Neutrino and astroparticle physics : Working group report

The contributions made to the Working Group activities on neutrino and astroparticle physics are summarised in this article. The topics discussed were leptogenesis in Left-Right symmetric model, inflationary models in Raman-Sundrum scenarios, ultra high energy cosmic rays and neutrino oscillations in 4 flavour and decaying neutrino models.Comment: 11 pages; arXiv copy of contribution to WHEPP-6 proceeding

Frequency dependent heat capacity within a kinetic model of glassy dynamics

There has been renewed interest in the frequency dependent specific heat of supercooled liquids in recent years with computer simulation studies exploring the whole frequency range of relaxation. The simulation studies can thus supplement the existing experimental results to provide an insight into the energy landscape dynamics. We here investigate a kinetic model of cooperative dynamics within the landscape paradigm for the dynamic heat capacity behavior. In this picture, the beta-process is modeled as a thermally activated event in a two-level system and the alpha-process is described as a beta-relaxation mediated cooperative transition in a double well. The model provides a description of the activated hopping in the energy landscape in close relation with the cooperative nature of the hopping event. For suitable choice of parameters, the model predicts a frequency dependent heat capacity that reflects the two-step relaxation behavior. Although experimentally obtained specific heat spectra of supercooled liquids till date could not capture the two-step relaxation behavior, this has been observed in a computer simulation study by Scheidler et. al. [Phys. Rev. B 63, 104204 (2001)]. The temperature dependence of the position of the low-frequency peak, due to the alpha-relaxation, shows a non-Arrhenius behavior as observed experimentally by Birge and Nagel [Phys. Rev. Lett. 54, 2674 (1985)]. The shape of the alpha-peak is, however, found to be temperature independent, in agreement with the simulation result. The high-frequency peak appears with considerably larger amplitude than the alpha-peak. We attempt a plausible reason for this observation that is in contrast with the general feature revealed by the dielectric spectroscopy.Comment: 10 pages, 10 figure

Spatio-temporal variability of summer monsoon rainfall over Orissa in relation to low pressure systems

The summer monsoon rainfall over Orissa occurs mostly due to low pressure systems (LPS) developing over the Bay of Bengal and moving along the monsoon trough. A study is hence undertaken to find out characteristic features of the relationship between LPS over different regions and rain-fall over Orissa during the summer monsoon season (June-September). For this purpose, rainfall and rainy days over 31 selected stations in Orissa and LPS days over Orissa and adjoining land and sea regions during different monsoon months and the season as a whole over a period of 20 years (1980-1999) are analysed. The principal objective of this study is to find out the role of LPS on spatial and temporal variability of summer monsoon rainfall over Orissa. The rainfall has been significantly less than normal over most parts of Orissa except the eastern side of Eastern Ghats during July and hence during the season as a whole due to a significantly less number of LPS days over northwest Bay in July over the period of 1980-1999. The seasonal rainfall shows higher interannual variation (increase in coefficient of variation by about 5%) during 1980-1999 than that during 1901-1990 over most parts of Orissa except northeast Orissa. Most parts of Orissa, especially the region extending from central part of coastal Orissa to western Orissa (central zone) and western side of the Eastern Ghats get more seasonal monsoon rainfall with the development and persistence of LPS over northwest Bay and their subsequent movement and persistence over Orissa. The north Orissa adjoining central zone also gets more seasonal rainfall with development and persistence of LPS over northwest Bay. While the seasonal rainfall over the western side of the Eastern Ghats is adversely affected due to increase in LPS days over west central Bay, Jharkhand and Bangladesh, that over the eastern side of the Eastern Ghats is adversely affected due to increase in LPS days over all the regions to the north of Orissa. There are significant decreasing trends in rainfall and number of rainy days over some parts of southwest Orissa during June and decreasing trends in rainy days over some parts of north interior Orissa and central part of coastal Orissa during July over the period of 1980-1999

A comparative study on performance of MM5 and WRF models in simulation of tropical cyclones over Indian seas

