Tsunami and the effects on coastal morphology and ecosystems: A report

Tsunamis are one of the most destructive natural hazards that affect the coastal areas. Tsunami waves that impact the coast with enormous energy are capable of destroying the objects on the coast and re-shaping the coastal geography, geomorphology and ecosystem. These waves can also cause extensive damage and disruption to human lives, their livelihood, infrastructure and economic activities. The 26 December 2004 Sumatra-Andaman earthquake, one of the largest recorded and deadliest tremor, created an unparalleled catastrophic tsunami wiping out thousands of human lives and throwing millions homeless. This event attracted the interest of several geoscientists in India and stimulated extensive scientific research. This article summarizes the tsunami related research work carried out in India during the past four years

Study of spatial-temporal variations in the green Noctiluca scintillans and diatom blooms in the Arabian Sea using MODIS data

Phytoplankton blooms of green Noctiluca scintillans (a dinoflagellate) and diatom, which appear in the Northern and Central Arabian Sea during winter are far-reaching and persistent. Generation of phytoplankton species images revealed a massive winter bloom with huge spatial extent in 2015. In contrast to this, the classified species images for 2013 indicated relatively weaker bloom with respect to its spread. A plot of total number of pixels classified as diatom and Noctiluca scintillans for different years revealed a cyclic pattern of the spread. The report deals with an approach to forecast the bloom / productivity of the oceanic waters in the Northern-Central Arabian Sea in a qualitative way making use of the systematic pattern of its distribution across the year

On the decreasing trend of the number of monsoon depressions in the Bay of Bengal

This study unravels the physical link between the weakening of the monsoon circulation and the decreasing trend in the frequency of monsoon depressions over the Bay of Bengal. Based on the analysis of the terms of Genesis Potential Index, an empirical index to quantify the relative contribution of large scale environmental variables responsible for the modulation of storms, it is shown here that the reduction in the mid-tropospheric relative humidity is the most important reason for the decrease in the number of monsoon depressions. The net reduction of relative humidity over the Bay of Bengal is primarily due to the decrease in the moisture flux convergence, which is attributed to the weakening of the low level jet, a characteristic feature of monsoon circulation. Further, the anomalous moisture convergence over the western equatorial Indian Ocean associated with the rapid warming of the sea surface, reduces the moisture advection into the Bay of Bengal and hence adversely affect the genesis/intensification of monsoon depressions. Hence, the reduction in the number of monsoon depression over the Bay of Bengal could be one of the manifestations of the differential rates in the observed warming trend of the Indian Ocean basi

The Indian ocean forecast system

In order to meet the ever growing demand for the prediction of oceanographic parametres in the Indian Ocean for a variety of applications, the Indian National Centre for Ocean Information Services (INCOIS) has recently set-up an operational ocean forecast system, viz. the Indian Ocean Forecast System (INDOFOS). This fully automated system, based on a state-of-the-art ocean general circulation model issues six-hourly forecasts of the sea-surface temperature, surface currents and depths of the mixed layer and the thermocline up to five-days of lead time. A brief account of INDOFOS and a statistical validation of the forecasts of these parametres using in situ and remote sensing data are presented in this article. The accuracy of the sea-surface temperature forecasts by the system is high in the Bay of Bengal and the Arabian Sea, whereas it is moderate in the equatorial Indian Ocean. On the other hand, the accuracy of the depth of the thermocline and the isothermal layers and surface current forecasts are higher near the equatorial region, while it is relatively lower in the Bay of Bengal

Coastal Multi-hazard vulnerability mapping: A case study along the coast of Nellore District, East Coast of India

The study area coastal zone of Nellore district is experiencing frequent inundation by natural disasters. The current study is focused on generating Multi-hazard vulnerability map using the parameters historical storm surge heights, future sea level, future shoreline and high resolution coastal topography. The area is experiencing the severe coastal erosion up to 7 m/y along some stretches poses a threat. An area totaling 1708.36 sq. km. is found to fall under the multi-hazard zone and the coastal population are under threat due to future storms, erosion, accelerated sea level rise, etc. The image enhancement, interpretation and GIS overlay techniques along with data used here are effective to produce Multi-hazard vulnerability maps. These Maps are become vital tools for the coastal disaster management during an event and to take suitable decision on the future developments

