A simulation technique for the determination of atmospheric water content with Bhaskara satellite microwave radiometer (SAMIR)

A simulation technique has been developed to estimate the integrated atmospheric water content over oceans using the 19·35 and 22·235 GHz brightness temperature data from satellite microwave radiometer (SAMIR) on board the Indian satellite Bhaskara. The results obtained have been compared with those from linear statistical regression and empirical methods as well as from the nearest radiosonde observations. Based on the simulation method, a map of total precipitable water for some of the Bhaskara passes in July 1980 over Bay of Bengal is given. The possible applications of such maps in the study of Indian summar monsoon and boundary layer characteristics have been pointed out.     

Aircraft measurements of SST using IR-radiometer and temperature corrections due to atmospheric effects

Using an airborne scanning IR-radiometer, measurements of sea surface temperature (SST) were made from nine different levels in the Sandheads region of the Bay of Bengal on 5 October 1978. To retrieve SST from the observed radiances a temperature correction scheme, which uses the radiosonde data in the vicinity of flight area, has been generated. Atmospheric effects which have been considered include absorption due to water vapour and carbon dioxide, and the re-emission from different atmospheric layers. The radiances observed at different altitudes when corrected by our scheme yield a fairly consistent value of SST. The special ship measurements of SST, at the same location, are found to have very good agreement with the SST retrieved from the observed radiances using our scheme. The temperature corrections turn out to be 0·3 and 3·3°C at 600 and 3000 meters respectively for the type of atmosphere which has been used in our study.     

An atmospheric instability derived with MODIS profile using real-time direct broadcast data over the Indian region

In this study, assessing the atmospheric instability, a new index, named here as MODIS (Moderate Resolution Imaging Spectroradiometer) profile index (MPI), has been statistically computed using temperature and moisture profile data from the real-time direct broadcast receiving systems installed at three places of India Meteorological Department. The training dataset has been prepared using MODIS temperature and moisture profile from the Aqua and Terra satellites over the Indian region for clear and convective weather conditions during the period of March to June 2011. The MPI values are produced at 5?×?5?km pixel resolution when at least 6 out of 9 FOVs from MODIS granules are found cloud free. If more than 3 FOVs are cloudy, the MPI has not been computed. The formulation of MPI and its comparison have been examined with well-established traditionally used K index, Lifted Index and total totals index derived from radiosonde profiles of temperature, pressure and humidity. It has been observed that in most of the cases, MPI has well correlated with those derived from ground truth observations. Therefore, spatially interpolated MPI can be utilized as an indicator for regional and location-specific forecast over the areas where radiosonde data are not available. The results also indicated that MPI can be used as a sensitive measure in very early stages of instability developments such as thunderstorm and rainfall because no other single stability index can provide a distinct threshold value for these events. Therefore, a single MPI value at a certain threshold can be treated as a stability index instead of other available indices. It is also being proposed that the inclusion of MPI as a stability parameter in physical or numerical modeling can improve accurate local severe storm predictions as a useful predictor and can also be used as diagnostic tools. The MPI can make a useful simulation using entire temperature and moisture profile data for the assessment of instability significantly to severe weather forecasting since other instability indices are often derived from a fixed pressure level quantity of vertical profile parameters.     

Capability ofBhaskara SAMIR to distinguish atmospheric water vapour and liquid water contents

An environmental model to compute microwave brightness temperatures for downward looking radiometers on board satellite is described. The effects of water vapour, oxygen and clouds on the brightness temperature have been studied for frequencies from 5 to 50 GHz for a standard tropical atmosphere. The effect of look angle on brightness temperture has also been investigated. Based on the model it has been shown that while the radiometers on boardBhaskara at 19·35 and 22·235 GHz are capable of giving the atmospheric water vapour and liquid water contents, the ability to distinguish these quantities is more for the combination of the frequencies 22·235 and 31 GHz.     

Atmospheric stability index using radio occultation refractivity profiles

A new stability index based on atmospheric refractivity at ~500 hPa level and surface measurements of temperature, pressure and humidity is formulated. The new index named here as refractivity based lifted index (RLI) is designed to give similar results as traditionally used lifted index derived from radiosonde profiles of temperature, pressure and humidity. The formulation of the stability index and its comparison with the traditional temperature profile based lifted index (LI) is discussed. The index is tested on COSMIC radio occultation derived refractivity profiles over Indian region. The forecast potential of the new index for rainfall on 2°×2° latitude–longitude spatial scale with lead time of 3–24 hours indicate that the refractivity based lifted index works better than the traditional temperature based lifted index for the Indian monsoon region. Decreasing values of RLI tend to give increasing rainfall probabilities.     

