Ammonia is predicted to be one of the major components in the depths of the ice giant planets Uranus and Neptune. Their dynamics, evolution, and interior structure are insufficiently understood and ...models rely imperatively on data for equation of state and transport properties. Despite its great significance, the experimentally accessed region of the ammonia phase diagram today is still very limited in pressure and temperature. Here we push the probed regime to unprecedented conditions, up to ∼350 GPa and ∼40 000 K. Along the Hugoniot, the temperature measured as a function of pressure shows a subtle change in slope at ∼7000 K and ∼90 GPa, in agreement with ab initio simulations we have performed. This feature coincides with the gradual transition from a molecular liquid to a plasma state. Additionally, we performed reflectivity measurements, providing the first experimental evidence of electronic conduction in high-pressure ammonia. Shock reflectance continuously rises with pressure above 50 GPa and reaches saturation values above 120 GPa. Corresponding electrical conductivity values are up to 1 order of magnitude higher than in water in the 100 GPa regime, with possible significant contributions of the predicted ammonia-rich layers to the generation of magnetic dynamos in ice giant interiors.
We report a comprehensive study of Mars dayglow observations focusing on upper atmospheric structure and seasonal variability. We analyzed 744 vertical brightness profiles comprised of ∼109,300 ...spectra obtained with the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. The dayglow emission spectra show features similar to previous UV measurements at Mars. We find a significant drop in thermospheric scale height and temperature between LS = 218° and LS = 337–352°, attributed primarily to the decrease in solar activity and increase in heliocentric distance. We report the detection of a second, low‐altitude peak in the emission profile of OI 297.2 nm, confirmation of the prediction that the absorption of solar Lyman alpha emission is an important energy source there. The
CO2+ UV doublet peak intensity is well correlated with simultaneous observations of solar 17–22 nm irradiance at Mars.
Key Points
Significant drop in thermospheric temperature between two Martian seasons
Detection of second layer of OI 297.2 nm emission below 100 km
Strong correlation between observed mid‐UV dayglow and simultaneously measured EUV flux at Mars
What's new in hyperkalemia management? Lefevre, F; Mousseaux, C; Bobot, M
La revue de medecine interne,
06/2024, Letnik:
45, Številka:
6
Journal Article
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Hyperkalemia is common in everyday clinical practice, and is a major risk factor for mortality. It mainly affects patients with chronic renal failure (CKD), diabetes or receiving treatment with ...inhibitors of the renin-angiotensin-aldosterone system (iRAAS). Therapeutic management aims not only to avoid the complications of hyperkalemia, but also to avoid discontinuation of cardio- and nephroprotective treatments such as iRAAS. The use of polystyrene sulfonate, widely prescribed, is often limited by patient acceptability. Recent data have cast doubt on its safety, particularly in terms of digestive tolerance. Two new potassium exchange molecules have appeared on the market: patiromer and zirconium sulfonate. Their value in clinical practice, and their acceptability in the event of prolonged prescription, remain to be demonstrated. The combination of a thiazide diuretic or an inhibitor of the sodium-glucose cotransporter type 2 (iSGLT2) with iRAAS therapy in CKD, may also improve control of kalemia. At present, there are no recommendations for the positioning of the various hypokalemic treatments. The choice of these treatments must be adapted to the patient's pathologies and consider the other expected effects of these molecules.
