Ocean -atmosphere interaction in the seasonal to decadal variations of tropical Atlantic climate

2005 2005

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Abstract (summary)

The tropical Atlantic ocean and atmosphere display distinct seasonal cycles with considerable year-to-year variations superimposed. The present study investigates processes and mechanisms important for tropical Atlantic climate and its variability, using numerical models and observational data, with an emphasis on ocean-atmosphere interaction. For the seasonal cycle, topics of particular interest are the rapid development of the monsoon-cold tongue complex in boreal summer and the oceanic response to the secondary acceleration of equatorial easterly winds in November; for interannual-to-decadal variability, they are the effect of the November thermocline shoaling on the equatorial zonal mode and the atmospheric response to the meridional sea surface temperature (SST) dipole mode.

Atmospheric model experiments indicate that interaction between the equatorial cold tongue and the West African monsoon is essential for the rapid seasonal transition from boreal spring to summer. Mechanisms are identified for the summertime acceleration of equatorial easterly wind, which contributes to rapid equatorial cooling by forcing upwelling and thermocline shoaling. Analysis of high-resolution satellite/in-situ data reveals the equatorial SST change associated with the November easterly wind acceleration and thermocline shoaling. This overlooked climatic feature is further shown to give rise to a new mode of tropical Atlantic variability---Atlantic Niño II---which resembles the boreal summer zonal mode but peaks in November--December, and is statistically independent of the preceding summer events. Atlantic Niño II significantly affects interannual rainfall variations in the coastal Congo-Angola region, and evolves into the meridional mode in the following spring, affecting rainfall variations in northeast Brazil. It thus fills an important climate predictability gap in time, during the season for which the local variability was otherwise poorly understood. The atmospheric model supports the idea that the tropical atmosphere responds and feeds back positively to the meridional dipole of SST anomalies. The resulting displacement of the tropical convective zone forces extratropical ocean-atmosphere anomalies, organizing them into a pan-Atlantic pattern.

Indexing (details)

0373: Geophysics
0415: Oceanography
0608: Atmosphere
Identifier / keyword
Pure sciences; Earth sciences; Atlantic Ocean; Climate; Decadal; Ocean-atmosphere interaction; Seasonal; Tropical
Ocean -atmosphere interaction in the seasonal to decadal variations of tropical Atlantic climate
Okumura, Yuko
Number of pages
Publication year
Degree date
School code
DAI-B 66/12, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
9780542441264, 0542441268
Xie, Shang-Ping
University of Hawai'i at Manoa
University location
United States -- Hawaii
Source type
Dissertations & Theses
Document type
Dissertation/thesis number
ProQuest document ID
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
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