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Atmospheric water vapor over Antarctica derived from Special Sensor Microwave/Temperature 2 data

By on May 9, 2021

first_imgIn polar regions, satellite microwave radiometry has not been successful in measuring the total water vapor (TWV) in the atmosphere. The difficulties faced in these regions arise from the very low water vapor burden of the atmosphere and the large and highly variable emissivities of ice surfaces in the microwave frequency range. By exploiting the advantages of the Special Sensor Microwave/Temperature 2 (SSM/T2), a method is developed to retrieve TWV over Antarctica from satellite data. This method shows very low sensitivities to the change of surface emissivity and to the presence of water clouds. However, ice clouds may have considerable effects. Results of radiative transfer model simulation show that they may cause one to underestimate TWV using the proposed method and that the amount of underestimation is proportional to the ice water path of the ice cloud. Validations using radiosonde measurements and numerical model analyzes suggest that SSM/T2 retrievals have a high accuracy (maximum error <10%) as long as TWV is <4.0 kg m−2. Above this value, retrievals show a systematic overestimation. Presumably, this is a result of the seasonal difference between the validation and the training radiosonde data sets. TWV retrievals of 1 year's SSM/T2 data show clearly the seasonal variation of water vapor over Antarctica. Throughout the year the mean TWV over West Antarctica is nearly twice as high as that over East Antarctica; the temporal fluctuation of TWV over West Antarctica is also significantly stronger than over East Antarctica. This suggests that precipitation and water vapor transport in West Antarctica are more active than in East Antarctica. Using the same year's TWV data, we estimated the mean residence time of atmospheric water vapor over the Antarctica to be merely 3–4 days. This, however, is much shorter than the global mean of 9–10 days.last_img read more

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The biology of the bigeye grenadier at South Georgia

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first_imgThe biology of the bigeye grenadier Macrourus holotrachys caught as by-catch in the Patagonian toothfish Dissostichus eleginoides longline fishery conducted around South Georgia was investigated to improve data available for fisheries management. Age estimates suggest that M. holotrachys is a moderately slow growing species (K = 0.10), reaching ages of >30 years and attaining total lengths (L-T) >80 cm (L-infinity = 33). The size at which 50% of females had started to mature (L-int50) for M. holotrachys was 21 cm pre-anal length (L-PA) and occurred at c. 9 years old. Estimates of natural mortality and Pauly’s growth performance index were found to be low (M = 0(.)09 and Phi = 2.82 respectively). Gonad maturity stage was described from macroscopic and histological investigation. Mature ovaries had oocytes at all developmental stages with between 22 and 55% likely to be spawned each year. Absolute fecundity ranged from 22 000 to 260 000 eggs and was positively correlated with both pre-anal length and mass. A highly skewed sex ratio of 32 : 1, females: males, was found for specimens caught by longlines but not for a small sample of shallower trawl-caught specimens. It is suggested that females are far more susceptible to longline capture than males. Macrourus holotrachys is a bentho-pelagic predator and scavenger that feeds on a wide range of fishes and invertebrates. The fish are long lived, slow-growing species typical of deep-water grenadiers; fisheries management strategies should reflect their probable susceptibility to overfishing. (C) 2004 The Fisheries Society of the British Isles.last_img read more

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Ground observations of chorus following geomagnetic storms

