• M N Patil

      Articles written in Journal of Earth System Science

    • A study of turbulent characteristics of atmospheric boundary layer over monsoon trough region using Kytoon and Doppler sodar

      K G Vernekar M N Patil B S Murthy

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      As a part of the MONTBLEX-90 observational programme, Kytoon and Doppler sodar observations were taken at Kharagpur. These data are analysed to study the turbulent characteristics of the atmospheric boundary layer in terms of stability, temperature structure function (CT2) and velocity structure function (Cv2).CT2follows aZ−4/3 law on most of the days, whereas the variation ofCV2is not systematic.CV2andCT2values are found to vary between 10−5−10−1 m4/3s−2 and 10−5−10−2°C2 m−2/3 respectively.

    • Fluxes of heat and momentum over sea surface during the passage of a depression in the north Bay of Bengal

      S Sivaramakrishnan M N Patil K G Vernekar

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      Time variation of surface fluxes of heat, moisture and momentum over a sea station (20°N 89°E) in the north Bay of Bengal has been computed by profile method for the period 18th–25th August 1990 using meteorological data of MONTBLEX-90 from ORVSagarkanya. The fluxes showed synoptic and diurnal variations which are marked during depression (20th–21st August) compared to their variation prior to and after this period. Variations of heat and water vapour fluxes were in phase. Night time fluxes are relatively high compared to day time. Average momentum transfer during depression was two to three times large. Variations in Bowen ratio were relatively large during day time. During depression, it varied between 0·2 in day time and about 0·3 at night and in the undisturbed period between −0·1 and 0·2 during day time and 0·2 and 0·25 at night. The study shows that the assumptionCD=CH=CE of the exchange coefficients normally used in estimating the fluxes by the bulk aerodynamic method is not appropriate becauseCH/CD≈2,CE/CD≈1·5 andCH/CE≈1·4.

    • 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

      M N PATIL T DHARMARAJ R T WAGHMARE SURENDER SINGH PRAKASH PITHANI RACHANA KULKARNI NARENDRA DHANGAR DEVENDRAA SIINGH G R CHINTHALU RAJ SINGH SACHIN GHUDE

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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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