Electron pitch angle diffusion by electrostatic electron cyclotron harmonic waves: The origin of pancake distributions

first_imgIt has been suggested that highly anisotropic electron pancake distributions are the result of pitch angle diffusion by electrostatic electron cyclotron harmonic (ECH) and whistler mode waves in the equatorial region. Here we present pitch angle diffusion rates for ECH wave spectra centered at different frequencies with respect to the electron gyrofrequency Ωe corresponding to spacecraft observations. The wave spectra are carefully mapped to the correct resonant electron velocities. We show that previous diffusion calculations of ECH waves at 1.5Ωe, driven by the loss cone instability, result in large diffusion rates confined to a small range of pitch angles near the loss cone and therefore cannot account for pancake distributions. However, when the wave spectrum is centered at higher frequencies in the band (> 1.6Ωe), the diffusion rates become very small inside the loss cone, peak just outside, and remain large over a wide range of pitch angles up to 60° or more. When the upper hybrid resonance frequency ωUHR is several times Ωe, ECH waves excited in higher bands also contribute significantly to pitch angle diffusion outside the loss cone up to very large pitch angles. We suggest that ECH waves driven by a loss cone could form pancake distributions as they grow if the wave spectrum extends from the middle to the upper part of the first (and higher) gyroharmonic bands. Alternatively, we suggest that pancake distributions can be formed by outward propagation in a nonhomogeneous medium, so that resonant absorption occurs at higher frequencies between (n + ½) and (n + 1)Ωe in regions where waves are also growing locally at < 1.5Ωe. The calculated diffusion rates suggest that ECH waves with amplitudes of the order of l mV m−1 can form pancake distributions from an initially isotropic distribution on a timescale of a few hours. This is consistent with recent CRRES observations of ECH wave amplitudes following substorm injections near geostationary orbit and the timescales for pancake formation. Persistent but much weaker ECH waves can further intensify and maintain pancake distributions during magnetically quiet periods.last_img read more

A magnetotelluric model of the Mana Pools basin, northern Zimbabwe

first_imgThe Mana Pools sedimentary basin lies within the Zambezi mobile belt in northern Zimbabwe. New and preexisting magnetotelluric data and the available seismic reflection data are used to constrain the basin structure and the depth to the electrical basement. Long-period magnetotelluric (LMT) data were collected at five stations along a 60 km north-south profile across the Mana Pools basin and onto the southern escarpment. These data augment an existing audiofrequency (AMT) data set from 11 sites in the same area. The subsurface apparent resistivities measured at periods sampling the basin are very low (a few Ωm). After processing both data sets, the estimated impedance tensor is decomposed, showing that the resistivity structure of the Mana Pools basin can be modeled two dimensionally. The ρ+ algorithm is used to show that there is no systematic offset in magnitude between the AMT and LMT data sets before they are combined. Minimum structure resistivity models of the Mana Pools basin compare well with the information from reflection seismic data and support its previous description as a half graben basin of ∼7 km depth. The excellent conductor in the Mana Pools basin is quite different to those seen elsewhere in the orogenic belt in that it is a feature of the sedimentary fill rather than the basement. The resistivity of the basement is low but no localized good conductor is observed; these low resistivities may result from a high degree of either chemical or tectonic alteration to the underlying rocks due to metamorphic processes and tectonic disruption during rift formation.last_img read more

An anticyclonic circulation above the Northwest Georgia Rise, Southern Ocean

first_imgData from a variety of sources reveal a warm-core anticyclonic circulation above the Northwest Georgia Rise (NWGR), an similar to2000-m high bathymetric feature north of South Georgia. The sense of the circulation is opposite to the general cyclonic flow in the Georgia Basin. The circulation shows the characteristics of a stratified Taylor column: dimensional analysis shows that the local bathymetry and hydrography are conducive to the formation of such. ERS2 altimeter data show that the column, whilst not fully permanent, is nonetheless a recurring feature. High concentrations of chlorophyll-a are observed at the centre of the circulation, indicating that the modulation of the physical environment has significant consequences for the local biogeochemical system via enhanced primary production. Enhanced chlorophyll-a extends in a long plume from the NWGR along pathways indicated by drifters; this passive redistribution may have consequences for the larger (basin-) scale ecosystem.last_img read more