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first_img[1] It has been suggested that whistler mode chorus waves play a role in acceleration and loss of radiation belt electrons during geomagnetic storms. In this paper we present data from a complete solar cycle ( 1992 – 2002) of nearly continuous (> 95%) VLF/ELF observations from the VLF/ELF Logger Experiment (VELOX) instrument at Halley station, Antarctica (76 degreesS, 27 degreesW, L = 4.3), to determine whether there is statistical evidence for enhanced whistler mode chorus waves during geomagnetic storms. The data comprise 1 s resolution measurements of ELF/VLF wave power in eight frequency bands from 500 Hz to 10 kHz. The variations in chorus activity during several storms, including the well-studied Bastille Day event ( 14 July 2000), show enhanced wave power but are variable from event to event. The average behavior has been found from a superposed epoch analysis using 372 storms with minimum Dst less than – 50 nT, including 82 large storms with minimum Dst less than – 100 nT. Compared with average prestorm levels, the chorus intensity decreases in the storm main phase but is enhanced in the recovery phase, typically maximizing a day after the storm onset. At 1 kHz the enhancement is independent of storm severity, suggesting a saturation effect, whereas larger storms produce larger wave intensities at higher frequencies in the chorus band ( e. g., 3 kHz), which is interpreted as the effect of a chorus source region located on lower L shells than for weaker storms. The storm chorus enhancement maximizes at postdawn local times, leading to a 24 hour recurrence effect. A long-enduring depression in wave intensities, of 10 days or more, is found near the top of the normal chorus band ( similar to 5 kHz). We suggest that this is due to precipitation from enhanced relativistic particle fluxes affecting the subionospheric propagation of spherics from nearby thunderstorm regions across the L = 2 – 4 zone.last_img read more

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Ecological contrasts across an Antarctic land-sea interface

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first_imgWe report the composition of terrestrial, intertidal and shallow sublittoral faunal communities at sites around Rothera Research Station, Adelaide Island, Antarctic Peninsula. We examined primary hypotheses that the marine environment will have considerably higher species richness, biomass and abundance than the terrestrial, and that both will be greater than that found in the intertidal. We also compared ages and sizes of individuals of selected marine taxa between intertidal and subtidal zones to test the hypothesis that animals in a more stressed environment (intertidal) would be smaller and shorter lived. Species richness of intertidal and subtidal communities was found to be similar, with considerable overlap in composition. However, terrestrial communities showed no overlap with the intertidal, differing from previous reports, particularly from further north on the Antarctic Peninsula and Scotia Arc. Faunal biomass was variable but highest in the sublittoral. While terrestrial communities were depauperate with low biomass they displayed the highest overall abundance, with a mean of over 3 × 105 individuals per square metre. No significant differences in ages of intertidal and subtidal individuals of the same species were found, with bryozoan colonies of up to 4 years of age being present in the intertidal. In contrast with expectation and the limited existing literature we conclude that, while the Antarctic intertidal zone is clearly a suboptimal and highly stressful habitat, its faunal community can be well established and relatively diverse, and is not limited to short-term opportunists or waifs and strays.last_img read more

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Half-century seasonal relationships between the Southern Annular Mode and Antarctic temperatures

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first_imgIn this short communication we examine the relationship between the Southern Hemisphere Annular Mode (SAM) and Antarctic near-surface temperatures using data from Antarctic stations for 1957-2004. This near half-century period is significantly longer than analysed in previous studies. Furthermore, the four seasons are considered independently while the longer datasets allow the temporal stability of the relationship to be investigated. A general pattern of positive (negative) correlations between the strength of the SAM and temperatures in the northern Antarctic Peninsula (East Antarctica) is shown to be valid for the last half century but detailed differences are established between the seasons. These include a seasonal change in the sign of the relationship at one station, while at others there are single seasons when temperatures there are or, in some cases, are not significantly related to the SAM. Generally, SAM-temperature correlations are stronger across Antarctica in austral autumn and summer. Estimates of the contribution that trends in the SAM have made to Antarctic near-surface temperature change between 1957 and 2004 are greatest in autumn: in this season they exceed 1°C at half the 14 stations examined with a maximum change of –1.4°C. There does not appear to have been any significant long-term change in the strength of SAM-temperature relationships over the period examined, even with the onset of ozone depletion. However, on an annual basis, the long-term relationship between the SAM and near-surface temperatures can be disrupted and even reversed at some stations although coastal East Antarctica appears stable in this respect. These findings give support to the exploitation of appropriate ice core data to determine longer-term changes in the SAM based upon transfer-functions derived from recent data.last_img read more

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Historical SAM variability. Part I: Century-length seasonal reconstructions

