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M. S. McPhaden and R. A. Knox

Abstract

The interaction of geostrophic zonal mean currents in an equatorial ocean with free, neutrally stable, internal Kelvin and inertio-gravity waves is investigated using a two-layer, reduced-gravity model. Solutions in the inertio-gravity range are obtained by a simple numerical integration scheme that allows several different background flows to be tested. It is found that, due to the interaction, the amplitudes and latitudinal distributions of wave zonal velocity are substantially altered from those which would occur in the absence of mean flow. Meanders of currents similar to those observed during GATE may be interpreted as advections of mean currents by wave meridional velocity. On the other hand, wave pressure (sea level) and meridional velocities are not greatly affected by the mean flow. These results may be of importance in attempting to fit equatorial wave theories to observations of zonal current, on the one hand, and of sea level fluctuations on the other.

Kelvin waves are treated using a perturbation expansion based on the small ratio of mean current speed to wave phase speed. The shear flow alters low-frequency Kelvin waves only slightly, introducing a small meridional velocity and a Doppler shift which could affect the speed of baroclinic adjustments in the tropics. At higher frequencies, the Kelvin wave becomes more like an inertio-gravity wave and may appear in velocity records as varicose meanders of the background current.

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T. P. Barnett, R. A. Knox, and R. A. Weller

Abstract

During January and February 1974 the NORPAX POLE experiment was carried out in the central Pacific to begin collection of data needed to design a large-scale ocean/atmosphere monitoring program. This paper describe features of the ocean temperature field observed during POLE within a region of about 400 km in diameter centered near 35°N, 155°W. The temperature field, which was approximately stationary during the month-long experiment, was dominated by a strong north-south gradient as expected. The east-west gradient was negligible. Superimposed on this mean field was energetic noise with typical rms isotherm displacements of 25 m near the bottom of the mixed layer. The characteristic horizontal scale of this noise was 50 km near the surface although the field appeared to be anisotropic. The energy, scale length and degree of anisotropy all decrease with depth. The implications of these observations to a sampling strategy are discussed as are other conclusions drawn from a statistical analysis of the temperature data.

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J. L. Spiesberger, T. G. Birdsall, K. Metzger, R. A. Knox, C. W. Spofford, and R. C. Spindel

Abstract

Phase-coded signals with 60 rms resolution were transmitted twice weekly for several months from acoustic sources at ∼2000 m depth in the Sargasso Sea to three bottom-mounted receives designed as West, East, and North stations at ranges approximately between 1000 and 2000 km. The transmission paths to West and East stations were entirely in the Sargasso Sea. The path to North station crossed the Gulf Stream and so traversed one of the most time- and range-dependent environments found anywhere in the ocean. Arrivals at all three stations were stable and could be identified from range-dependent ray traces. Travel times at West station clearly change is response to the warming of the seasonal thermocline from spring to summer. The travel-time change with predictions. Travel-time changes at North station primarily respond to the north-south meandering of the Gulf Stream.

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John A. Knox, Jared A. Rackley, Alan W. Black, Vittorio A. Gensini, Michael Butler, Corey Dunn, Taylor Gallo, Melyssa R. Hunter, Lauren Lindsey, Minh Phan, Robert Scroggs, and Synne Brustad

Using publicly available information gleaned from over 1700 found-and-returned objects on the “Pictures and Documents found after the 27 April 2011 Tornadoes” Facebook page, the authors have created a database of 934 objects lofted by at least 15 different tornadoes during the 27 April 2011 Super Outbreak in the southeast United States. Analysis of the takeoff and landing points of these objects using GIS and high-resolution numerical trajectory modeling techniques extends previous work on this subject that used less specific information for much smaller sets of tracked tornado debris. It was found that objects traveled as far as 353 km, exceeding the previous record for the longest documented tornado debris trajectory. While the majority of debris trajectories were 10° to the left of the average tornado track vector, the longest trajectories exhibited a previously undocumented tendency toward the right of the average tornado track vector. Based on results from a high-resolution trajectory model, a relationship between this tendency and the altitude of lofting of debris is hypothesized, with the debris reaching the highest altitudes taking the rightmost trajectories. The paper concludes with a discussion of the pros and cons of using social media information for meteorological research.

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