Enhancement factors for grounded ice and ice shelves inferred from an anisotropic ice-flow model

first_imgPolar ice is known to be one of the most anisotropic natural materials. For a given fabric the polycrystal viscous response is strongly dependent on the actual state of stress and strain rate. Within an ice sheet, grounded-ice parts and ice shelves have completely different stress regimes, so one should expect completely different impacts of ice anisotropy on the flow. The aim of this work is to quantify, through the concept of enhancement factors, the influence of ice anisotropy on the flow of grounded ice and ice shelves. For this purpose, a full-Stokes anisotropic marine ice-sheet flowline model is used to compare isotropic and anisotropic diagnostic velocity fields on a fixed geometry. From these full-Stokes results, we propose a definition of enhancement factors for grounded ice and ice shelves, coherent with the asymptotic models used for these regions. We then estimate realistic values for the enhancement factors induced by ice anisotropy for grounded ice and ice shelves.last_img read more

Validating the use of intrinsic markers in body feathers to identify inter-individual differences in non-breeding areas of northern fulmars

first_imgMany wildlife studies use chemical analyses to explore spatio-temporal variation in diet, migratory patterns and contaminant exposure. Intrinsic markers are particularly valuable for studying non-breeding marine predators, when direct methods of investigation are rarely feasible. However, any inferences regarding foraging ecology are dependent upon the time scale over which tissues such as feathers are formed. In this study, we validate the use of body feathers for studying non-breeding foraging patterns in a pelagic seabird, the northern fulmar. Analysis of carcasses of successfully breeding adult fulmars indicated that body feathers moulted between September and March, whereas analyses of carcasses and activity patterns suggested that wing feather and tail feather moult occurred during more restricted periods (September to October and September to January, respectively). By randomly sampling relevant body feathers, average values for individual birds were shown to be consistent. We also integrated chemical analyses of body feather with geolocation tracking data to demonstrate that analyses of δ13C and δ15N values successfully assigned 88 % of birds to one of two broad wintering regions used by breeding adult fulmars from a Scottish study colony. These data provide strong support for the use of body feathers as a tool for exploring non-breeding foraging patterns and diet in wide-ranging, pelagic seabirds.last_img read more

Spectral Characterization of the AisaOWL

first_imgThe AisaOWL is a recent-to-market thermal hyperspectral instrument. As such, there is little information about the sensor performance in the literature. The sensor covers the 7.6-12.6 μm part of the long-wave infrared region with 102 continuous bands, and is capable of imaging in low-light conditions. This paper presents an independent characterization of the AisaOWL sensor, examining the spectral accuracy of black body measurements at different temperatures and validating manufacturer recommendations for warm-up, integration, and calibration times. This analysis is essential for establishing high quality operational procedures and in giving confidence to users of the data. In this paper, the sensor has been found to have a maximum error of 2 °C in absolute temperature measurement, and provides spectra most accurate in the 8-9 μm region. The recommended warm-up time of 15 min has been confirmed, with a 1% increase in error identified for data collected only 7 min after switch on. The optimal integration time of 1.18 ms has been validated and an exponential decrease in performance observed outside the 0.85-1.2 ms range. The detector used by the sensor is shown to have stability issues and this has been examined by comparing black body data processed with different calibration data. While the detector is operating in a stable regime compatible with the calibration, these black body readings stay within 5% across the central bands, approaching 10% below 8μ m and just exceeding 20% above 11 μm.last_img read more

Prospects for metazoan life in sub-glacial Antarctic lakes: the most extreme life on Earth?

first_imgAbout 400 subglacial lakes are known from Antarctica. The question of whether life unique of subglacial lakes exists has been paramount since their discovery. Despite frequent evidence of microbial life mostly from accretion ice, subglacial lakes are characterized by physiologically hostile conditions to metazoan life, as we know it. Pure water (salinity ≤0.4–1.2%), extreme cold (−3°C), high hydrostatic pressure, areas of limited or no oxygen availability and permanent darkness altogether require physiological adaptations to these harsh conditions. The record of gene sequences including some associated with hydrothermal vents does foster the idea of metazoan life in Lake Vostok. Here, we synthesize the physico-chemical environment surrounding sub-glacial lakes and potential sites of hydrothermal activity and advocate that the physico-chemical stability found at these sites may be the most likely sites for metazoan life to exist. The unique conditions presented by Lake Vostok may also offer an outlook on life to be expected in extra-terrestrial subglacial environments, such as on Jupiter’s moon Europa or Saturn’s moon Enceladus.last_img read more

