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Observational Aspects of Tropical Mesoscale Convective Systems Over Southeast India

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J. Earth Syst. Sci. (2020) 129 65 Ó Indian Academy of Sciences https://doi.org/10.1007/s12040-019-1300-9 (0123456789().,-volV)(0123456789().,-volV) Observational aspects of tropical mesoscale convective systems over southeast India 1,5, 2 3 4 AMADHULATHA * ,MRAJEEVAN ,TSMOHAN and S B THAMPI 1 National Atmospheric Research Laboratory, Gadanki 517 502, India. 2 Ministry of Earth Sciences, New Delhi, India. 3 Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates. 4 Doppler Weather Radar Division, India Meteorological Department, Chennai, India. 5 Present address: Korea Institute of Atmospheric Prediction Systems, Seoul, South Korea. *Corresponding author. e-mail: [email protected] MS received 17 April 2019; revised 31 August 2019; accepted 16 September 2019 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 Beld mill, surface weather station, Cux tower, microwave radiometer and wind proBlers) available at Gadanki (13.5°N/79.2°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 electriBcation. Deep (shallow) vertical extents with high (low) reCectivity and cloud liquid water; dominant upward (downward) motion reveals 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 Cuxes are noticed in connection to cold pool of the system. Increase (decrease) in temperature, moisture and equivalent potential temperature (he) 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 he ridge in storm environment. Blend of observations provided considerable insight of electrical, microphysical, thermodynamic, dynamic and kinematic fea- tures of MCS. Keywords. Mesoscale convective systems; cloud to ground lightning; isentropic sloping; wind proBler; microwave radiometer; doppler weather radar. 1. Introduction ensemble of thunderstorms that produces a con- tiguous precipitation area of around 100 km or Mesoscale convective systems (MCSs) are impor- more in at least one direction (Houze 2004). These tant links between convection and the large scale systems are characterized by regions of both con- atmospheric circulation. MCS is deBned as an vective and stratiform regions of precipitation. 65 Page 2 of 26 J. Earth Syst. Sci. (2020) 129 65 Long-lasting, slow moving MCSs are major cause various observations to characterize these convec- of Cooding, and these systems often contain hail, tive systems (Wang 2004; Parker and Johnson strong winds, and lightning. Cloud to ground (CG) 2004; Kim and Lee 2006; Ramis 2009; DeLonge lightning associated with these systems can cause et al. 2010; Lagouvardos et al. 2013; Helms and serious hazards to aviation and satellite launch Harts 2015; Zhong et al. 2015). Key factors operations. Understanding and predicting these responsible for the formation of MCS around dif- severe convective systems is therefore of great ferent parts of the globe include synoptic scale socio-economic significance. Formation, intensiB- forcing mechanisms, topography, diurnal cycle of cation and propagation of MCS are mostly gov- insolation and strong low level temperature and erned by synoptic and mesoscale conditions of the moisture advections (Mapes et al. 2003; Moore atmosphere (Johns and Doswell 1992). Important et al. 2003; Rasmussen and Houze 2011; Wapler factors responsible for the formation of these sys- and James 2015). Houze (1982) established that tems include moisture supply, static stability, the life cycle of tropical MCS is characterized by vertical motion and orographic eAects (Doswell convective towers in growth phase; convective and et al. 1996, 1998). Better understanding of these stratiform regions in mature phase and dominant factors is important for improved weather fore- stratiform regions in decay phase. Furthermore, casting of these severe convective systems (Weck- the updrafts and downdrafts during different pha- werth et al. 2008). Further, to investigate various ses of convective system and the role of mesoscale mechanisms related to genesis of MCSs resulting downdrafts in the generation of convective from thermal and moisture advections, high reso- updrafts along the gust front and its eAect on lution observations are necessary. longevity of MCS are well demonstrated by Rut- During