S. B. Morwal

The Convective Boundary Layer over the Deccan Plateau, India during the summer monsoon

The thermodynamic structure of the Convective Boundary Layer (CBL) over the Deccan Plateau, India has been investigated using aerological data during the summer monsoon seasons of 1980 and 1981. Conserved-variable analysis and the saturation-point approach, which were used in this study, suggest that the top of the CBL varied between 700–600 mb during the monsoon. The air above the top of the CBL during a weak monsoon was estimated to have subsided for 4 days with a subsidence rate of 30 mb day-1.

A convectively-driven boundary layer in the monsoon trough

Characteristic features of the convectively driven monsoon-trough boundary layer have been explored using the conserved-variable method of analysis. Aerological observations during the Monsoon Trough Boundary Layer Experiment 1990 (MONTBLEX-90) during 18–20 August have been used to investigate the thermodynamic features of the Convective Boundary Layer (CBL). Thermodynamic parameters such asθe,θes have been used to study the dynamical aspects of the CBL. Also, mixed-layer heights at an inland station, in the monsoon trough region, obtained from SODAR, are used to document the saturation of the mixed layer after the onset of the monsoon.

Convective boundary layer in the region of the monsoon trough - a case study

A case study of the convectively driven monsoon boundary layer has been carried out using the acrological observations at four stations in the region of monsoon trough during Monsoon Trough Boundary Layer Experiment (MONTBLEX) 1988. The Convective Boundary Layer (CBL) in the region of monsoon trough did not show double mixing line structure. A single mixing line representing the CBL with different stabilities with respect to the convective activities was observed.

Thermodynamic structure of the atmospheric boundary layer over the Arabian sea as revealed by Monsoon-77 data

The thermodynamic structure of the Atmospheric Boundary Layer (ABL) over the Arabian sea region has been studied with the help of 135 aerological observations obtained during MONSOON-77 in the region (10–14° N, 64–68° E) by USSR research vessels. Low-level inversions were observed over the western Arabian sea region (west of 66° E) in association with suppressed convection. The different sublayers of the ABL, viz. the mixed layer, the cloud layer and the inversion/isothermal/stable layer were identified. The low-level stability analysis indicated that in the region east of 66° E, conditions were favourable for deep convection. The thermodynamic transformation of the boundary layer after precipitation was documented.

Variability of monsoon intracloud and intercloud microphysics over the Indian subcontinent

Intracloud/intercloud variability of microphysical quantities during different monsoon conditions has been studied for the first time over India using in situ observations of cloud microphysics collected during the Cloud-Aerosol Interaction and Precipitation Enhancement Experiment 2009. The observations for two inland locations (Hyderabad and Bareilly) for different phases of monsoon (preonset, onset, break, and active) have been used to investigate the entrainment and mixing processes which are defined with adiabatic fraction (ADFR)   ~ 0.59) with moderate concentration (  ~ 436 cm−3), an average re of 8 µm, and high value of factor k (0.774 ± 0.035). During break monsoon (Bareilly), clouds were diluted (  ≤ 0.2) having numerous (  > 1000 cm−3) smaller droplets (re ≤ 6 µm) and a low value of factor k (0.678 ± 0.064). The clouds had similar characteristics (  ~ 0.4 having lesser (  ~ 300 cm−3) droplets with re > 8 µm) over both stations during onset/active monsoon conditions. The investigation of the variability of intracloud and intercloud microphysics revealed positive correlation between factor k and N and no detectable correlation between factor k and N, respectively, and are sensitive to ADFR.

