A. N. V. Satyanarayana

Coastal vulnerability assessment studies over India: a review

Coastal areas are one of the key systems for global sustainability. These are the transition areas between land and sea. Coastal regions gained importance because of multiple uses, like high productivity of the ecosystem, highly concentrated population, industrial friendly, waste disposal, tourism, transportation, strategic planning in military and many more. These coasts are always in a dynamic state trying to change, and nature always works for maintaining the equilibrium. India, with most diverse ecosystem, high productivity and thickly populated over coastal region, has gained its very own importance. Despite all of these, Indian coasts are under threat due to multiple stresses like global climate change and human intervention. These stresses are driving vulnerabilities like sea-level rise, coastal erosion, frequent extreme events, and saltwater encroachment. In this critical scenario, coastal management has become one of the very important issues in the last two decades. Thus, coastal vulnerability assessment methods have been developed to identify and manage the vulnerable areas over the coast. In the present review, we focussed on different vulnerabilities to coast of India and one of the assessment methods, coastal vulnerability index methodology, applied over India. Vulnerability assessment is the process where we identify the problem, quantify it, and assess the risk rate in formulating development strategies to reduce the risk and vulnerabilities. Proper planning and protection strategies for Indian coast must be taken swiftly by the coastal management and policy makers to safeguard coastal ecosystem and livelihoods. In recent years, there has been much focus on coastal vulnerability assessments using various kinds of data. Most of the reported studies over Indian coast are based on remote sensing and GIS methods.

A STUDY ON ATMOSPHERIC BOUNDARY-LAYER CHARACTERISTICS AT ANAND, INDIA USING LSP EXPERIMENTAL DATA SETS

An attempt is made to study the planetary boundary layer (PBL) characteristics during the winter period at Anand (22.4°N, 72.6°E), a semi-arid region, which is located in the western part of India. A one-dimensional turbulent kinetic energy (TKE) closure model is used for the study. The structure of the PBL,which consists of profiles of zonal and meridional components of wind,potential temperature and specific humidity, is simulated. A one-dimensional soil heat and moisture transport parameterization scheme is incorporated for the accurate representation of the energy exchange processes at the soil-atmosphere interface. The diurnal variation of fluxes of sensible heat, latent heat, shortwave radiation, net radiation and soil flux, soil temperature at different depths, Richardson number and TKE at the height of the constant flux layer is studied. The model predictions are compared with the available observations obtained from a special Land Surface Processes (LSP) experiment.

Surface energy and radiation budget over a tropical station: An observational study

This study attempts to understand the variations in the radiation and surface energy budget parameters during days of occurrence and non occurrence of convective activity such as thunderstorms at Ranchi (23°25′N, 85°26′E), India using the special experimental data sets obtained during pre-monsoon month of May, 2008. For this purpose five continuous thunderstorm days (TD) of varying intensity, along with three non-thunderstorm days (NTD) preceding the TD are considered. Thunderstorms occurred at site are multi-cellular in nature. Change of wind direction and strong gusty winds are noticed in TD cases. Pre-dominant wind direction is south westerly for the TD; it is northwesterly during NTD. Sudden drop of air temperature and rise of relative humidity and rise/drop in atmospheric pressure is noticed during TD are found to be proportional to the intensity of thunderstorm event. More partitioning of net radiation (QN) is in to latent heat flux (QE) and the contribution of sensible heat flux (QH) and soil heat flux (QG) are same during TD. But in the NTD more partitioning of QN is in to QH followed by QG that of QE. Significant differences in radiation and energy budget components are noticed during TD and NTD events.

