• V Gopalakrishnan

      Articles written in Journal of Earth System Science

    • Airborne measurements of submicron aerosols across the coastline at Bhubaneswar during ICARB

      P Murugavel V Gopalakrishnan Vimlesh Pant A K Kamra

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      Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20° 25′N, 85° 83′E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) programme conducted in March–April 2006. The measurements made during the constant-level flights at 0.5, 1, 2 and 3 km altitude levels extend ∼100 km over land and ∼150km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm-3 at 0.5 km level but are almost constant at ∼6000 cm-3 and ∼800 cm-3 at 2 and 3 km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm-3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110nm diameter which shifts to 70 nm diameter at 2 and 3 km levels. However, at the peak at 1 km level, number concentration has a bimodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new particles from coastal regions.

    • Anomalous electric field changes and high flash rate beneath a thunderstorm in northeast India

      S D Pawar P Murugavel V Gopalakrishnan

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      In spite of many experimental and theoretical studies the relationships between storm dynamics, severe weather,and lightning activity have been least understood.Measurements of electric field made under a severe thunderstorm at a northeastern Indian station,Guwahati,India are reported. Lightning flash rate increases drastically to about 84 flashes per minute (fpm)during the active stage which lasted for about 7 minutes,from about 15 flashes per minute during the initial phase of thunderstorm.Sudden increase in lightning flash rate (‘lightning jump ’)of about 65 fpm/min is also observed in the beginning of the active stage.The dissipating stage is marked by slow and steady decrease in lightning frequency.Despite very high flash rate during the active stage, no severe weather conditions are observed at the ground.It is proposed that the short duration of the active stage might be the reason for the non-observance of severe weather conditions at the ground.Analysis of Skew-t graph at Guwahati suggests that vertical distribution of Convective Available Potential Energy (CAPE)also may play some role in non-occurrence of severe weather at ground in spite of large lightning flash rate and lightning jump observed in this thunderstorm.Further,all electric field changes after a lightning discharge indicates the presence of strong Lower Positive Charge Centers (LPCC)in the active and dissipation stages. This suggests that LPCC plays an important role in initiation of lightning discharges in these stages.

    • New particle formation by ion-induced nucleation during dissipation stage of thunderstorm

      S D Pawar P Murugavel V Gopalakrishnan

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      A case of new particle formation observed during dissipation stage of a thunderstorm at a tropical station, Pune, India on 3 June 2008 is reported. The flash rate and rainfall intensity increased as high as 110 flashes per 5 minutes and 150 mm hour−1 respectively during the active stage of thunderstorm, and then gradually decreased during the dissipation stage. The number concentration of particles in the size range of 10–100 nm sharply increased from 350 particles cm-3 to ∼8000 particles cm-3 during the dissipation stage of a thunderstorm and grew to larger diameter subsequently. Observations suggest that the atmospheric conditions such as (i) reduced background aerosol concentration after heavy rain, (ii) high humidity condition, and (iii) increased ion concentration during the dissipation stage by corona discharges, favoured generation of new particles by ion-induced nucleation (IIN). Observations also suggest that generation of unipolar ions by corona discharges may be more favourable for IIN and subsequent growth of the particles.

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