Atmospheric phenomena deduced from radiosonde and GPS occultation measurements for various application related studies

The tropopause height and tropopause temperature are sensitive to temperature changes in troposphere and stratosphere. These are the measures of global climatic variability. Atmospheric profiles of temperature, refractivity and water vapour are always needed for communication, navigation and atmospheric modeling studies. The tropopause characteristics over the Indian region have been studied using radio occultation measurements (CHAMP) on the basis of cold point criterion. Tropopause height shows large variation in the latitude range ∼30°–40°N during winter. Tropopause temperature less than −82°C, assumed to facilitate troposphere to stratosphere air transport, is observed at a number of tropical Indian locations and no seasonal pattern is observed in its occurrence. The bias in temperature and refractivity deduced from radiosonde and radio occultation measurements is also presented.     

Estimation of surface latent heat fluxes from IRS-P4/MSMR satellite data

The brightness temperatures of the Microwave sensor MSMR (Multichannel Scanning Microwave Radiometer) launched in May 1999 onboard Indian Oceansat-1 IRS-P4 are used to develop a direct retrieval method for latent heat flux by multivariate regression technique. The MSMR measures the microwave radiances at 8 channels at frequencies of 6.6, 10.7, 18 and 21 GHz at both vertical and horizontal polarizations. It is found that the surface LHF (Latent Heat Flux) is sensitive to all the channels. The coefficients were derived using the National Centre for Environmental Prediction (NCEP) reanalysis data of three months: July, September, November of 1999. The NCEP daily analyzed latent heat fluxes and brightness temperatures observed by MSMR were used to derive the coefficients. Validity of the derived coefficients was checked within situ observations over the Indian Ocean and with NCEP analyzed LHF for global points. The LHF derived directly from the MSMR brightness temperature (Tb) yielded an accuracy of 35 watt/m². LHF was also computed by applying bulk formula using the geophysical parameters extracted from MSMR. In this case the errors were higher apparently due to the errors involved in derivation of the geophysical parameters.     

Characterization of the atmospheric boundary layer from radiosonde observations along eastern end of monsoon trough of India

In this paper, a comparison of two methods for the calculation of the height of atmospheric boundary layer (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature (?? _v ) profile for the determination of mixed layer heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number (R _{i B} ) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH.     

Total precipitable water in the atmosphere over India

Electromagnetic radiation, in its passage through the atmosphere, is attenuated by absorption and scattering by atmospheric gases, dust and aerosols. The most important absorber is water vapour and the most significant parameter in atmospheric absorption studies is the total precipitable water in the atmosphere. The present paper summarises the results of a study made to compute the total precipitable water in the atmosphere over India using radiosonde and other data, as part of a programme for the computation of direct, global and diffuse solar radiation at the ground from the solar constant. Using values of air temperature and dew point from the ground up to 250 mb at 19 radiosonde stations and surface water vapour mixing ratio values at 105 surface observatories in India, precipitable water amounts have been computed for 124 stations, for each month and for the whole year. The paper describes the techniques used to extend the total precipitable water amounts derived from radiosonde data at 19 stations to 124 stations covering the major climatic zones in the country and presents the results in the form of 12 maps showing the spatial and temporal distribution of total precipitable water over India     

Calculated diffusion coefficients and the growth rate of olivine in a basalt magma

Concentration gradients in glass adjacent to skeletal olivines in a DSDP basalt have been examined by electron probe. The glass is depleted in Mg, Fe, and Cr and enriched in Si, Al, Na, and Ca relative to that far from olivine. Ionic diffusion coefficients for the glass compositions are calculated from temperature, ionic radius and melt viscosity, using the Stokes-Einstein relation. At 1170°C, the diffusion coefficient of Mg²⁺ ions in the basalt is 4·5.10^?9 cm²/s. Comparison with measured diffusion coefficients in a mugearite suggests this value may be 16 times too small. The concentration gradient data and the diffusion coefficients are used to calculate instantaneous olivine growth rates of 2–6.10^?7 cm/s. This is too slow for olivine to have grown in situ during quenching. Growth necessarily preceded emplacement such that the composition of the crystals plus the enclosing glass need not be that of a melt. The computed olivine growth rates are compatible with the rate of crystallization deduced for the Skaegaard intrusion.     

