https://libjncir.jncasr.ac.in/xmlui/handle/10572/1520 2026-04-04T05:35:29Z 2026-04-04T05:35:29Z Mukund, V. Singh, D. K. Ponnulakshmi, V. K. Subramanian, Ganesh Sreenivas, K. R. https://libjncir.jncasr.ac.in/xmlui/handle/10572/2449 2017-02-21T10:25:22Z 2014-01-01T00:00:00Z

Field and laboratory experiments on aerosol-induced cooling in the nocturnal boundary layer Mukund, V.; Singh, D. K.; Ponnulakshmi, V. K.; Subramanian, Ganesh; Sreenivas, K. R. Heat transfer processes in the nocturnal boundary layer (NBL) influence the surface energy budget and play an important role in many micrometeorological processes, including the formation of inversion layers, radiation-fog and in the control of air-quality near the ground. Under calm and clear-sky conditions, radiation plays an important role in determining the characteristics of the NBL. In this article, we report observations, close to ground, of hypercooling that has a radiative origin, and which leads to anomalous vertical temperature profiles with elevated minima. In addition, a laboratory experimental set-up is developed that is capable of capturing the thermal structure of the NBL, close to ground, under various conditions. Results from the laboratory experiments indicate that the high cooling rates near the ground, observed in the field experiments, arise from a near-surface heterogeneity in the (aerosol-laden) NBL; a feature ignored in radiation models used for atmospheric simulations. Many of these models nevertheless predict preferential near-ground cooling in apparent agreement with our field observations. However, the cooling is spurious, and arises from the use of an incorrect frequency-averaged transmittance in the radiation model. Based on our observations, a non-dimensional number is proposed that characterizes the evolution in the lowest metres of the NBL; in particular, the effect of radiation on the NBL thermal structure. Our results should help in parametrizing NBL transport process, and highlight the need to account for both the effects of aerosols close to the ground and a varying ground emissivity, via appropriate boundary conditions in general circulation and climate models. Restricted Access

2014-01-01T00:00:00Z Diwan, Sourabh S. Prasanth, P. Sreenivas, K. R. Deshpande, S. M. Narasimha, Roddam https://libjncir.jncasr.ac.in/xmlui/handle/10572/2443 2017-02-21T10:25:16Z 2014-01-01T00:00:00Z

Cumulus-Type Flows in the Laboratory and on the Computer: Simulating Cloud Form, Evolution, and Large-Scale Structure Diwan, Sourabh S.; Prasanth, P.; Sreenivas, K. R.; Deshpande, S. M.; Narasimha, Roddam Cumulus clouds, which are among the largest sources of uncertainty in climate change science and tropical circulation, have to-date resisted the numerous attempts made during the last six decades to unravel their cloud-scale dynamics. One major reason has been the lack of a convincing fluid-dynamical model and the difficulty of making repeatable measurements in an inherently transient flow. This article summarizes recent work showing that cumulus-type f lows can be generated in the laboratory by releasing volumetric heat into a plume above a height analogous to cloud condensation level and in quantities dynamically similar to the release of latent heat in the natural cloud. Such a transient diabatic plume (TDP) seems to mimic cumulus clouds with adiabatic/pseudoadiabatic processes of latent heat release. With appropriate heating profile histories, the TDP simulates a variety of cumulus-cloud forms, from cumulus congestus to cumulus fractus, and permits tracking their evolution through a complete life cycle. Selected examples of such laboratory simulations are supported by preliminary results from direct numerical simulations based on the Navier-Stokes-Boussinesq equations. These simulations suggest that the baroclinic torque plays an important role in the dynamics of both large- and small-scale motions in cloud-type flows. Restricted Access

2014-01-01T00:00:00Z