[1] High resolution observations of atmospheric and oceanic variables are carried out at northern Bay of Bengal from 22nd July to 6th August 2009 on-board ORV Sagar kanya under the Continental Tropical Convergence Zone research/observational programme. Freshening of surface layer by more than 4 psu within 24 hours is observed, which is followed by warming in the surface layer temperature. The heat and salt budget analysis primarily indicates dominant role of advection processes on the evolution of temperature and salinity. The amount of rainfall received at observation site could not explain the observed freshening, thus an extensive analysis using wavelet coherence is done to find out the source of advected fresh water to the observed location. It is found that surface salinity in the northern Bay of Bengal (at 15°N) varies coherently with the rainfall over Ganga-Brahmaputra catchment area on intraseasonal time scale and with lag of about 60 days. Based on above observations, this study hypothesize that the intraseasonal rainfall variation modulates the amount of river discharge, which in turn modulates the salinity over northern Bay of Bengal on intraseasonal time scale. Since surface warming always follows the surface freshening, the time delay between the rainfall over catchment area and freshening at northern Bay of Bengal may explain the post monsoon warming. Importance of atmosphere-ocean coupling in driving the dynamics of the northern bay of Bengal has been clearly brought out in this study.
Abstract. Sea breeze initiated convection and precipitation is investigated along the east coast of India during the Indian southwest monsoon season. The sea breeze circulations are observed approximately 70 to 80% of the days during the summer months (June to August) along the Chennai coast. Observations of average sea breeze wind speeds are stronger at a rural location as compared to the wind speeds observed inside the urban region of Chennai.The sea breeze circulation is shown to be the dominant mechanism for initiating rainfall during the Indian southwest monsoon season. Roughly 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to the convection initiated by sea breeze circulation.
Sedimentation studies have been carried out to optimize the dispersion conditions of aqueous alumina nanopowder suspensions with or without dispersants (ammonium salt of polymethacrylic acid or rhamnolipids at 15%). Different dispersant dosages, solid loadings, pulp densities and pH values were examined. The iso-electric point (IEP) of the alumina nanopowder was found to be pHiep= 9.2. The experiments revealed that the polymethacrylic acid was more effective as dispersant than rhamnolipids in a wide range of pH at all solid-loading conditions tested. Optimum dispersant dosages for polymethacrylic acid and rhamnolipids to achieve maximum stability of alumina nanodispersion at iso-electric point were found to be 9.25 mg/g and 57.75 mg/g solids, respectively.
Doppler radar derived wind speed and direction profiles showed a well developed sea breeze circulation over the Chennai, India region on 28 June, 2003. Rainfall totals in excess of 100 mm resulted from convection along the sea breeze front. Inland propagation of the sea breeze front was observed in radar reflectivity imagery. High-resolution MM5 simulations were used to investigate the influence of Chennai urban land use on sea breeze initiated convection and precipitation. A comparison of observed and simulated 10 m wind speed and direction over Chennai showed that the model was able to simulate the timing and strength of the sea breeze. Urban effects are shown to increase the near surface air temperature over Chennai by 3.0 K during the early morning hours. The larger surface temperature gradient along the coast due to urban effects increased onshore flow by 4.0 m s −1 . Model sensitivity study revealed that precipitation totals were enhanced by 25 mm over a large region 150 km west of Chennai due to urban effects. Deficiency in model physics related to night-time forecasts are addressed.
Sea breeze, the onshore wind over a coastal belt during daytime, is a welcoming weather phenomenon as it modulates the weather condition by moderating the scorching temperature and acts as a favourable mechanism to trigger convection and induce precipitation over coastal and interior locations. Sea breeze aids dispersal of pollutants as well. Observational studies about its onset, depth of circulation and induced precipitation have been carried out in this paper for the period April to September, 2004-2005 using a S-band Doppler Weather Radar functioning at Cyclone Detection Radar Station, India Meteorological Department, Chennai, India. The onset of sea breeze has been observed to be between 0900 and 1000 UTC with the earliest onset at 0508 UTC and late onset at 1138 UTC. The frequency is greater during the southwest monsoon season, viz., June -September and the frequency of initial onset is greater in north Chennai. The modal length of sea breeze is between 20 and 50 km with extreme length as high as 100 km also having been observed. Though the inland penetration is on average 10 to 20 km, penetration reaching 100 km was also observed on a number of cases. The induced convection could be seen in the range 50-100 km in more than 53% of the cases. The mean depth of sea breeze circulation is 300-600 m but may go well beyond 1000 m on conducive atmospheric conditions.
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