Mean Jets and Mesoscale Variability of the Antarctic Circumpolar Current in Drake Passage from Shipboard ADCP Observations

Using acoustic Doppler current profiler (ADCP) observations made between 1999 and 2002, we examine the mean jets and mesoscale variability in the surface layer velocity structure of the Antarctic Circumpolar Current (ACC) in Drake Passage. The data were acquired from an ongoing sampling program of underway ADCP observations from the U.S. Antarctic icebreakers, RVIB Laurence M. Gould and RVIB Nathaniel B. Palmer, supported by the NSF Office of Polar Programs. The L. M. Gould crosses Drake Passage approximately 2-4 times per month, and its track across the passage varies although the duration of each crossing is about 2 days. The northern starting point is always Isla de los Estados at the southeast tip of Tierra del Fuego, but the southern end point varies, exiting Drake Passage between 55-65 degrees W. We examine the Eulerian velocity statistics both by spatial binning as well as projected onto a mean section. The ACC is characterized by a series of relatively narrow eastward jets, separated by broader bands of weaker flow, and a high degree of mesoscale variability. Three jets associated with temperature fronts observed in concurrent repeat XBT sections dominate the annual means: the Subantartic Front (SAF), the Polar Front (PF), and the Southern Front (SF). Velocity variance is highest over the northern half of the Passage, due in part to seasonal variability in the SAF and the PF.