Comprehensive test of different cumulus parameterization schemes for the simulation of the Indian summer monsoon

Summary The global spectral model of NCMRWF at T80 horizontal resolution and 18 vertical levels has been integrated for the summer season (July) using different cumulus parameterization schemes namely, the Simplified Arakawa-Schubert scheme (SAS), the Relaxed Arakawa-Schubert Scheme (RAS), and the Kuo-type cumulus parameterization scheme (KUO). The results have been compared with mean analysis of the operational NCMRWF model (ANA) and other available observations. Results indicate that, while the global distributions of basic fields such as the wind, temperature and moisture are fairly well simulated by all the three schemes, there are many differences seen in the simulation of the typical features of the Indian summer monsoon. The strength of the Low Level Westerly Jet (LLWJ), the Cross Equatorial Flow (CEF), and the Tropical Easterly Jet (TEJ) are better simulated by RAS and SAS as compared to ANA than the KUO scheme. RAS and SAS produce strong rising motion owing to strong intensity of convection produced by these two schemes. This in turn produces stronger Hadley cell by RAS and SAS than compared to the KUO scheme. Simulation of the 200 mb velocity potential and divergent wind by RAS and SAS produced two prominent centers, one in the Bay of Bengal and another in the Western Pacific, which correspond to the intense latent heating by cumulus convection during the active monsoon phase. The velocity potential and divergent winds were weaker in KUO, than compared to RAS and SAS. The simulation of OLR is improved by RAS as compared to observations. The cold bias produced by KUO at 200 mb is reduced by RAS and is substantially improved by SAS. Study of observed and simulated rainfall indicated that RAS and SAS produced better distribution of precipitation over the Western Ghat Mountains and the Arakan coast, where deep cumulus convection is produced due to orographic forcing of the warm moist air. The KUO scheme underestimated the rainfall over these two regions, but produced slightly better distribution of rainfall over the northwest and central India, where the intensity of convection is relatively weaker. Evaluation of overall dynamics, thermal structure and rainfall indicates that in general, SAS is able to provide relatively better results compared to other two schemes. Received October 3, 2000/Revised December 5, 2000     

The retention of ammonia and sulfur dioxide during riming of ice particles and dendritic snow flakes: laboratory experiments in the Mainz vertical wind tunnel

Laboratory experiments were carried out in the Mainz vertical wind tunnel to determine the retention of the trace gases ammonia and sulfur dioxide dissolved in supercooled cloud droplets during riming. The conditions during riming were similar to the ones in atmospheric mixed phase clouds: temperatures from ?18 °C to ?5 °C, liquid water contents between 1 and 1.5 g m^?3, liquid drop radii between 10 and 20 μm, liquid phase concentrations from 1 to 22 mg/l. As collectors, floating ice particles and snow flakes with diameters between 6 mm and 1.5 cm were used. After riming the retention coefficients, i.e. the fractions of the species which remained in the ice phase after freezing were determined. Retention coefficients lying between 0.1 and 1.0 were measured depending on the solubility and dissociation of the trace gas, liquid phase concentration, ambient air temperature, and shape of rimed collector. This can be explained from the chemists’ point of view by the effective Henry’s law constant of the species and physically with the rate of latent heat removal from the rimed collector during freezing. Parameterizations derived from the different experimental cases describe the retention coefficients as a function of temperature. In general, an average retention of ammonia of 92?±?21 % was determined independently of liquid phase concentration while mean values for sulfur dioxide were 53?±?10 % at low liquid phase concentrations and 29?±?7 % at high liquid phase concentrations.     

Asymmetric impact of rainfall on India’s food grain production: evidence from quantile autoregressive distributed lag model

This study used a quantile autoregressive distributed lag (QARDL) model to capture asymmetric impact of rainfall on food production in India. It was found that the coefficient corresponding to the rainfall in the QARDL increased till the 75th quantile and started decreasing thereafter, though it remained in the positive territory. Another interesting finding is that at the 90th quantile and above the coefficients of rainfall though remained positive was not statistically significant and therefore, the benefit of high rainfall on crop production was not conclusive. However, the impact of other determinants, such as fertilizer and pesticide consumption, is quite uniform over the whole range of the distribution of food grain production.     

Radiocarbon evidence of paleo-recharge (pre-Saraswati period) of potential deep aquifer in Thar desert

The Oil and Natural Gas Corporation Limited (ONGC), India, embarked upon exploration and exploitation of deep groundwater under the project named as “Saraswati” in arid Thar desert, Rajasthan, with a societal mission of providing water to the local people and cattle. A 555 m deep well drilled by the ONGC near Jaisalmer town in 2006 encountered a potential aquifer at a depth of 450–500 m. Radiocarbon dating of this well water indicated paleorecharge to be >40,000 yr BP (uncorrected) (Before Present with respect to 1950 AD), while the medium depth (∼200 m) well waters around that area showed an age range of ∼9,000 to 17,000 yr BP (uncorrected). These waters represent pre-Saraswati era recharge, because the mighty Saraswati flowed in this region between 7000–4000 yr BP. The stable isotope (δD and δ¹⁸O) and Total Dissolved Solids (TDS) data of these waters clearly indicated absence of communication between the two aquifers (deep and medium depth). However, the extension of this deep aquifer needs to be determined.     

