Numerical investigation of the Somali jet interaction with the Western Ghat Mountains

Several major features of the interaction of the Somali jet with the Western Ghat Mountains have been observed. These include a pressure ridge, strong vertical motions, and occurrences of highly reflective cloud and heavy rainfall rates along the west coast of India. A triple nested regional weather prediction model has been used to investigate the dynamic interaction between the Somali jet and the Western Ghat Mountains. Two numerical experiments were conducted; one with the topography of western India and the other without. In the experiment without topography, the Western Ghat Mountains were removed from the innermost domain. The results for the innermost domain in the two experiments were analyzed and compared. The results from the simulation with topography captured several of the observed features of the Somali jet interaction with the Western Ghat Mountains. The simulation without topography failed to reveal these features. The results suggest that the blocking effect of the Western Ghats plays an important role in the prediction of the rainfall over the west coast of India

Monte Carlo simulations of pulse propagation in massive multichannel optical fiber communication systems

We study the combined effect of delayed Raman response and bit pattern randomness on pulse propagation in massive multichannel optical fiber communication systems. The propagation is described by a perturbed stochastic nonlinear Schr\"odinger equation, which takes into account changes in pulse amplitude and frequency as well as emission of continuous radiation. We perform extensive numerical simulations with the model, and analyze the dynamics of the frequency moments, the bit-error-rate, and the mutual distribution of amplitude and position. The results of our numerical simulations are in good agreement with theoretical predictions based on the adiabatic perturbation approach.Comment: Submitted to Physical Review E. 8 pages, 5 figure

Sensitivity of monsoon circulation and precipitation over India to model horizontal resolution and orographic effects

A triple-nested regional weather prediction model was used to investigate the effects of the model horizontal resolution and orography on southwest monsoon precipitation over India. Numerical experiments with different resolution topography and different horizontal resolution model domains were conducted. Simulation results indicate that both the distribution and intensity of simulated southwest monsoon precipitation over India is highly sensitive to model horizontal resolution and topography. The model with a finer resolution is able to predict mesoscale organization of rainfall over the land mass. Rainfall predicted over the coarse domain is much less than that observed owing to its unrealistic representation of orographic effects and mesoscale forcings. Simulated wind speed, surface pressure, and latent and sensible heat flux distributions are also sensitive to the model resolution. Larger values and more detailed structure of the distribution of the wind speed and latent and sensible heat fluxes are simulated in the finer domains

Numerical study of the role of land-air-sea interactions for the northeasterly monsoon circulations over Indian Ocean during INDOEX

One of the principal objectives of the Indian Ocean Experiment (INDOEX) was to study the aerosol transport from the Indian subcontinent to the pristine oceanic environment. The underlying hypothesis for INDOEX is that, during the northeasterly monsoon, the intruding aerosols and other anthropogenic pollutants can entrain into the Inter Tropical Convergence Zone (ITCZ) and the Equatorial Indian Ocean and finally into the clouds. The altered clouds influence the radiative transfer processes at the regional and possibly global scale. The driving mechanism for the regional transport was the boundary layer circulation. In this study, it was hypothesized that the circulation pattern, which affects the regional transport, was strongly influenced by the land-air-sea interactions. To test this, a zonally symmetric version of a primitive equation numerical weather prediction model, called the Advanced Regional Prediction System (ARPS), was used. A number of numerical experiments were performed for a 2-D domain ranging from 14°N to 16°S centered over 76°E. In the experiments, the influence of land-sea interaction (differential heating), topography (Western Ghats), and the thermal gradients (SST and land surface temperature) on the coastal circulations over Equatorial Indian Ocean were studied. Results indicated a strong land-air-sea interaction and feedback teleconnection between the local and large scale features. Interestingly, the model generated land influence to the order of 1000 km offshore in the simulation domain, consistent with different observations. Results suggest that the oceanic environment in the northeast monsoon over Arabian Sea and the Indian Ocean can display significant diurnal variability and heterogeneity due to topography and surface temperature gradients, and that the local features have interactive feedback on the large scale circulations and transport

Application of three-dimensional triple nested mesoscale model for assessing the transport and boundary layer variability over the Indian Ocean during INDOEX

A three-dimensional triple nested domain version of MM5 was applied for INDOEX region (40.12°N- 32.04°S; 32.10°E-117.90°E) to study the regional flow patterns and associated transport using backward and forward trajectories. The model was integrated for 48- h period starting 00 UTC 5 March 1999. From the simulations a mapping of the temporal and spatial variations in the marine boundary layer (MBL) heights were obtained. The boundary layer heights were verified using actual ship-based sounding from RV Ronald H. Brown and a good agreement was found. The model simulated significant variability in the MBL heights both spatially and temporally. During the daytime, the continental boundary layer was ~ 1500 m deep while over the ocean, the MBL was shallow (~ 300 m) near the coast, and it increased steadily towards the ITCZ where MBL heights of ~ 1000 m were encountered. During night there was a reversal with the continental boundary layer heights averaging less than 500 m while over the ocean, particularly over the ITCZ, the MBL heights were ~ 1000 to 1500 m. This variability in the MBL heights significantly affected the transport pattern over the INDOEX region. Both the backward and forward trajectories showed distinct characteristics depending on the source region (eastern or western coastal landmass, equator, or near ITCZ). Near the coast, there was an evidence for localized circulation in which the air parcels were trapped along the coast. For the open oceans (both near the ITCZ as well as equator) the air parcel trajectories continued over a significant distance. Results suggest that MM5 can be successfully applied for diagnostic studies related to INDOEX, and that the boundary layer heights and the variations in the air parcel transport need to be considered for interpreting the surface measurements

