The North American summer monsoon is documented, using precipitation data
together with gridded data for outgoing long-wave radiation (OLR), geopotential height
and wind at various levels. The upper level divergence field is diagnosed and compared
with the precipitation field. A simple wet-dry precipitation index is used to date the
monsoon onset at stations with daily precipitation data.
The analysis shows that the monsoon rains advance northward rapidly from late
June to early July. The monsoon onset is accompanied by the development of a
pronounced anticyclone at the jet stream level, by sea-level pressure rises over the
southwestern United States, and by decreases in climatological mean rainfall over
adjacent regions of the United States, Mexico and the Caribbean. This coherent pattern
of rainfall changes, that covers much of North and Central America, is shown to be
dynamically consistent with the circulation changes aloft. Hence, the monsoon onset is
embedded within a planetary-scale pattern of circulation changes. The demise of the
monsoon and the associated upper level anticyclone, which takes place around September
of the year, is more gradual than the onset, and it is accompanied by an increase in
rainfall throughout much of the surrounding region.
The monsoon exhibits substantial interannual variability with regard to intensity
and onset date.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/8953 |
| Date | 05 1900 |
| Creators | Okabe, Ian T. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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