Search Results
You are looking at 1 - 3 of 3 items for :
- Author or Editor: Peter F. Lester x
- Journal of Applied Meteorology and Climatology x
- Refine by Access: All Content x
Abstract
In order to study the physical aspects of intermittent turbulence in the free atmosphere, it is suggested that terms of an “instantaneous” turbulent energy budget be computed from data collected by aircraft. This can be accomplished through the application of numerical filters to specify mean and turbulence parameters as a function of distance along the aircraft track.
The proposed analysis is illustrated with data from a highly intermittent turbulence record derived from a flight through a rotor. Results are compatible with the known characteristics of the rotor, thus suggesting the feasibility of the technique. Some difficulties are encountered in the satisfaction of the Reynolds averaging rules because of the requirement for a gap in the velocity spectrum and the existence of a finite cutoff interval for a practical numerical filter.
Abstract
In order to study the physical aspects of intermittent turbulence in the free atmosphere, it is suggested that terms of an “instantaneous” turbulent energy budget be computed from data collected by aircraft. This can be accomplished through the application of numerical filters to specify mean and turbulence parameters as a function of distance along the aircraft track.
The proposed analysis is illustrated with data from a highly intermittent turbulence record derived from a flight through a rotor. Results are compatible with the known characteristics of the rotor, thus suggesting the feasibility of the technique. Some difficulties are encountered in the satisfaction of the Reynolds averaging rules because of the requirement for a gap in the velocity spectrum and the existence of a finite cutoff interval for a practical numerical filter.
Abstract
Data derived from the flight tapes of two airliners that experienced severe turbulence near thunderstorm tops are used to produce quantitative descriptions of the turbulence and its environment. The likely turbulence-producing processes include a three-dimensional turbulent wake in the lee of a squall line and an updraft in the top of a thunderstorm. Results suggest that current procedures for using surface and airborne weather radar for routing aircraft near thunderstorm tops should be reexamined. Also, although useful rules for safe flight near thunderstorm tops already exist, there is evidence that they are not universally applied.
Abstract
Data derived from the flight tapes of two airliners that experienced severe turbulence near thunderstorm tops are used to produce quantitative descriptions of the turbulence and its environment. The likely turbulence-producing processes include a three-dimensional turbulent wake in the lee of a squall line and an updraft in the top of a thunderstorm. Results suggest that current procedures for using surface and airborne weather radar for routing aircraft near thunderstorm tops should be reexamined. Also, although useful rules for safe flight near thunderstorm tops already exist, there is evidence that they are not universally applied.
Abstract
The characteristics of the lower turbulent zone (LTZ) which is associated with mountain lee waves have been investigated through the analysis of aircraft observations made near Boulder, Colo. Numerical filters and statistical analysis techniques have been applied to the data from six cases to yield vertical sections of potential temperature, horizontal wind, and turbulence intensity along the aircraft paths. One case study is presented to illustrate the structure of the LTZ and its changes during a frontal passage. In addition, the main features of all the analyses are summarized in the form of a schematic vertical section.
The horizontal dimension of the LTZ varied between 25 and more than 65 km downstream of the first lee wave trough. The vertical dimensions ranged from a few hundred meters AGL at the lee wave troughs to 3 km AGL at the wave crests. Turbulence levels were light, moderate or severe over more than 90% of the total distance flown in the LTZ (nearly 1100 km). Severe turbulence was commonly encountered near the upstream side of the rotor, where the largest horizontal and vertical wind and temperature gradients were also found.
The kinetic energy dissipation rate for a large, long-lived LTZ, such as occurs under hydraulic jump conditions, was estimated to be 20–100 W m−2; thus, the LTZ may play an important role in the large-scale energetics of the atmosphere.
Abstract
The characteristics of the lower turbulent zone (LTZ) which is associated with mountain lee waves have been investigated through the analysis of aircraft observations made near Boulder, Colo. Numerical filters and statistical analysis techniques have been applied to the data from six cases to yield vertical sections of potential temperature, horizontal wind, and turbulence intensity along the aircraft paths. One case study is presented to illustrate the structure of the LTZ and its changes during a frontal passage. In addition, the main features of all the analyses are summarized in the form of a schematic vertical section.
The horizontal dimension of the LTZ varied between 25 and more than 65 km downstream of the first lee wave trough. The vertical dimensions ranged from a few hundred meters AGL at the lee wave troughs to 3 km AGL at the wave crests. Turbulence levels were light, moderate or severe over more than 90% of the total distance flown in the LTZ (nearly 1100 km). Severe turbulence was commonly encountered near the upstream side of the rotor, where the largest horizontal and vertical wind and temperature gradients were also found.
The kinetic energy dissipation rate for a large, long-lived LTZ, such as occurs under hydraulic jump conditions, was estimated to be 20–100 W m−2; thus, the LTZ may play an important role in the large-scale energetics of the atmosphere.
