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Abram B. Bernstein
and
John A. Young

Abstract

Vertical gradients are usually calculated by a finite-difference approximation, where the level of interest is midway between the levels at which measurements are made. When this approach is used, considerable error may occur if the gradient varies with height, i.e., if the profile is not linear. Near the ground, non-linearity is the rule rather than the exception. The finite-difference approach may still be used, but measurements must be made at heights determined by the form of the profile, and not at heights equally distant from the level of interest.

A set of charts is presented showing the heights at which the sensors must be mounted to give the gradient at the level of interest, and the height to which the gradient as usually measured actually applies. Correction factors are derived so that the gradient at any level may be determined from measurements at any two heights, provided the form of the profile is known. Use of this technique eliminates one source of error in comparison of gradient measurements from different locations, and in determination of parameters in which one or more gradient measurements at a predetermined level are required.

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J. K. Angell
and
A. B. Bernstein

Abstract

Double-theodolite pilot balloon observations at the instrumented WKY television tower in Oklahoma City suggest that the anemometers located 3 m from the tower underestimate the mean wind speed by 0.8 m s−1 (∼7%) when the anemometers are upwind of the tower. Tetroon flights past the tower tend to confirm these results.

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J. K. Angell
and
A. B. Bernstein

Abstract

Double-theodolite pilot balloon observations at 6 min intervals at two stations upwind and two stations downwind of Oklahoma City provide new information concerning the influence, at heights up to 700 m, of an isolated urban area on a strong (12 m s−1 daytime air flow. Constant volume balloons (tetroons) flown along the line of the pilot balloon stations provide vertical velocity information. During the three days of the experiment the wind speed was a maximum downwind of the city, and the tetroon height traces suggest that this speed maximum results from the downward transport of the faster moving air aloft due to sinking motion in the lee of the city induced by the barrier or heat island effect of the city. The derived wind speed and direction fluctuations (of at least 15 min period) are a maximum near city-center, with low-level speed fluctuations 60% greater than over rural areas. Lagged correlations between stations suggest that, over and upwind of the city, these speed fluctuations are transported approximately with the mean wind, but downwind of the city the fluctuations occur nearly simultaneously at different locations, presumably indicating the effect of the city in breaking up coherent, traveling flow structures.

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I. Gultepe
,
T. Kuhn
,
M. Pavolonis
,
C. Calvert
,
J. Gurka
,
A. J. Heymsfield
,
P. S. K. Liu
,
B. Zhou
,
R. Ware
,
B. Ferrier
,
J. Milbrandt
, and
B. Bernstein

Ice fog and frost occur commonly (at least 26% of the time) in the northern latitudes and Arctic regions during winter at temperatures usually less than about –15°C. Ice fog is strongly related to frost formation—a major aviation hazard in the northern latitudes. In fact, it may be considered a more dangerous event than snow because of the stronger aircraft surface adhesion compared to snow particles. In the winter of 2010/11, the Fog Remote Sensing and Modeling–Ice Fog (FRAM-IF) project was organized near Yellowknife International Airport, Northwest Territories, Canada, with the main goals of advancing understanding of ice fog microphysical and visibility characteristics, and improving its prediction using forecast models and remotesensing retrievals. Approximately 40 different sensors were used to measure visibility, precipitation, ice particle spectra, vertical thermodynamic profiles, and ceiling height. Fog coverage and visibility parameters were estimated using both Geostationary Operational Environmental Satellites (GOES) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. During this project, the inversion layer usually was below a height of 1.5 km. High humidity typically was close to the ground, frequently producing ice fog, frost, and light snow precipitation. At low temperatures, snow crystals can be swept away by a very low wind speed (∼1 m s−1). Ice fog during the project was not predicted by any forecast model. These preliminary results in the northern latitudes suggest that ice fog and frost studies, over the Arctic regions, can help us to better understand ice microphysical processes such as ice nucleation, visibility, and parameterizations of ice fog.

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John R. Mecikalski
,
Wayne F. Feltz
,
John J. Murray
,
David B. Johnson
,
Kristopher M. Bedka
,
Sarah T. Bedka
,
Anthony J. Wimmers
,
Michael Pavolonis
,
Todd A. Berendes
,
Julie Haggerty
,
Pat Minnis
,
Ben Bernstein
, and
Earle Williams

Advanced Satellite Aviation Weather Products (ASAP) was jointly initiated by the NASA Applied Sciences Program and the NASA Aviation Safety and Security Program in 2002. The initiative provides a valuable bridge for transitioning new and existing satellite information and products into Federal Aviation Administration (FAA) Aviation Weather Research Program (AWRP) efforts to increase the safety and efficiency of project addresses hazards such as convective weather, turbulence (clear air and cloud induced), icing, and volcanic ash, and is particularly applicable in extending the monitoring of weather over data-sparse areas, such as the oceans and other observationally remote locations.

ASAP research is conducted by scientists from NASA, the FAA AWRP's Product Development Teams (PDT), NOAA, and the academic research community. In this paper we provide a summary of activities since the inception of ASAP that emphasize the use of current-generation satellite technologies toward observing and mitigating specified aviation hazards. A brief overview of future ASAP goals is also provided in light of the next generation of satellite sensors (e.g., hyperspectral; high spatial resolution) to become operational in the 2007–18 time frame.

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