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Evaluation of the impact of high-resolution winds on the coastal waves
Full text linkThis study discusses the impact of high-resolution winds on the coastal waves and analyses the effectiveness of the high-resolution winds in recreating the fine-scale features along the coastal regions during the pre-monsoon season (March–May). The influence of the diurnal variation of winds on waves is studied for the Tamil Nadu coastal region using wind fields from weather research and forecast (WRF) (3 km) and European Centre for Medium-Range Weather Forecasts (ECMWF) (27.5 km). The improvement in the coastal forecast is then quantified with wave rider buoy observations. The high-resolution wind fields simulated fine-scale features like land–sea breeze events and showed good agreement with observation results. The error in the wave height and period is reduced by 8% and 46%, respectively, with the use of high-resolution forcing winds WRF over ECMWF, although the overestimation of wave energy on high frequencies due to overestimated WRF winds remains as a challenge in forecasting. The analysis also shows the importance of accurate wave forecast during a short-duration sudden wind (~12 m/s) occurrence in southern Tamil Nadu near Rameswaram during the pre-monsoon period. Low pressure forms over Tamil Nadu due to the land surface heating, resulting in a sudden increase of winds. High winds and steep waves which cause damage to the property of the coastal community near Rameswaram also were well simulated in the high-resolution forecast system with WRF winds
Tidal Circulation in the Hooghly Estuary and Adjacent Coastal Oceans
No full textA terrain-following ocean general circulation model is implemented for simulating tidal and residual circulation patterns in the Hooghly Estuary and its adjacent coastal oceans (HECO) on the east coast of India. The model is forced with time-varying tidal levels and momentum fluxes at the eastern and southern open boundaries, and winds at the air�sea interface. Simulated tidal levels and currents are compared well with the observations. Based on model solutions, spatial patterns of semi-diurnal and diurnal tides and circulation are described. The residual circulation shows prevalence of ocean-ward along channel flow from north to south with distinct differential circulation patterns on its right and left flanks of the outer estuary. A mesoscale eddy associated with residual circulation has been occurring in the southwestern flank of the HECO, adjacent to the Digha coast. This is associated with enriched chlorophylla concentration (Chla), causing the region as the suitable place for the fishing activity. The residual currents in the left of the channel (toward the Sunderban) in the southeastern flank of the HECO are eastward and diverging in nature and are associated with reduced Chla. © 2019, Indian Society of Remote Sensing
Impact of multiyear La Niña events on the South and East Asian summer monsoon rainfall in observations and CMIP5 models
No full textImpact of multi-year La Niña events on South and East Asian summer monsoon rainfall are examined in the observations and Coupled Model Intercomparison Project Phase 5 (CMIP5) models. The analysis is carried out for the successive two summers, referred to as the first and second years during the period of 1948–2016. Composite analysis suggests that La Niña related sea surface temperature cooling is slightly high in the central and eastern equatorial Pacific during the first year summer. This anomalous cooling associated with La Niña is slightly shifted towards south and south-central Pacific Ocean during the second year. An Atlantic Niño like pattern is evident in the first year unlike the second year. Negative rainfall anomalies are apparent over most of the south Asian region except Bangladesh and Sundarbans, during the first year. Moisture convergence corroborated by low-level circulation to the north of Bangladesh and central India supports the positive rainfall anomalies in the first year. A weak circulation and negative vertically integrated moisture (VIM) anomalies in the rest of the subcontinent are consistent with the negative rainfall anomalies. In addition to these changes, the Atlantic Niño has also been found to be influencing the South Asian rainfall, remotely, during the first year. In the case of the second year, positive rainfall anomalies over the south Asian monsoon region is noted. An anomalous low-level cyclonic circulation over the central Bay of Bengal enhanced the moisture transport into the Indian subcontinent, causing positive rainfall anomalies. Moreover, an anomalous upper level divergence extends from the southeast Indian Ocean, towards the Indian subcontinent, due to La Niña’s response in the second year, which is found to be weak in the first year. This clearly suggests that the enhanced rainfall over the South Asian region is influenced remotely by La Niña forcing as well as local circulation changes during both the years. The East Asian monsoon region reported a tri-pole like structure