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189 results on '"MacAYEAL, Douglas R."'

60. Transoceanic wave propagation links iceberg calving margins of Antarctica with storms in tropics and Northern Hemisphere

Author

MacAyeal, Douglas R., primary, Okal, Emile A., additional, Aster, Richard C., additional, Bassis, Jeremy N., additional, Brunt, Kelly M., additional, Cathles, L. Mac., additional, Drucker, Robert, additional, Fricker, Helen A., additional, Kim, Young-Jin, additional, Martin, Seelye, additional, Okal, Marianne H., additional, Sergienko, Olga V., additional, Sponsler, Mark P., additional, and Thom, Jonathan E., additional

Published
2006
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88. Acoustic reflection from a sea bottom with linearly increasing sound speed.

Author

Williams, A. O. and MacAyeal, Douglas R.

Abstract

We calculate the acoustic reflection coefficient for plane waves, in a homogeneous fluid half-space, incident at arbitrary angle upon an underlying half-space of unconsolidated bottom sediments. The lower half-space, treated here as a fluid, has constant density and a sound speed that increases linearly with depth. An exact formal expression is found for the complex reflection coefficient R, in terms of a modified Bessel function. With no absorption, | R | is unity for all angles except at normal incidence, as would also be expected from ray theory. Assuming bottom absorption, we derive an analytical approximation for R, valid for incident angles [variant_greek_theta] (measured from the interface normal) in the range 10°<=[variant_greek_theta]<=70°, for acoustic frequencies f>=10 Hz, and to about 80° for f>=70 Hz. A high-frequency limit and a small-angle approximation are found. Use of a pseudolinear gradient, suitable at large angles, could extend [variant_greek_theta] to 90°. A more realistic model having layers in the upper part of the bottom is discussed briefly. [ABSTRACT FROM AUTHOR]

Published
1979
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89. Drifting snow threshold measurements near McMurdo station, Antarctica: A sensor comparison study

Author

Leonard, Katherine C., Tremblay, L.-Bruno, Thom, Jonathan E., and Macayeal, Douglas R.

Abstract

We present the results of an Antarctic spring field study of snow drift threshold measurements made using two custom drift sensors and a commercial parts-counting device. All three sensor types worked well at detecting drifting snow events, but the sensors recorded different magnitudes (particle count per unit time) of drift. Each sensor has a unique detection threshold for particle size, and responded differently to identical wind and snow conditions, although the particle counts from the different sensors are linearly related at low wind speeds. The drift threshold is defined here as the minimum friction velocity at which drifting snow was observed during more than 10% of measurements at that wind speed. The results of this multi-sensor study demonstrate that the drift threshold is lower (friction velocity of 0.2. m/s) for very small particles that are likely transported in suspension than for coarse-grained saltating particles (0.25. m/s). These friction velocities correspond to 10-meter wind speeds of 5.6 and 7.2. m/s respectively for the conditions during this experiment. The commercially available parts counter is recommended as a low-cost alternative to custom-built drift sensors for use in future field studies of drifting and blowing snow. © 2011 Elsevier B.V.

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