The Response of Birds to Abrupt Natural Hazards as Observed using Weather Radar

Numerous studies have addressed the important question of how species are impacted by seasonal variability, climate change, urbanization and land use effects, and other anthropogenic and natural shifts in habitats. In this study, we have analyzed the severe weather outbreak that occurred November 7, 2011 in close proximity to several established nature reserves in southwestern Oklahoma. A key component of this study is the polarimetric capabilities of the national weather radar network to discriminate amongst biological and non-biological scatter. An investigation into polarimetric radar data taken during the tornado outbreak reveals unusual reflectivity values that are not normally associated with meteorological or debris signatures, due to their location within the storm itself, i.e., not in a strong updraft region. It is hypothesized that these unusual signatures are in fact biological in nature, specifically the waterfowl, which are known to be present in Oklahoma during this particular time of year. The scatter from these biological entities, so called “bioscatter”, can be characterized by spatial regions within the polarimetric radar data corresponding to low values of correlation coefficient (ρ_hv), enhanced standard deviations in the differential phase (φ_DP), differential reflectivity (ZDR), and hydrometeor classification.

To accomplish this, these biological signatures will be analyzed using weather data visualization tools and by focusing on different elevation angles of several polarimetric radars and their corresponding volume coverage pattern (VCP). Observational data from several weather radars, including KOUN, KVNX, KINX, KTLX, and TOKC are used to quantify these biotic responses. These methods allow us to compile a backwards trajectory of the unusual signatures, which can be examined in light of current understanding of severe storm dynamics. Surface data from several Oklahoma Mesonet sites surrounding the two nature reserves in question (Fort Cobb Reservoir and Tom Steed Reservoir) have been evaluated to distinguish any correlations in surface atmospheric conditions related to the storm's presence. Additionally, the polarimetric and non-polarimetric radar data have been organized and analyzed at multiple elevation angles with the intent to distinguish regions not associated with hydrometeors or organic debris. This procedure facilitates the construction of backwards trajectories of the unusual signatures with high confidence that these signatures are in fact ascending and fleeing from the storm. It can be expected through interpolation of different elevation angles of the radar data that the change in size and location of the signatures in reference to relative storm movement can be proven to be ascending biological scatterers with no affiliation to debris.

Once identified as biological in nature and, in fact, fleeing from the approaching severe weather, this knowledge can significantly aid in future forecasting of severe weather events that contain elements that are independent from the storm. If this is the case, then such observations will enhance our ability to address a variety of research questions related to animal behavior. For example, what environmental cues do birds use when deciding whether to seek shelter or flee as severe weather approaches? Flying in rain can be energetically expensive for birds; however, it seems plausible that that they would chose flight over potential exposure to strong winds and hail. While the exact behavior of animals is not well known or predictable, discovering the particular path that these biological signatures have taken in the response to abrupt severe weather can provide a multitude of advances in the new research area of aeroecology. The use of the upgraded WSR-88D network is thus instrumental in this research study, as these signatures are not easily detected on non-polarized radar.