• A Madhulatha

      Articles written in Journal of Earth System Science

    • All-sky radiance simulation of Megha-Tropiques SAPHIR microwave sensor using multiple scattering radiative transfer model for data assimilation applications

      A Madhulatha John P George E N Rajagopal

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      Incorporation of cloud- and precipitation-affected radiances from microwave satellite sensors in data assimilation system has a great potential in improving the accuracy of numerical model forecasts over the regions of high impact weather. By employing the multiple scattering radiative transfer model RTTOVSCATT,all-sky radiance (clear sky and cloudy sky) simulation has been performed for six channel microwave SAPHIR (Sounder for Atmospheric Profiling of Humidity in the Inter-tropics by Radiometry) sensors of Megha-Tropiques (MT) satellite. To investigate the importance of cloud-affected radiance data in severe weather conditions, all-sky radiance simulation is carried out for the severe cyclonic storm

      ‘Hudhud’ formed over Bay of Bengal. Hydrometeors from NCMRWF unified model (NCUM) forecasts are used as input to the RTTOV model to simulate cloud-affected SAPHIR radiances. Horizontal and vertical distribution of all-sky simulated radiances agrees reasonably well with the SAPHIR observed radiancesover cloudy regions during different stages of cyclone development. Simulated brightness temperatures of six SAPHIR channels indicate that the three dimensional humidity structure of tropical cyclone is well represented in all-sky computations. Improved correlation and reduced bias and root mean squareerror against SAPHIR observations are apparent. Probability distribution functions reveal that all-sky simulations are able to produce the cloud-affected lower brightness temperatures associated with cloudy regions. The density scatter plots infer that all-sky radiances are more consistent with observed radiances.Correlation between different types of hydrometeors and simulated brightness temperatures at respective atmospheric levels highlights the significance of inclusion of scattering effects from different hydrometeors in simulating the cloud-affected radiances in all-sky simulations. The results are promisingand suggest that the inclusion of multiple scattering radiative transfer models into data assimilation system can simulate the cloud-affected microwave radiance data which provide detailed information on three dimensional humidity structure of the atmosphere in the presence of cloud hydrometeors.

    • Observational aspects of tropical mesoscale convective systems over southeast India


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      To enhance the knowledge of various physical mechanisms related to the evolution of Tropical Mesoscale Convective Systems (MCSs), detailed analysis has been performed using suite of observations (weather radar, electric field mill, surface weather station, flux tower, microwave radiometer and wind profilers) available at Gadanki ($13.5^{0}\rm{N}/79.2^{0}\rm{E}$), located over southeast India. Analysis suggests that these systems developed in warm, moist environment associated with large scale low level convergence. Significant variations in cloud to ground (CG) lightning activity indicate the storm electrification. Deep (shallow) vertical extents with high (low) reflectivity and cloud liquid water; dominant upward (downward) motionreveals variant distribution in convective (stratiform) portions. Existence of both +CG and –CG Cashes in convective regions, dominant –CG in stratiform regions explains the relation between lightning polarity and rain and cloud type. Sharp changes in surface meteorological variables and variations in surface fluxes are noticed in connection to cold pool of the system. Increase (decrease) in temperature, moisture and equivalent potential temperature ($\theta$e) within the boundary layer in convective (stratiform) regions associated with latent heat warming (cooling) of air parcel are apparent. Presence of updrafts and downdrafts in convective region and dominant downdrafts in stratiform regions are evident from vertical velocity measurements. Isentropic upgliding (downgliding) illustrate the existence of isentropic ascents (descent) of air parcels in the storm vicinity. Veering (backing) of wind due to warm (cold) and moist (dry) air advections demonstrated the formation of $\theta$e ridge in storm environment. Blend of observations provided considerable insight of electrical, microphysical, thermodynamic, dynamic and kinematic features of MCS.

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