Air-Sea Interaction Processes at Light Winds Observed from a Coastal Tower
Keywords:Turbulence, intermittence, wind waves, radar return.
AbstractAirflows, sea-surface waves, near-surface currents and X-band radar sea-returns were measured from a nearshore tower in 4-m deep water located in the Delaware Bay, during the passage of typical weather patterns. Intermittent violent momentum transfers, burstings, from air to water were clearly observed from measurements of the airflow turbulence. The scaling of mean periods between bursts and between sweeps with dominant wave period and the outer and inner variables of the turbulent airflow confirms that both, dominant wind waves and energy containing airflow eddies, share a role in the triggering of burstings. The three-dimensionality of the airflow in the field facilitates the reattachment manifested by the sweep events, and makes the latter similar to the bursts in terms of number and contribution to the mean Reynolds stress. The contribution of bursting events to the mean Reynolds stress is stronger than in laboratory flows and exceeds 100%. Wavelet analysis was applied to the surface wave data, and revealed uniformly distributed instants of bursts and sweeps over dominant wind wave profile. Using surface elevations and radar return data, no modifications of the surface roughness were found during bursting events.