Synoptic maps of temperature and velocity within the Subantarctic Front south of Australia

From April 1995 to March 1997 a 450‐km array of inverted echo sounders, horizontal electric field recorders, and current meters measured the horizontal and vertical structure of the current, temperature, and salinity fields associated with the Subantarctic Front (SAF) south of Australia. Synoptic maps of the temperature and velocity fields often show the SAF divided into two zonally separated jets, which are also found in the mean. These jets were in close proximity yet directed toward different azimuths. The daily maps also show that the SAF often flowed as a single strong jet, during which times it underwent vigorous meandering, with crest‐to‐trough meridional distances ∼250 km. These meanders stalled within the array and contorted to form “S”‐shaped paths. In one case a cold‐core ring was formed. Propagating meanders have periods of 20–70 days, wavelengths of 240–420 km, and phase speeds of 12–6 km d−1. Deep currents reveal strong cyclones and anticyclones propagating primarily eastward through the array beneath the meandering jet. Thus, at times the deep flow is aligned with the upper flow, whereas at other times, significant barotropic flows cross the upper front. Occasionally, the northern Polar Front was also found within the array. The observed variability illustrates how the interaction of a meandering current with transient features such as meanders and eddies makes the identification of a front difficult when a single isotherm or isopycnal is utilized as the definition.