Determination of accuracy of particle size by acoustic scattering using a modified Born approximation

761-770Accuracy of a recently proposed modified Born approximation (MBA) has been examined for size determination of an isolated scatterer. Two methods have been employed for this purpose. One is based on the analysis of the angular scattering pattern of plane waves and the other on analysis of the power spectrum of the backscattered pulse. In each case, domain of validity of the modified Born approximation for size determination has been assessed for two exactly soluble test models, namely, the scattering by a sphere and an infinitely long cylinder. For completeness, comparisons with conventional Born approximation (BA) results have also been made. The performances of the approximations have been examined for scatterers whose size parameters vary over a range 3 to 75. Mismatches of the density and compressibility are less than 15% in these calculations. Numerical results show that MBA indeed has a larger validity domain in comparison to BA for an intermediate size weak scatterer. </span

Pre-onset land surface processes and 'internal' interannual variabilities of the Indian summer monsoon

It is proposed that, land-atmosphere interaction around the time of monsoon onset could modulate the first episode of climatological intraseasonal oscillation (CISO) and may generate significant 'internal' interannual variation in the Indian summer monsoon rainfall. The regional climate model RegCM3 is used over Indian monsoon domain for 27 years of control simulation. In order to prove the hypothesis, another two sets of experiment are performed using two different boundary conditions (El Nino year and non-ENSO year). In each of these experiments, a single year of boundary conditions are used repeatedly year after year to generate 'internal' interannual monsoon variability. Simulation of monsoon climate in the control model run is found to be in reasonably good agreement with observation. However, large rainfall bias is seen over Arabian Sea and Bay of Bengal. The interannual monsoon rainfall variability are of the same order in two experiments, which suggest that the external influences may not be important on the generation of 'internal' monsoon rainfall variability. It is shown that, a dry (wet) pre-onset land-surface condition increases (decreases) rainfall in June which in turn leads to an anomalous increase (decrease) in seasonal (JJAS) rainfall. The phase and amplitude of CISO are modulated during May-June and beyond that the modulation of CISO is quite negligible. Though the pre-onset rainfall is unpredictable, significant modulation of the post-onset monsoon rainfall by it can be exploited to improve predictive skill within the monsoon season

Effects of multilayer snow scheme on the simulation of snow: Offline Noah and coupled with NCEPCFSv2

Abstract The Noah version 2.7.1 is a moderately complex land surface model (LSM), with a single layer snowpack, combined with vegetation and underlying soil layer. Many previous studies have pointed out biases in the simulation of snow, which may hinder the skill of a forecasting system coupled with the Noah. In order to improve the simulation of snow by the Noah, a multilayer snow scheme (up to a maximum of six layers) is introduced. As Noah is the land surface component of the Climate Forecast System version 2 (CFSv2) of the National Centers for Environmental Prediction (NCEP), the modified Noah is also coupled with the CFSv2. The offline LSM shows large improvements in the simulation of snow depth, snow water equivalent (SWE), and snow cover area during snow season (October to June). CFSv2 with the modified Noah reveals a dramatic improvements in the simulation of snow depth and 2 m air temperature and moderate improvements in SWE. As suggested in the previous diagnostic and sensitivity study, improvements in the simulation of snow by CFSv2 have lead to the reduction in dry bias over the Indian subcontinent (by a maximum of 2 mm d−1). The multilayer snow scheme shows promising results in the simulation of snow as well as Indian summer monsoon rainfall and hence this development may be the part of the future version of the CFS

Linkage between precipitation isotopes and biosphere-atmosphere interaction observed in northeast India

© 2022, The Author(s).The intra-seasonal variation in precipitation isotopes shows a characteristic declining trend over northeast India. As of now, no mechanism offers a consistent explanation of this trend. We have performed the isotopic analysis of precipitation (rain) and estimated net ecosystem exchange and latent heat fluxes using an eddy-covariance system in northeast India. Additionally, we have used a diagnostic model to determine the recycled rainfall in this region. We find a strong link between the enhanced ecosystem productivity and isotopic enrichment in rainwater during the premonsoon season. Subsequently, on the advent of monsoon, the Bay of Bengal generated moisture enters this region and depletes the isotopic values. Additionally, the regional-scale convective activities produce periodic lows in the precipitation isotopes. Contrary to the general understanding, our study shows that the internal factors, such as the local land-atmosphere interactions, rather than the external influences, play a significant role in governing the precipitation isotopes in northeast India.11Ysciescopu