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A quantitative estimate of the ducted whistler power within the outer plasmasphere

first_imgFrom a statistical study of ductedwhistlers observed at Halley, Antarctica, in 1996, which had propagated on paths in the range L=2.5–4.5, we report mean occurrence rates, numbers of components per whistler, intensities, etc. for night and day conditions and in different seasons at solar minimum. We found an average whistler rate of and 3 components per whistler. Received whistler amplitudes were measured as a function of frequency and were in the range 2–40 fT, typically 10 fT at 4 kHz. Combining these results with a propagation model, we estimate mean whistler duct output powers to be around 1–10 mW, (≃0.1–1 mJ per whistler in the 3–5 kHz band). Inferred typical equatorial wave fields for ductedwhistlers of 0.3 pT led to estimated radiation belt lifetimes for 1–100 keV electrons due to gyroresonance with ductedwhistlers of 2×106 days. This compares with published lifetimes due to plasmaspheric hiss of order 105 days or less, and we conclude that, on average, lightning which enters and propagates in magnetospheric ducts, although known to cause pitch angle scattering and precipitation of trapped electrons, does not significantly affect the radiation belt fluxes in a statistical sense. We have compared our results with those from a similar study by Burgess and Inan (J. Geophys. Res. 98 (1993) 15,643–15,665). In a separate investigation of multi-component whistlers received in winter at quiet times, using the same methodology, we have found that the duct output power generally decreases with increasing L. This is consistent with previous theoretical work and parallels a similar experimental conclusion with respect to higher-frequency whistler-mode signals from VLF transmitters.last_img read more

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Enhanced sexual reproduction in bryophytes at high latitudes in the maritime Antarctic

first_imgContrary to the generally accepted hypothesis that bryophyte fertility decreases with increasing latitude and therefore climatic severity, a detailed study of bryophyte reproductive strategies at sites in the southern maritime Antarctic (68–72°S) has revealed that an unexpectedly high proportion of species is capable of producing sporophytes. Of the regional bryoflora, 43% (19 species; 17 mosses, 2 liverworts) in Marguerite Bay and 47% (17 species; 16 mosses, 1 liverwort) in Alexander Island are known to produce sporophytes, although the number fruiting at comparable latitudes on the colder and more arid Antarctic continent is less (33%). These numbers and proportions are much greater than were previously known at such relatively high southern polar latitudes. Sporophytes of several species are recorded for the first time within the Antarctic biome, while those of two liverworts (Lophozia excisa and Cephaloziella varians) are reported for the first time south of 62°S. High incidence of sporophyte production is attributed to locally favourable microclimatic conditions producing small-scale ‘oases’. The large majority of fertile mosses are monoecious short acrocarps growing on rather calcareous soils. Spore production and size data for a number of species are compared with previously published studies of the same or closely related species from the northern maritime Antarctic and sub-Antarctic, but no consistent trends are revealed between species over the latitudinal gradient.last_img read more

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Statistical analysis of thermospheric gravity waves from Fabry-Perot Interferometer measurements of atomic oxygen

first_imgData from the Fabry-Perot Interferometers at KEOPS (Sweden), Sodankylä (Finland), and Svalbard (Norway), have been analysed for gravity wave activity on all the clear nights from 2000 to 2006. A total of 249 nights were available from KEOPS, 133 from Sodankylä and 185 from the Svalbard FPI. A Lomb-Scargle analysis was performed on each of these nights to identify the periods of any wave activity during the night. Comparisons between many nights of data allow the general characteristics of the waves that are present in the high latitude upper thermosphere to be determined. Comparisons were made between the different parameters: the atomic oxygen intensities, the thermospheric winds and temperatures, and for each parameter the distribution of frequencies of the waves was determined. No dependence on the number of waves on geomagnetic activity levels, or position in the solar cycle, was found. All the FPIs have had different detectors at various times, producing different time resolutions of the data, so comparisons between the different years, and between data from different sites, showed how the time resolution determines which waves are observed. In addition to the cutoff due to the Nyquist frequency, poor resolution observations significantly reduce the number of short-period waves (5 h) detected. Comparisons between the number of gravity waves detected at KEOPS and Sodankylä over all the seasons showed a similar proportion of waves to the number of nights used for both sites, as expected since the two sites are at similar latitudes and therefore locations with respect to the auroral oval, confirming this as a likely source region. Svalbard showed fewer waves with short periods than KEOPS data for a season when both had the same time resolution data. This gives a clear indication of the direction of flow of the gravity waves, and corroborates that the source is the auroral oval. This is because the energy is dissipated through heating in each cycle of a wave, therefore, over a given distance, short period waves lose more energy than long and dissipate before they reach their target.last_img read more