Unprecedented hailstorms over north peninsular India during February–March 2014

Unprecedented, widespread, and devastating hailstorms occurred during February and March 2014 over north peninsular India (study area). A diagnostic study has been carried out to understand the causes for the same. Over the study area the atmosphere was convectively unstable due to the incursion of warm and moist air from Bay of Bengal and Arabian Sea which was overlaid by cold and dry midlatitude westerlies caused due to the unusual upper oceanic heat content of the Pacific Ocean. At the surface and lower levels, anticyclonic flow over the central India produced easterly winds and cyclonic circulation over Arabian Sea at 850 hPa level produced westerly winds over the peninsular India. Meeting of these winds caused convergence of moist air in the lower levels. The troughs in the upper level westerlies provided the divergence in the upper levels. As a consequence of this convergence/divergence structure, synoptic-scale slow rising motion occurred over the study region. This released the convective instability to cause deep and wide convection with cloud bases at ~1500 m above mean sea level and tops well above the freezing level. Release of latent heat of deposition of water vapor provided extra buoyancy and produced strong updrafts causing explosive growth of the clouds reaching to very high levels and formation of large hails in the clouds. This atmospheric setup was a result of combined effect of planetary and synoptic forcings which persisted for ~3 weeks.

A Micro Rain Radar for Precipitation Characterization

Precipitation is the end product of many weather systems. A measurement of this quantity is needed not only for an understanding of atmospheric processes but also for a wide range of practical applications ranging from flood forecasting and water resource management to microwave communications. Depending on the applications, it may be necessary to measure the amount of precipitation, its rate with specified time resolution, its phase (liquid or solid), its spatial and temporal distribution, its vertical profile, its size spectrum and in some cases its chemical composition. The conventional instrument for rain measurement at the ground is the rain gauge which measures the volume of water falling over known area and it is measured manually at regular intervals. Recording gauges measure the rate of precipitation. Use of a remote sensing method to measure or estimate precipitation proved to be more reliable and accurate in recent days. These devices would capture isolated heavy rain rates which may be missed ...

Marine boundary layer characteristics during a cyclonic storm over the Bay of Bengal

During the period 12–16 June 1996 a tropical cyclonic storm formed over the southwest Bay of Bengal and moved in a north-northeasterly direction. The thermodynamic characteristics of this system are investigated by utilizing the surface and upper air observations collected onboardORV Sagar Kanya over the Bay of Bengal region. The response of the cyclonic storm is clearly evident from the ship observations when the ship was within the distance of 600–800 km from the cyclonic storm. This study explores why (i) the whole atmosphere from surface to 500 hPa had become warm and moist during the cyclonic storm period as compared to before and after the formation of this system and (ii) the lower layer of the atmosphere had become stable during the formative stage of the cyclonic storm.

Thermodynamic structure of the marine atmosphere over the region 80–87°E along 13°N during August (phase II) BOBMEX-99

Thermodynamic structure of the marine atmosphere in the region between 80 and 87‡E along 13‡N over the Bay of Bengal was studied using 13 high resolution radiosonde profiles from surface-400 hPa collected onboard ORV Sagar Kanya during the period 27th–30th August, during BOBMEX-99. Saturation point concept, mixing line analysis and conserved variable diagrams have been used to identify boundary layer characteristics such as air mass movement and stability of the atmosphere. The results showed relatively dry air near the ocean surface between 1000 and 950 hPa. This feature is confirmed by the conserved þetav structure in this layer. Further, þetav seldom showed any inversions in this region. The þetae and þetaes profiles showed persistent low cloud layers between 900 and 700 hPa. The conserved variable diagrams (þetae-q) showed the existence of double mixing line structures approximately at 950 and 700 hPa levels.

ON THE DYNAMICAL ASPECTS OF THE MONSOON BOUNDARY LAYER

Characteristic variations in the three forces, viz., pressure gradientforce, Coriolis force and frictional force, in the monsoon boundary layerhave been explored with the help of a one-dimensional model. The windobservations carried out at an inland station during MONTBLEX-90 have beenutilised for this purpose. Variations were observed in the three forcesduring active and break monsoon periods. The height at which the Coriolis andpressure gradient forces showed balance ranged from 360–700 m and500–600 m during break and active periods respectively.