The role of radiative transfer in maintaining the Indian summer monsoon circulation

The radiative-convective feedback and land-sea thermal forcing play significant roles in maintenance of the summer monsoon circulation over the Indian sub-continent. In this study, the role of radiative transfer in maintaining the monsoon circulation is examined with numerical sensitivity experiments. For this purpose, a sixteen layer primitive equation limited area model is used to perform numerical simulations with and without atmospheric radiative transfer processes parameterized in the model. The initial values and boundary conditions for the numerical integrations of the model are derived from operational analyses of the ECMWF, UK. The results show that the radiative transfer is essential in maintaining the intensity of the low level Somali Jet as well as the upper level Tropical Easterly Jet (TEJ) over the Indian sub-continent and adjoining seas. The meridional circulation over the region is also well simulated. As a result, enough moisture transports from the warm equatorial region to simulate more realistic orographic precipitation in the windward side of the mountains along the West coast of India. Without radiative transfer processes in the model atmosphere the simulated monsoon circulation weakens, moisture transport decreases and the precipitation lessens

rp-Process weak-interaction mediated rates of waiting-point nuclei

Electron capture and positron decay rates are calculated for neutron-deficient Kr and Sr waiting point nuclei in stellar matter. The calculation is performed within the framework of pn-QRPA model for rp-process conditions. Fine tuning of particle-particle, particle-hole interaction parameters and a proper choice of the deformation parameter resulted in an accurate reproduction of the measured half-lives. The same model parameters were used to calculate stellar rates. Inclusion of measured Gamow-Teller strength distributions finally led to a reliable calculation of weak rates that reproduced the measured half-lives well under limiting conditions. For the rp-process conditions, electron capture and positron decay rates on $^{72}$Kr and $^{76}$Sr are of comparable magnitude whereas electron capture rates on $^{78}$Sr and $^{74}$Kr are 1--2 orders of magnitude bigger than the corresponding positron decay rates. The pn-QRPA calculated electron capture rates on $^{74}$Kr are bigger than previously calculated. The present calculation strongly suggests that, under rp-process conditions, electron capture rates form an integral part of weak-interaction mediated rates and should not be neglected in nuclear reaction network calculations as done previously.Comment: 13 pages, 4 figures, 4 tables; Astrophysics and Space Science (2012

Ground and excited states Gamow-Teller strength distributions of iron isotopes and associated capture rates for core-collapse simulations

This paper reports on the microscopic calculation of ground and excited states Gamow-Teller (GT) strength distributions, both in the electron capture and electron decay direction, for $^{54,55,56}$Fe. The associated electron and positron capture rates for these isotopes of iron are also calculated in stellar matter. These calculations were recently introduced and this paper is a follow-up which discusses in detail the GT strength distributions and stellar capture rates of key iron isotopes. The calculations are performed within the framework of the proton-neutron quasiparticle random phase approximation (pn-QRPA) theory. The pn-QRPA theory allows a microscopic \textit{state-by-state} calculation of GT strength functions and stellar capture rates which greatly increases the reliability of the results. For the first time experimental deformation of nuclei are taken into account. In the core of massive stars isotopes of iron, $^{54,55,56}$Fe, are considered to be key players in decreasing the electron-to-baryon ratio ($Y_{e}$) mainly via electron capture on these nuclide. The structure of the presupernova star is altered both by the changes in $Y_{e}$ and the entropy of the core material. Results are encouraging and are compared against measurements (where possible) and other calculations. The calculated electron capture rates are in overall good agreement with the shell model results. During the presupernova evolution of massive stars, from oxygen shell burning stages till around end of convective core silicon burning, the calculated electron capture rates on $^{54}$Fe are around three times bigger than the corresponding shell model rates. The calculated positron capture rates, however, are suppressed by two to five orders of magnitude.Comment: 18 pages, 12 figures, 10 table

Lifetime Measurements in 120Xe

Lifetimes for the lowest three transitions in the nucleus $^{120}$Xe have been measured using the Recoil Distance Technique. Our data indicate that the lifetime for the $2_{1}^{+} \to 0_{1}^{+}$ transition is more than a factor of two lower than the previously adopted value and is in keeping with more recent measurements performed on this nucleus. The theoretical implications of this discrepancy and the possible reason for the erroneous earlier results are discussed. All measured lifetimes in $^{120}$Xe, as well as the systematics of the lifetimes of the 2$_{1}^{+}$ states in Xe isotopes, are compared with predictions of various models. The available data are best described by the Fermion Dynamic Symmetry Model (FDSM).Comment: 9 pages, RevTeX, 3 figures with Postscript file available on request at [email protected], [email protected]. Submitted to Phys. Rev.

Numerical simulation of the sensitivity of summer monsoon circulation and rainfall over india to land surface processes

The influence of soil moisture and vegetation variation on simulation of monsoon circulation and rainfall is investigated. For this purpose a simple land surface parameterization scheme is incorporated in a three-dimensional regional high resolution nested grid atmospheric model. Based on the land surface parameterization scheme, latent heat and sensible heat fluxes are explicitly estimated over the entire domain of the model. Two sensitivity studies are conducted; one with bare dry soil conditions (no latent heat flux from land surface) and the other with realistic representation of the land surface parameters such as soil moisture, vegetation cover and landuse patterns in the numerical simulation. The sensitivity of main monsoon features such as Somali jet, monsoon trough and tropical easterly jet to land surface processes are discussed. Results suggest the necessity of including a detailed land surface parameterization in the realistic short-range weather numerical predictions. An enhanced short-range prediction of hydrological cycle including precipitation was produced by the model, with land surface processes parameterized. This parameterization appears to simulate all the main circulation features associated with the summer monsoon in a realistic manner