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first_imgSeasonal reconstructions of the Southern Hemisphere annular mode (SAM) index are derived to extend the record before the reanalysis period, using station sea level pressure (SLP) data as predictors. Two reconstructions using different predictands are obtained: one [Jones and Widmann (JW)] based on the first principal component (PC) of extratropical SLP and the other (Fogt) on the index of Marshall. A regional-based SAM index (Visbeck) is also considered. These predictands agree well post-1979; correlations decline in all seasons except austral summer for the full series starting in 1958. Predictand agreement is strongest in spring and summer; hence agreement between the reconstructions is highest in these seasons. The less zonally symmetric SAM structure in winter and spring influences the strength of the SAM signal over land areas, hence the number of stations included in the reconstructions. Reconstructions from 1865 were, therefore, derived in summer and autumn and from 1905 in winter and spring. This paper examines the skill of each reconstruction by comparison with observations and reanalysis data. Some of the individual peaks in the reconstructions, such as the most recent in austral summer, represent a full hemispheric SAM pattern, while others are caused by regional SLP anomalies over the locations of the predictors. The JW and Fogt reconstructions are of similar quality in summer and autumn, while in winter and spring the Marshall index is better reconstructed by Fogt than the PC index is by JW. In spring and autumn the SAM shows considerable variability prior to recent decades.last_img read more

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Radiation belt electron precipitation due to geomagnetic storms: Significance to middle atmosphere ozone chemistry

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first_imgGeomagnetic storms triggered by coronal mass ejections and high-speed solar wind streams can lead to enhanced losses of energetic electrons from the radiation belts into the atmosphere, both during the storm itself and also through the poststorm relaxation of enhanced radiation belt fluxes. In this study we have analyzed the impact of electron precipitation on atmospheric chemistry (30-90 km altitudes) as a result of a single geomagnetic storm. The study conditions were chosen such that there was no influence of solar proton precipitation, and thus we were able to determine the storm-induced outer radiation belt electron precipitation fluxes. We use ground-based subionospheric radio wave observations to infer the electron precipitation fluxes at L = 3.2 during a geomagnetic disturbance which occurred in September 2005. Through application of the Sodankyla Ion and Neutral Chemistry model, we examine the significance of this particular period of electron precipitation to neutral atmospheric chemistry. Building on an earlier study, we refine the quantification of the electron precipitation flux into the atmosphere by using a time-varying energy spectrum determined from the DEMETER satellite. We show that the large increases in odd nitrogen (NOx) and odd hydrogen (HOx) caused by the electron precipitation do not lead to significant in situ ozone depletion in September in the Northern Hemisphere. However, had the same precipitation been deposited into the polar winter atmosphere, it would have led to >20% in situ decreases in O-3 at 65-80 km altitudes through catalytic HOx cycles, with possible additional stratospheric O-3 depletion from descending NOx beyond the model simulation period.last_img read more

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Seasonal cycle of CO2 from the sea ice edge to island blooms in the Scotia Sea, Southern Ocean

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first_imgThe Scotia Sea region contains some of the most productive waters of the Southern Ocean. It is also a dynamic region through the interaction of deep water masses with the atmosphere. We present a first seasonally-resolved time series of the fugacity of CO2 (fCO2) from spring 2006, summer 2008, autumn 2009 and winter (potential temperature minimum) along a 1000 km transect from the pack ice to the Polar Front to quantify the effects of biology and temperature on oceanic fCO2. Substantial spring and summer decreases in sea surface fCO2 occurred in phytoplankton blooms that developed in the naturally iron-fertilised waters downstream (north) of South Georgia island (54–55°S, 36–38°W) and following sea ice melt (in the seasonal ice zone). The largest seasonal fCO2 amplitude (ΔfCO2) of − 159 μatm was found in the South Georgia bloom. In this region, biological carbon uptake dominated the seasonal signal, reducing the winter maxima in oceanic fCO2 by 257 μatm by the summer. In the Weddell–Scotia Confluence, the southern fringe of the Scotia Sea, the shift from wintertime CO2-rich conditions in ice covered waters to CO2 undersaturation in the spring blooms during and upon sea ice melt created strong seasonality in oceanic fCO2. Temperature effects on oceanic fCO2 ranged from ΔfCO2 sst of ~ 55 μatm in the seasonal ice zone to almost double that downstream of South Georgia (98 μatm). The seasonal cycle of surface water fCO2 in the high-nutrient low-chlorophyll region of the central Scotia Sea had the weakest biological control and lowest seasonality. Basin-wide biological processes dominated the seasonal control on oceanic fCO2 (ΔfCO2 bio of 159 μatm), partially compensated (43%) by moderate temperature control (ΔfCO2 sst of 68 μatm). The patchwork of productivity across the Scotia Sea creates regions of seasonally strong biological uptake of CO2 in the Southern Ocean.last_img read more