Utah downs Rockets 100-89, Harden leaves game in 4th

first_imgOctober 24, 2018 /Sports News – Local Utah downs Rockets 100-89, Harden leaves game in 4th Written by Tags: Basketball/James Harden/NBA/Utah Jazz FacebookTwitterLinkedInEmailHOUSTON (AP) — Donovan Mitchell scored 38 points to lead the Utah Jazz to a 100-89 victory over the Houston Rockets on Wednesday night in a game James Harden left with an apparent injury.The Rockets got within five points midway through the fourth quarter but Harden headed to the locker room soon after and didn’t return. It was unclear how he was injured or what the problem was and the team didn’t immediately provide on update on his condition.With Harden out the game, the Jazz regained control, scoring the next 10 points to make it 94-79 and cruise to the victory.Harden scored 29 points and Carmelo Anthony had a season-high 22 for the Rockets, who were missing two starters. Chris Paul finished up a two-game suspension for his role in a fight with the Lakers last week and James Ennis sat out with a strained right hamstring.Eric Gordon made his second straight start in place of Paul and Michael Carter-Williams made his first start of the season with Ennis on the bench.Utah got this season’s series with Houston off on a good note after the Rockets beat the Jazz 4-1 in the Western Conference semifinals after winning all four regular-season meetings.The Jazz had a 15-point lead early in the fourth after scoring the first six points of the quarter. Houston got going after that, scoring the next seven points, with the first four from Clint Capela and a 3 from Anthony to make it 81-75 with about nine minutes left.Mitchell hit a 3-pointer with less than eight minutes to go to leave the Jazz up by nine. Harden re-entered the game soon after that and made a jump shot after a steal by P.J. Tucker. Tucker grabbed another steal on the next possession and dished it to Harden, who found Capela ahead of the defense for a slam dunk that cut the lead to 84-79 and had Jazz coach Quin Snyder calling for a timeout as Harden implored the crowd to get louder.The Jazz led by eight at halftime after holding Houston to just 15 points in the second quarter and had pushed the lead to 16 midway through the third after a 3-pointer by Joe Ingles. The Rockets went on a 10-4 run after that, capped by a steal by Carter-Williams and 3-pointer by Tucker to cut the lead to 68-58 with about four minutes left in the quarter.Utah extended the lead to 11 late in the third quarter on a 3-pointer by Jae Crowder and was up 75-66 entering the fourth.TIP-INSJazz: Raul Neto missed his fourth straight game with a hamstring injury. … Rudy Gobert had 12 points and 13 rebounds. … Ingles added 11 points.Rockets: Centers Nene (right calf tightness) and Zhou Qi (left knee sprain), and forward Marquese Chriss (left ankle sprain) did not play. … Anthony hadn’t scored more than nine points in any of the first three games.UP NEXTJazz: Visit New Orleans on Saturday.Rockets: Host Clippers on Friday. Associated Presslast_img read more

Weber State Football Announces Three-Game Series With Dixie State. Trailblazers Also Enter Agreement With NAU

first_img Written by Brad James Tags: Division I/Dixie State/Northern Iowa/Stewart Stadium/Weber State Football/Wyoming Additionally, Dixie State and Northern Arizona have entered into a six-game series effective in 2023. The first game in the series will be October 10, 2020 at Stewart Stadium in Ogden. As was also announced Friday, Dixie State will play Southern Utah at Cedar City in 2020 and 2022 and will host the Thunderbirds in 2024. January 15, 2019 /Sports News – Local Weber State Football Announces Three-Game Series With Dixie State. Trailblazers Also Enter Agreement With NAU The Wildcats and Trailblazers will meet on the gridiron in the 2020, 2021 and 2022 seasons. The squads will square off twice in Ogden and once in St. George. There will be a return game in 2021 at St. George and the Trailblazers will return the favor in 2022 at Stewart Stadium. Dixie State will face Northern Arizona at Flagstaff, Ariz. at the Walkup Skydome in 2023, 2025 and 2027. The Wildcats won the only previous match-up in history as in 2008, Weber State routed Dixie State 44-7, also at Stewart Stadium. This completes the 2020 schedule for the Wildcats as in other non-conference games that season, they will face Wyoming and Northern Iowa. The Trailblazers will host the Lumberjacks in 2024, 2026 and 2028. FacebookTwitterLinkedInEmailOGDEN, Utah-Tuesday, Weber State football announced a three-game series with Dixie State upon the advancement of the Trailblazers’ football program to Division I in 2020 as confirmed last Friday.last_img read more

Exum Injures Patellar Tendon, Out Indefinitely

first_imgMarch 18, 2019 /Sports News – Local Exum Injures Patellar Tendon, Out Indefinitely Written by The Australian guard suffered a patellar tendon injury during Friday’s win over Minnesota and he’s out indefinitely.  Tags: Dante Exum/NBA/Utah Jazz FacebookTwitterLinkedInEmail (Salt Lake City, UT)  —  The injury bug is biting Jazz guard Dante Exum once again.  Exum had just come back on last Monday after missing 25 games with an ankle sprain and bone bruise. Robert Lovelllast_img read more