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Statistical Characteristics of Convective Storms in Darwin, Northern Australia
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2006 (English)Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This M. Sc. thesis studies the statistical characteristics of convective storms in a

monsoon regime in Darwin, northern Australia. It has been conducted with the use

of radar. Enhanced knowledge of tropical convection is essential in studies of the

global climate, and this study aims to bring light on some special characteristics of

storms in a tropical environment. The observed behaviour of convective storms can

be implemented in the parameterisation of these in cloud-resolving regional and

global models. The wet season was subdivided into three regimes; build-up and

breaks, the monsoon and the dry monsoon. Using a cell tracking system called

TITAN, these regimes were shown to support different storm characteristics in terms

of their temporal, spatial and height distributions. The build-up and break storms

were seen to be more vigorous and particularly modulated diurnally by sea breezes.

The monsoon was dominated by frequent but less intense and vertically less

extensive convective cores. The explanation for this could be found in the

atmospheric environment, with monsoonal convection having oceanic origins

together with a mean upward motion of air through the depth of the troposphere.

The dry monsoon was characterised by suppressed convection due to the presence of

dry mid-level air. The effects of wind shear on convective line orientations were

examined. The results show a diurnal evolution from low-level shear parallel

orientations of convective lines to low-level shear perpendicular during build-up and

breaks. The monsoon was dominated by complex orientations of convective lines.

The thesis includes a study of merged and splitted cells, which have been separated

from other storms, and mergers were shown to support more vigorous convection in

terms of height distribution and reflectivity profiles. They were also seen to be the

most long-lived category of storms as well as the most common type. Split storms

were generally weaker, indicative of their general tendency to decay shortly after the

split occurred.

Abstract [sv]

En statistisk studie av konvektiva celler i en miljö som präglas av

monsunförhållanden har utförts i Darwin, norra Australien, med hjälp av radar.

En ökad förståelse for tropisk konvektion är nödvändig for att kunna studera

klimatet globalt. Denna studie har bidragit till denna kunskapsbas genom att studera

några viktiga parametrar hos konvektiva celler i en tropisk miljö. De observerade

egenskaperna hos dessa celler kan implementeras i parametriseringen av

högupplösta regionala och globala modeller. Regnperioden delades upp i tre olika

regimer; uppbyggnad och avbrott, monsun och torr monsun. Genom att använda ett

cellsökande system kallat TITAN, visade sig dessa regimer uppvisa olika

karakteristika vad gäller tids- och rumsmässig samt vertikal distribution av

konvektionsceller. Uppbyggnad- och avbrottsregimen dominerades av mäktiga och

intensiva konvektionsceller, och modulerades av sjöbrisar på en daglig basis.

Monsunen dominerades av talrika men mindre intensiva celler. Anledningen till

detta kan finnas i atmosfäriska förhållanden, dar monsunen dominerades av

konvektionsceller med oceanisk härkomst och allmän hävning genom större delen av

troposfären. Den torra monsunen präglades av försvagad konvektion på grund av

närvaron av mycket torr luft på medelhöga nivåer. Effekten av vindskjuvning på

orienteringen av bylinjer undersöktes. Resultaten visar att en daglig övergång från en

orientering som var parallell med vindskjuvningsvektorn till en vinkelrät orientering

dominerade under uppbyggnad och avbrott. Monsunen präglades av komplexa

orienteringar av bylinjer.

Sammanväxande och splittrande celler separerades fran andra celler och undersöktes

speciellt. De sammanväxande cellerna uppvisade mer intensiv konvektion och större

vertikal maktighet. Denna kategori av celler, som var den vanligaste typen av ickeisolerade

celler, levde också längre än andra celltyper. Splittrande celler var generellt

svagare än andra celler, vilket indikerade den generella tendensen för denna celltyp

att brytas ner strax efter det att en splittring ägt rum.

Place, publisher, year, edition, pages
2006.
Series
Examensarbete vid Institutionen för geovetenskaper, ISSN 1650-6553 ; 125
Keyword [en]
convective storms characteristics, precipitation, radar, monsoon, Australia
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:uu:diva-303874OAI: oai:DiVA.org:uu-303874DiVA: diva2:974301
Subject / course
Meteorology
Available from: 2016-10-04 Created: 2016-09-26 Last updated: 2016-10-04Bibliographically approved

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