Wave prediction and hindcast studies are important in ocean engineering, coastal infrastructure development and management. In view of sparse and infrequent in-situ observations, model derived hindcast wave data can be used for the assessment of wave climate in offshore and coastal areas. In the present study, MIKE 21 SW Model has been used to carry out wave hindcast experiments in the Indian Ocean. Model runs have been made for the year 2005 using QuickSCAT scatterometer winds blended with ECMWF model winds. In order to study the impact of southern ocean swells, the model has been run in two different domains, with the southern boundary being shifted far south for the Domain 60S model. The model simulated wave parameters have been validated by comparing with buoy and altimeter data and various statistical yardsticks have been employed to quantify the validation. Possible reason for the poorer performance of the model in the Arabian Sea has also been pointed out.
Abstract:The India-France SARAL/AltiKa mission is the first Ka-band altimetric mission dedicated primarily to oceanography. The mission objectives were firstly the observation of the oceanic mesoscales but also global and regional sea level monitoring, including the coastal zone, data assimilation, and operational oceanography. SARAL/AltiKa proved also to be a great opportunity for inland waters applications, for observing ice sheet or icebergs, as well as for geodetic investigations. The mission ended its nominal phase after three years in orbit and began a new phase (drifting orbit) in July 2016. The objective of this paper is to highlight some of the most remarkable achievements of the SARAL/AltiKa mission in terms of scientific applications. Compared to the standard Ku-band altimetry measurements, the Ka-band provides substantial improvements in terms of spatial resolution and data accuracy. We show here that this leads to remarkable advances in terms of observation of the mesoscale and coastal ocean, waves, river water levels, ice sheets, icebergs, fine scale bathymetry features as well as for the many related applications.
The study has been motivated by the desire to assess the performance of sea surface salinity (SSS) from the Soil Moisture and Ocean Salinity (SMOS) satellite launched by the European Space Agency. Daily Level 3 product on a 0.25 • × 0.25 • grid for the year 2010 has been used for this assessment in the Indian Ocean. Various data sets, like the in situ data sets available from the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoys and Argo floats and also the data sets from modular ocean model version 3 simulations, have been utilized for this purpose. Comparison made at two buoy locations suggests good quality of SMOS SSS with root-mean-square error of the order of 0.36 and 0.34 psu. The triple collocation method, which explicitly takes into account the error characteristics of the SMOS, Argo, and model data sets, has been used for further validation of the SMOS data. Since the Indian Ocean exhibits characteristically different patterns of SSS in its different subregions, the study area has been divided into different such subregions. The SMOS-derived SSS appears to be of very good quality in the equatorial Indian Ocean and southern Indian Ocean, while the data are of poorer quality in the Arabian Sea and the Bay of Bengal possibly because of the errors in SSS retrieval due to the land contamination and strong winds. Index Terms-Argo floats, functional relationship (FR), modular ocean model (MOM) version 3 (MOM3) ocean model, Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoys, Soil Moisture and Ocean Salinity (SMOS) salinity, triple collocation.
Dust storm, a natural hazard, has a direct impact on daily life for a short period. Dust storms are periodic events over India, especially in northern regions. This study has been carried out to investigate the dust impacts on the aerosol characteristics over Dehradun (DDN) during pre-monsoon (March-June), 2012 using ground measurements, satellite observations and model simulations. The measurements illustrate the distinct monthly impact on the aerosol properties with maximum dust loading during May (aerosol optical depth at 500 nm (AOD 500 ) = 0.72 ± 0.18) over DDN, which is confirmed with the Terra-MODIS (AOD 550 = 0.70 ± 0.19) measurements. The major dust loading was recorded in aerosol measurements during May at the station, which permitting to examine the influence of dust transports on the aerosol characteristics. Spectral variation of AOD and Angstrom exponent (α) values displayed day to day variation of aerosol during dust episodes. Analysis of aerosol types and seven-day back-trajectories reveal the transportation of desert dust during May over DDN. The Optical Properties of Aerosols and Clouds (OPAC) model was used to compute the aerosol optical properties (e.g., Single scattering albedo (SSA) and asymmetry parameter (g)) and size distribution. The high values of SSA and g are indicating the dust loading in the atmosphere during May. Aerosol volume concentration at the coarse mode (geometric mean radii (R V ) = 2.89 ± 0.027 µm) is found to be increased in the May, whereas decrement has been observed in the finer mode (R V = 0.16 ± 0.006 µm). The aerosol direct radiative forcing (ARF) was computed using Santa Barbara Discrete Ordinate Atmospheric Radiative Transfer (SBDART) model in the shortwave (SW) region (0.25-4.00 µm). The mean top of the atmosphere (TOA) and surface forcing come out to be -14.
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