The Spatial and Temporal Evolution of a Cluster of SOFAR Floats in the POLYMODE Local Dynamics Experiment (LDE)

Up to forty neutrally buoyant floats (20 at 700 m, 20 at 1300 m) were used in the POLYMODE Local Dynamics Experiment (LDE) to provide a quasi-Lagrangian description of the structure and evolution of the mesoscale eddy field in a limited region characterized by higher kinetic energy levels than those obtained in MODE. This paper is an overview and summary of the data collected. The temporal development of the two-level float array is presented in a sequence of maps, each spanning five days. In these one readily notices an “oscillation” of floats at 1300 m in a NE-SW direction before the cluster breaks apart. At 700 m the float cluster subdivides much more rapidly. The first setting of 700-m floats drifts to the west; the second group, launched two months later, goes far to the east. Ensemble averages as a function of time of the floats at 1300 m reveal great sensitivity to the “oscillatory” velocity field while the array is “tight” or coherent the corresponding 700-in averages, although noisy, show clearly the westward and eastward motion of the first and second clusters respectively. Grand averages for μ, υ (cm s−1), and kinetic energy (ergs gm−1) are (−1.8, 0., 80) and (−1.6, 0., 34) for the shallow and deep floats. The spatial correlation functions show 1arge scales of coherence. The zero-crossing of the transverse-velocity correlation function is about 100 km for both the 700- and 1300-m floats compared to 55 km for the 1500-m goats in MODE. The longitudinal correlation scale is also much larger.