Path-integrated growth of electrostatic waves: The generation of terrestrial myriametric radiation

first_imgIt is generally accepted that electrostatic wave energy is the source of terrestrial myriametric radiation (TMR), but there are several theories to suggest how this energy is converted into TMR. The linear mode conversion “window” theory of Jones (1976, 1980), which in the past has been considered by some to be too inefficient to account for the observed wave amplitudes, is considered here. First, the ray tracing program HOTRAY is described. This program is used to trace electromagnetic and electrostatic waves in a hot magnetized plasma and to calculate the path‐integrated growth rates for a realistic unstable particle distribution function. A density model is constructed from wave observations made by DE 1 of an event where TMR was beamed to northern and southern latitudes from a source very close to the magnetic equator. Ray tracing shows that backward propagating electrostatic waves can refract into electromagnetic Z mode waves and transport energy to the so‐called radio window at the equator. At this point, mode conversion of energy into O mode radiation is assumed to take place. Ray tracing of O mode radiation from the radio window shows that TMR is beamed to northern and southern latitudes as observed and as predicted by the theory. Path‐integrated growth rates show that the electrostatic waves amplify by a factor ≥42 from the background fluctuation level before reaching the window. This is sufficient to account for the observed TMR wave amplitudes which require the waves to amplify by a factor ≥20. Increasing the depth of the loss cone, or increasing the hot plasma density, to within observed limits, increases the wave amplification up to a factor of 104. Strong Landau and cyclotron damping from the hot plasma component restricts the efficient transfer of energy to the radio window to within a few tenths of a degree in latitude about the magnetic equator. Thus the strongest TMR is emitted from the equator. In general, TMR beamed to northern latitudes from radio windows north of the equator is stronger than that beamed to southern latitudes; conversely, TMR beamed to northern latitudes from radio windows south of the equator is generally weaker than that beamed to southern latitudes. It is shown that electrostatic wave energy can still be transported efficiently to the radio window for magnetic field intensity variations of 1 or 2%. Thus the generation of TMR is not sensitive to variations in the magnetic field strength of this magnitude.last_img read more

Effects of feeding and starvation on the metabolic rate of the necrophagous Antarctic amphipod Waldeckia obesa (Chevreux, 1905)

first_imgThe marked seasonality of high latitude marine ecosystems means that the relationship between nutrition and metabolism is of particular interest, for many polar organisms must survive long periods without food. One hundred individuals of the scavenging lysianassoid amphipod Waldeckia obesa (Chevreux, 1905) were collected from Antarctica and then maintained in cold-water aquaria at the British Antarctic Survey in Cambridge. One group were fed and then starved for 64 days, during which time oxygen consumption fell to 60% of the initial value, and ammonia excretion to 20%. The initial decrease in metabolism occurred in about 5 days, after which time ammonia excretion remained roughly constant whereas oxygen consumption (and hence O:N atomic ratio) oscillated. O:N ratio and proximate composition estimated stoichiometrically from elemental composition both indicated the use of protein and lipid as metabolic substrates during starvation. Fed amphipods exhibited a classic post-prandial increase in metabolism (specific dynamic action, SDA): oxygen consumption and ammonia excretion increased rapidly to a level between 4 and 7.5 times the prefeeding levels, respectively. These are the largest increases of metabolic rate with feeding so far reported for a marine invertebrate and the overall SDA response lasted 8–10 days. O:N ratios indicated that metabolism 2–4 days after feeding was dominated by protein metabolism.last_img read more

Cenozoic tectonic history, seismicity and palaeoseismicity of the Antarctic Peninsula Pacific margin

first_imgGlobal earthquake catalogues do not record any earthquakes south of Bransfield Strait beneath the AntarcticPeninsula or its flanking continental shelves. Such low seismicity is consistent with neotectonic interpretations which show the area south of Bransfield Strait as part of the modern Antarctic plate. However, the magnitude distribution of earthquakes located in the wider region indicates that the threshold for location of events in this area was at least mb=4.5 before 1996. Plate tectonic reconstructions indicate that rapid subduction was taking place along the entire Pacific margin of the Antarctic Peninsula at the start of the Cenozoic era. By analogy with active subduction zones, and by reference to statistical relationships between seismicity parameters and other measurable parameters of modern subduction zones, it is inferred that this was an area of intense seismic activity at that time. On the same basis, wellconstrainedtectonic events affecting this margin imply that seismic activity decreased in stages during the Cenozoicera. Global catalogues list four earthquakes beneath the continental rise west of the Antarctic Peninsula. Theseoccurred in oceanic lithosphere 16–49 Ma in age and do not appear to be associated with oceanic fracture zones.Harvard CMT focal mechanisms for two of theselast_img read more

