The turbopause is the demarcation between atmospheric mixing by turbulence (below) and molecular diffusion (above). When studying concentrations of trace species in the atmosphere, and particularly ...long-term change, it may be important to understand processes present, together with their temporal evolution that may be responsible for redistribution of atmospheric constituents. The general region of transition between turbulent and molecular mixing coincides with the base of the ionosphere, the lower region in which molecular oxygen is dissociated, and, at high latitude in summer, the coldest part of the whole atmosphere. This study updates previous reports of turbopause altitude, extending the time series by half a decade, and thus shedding new light on the nature of change over solar-cycle timescales. Assuming there is no trend in temperature, at 70° N there is evidence for a summer trend of ∼ 1.6 km decade−1, but for winter and at 52° N there is no significant evidence for change at all. If the temperature at 90 km is estimated using meteor trail data, it is possible to estimate a cooling rate, which, if applied to the turbopause altitude estimation, fails to alter the trend significantly irrespective of season. The observed increase in turbopause height supports a hypothesis of corresponding negative trends in atomic oxygen density, O. This supports independent studies of atomic oxygen density, O, using mid-latitude time series dating from 1975, which show negative trends since 2002.
The machinery that conducts the light-driven reactions of oxygenic photosynthesis is hosted within specialized paired membranes called thylakoids. In higher plants, the thylakoids are segregated into ...two morphological and functional domains called grana and stroma lamellae. A large fraction of the luminal volume of the granal thylakoids is occupied by the oxygen-evolving complex of photosystem II. Electron microscopy data we obtained on dark- and light-adapted Arabidopsis thylakoids indicate that the granal thylakoid lumen significantly expands in the light. Models generated for the organization of the oxygen-evolving complex within the granal lumen predict that the light-induced expansion greatly alleviates restrictions imposed on protein diffusion in this compartment in the dark. Experiments monitoring the redox kinetics of the luminal electron carrier plastocyanin support this prediction. The impact of the increase in protein mobility within the granal luminal compartment in the light on photosynthetic electron transport rates and processes associated with the repair of photodamaged photosystem II complexes is discussed.
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We present here the Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM) quiet NmF2, perturbation NmF2, and quiet hmF2 models. These models provide peak ionospheric characteristics for a domain ...above 50°N geomagnetic latitude. Model fitting is undertaken using all available ionosonde and radio occultation electron density data, constituting a data set of over 28 million observations. A comprehensive validation of the model is undertaken, and performance is compared to that of the International Reference Ionosphere (IRI). In the case of the quiet NmF2 model, the E‐CHAIM model provides a systematic improvement over the IRI Union Radio Scientifique Internationale maps. At all stations within the polar cap, we see drastic RMS error improvements over the IRI by up to 1.3 MHz in critical frequency (up to 60% in NmF2). These improvements occur primarily during equinox periods and at low solar activities, decreasing somewhat as one tends to lower latitudes. Qualitatively, the E‐CHAIM is capable of representing auroral enhancements in NmF2, as well as the location and extent of the main ionospheric trough, not reproduced by the IRI. The included NmF2 storm model demonstrates improvements over the IRI by up to 35% and over the quiet time E‐CHAIM model by up to 30%. In terms of hmF2, over the validation periods used in this study, we found overall RMS errors of ~13 km for E‐CHAIM, with IRI2007 overall hmF2 errors ranging between 16 km and 22 km. The E‐CHAIM performs comparably to or slightly better than the IRI within the polar cap; however, significant improvements are found within the auroral oval.
Plain Language Summary
We here present a new high‐latitude representation of the peak electron density and height of the ionosphere. This new model provides quiet time representations of the peak ionospheric density and height, as well as an empirical storm time representation for the peak density. Taking advantage of new instrument deployments at high latitudes and a regional modeling approach, we see significant improvements (by 60% or more) over the current international standard for ionospheric specification, the International Reference Ionosphere (IRI). Qualitatively, the new model features a significant improvement in horizontal resolution over the IRI, where it is capable of representing auroral enhancements in peak density, as well as the location and extent of the upper midlatitude density depletion known as the main ionospheric trough (MIT). Both of these significant features fail to be modeled by the IRI. This improved model will have significant implications for high frequency (HF) communications and over the horizon radar planning at high latitudes, which are becoming increasingly important as the Arctic becomes more open to sea traffic.
