfer theory. Detailed albedo measurements were carried out during summer and winter in different snow and ice media in 1997-98 at different selected sites at Antarctica. The average albedo values were found to be high (90 per cent) in snow medium, moderate (83 per cent) in shelf ice and very low (50 per cent) in continental ice medium. The albedo was found to be a function of cloud amount, increasing with the amount and thickness. In white-out condition during blizzards, high albedo (average 83 per cent) was found as compared to clear sky day (76 per cent) and after blizzard (average 78 per cent). It showed dependence on the type and age of snow also. New snowfall over old snow displayed higher values (90 per cent) than older snow (70 per cent) and decreased with the age of snow from 13-16 per cent. Natural melt-water in snowpack increases from 1-10 per cent, resulting in albedo decay from 7-10 per cent. As the minimum solar elevation angle in Antarctica goes to 3°, strong qualitative analyses have been made of the dependence of albedo on the solar elevation angle. Albedo values showed diurnal hysteresis and morning values were found to be higher than evening values at the same angle of elevation. The dependence was slight for solar elevations during day time when e >:.. 12-15°, but became larger with low angles when e = 3-12°. Solar insolations were also calculated for different months in order to calculate short wave radiation absorbed by snow and ice media. Insolations in different months at different selected sites lie in the ranges 10-540 In/day (August-October), 350-911 In/day (November-December) and 190- 755 In/day (January-February). Net energy balance was calculated using model and was found to be negative most of the time.
Bond Growth under Temperature Gradient
Grain and band growth for dry snow are determined by the distribution of temperature and temperature gradient in the snow matrix. From the standpoint of particle approach and based on cubic packing structure, a bond growth model has been developed for TO metamorphism. The paper highlights the importance of bond formation and its effect on snow viscosity and finally on the rate of settlement. This is very important for developing a numerical snowpack model if microstructure is considered to be a basic parameter. A few experiments have been carried out to validate bond formation under temperature gradient.
Frostbite, the severest form of cold injury, is a major health hazard and a serious medical problem for the Armed Forces operating in snow-bound areas at high altitudes. Detailed experiments on susceptibility, prevention and treatment were conducted to find out suitable measures to prevent, treat and ameliorate cold injuries. Experiments conducted on monkeys have shown that animals with higher peripheral vascular response are better protected against cold injury. Measurements of cold-induced vasodilatation (CIVD), heat output and peripheral blood flow under local cold stress can be used to screen out highly prone individuals to frostbite. Cold acclimatisation was effective in raising the peripheral vascular response and thereby lessening the degree of injury. Frostbite having occurred, its treatment is not very satisfactory. This is primarily due to the time lag between occurrence of frostbite and initiation of therapy, which plays a vital role in its curative action. Keeping this in view, many experiments have been conducted on this treatment. Pilot studies were carried out using various drugs and vitamins, and also procedures like rapid rewarming in warm water, tea decoction, turnip (shalgum) decoction, etc., singly as well as in combination, for treatment. The most encouraging result was obtained by the procedure of rapid rewarming in tea decoction maintained at 37-39 °C immediately after cold exposure, followed by combined therapy of aspirin (5 mglkg) and pentoxifylline (40 mglkg) along with vitamin C (50 mglkg) twice daily for 7 days.
Knowledge-Based System for Forecasting Snow Avalanches of
In this paper an attempt has
been made to use artificial intelligence in avalanche forecasting and drule-based expert
system for predicting direct action avalanches of Chowkibal-Tangdhar axis (J&K). Using
the form of rules. The condition attributes of the rule- based system are 28 variables
selected from I 154 samples of snow-met and snow Profile data. The relative contribution
of each variable on avalanche days and non-avalanche days and their influence on sitewise
release of avalanche was studied to formulate 358 rules. These rules, which include 173
decision rules, were finally implemented and validated for running the model. Sixty-three
samples of snow-met
data and pit profile data attributing to avalanche days and 54 samples of non-avalanche
days were run on the model. The results show that the knowledge-based model can predict
with 76 per cent efficiency. The misclassified results accounted for 28.2 per cent of 117
test samples.