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Comparing electron precipitation fluxes calculated from pitch angle diffusion coefficients to LEO satellite observations

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first_imgParticle precipitation is a loss mechanism from the Radiation Belts whereby particles trapped by the Earth’s magnetic field are scattered into the loss cone due to wave‐particle interactions. Energetic electron precipitation creates ozone destroying chemicals which can affect the temperatures of the polar regions, therefore it is crucial to accurately quantify this impact on the Earth’s atmosphere. We use bounce‐averaged pitch angle diffusion coefficients for whistler mode chorus waves, plasmaspheric hiss and atmospheric collisions to calculate magnetic local time (MLT) dependent electron precipitation inside the field of view of the Polar Orbiting Environmental Satellites (POES) T0 detector, between 26‐30 March 2013. These diffusion coefficients are used in the BAS Radiation Belt Model (BAS‐RBM) and this paper is a first step towards testing the loss in this model via comparison with real world data. We find the best agreement between the calculated and measured T0 precipitation at L* > 5 on the dawnside for the > 30keV electron channel, consistent with precipitation driven by lower band chorus. Additional diffusion is required to explain the flux at higher energies and on the dusk side. The POES T0 detector underestimates electron precipitation as its field of view does not measure the entire loss cone. We demonstrate the potential for utilizing diffusion coefficients to reconstruct precipitating flux over the entire loss cone. Our results show that the total precipitation can exceed that measured by the POES > 30 keV electron channel by a factor that typically varies from 1 to 10 for L* = 6, 6.5 and 7.last_img read more

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Utah Baseball Falters in Twinbill Against Oregon

By on May 8, 2021

first_imgMarch 31, 2019 /Sports News – Local Utah Baseball Falters in Twinbill Against Oregon FacebookTwitterLinkedInEmailSALT LAKE CITY, Utah – Utah dropped its twinbill with Oregon on Sunday, March 31 at Smith’s Ballpark.With bad weather pushing the series back, Utah and Oregon played a double header on Sunday.In the first game of the day, Joshua Tedeschi rolled through the first two innings striking out four, but the Ducks struck first taking the lead in the third with two hits to go up 2-0.Utah got one back as Oliver Dunn homered in the third and then took the lead 3-2 on a sac fly from Shea Kramer and a walk from Chris Rowan, Jr. in the bottom of the fourth.The Utes held the lead until the seventh inning when Oregon scored two, but in the bottom half, Matt Richardson tied things up with his first homer of the year.After a scoreless eighth, things headed to the ninth tied, but Oregon scored five runs with a grand slam being a big part of it. The Utes tried to mount a comeback scoring two more runs off of a Dunn triple that knocked in Briley Knight. Dunn came home with a wild pitch.Oregon then buckled down to get the win and clinch the series and used that momentum early in the second game of the day.The Ducks scored two runs in the first and then two more in the second to take an early 4-0 lead.Utah’s bats were quiet until the seventh inning. Richardson’s big day continued as he doubled to clear the bases to get within one run. Unfortunately, the Utes couldn’t muster any more offense as they fell in the second game 6-3.Dunn had a great day at the plate going 5-9. He scored two runs and had two RBI in the first game of the day. Richardson led the team with four RBI on the day.Tedeschi went 6.1 innings in the first game allowing four runs in his no decision. Zac McCleve ended up taking the loss to fall to 1-1 on the year.Riley Pierce got the start in the second game, but Brett Brocoff took over in the second inning and pitched five innings and only allowed two earned runs.Utah is 7-15 on the year after the weekend.They will now host BYU at Smith’s Ballpark on Tuesday, April 2 followed by a weekend on the road at No. Oregon State. Tags: Oregon Ducks/Pac 12/Utah Utes Baseball Written by Robert Lovelllast_img read more

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