Tropical cyclone is one of the most devastating and deadly weather phenomenon worldwide. It is a result of organized intense convective activities over warm tropical oceans. In recent years mesoscale models are extensively used for simulation of genesis, intensification and movement of tropical cyclones. In this study, the recent three very severe cyclonic storms generated over Indian seas (Bay of Bengal and Arabian Sea) are considered. During 26-29 April 2006, a very severe tropical cyclone, known as Mala, developed over the Bay of Bengal and crossed the Arakan coast of Myanmar on 29 April 2006. During 2-7 June 2007, a super cyclonic storm, known as Gonu, developed over the Arabian sea and crossed the Makran coast on 7 June 2007. During 11-16 November 2007, a very severe cyclonic storm, known as Sidr, developed over the Bay of Bengal and crossed the Khulna-Barisal coast of Bangladesh on 15 November 2007. In the present study, two state-ofthe- art mesoscale models, MM5 and WRF, developed at the National Center for Atmospheric Research (NCAR), USA, have been used to evaluate the performances of both the models in the simulation of the above-mentioned tropical cyclones. The performances of both the models have been calculated by integrating with 15 different initial conditions, i.e. each case with five different initial conditions. A number of meteorological fields, viz. central pressure, wind and precipitation have been verified against observations/ verification analyses. The vector displacement error in track forecast has also been calculated using the best track provided by the India Meteorological Department. The results indicate that the WRF model has better performance in respect of track and intensity prediction than the MM5 model

Interannual variability of summer monsoon rainfall over Orissa in relation to tropospheric circulation features

The summer monsoon rainfall over Orissa shows largescale interannual variability due to variation in the characteristics of meteorological parameters like temperature, pressure/geopotential height and wind at surface and in the troposphere. A study was therefore undertaken to find out the characteristic features of surface and upper air meteorological parameters in the troposphere and their relationship with summer monsoon rainfall over Orissa. For this purpose, rainfall data over 31 uniformly distributed stations in Orissa along with the surface meteorological parameters at seven stations and upper air parameters at different standard isobaric levels up to 200 hPa over four stations in Orissa and its neighbourhood during summer monsoon season over a period of 19 years (1980-98) have been considered. The principal objective of this study is to find out the contribution of different meteorological parameters in the spatio-temporal variability of summer monsoon rainfall over Orissa. The interannual variability of rainfall mostly depends on the interannual variation of wind over Orissa and its neighbourhood. Strong northeasterlies over north coastal Orissa along with the southeasterly winds over Gangetic West Bengal and northwesterlies over northwest Orissa, south Orissa and north coastal Andhra Pradesh at the lower and mid-tropospheric levels are favourable for good rainfall over Orissa as a whole. They are also favourable for good rainfall over the western side of the Eastern Ghats and over the central zone, extending from the central part of coastal Orissa to western Orissa. This pattern of wind is also associated with the synoptic disturbances over northwest Bay of Bengal. Hence, the higher/lower number of days of synoptic disturbances over the NW Bay causes excess/deficient rainfall over Orissa. The stronger gradient of mean sea-level pressure and geopotential over the region to the south of the monsoon trough passing through north coastal Orissa at lower and mid-tropospheric level, is favourable for good rainfall over Orissa. Divergence at the upper troposphere (200 hPa) due to a trough in the upper tropospheric westerlies to the right of Visakhapatnam and an east-west ridge to the south of Visakhapatnam and over the NW Bay is favourable for rainfall over Orissa. There is no significant trend in both zonal and meridional winds at the upper troposphere (200 hPa) over the region, supporting insignificant trend in summer monsoon seasonal rainfall over Orissa during 1980-98

Some characteristics of very heavy rainfall over Orissa during summer monsoon season