in the rainfall anomalies, with positive values over southern and central China and negative over parts of Myanmar, Thailand and Cambodia regions and north-east China—North Korea during the first year and vice-versa in the second year. A positive–negative–positive structure in the VIM anomalies is seen in the East Asian region and it supports similar rainfall anomalies during the second year. We have further examined the ability of CMIP5 models in representing multiyear La Niña teleconnections to the south and East Asian summer monsoons. Some models are able to reproduce the South Asian rainfall and circulation anomalies well in the second year, but failed to do so, in the first. The factors responsible for weak teleconnections in the models are discussed in detail
Seasonal dynamics of phytoplankton in response to environmental variables in contrasting coastal ecosystems
No full textSeasonal distribution of phytoplankton community and size structure was assessed in three different tropical ecosystems of the western Bay of Bengal viz. estuary (Mahanadi), lagoon (Chilika), and coastal waters (off Gopalpur) in response to ambient hydrobiology. Salinity regimes differentiated the study regions as contrasting ecosystems irrespective of seasons (pre-monsoon, monsoon, post-monsoon). Taxonomic account revealed a total no of 175, 65, and 101 phytoplankton species in the estuary, lagoon, and coastal waters, respectively. Prevalence of marine, brackish, and fresh water types in the coastal waters, lagoon, and estuary, respectively, characterized the contrasting nature of the study regions in hosting the phytoplankton community. In general, phytoplankton abundance was observed in increasing order of coastal waters > estuary > lagoon during post-monsoon and pre-monsoon, while lagoon > coastal waters > estuary during monsoon. Bacillariophyta dominated the phytoplankton community in the estuary and coastal waters during all the seasons. In contrast, the lagoon exhibited a diverse array of phytoplankton group such as cyanophyta, dinophyta, and bacillariophyta during monsoon, post-monsoon, and pre-monsoon, respectively. Over the seasons, microphytoplankton emerged as the dominant phytoplankton size class in the coastal waters. Diversely, nanophytoplankton contributed to major fraction of chlorophyll-a concentration in the estuary and lagoon. Interestingly, pre-monsoon dinophyta bloom (causative species: Noctiluca scintillans with cell density 9 × 104 cells·l−1) and monsoon bacillariophyta bloom (causative species: Asterionellopsis glacialis 5.02 × 104 cells·l−1) resulted decline in species diversity. Multivariate statistical analysis deciphered salinity as a major environmental player in determining the distribution, diversity, and composition of phytoplankton communities in the three contrasting environments. Trophic state indices signified the lagoon and estuary as hypereutrophic during all season. The coastal water was marked as highly eutrophic through trophic state index during monsoon and pre-monsoo
Role of lunar phases, rainfall, and wind in predicting Hilsa shad (Tenualosa ilisha) catch in the northern Bay of Bengal
No full textHilsa (Tenualosa ilisha) is an important commercial fish in India. This study investigates relationships among Hilsa catch per unit effort (CPUE) and the corresponding lunar phase, rainfall variability, wind vector, and month in the northern Bay of Bengal. Hilsa catch during the monsoon season of three consecutive years (2013–2015) was analyzed by using a Generalized Least Square model with lunar phase and monsoon months (June–September) as categorical variables and wind direction as circular variable. Significantly higher Hilsa catch was observed during the waning crescent and waxing gibbous lunar phases and during easterly winds. There was no significant effect of wind velocity. Daily rainfall was significantly correlated with Hilsa migration toward the estuary. Among the four monsoon months, September exhibited the most positive significant correlation with the Hilsa CPUE. Model predicted CPUE underestimated the actual CPUE in 2016 by 20
On the future of Argo: A global, full-depth, multi-disciplinary array
Full text linkThe Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo's global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities
On the relationship between the Indian summer monsoon rainfall and the EQUINOO in the CFSv2
