SEMINAR: AOML Seminar - September 21, 2012 - 10:30 a.m. - Dr. Verena Hormann - " Interannual North Equatorial ,Countercurrent variability and its relation,to tropical Atlantic climate modes"

[Aoml.Receptionist <aoml.receptionist@noaa.gov>]

 AOML Seminar

Date:          Friday, September 21, 2012

Time:         10:30 a.m. – refreshments at 10:15 a.m.  

Location:   AOML First-Floor Conference Room

Speaker:     Dr. Verena Hormann, PhOD/CIMAS  

Title:          "Interannual North Equatorial   
Countercurrent variability and its relation
to tropical Atlantic climate modes"

 

Abstract:  A synthesis product of the surface geostrophic circulation is used to quantify the

interannual variability of the wind-driven North Equatorial Countercurrent (NECC). The

first mode of a complex empirical orthogonal function (CEOF) decomposition of zonal

geostrophic velocity in the NECC region reveals pronounced latitudinal displacements in

addition to variations in current strength. While north-south migrations of the NECC are

mainly captured by the real pattern, the imaginary pattern accounts for variations in its

strength. Associated with these spatial patterns is prevailing propagation toward the

northwest that is most pronounced northward of the mean NECC position ( ~6°N). There is

evidence that the zonal propagation characteristics are consistent with long Rossby waves

forced in the northeastern tropical Atlantic. The relationship between interannual NECC

variations and the tropical Atlantic climate modes is investigated through regression

and composite analyses. Sea surface temperature and wind stress patterns resembling the

meridional and zonal modes are found for the CEOF regression. Composite analysis further

shows consistent patterns for warm phases of the meridional mode and cold phases of

the zonal mode; the response of the NECC to a positive meridional and negative zonal mode

event may be viewed as a northward shift of its core and a current strengthening,

respectively. These results support a link between the two dominant tropical Atlantic

climate modes and show that the relation between interannual NECC variability and the

meridional and zonal modes can primarily be regarded as a response to changes in the

wind field.