Atmospheric circulation impacts on winter maximum sea ice extent in the west Antarctic Peninsula region (1979-2001)

first_imgIncreasing evidence exists that the strong warming of the West Antarctic Peninsula (WAP) region since the 1950s is related to reduced sea ice that is likely to be due to changes in the atmospheric circulation. Over twenty years of sea ice extent, ice motion and reanalysed near-surface wind data are used to establish that winter ice extent in the West Antarctic Peninsula (WAP) region is largely determined by the meridional (north-south) atmospheric circulation. A remarkably strong ice extent-wind relationship is found in the WAP. No other Antarctic or comparable sub-Arctic sea ice region shows this. Ice motion data confirm wind-induced drift is crucial for extensive winter ice to occur. Reasons for winter ice extent and winds being more strongly correlated in the WAP than in other parts of the Antarctic are discussed along with implications for understanding the observed warming.last_img read more

The effect of environmental change on vascular plant and cryptogam communities from the Falkland Islands and the Maritime Antarctic

first_imgBackground: Antarctic terrestrial vegetation is subject to one of the most extreme climates on Earth. Currently, parts of Antarctica are one of the fastest warming regions on the planet. During 3 growing seasons, we investigated the effect of experimental warming on the diversity and abundance of coastal plant communities in the Maritime Antarctic region (cryptogams only) and the Falkland Islands (vascular plants only). We compared communities from the Falkland Islands (51 S, mean annual temperature 7.9 degrees C), with those of Signy Island (60 degrees S, – 2.1 degrees C) and Anchorage Island (67 degrees S, -2.6 degrees C), and experimental temperature manipulations at each of the three islands using Open Top Chambers (OTCs).Results: Despite the strong difference in plant growth form dominance between the Falkland Islands and the Maritime Antarctic, communities across the gradient did not differ in total diversity and species number.During the summer months, the experimental temperature increase at 5 cm height in the vegetation was similar between the locations (0.7 degrees C across the study). In general, the response to this experimental warming was low. Total lichen cover showed a non-significant decreasing trend at Signy Island (p < 0.06). In the grass community at the Falkland Islands total vegetation cover decreased more in the OTCs than in adjacent control plots, and two species disappeared within the OTCs after only two years. This was most likely a combined consequence of a previous dry summer and the increase in temperature caused by the OTCs.Conclusion: These results suggest that small temperature increases may rapidly lead to decreased soil moisture, resulting in more stressful conditions for plants. The more open plant communities (grass and lichen) appeared more negatively affected by such changes than dense communities (dwarf shrub and moss).last_img read more

Multiple sources supply eolian mineral dust to the Atlantic sector of coastal Antarctica: Evidence from recent snow layers at the top of Berkner Island ice sheet

first_imgThe Sr and Nd isotopic composition of dust extracted from recent snow layers at the top of Berkner Island ice sheet (located within the Filchner–Ronne Ice Shelf at the southern end of the Weddell Sea) enables us, for the first time, to document dust provenance in Antarctica outside the East Antarctic Plateau (EAP) where all previous studies based on isotopic fingerprinting were carried out. Berkner dust displays an overall crust-like isotopic signature, characterized by more radiogenic 87Sr/86Sr and much less radiogenic 143Nd/144Nd compared to dust deposited on the EAP during glacial periods. Differences with EAP interglacial dust are not as marked but still significant, indicating that present-day Berkner dust provenance is distinct, at least to some extent, from that of the dust reaching the EAP. The fourteen snow-pit sub-seasonal samples that were obtained span a two-year period (2002–2003) and their dust Sr and Nd isotopic composition reveals that multiple sources are at play over a yearly time period. Southern South America, Patagonia in particular, likely accounts for part of the observed spring/summer dust deposition maxima, when isotopic composition is shifted towards “younger” isotopic signatures. In the spring, possible additional inputs from Australian sources would also be supported by the data. Most of the year, however, the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in East Antarctica, which carry old-crust-like isotopic fingerprints. Whether the restricted East Antarctic ice-free areas produce sufficient eolian material has yet to be substantiated however. The fact that large (> 5 μm) particles represent a significant fraction of the samples throughout the entire time-series supports scenarios that involve contributions from proximal sources, either in Patagonia and/or Antarctica (possibly including snow-free areas in the Antarctic Peninsula and other areas as well). This also indicates that additional dust transport, which does not reach the EAP, must occur at low-tropospheric levels to this coastal sector of Antarctica.last_img read more