Orissa is one of the most flood prone states of India. The floods in Orissa mostly occur during monsoon season due to very heavy rainfall caused by synoptic scale monsoon disturbances. Hence a study is undertaken to find out the characteristic features of very heavy rainfall (24 hours rainfall ≥125 mm) over Orissa during summer monsoon season (June-September) by analysing 20 years (1980-1999) daily rainfall data of different stations in Orissa. The principal objective of this study is to find out the role of synoptic scale monsoon disturbances in spatial and temporal variability of very heavy rainfall over Orissa. Most of the very heavy rainfall events occur in July and August. The region, extending from central part of coastal Orissa in the southeast towards Sambalpur district in the northwest, experiences higher frequency and higher intensity of very heavy rainfall with less interannual variability. It is due to the fact that most of the causative synoptic disturbances like low pressure systems (LPS) develop over northwest (NW) Bay of Bengal with minimum interannual variation and the monsoon trough extends in west-northwesterly direction from the centre of the system. The very heavy rainfall occurs more frequently with less interannual variability on the western side of Eastern Ghat during all the months and the season except September. It occurs more frequently with less interannual variability on the eastern side of Eastern Ghat during September. The NW Bay followed by Gangetic West Bengal/Orissa is the most favourable region of LPS to cause very heavy rainfall over different parts of Orissa except eastern side of Eastern Ghat. The NW Bay and west central (WC) Bay are equally favourable regions of LPS to cause very heavy rainfall over eastern side of Eastern Ghat. The frequency of very heavy rainfall does not show any significant trend in recent years over Orissa except some places in north-east Orissa which exhibit significant rising trend in all the monsoon months and the season as a whole

Some characteristics of low pressure systems and summer monsoon rainfall over Orissa

The present study was undertaken to find out characteristic features like frequency, intensity, movement, region of formation, days of occurrence, etc. of synoptic disturbances such as low, depression, cyclonic storm, etc. forming over Orissa and neighbouring sea and land regions during summer monsoon season (June- September). The study is based on the data of 20 years (1980-1999). The principal objective of this study was to understand the contribution of the low pressure systems (LPS) including low, depression and cyclonic storm to interannual variability of summer monsoon rainfall over Orissa. Most of the LPS develop over northwest (NW) Bay of Bengal and move towards east Madhya Pradesh across Gangetic West Bangal (GWB) during June, July and across Orissa during August and September. The rainfall over Orissa is more related with the frequency of LPS days over Orissa and adjoining land/sea regions than with the frequencies of LPS, cyclonic disturbances (CD) and CD days over those regions. The seasonal monsoon rainfall over Orissa is significantly higher with higher frequency of LPS days over NW Bay and Orissa. It is less with higher frequency of LPS days over Jharkhand followed by west central Bay off north coastal Andhra Pradesh and Bangladesh. The frequencies of monsoon low days are higher over NW Bay and Orissa thus compensating the adverse impact of reduced CD and CD days on rainfall over Orissa in recent years. The monthly and seasonal monsoon rainfall over Orissa show no significant trends in recent years. It may be due to insignificant trends in those LPS days which are significantly correlated with rainfall over Orissa

Inter-annual variability of summer monsoon rainfall over Orissa (India) in relation to cyclonic disturbances

The summer monsoon rainfall over Orissa, a state on the eastern coast of India, is more significantly related than Indian summer monsoon rainfall (ISMR) to the cyclonic disturbances developing over the Bay of Bengal. Orissa experiences floods and droughts very often due to variation in the characteristics of these disturbances. Hence, an attempt was made to find out the inter-annual variability in the rainfall over Orissa and the frequencies of different categories of cyclonic disturbances affecting Orissa during monsoon season (June-September). For this purpose, different statistical characteristics, such as mean, coefficient of variation, trends and periodicities in the rainfall and the frequencies of different categories of cyclonic disturbances affecting Orissa, were analysed from 100 years (1901-2000) of data. The basic objective of the study was to find out the contribution of inter-annual variability in the frequency of cyclonic disturbances to the inter-annual variability of monsoon rainfall over Orissa. The relationship between summer monsoon rainfall over Orissa and the frequency of cyclonic disturbances affecting Orissa shows temporal variation. The correlation between them has significantly decreased since the 1950s. The variation in their relationship is mainly due to the variation in the frequency of cyclonic disturbances affecting Orissa. The variability of both rainfall and total cyclonic disturbances has been above normal since the 1960s, leading to more floods and droughts over Orissa during recent years. The inter-annual variability of seasonal rainfall over Orissa and the frequency of cyclonic disturbances affecting Orissa during monsoon season show a quasi-biennial oscillation period of 2-2.8 years. There is least impact of El Nino southern oscillation (ENSO) on inter-annual variability of both the seasonal rainfall over Orissa and the frequencies of monsoon depressions/total cyclonic disturbances affecting Orissa

