Repository logo
 

Intraseasonal variability of the west African monsoon and African easterly waves during boreal summer

Simple item page
dc.contributor.authorAlaka, Ghassan J., Jr., author
dc.contributor.authorMaloney, Eric D., advisor
dc.contributor.authorSchubert, Wayne H., committee member
dc.contributor.authorVenayagamoorthy, Subhas, committee member
dc.coverage.spatialAfrica
dc.date.accessioned2007-01-03T04:51:26Z
dc.date.available2007-01-03T04:51:26Z
dc.date.issued2010
dc.description.abstractSubstantial subseasonal variability in African easterly wave (AEW) activity and cyclogenesis frequency occurs in the main hurricane development region of the Atlantic during boreal summer. A complete understanding of intraseasonal variability in the Atlantic and west Africa during boreal summer requires analysis of how the Madden-Julian Oscillation (MJO) modulates the west African monsoon and consequently AEWs. Because the MJO is predictable a few weeks in advance, understanding how and why the MJO impacts the west African monsoon may have a profound influence on Atlantic tropical cyclone prediction. This study documents the MJO influence on the west African monsoon system during boreal summer using a variety of reanalysis and satellite datasets. This study aims to identify and explain the MJO teleconnection to the west African monsoon, and the processes that induce precipitation and AEW variability in this region. Intraseasonal west African and Atlantic convective anomalies on 30-90 day timescales are likely induced by equatorial Kelvin and Rossby waves generated in the Indian Ocean and west Pacific by the MJO. Previous studies have hypothesized that an area including the Darfur mountains and the Ethiopian highlands is an initiation region for AEWs. It is shown here that the initial MJO influence on precipitation and AEW activity in the African monsoon appears to occur in these regions, where eddy kinetic energy (EKE) anomalies first appear in advance of MJO-induced periods of enhanced and suppressed AEW activity. In the initiation region, upper tropospheric temperature anomalies are reduced, the atmosphere moistens by horizontal advection, and an eastward extension of the African easterly jet occurs in advance of the MJO wet phase of the African monsoon, when AEW activity is also enhanced. These factors all support strong precursor disturbances in the initiation region that seed the African easterly jet and contribute to downstream development of AEWs. Opposite behavior occurs in advance of the MJO dry phase. Moisture and eddy kinetic energy (EKE) budgets are examined to provide further insight as to how the MJO modulates and initiates precipitation and AEW variability in this region. In particular, meridional moisture advection anomalies foster moistening in the initiation region by anomalous flow acting across the mean moisture gradient. Additionally, positive (negative) upstream EKE tendency anomalies in advance of the MJO convective maximum (minimum) over tropical north Africa suggest wave growth (decay) near the entrance of the AEJ, while enhanced (suppressed) conversion of eddy available potential energy (EAPE) to EKE and barotropic conversion maintains downstream AEW growth (decay).
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.identifierAlaka_colostate_0053N_10174.pdf
dc.identifierETDF2010200101ATMS
dc.identifier.urihttp://hdl.handle.net/10217/44834
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2000-2019
dc.rightsCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.
dc.subjectteleconnection
dc.subjectmonsoon
dc.subjectMJO
dc.subjecteasterly wave
dc.subjectconvection
dc.subjectMadden-Julian oscillation
dc.subjectMonsoons -- Africa, West
dc.subjectAfrica
dc.titleIntraseasonal variability of the west African monsoon and African easterly waves during boreal summer
dc.typeText
dcterms.rights.dplaThis Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
thesis.degree.disciplineAtmospheric Science
thesis.degree.grantorColorado State University
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (M.S.)

Files

Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
Alaka_colostate_0053N_10174.pdf
Size:
14.71 MB
Format:
Adobe Portable Document Format
Description:
Download

Collections

2000-2019
Theses and Dissertations