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Sarma A.C.,Patkai Christian College | Deshamukhya A.,Assam University | Narayana Rao T.,Clouds and Convective Systems Group | Sharma S.,Kohima Science College
Meteorological Applications | Year: 2016

A study was carried out to investigate the rain drop size distribution (DSD) characteristics during strong bright band (SBB), weak bright band (WBB) and no bright band (NBB) regimes of stratiform rain by using an L-band wind profiler and Joss-Waldvogel disdrometer at Gadanki (13.5°N, 79.20°E), a tropical station in India. The stratiform events with SBB (bright band width >0.49 km) are associated with larger mean drops (Dm) at ground level compared with WBB and NBB situations. Different shapes of raindrop DSDs during these three situations suggest different microphysical processes involved in the evolution of rain DSDs. During SBB regimes, the raindrop spectrum, which is found to be governed predominantly by an aggregation process, is size controlled. On the other hand, during WBB regimes, the raindrop spectrum, which is found to be governed predominantly by a riming process, is number controlled. A new rain DSD parameterization scheme, P (Z, N0 *), is proposed in the framework of multi-parameter radar observation. The considered parameters are radar reflectivity factor (Z) and normalized scale parameter (N0 *). These two parameters are found to be mutually independent. Reasonable improvement in the estimation of rain intensity is observed by the developed P(Z, N0 *) scheme compared with P(Z) and P(Z, Dm). The rain DSDs simulated by the developed P(Z, N0 *) scheme are in good agreement with the observed spectrum. © 2016 Royal Meteorological Society.

Madala S.,Indian Institute of Technology Kharagpur | Satyanarayana A.N.V.,Indian Institute of Technology Kharagpur | Rao T.N.,Clouds and Convective Systems Group
Atmospheric Research | Year: 2014

In the present study, an attempt has been made to simulate three severe thunderstorm events that occurred over Gadanki (13.5° N, 79.2° E) region of the Mesosphere-Stratosphere-Troposphere (MST) Radar facility using Weather Research Forecasting (WRF ARW version 3.2) model. We examined the performance of five planetary boundary layer (PBL) parameterization schemes namely, the Yonsei University (YSU), Mellor-Yamada-Janjic (MYJ), Mellor-Yamada Nakanishi and Niino Level 2.5 PBL (MYNN2), and Medium-Range Forecast (MRF) and Asymmetric Convective Model version 2 (ACM2) and three cumulus parameterization schemes Kain-Fritisch (KF), Betts-Miller-Janjic (BMJ) and Grell-Devenyi ensemble scheme (GD) in simulating boundary layer parameters, thermodynamic structure and vertical velocity profiles on the days of the thunderstorm events. Triple nested domain having the inner-most domain of 3. km grid resolution over the study area is considered. The model simulated parameters are validated with the available in situ meteorological observations obtained from micro-meteorological tower, radiosonde, MST radar wind profiler and observed rainfall along with the surface fluxes at Gadanki. After validating the model simulations with the available PBL observations and the statistical assessment reveal that the MYJ scheme could be able to capture the characteristic variations of surface meteorological variables such as air temperature, relative humidity, wind component, vertical profiles of wind, relative humidity and equivalent potential temperature and surface layer fluxes during the study period. Cores of strong convective updrafts with a time lag and lead of one and half hour are better represented by the model with MYJ scheme with GD as seen in the vertical velocity profiles obtained from MST radar observations. The present study advocates that the MYJ-GD combination is suitable for the simulation of thunderstorm events over the study region. © 2014 Elsevier B.V.

Satyanarayana A.N.V.,Indian Institute of Technology Kharagpur | Sultana S.,Indian Institute of Technology Kharagpur | Narayana Rao T.,Clouds and Convective Systems Group | Satheesh Kumar S.,Clouds and Convective Systems Group
Atmospheric Research | Year: 2014

Mesoscale convective systems (MCSs) wreak lots of havoc and severe damage to life and property due to associated strong gusty winds, rainfall and hailstorms even though they last for an hour or so. Planetary boundary layer (PBL) plays an important role in the transportation of energy such as momentum, heat and moisture through turbulence into the upper layers of the atmosphere and acts as a feedback mechanism in the generation and sustenance of MCS. In the present study, three severe thunderstorms that occurred over mesosphere-stratosphere-troposphere (MST) radar facility at National Atmospheric Research Laboratory (NARL), Gadanki, India, have been considered to understand turbulence, energy exchanges and wind structure during the different epochs such as pre-, during and after the occurrence of these convective episodes. Significant changes in the turbulence structure are noticed in the upper layers of the atmosphere during the thunderstorm activity. Identified strong convective cores with varying magnitudes of intensity in terms of vertical velocity at different heights in the atmosphere discern the presence of shallow as well as deep convection during initial, mature and dissipative stages of the thunderstorm. Qualitative assessments of these convective cores are verified using available Doppler Weather Radar imageries in terms of reflectivity. The MST radar derived horizontal wind profiles are in good comparison with observed radiosonde winds. Significant variations in the surface meteorological parameters, sensible heat flux and turbulent kinetic energy as well as horizontal wind profiles are noticed during the different epochs of the convective activity. This work is useful in evaluating the performance of PBL schemes of mesoscale models in simulating MCS. © 2014 Elsevier B.V.

Sandeep A.,Clouds and Convective Systems Group | Rao T.N.,Clouds and Convective Systems Group | Ramkiran C.N.,Sri Venkateswara University | Rao S.V.B.,Sri Venkateswara University
Boundary-Layer Meteorology | Year: 2014

The differences and similarities in atmospheric boundary-layer (ABL) characteristics, in particular the ABL height, evolution and wind field, between two contrasting episodes of the Indian summer monsoon have been studied using measurements from wind profilers and an instrumented 50-m tower at Gadanki in India. The observed differences are discussed in light of various forcing mechanisms, in particular the effect of soil moisture on the surface energy balance and ABL. The differences in ABL height, its evolution and the wind field between episodes are quite pronounced. Wet episodes not only have a shallower ABL but also the growth is delayed by 1–4 h when compared with that for dry episodes. Abundant soil moisture during the wet episodes (a factor of two greater than during the dry episodes) reduces the buoyancy flux, and thereby not only limits the ABL height but also delays the commencement of ABL growth. The low-level jet (LLJ) is stronger during the dry episodes and has a larger diurnal range than during the wet episodes. The highest occurrence and magnitude of LLJ apparent at a height of 1.5 km during early morning hours shift progressively with height and time till the afternoon, following ABL evolution. The weaker LLJ during the wet episodes is attributed to its southward migration from its mean position (15°N). Larger signal-to-noise ratio and spectral width values are observed during the early night to midnight, compared to noon-time, when the ABL is buoyantly turbulent. © 2014, Springer Science+Business Media Dordrecht.

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