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Geology topics

W. Seegar

Publications and source records attributed to W. Seegar.

4 recordsLinked to original sources
USGS2003

Measurements of thermal updraft intensity over complex terrain using American white pelicans and a simple boundary-layer forecast model

An examination of boundary-layer meteorological and avian aerodynamic theories suggests that soaring birds can be used to measure the magnitude of vertical air motions within the boundary layer. These theories are applied to obtain mixed-layer normalized thermal updraft intensity over both flat and complex terrain from the climb rates of soaring American white pelicans and from diagnostic boundary-layer model-produced estimates of the boundary-layer depth z i and the convective velocity scale w * . Comparison of the flatland data with the profiles of normalized updraft velocity obtained from previous studies reveals that the pelican-derived measurements of thermal updraft intensity are in close agreement with those obtained using traditional research aircraft and large eddy simulation (LES) in the height range of 0.2 to 0.8 z i . Given the success of this method, the profiles of thermal vertical velocity over the flatland and the nearby mountains are compared. This comparison shows that these profiles are statistically indistinguishable over this height range, indicating that the profile for thermal updraft intensity varies little over this sample of complex terrain. These observations support the findings of a recent LES study that explored the turbulent structure of the boundary layer using a range of terrain specifications. For terrain similar in scale to that encountered in this study, results of the LES suggest that the terrain caused less than an 11% variation in the standard deviation of vertical velocity.

Boundary-Layer Meteorology↗
USGS2002

American white pelican soaring flight times and altitudes relative to changes in thermal depth and intensity

We compared American White Pelican (Pelecanus erythrorhynchos) soaring flight times and altitudes to model-produced estimates of thermal depth and intensity. These data showed that pelican soaring flight was confined to the thermal layer, and that the vertical extent of the soaring flight envelope increased with increases in thermal depth. Pelicans soaring cross-country between foraging and breeding sites flew mainly within the middle of the thermal layer, regardless of its depth. In contrast, pelicans engaged in wandering flight near foraging sites typically confined their flight to the lower thermal layer. Pelicans soaring cross-country likely flew higher in the thermal layer to maximize cross-country soaring performance, while pelicans soaring locally presumably flew lower because additional altitude was unneeded for gliding short distances. An analysis of pelican flight times relative to model-produced estimates of thermal intensity suggested that pelicans began soaring as soon as sufficiently strong thermals developed daily.

The Condor↗
USGS1995

The use of satellite systems for the study of bird migration

The Argos satellite system, with two or more polar-orbiting satellites, provides the basis for receiving radio signals from transmitters and for estimating locations of those transmitters anywhere around the earth. We briefly relate the development of platform-transmitter terminals small enough to be placed on birds, but powerful enough to send signals to the satellites. We review the use of this recent technology in avian studies, including several applications to bird migration. We also describe the type of information we are obtaining from three of our current studies of migratory birds.

Israel Journal of Zoology↗