• T Dharmaraj

      Articles written in Journal of Earth System Science

    • The influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

      M N Patil R T Waghmare T Dharmaraj G R Chinthalu Devendraa Siingh G S Meena

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      Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurementsof wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16◦44'N, 77◦59'E) in the south-west monsoon season. Using these observations, an attempt was made to investigatethe behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin–Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds greater than 4 m s−1; under stable regime for wind speeds less than 2 m s−1 and under neutral regime for wind speeds in the range of 2–3 m s$^{−1}$. All the three stability regimes were mixed for wind speeds 3–4 m s$^{−1}$. The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions.

    • Observations of carbon dioxide and turbulent Cuxes during fog conditions in north India


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      The occurrence of thick fog for longer duration in the northern regions of India disturbs the aviation, roadtransportation and other day to day activities. To understand the turbulence properties during fog period,we measured the atmospheric turbulent parameters along with carbon dioxide concentrations in theatmospheric boundary layer using eddy covariance system. These measurements were conducted over the agricultural station, Hisar, India, during the months of January–February of the year 2017 and 2018.During this period, total five thick fog events and three moderate fog events were captured. The turbulentparameter such as friction velocity, stability, sensible and latent heat fluxes are presented with respect tofog events. During the study period, the western disturbance persists over the north Pakistan andneighborhood region which advects the large amount of moisture into the lower troposphere and furtherthrough evaporation. It enforces stable and clear sky atmospheric conditions and reduces the surfacetemperature leading to the formation of strong surface-based temperature inversion which facilitatesthe fog formation in the study region. The land surface processes with neutral stability conditions in thesurface layer, play significant role to sustain fog in the study region. The observations show substantialincrease of carbon dioxide concentration during the thick fog events. The foggy days did not depict thediurnal pattern in flux of $\rm{CO}_{2}$. The anomalies of the meteorological parameters during foggy days and clear sky are analyzed. The foggy conditions (04:00–10:00 h, IST) are found to be characterized with low wind speed, high relative humidity with remarkable fluctuations in dew point temperature. Also, the sensible and latent heat flux shows remarkable changes during foggy and clear sky conditions.

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