Mixture Theory of Mass Transfer Based upon Microstructure
Robert L. Brown, Michael Q. Edens and Michael Barber
A mixture theory has been developed to model equitemperature metamorphism of snow. This formulation is a volume fraction theory which models the interchange of mass between the constituents making up the mixture. The formulation has been developed so that the microstructure of the material is included to correctly describe the mechanical and thermal processes. The second law of thermodynamics is used to impose restrictions upon the various constitutive relations. These constitutive relations are then described in terms of microstructure of the material. The microstructure of each constituent is represented by constituent size (mean grain size, intergranular bond size), intergranular neck geometry, specific free surface area and dispersed density. The resulting formulation is then used to model equitemperature metamorphism of snow by determining the time-dependent changes in the distribution of grain size, neck size and dispersed densities of each of the constituents. The results obtained show that the formulation can describe how the material changes under equitemperature conditions. However, it is noted that since microstructure significantly affects the rate of metamorphism, an accurate determination of the microstructure (including grain and neck size distribution) is necessary for this approach to accurately predict changes in the material due to metamorphism.
Applications of a Nonlinear Constitutive Equation for Creeping Snow
In the seventies the author carried out numerous laboratory tests, simultaneously performed under six different states of stress and deformation (totally 121 identical three samples tested). The aim was to obtain a three dimensional nonlinear constitutive equation, i.e., one which higher applies to stresses. The theoretical background was a constitutive equation consistent with the principle of maximum entropy production. The irreversible part -which was exclusively considered -depends only on the dissipation function, represented by an exponential series. The final result consists of nine coefficients of three invariants of the stress tensor. Unfortunately, the resulting equation was never used to resolve practical problems in snow mechanics. This paper is aimed to demonstrate the usefulness of the equation by means of simple examples. For a uniform horizontal snow cover, it was firstly shown that snow behaves strongly non-symmetrically under compression and tension. And secondly, it was seen that the settlement (compression) deformation rates are up to se per cent higher than those with linear behaviour. In an other example, the development of a shear crack on the occasion of snow slab release has demonstrated that fracture starts earlier up slope and propagates faster than downslope. On the other hand, linearity between shear stresses and shear deformation can be justified.
Numerical simulation of seasonal snowcover has attracted the interest of many scientists in the recent past The present paper summarises chronologically developments in the understanding of snow properties and discusses various modelling approaches towards simulating the snowpack numerically. The authors describe the evolution of snowcover and the intricate relationship between the evolving snowpack and the atmosphere. The governing equations that describe the evolution of snowcover have been discussed. The merits and limitations of each equation describing a single process have been explained. Modelling strategies adopted by various workers have been analysed, and lastly the requirements of a perfect model have been brought out. In the absence of complete answers to many other processes, a strategy for the development of an operational snowcover model has been discussed.
North-west Himalayan region comprises five mountain ranges. Their orientation and complex terrain influence the weather over the region. Sudden altitudinal changes also affect the weather systems to a considerable extent. Due to the prevailing inhomogeneous topography, various dynamicand thermal processes take place at mesoscale level. In synoptic scale, during winter seasons, weather systems, named, western disturbance (WD), take their Southerly track and travel over J&K, HP and hills of western UP, and yield considerable amount of precipitation. On the basis of past historical data collected over J&K region, the pattern of snowfall and its frequency distribution was studied using statistical means. Variation of these snowfall spells was also studied to understand spatial and temporal changes in their distribution. A brief case study of a WD has been carried out to estimate moisture flux inflow over Himalayas.
Statistical-Based
Forecasting of Avalanche Prediction
This paper describes the study carried out to predict few meteorological parameters of the next day using the observed parameters of previous day through statistical methods. Multiple linear regression model was formulated for a hill station, Patsio, situated between Manali and Leh, for two winter months (December and January) separately. Twelve meteorological parameters were predicted using 18 predictors observed on the previous day. Ten years data has been used for the computation of regression coefficients. A comparison of the forecasted parameters with the observations was made through the regression model. The prediction of the developed regression model was reasonably close to the observations. The relevant statistical error associated with the linear model (standard error) was also estimated. The output of this regression model will be useful in developing knowledge-based and statistical-based avalanche forecasting model.
Nishkam Kasturiya, M.S. Subbulakshmi, S.C. Gupta and Hans Raj
System design of cold weather protective clothing is a critical process, as it involves consideration of the effects of a number of external and internal parameters like environmental factors and physical, physico-mechanical and psychological parameters. The bulk and weight of the textile materials used in protective clothing should be as low as possible, so that clothing does not create physical stress and discomfort to the soldier and does not affect his combat duties adversely. This paper discusses the essential factors involved in the designing of cold weather protective clothing and different insulating materials available in the market for developing better protective clothing. Different stores developed at the Defence Materials & Stores Research & Development Establishment, Kanpur, the order of arrangement of various insulating materials in those stores and the protection level achieved are discussed.