Intensity of tropical cyclones during pre- and post-monsoon seasons in relation to accumulated tropical cyclone heat potential over Bay of Bengal

The aim of the present study is to understand the impact of oceanic heat potential in relation to the intensity of tropical cyclones (TC) in the Bay of Bengal during the pre-monsoon (April–May) and post-monsoon (October–November) cyclones for the period 2006–2010. To accomplish this, the two-layer gravity model (TLGM) is employed to estimate daily tropical cyclone heat potential (TCHP) utilizing satellite altimeter data, satellite sea surface temperature (SST), and a high-resolution comprehensive ocean atlas developed for Indian Ocean, subsequently validated with in situ ARGO profiles. Accumulated TCHP (ATCHP) is estimated from genesis to the maximum intensity of cyclone in terms of minimum central pressure along their track of all the cyclones for the study period using TLGM generated TCHP and six-hourly National Centre for Environmental Prediction Climate Forecast System Reanalysis data. Similarly, accumulated sea surface heat content (ASSHC) is estimated using satellite SST. In this study, the relationship between ATCHP and ASSHC with the central pressure (CP) which is a function of TC intensity is developed. Results reveal a distinct relationship between ATCHP and CP during both the seasons. Interestingly, it is seen that requirement of higher ATCHP during pre-monsoon cyclones is required to attain higher intensity compared to post-monsoon cyclones. It is mainly attributed to the presence of thick barrier layer (BL) resulting in higher enthalpy fluxes during post-monsoon period, where as such BL is non-existent during pre-monsoon period.

Response of upper ocean during passage of MALA cyclone utilizing ARGO data

In the present study an attempt has been made to study the response of the upper ocean atmospheric interactions during the passage of a very severe cyclonic storm (VSCS) ‘MALA’ formed over the Bay of Bengal (BoB) on 24 April 2006. Deepening of mixed layer depth (MLD), weakening of barrier layer thickness (BLT) associated with a deeper 26 °C isotherm level (D26) is observed after the MALA passage. Tropical cyclone heat potential (TCHP) and depth averaged temperature (T100) exhibit a good degree of correlation for higher values. The passage of MALA cyclone also resulted in cooling the sea surface temperature (SST) by 4–5 °C. The findings suggest that turbulent and diapycnal mixing are responsible for cooler SSTs. Turbulent air–sea fluxes are analyzed using Objectively Analyzed air–sea Fluxes (OAFlux) daily products. During the mature stage of MALA higher latent heat flux (LHF), sensible heat flux (SHF), and enthalpy (LHF + SHF) are observed in the right side of this extreme event.

Response of upper ocean and impact of barrier layer on Sidr cyclone induced sea surface cooling

In the present study an attempt has been made to investigate the impact of salinity stratification on the SST during the tropical cyclone (TC) passage. In this context, a severe post monsoon cyclone, Sidr, (Category 4) that developed over the south-eastern Bay of Bengal (BoB) during 11–16 November, 2007 was chosen as a case study. Pre-existence of a thick barrier layer (BL), temperature inversions and a higher effective oceanic layer for cyclogenesis (EOLC) were noticed along the path of the Sidr cyclone. The analysis of available Argo floats along the Sidr cyclone track also revealed less cooling during as well as after its passage as was reported from satellite derived SST. The role of BL on Sidr induced sea surface cooling was investigated using a diagnostic mixed layer model. Model results also depict the reduced sea surface cooling during the passage of Sidr. This is attributed to the presence of BL which results in the inhibition of the entrainment of cool thermocline water into the shallow mixed layer. Climatological as well as in situ observations of tropical cyclone heat potential (TCHP) and EOLC shows that the Sidr cyclone propagated towards the regions of higher EOLC.

Surface Energy Exchanges during Pre-monsoon Thunderstorm Activity over a Tropical Station Kharagpur

In the present study an attempt has been made to understand the variation of surface energy fluxes such as net radiation, sensible, latent and soil heat during different epochs of thunderstorm activity at Kharagpur. The study also focuses in delineating the difference in the surface energy budget from the days of thunderstorm activity to fair weather days in the pre-monsoon months (April and May) which is locally known as thunderstorm season. For this purpose, experimental data obtained from the Severe Thunderstorms- Observations and Regional Modeling (STORM) programme during pre-monsoon months of 2007, 2009 and 2010 at Kharagpur (22°30′N, 87°20′E), West Bengal, India are used. The present study reveals quick response, in the order of a few days, in the variations of transport of energy fluxes at soil-atmosphere interface to the upper atmosphere vis-à-vis to the occurrence of thunderstorm activity. Rise of surface sensible heat flux to the level of surface latent heat flux a day or two before the occurrence of a thunderstorm has been identified as a precursor signal for the thunderstorm occurrence over Kharagpur. Distinguishable differences are found in the partitioning of the surface energy fluxes to that of net radiation between thunderstorm and non-thunderstorm days. The present study reveals more Bowen’s ratio during thunderstorm days to that of nonthunderstorm days. These results are useful in validating mesoscale model simulations of thunderstorm activity.