No full textSeveral recent studies have shown that positive (negative) phase of Equatorial Indian Ocean Oscillation (EQUINOO) is favourable (unfavourable) to the Indian summer monsoon. However, many ocean–atmosphere global coupled models, including the state-of-the-art Climate Forecast System (CFS) version 2 have difficulty in reproducing this link realistically. In this study, we analyze the retrospective forecasts by the CFS model for the period 1982–2010 with an objective to identify the reasons behind the failure of the model to simulate the observed links between Indian summer monsoon and EQUINOO. It is found that, in the model hindcasts, the rainfall in the core monsoon region was mainly due to westward propagating synoptic scale systems, that originated from the vicinity of the tropical convergence zone (TCZ). Our analysis shows that unlike in observations, in the CFS, majority of positive (negative) EQUINOO events are associated with El Niño (La Niña) events in the Pacific. In addition to this, there is a strong link between EQUINOO and Indian Ocean Dipole (IOD) in the model. We show that, during the negative phase of EQUINOO/IOD, northward propagating TCZs remained stationary over the Bay of Bengal for longer period compared to the positive phase of EQUINOO/IOD. As a result, compared to the positive phase of EQUINOO/IOD, during a negative phase of EQUINOO/IOD, more westward propagating synoptic scale systems originated from the vicinity of TCZ and moved on to the core monsoon region, which resulted in higher rainfall over this region in the CFS. We further show that frequent, though short-lived, westward propagating systems, generated near the vicinity of TCZ over the Bay moved onto the mainland were responsible for less number of break monsoon spells during the negative phase of EQUINOO/IOD in the model hindcasts. This study underlines the necessity for improving the skill of the coupled models, particularly CFS model, to simulate the links between EQUINOO/IOD and the Indian summer monsoon for reliable predictions of seasonal and intraseasonal variation of Indian summer monsoon rainfall
Assessment of Tsunami Preparedness in East Coast of India through Mega Mock Tsunami Drill conducted on 24 November 2017
Full text linkThough 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
A Report on implementation of operational Global and Indian Ocean HYCOM at INCOIS
Full text linkA state of the art operational forecasting system with data assimilation (DA) is established at INCOIS, which is the first of it's kind in the country. The Indian Ocean model is the highest resolution operational system with DA available for the basin compared to any operational agency in the world. The core of the system is a 1/16th eddy resolving Indian ocean Hybrid Coordinate Model (HYCOM), nested to a 1/4th Global HYCOM which provides lateral boundary conditions to the high-resolution model. The system uses data assimilation scheme based on Tentral Statistical Interpolation (T-SIS) scheme. A five-year hindcast for the period 2012 to 2016 has been carried out
using both setups. This report presents a detailed evaluation of both global and Indian ocean models
in comparison with observations and two other established systems, NRL HYCOM and GODAS from INCOIS. The five-year hindcast results show that both Indian Ocean and global model simulated SST, SSS, SLA, currents and vertical structure of the ocean favourably when compared with observations and other models. Bias, RMSD, correlation and skill score compared to observations from each of the four models for selected parameters are evaluated as part of this exercise. Sea-level and currents, show a notable better performance for the new setups at INCOIS over NRL-HYCOM and INCOIS-GODA
LETKF-ROMS: An improved predictability system for the Indian Ocean
Full text linkWe have developed the assimilation scheme Local Ensemble Transform Kalman Filter (LETKF) and interfaced with the present basin-wide operational ROMS set-up ( 1/12 degree horizontal resolution ) that assimilates in-situ temperature and salinity from RAMA moorings, NIOT buoys and Argo floats. The system also assimilate satellite track data of sea-surface temperature from AMSR-E. The speciality of this assimilation system is that it comprises of ensembles that are initialized with different model coefficients like diffusion parameters and the ensemble members also respond to two different mixing schemes - K profile parameterization and
Mellor-Yamada. This aids in maintaining the spread of the ensemble intact - which has always been a challenging task. We have also employed a localization radius of
~200 km, i.e., observations influence the prognostic state variables that fall within this range. The assimilation system is also bestowed with better representative error estimates - a method developed in-house along the likes of Etherton et al. The ensemble members were forced with ensemble atmospheric fluxes provided by National Centre for Medium Range Weather Forecast (NCMRWF). Assimilation was performed every five day. We show that the assimilated system simulates the ocean state better than the present operational basin-wide ROMS. We validate it extensively against multiple observations ranging from RAMA moorings to ADCP observations across both dependent variables like temperature and salinity and independent variables like sealevel anomaly and currents. We show that assimilation improves the overall ocean state except at few isolated locations. It improves the correlation with respect to
observations and reduces the root-mean-squared error. We also show that assimilation improves the estimation of mixed layer depth and 20 degree isotherm (which are diagnostic variables) thereby proving that the subsurface conditions are better simulated