Interpretation of the "flying eagle" radar signature in supercells

A common feature of supercells on radar displays is a winged appearance of the reflectivity field in the forward-flank of the storm. This so-called “flying eagle” signature or “V-notch” often generates intrigue and confusion. A common explanation circulating in the meteorology community is one that invokes an analogy to obstacle flow, perhaps stemming from early publications. However, more recent research has shown that the updraft is not a solid obstacle and thus the analogy is rather tenuous.

Linear theory suggests that shear-induced pressure perturbations cause a deflection of the environmental flow as it impinges on the updraft. Hydrometeors falling into this perturbed flow follow trajectories that can explain at least part of this signature. This interpretation is not new; however, we investigate it in detail here in an attempt to alleviate some confusion. Also, there are no known publications in the literature that specifically address this signature. In fact, a paper published in April 2008 remarks that the mechanism that produces the winged appearance in reflectivity fields “remains unknown.”

In addition to the theoretical explanation, observational data are presented to investigate the vertical structure of the signature as well as its evolution. Polarimetric radar data are invoked to illuminate potential microphysical differences in each “wing.” Lastly, any ties to storm severity and tornado development are explored.