Wind Forcing over the Southwest Atlantic: Comparison between Observations and ECMWF Analyses

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  • 1 Centre National de la Recherche Scientifique, Laboratoire d'Océanographie Dynamique et Climatologie, Université Pierre et Marie Curie, Paris, France
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Abstract

Oceanic variability in the southwest Atlantic is dominated by temporal scales at the annual, semiannual, and few-month periods. It is now examined if the timescales present in the local wind forcing (wind vector and wind stress curl) match the timescales in oceanic variability.

Wind observations from land stations in South America and from ship observations in the Argentine Basin are examined to assess the validity and limitations of the European Centre for Medium-Range Weather Forecasts (ECMWF) wind analyses in the South Atlantic. The comparison is carried out over the five-year period 1986–90. The amount of observations, their statistics, and the temporal scales are examined. The major discrepancy the authors find is due to land–sea effects that are not resolved in the ECMWF model. Furthermore, the agreement in amplitude and phase of the two dominant signals, the annual and semiannual signals, is remarkable. The temporal scales present in the wind stress curl derived from ECMWF analyses are then examined. All the periods of oceanic variability (annual, semiannual, and a few months) are clearly present in the local wind stress curt over the Brazil-Malvinas confluence region. This suggests that in the southwest Atlantic the local wind forcing may play an essential role in the oceanic variability.

Abstract

Oceanic variability in the southwest Atlantic is dominated by temporal scales at the annual, semiannual, and few-month periods. It is now examined if the timescales present in the local wind forcing (wind vector and wind stress curl) match the timescales in oceanic variability.

Wind observations from land stations in South America and from ship observations in the Argentine Basin are examined to assess the validity and limitations of the European Centre for Medium-Range Weather Forecasts (ECMWF) wind analyses in the South Atlantic. The comparison is carried out over the five-year period 1986–90. The amount of observations, their statistics, and the temporal scales are examined. The major discrepancy the authors find is due to land–sea effects that are not resolved in the ECMWF model. Furthermore, the agreement in amplitude and phase of the two dominant signals, the annual and semiannual signals, is remarkable. The temporal scales present in the wind stress curl derived from ECMWF analyses are then examined. All the periods of oceanic variability (annual, semiannual, and a few months) are clearly present in the local wind stress curt over the Brazil-Malvinas confluence region. This suggests that in the southwest Atlantic the local wind forcing may play an essential role in the oceanic variability.

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