Continental-scale temperature variability during the past two millennia

first_imgPast global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.last_img read more

Getz Ice Shelf melting response to changes in ocean forcing

first_imgThe large and complex Getz Ice Shelf extends along nearly half of the West Antarctic coastline in the Amundsen Sea, and is exposed to a more variable ocean environment than most other Pacific sector ice shelves. Ocean temperature, salinity and dissolved oxygen profiles acquired near its sub-ice cavity openings are used here to estimate seawater transports and meltwater fractions. More complete coverage during 2000 and 2007 brackets most of the variability observed from 1994 to 2011, and yearlong records near one ice front support the use of summer profiles to determine annual basal melt rates. We find area average rates of 1.1 and 4.1 m/yr, higher in 2007 when a larger volume of warmer deep water occupied the adjacent continental shelf, and the ocean circulation was stronger. Results are consistent with changes in thermocline depths relative to ice shelf draft and mass transports onto the adjacent continental shelf. We also calculate steady state and actual melting of 2.5 and 4.6 m/yr in 2007-2008 from satellite measurements of ice flux, modeled accumulation, and thinning from 2003-2008. This implies a positive mass balance in 2000, but negative in 2007, when the Getz was producing more meltwater than any of the larger, slower-melting or smaller, faster-melting ice shelves.last_img read more

Techera, Blondell score in Whitecaps’ 2-0 win over RSL

first_img Associated Press April 27, 2018 /Sports News – Local Techera, Blondell score in Whitecaps’ 2-0 win over RSL FacebookTwitterLinkedInEmailVANCOUVER, British Columbia (AP) — Cristian Techera connected on a penalty kick, Anthony Blondell scored his first MLS goal and the Vancouver Whitecaps beat Real Salt Lake 2-0 on Friday night to snap a three-game losing streak.Techera scored in the 76th minute after midfielder Nick Besler pulled down Vancouver’s Nicolas Mezquida in the penalty box. Techera celebrated by pulling off his jersey, resulting in an ejection for a second yellow card.Just three minutes later Alphonso Davies, who had subbed into the game in the 61st minute, had a nice run down the side of the field, then passed to an open Blondell, who tipped the ball into the net.The Whitecaps (4-4-1) rebounded from a 6-0 loss at Sporting Kansas City, the worst defeat in the team’s MLS history. Real Salt Lake (3-4-1) is 1-8-1 in its past 10 games at BC Place Stadium. Written by Tags: MLS/Real Salt Lake/Soccerlast_img read more

BYU Baseball Hosts San Francisco This Weekend

first_img Brad James FacebookTwitterLinkedInEmailPROVO, Utah-Thursday through Saturday, BYU baseball (31-13, 15-6 in West Coast Conference play) hosts San Francisco (27-22, 14-10 in WCC play) for the Cougars’ last homestand of the season. Should BYU win this series as well as next week’s games at Santa Clara, the Cougars will secure the top seed in the WCC tournament May 23-25 at Stockton, Calif. May 8, 2019 /Sports News – Local BYU Baseball Hosts San Francisco This Weekend Senior outfielder Brock Hale continues to lead the Cougars in batting average (.341) and home runs (8). Sophomore infielder Jackson Cluff continues to lead BYU in RBI (48). The Dons are led by redshirt junior catcher Robert Emery in batting average (.318). center_img Tags: Alex Pham/Brock Hale/BYU Baseball/Easton Walker/Jackson Cluff/Jonathan Allen/Julian Washburn/Justin Sterner/Reid McLaughlin/Robert Emery/San Francisco Baseball/Santa Clara Sophomore right-handed pitcher Julian Washburn has the Dons’ best record at 8-1 and his fellow sophomore right-hander Alex Pham has a team-best 76 strikeouts. Senior outfielder Jonathan Allen leads San Francisco in both home runs (17) and RBI (54). Written by Sophomore right-handed pitcher Easton Walker (6-0, 1.30 ERA) is the ace of the Cougars’ staff. Freshman right-hander Reid McLaughlin (5-1, 2.06 ERA) and sophomore right-hander Justin Sterner (8-3, 2.63 ERA) are stalwarts on the mound for BYU as well.last_img read more