Location-specific prediction of the probability of occurrence and quantity of precipitation over the Western Himalayas

Northwest India is composed, in part, of complex Himalayan mountain ranges having different altitudes and orientations, causing the prevailing weather conditions to be complex. During winter, a large amount of precipitation is received in this region due to eastward-moving low pressure synoptic weather systems called western disturbances (WDs). The objective of the present study is to use the perfect prognostic method (PPM) for probability of precipitation (PoP) forecasting and quantitative precipitation forecasting (QPF). Three observatories in the western Himalayan region, namely, Sonamarg, Haddan Taj, and Manali, are selected for development of statistical dynamical models for location-specific prediction of the occurrence and quantity of precipitation. Reanalysis data from the National Centers for Environmental Prediction (NCEP), and upper-air and surface observations from the India Meteorological Department (IMD), are used to develop statistical dynamical models for PoP and QPF for winter, that is, December, January, February, and March (DJFM). Models are developed with data from DJFM 1984-96 and tested with data from DJFM 1996-97. Four experiments are carried out with four different sets of predictors to evaluate the performance of the models with independent datasets. They are 1) NCEP-NCAR reanalysis data, 2) operational analyses from the National Centre for Medium RangeWeather Forecasting (NCMRWF) in India, 3) day 1 forecasts with a T80 global spectral model at NCMRWF, and 4) forecasts from the regional fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) day 1 forecast. Forecast skills are examined for these four experiments and for direct numerical model outputs of T80 day 1 and MM5 day 1 forecasts at these three stations. It is found that a best prediction is made with an accuracy of 89% at Haddan Taj using the MM5 day 1 forecast as predictors in the PoP model. In the case of the QPF model, a maximum 85% accuracy is achieved using the MM5 day 1 forecast variables as predictors. Thus, use of numerical model output from MM5 as predictors in statistical dynamical models based on the PPM concept provides definite improvements in the prediction of occurrence and quantity of precipitation as compared to the direct numerical model output

Simulation of a severe thunderstorm event during the field experiment of STORM programme 2006, using WRF-NMM model

In the tropics, most of the extreme weather events are convective in nature. Many parts over the Indian region experience thunderstorms at higher frequency during the pre-monsoon months (March-May), when the atmosphere is highly unstable because of high temperatures prevailing at lower levels. During April and May, the eastern and northeastern parts of the country, i.e. Gangetic West Bengal, Jharkhand, Orissa, Bihar, Assam and parts of other northeastern states are affected by higher frequency of severe thunderstorms, locally named as 'Kal-baishakhi' or 'Nor'westers'. Realizing the importance of better understanding and prediction of these severe local storms over east and northeast India and their socio-economic impact, the Department of Science and Technology, Government of India organized a national coordinated programme on 'Severe Thunderstorm Observation and Regional Modelling (STORM)' to be carried out in the premonsoon season of 2006-10. Mesoscale models are essential for the accurate prediction of such high-impact weather events. In the present study, an attempt has been made to simulate one thunderstorm event that occurred on 20 May 2006 at Kolkata (22.52°N, 88.37°E) during the field experiment of STORM 2006, using Non-hydrostatic Mesoscale Model (NMM) core of the Weather Research and Forecasting (WRF) system with different initial conditions. This model has been developed by the National Oceanic and Atmospheric Administration/National Centers for Environment Prediction. The model results are validated with STORM field experiment data. The model performed well in capturing stability indices, which act as indicators of severe convective activity along with the thunderstorm-affected parameters as in the observations. The results of these analyses show that the 3 km WRF-NMM has better capability when it comes to thunderstorm simulation. This suggests that high-resolution models have the potential to provide unique and valuable information for severe thunderstorm forecasters