Brazilian efforts towards a Lagrangean description of surface

Brazilian efforts towards a Lagrangean description of surface currents and eddies in the Southwestern Atlantic Ocean Ronald Buss de Souza 1 João A. Lorenzzetti 1 Maurício Magalhães Mata 2 Carlos A. E. Garcia 2 Marcelo Sandin Dourado 1 1 Instituto 2 Fundação Nacional de Pesquisas Espaciais (INPE) Universidade Federal do Rio Grande (FURG)

Overview of the presentation • Currents and frontal systems; • Mesoscale features at the Brazil-Malvinas Confluence region; • The sinergy between buoy and satellite data; • Eddies observed in satellite images; • Eddies observed in buoy trajectories; • Eddy statistics; • Empirical relationships for the eddies; • The history of drifting buoy programmes in Brazil; • GTS drifting buoy data in the SW Atlantic Ocean; • Some results: COROAS; • Some results: PNBoia; • Some results: GOAL; • Conclusions.

Currents and frontal systems Antarctic Circumpolar Current; South Atlantic Current; Malvinas Current; Brazilian Coastal Current; Polar Front/Antarctic Convergence Subtropical Convergence. Source: Peterson e Stramma (1991)

Mesoscale features at the BMC region • The Brazil-Malvinas Confluence (BMC) is one of the most dynamically active regions of the World Ocean; • Eddies play an important (but not well understood) role in the across-front changes of properties in the World Ocean; • Many eddies are formed and shed every year from high amplitude meanders present in the BMC region; 43 o. S AVHRR SST image taken in February 1985 (Olson et al. , 1988) • Olson et al. (1988) presented a classic figure showing a large warm core eddy shed from the Brazil Current towards the Subantarctic environment; • The authors have also made the first Lagrangean descriptions of an eddy from the BC.

Mesoscale features at the BMC region: eddies • Legeckis and Gordon (1982) • Satellite data between 1975, 1976 e 1978; • Warm core eddies formed by the BC retraction at periods of a week; • Elliptical, ~180 km x 120 km; • Translations towards the south at 4 km/day to 35 km/day. • Garzoli (1993) • Inverted echosounders used to observe eddies; • Diameters between 100 km and 150 km; • Gordon (1989) • At least 6 eddies could be formed every year • They could be transported towards the eastern side of the South Atlantic gyre. • Smythe-Wright et al. (1996), Hooker and Brown (1996), Garfield (1990), Olson (1991), Schmid et al. (1995), Podestá (1997), Souza (2000), Lentini et al. (2002), among others

Mesoscale features at the BMC region: eddies • Questions still to be addressed: • How many eddies are being formed at the BMC region every year? • How long do they last? • Where are they being transported to? • How is their tri-dimensional structure? • What is their impact for the weather and climate of South America? • Many others. . . • The search for answers from the Brazilian community: • Establishment of continuous observing programmes; • Multi-disciplinary teams; • Description of the currents and eddies by using satellite and Lagrangean data.

The sinergy between buoy and satellite data Surface buoy trajectories tend to follow regions of maximum thermal gradients. Comparing the tracks with the images can be helpful to guess past behaviour of the frontal structures.

Eddies observed in satellite images (Rd = (g Ho)1/2 / f )

Eddies observed in buoy trajectories + BC +BCC +SAC Relationship between Rd and the eddies diameter: D/Rd < 1: turbulent flow D/Rd >> 1: well defined eddy field (Rd = (g Ho)1/2 / f ) Relationship between Ro and the eddies diameter: Strutures ranging from non-linear to quasi-geostrofic or geostrofic ones. (Ro = U / f. L)

Eddy statistics

Empirical relationships for the eddies

The history of drifting buoy programmes in Brazil • The development of an in-house technology came together with the COROAS project in 1993; • Projects PNBoia and GOAL came later. . . • Project MEDICA had used past technologies but launched a sole LCD in 1994 at the Polar Front.

The history of drifting buoy programmes in Brazil A Low Cost Drifter being launched at the Brazil-Malvinas Confluence region from the N. Ap. Oc. Ary Rongel in November 2003. Four of such instruments were deployed as part of GOAL project.

The history of drifting buoy programmes in Brazil

GTS drifting buoy data in the SW Atlantic Ocean GTS data from the Atlantic Oceanographic and Meteorological Laboratory (AOML), Drifting Buoy Data Assembly Center, NOAA. http: //www. aoml. noaa. gov/phod/dac. html

Some results: COROAS Source: Souza (2000)

Some results: COROAS

The Brazilian Coastal Current

The Brazilian Coastal Current BCC (a, b) and BC (c, d) extreme positions between 1982 and 1995 from MCSST images. Source: Souza e Robinson (2004). Sardinella brasiliensis total catch at the southern coast of Brazil between 1980 and 1990. Source: Sunyé and Servain (1998).

Some results: PNBoia Source: Assireu (2003)

Some results: GOAL, November 2002 eddy ED 1 C D A B 1, B 2 XBT profiles inside ED 1 in November 2002. AMSR-E SST image of 15 November 2002.

Some results: GOAL, November 2002 eddy ED 1 Temporal evolution of ED 1 between September and November 2003 at the BMC region recovered from AMSR-E images.

Some results: GOAL, November 2003 eddies AVHRR SST image in 5 November 2003. Buoy trajectories and positional time series from November 2003 to August 2004.

Some results: GOAL, Brazil Current return flow Buoy trajectories and positional time series between 11 and 21 November 2003. AVHRR SST image of 5 November 2003.

Some results: GOAL, Brazil Current return flow

Some results: GOAL, XBT profiles XBT profile along the N. Ap. Oc. Ary Rongel route in November 2003.

Conclusions • Brazil is continuously launching drifting buoys into the ocean since the COROAS project as part of WOCE; • Recent programmes such as the PNBoia and Pro. Antar/GOAL hae taken the opportunity to widening the sampling of waters in the South Atlantic Oean; • Multidisciplinary projects using Lagrangian data in conjuntion with satellite data are contributing to a better understanding of the currents and associated features in the Southwestern Atlantic Ocean; • Some areas such as the continental shelf off South America are still very poorly sampled.