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The eradication of feral cats from Ascension Island and its subsequent recolonization by seabirds

first_imgThe introduction of mammal predators to islands often results in rapid declines in the number and range of seabirds. On Ascension Island the introduction of cats in 1815 resulted in extirpation of large seabird colonies from the main island, with relict populations of most species persisting only in cat-inaccessible locations. We describe the eradication of feral cats from this large and populated island. The campaign had to minimize risk to humans and maintain domestic animals in a state that prevented them reestablishing a feral population. Feral cat numbers declined rapidly in response to the strategic deployment of poisoning and live trapping, and cats were eradicated from the island within 2 years. During the project 38% of domestic cats were killed accidentally, which caused public consternation; we make recommendations for reducing such problems in future eradications. Since the completion of the eradication campaign cat predation of adult seabirds has ceased and five seabird species have recolonized the mainland in small but increasing numbers. Breeding success of seabirds at Ascension was low compared to that of conspecifics elsewhere, and the roles of food availability, inexperience of parent birds and black rat predation in causing this warrant further investigation. It is likely that the low breeding success will result in the rate of increase in seabird populations being slow.last_img read more

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Antarctica and the Strategic Plan for Biodiversity 2011–2020

first_imgThe Strategic Plan for Biodiversity, adopted under the auspices of the Convention on Biological Diversity, provides the basis for taking effective action to curb biodiversity loss across the planet by 2020—an urgent imperative. Yet, Antarctica and the Southern Ocean, which encompass 10% of the planet’s surface, are excluded from assessments of progress against the Strategic Plan. The situation is a lost opportunity for biodiversity conservation globally. We provide such an assessment. Our evidence suggests, surprisingly, that for a region so remote and apparently pristine as the Antarctic, the biodiversity outlook is similar to that for the rest of the planet. Promisingly, however, much scope for remedial action exists.last_img read more

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Synchronous timing of abrupt climate changes during the last glacial period

first_imgAbrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies.last_img read more

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Marine Important Bird and Biodiversity Areas for penguins in Antarctica, targets for conservation action.

first_imgGlobal targets for area-based conservation and management must move beyond threshold-based targets alone and must account for the quality of such areas. In the Southern Ocean around Antarctica, a region where key biodiversity faces unprecedented risks from climate change and where there is a growing demand to extract resources, a number of marine areas have been afforded enhanced conservation or management measures through two adopted marine protected areas (MPAs). However, evidence suggests that additional high quality areas could benefit from a proposed network of MPAs. Penguins offer a particular opportunity to identify high quality areas because these birds, as highly visible central-place foragers, are considered indicator species whose populations reflect the state of the surrounding marine environment. We compiled a comprehensive dataset of the location of penguin colonies and their associated abundance estimates in Antarctica. We then estimated the at-sea distribution of birds based on information derived from tracking data and through the application of a modified foraging radius approach with a density decay function to identify some of the most important marine areas for chick-rearing adult penguins throughout waters surrounding Antarctica following the Important Bird and Biodiversity Area (IBA) framework. Additionally, we assessed how marine IBAs overlapped with the currently adopted and proposed network of key management areas (primarily MPAs), and how the krill fishery likely overlapped with marine IBAs over the past five decades. We identified 63 marine IBAs throughout Antarctic waters and found that were the proposed MPAs to be adopted, the permanent conservation of high quality areas for penguin species would increase by between 49 and 100% depending on the species. Furthermore, our data show that, despite a generally contracting range of operation by the krill fishery in Antarctica over the past five decades, a consistently disproportionate amount of krill is being harvested within marine IBAs compared to the total area in which the fishery operates. Our results support the designation of the proposed MPA network and offer additional guidance as to where decision-makers should act before further perturbation occurs in the Antarctic marine ecosystem.last_img read more

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Hsu’s late shot seals 6-4 BYU win over Gonzaga in ESPNU featured game

