Gravity wave penetration into the thermosphere: sensitivity to solar cycle variations and mean winds

We previously considered various aspects of gravity wave penetration and effects at mesospheric and thermospheric altitudes, including propagation, viscous effects on wave structure, characteristics, and damping, local body forcing, responses to solar cycle temperature variations, and filtering by mean winds. Several of these efforts focused on gravity waves arising from deep convection or in situ body forcing accompanying wave dissipation. Here we generalize these results to a broad range of gravity wave phase speeds, spatial scales, and intrinsic frequencies in order to address all of the major gravity wave sources in the lower atmosphere potentially impacting the thermosphere. We show how penetration altitudes depend on gravity wave phase speed, horizontal and vertical wavelengths, and observed frequencies for a range of thermospheric temperatures spanning realistic solar conditions and winds spanning reasonable mean and tidal amplitudes. Our results emphasize that independent of gravity wave source, thermospheric temperature, and filtering conditions, those gravity waves that penetrate to the highest altitudes have increasing vertical wavelengths and decreasing intrinsic frequencies with increasing altitude. The spatial scales at the highest altitudes at which gravity wave perturbations are observed are inevitably horizontal wavelengths of ~150 to 1000 km and vertical wavelengths of ~150 to 500 km or more, with the larger horizontal scales only becoming important for the stronger Doppler-shifting conditions. Observed and intrinsic periods are typically ~10 to 60 min and ~10 to 30 min, respectively, with the intrinsic periods shorter at the highest altitudes because of preferential penetration of GWs that are up-shifted in frequency by thermospheric winds

DYNAMICS, MOVEMENTS, AND FEEDING ECOLOGY OF A NEWLY PROTECTED WOLF POPULATION IN NORTHWESTERN MINNESOTA

The gray wolf Canis lupus occupies only about 1 percent of its former range in the lower 48 states (Mech 1974a). Most of the range is in northern Minnesota, where the resident population is classified as threatened by the U.S. Department of the Interior. Wolves have been and will continue to be the subject of considerable controversy in Minnesota. The first scientific study of wolves in Minnesota was conducted by Olson (1938a,b). That and all subsequent re- search was in the Superior National Forest (SNF) of northeastern Minnesota even though wolves inhabit approximately the northern third of the state. Consequently, until the present study, little was known about wolves in northwestern Minnesota, although it is highly desirable to have such information if wolves throughout Minnesota are to be managed wisely

The Impact of Hydrodynamic Mixing on Supernova Progenitors

Recent multidimensional hydrodynamic simulations have demonstrated the importance of hydrodynamic motions in the convective boundary and radiative regions of stars to transport of energy, momentum, and composition. The impact of these processes increases with stellar mass. Stellar models which approximate this physics have been tested on several classes of observational problems. In this paper we examine the implications of the improved treatment on supernova progenitors. The improved models predict substantially different interior structures. We present pre-supernova conditions and simple explosion calculations from stellar models with and without the improved mixing treatment at 23 solar masses. The results differ substantially.Comment: 12 pages, 2 figures, accepted for publication in the Astrophysical Journal Letter

Genomic signatures of host-associated divergence and adaptation in a coral-eating snail, Coralliophila violacea (Kiener, 1836).

The fluid nature of the ocean, combined with planktonic dispersal of marine larvae, lowers physical barriers to gene flow. However, divergence can still occur despite gene flow if strong selection acts on populations occupying different ecological niches. Here, we examined the population genomics of an ectoparasitic snail, Coralliophila violacea (Kiener 1836), that specializes on Porites corals in the Indo-Pacific. Previous genetic analyses revealed two sympatric lineages associated with different coral hosts. In this study, we examined the mechanisms promoting and maintaining the snails' adaptation to their coral hosts. Genome-wide single nucleotide polymorphism (SNP) data from type II restriction site-associated DNA (2b-RAD) sequencing revealed two differentiated clusters of C. violacea that were largely concordant with coral host, consistent with previous genetic results. However, the presence of some admixed genotypes indicates gene flow from one lineage to the other. Combined, these results suggest that differentiation between host-associated lineages of C. violacea is occurring in the face of ongoing gene flow, requiring strong selection. Indeed, 2.7% of all SNP loci were outlier loci (73/2,718), indicative of divergence with gene flow, driven by adaptation of each C. violacea lineage to their specific coral hosts

