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W. McKeown
,
F. Bretherton
,
H. L. Huang
,
W. L. Smith
, and
H. L. Revercomb

Abstract

Evidence for the radiometric determination of air–water interface temperature gradients is presented. Inherent radiometric characteristics in the water molecule cause variations in the absorption coefficient that allow radiation at near-infrared frequencies (2000–5000 wavenumbers, 2.0–5.0 μm) to carry information about subsurface water temperatures. This radiation leaving the surface is predominantly sensitive to water temperature in the layer between the surface and the “effective optical depth” (inverse of the absorption coefficient). Where atmospheric transmittance is high and/or the instrument is near the liquid, the radiance variations with frequency record temperature variations with depth. To measure the small radiance variations with frequency, an instrument must be radiometrically stable in suitable frequency bands with low instrument noise.

A simulation of this technique's use for airborne beat flux measurement indicated feasibility from low altitudes at night. Laboratory experiments produced radiometric signals that strongly indicated that the thermal structures in an air–water interface can be studied in detail. Corrected for variations of emissivity and reflectivity with frequency, the water spectra showed multiple correlations with those gradients inferred from bulk temperature measurements that assumed conductive heat loss. The use of high spectral resolution increased the vertical resolution of the interface thermal structures. Although high spectral resolution is not required for a field application, problems of system noise, atmospheric absorption, and solar reflection are more tractable with its use.

This technique may be useful in laboratory studies of thermal structures relevant to heat and gas flow that reside in the air–water interface.

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Katherine E. McKeown
,
Michael M. French
,
Kristofer S. Tuftedal
,
Darrel M. Kingfield
,
Howard B. Bluestein
,
Dylan W. Reif
, and
Zachary B. Wienhoff

Abstract

Rapid-scan polarimetric data analysis of the dissipation of a likely violent supercell tornado that struck near Sulphur, Oklahoma, on 9 May 2016 is presented. The Rapid X-band Polarimetric Radar was used to obtain data of the tornado at the end of its mature phase and during its entire dissipation phase. The analysis is presented in two parts: dissipation characteristics of the tornadic vortex signature (TVS) associated with the tornado and storm-scale polarimetric features that may be related to processes contributing to tornado dissipation. The TVS exhibited near-surface radial velocities exceeding 100 m s−1 multiple times at the end of its mature phase, and then underwent a two-phased dissipation. Initially, decreases in near-surface intensity occurred rapidly over a ~5-min period followed by a slower decline in intensity that lasted an additional ~12 min. The dissipation of the TVS in time and height in the lowest 2 km above radar level and oscillatory storm-relative motion of the TVS also are discussed. Using polarimetric data, a well-defined low reflectivity ribbon is investigated for its vertical development, evolution, and relationship to the large tornadic debris signature (TDS) collocated with the TVS. The progression of the TDS during dissipation also is discussed with a focus on the presence of several bands of reduced copolar correlation coefficient that extend away from the main TDS and the eventual erosion of the TDS as the tornado dissipated. Finally, TVS and polarimetric data are combined to argue for the importance of a possible internal rear-flank downdraft momentum surge in contributing to the initial rapid dissipation of the tornado.

Free access
William L. Smith
,
R. O. Knuteson
,
H. E. Revercomb
,
W. Feltz
,
H. B. Howell
,
W. P. Menzel
,
N. R. Nalli
,
Otis Brown
,
James Brown
,
Peter Minnett
, and
Walter McKeown

The Atmospheric Emitted Radiance Interferometer (AERI) was used to measure the infrared radiative properties and the temperature of the Gulf of Mexico during a 5-day oceanographic cruise in January 1995. The ocean skin temperature was measured with an accuracy believed to be better than 0.1 °C. The surface reflectivity/emissivity was determined as a function of view angle and sea state. The radiative properties are in good theoretical consistency with in situ measurements of ocean bulk temperature and the meteorological observations made from the oceanographic vessel. The AERI and in situ measurements provide a strong basis for accurate global specifications of sea surface temperature and ocean heat flux from satellites and ships.

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