ALBERT

Description: This dataset is a collection of moored velocity data used in the study “Sources and pathways of intraseasonal meridional kinetic energy in the equatorial Atlantic Ocean” (Körner et al., 2022) to analyze the representation of meridional intraseasonal velocity variability in a general circulation model. The observational velocity data were collected at five different locations along the equator. At 0°N, 35°W velocity data were collected by single-point current meters in four different depths from October 1992 until May 1994. Between August 2004 and June 2006 an acoustic Doppler current profiler (ADCP) and single-point current meters collected data at 0°N, 35°W. Moorings at 0°N, 23°W provide velocity measurements from December 2001 to June 2021 (apart from a period from December 2002 to February 2004 when no mooring was in place). At 0°N, 10°W velocity data were collected between May 2003 to March 2019 using ADCPs and single-point current meters. However, the mooring was not consecutively installed leading to data gaps of up to two years. Between 2007 and 2011 ADCPs recorded velocity data at 0°N, 0°E.

Description: Multiyear moored velocity observations of the Angola Current near 11°S reveal a weak southward mean flow superimposed by substantial intraseasonal to seasonal variability, including annual and semiannual cycles with distinct baroclinic structures. In the equatorial Atlantic these oscillations are associated with basin-mode resonances of the fourth and second baroclinic modes, respectively. Here, the role of basin-mode resonance and local forcing for the Angola Current seasonality is investigated. A suite of linear shallow-water models for the tropical Atlantic is employed, each model representing a single baroclinic mode forced at a specific period. The annually and semiannually oscillating forcing is given by 1) an idealized zonally uniform zonal forcing restricted to the equatorial band corresponding to a remote equatorial forcing or 2) realistic, spatially varying Fourier components of wind stress data that include local forcing off Angola, particularly alongshore winds. Model-computed modal amplitudes are scaled to match moored velocity observations from the equatorial Atlantic. The observed annual cycle of alongshore velocity at 11°S is well reproduced by the remote equatorial forcing. Including local forcing slightly improves the agreement between observed and simulated semiannual oscillations at 11°S compared to the purely equatorial forcing. However, the model-computed semiannual cycle lacks amplitude at middepth. This could be the result of either underestimating the strength of the second equatorial basin mode of the fourth baroclinic mode or other processes not accounted for in the shallow-water models. Overall, the findings underline the importance of large-scale linear equatorial wave dynamics for the seasonal variability of the boundary circulation off Angola.

Description: CTD, VMADCP, LADCP and mooring data of several SFB754 cruises