WOLF DISTRIBUTION AND ROAD DENSITY IN MINNESOTA

Distribution of the wolf (Canis lupus) in parts of Wisconsin (Thiel 1985) and Michigan and Ontario (Jensen et al. 1986) has been related to the density of roads passable by 2-wheel-drive vehicles. Wolves in those regions generally do not occur where road densities exceed 0.58 km/km2, whereas similar areas nearby with fewer roads do contain wolves. In a small segment of the wolf range in Minnesota, wolves did not have territories where roads exceeded a density of 0.73 km/km2 (T. K. Fuller, Minn. Dep. Nat. Resour., unpubl. data). In another small area of Minnesota with 0.73 km of roads/ km2, \u3e50% of known wolf mortality was caused by humans despite prohibitions of the Endangered Species Act, but wolves survived there probably because the area was surrounded by an extensive wilderness reservoir (L. D. Mech, un-publ. data)

WOLF DISTRIBUTION AND ROAD DENSITY IN MINNESOTA

Distribution of the wolf (Canis lupus) in parts of Wisconsin (Thiel 1985) and Michigan and Ontario (Jensen et al. 1986) has been related to the density of roads passable by 2-wheel-drive vehicles. Wolves in those regions generally do not occur where road densities exceed 0.58 km/km2, whereas similar areas nearby with fewer roads do contain wolves. In a small segment of the wolf range in Minnesota, wolves did not have territories where roads exceeded a density of 0.73 km/km2 (T. K. Fuller, Minn. Dep. Nat. Resour., unpubl. data). In another small area of Minnesota with 0.73 km of roads/ km2, \u3e50% of known wolf mortality was caused by humans despite prohibitions of the Endangered Species Act, but wolves survived there probably because the area was surrounded by an extensive wilderness reservoir (L. D. Mech, un-publ. data)

A Boreing Night of Observations of the Upper Mesosphere and Lower Thermosphere Over the Andes Lidar Observatory

A very high-spatial resolution (∼21-23 m pixel at 85 km altitude) OH airglow imager at the Andes Lidar Observatory at Cerro Pach´on, Chile observed considerable ducted wave activity on the night of October 29-30, 2016. This instrument was collocated with a Na wind-temperature lidar that provided data revealing the occurrence of strong ducts. A large field of view OH and greenline airglow imager showed waves present over a vertical extent consistent with the altitudes of the ducting features identified in the lidar profiles. While waves that appeared to be ducted were seen in all imagers throughout the observation interval, the wave train seen in the OH images at earlier times had a distinct leading non-sinusoidal phase followed by several, lower-amplitude, more sinusoidal phases, suggesting a likely bore. The leading phase exhibited significant dissipation via small-scale secondary instabilities suggesting vortex rings that progressed rapidly to smaller scales and turbulence (the latter not fully resolved) thereafter. The motions of these small-scale features were consistent with their location in the duct at or below ∼83-84 km. Bore dissipation caused a momentum flux divergence and a local acceleration of the mean flow within the duct along the direction of the initial bore propagation. A number of these features are consistent with mesospheric bores observed or modeled in previous studies

Airglow observations of dynamical (wind shear-induced) instabilities over Adelaide, Australia, associated with atmospheric gravity waves

While several observations have been made in recent years of instability features in airglow images of atmospheric gravity waves (AGWs), such measurements are still rare. To date, these features are characterized by appearing to be aligned perpendicular to the AGW wave fronts. Multi-instrument observations confirm the theoretical prediction that such features are caused by convective instabilities where the AGW-induced temperature variation causes the total lapse rate to exceed the adiabatic lapse rate. In February 2000, airglow observations were obtained at Buckland Park, Australia, which showed instability features with a different characteristic. These images showed small-scale (less than 10 km horizontal wavelength) features aligned parallel to the larger scale AGW wave fronts. These features were only seen in OH images, not in O2A images, indicating that they originate below 90 km altitude. Simultaneous MF radar wind data reveal the presence of a mean wind shear which, during the period of the small-scale features, was aligned nearly in the direction of AGW propagation. In addition, the larger scale AGW approached a critical level near 90 km altitude. While the wind shear itself is not large enough to cause an instability, an analysis of the data suggests that the small-scale features are the result of a dynamic (wind shear-induced) instability in the 87–90 km altitude region. The instability was due to a combination of the background wind shear and the large shear induced by the passage of the larger scale AGW as it approached the critical level.J. H. Hecht, R. L. Walterscheid and R. A. Vincen