At early wake ages, aircraft generated wake vortices are typically in the form of a pair of trailing line vortices. Over time, the vortex pair twists as it interacts with the ambient environment and its own instability. At a later time, the twisted vortex pair could link together and snap into a vortex ring, creating regions devoid of vortices behind an aircraft. Many field measurements of aircraft wake vortices have been obtained using the Lockheed Martin Coherent Technologies WindTracer~? pulsed lidar. These lidar measurements are obtained on a thin vertical section across the flight path of an aircraft. The effect of rings on the pulsed lidar measurements is examined in this manuscript. Time histories of two-dimensional images of aircraft wake vortices obtained using a phased microphone array are analyzed together with concurrent lidar measurements. These data were obtained in a field test performed at the Denver International Airport in September 2003. The analysis showed that the time differences between the ring formation times from the microphone data and the end of the lidar vortex measurements are small for most of the runs. These small time differences are consistent with the spatial gaps devoid of vortices when a ring is formed.
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