Wyrtki Jets: Role of intraseasonal forcing

Direct current measurements observed from the acoustic Doppler current profilers in the equatorial Indian Ocean (EIO) and solutions from an ocean general circulation model are investigated to understand the dynamics of the Wyrtki jet. These jets are usually described as semiannual direct wind forced zonal currents along the central and eastern EIO. We show that both, spring and fall, Wyrtki jets show predominant semiannual spectral peaks, but significant intraseasonal energy is evident during spring in the central and eastern EIO. We find that for the semiannual band, there is a strong spectral coherence between the overlying winds and the currents in the central EIO, but no coherency is observed in the eastern part of the EIO. Moreover, for the intraseasonal band, strong coherency between the winds and currents is evident. During spring, intraseasonal currents induced by the Madden–Julian oscillation (MJO) superimpose constructively with semiannual currents and thus intensify the strength of the spring Wyrtki jet. Also, the atmospheric intraseasonal variability accounts for the interannual variabilities observed in spring Wyrtki jet

Following tagged Yellowfin tuna along the east coast of India explains its feeding behavior: a case study in the Bay of Bengal

Horizontal movement of pelagic fish predator, Yellowfin (Thunnus albacares) tuna, in the oceanic waters of Bay of Bengal has been decoded. Pop-up Satellite Archival Tags (PSATs) were attached to adult tunas to study their distribution and migration. For this, environmental satellite data were matched with the tag locations to understand and characterize habitats of this species. A sub-set of the tag data was selected corresponding to the maximum resident time of tuna indicated by a high density data points. The tagged tuna spent 60 to 70% of its time in the waters having surface temperature within 28o to 29.5oC and sea surface height anomaly within+5 to +12 cm. The tag positions were located on the satellite images; chlorophyll, sea surface temperature, zooplankton and sea surface height anomaly. The two conditions, specific range of temperature and prey abundance, were found necessary for aggregation of tuna

Successful monitoring of the 11 April 2012 tsunami off the coast of Sumatra by Indian Tsunami Early Warning Centre

The Indian Tsunami Early Warning Centre (ITEWC) in Hyderabad monitored the 11 April 2012 tsunami off the coast of Sumatra, which was generated by a shallow strike-slip earthquake and it largest aftershock of magnitude Mw (mB) 8.5 and 8.2 respectively, that occurred inside the subducting slab of the Indian plate. The earthquake generated a small ocean-wide tsunami that has been recorded by various tide gauges and tsunami buoys located in the Indian Ocean region. ITEWC detected the earthquake within 3 min 52 s and issued six advisories (bulletins) according to its Standard Operating Procedure. The ITEWC performed well during the event, and avoided false alarms and unnecessary public evacuations, especially in the mainland part of India region

Assessment of Tsunami Preparedness in East Coast of India through Mega Mock Tsunami Drill conducted on 24 November 2017

Though tsunamis are infrequent, the death toll from tsunamis is huge compared with other natural disasters. The 26 December 2004 Indian Ocean tsunami resulted in disastrous loss of life and property. The major challenge with tsunamis is that they are infrequent, which requires great persistence in sustaining the process of capacity building and preparedness. Because of this infrequency, instruction through tsunami mock drills is the best way to train coastal communities to prepare for devastating actual events. The situational awareness and ability to respond quickly is best achieved through pre-event education and mock drills. The Tsunami mock drills evaluates the ability of warning centre and disaster offices to respond to a tsunami. The drills also educate the public on: where they would receive the official warnings, by which means, what those warnings indicate, how to understand them, and what they need to do in response. INCOIS in collaboration with MHA and NDMA has conducted mega mock tsunami mock drill on 24 November, 2017 to East coast of India. Disaster Management Organisations of Andhra Pradesh, Odisha, Puducherry, Tamil Nadu and West Bengal participated in the drill. They took the drill to community level and executed evacuations at different villages. The average elapsed time achieved from time of receipt of warning to activating the public notification systems was 30 minutes. This is great achievement compared with previous mock drills as it has substantially improved, though the involvement of communities was at huge level. The Tsunami mock drill was very successful which enhanced the awareness and preparedness among the coastal people of East Coast of Indi

Basin-wide sea level coherency in the tropical Indian Ocean driven by Madden–Julian Oscillation

Changes in sea level may be attributed either to barotropic (involving the entire water column) or baroclinic processes (governed by stratification). It has been widely accepted that barotropic sea level changes in the tropics are insignificant at intraseasonal time scales (periods of 30–80 days). Based on bottom pressure records, we present evidence for significant basin-wide barotropic sea level variability in the tropical Indian Ocean during December–April with standard deviations amounting to ∼30–60% of the standard deviation in total intraseasonal sea level variability. The origin of this variability is linked to a small patch of wind over the Eastern Indian Ocean, associated with boreal winter Madden–Julian Oscillations (MJO). These large fluctuations are likely to play a prominent role in the intraseasonal sea level and mass budgets. Because of their much faster propagation than baroclinic processes, they allow the basin to adjust to climatic perturbations much more rapidly than was previously thought