Observed and Modeled Mesoscale Variability Near the Gulf Stream and Kuroshio Extension

摘要

Our earliest intercomparisons between western North Atlantic data and eddy-resolving two-layer quasi-geostrophic symmetric-double-gyre steady wind-forced numerical model results focused on the amplitudes and largest horizontal scales in patterns of eddy kinetic energy, primarily abyssal. Here, intercomparisons are extended to recent eight-layer model runs and new data which allow expansion of experiments are shown to have realistic zonal, vertical, and temporal eddy scales in the vicinity of the Kuroshio Extension in one case and the Gulf Stream in the other. Model zonal mean speeds are larger than observed, but vertical shears are in general agreement with the data. A longitudinal displacement between the maximum intensity in surface and abyssal eddy fields as observed for the North Atlantic is not found in the model results since the numerical simulations examined are highly idealized, the zero-order agreement between modeled andobserved basic characteristics of mid-latitude jets and their associated eddy fields suggests that such properties are predominantly determined by the physical mechanisms which dominate the models, where the fluctuations are the result of instability processes. (Reprints).