218 research outputs found
Gravity Waves Emitted From Kelvin‐Helmholtz Instabilities
No full textFritts, Wang, Lund, and Thorpe (2022, https://doi.org/10.1017/jfm.2021.1085) and Fritts, Wang, Thorpe, and Lund (2022, https://doi.org/10.1017/jfm.2021.1086) described a 3-dimensional direct numerical simulation of interacting Kelvin-Helmholtz instability (KHI) billows and resulting tube and knot (T&K) dynamics that arise at a stratified shear layer defined by an idealized, large-amplitude inertia-gravity wave. Using similar initial conditions, we performed a high-resolution compressible simulation to explore the emission of GWs by these dynamics. The simulation confirms that such shear can induce strong KHI with large horizontal scales and billow depths that readily emit GWs having high frequencies, small horizontal wavelengths, and large vertical group velocities. The density-weighted amplitudes of GWs reveal “fishbone” structures in vertical cross sections above and below the KHI source. Our results reveal that KHI, and their associated T&K dynamics, may be an important additional source of high-frequency, small-scale GWs at higher altitudes
Supplementary data for "The PMC Turbo balloon mission to measure gravity waves and turbulence in Polar Mesospheric Clouds: Camera, telemetry, and software performance"
No full textThere are three separate files containing images from PMC Turbo cameras during its flight in July 2018. Image data were taken aboard the PMC Turbo instrument described in Fritts et al. (2019) "PMC Turbo: Studying Gravity Wave and Instability Dynamics in the Summer Mesosphere Using Polar Mesospheric Cloud Imaging and Profiling From a Stratospheric Balloon," https://doi.org/10.1029/2019JD030298.The Polar Mesospheric Cloud Turbulence (PMC Turbo) instrument consists of a balloon-borne platform which hosts seven cameras and a Rayleigh lidar. During a six-day flight in July 2018, the cameras captured images of Polar Mesospheric Clouds (PMCs) with a sensitivity to spatial scales from ~20 m to 100 km at a ~2-s cadence and a full field of view (FOV) of hundreds of kilometers. We developed software optimized for imaging of PMCs, controlling multiple independent cameras, compressing and storing images, and for choosing telemetry communication channels. We give an overview of the PMC Turbo design focusing on the flight software and telemetry functions. We describe the performance of the system during its first flight in July 2018. The images uploaded here support the paper in demonstrating the performance of the PMC Turbo instrument.NASA 80NSSC18K0050NASA 80NSSC20K0178Kjellstrand, Carl B; Jones, Glenn; Geach, Christopher P; Williams, Bifford P; Fritts, David C; Miller, Amber D; Hanany, Shaul; Limon, Michele; Reimuller, Jason. (2020). Supplementary data for "The PMC Turbo balloon mission to measure gravity waves and turbulence in Polar Mesospheric Clouds: Camera, telemetry, and software performance". Retrieved from the University Digital Conservancy, https://doi.org/10.13020/df2m-a470
Studies of inertio-gravity waves induced by geostrophic adjustment of the atmospheric jet stream
No full textDissertation (Ph.D.) University of Alaska Fairbanks, 1991Motivated by observations revealing very low frequency gravity waves throughout the lower and middle atmosphere, this thesis investigates inertio-gravity waves (IGWs) radiating from an ageostrophic jet stream assuming geostrophic adjustment to be the source mechanism. Fourier integral and Green's function techniques are employed to solve this problem. The ageostrophic components of the motion field are described by an initially unbalanced Gaussian velocity field which has been chosen to have infinite and localized zonal extents corresponding to two-dimensional (2-D) and three-dimensional (3-D) cases. The adjustment process permits the radiation of IGWs and the attainment of an induced geostrophically balanced mean circulation. The results of this thesis reveal IGW radiation from the initially unbalanced momentum source with frequencies near f (inertial frequency) and most of the disturbance energy associated with the IGW field. This research thus confirms geostrophic adjustment may be a major source of the low frequency gravity waves in the atmosphere. IGW structure includes primarily meridional wave propagation, with vertical and horizontal scales that depend on the initial unbalance configuration. The 3-D solutions at large distances from the jet core along the jet axis exhibit a change in IGW character from primarily meridional propagation at early times to largely zonal propagation at later times due to delayed arrival of IGW activity from more distant source regions. The induced mean flows in the 2-D and 3-D cases represent small fractions of the initial energy, insure conservation of potential vorticity, and reflect to a large degree the character of the momentum source
Radar observations of a 3-day Kelvin wave in the equatorial mesosphere
No full textMesospheric radars are used to investigate the characteristics of a Kelvin wave from two equatorial sites: Jakarta, Indonesia, in the western Pacific and Christmas Island in the central Pacific. Our study focuses on the time span from mid-January through mid-October 1993. A Kelvin wave with a period near 3 days was detected throughout this 9-month duration, although it underwent deep amplitude modulations on a similar to 20-day timescale. A fitting procedure is applied to study the phase/amplitude behavior of the wave. The vertical wavenumber was measured by the radars and found to be small, wandering around zero with only a weak bias toward downward phase progression. The long vertical wavelength suggests that the wave was predominantly zonal wavenumber 1. The amplitude of the wave measured by the Jakarta meteor scatter radar was much larger than the amplitude measured by the MF partial reflection radar at Christmas Island. The smaller wave amplitude at Christmas Island could at least partially be due to a measurement bias associated with MF radars. The radar at Jakarta is a VHF meteor scatter radar and is not susceptible to this bias. However, the mean velocities and the amplitudes of the tidal and quasi 2-day wave components were in good agreement at the two sites. The estimated 9-month averaged zonal acceleration was similar to 0.67 m s(-1)day(-1) over Jakarta at 94-98km and only about half as large over Christmas Island. The magnitude of the zonal acceleration occasionally showed large enhancements which suggest the importance of refractive effects associated with vertical and temporal variations in the mean winds. The larger 3-day wave amplitudes and inferred acceleration at Jakarta may reflect its location in the western Pacific, a region of high convection, and hence an excitation region for equatorial waves. The relative phase of the wave between the two radar sites gradually shifted over a timescale of weeks. These smooth variations in relative phase are suggestive of a superposition of waves with different zonal wavenumbers, perhaps radiating preferentially from one longitude. The phase of the wave as a function of altitude and time was much more disordered at Jakarta than at Christmas Island. The conjecture can be made that the more chaotic phase structure observed over Jakarta is due to higher-order zonal wavenumber components which weaken as they propagate eastward.Dennis M. Riggin, David C. Fritts, Toshitaka Tsuda, Takuji Nakamura, Robert A. Vincen
Radial Growth of Beech and Soil Moisture in a Central Ohio Forest During the Growing Season of 1952
No full textAuthor Institution: Department of Botany and Plant Pathology, The Ohio State University, Columbus 1
Errant inferences of gravity wave momentum and heat fluxes using airglow and lidar instrumentation: Corrections and cautions
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