A long-term ozone loss time series is necessary to understand the evolution of ozone in Antarctica. Therefore, we construct the time series using ground-based, satellite and bias-corrected ...multi-sensor reanalysis (MSR) data sets for the period 1989–2010. The trends in ozone over 1979–2010 are also estimated to further elucidate its evolution in the wake of decreasing halogen levels in the stratosphere. Our analysis with ground-based observations shows that the average ozone loss in the Antarctic is about −33 to −50% (−90 to −155 DU (Dobson Unit)) in 1989–1992, and then stayed at around −48% (−160 DU). The ozone loss in the warmer winters (e.g. 2002 and 2004) is lower (−37 to −46%), and in the very cold winters (e.g. 2003 and 2006) it is higher (−52 to −55%). These loss estimates are in good agreement with those estimated from satellite observations, where the differences are less than ±3%. The ozone trends based on the equivalent effective Antarctic stratospheric chlorine (EEASC) and piecewise linear trend (PWLT) functions for the vortex averaged ground-based, Total Ozone Mapping Spectrometer/Ozone Monitoring Instrument (TOMS/OMI), and MSR data averaged over September–November exhibit about −4.6 DU yr−1 over 1979–1999, corroborating the role of halogens in the ozone decrease during the period. The ozone trends computed for the 2000–2010 period are about +1 DU yr−1 for EEASC and +2.6 DU yr−1 for the PWLT functions. The larger positive PWLT trends for the 2000–2010 period indicate the influence of dynamics and other basis functions on the increase of ozone. The trends in both periods are significant at 95% confidence intervals for all analyses. Therefore, our study suggests that Antarctic ozone shows a significant positive trend toward its recovery, and hence, leaves a clear signature of the successful implementation of the Montreal Protocol.
The 2.3μm spectral window has been used to constrain the composition of the lower atmosphere (in the 30–40 km altitude range) on the night side of Venus for more than thirty years. Here, we present a ...follow-up study of Marcq et al. (2008), but using the full VIRTIS-H/Venus Express data archive as well as an updated radiative transfer forward model. We are able to confirm a latitudinal increase of CO of about 30% between 0° and 60°N, as well as an anti-correlated vertical shift of OCS profile by about −1km in the same latitude range. Both variations are about twice smaller in the southern hemisphere. Correlations of low latitude CO and OCS variations with zonally shifted surface elevation is tentatively found. These results are consistent with CO and OCS variations resulting from the competition between local thermochemistry and a Hadley-cell-like general circulation, albeit influenced by the orography. Finally, no evidence for spatial variations of water vapor (combined H2O and HDO) or sulfur dioxide could be evidenced in this data set; better constraining possible variations of these species would require future missions to include infrared spectrometers operating at a spectral resolving power higher than ∼104, such as VenSpec-H onboard EnVision.
Plain Language Summary Remotely measuring the composition of the Venusian atmosphere below the clouds is challenging, yet yields invaluable insights about the atmospheric chemistry, circulation and interaction with the surface and interior of the planet. The VIRTIS-H instrument on board ESA’s Venus Express orbiter (2006–2014) provides a rich data set in this regard, thanks to its ability to observe and analyze, on the night side of the planet, the infrared radiation emitted by the deep atmospheric layers. The results of our analyses confirm the previously observed trends for the variations of two trace gases (carbon monoxide and carbonyl sulfide) with latitude, explained by the combined effects of chemical reactions and transport by the atmospheric circulation. Variations of carbon monoxide may also be linked to the variations of ground elevation, confirming the link between surface topography and atmospheric circulation. However, we were unable to separate the signature of heavy water vapor from ordinary water vapor or to detect any variations in sulfur dioxide, both of which require more powerful infrared instruments such as those planned on future Venus orbiters such as ESA’s EnVision.
•The latitudinal variability of carbon monoxide on Venus is confirmed, as well as its anticorrelation with carbonyl sulfide.•Zonal variations of carbon monoxide near the equator may be correlated with zonally shifted surface elevation.•No variations of water vapor and sulfur dioxide were found; a spectral resolving power nearing 10000 is needed to further investigate.
•The thermal structure of the upper atmosphere of Venus predicted by a groundto- thermosphere 3D model for Venus is presented. The model includes the main processes contributing to the thermal ...balance of the atmosphere of Venus from 90 to 150 km, as well as a photochemical model and a non-orographic gravity waves parameterisation.•A succession of warm and cold layers is predicted: the role of radiative, photochemical and dynamical effects is described.•A comparison of model results with a selection of recent measurements shows an overall good agreement in terms of trends and order of magnitude.•Significant data-model discrepancies are also discerned and discussed. Among them, altitude layer of the predicted mesospheric local maximum (between 100–120 km) is higher then observed; thermosphere temperatures are about 40–50 K colder and up to 30 K warmer then measured at terminator and nighttime, respectively.