Analysis of experimental data on divalent cation diffusion kinetics in aluminosilicate garnets with application to timescales of peak Barrovian metamorphism,Scotland

We present a new statistical framework to analyze the diffusion data for divalent cations (Fe, Mg, Mn, and Ca) in aluminosilicate garnet using published experimental data and an Arrhenius relationship that accounts for dependence on temperature, pressure, garnet unit-cell dimension, and oxygen fugacity. The regression is based on Bayesian statistics and is implemented by the Markov chain Monte Carlo approach. All reported experimental uncertainties are incorporated, and the data are weighted by the precision of the experimental conditions. We also include a new term, the inter-experiment bias, to compensate for possible inconsistencies among experiments and to represent any experimental variability not explicitly presented in the Arrhenius relationship (e.g., water content, defect density). At high temperatures where most experiments were conducted, the diffusion coefficients calculated with the new parameters agree well with previous diffusion models (e.g., Chakraborty and Ganguly in Contrib Mineral Petrol, 111:74–86, 1992; Carlson in Am Mineral, 91:1–11, 2006). However, the down-temperature extrapolation leads to notable differences at lower temperatures for common petrological applications. For example, at 600 °C, the diffusion coefficients of Fe and Mn are one half-to-one order of magnitude faster and the diffusion coefficient of Ca is about one order of magnitude slower than calculated with parameters in Carlson (2006). Our statistical analysis also provides well-defined uncertainty bounds for timescale estimates based on garnet diffusion profiles. Application of the newly derived coefficients indicates that the timescale of the thermal peak of Barrovian metamorphism (Dalradian belt of Scotland) is about four to seven times longer than that estimated using previously published diffusion coefficients. The peak is still geologically brief, however—of the order of 10⁶ years (0.75 Myr +0.70/?0.36 Myr; ±1σ). This brevity requires pulsed advective heat input, as provided by syn-orogenic mafic magmatism in these rocks.     

Density profiles in molecular cloud cores associated with high-mass star-forming regions

Radial density profiles for the sample of dense cores associated with high-mass star-forming regions from southern hemisphere have been derived using the data of observations in continuum at 250 GHz. Radial density profiles for the inner regions of 16 cores (at distances ≲0.2−0.8 pc from the center) are close on average to the ρ ∝ r ^−α dependence, where α = 1.6 ± 0.3. In the outer regions density drops steeper. An analysis with various hydrostatic models showed that the modified Bonnor-Ebertmodel, which describes turbulent sphere confined by external pressure, is preferable compared with the logotrope and polytrope models practically in all cases. With a help of the Bonnor-Ebert model, estimates of central density in a core, non-thermal velocity dispersion and core size are obtained. The comparison of central densities with the densities derived earlier from the CS modeling reveals differences in several cases. The reasons of such differences are probably connected with the presence of density inhomogenities on the scales smaller than the telescope beam. In most cases non-thermal velocity dispersions are in agreement with the values obtained from molecular line observations.     

An XRD study of the crystal structure of gearksutite and its stability during heating to 300°C

The crystal structure of gearksutite, Ca and Al hydrofluoride CaAlF₄(OH) · H₂O, was refined using the Rietveld method with power diffraction data. The thermal stability of its crystal structure was studied for the first time using high-temperature XRD. Thermal XRD study of the mineral in the temperature range from 25 to 300°C revealed its stability to temperatures of 300-310°C. The mineral began to decay at temperatures greater than 300°C. The increase in the unit-cell parameters was established and the coefficients of thermal expansion were calculated.     

