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ABSTRACT:The ability of the stratospheric Quasi-Biennial Oscillation (QBO) to modulate tropospheric circulation allows it to modulate tracks of tropical cyclones (TCs). This possibility is examined using data on the cyclone tracks over the Bay of Bengal (BOB) during the period 1948-2010. TC tracks (excluding the El Niño-Southern Oscillation years) when stratified as per the phases of QBO show the evidence of influence of stratospheric QBO on tracks. In pre-monsoon and post-monsoon seasons, during easterly phase of QBO, cyclones move westward/northwestward while during westerly phase they move northward/northeastward. The evidence of influence of QBO on modulation of TC tracks is reported for the first time during pre-satellite period and satellite period over the BOB. The QBO influence is observed to be significantly stronger during easterly phase as compared to that in the westerly phase. Numbers of cyclones are more during easterly phase (during pre-monsoon and post-monsoon) than during the westerly phase. A mechanism is proposed whereby QBO of the zonal winds in the stratosphere influences the movement of cyclone tracks in the BOB by redistributing deep convection associated with cyclones by modulating steering winds. The possible interaction between QBO and cyclone activity is investigated through the variation of tropopause height, geo-potential height and Outgoing Longwave Radiations.

Vertical profiles of carbon monoxide (CO) and ozone retrieved from Tropospheric Emission Spectrometer have been analyzed during two super cyclone systems Mala and Sidr. Super cyclones Mala and Sidr traversed the Bay of Bengal (BOB) region on April 24-29, 2006 and November 12-16, 2007 respectively. The CO and ozone plume is observed as a strong enhancement of these pollutants in the upper troposphere over the BOB, indicating deep convective transport. Longitude-height cross-section of these pollutants shows vertical transport to the upper troposphere. CO mixing ratio ~90 ppb is observed near the 146-mb level during the cyclone Mala and near 316 mb during the cyclone Sidr. Ozone mixing ratio ~60-100 ppb is observed near the 316-mb level during both the cyclones. Analysis of National Centers for Environmental Prediction (NCEP) reanalysis vertical winds (omega) confirms vertical transport in the BOB.

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Abstract. The devastating episode (17–18 June 2013) at Kedarnath (Uttrakhand, India) caused huge loss of lives and physical/material wealth. To understand this catastrophic event, rainfall/convective data and associated climate meteorological parameters are investigated. Low pressure zone with very high cloud cover (60–90%), and relative humidity (70–100%) associated with low (< 4 m s−1) wind velocity over Kedarnath region during 15–17 June are observed. The cause of disaster seems to be the heavy and continuous rainfall associated with snow melting and over flooding/collapse of the Chorabari Lake, located upstream. Monsoon advancement was much faster due to the presence of convectively active phase of the Madden Julian Oscillation.