first_img Written by Robert Lovell Tags: Baseball/BYU Cougars/WCC March 22, 2018 /Sports News – Local Hsu’s late shot seals 6-4 BYU win over Gonzaga in ESPNU featured game FacebookTwitterLinkedInEmailPROVO, Utah – Brian Hsu hit a two-run blast in the seventh inning to break a tie and give BYU a 6-4 win on ESPNU in the first of a three-game set against Gonzaga Thursday night at Larry H. Miller Field.“The guys came out fighting tonight,” BYU head coach Mike Littlewood said. “To get this win was really good, and it should make us come out relaxed and ready to play tomorrow (Friday).”The Cougars (11-9, 1-3 West Coast Conference) got their first league win as the Bulldogs fell to 11-9, 2-2 (WCC).Gonzaga put its first batter on after a BYU throwing error. He came around to score to give the Bulldogs an early one-run lead.Keaton Kringlen singled to lead off the bottom of the second. A walk and a sacrifice bunt gave way to Jarrett Perns’ sacrifice fly to center field that pushed Kringlen across to tie the game.Both teams scored a run in the third inning. For the Cougars, Daniel Schneemann lined a single over third base to drive home Brennon Anderson from second base.In the fifth, BYU took the lead when Anderson doubled to the left-center gap to score Perns, who led off the inning with a single. Schneemann blooped one into shallow center field to bring Anderson around and make it 4-2 for the Cougars.BYU starter Jordan Wood surrendered two runs in the sixth to square the score at 4-4 before escaping.Hsu launched a home run just inside the left foul pole to make it a 6-4 Cougar lead in the bottom of the seventh. Anderson, who had walked, scored his third run of the game on the shot.Wood (2-1) was replaced on the mound after 7.1 innings and 117 pitches. He allowed eight hits and three earned runs, while fanning six Bulldogs.Drew Zimmerman came on for BYU and recorded five outs without any Gonzaga hits or walks for his second save off the season. Casey Jacobsen, who was brought on as a defensive replacement at third base in the ninth, made a diving play for the second out.The Cougars host the Bulldogs on Friday and Saturday.last_img read more

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Grizzlies Hammer Bees

first_imgMay 2, 2018 /Sports News – Local Grizzlies Hammer Bees Robert Lovell Written by FacebookTwitterLinkedInEmail(Salt Lake City, UT)  —  The Bees poured it on late to rally past the Grizzlies 13-9 at Smith’s Ballpark.Michael Hermosillo hit a grand-slam in the sixth inning to put Salt Lake ahead for good.  David Fletcher and Jabari Blash also went deep in the winning effort.Jake Jewell got credit for the win and Taylor Cole locked down the six-out save.The Bees improved to 16-and-10 and will play the third of four with Fresno tonight.  First pitch is 6:35 p.m. Tags: Baseball/PCL/Salt Lake Beeslast_img read more

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Rockets blast Jazz 113-92 to take series lead

first_img Associated Press May 4, 2018 /Sports News – Local Rockets blast Jazz 113-92 to take series lead FacebookTwitterLinkedInEmailSALT LAKE CITY (AP) — James Harden had 25 points and 12 assists to lead Houston to a 113-92 win over Utah in Game 3 of their Western Conference semifinals series on Friday night.Eric Gordon added 25 points and Chris Paul had 15 points, seven rebounds and six assists for the Rockets. Houston beat Utah in Salt Lake City for the third time this season to take a 2-1 series lead. Game 4 is on Sunday.Royce O’ Neale scored 17 points. Alec Burks chipped in 14 points while Rudy Gobert added 12 points and nine rebounds for the Jazz.Utah never got on track on offense. The Jazz shot poorly over the first three quarters and committed 16 turnovers. Houston scored 19 points off those turnovers.On the heels of a listless first-half effort in Game 2, Houston avoided enduring another slow start. The Rockets picked apart Utah’s defense practically from the opening tip.Houston opened the game by scoring baskets on six of its first seven possessions. Harden capped the flurry with his first basket to put the Rockets up 15-5. It only grew worse for the Jazz from there. The Rockets led by as many as 22 in the first quarter, taking a 37-15 lead on back-to-back baskets from Harden and Gerald Green.Houston made 16 of its 26 shots in the first quarter and totaled 39 points in the period. As effective as the Rockets were on offense, their defense proved equally troublesome for Utah. They forced the Jazz to commit six turnovers before the second quarter and scored nine points off those turnovers.Utah cut Houston’s lead 49-34 midway through the second quarter after O’ Neale scored three straight baskets to fuel a 9-0 run. Clint Capela ended the run with a dunk and the Rockets proceeded to outscore the Jazz 31-9 over a 10 minute stretch extending into the third quarter. They pushed their lead to 80-43 on a driving layup from Ariza with 8:01 left in the quarter.TIP-INS:Rockets: Gordon finished with a postseason-high in points. …Houston did not commit a turnover in the first quarter. … The Rockets outscored the Jazz 20-10 in fastbreak points after totaling just five in Game 2. … Houston finished with 50 points in the paint for the second straight game.Jazz: Derrick Favors exited with an ankle sprain in the third quarter. Favors totaled two points, two rebounds and two assists in 13 minutes. … Houston’s 39 first quarter points is the most given up by Utah in any quarter in a playoff game this season. … Donovan Mitchell scored only 10 points after going just 4-of-16 from the field. Tags: Basketball/Houston Rockets/NBA/NBA Playoffs/Utah Jazz Written bylast_img read more

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