the last few decades, considerable ledge et al. (1988). The conceptual model designed attention has been given to MCS by conducting for tropical cloud clusters can be applied to mid- various Beld campaigns, satellite measurements, latitude convective systems; however, the systems and high resolution numerical simulations and by vary in the horizontal arrangement of the convec- developing theoretical models. Role of observations tive and stratiform precipitation (Houze 1989). and modeling eAorts to understand and predict Kinematic structure of several tropical and mid- storm initiation, evolution, dynamics and scale latitude MCS using wind proBler observations interactions associated with the MCSs are dis- explained the dominant updraft (downdraft) cores cussed in review papers by Wilson et al. (1998), in the convective (stratiform) regions (Cifelli and Houze (2004), and MoncrieA (2010). Considerable Rutledge 1998; Giangrande et al. 2013). Electrical insight into the evolution of tropical MCS has been structure from electric Beld mill observations gained from various Beld experiments such as reported dominant negative (positive) CG light- GATE (Global Atmospheric Research Program ning Cashes in convective (stratiform) components (GARP) Atlantic Tropical Experiment) (Houze of mid-latitude and tropical MCSs (Rutledge and and Betts 1981), TOGA/COARE (Tropical MacGorman 1988; Lang et al. 2004). Environ- Ocean-Global Atmosphere/Coupled Ocean-Atmo- mental characteristics using radiosonde observa- sphere Response Experiment) (Jorgensen et al. tions revealed that the organization and 1997), International H2O Project (IHOP˙2002) development of tropical (Halverson et al. 2002) and (Marsham et al. 2011), African Monsoon Mul- warm season mid-latitude MCS (Moore et al. 2003) tidisciplinary Analyses (AMMA) (Guy et al. 2011), are aided by moderate to large Convective Avail- Dynamics of the Madden–Jullian Oscillation able Potential Energy (CAPE), small Convective (MJO)/Atmospheric Radiation Measurement Inhibition (CIN) and moderate unidirectional low (ARM) MJO Investigation Experiment level wind shear. Significant variations in surface (DYNAMO/AMIE) (Zuluaga and Houze 2013); meteorological features are evident with the pas- (CINDY/DYNAMO) (Zhang and Yoneyama sage of gust front in the environment of tropical 2017), Tropical Warm Pool International Cloud and mid-latitude MCSs (Houze 1979; Johnson and Experiment (TWP-ICE)(Collis et al. 2013) and Hamilton 1988). And also, enhancement in sensible Large Scale Biosphere-Atmosphere (LBA) experi- and latent heat Cuxes associated with higher sur- ment (Laurent et al. 2002). face winds behind the leading edge of tropical MCS Other than campaign-based experiments, environment are reported by Johnson and Nicholls numerous diagnostic studies also been performed (1983). Furthermore, the thermodynamic structure over different parts of the world by making use of of troposphere using continuous observations from J. Earth Syst. Sci. (2020) 129 65 Page 3 of 26 65 Microwave Radiometer (MWR) has provided the experimental data various observational and information of mesoscale phenomena over different numerical studies are carried out to understand regions in greater detail (Chan and Hon 2011; basic characteristics of MCSs over northeast India Cimini et al. 2011; Madhulatha et al. 2013; Ware (Abhilash et al. 2007, 2010; Joseph 2009; Litta et al. 2013). Using simultaneous wind proBler and et al. 2012). For example, based on electric Beld radiometer observations, wind gusts associated measurements, it is inferred that most systems in with intense convective weather are also studied this region are associated with positive-dipole type (Chan and Wong 2008). Research from many charge structure (Gopalakrishnan et al. 2011). investigators emphasized the role of different Similarly, Cux tower measurements reported the observations in explaining various MCS features variations in surface sensible and latent heat Cuxes over different parts of globe. due to changes in surface temperature and mois- On the other hand, in India, diagnostic studies ture in the storm environment (Tyagi et al. 2012). have been carried out using individual observations Further, radiosonde observations have showed the to understand the tropical convective systems.
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