We present here the thermal structure of the upper atmosphere of Venus predicted by a full self-consistent Venus General Circulation Model (VGCM) developed at Laboratoire de Météorologie Dynamique (LMD) and extended up to the thermosphere of the planet. Physical and photochemical processes relevant at those altitudes, plus a non-orographic GW parameterisation, have been added. All those improvements make the LMD-VGCM the only existing ground-to-thermosphere 3D model for Venus: a unique tool to investigate the atmosphere of Venus and to support the exploration of the planet by remote sounding. The aim of this paper is to present the model reference results, to describe the role of radiative, photochemical and dynamical effects in the observed thermal structure in the upper mesosphere/lower thermosphere of the planet. The predicted thermal structure shows a succession of warm and cold layers, as recently observed. A cooling trend with increasing latitudes is found during daytime at all altitudes, while at nighttime the trend is inverse above about 110 km, with an atmosphere up to 15 K warmer towards the pole. The latitudinal variation is even smaller at the terminator, in agreement with observations. Below about 110 km, a nighttime warm layer whose intensity decreases with increasing latitudes is predicted by our GCM. A comparison of model results with a selection of recent measurements shows an overall good agreement in terms of trends and order of magnitude. Significant data-model discrepancies may be also discerned. Among them, thermospheric temperatures are about 40–50 K colder and up to 30 K warmer than measured at terminator and at nighttime, respectively. The altitude layer of the predicted mesospheric local maximum (between 100 and 120 km) is also higher than observed. Possible interpretations are discussed and several sensitivity tests performed to understand the data-model discrepancies and to propose future model improvements.
We present a detailed discussion of the chemical and dynamical processes in the Arctic winters 1996/1997 and 2010/2011 with high resolution chemical transport model (CTM) simulations and space-based ...observations. In the Arctic winter 2010/2011, the lower stratospheric minimum temperatures were below 195 K for a record period of time, from December to mid-April, and a strong and stable vortex was present during that period. Simulations with the Mimosa-Chim CTM show that the chemical ozone loss started in early January and progressed slowly to 1 ppmv (parts per million by volume) by late February. The loss intensified by early March and reached a record maximum of ~2.4 ppmv in the late March–early April period over a broad altitude range of 450–550 K. This coincides with elevated ozone loss rates of 2–4 ppbv sh−1 (parts per billion by volume/sunlit hour) and a contribution of about 30–55% and 30–35% from the ClO-ClO and ClO-BrO cycles, respectively, in late February and March. In addition, a contribution of 30–50% from the HOx cycle is also estimated in April. We also estimate a loss of about 0.7–1.2 ppmv contributed (75%) by the NOx cycle at 550–700 K. The ozone loss estimated in the partial column range of 350–550 K exhibits a record value of ~148 DU (Dobson Unit). This is the largest ozone loss ever estimated in the Arctic and is consistent with the remarkable chlorine activation and strong denitrification (40–50%) during the winter, as the modeled ClO shows ~1.8 ppbv in early January and ~1 ppbv in March at 450–550 K. These model results are in excellent agreement with those found from the Aura Microwave Limb Sounder observations. Our analyses also show that the ozone loss in 2010/2011 is close to that found in some Antarctic winters, for the first time in the observed history. Though the winter 1996/1997 was also very cold in March–April, the temperatures were higher in December–February, and, therefore, chlorine activation was moderate and ozone loss was average with about 1.2 ppmv at 475–550 K or 42 DU at 350–550 K, as diagnosed from the model simulations and measurements.
Sudden stratospheric warmings (SSWs) are associated with rapid rise in temperature in a short period of time in the polar vortex and reversal of the zonal winds in major warming conditions. Although ...SSWs are primarily driven by the planetary waves emanating from the troposphere, the exact reasons and factors responsible for the wave forcing are still to be uncovered. The severity and frequency of SSWs in the context of climate change are uncertain and warrant in-depth studies. Here, therefore, we characterize the most intense warming events in the southern polar region in the observed history for the past 41 years: the SSWs in 2019, 2002 and 1988. The 2019 minor warming began in response to the intense zonal wavenumber 1 forcing. The wave 1 amplitude was larger than that of 2002 and 1988, but wave 2 forcing was key for the major warming in 2002. The onset of warming took place in early (3
–
5) September and lasted until mid-(19–21) September in 2019. This minor warming was the longest as compared to that in the other years. The corresponding ozone loss was about 3.6 ppmv, the ozone hole area shrunk to 8 million km
2
during the period of peak warming, and the ozone loss amount was higher in 2019 than that in the other 2 years. The 2019 spring had a PSC area of 5 million km
2
, and the vortex area was as small as 24 million km
2
in the peak warming period. A variability of similar nature was also identified in the springs of 1988 and 2002. Henceforth, this study gives new insights into the unique dynamical situations in the warmest years of the southern polar stratospheric region in the observed history.