Variation ofF-region nighttime neutral temperatures with equatorial spread-F activity

NighttimeF-region temperatures have been obtained over Mount Abu (24·6°N, 72·7°E geographic, 15·0° geomagnetic latitude) by monitoring OI 6300 Å line widths, using Fabry-Perot spectrometer. Enhancement in neutral temperatures associated with spread-F activity over Thumba (8·5°N, 76·8°E geographic, 0·6°S geomagnetic), which is on the magnetic equator were reported earlier. Additional data over Mt Abu for seven days bring out the following major features. (i) In theF-region over Mt Abu, the neutral temperature enhancements upto 200°K are observed on most of the nights when there is spread-F activity over the magnetic equator. (ii) There are no occasions which show temperature enhancements over Mt Abu without spread-F activity over the equator. On such occasions the observed atmospheric temperatures agree very well with those calculated on the basis of the Jachhia atmospheric model, both for magnetically quiet as well as disturbed days. (iii) There is a good indication that the increase inF-region temperature over Mt Abu is delayed with respect to the onset of spread-F over Thumba by approximately 15–30 min.     

Field measurements of the flux and speed of wind-blown sand

A field experiment was conducted to measure the flux and speed of wind-blown sand under known conditions in a natural setting. The experiment, run at Pismo Beach, California, involved a tract 100 m long (parallel with the wind) by 20 m wide. The site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary-layer, temperature probes to determine atmospheric stability and wind vanes to determine wind direction. From these measurements, wind friction speeds were derived for each experimental run. In order to measure sand saltation flux, a trench 3 m long by 10 m wide (transverse to the wind direction) by 0·5 m deep was placed at the downwind end of the tract and lined with 168 collector bins, forming an ‘egg-box’ pattern. The mass of particles collected in each bin was determined for four experimental runs. In order to assess various sand-trap systems used in previous experiments, 12 Leatherman traps, one Fryberger trap and one array of Ames traps were deployed to collect particles concurrently with the trench collection. Particle velocities were determined from analysis of high-speed (3000 and 5000 frames per second) motion pictures and from a particle velocimeter. Sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined. Fluxes for each run were calculated using various previously published expressions, and then compared with the flux derived from the trench collection. Results show that Bagnold's (1941) model and White's (1979) equation most closely agree with values derived from the trench. Comparison of the various collector systems shows that the Leatherman and Ames traps most closely agree with the flux derived from the trench, although these systems tended to under-collect particles. Particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories. Results show that particle velocities from the velocimeter are in the range 0·5–7·0 m s^?1, compared to a wind friction velocity of 0·32–0·43 m s^?1 and a wind velocity of 2·7–3·9 m s^?1 at the height of the particle measurements. Descending particles tended to exceed the speeds of ascending particles by ～ 0·5 m s^?1.     

Surface chemistry and dissolution kinetics of glassy rocks at 25°C

The weathering rates and mechanisms of three types of glassy rocks were investigated experimentally at 25 °C, pH 1.0 to 6.2, and reaction times as much as to 3 months. Changes in major element chemistry were monitored concurrently as a function of time in the aqueous solution and within the near surface region of the glass. Leach profiles, obtained by a HF leaching technique, displayed near-surface zones depleted in major cations. These zones increased in depth with increasing time and decreasing pH of reactions. Release rates into the aqueous solution were parabolic for Na and K and linear for Si and Al. A coupled weathering model, involving surface dissolution with concurrent diffusion of Na, K, and Al, produced a mass balance between the aqueous and glass phases. Steady state conditions are reached at pH 1.0 after approximately 3 weeks of reaction. Steady-state is not reached even after 3 months at pH 6.2.An interdiffusion model describes observed changes in Na diffusion profiles for perlite at pH 1.0. The calculated Na self-diffusion coefficient of 5 × 10^?19 cm²·s^?1 at 25°C approximates coefficients extrapolated from previously reported high temperature data for obsidian. The self-diffusion coefficient for H₃O⁺, 1.2 × 10^?20 cm²·s^?1, is similar to measured rates of water diffusion during hydration of obsidian to form perlite.     

Identification and comparison of perennial yield estimation models using Mt. Amiata Aquifer (southern Tuscany,Italy) as an example

With the principal aim of identifying and comparing suitable evaluation and forecasting models of perennial yield, detailed hydrogeological research was conducted on the cold phreatic aquifer located in the volcanites of Mount Amiata, southern Tuscany's most important water reservoir. The study was based on spring discharge, precipitation, and temperature data. It permitted the identification of the following models: (1) ratios between discharge values measured at the springs, (2) depletion urve analysis of the springs, (3) multiple regression with climatic data, and (4) water balance, coefficients of potential infiltration and runoff coefficients derived on a physiographic basis. Analysis of the results obtained using these models shows their excellent ability to forecast in the medium and long term; for short-term (yearly) forecasts, highly satisfactory results have been obtained for most of the methods used. With regard to Mt. Amiata's average perennial yield, it is estimated at 55×10⁶ m³/yr (the maximum deviation among the various evaluations performed varies from 4 to 8 percent), and it presents a decreasing trend, which is proportional to the reduction of local precipitation.     

