Formation of solar nebula and mass distribution in the planetary system

The formation of the solar nebula and the distribution of mass in its planetary system is studied. The underlying idea is that the protosun, fragmented out from an interstellar cloud as a result of cluster formation, gathered the planetary material and, hence, spin angular momentum by gravitational accretion during its orbital motion around the centre of the Galaxy. The study gives the initial angular momentum of the solar nebula nearly equal to the present value of the solar system.     

RAYLEIGH WAVES IN A MULTI-LAYERED MEDIUM WITH APPLICATIONS TO MICROSEISMS

Summary. An analysis is presented for the propagation of Rayleigh waves in a multi-layered medium with water as the uppermost layer from which it is possible to obtain the group velocity as well as the phase velocity for the Rayleigh waves in an oceanic path with the ocean bed consisting of two upper layers each of uniform composition and finite thickness, underlain by ultrabasic rock extended to large depths. The results have been applied in the analysis of microseisms associated with cyclones and "norwesters". It has been shown that the period of the microseisms recorded at different stations depends critically on the structure of the continental shelf. The results obtained in the present paper, when compared with the nature of the recorded microseisms associated with cyclones, and their variations, give useful information about the depth and structure of the ocean beds.     

On the impact of divergent part of the wind computed from INSAT OLR data on global analysis and forecast fields

Summary In this paper, a procedure for the computation of the divergent part of wind from Outgoing Longwave Radiation (OLR) data is described. This divergent part is included in the global analysis scheme and its impact is studied by computing the vertical velocity, velocity potential etc., using the analysed fields with and without modifying the divergent part and also making 24 hr and 48 hr rainfall forecasts.Results show that magnitudes of vertical velocity were increased when the divergent part was modified in the wind analysis. There were also changes observed in the analysed wind field over convective regions and the changes over the oceanic regions were higher, suggesting that the impact of divergent part is more pronounced over data sparse regions. Marginal increase was observed in 24 hr and 48 hr rainfall forecast over the Indian region. The area averaged rainfall forecast at each time step in the first 6 hours of model integration was also higher in the case when the wind field contained the divergent part.To sum up, it can be stated that the inclusion of the divergent part from OLR data in the initial wind field has brought out positive impact on the wind analyses and rainfall forecast.With 12 Figures     

On the scavenging of SO2 by large and small rain drops: V. A wind tunnel and theoretical study of the desorption of SO2 from water drops containing S(IV)

An experimental and theoretical study has been carried out to investigate the rate of desorption of SO₂ from water drops falling at terminal velocity in air. The experiments were carried out in the Mainz vertical wind tunnel in which water drops of various sizes containing S(IV) in various concentrations were freely suspended in the vertical airstream of the tunnel. The results of these experiments were compared with the predictions of three theoretical models, and with the experiments of Walceket al. This comparison shows that the predictions of the diffusion model of Kronig and Brink in the formulation given by Walcek and Pruppacher agree well with the experimental results for all relevant large and small rain-drop sizes, and for all considered concentrations of S(IV) inside the drops. In contrast, the predictions of the diffusion model which assumes complete internal mixing inside a drop agrees with the experimental results only if the concentration of S(IV) inside the drop is less than that equivalent of an equilibrium SO₂ concentration of 15 ppbv. At larger concentrations, the theoretical predictions of the model for complete internal mixing progressively deviate from the experimental results. It is further shown that Barrie's double film model can be used to interpret the resistance to diffusion inside a drop in terms of a diffusion boundary layer inside the drop which increases in thickness with decreasing concentration of S(IV). Applying our results to the desorption of SO₂ from small and large rain drops falling below an assumed cloud base, shows that for typical contents of S(IV) inside the drops substantial amounts of SO₂ will desorb from these drops unless H₂O₂ is present in the surrounding air.     

On the scavenging of organic gases by cloud and raindrops: I. A theoretical and experimental study of acetaldehyde absorption and desorption for water drops in air

Our previously developed theoretical models for describing the rate at which water-soluble atmospheric trace gases are scavenged by cloud and rindrops were evaluated for the case of acetaldehyde being absorbed and desorbed by water drops of radii between 250 to 2500 m radius. The experimental verification of our theoretical predictions was carried out in the UCLA 33 m high precipitation shaft in which falling water drops were allowed to come to terminal velocity before passing through a chamber of variable lengths filled with air containing acetaldehyde at various partial pressures. For all drop sizes studied, the experimental results and the theoretical predictions were in reasonable agreement.     

On the torsional vibration of a finite circular cylinder of non-homogeneous material by a particular type of twist on one of its plane ends

Summary In the present note, the problem of torsional vibration of a finite circular cylinder of non-homogeneous material has been considered. The lateral surface of the cylinder is assumed to be free from shearing stress. One end of the cylinder is taken to be fixed while a circular region on the other end which is not fixed is acted over by a periodic shearing force.     

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit.     

Validation of two gridded soil moisture products over India with <Emphasis Type="Italic">in-situ</Emphasis> observations

Surface level soil moisture from two gridded datasets over India are evaluated in this study. The first one is the UK Met Office (UKMO) soil moisture analysis produced by a land data assimilation system based on Extended Kalman Filter method (EKF), which make use of satellite observation of Advanced Scatterometer (ASCAT) soil wetness index as well as the screen level meteorological observations. Second dataset is a satellite soil moisture product, produced by National Remote Sensing Centre (NRSC) using passive microwave Advanced Microwave Scanning Radiometer 2 measurements. In-situ observations of soil moisture from India Meteorological Department (IMD) are used for the validation of the gridded soil moisture products. The difference between these datasets over India is minimum in the non-monsoon months and over agricultural regions. It is seen that the NRSC data is slightly drier (0.05%) and UKMO soil moisture analysis is relatively wet during southwest monsoon season. Standard AMSR-2 satellite soil moisture product is used to compare the NRSC and UKMO products. The standard AMSR-2 and UKMO values are closer in monsoon season and AMSR-2 soil moisture is higher than UKMO in all seasons. NRSC and AMSR-2 showed a correlation of 0.83 (significant at 0.01 level). The probability distribution of IMD soil moisture observation peaks at 0.25 m³/m³, NRSC at 0.15 m³/m³, AMSR-2 at 0.25 m³/m³ and UKMO at 0.35 m³/m³ during June–September period. Validation results show UKMO analysis has better correlation with in-situ observations compared to the NRSC and AMSR-2 datasets. The seasonal variation in soil moisture is better represented in UKMO analysis. Underestimation of soil moisture during monsoon season over India in NRSC data suggests the necessity of incorporating the actual vegetation for a better soil moisture retrieval using passive microwave sensors. Both products have good agreement over bare soil, shrubs and grassland compared to needle leaf tree, broad leaf tree and urban land cover types.