A detailed analysis of the polar ozone loss processes during 10 recent Antarctic winters is presented with high-resolution MIMOSA-CHIM (Modele Isentrope du transport Meso-echelle de l'Ozone ...Stratospherique par Advection avec CHIMie) model simulations and high-frequency polar vortex observations from the Aura microwave limb sounder (MLS) instrument. The high-frequency measurements and simulations help to characterize the winters and assist the interpretation of interannual variability better than either data or simulations alone. Our model results for the Antarctic winters of 2004-2013 show that chemical ozone loss starts in the edge region of the vortex at equivalent latitudes (EqLs) of 65-67 degree S in mid-June-July. The loss progresses with time at higher EqLs and intensifies during August-September over the range 400-600 K. The loss peaks in late September-early October, when all EqLs (65-83 degree S) show a similar loss and the maximum loss (> 2 ppmv - parts per million by volume) is found over a broad vertical range of 475-550 K. In the lower stratosphere, most winters show similar ozone loss and production rates. In general, at 500 K, the loss rates are about 2-3 ppbv sh-1 (parts per billion by volume per sunlit hour) in July and 4-5 ppbv sh-1 in August-mid-September, while they drop rapidly to 0 by mid-October. In the middle stratosphere, the loss rates are about 3-5 ppbv sh-1 in July-August and October at 675 K. On average, the MIMOSA-CHIM simulations show that the very cold winters of 2005 and 2006 exhibit a maximum loss of ~ 3.5 ppmv around 550 K or about 149-173 DU over 350-850 K, and the warmer winters of 2004, 2010, and 2012 show a loss of ~ 2.6 ppmv around 475-500 K or 131-154 DU over 350-850 K. The winters of 2007, 2008, and 2011 were moderately cold, and thus both ozone loss and peak loss altitudes are between these two ranges (3 ppmv around 500 K or 150 plus or minus 10 DU). The modeled ozone loss values are in reasonably good agreement with those estimated from Aura MLS measurements, but the model underestimates the observed ClO, largely due to the slower vertical descent in the model during spring.
The SPICAM/MEX ultraviolet spectrometer probed the Martian atmosphere with the occultation method from 2004 until 2014. SPICAM/MEX performed both stellar and solar occultations during in total four ...Martian Years with good spatial and seasonal coverages. We have analyzed these occultations and performed a rigorous quality check of the retrievals to eliminate false detections. We present the observed features of the vertical distribution of Martian ozone, a key chemical species. Stellar occultations probe the nightside atmosphere, whereas solar occultations are acquired at the terminator (sunrise or sunset), enabling the study of the day–night transition of this photochemically active species. Comparison of the observations with a global climate model show a good overall agreement. However, quantitative differences are found in certain regions, possibly related to difficulties in correct modeling of the water cycle. Our dataset allows us to study certain particular features of Martian ozone. The low- and midlatitude ozone layer forming during northern spring is mapped in both hemispheres and its night–terminator variations are probed with the combination of stellar and solar occultations. The southern polar winter vortex shows hints of the well-known mid-altitude ozone layer already detected previously. During the northern polar spring, SPICAM observes the top of the lower atmosphere ozone layer above 10 km, showing O3 concentrations that the model reproduces quite well. SPICAM observations are in good agreement with previously published observations from other instruments.
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•We present a climatology of O3 vertical distribution from SPICAM/MEX UV occultations.•Solar and stellar occultations allow us to follow the terminator–night variation of ozone.•The observations detect the aphelion ozone layer at ∼35 km, and polar ozone in certain seasons.
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