Showing papers by "Dale Lawrence published in 2016"
TL;DR: In this paper, a high-Reynolds number direct numerical simulation (DNS) is employed to explore the instability and turbulence dynamics accompanying an idealized multiscale flow that approximates such environments observed throughout the atmosphere.
Abstract: A high–Reynolds number direct numerical simulation (DNS) is employed to explore the instability and turbulence dynamics accompanying an idealized multiscale flow that approximates such environments observed throughout the atmosphere. The DNS describes the superposition of a stable gravity wave (GW) and a stable, oscillatory, finescale shear flow that together yield significant wave–wave interactions, GW breaking, Kelvin–Helmholtz instabilities (KHI), fluid intrusions, and turbulence. Larger-scale GW breaking and KHI events account for the strongest turbulence intensities, with intrusions competing with KHI and GW breaking at smaller spatial scales and later times. These dynamics drive a series of sheet-and-layer structures in the velocity, stability, and dissipation fields that persist for many buoyancy periods. Measures of local turbulence intensities include energy dissipation rates, Ozmidov and Thorpe scales (LO and LT, respectively), and a buoyancy Reynolds number sufficient to ensure sustaine...
40 citations
TL;DR: In this article, the SOUSY radar was used at the Jicamarca Radio Observatory (JRO) near Lima, Peru, where the radar controller and acquisition system were upgraded with state-of-the-art parts to take full advantage of its potential for high-resolution atmospheric sounding.
Abstract: . The SOUSY (SOUnding SYstem) radar was relocated to the Jicamarca Radio Observatory (JRO) near Lima, Peru, in 2000, where the radar controller and acquisition system were upgraded with state-of-the-art parts to take full advantage of its potential for high-resolution atmospheric sounding. Due to its broad bandwidth (4 MHz), it is able to characterize clear-air backscattering with high range resolution (37.5 m). A campaign conducted at JRO in July 2014 aimed to characterize the lower troposphere with a high temporal resolution (8.1 Hz) using the DataHawk (DH) small unmanned aircraft system, which provides in situ atmospheric measurements at scales as small as 1 m in the lower troposphere and can be GPS-guided to obtain measurements within the beam of the radar. This was a unique opportunity to make coincident observations by both systems and to directly compare their in situ and remotely sensed parameters. Because SOUSY only points vertically, it is only possible to retrieve vertical radar profiles caused by changes in the refractive index within the resolution volume. Turbulent variations due to scattering are described by the structure function parameter of refractive index Cn2. Profiles of Cn2 from the DH are obtained by combining pressure, temperature, and relative humidity measurements along the helical trajectory and integrated at the same scale as the radar range resolution. Excellent agreement is observed between the Cn2 estimates obtained from the DH and SOUSY in the overlapping measurement regime from 1200 m up to 4200 m above sea level, and this correspondence provides the first accurate calibration of the SOUSY radar for measuring Cn2.
12 citations
Journal Article•
TL;DR: In this article, the authors used a UAV as an observation tool of the lower atmosphere for the ShureX (Shigaraki, UAV-Radar Experiment) campaign using simultaneously small UAVs and the MU radar.
Abstract: Turbulence mixing is an important process that contributes to the vertical transport of heat and substance, but it is difficult to be observed because its scale is very small. The atmospheric radar transmits the radiowave and receives backscattered echoes from turbulence to measure wind velocity profiles with high time resolution, so it has advantage in the observation of atmospheric turbulence. The MU (Middle and Upper atmosphere) radar is the atmospheric radar located at Shigaraki, Koka, Shiga Prefecture, has the center frequency of 46.5 MHz, the antenna diameter of 103 m, and the peak output power of 1 MW, and has been operated since 1984. In 2004 it is upgraded to enable radar imaging observation which provides us the improved range resolution data. The MU radar can be most accurately image the turbulence structure and is the most powerful tool to study the relationship to meso-synoptic scale phenomena. For example, although atmospheric turbulence due to the Kelvin-Helmholtz instability is known to occur in strong wind shear region, continuous turbulence structure under the cloud base has been imaged by the MU radar. In recent years, small unmanned aerial vehicle (UAV) has been attracting attention as an observation tool of the lower atmosphere. As Japan-USA-France international collaborative research, ShUREX (Shigaraki, UAV-Radar Experiment) campaign using simultaneously small UAVs developed by the University of Colorado and the MU radar has been carried out in last June. The UAV is a small (wing width 1 m), lightweight (700 g), low cost (about $1,000), reusable, autonomous flight possible using GPS, and it is possible to obtain a high-resolution data of the turbulence parameters by the temperature sensor of 100-Hz sampling, in addition to temperature, humidity, and barometric pressure data of 1-Hz sampling. Take-off and landing of the UAV was carried out at a pasture in 1-km southwest from the MU Observatory. Since the UAV cannot take off with their own runway, a method of take-off by pulling a rubber (Bungee method) or a method of the release at the appropriate altitude from a meteorological balloon filled with helium (Balloon method) is used. The flight method previously programmed in advance takeoff before, it is also possible to change the flight method after takeoff according to the situation. It is possible to continuously fly about one hour. The time-altitude cross-section of the echo intensity obtained with the range imaging mode of the MU radar is shown in figure. Triangular shape of the echoes underlying during 8:10-8:40 is due to UAV. Strong echoes (turbulence) in the vicinity of the cloud base at 4-5 km are observed. Currently, we are analyzing the observation data of the MU radar and UAV in details. Atmospheric turbulence is present everywhere, impact on human life is not small, and the observation and prediction also for the safe operation of the aircraft is an important issue. We plan a second campaign using UAVs and the MU radar in the following fiscal year.
4 citations
13 Sep 2016
TL;DR: In this article, the authors solved the inverse problem numerically: first for a desired SRP force or SRP moment and subsequently for the fully coupled inverse problem, which was subsequently applied to track a reference trajectory that corrects for injection errors into a solar sail Sun-Earth sub-L1 halo orbit.
Abstract: A heliogyro is a solar sail concept that divides the solar sail membrane into a number of long, slender blades of film extended from a central hub, maintained in a flat state through spin-induced tension. The heliogyro can redirect and scale the solar radiation pressure (SRP) force and can achieve attitude control by twisting the blades, similar to a helicopter rotor. Different pitch profiles exist, including pitching the blades in a collective, cyclic or combined collective and cyclic manner. While the forward mapping, i.e., computing the SRP force and moment generated by the heliogyro for a given pitch profile, is straightforward, the inverse of the problem is much more complex. However, this inverse problem (finding the blades’ pitch that results in a desired SRP force and/or moment) is crucial for heliogyro mission design and operations. This paper therefore solves the inverse problem numerically: first, only for a desired SRP force or SRP moment and subsequently for the fully coupled inverse problem. The developed methods are subsequently applied to track a reference trajectory that corrects for injection errors into a solar sail Sun-Earth sub-L1 halo orbit. I. Introduction
1 citations