Showing papers by "Mahen Konwar published in 2011"

Microphysics of Premonsoon and Monsoon Clouds as Seen from In Situ Measurements during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX)

Abstract: Analysis of the microphysical structure of deep convective clouds using in situ measurements during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over the Indian peninsular region is presented. It is shown that droplet size distributions (DSDs) in highly polluted premonsoon clouds are substantially narrower than DSDs in less polluted monsoon clouds. High values of DSD dispersion (0.3–0.6) and its vertical variation in the transient and monsoon clouds are related largely to the existence of small cloud droplets with diameters less than 10 μm, which were found at nearly all levels. This finding indicates the existence of a continuous generation of the smallest droplets at different heights. In some cases this generation of small droplets leads to the formation of bimodal and even multimodal DSDs. The formation of bimodal DSDs is especially pronounced in monsoon clouds. Observational evidence is presented to suggest that in-cloud nucleation at elevated layers is a f...

Microphysics of pre-monsoon and monsoon clouds as seen from in situ measurements during CAIPEEX

Abstract: Analysis of the microphysical structure of deep convective clouds using in situ measurements during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over the Indian peninsular region is presented. It is shown that droplet size distributions (DSDs) in highly polluted premonsoon clouds are substantially narrower than DSDs in less polluted monsoon clouds. High values of DSD dispersion (0.3-0.6) and its vertical variation in the transient and monsoon clouds are related largely to the existence of small cloud droplets with diameters less than 10 µm, which were found at nearly all levels. This finding indicates the existence of a continuous generation of the smallest droplets at different heights. In some cases this generation of small droplets leads to the formation of bimodal and even multimodal DSDs. The formation of bimodal DSDs is especially pronounced in monsoon clouds. Observational evidence is presented to suggest that in-cloud nucleation at elevated layers is a fundamental mechanism for producing multimodal drop size distribution in monsoon clouds as well as in most deep convective clouds. These findings indicate that inclusion of continued nucleation away from the cloud base into numerical models should be considered to predict microphysics and precipitation of clouds in monsoons and other cloud-related phenomena.

Vertical variation of low‐frequency oscillations in UHF radar derived winds at a tropical Indian station

Abstract: [1] Signatures of the low-frequency intraseasonal oscillations and their vertical variation in the lower troposphere are studied using multilevel wind observations made at a tropical Indian station, Pune (18°32′N, 73°51′E), from wind profiler/UHF radar during the period June 2003 to May 2006. Spectral analysis using fast Fourier transform showed the presence of oscillations (30–40 days and 50–70 days) in daily mean zonal winds and revealed their evolution in height-period structures. The 30–40 days oscillation mode has the largest amplitude compared to the other modes in zonal and meridional winds. All oscillation modes have much less amplitude in the vertical wind component. The high temporal (3 hourly) zonal and meridional wind observations obtained during the southwest monsoon period (June to September, JJAS) during the years 2003, 2004, and 2005 showed a prominent regime of oscillation, namely, 30–40 days and a moderate signature of 10–20 day mode. In all three years it is seen that these oscillations are not occurring as a single-frequency sinusoidal oscillation but are seen as broadband spectrum. The amplitude of these wave modes showed significant vertical variation. The vertical structures of radar-observed intraseasonal oscillations (30–40 days mode) and Tropical Rainfall Measuring Mission derived mean precipitation intensity during the monsoon period (JJAS) during the years 2003–2005 showed a reasonable comparison. The results presented in this study show significant intraseasonal and interannual variability in lower tropospheric winds, which are closely related to the performance of the southwest monsoon.