Key Points
An empirical quiet time and storm time NmF2 model has been developed for high‐latitude regions
An empirical quiet time hmF2 model has been developed for high‐latitude regions
The proposed models represent a significant improvement over the use of the IRI at high latitudes
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This study presents the complete set of stable noble gases for Barnett Shale and Strawn Group production gas together with stray flowing gas in the Trinity Aquifer, Texas. It places new constraints ...on the source of this stray gas and further shows that Barnett and Strawn gas have distinct crustal and atmospheric noble gas signatures, allowing clear identification of these two sources. Like stray gas, Strawn gas is significantly more enriched in crustal 4He*, 21Ne*, and 40Ar* than Barnett gas. The similarity of Strawn and stray gas crustal noble gas signatures suggests that the Strawn is the source of stray gas in the Trinity Aquifer. Atmospheric 22Ne/36Ar ratios of stray gas mimic also that of Strawn, further reinforcing the notion that the source of stray gas in this aquifer is the Strawn. While noble gas signatures of Strawn and stray gas are consistent with a single-stage water degassing model, a two-stage oil modified groundwater exsolution fractionation model is required to explain the light atmospheric noble gas signature of Barnett Shale production gas. These distinct Strawn and Barnett noble gas signatures are likely the reflection of distinct evolution histories with Strawn gas being possibly older than that of Barnett Shale.
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The demand for energy around the world is increasing, specifically the demand for petroleum-based energy. Appeasing this growing energy demand without irreparably damaging the environment is of ...primary concern. With rising fuel prices and environmental concerns, alternative fuels could satisfy the need for renewable energy with low environmental impact. Some of the more popular alternative fuels for new vehicles are ethanol, hydrogen, and biodiesel. Although gasoline engines are expected to be replaced by hydrogen-powered fuel cells, compression-ignition engines, the diesel engines, are expected to remain in use for high-power applications because of limitations of hydrogen-storage densities. The viable environmental friendly alternative fuel for compression-ignition engines is methyl esters (commonly known as biodiesel), which is derived from vegetable oils or animal fats. Using biodiesel instead of conventional diesel fuel reduces emissions such as the overall life cycle of carbon dioxide (CO2), particulate matter, carbon monoxide, sulfur oxides (SOx), volatile organic compounds (VOCs), and unburned hydrocarbons significantly. However, biodiesel increases nitrogen oxides (NOx) emissions, mostly NO and NO2, which are considered as zone A hazardous compounds. This paper reviews the kinetics of NOx formation in relation to thermal, prompt, and fuel NOx formation processes and critically reviews the techniques that have been attempted to reduce NOx emissions from mechanisms to effectively reduce the NOx formation with biodiesel fuel.
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Double-slit interference experiments using monochromatic hard X-rays with the energy of 25 keV are presented. The experiments were performed at a synchrotron source with a distance of 110 m between ...the interferometer and the detector to produce an interference pattern with a sufficiently broad period that could be adequately sampled by a photon-counting detector with 75 micrometre pixels. In the single-particle version of the experiment, over one million image frames with a single registered photon in each one were collected. The sum of these frames showed a clear presence of the interference pattern with the expected period. Subsequent analysis provided an objective estimation of the minimal number of detected photons required to determine, in accordance with the Rose criterion, the presence of the photon interference. Apart from a general theoretical interest, these investigations were aimed at exploring the possibility of medical X-ray phase-contrast imaging in photon-counting regime at minimal radiation doses.