Shallow slides and pockmark swarms in the Eivissa Channel, western Mediterranean Sea

Four slides, the Ana, Joan, Nuna and Jersi slides, have been imaged on the seafloor along the Balearic margin of the Eivissa Channel in the western Mediterranean. They have areas of up to 16 km² and occur in water depths ranging between 600 and 900 m. Volumes range from 0·14 to 0·4 km³. Their headwall scarps, internal architecture and associated deposits are characterized using a combination of swath bathymetry data and very high‐resolution seismic reflection profiles. In general, they show horseshoe‐shaped headwall scarps and distinct depositional lobes with positive relief. Internally, the slide bodies are mostly composed of transparent seismic facies. Chaotic facies are observed at the toe of some of the slides, and blocks of coherent stratified facies embedded in the slide deposit have also been identified. The reflection profiles demonstrate that the four slides share the same slip horizon, which corresponds to a distinctive continuous, high‐amplitude reflector. Furthermore, the geometry of the headwall scars of the Nuna and Ana slides reveals evidence of pockmarks, and fluid escape features are also present further upslope. This indicates a possible link between fluid escape features and destabilization of the upper sediment layers. In addition, these well‐characterized slides demonstrate the pitfalls associated with calculating the volume of the slide masses using headwall scarp heights and the assumed preslide seafloor topography in the absence of seismic data. The internal structure also demonstrates that transport distances within the slides are generally low and poorly characterized by headwall scarp to slide toe lengths.     

Rain rate measurements over global oceans from IRS-P4 MSMR

In this paper rain estimation capability of MSMR is explored. MSMR brightness temperature data of six channels corresponding to three frequencies of 10, 18 and 21 GHz are colocated with the TRMM Microwave Imager (TMI) derived rain rates to find a new empirical algorithm for rain rate by multiple regression. Multiple correlation analysis involving various combinations of channels in linear and non-linear forms and rain rate from TMI is carried out, and thus the best possible algorithm for rain rate measurement was identified which involved V and H polarized brightness temperature measurements at 10 and 18 GHz channels. This algorithm explained about 82 per cent correlation (r) with rain rate, and 1.61 mm h^-1 of error of estimation. Further, this algorithm is used for generating global average rain rate map for two contrasting months of August (2000) and January (2001) of northern and southern hemispheric summers, respectively. MSMR derived monthly averaged rain rates are compared with similar estimates from TRMM Precipitation Radar (PR), and it was found that MSMR derived rain rates match well, quantitatively and qualitatively, with that from PR.     

In situ neutron diffraction study of deuterated portlandite Ca(OD)2 at high pressure and temperature

The structure of deuterated portlandite, Ca(OD)₂, has been investigated using time-of-flight neutron diffraction at pressures up to ∼4.5 GPa and temperatures up to ∼823 K. Rietveld analysis of the data reveals that with increasing pressure, unit-cell parameter c decreases at a rate about 4.5 times larger than that for a, which is largely due to rapid contraction of the interlayer spacing in this pressure range. Fitting of the determined cell volumes to the third-order Birch–Murnaghan equation of state yields a bulk modulus (K ₀) of 32.2 ± 1.0 GPa and its first derivative (K ₀′) of 4.4 ± 0.6. Moreover, on compression, hydrogen-mediated interatomic interactions within the interlayer become strengthened, as reflected by decreases in interlayer D···O and D···D distances with increasing pressure. Correspondingly, D–D, the distance between the three equivalent sites over which D is disordered, increases, suggesting a pressure-induced hydrogen disorder. This behavior is similar to that reported in brucite at elevated pressure. On heating at ∼2.1 GPa, cell parameter c increases more rapidly than a, as expected. However, because of the pressure effect, the thermal expansion coefficients, particularly along c, are much smaller than those at ambient pressure. With increasing temperature, the three partially occupied D sites become further apart, and the D-mediated interactions, mainly the interlayer D···D repulsion, become weakened.