PERSISTENT WESTWARD FLOW IN THE AZORES CURRENT AS SEEN FROM ALTIMETRYAND HYDROGRAPHY

Temporal and spatial variability of the eastward flowing, jet-like Azo res Current is investigated by applying a new method for combining alt imetry with hydrography in order to produce absolute surface geostroph ic currents [Challenor et al., 1996]. The altimeter surface measuremen ts contain information about both the geoid and the geostrophic ocean circulation: the geoid signal dominates and is generally not sufficien tly well known at the small length scales required to identify the mes oscale ocean signal. In this study, hydrography is used to distinguish the mean ocean signal from the geoid along an ERS 1 satellite track s outh of the Azores during both 3-day repeat phases and thereby determi ne cross-stream absolute dynamic topography of the Azores Current at h igh temporal resolution. Hydrographic data collected near 28 degrees W in March 1992 is combined with ERS 1 altimeter data from January-Marc h 1992 and January to early April 1994. Time series of 3-day repeat pr ofiles of absolute surface geostrophic velocity perpendicular to the a ltimeter/cruise track are examined. The Azores Current absolute veloci ty profile along this track is rather coherent: the current variabilit y is less than the mean. Surprisingly, a persistent westward flow of s imilar to 25 cm s(-1) is observed near 35 degrees N, 28 degrees W. Thi s flow appears to be a ''retroflection'' from the main eastward flowin g current. An isopycnal analysis reveals the westward flow to be coole r (by 0.5 degrees C) and fresher (by 0.15 practical salinity units) th an the main body of the Azores Current. The now appears to persist thr oughout each of the above 3-month periods in late winter/early spring, but the question of whether this is a seasonal feature or more perman ent remains open. It is suggested that the westward flow is topographi cally controlled.