This study uses stable noble gases' (He, Ne, Ar, Kr, Xe) volume fractions and isotopic ratios from Antrim Shale natural gas to assess compositional variability and vertical fluid migration within ...this reservoir, in addition to distinguishing between the presence of thermogenic versus biogenic methane. R/Ra values, where R is the measured 3He/4He ratio and Ra is the atmospheric value of 1.384±0.013×10−6, vary from 0.01 to 0.34 suggesting a largely dominant crustal 4He component with minor atmospheric and mantle contributions. Crustal 21Ne, 40Ar and 136Xe contributions are also present but the atmospheric component is largely dominant for these gases. Crustal contributions for 21Ne, 40Ar and 136Xe vary between 1.1% and 12.5%, between 0.7% and 19% and between 0.1% and 2.7%, respectively. A few samples present higher than atmospheric 20Ne/22Ne ratios pointing to the presence of a small mantle Ne component. High horizontal and vertical variability of noble gas signatures in the Antrim Shale are observed. These are mainly due to variable noble gas input from deep brines and, to a smaller extent, variable in-situ production within different layers of the Antrim Shale, in particular, the Lachine and Norwood members. Estimated 4He ages, considering external 4He input for Antrim Shale water, vary between 0.9ka and 238.2ka and match well for most samples with the timing of the major Wisconsin glaciation, suggesting that Antrim Shale water was influenced by glaciation-induced recharge. Consistency between measured and predicted 40Ar/36Ar ratios assuming Ar release temperatures ≥250°C supports a thermogenic origin for most of the methane in these samples. This thermogenic methane is likely to originate at greater depths, either from the deeper portion of the Antrim Shale in the central portion of the Michigan Basin or from deeper formations given that the thermal maturity of the Antrim Shale in the study area is rather low.
•Antrim Shale noble gases spatial variability is mostly due to variable deep brine migration input.•Antrim Shale water ages are consistent with Wisconsin glaciation-induced recharge.•Antrim Shale noble gas signatures are consistent with a dominant thermogenic methane component
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We present the first horizontal divergence and relative vorticity measurements at polar mesospheric altitudes measured from the ground. Our technique relies on combining information from two specular ...meteor radars (SMRs) separated 130 km at polar latitudes, specifically, the Andenes and Tromsø radars in northern Norway. The resulting values are obtained over a region that spans an approximate area of 400 km diameter at mesospheric altitudes. The temporal and vertical resolution are 1 h and 2 km in altitude. The technique not only allows to obtain the gradient terms of the horizontal wind, that in turn are used to derive the horizontal divergence and relative vorticity, but also improves the horizontal sampling compared to single SMRs. Synthetic data are used to qualitatively test the technique and identify potential sources of biases on the resulting measurements. For example, we have found that an apparent large mean vertical velocity is obtained, after averaging many days, if there is a persistent divergent field. We present a climatology of the resulting wind field parameters from 12 years of continuous observations and focus on the summer results. We found a persistent altitudinal pattern in both the horizontal divergence and relative vorticity fields during all northern hemispheric summers. The horizontal divergence is mainly positive decreasing in magnitude below ∼86 km, and the relative vorticity is negative/positive below/above ∼88 km over northern Norway.
Plain Language Summary
We present a novel approach to measure new parameters of the wind field at altitudes between 80 and 100 km at polar latitudes. The approach consists of using closely located radars. These radars measure the winds from observing the time evolution of meteor trails. Since the echos from meteor trails are strong, the radars used are relatively small. We have analyzed data from radars in northern Norway that have been operating for more than 12 years. This is the first time that such data sets are combined to explore new parameters like horizontal divergence and relative vorticity. The climatology of this new parameters shows that there are persistent and well‐identified patterns at the polar summer mesosphere. We expect that the new parameters will be useful in future efforts to improve the understanding of processes in this part of the atmosphere.