Performance Evaluation of Convective Parameterization Schemes of WRF-ARW Model in the Simulation of Pre-monsoon Thunderstorm Events over Kharagpur using STORM Data Sets

Thunderstorms associated with severe gusty winds and lightening cause loss of life and property even though they last for an hour or so. Forecasting of these severe weather events is highly essential due to their impact on socioeconomic conditions of affected regions. Kharagpur (22°30′ N, 87°20′ E) is in the region of Gangetic West Bengal (GWB) affected by high frequency of occurrence of thunderstorms during pre-monsoon months. In the present study an attempt has been made to understand the performance of convective parameterization schemes (e.g. Kain-Fritsch, Grell-Devenyi ensemble and Betts-Miller-Janjic) of a meso-scale model WRF-ARW version 3.2 in simulating pre-monsoon thunderstorm events that occurred during 12 May 2009 and 5 May 2010 over Kharagpur. Numerical experiments are carried out by considering convection explicitly. The model simulations are compared with the available observations. Statistical evaluation of simulated parameters along with the observations revealed Grell-Devenyi ensemble and KainFritsch schemes performed reasonably well in representing the thermodynamical state of atmosphere during the thunderstorm events. General Terms Mesoscale model, Statistical evaluation, Simulation.

Delineation of spatio-temporal changes of shoreline and geomorphological features of Odisha coast of India using remote sensing and GIS techniques

Odisha coast is a dynamic region wherein both natural and anthropogenic processes affecting the shape and position of the shoreline vis-à-vis the coastal processes are prevalent in this region. Geomorphology such as lagoons, tidal flats, mangrove swamps and shoreline is a rapidly changing phenomenon along this coast mainly due to tides, waves, oceanic currents and storm surges. Keeping in view of the above, the present study mainly focused on decadal changes of shoreline and land cover changes, and delineation of geomorphological units along the Odisha coast using geospatial technologies for the period 1990–2009. Spatio-temporal analysis of remote sensing data indicated notable shoreline changes at cyclone land fall locations along the Odisha coast, wherein erosion (loss) and accretion (gain) rates were observed to be high at Paradeep and Kendrapada. During the study period, the rate of accretion was observed to be higher during 1999–2009 compared to 1990–1999. Coastal geomorphology landforms distributions indicate that the swale complex, older and younger coastal plains, tidal flats and mangrove swamp are the dominant features. Long-term land cover analysis indicated that the vegetation cover loss happened in the high vegetated areas during the period 1990–1999 and regeneration during the period 1999–2009.

Formulation of stability-dependent empirical relations for turbulent intensities from surface layer turbulence measurements for dispersion parameterization in a lagrangian particle dispersion model

Season- and stability-dependent turbulence intensity (σu/u*, σv/u*, σw/u*) relationships are derived from experimental turbulence measurements following surface layer scaling and local stability at the tropical coastal site Kalpakkam, India for atmospheric dispersion parameterization. Turbulence wind components (u′, v′, w′) measured with fast response UltraSonic Anemometers during an intense observation campaign for wind field modeling called Round Robin Exercise are used to formulate the flux–profile relationships using surface layer similarity theory and Fast Fourier Transform technique. The new relationships (modified Hanna scheme) are incorporated in a Lagrangian Particle Dispersion model FLEXPART-WRF and tested by conducting simulations for a field tracer dispersion experiment at Kalpakkam. Plume dispersion analysis of a ground level hypothetical release indicated that the new turbulent intensity formulations provide slightly higher diffusivity across the plume relative to the original Hanna scheme. The new formulations for σu, σv, σw are found to give better agreement with observed turbulent intensities during both stable and unstable conditions under various seasonal meteorological conditions. The simulated concentrations using the two methods are compared with those obtained from a classical Gaussian model and the observed SF6 concentration. It has been found that the new relationships provide comparatively higher diffusion across the plume relative to the model default Hanna scheme and provide downwind concentration results in better agreement with observations.