Climate variability over the American monsoon and Amazonian regions during the last decades
text This dissertation aims to identify the main changes in monsoon activity observed over the American monsoon and Amazonian regions during the last decades and the possible links between such changes. To address this, several observational and reanalysis datasets were used. The results suggest the...
Main Author: | |
---|---|
Other Authors: | , , , , |
Format: | Thesis |
Language: | English |
Published: |
2011
|
Subjects: | |
Online Access: | http://hdl.handle.net/2152/ETD-UT-2011-08-3791 |
id |
ftunivtexas:oai:repositories.lib.utexas.edu:2152/ETD-UT-2011-08-3791 |
---|---|
record_format |
openpolar |
spelling |
ftunivtexas:oai:repositories.lib.utexas.edu:2152/ETD-UT-2011-08-3791 2023-05-15T17:32:59+02:00 Climate variability over the American monsoon and Amazonian regions during the last decades Arias-Gómez, Paola Andrea, 1979- Fu, Rong Cook, Kerry H. Dickinson, Robert E. Mo, Kingtse C. Yang, Zong-liang 2011-08 application/pdf http://hdl.handle.net/2152/ETD-UT-2011-08-3791 eng eng http://hdl.handle.net/2152/ETD-UT-2011-08-3791 2152/ETD-UT-2011-08-3791 North American monsoon South American monsoon Climate variability Amazon forests Monsoon Dry regime Wet season thesis 2011 ftunivtexas 2020-12-23T22:19:47Z text This dissertation aims to identify the main changes in monsoon activity observed over the American monsoon and Amazonian regions during the last decades and the possible links between such changes. To address this, several observational and reanalysis datasets were used. The results suggest the occurrence of two regime types of the North American monsoon during 1948-2009: two dry regimes during 1948-1959 and 1990-2009 and one wet regime during 1960-1989. The occurrence of such regimes is modulated by the Atlantic Multidecadal Oscillation. However, the two dry regimes have different causes. In particular, the more recent dry regime is mainly due to both an anomalous westward expansion of the North Atlantic Subtropical High and a northward displacement of the subtropical jet stream over the United States. The former enhances the low-level flow from the Gulf of Mexico to the Great Plains and weakens moisture transport to Mexico and the southwestern US. In addition to such a weakening of the North American monsoon during the last two decades, this research shows that the American monsoon systems have shortened after 1978 due to a trend toward earlier retreats of the North American monsoon and delayed onsets of the southern Amazon wet season. These changes produce a longer transition season between both monsoon systems. Whether these changes are caused by a common factor or they are the consequence of independent and unrelated causes was not clear previously. The results discussed here indicate that the observed changes in the American monsoons are partially a consequence of the westward expansion of the North Atlantic surface high observed since 1978. Such a westward expansion enhances the activity of easterly waves over the southern Caribbean Sea and northern South America, producing a dominant easterly flow over the region, which in turn prevents the reversal of the cross-equatorial flow necessary to transport moisture to the southern Amazon and the South American monsoon domain and contributes to its delayed onset. This investigation provides evidence that the shortening and weakening of the American monsoons and the lengthening of the transition season between them are associated with the same large-scale forcing, which may be caused by anthropogenic influence. Geological Sciences Thesis North Atlantic The University of Texas at Austin: Texas ScholarWorks |
institution |
Open Polar |
collection |
The University of Texas at Austin: Texas ScholarWorks |
op_collection_id |
ftunivtexas |
language |
English |
topic |
North American monsoon South American monsoon Climate variability Amazon forests Monsoon Dry regime Wet season |
spellingShingle |
North American monsoon South American monsoon Climate variability Amazon forests Monsoon Dry regime Wet season Arias-Gómez, Paola Andrea, 1979- Climate variability over the American monsoon and Amazonian regions during the last decades |
topic_facet |
North American monsoon South American monsoon Climate variability Amazon forests Monsoon Dry regime Wet season |
description |
text This dissertation aims to identify the main changes in monsoon activity observed over the American monsoon and Amazonian regions during the last decades and the possible links between such changes. To address this, several observational and reanalysis datasets were used. The results suggest the occurrence of two regime types of the North American monsoon during 1948-2009: two dry regimes during 1948-1959 and 1990-2009 and one wet regime during 1960-1989. The occurrence of such regimes is modulated by the Atlantic Multidecadal Oscillation. However, the two dry regimes have different causes. In particular, the more recent dry regime is mainly due to both an anomalous westward expansion of the North Atlantic Subtropical High and a northward displacement of the subtropical jet stream over the United States. The former enhances the low-level flow from the Gulf of Mexico to the Great Plains and weakens moisture transport to Mexico and the southwestern US. In addition to such a weakening of the North American monsoon during the last two decades, this research shows that the American monsoon systems have shortened after 1978 due to a trend toward earlier retreats of the North American monsoon and delayed onsets of the southern Amazon wet season. These changes produce a longer transition season between both monsoon systems. Whether these changes are caused by a common factor or they are the consequence of independent and unrelated causes was not clear previously. The results discussed here indicate that the observed changes in the American monsoons are partially a consequence of the westward expansion of the North Atlantic surface high observed since 1978. Such a westward expansion enhances the activity of easterly waves over the southern Caribbean Sea and northern South America, producing a dominant easterly flow over the region, which in turn prevents the reversal of the cross-equatorial flow necessary to transport moisture to the southern Amazon and the South American monsoon domain and contributes to its delayed onset. This investigation provides evidence that the shortening and weakening of the American monsoons and the lengthening of the transition season between them are associated with the same large-scale forcing, which may be caused by anthropogenic influence. Geological Sciences |
author2 |
Fu, Rong Cook, Kerry H. Dickinson, Robert E. Mo, Kingtse C. Yang, Zong-liang |
format |
Thesis |
author |
Arias-Gómez, Paola Andrea, 1979- |
author_facet |
Arias-Gómez, Paola Andrea, 1979- |
author_sort |
Arias-Gómez, Paola Andrea, 1979- |
title |
Climate variability over the American monsoon and Amazonian regions during the last decades |
title_short |
Climate variability over the American monsoon and Amazonian regions during the last decades |
title_full |
Climate variability over the American monsoon and Amazonian regions during the last decades |
title_fullStr |
Climate variability over the American monsoon and Amazonian regions during the last decades |
title_full_unstemmed |
Climate variability over the American monsoon and Amazonian regions during the last decades |
title_sort |
climate variability over the american monsoon and amazonian regions during the last decades |
publishDate |
2011 |
url |
http://hdl.handle.net/2152/ETD-UT-2011-08-3791 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_relation |
http://hdl.handle.net/2152/ETD-UT-2011-08-3791 2152/ETD-UT-2011-08-3791 |
_version_ |
1766131320082137088 |