Key Points
First direct measurements of mesoscale horizontal divergence and relative vorticity in the polar MLT region
The height transition from negative to positive horizontal divergence in the polar summer indicates the height of maximum mean vertical wind
The transition height of horizontal divergence is slightly higher than for the relative vorticity in the polar summer mesosphere
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The seasonal and interannual variabilities of mesospheric semidiurnal tides (SDT) are investigated using specular meteor radar‐based winds. The horizontal wind observations during 2003 to 2014 from a ...high‐latitude station, Andenes (69°N, 16°E), and during 2008 to 2014 from a midlatitude station, Juliusruh (54°N, 13°E), are used. It has been observed that the amplitudes of mesospheric SDTs are enhanced at both stations during August–September of all the years. These enhancements show a systematic behavior with that of the low‐latitude stratospheric quasi‐biennial oscillation (QBO), which is characterized based on winds from radiosonde data. The SDT amplitude values during enhancement are below/above mean level for those years in which the QBO wind at 50 hPa is westward/eastward (QBOw/QBOe). The average SDT amplitudes during the August–September enhancement duration are found to vary hand in hand with the low‐latitude QBO wind, suggesting QBO modulation of SDT. Stratospheric and lower mesospheric zonal wind perturbations from MERRA reanalysis data show weak local forcing in the Northern Hemisphere and indication of enhanced quasi‐stationary planetary waves (SPW) in the Southern Hemisphere. Based on these observations and some earlier results, we hypothesize that the QBOw/QBOe wind damp/enhance the southern hemispheric SPW of wave number 1 (SPW1). This modulated SPW1 then interacts with the northern midlatitude and high‐latitude SDTs to imprint the signature of QBO on them.
Key Points
Enhanced mesospheric semidiurnal tide in northern midlatitudes and high latitudes during August‐September
Semidiurnal tidal amplitudes during August‐September enhancement are above/below mean level for QBO eastward/westward wind
QBO modulation of northern semidiurnal tides is teleconnected via interhemispheric coupling of southern planetary waves
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The noble gas temperature climate proxy is an established tool that has previously been applied to determine the source of groundwater recharge, however, unanswered questions remain. In fractured ...media (e.g., volcanic islands) recharge can be so rapid that groundwater is significantly depleted in heavy noble gases, indicating that the water has retained noble gas concentrations from higher elevations. Previous studies of rain samples have confirmed a match to patterns seen in fractured‐rock groundwater for heavy noble gases along with a significant helium excess. Snow has been shown to be a credible source for both the helium excess and the observed heavy noble gas pattern. Here, liquid cloud water samples were collected at two mountainous sites and analyzed for noble gas concentrations. A pattern like that of rainwater was found. However, an analysis of diffusive uptake of noble gases into cloud water demonstrates that droplets of 1 mm diameter and smaller should be in constant solubility equilibrium with the atmosphere. To explain this, we present a novel hypothesis that relies on the assumption that liquid water consists of two types of water molecule clusters bounded by hydrogen bonds: a low‐density ice‐like structure and a high‐density condensed structure. In this model, the pressure gradient near the surface of a droplet resulting from surface tension could allow for the formation of a surface layer that is rich in ice‐like low density clusters. This can explain both the helium excess and the heavy noble gas depletion seen in the samples.
Plain Language Summary
Highly anomalous solubility values for atmospheric noble gases in small water droplets within clouds were found for samples from Puerto Rico and Virginia, USA. Various possible mechanisms were examined to explain the pattern of helium excess along with highly depleted argon, krypton, and xenon. A hypothesis is presented that assumes that an ice‐like coating forms on micron‐scale droplets due to the presence of large pressure gradients near the surface of small water droplets. It is assumed that these gradients can separate high density water molecule clusters from low density (ice‐like) clusters because of buoyancy forces near the surface of the droplets. If confirmed by further research, this hypothesis has implications for the physics of cloud formation.
Key Points
Noble gases are not in solubility equilibrium with liquid cloud water
Standard solubility models suggest that drops small than 1 mm should always be in equilibrium
The discrepancy can be explained if internal droplet pressure gradients favor the formation of an ice‐like surface on the droplet
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