Secondary dynamical spectra of pulsars as indicators of inhomogeneities in the interstellar plasma

Observations of ten bright pulsars were obtained on the Giant Meter-wavelength Radio Telescope (GMRT, India) in order to study the effects of scattering of their radio waves by contructing and analyzing secondary dynamical spectra. The observations were conducted at 610 and 1420 MHz using a digital spectral analyzer operating in a real-time regime. The frequency resolution was 32.5 or 65.1 kHz, and the readout time was from 61.44 to 512 μs. Archival data for five pulsars at 327 MHz were also used. Procedures for normalizing the spectra and for constructing the secondary dynamical spectra were developed. Parabolic arcs were found in the secondary spectra of four pulsars (B1642-03, B1556-44, B2154+40, and B2021+51). The curvature of these arcs can be used to determine the distance to the effective scattering screen. In all cases, these screens are located relatively near the pulsars themselves.     

Chemical fractionation of metals in freshly deposited marine estuarine sediments of sundarban ecosystem,India

Sediment metal profiles were carefully examined for their distribution, chemical fractions, and mobility in three major marine-estuarine transects in the world’s largest mangrove (Sundarban) ecosystem because anthropogenic influences had been very often noticed. The level of pollutants was determined by CF and PLI. Metal contents in the freshly deposited sediment of Hugli transect were relatively high (Pb, Fe, Zn, Mn, Ni, and Co) in comparison to Matla and Saptamukhi due to lithogenic contribution from large catchments area (8 × 10⁵ km²). Principal component analysis and correlation coefficient revealed that the concentrations of metals were mainly governed by the variability of the sediment properties. Sediment was subjected to sequential chemical extractions to delineate metal fractions, namely exchangeable, carbonate, Fe–Mn oxide, organic, and residual. This indicated a valuable insight into the geochemical mode of the metal retention and their environmental behavior. Single extraction did not help significantly to explain the metal profiling.     

Deep learning for predicting the monsoon over the homogeneous regions of India

Indian monsoon varies in its nature over the geographical regions. Predicting the rainfall not just at the national level, but at the regional level is an important task. In this article, we used a deep neural network, namely, the stacked autoencoder to automatically identify climatic factors that are capable of predicting the rainfall over the homogeneous regions of India. An ensemble regression tree model is used for monsoon prediction using the identified climatic predictors. The proposed model provides forecast of the monsoon at a long lead time which supports the government to implement appropriate policies for the economic growth of the country. The monsoon of the central, north-east, north-west, and south-peninsular India regions are predicted with errors of 4.1%, 5.1%, 5.5%, and 6.4%, respectively. The identified predictors show high skill in predicting the regional monsoon having high variability. The proposed model is observed to be competitive with the state-of-the-art prediction models.     

Mirror matter in the solar system: new evidence for mirror matter from Eros

Mirror matter is an entirely new form of matter predicted to exist if mirror symmetry is a fundamental symmetry of nature. Mirror matter has the right broad properties to explain the inferred dark matter of the Universe and might also be responsible for a variety of other puzzles in particle physics, astrophysics, meteoritics and planetary science. It is known that mirror matter can interact with ordinary matter non-gravitationally via photon-mirror photon kinetic mixing. The strength of this possibly fundamental interaction depends on the (theoretically) free parameter ε. We consider various proposed manifestations of mirror matter in our solar system examining in particular how the physics changes for different possible values of ε. We find new evidence for mirror matter in the solar system coming from the observed sharp reduction in crater rates (for craters less than about 100 m in diameter) on the asteroid 433 Eros. We also re-examine various existing ideas including the mirror matter explanation for the anomalous meteorite events, anomalous slow-down of Pioneer spacecraft etc.     

Spatial modeling using high resolution image for future shoreline prediction along Junput Coast,West Bengal,India

National policies and legal decisions are very much dependent on the position of the shoreline. Shoreline change rates are frequently employed to summarize historical shoreline movements. This also helps to predict the future position of the shoreline based on the perceived historical trends. In this regard, the future shoreline positions at both the long-term, that is 2050, and short-term, that is 2015, time interval was predicted using the End Point Rate (EPR) model along the Junput Coast of West Bengal, India. The whole project work was divided into five parts. The first part showed the detection of shoreline from satellite data like IRS LISS Ⅳ and Landsat 7 ETM+ and from the Survey of India Toposheet. The second part gave the glimpse of the dynamic segmentation of the shoreline to get the dynamically segmented nodal points along the shoreline. Shoreline prediction for the years 2015 and 2050 using End Point Rate (EPR) model was done in the third part. In the fourth part, Coastal Terrain Model (CTM) was prepared, and the digital shoreline estimated. The model result was validated and accuracy assessed with respect to the GPS data collected from the field at the fifth stage. Finally at the end of the present work, limitations of the project and the future scope of the work was sited.     

Assessment of degraded lands of puruliya district, west bengal using remotely sensed data

Land degradation in Puruliya district, West Bengal was assessed using remote sensing techniques. Analysis of satellite data (False Colour Composite in 1:50,000 scale) was carried out visually and subsequent ground verification and translation of imgae interpretation units into various categories of degraded lands. The results indicate that 31.8 per cent area of the district suffers from one or the other kind of land degradation. Water induced soil erosion is the major problem which accounts for 31.3 per cent area of the district. Land degradation due to waterlogging is limited to only 0.3 per cent area whereas 0.2 per cent area is degraded due to rock quarries, brick kiln and indus-trial effluents.