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Climate variations of genesis and rapid intensification of tropical cyclones in the southern hemisphere

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Item Summary

Title:Climate variations of genesis and rapid intensification of tropical cyclones in the southern hemisphere
Authors:Dayal, Kavina Shaanu
Keywords:tropical cyclones
Date Issued:Aug 2014
Publisher:[Honolulu] : [University of Hawaii at Manoa], [August 2014]
Abstract:This thesis focuses on short-term climate variation of tropical cyclones in the Southern Hemispheric Ocean. Two major research areas are explored: (1) the modulation of tropical cyclone genesis by the Madden-Julian Oscillation (MJO), and (2) seasonal and intraseasonal variability of rapid intensification (RI). The observed modulation of tropical cyclone (TC) genesis is examined using 32-years of outgoing longwave radiation (OLR), reanalysis winds and TC best track data. A newly introduced MJO index based on the convective anomalies of large OLR variability centers shows a much stronger modulation of TC genesis by MJO than previously detected. An increased number of TC formations are observed during the enhanced convective phase of MJO than during a dry phase. The modulation is more pronounced to the east of 70°E in South-Indian Ocean (SIO) with a modulation ratio of 2:1 and to the west of 170°W in the SPO with a modulation ratio of 7:1. The stronger modulation in SPO is mainly due to: (1) MJO-induced wind fields are larger than the background mean flow, (2) TC genesis location being consistent with MJO basic state, i.e., TCs co-occur over the region of MJO-induced low-level circulation and enhanced convection, and (3) TC genesis occurs in the South-Pacific convergence zone upon which MJO has a strong modulation. Analysis of large-scale dynamic and thermodynamic environmental conditions reveal low-level relative vorticity is strongly attributable to TC genesis modulation in both ocean basins where SPO has an additional contribution from mid-tropospheric relative humidity that is also modulated by MJO-induced perturbations. The MJO has little effect on TC genesis in SW Indian Ocean because of the existence of favorable climatological environmental conditions throughout the TC season, and TCs form further away from the equator where the MJO signal is very weak or non-existent.
Description:M.S. University of Hawaii at Manoa 2014.
Includes bibliographical references.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Meteorology

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