Laboratory experiments confirm the polarization of auroral emissions.

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Night light polarization: modeling and observations of light pollution in the presence of aerosols and background skylight or airglow

Aurorae and nightglow are faint atmospheric emissions visible during night-time at several wavelengths. These emissions have been extensively studied but their polarization remains controversial. A great challenge is that light pollution from cities and scattering in the lower atmosphere interfere with polarization measurements. We introduce a new polarized radiative transfer model able to compute the polarization measured by a virtual instrument in a given nocturnal environment recreating real world conditions (atmospheric and aerosol profiles, light sources with complex geometries, terrain obstructions).The model, based on single scattering equations in the atmosphere, is tested on a few simple configurations to assess the effect of several key parameters in controlled environments. {Our model constitutes a proof of concept for polarization measurements in nocturnal conditions, that calls for further investigations. In particular, we discuss how multiple-scattering (neglected in the present study) impacts our observations and their interpretation, and the future need for inter-calibrating the source and the polarimeter in order to optimally extract the information contained in this kind of measurements. The model outputs are compared to field measurements in five wavelengths. A convincing fit between the model predictions and observations is found in the three most constrained wavelengths despite the single scattering approximation. Several applications of our model are discussed that concern the polarization of aurorae, the impact of light pollution, or aerosols and air pollution measurements

Night light polarization: modeling and observations of light pollution in the presence of aerosols and background skylight or airglow

Aurorae and nightglow are faint atmospheric emissions visible during night-time at several wavelengths. These emissions have been extensively studied but their polarization remains controversial. A great challenge is that light pollution from cities and scattering in the lower atmosphere interfere with polarization measurements. We introduce a new polarized radiative transfer model able to compute the polarization measured by a virtual instrument in a given nocturnal environment recreating real world conditions (atmospheric and aerosol profiles, light sources with complex geometries, terrain obstructions).The model, based on single scattering equations in the atmosphere, is tested on a few simple configurations to assess the effect of several key parameters in controlled environments. {Our model constitutes a proof of concept for polarization measurements in nocturnal conditions, that calls for further investigations. In particular, we discuss how multiple-scattering (neglected in the present study) impacts our observations and their interpretation, and the future need for inter-calibrating the source and the polarimeter in order to optimally extract the information contained in this kind of measurements. The model outputs are compared to field measurements in five wavelengths. A convincing fit between the model predictions and observations is found in the three most constrained wavelengths despite the single scattering approximation. Several applications of our model are discussed that concern the polarization of aurorae, the impact of light pollution, or aerosols and air pollution measurements

Night light polarization: modeling and observations of light pollution in the presence of aerosols and background skylight or airglow

Aurorae and nightglow are faint atmospheric emissions visible during night-time at several wavelengths. These emissions have been extensively studied but their polarization remains controversial. A great challenge is that light pollution from cities and scattering in the lower atmosphere interfere with polarization measurements. We introduce a new polarized radiative transfer model able to compute the polarization measured by a virtual instrument in a given nocturnal environment recreating real world conditions (atmospheric and aerosol profiles, light sources with complex geometries, terrain obstructions).The model, based on single scattering equations in the atmosphere, is tested on a few simple configurations to assess the effect of several key parameters in controlled environments. {Our model constitutes a proof of concept for polarization measurements in nocturnal conditions, that calls for further investigations. In particular, we discuss how multiple-scattering (neglected in the present study) impacts our observations and their interpretation, and the future need for inter-calibrating the source and the polarimeter in order to optimally extract the information contained in this kind of measurements. The model outputs are compared to field measurements in five wavelengths. A convincing fit between the model predictions and observations is found in the three most constrained wavelengths despite the single scattering approximation. Several applications of our model are discussed that concern the polarization of aurorae, the impact of light pollution, or aerosols and air pollution measurements

At the source of the polarisation of auroral emissions: experiments and modeling

International audienceA polarised radiative transfer model (POMEROL) has been developed to compute the polarisation measured by a virtual instrument in a given nocturnal environment. This single-scattering model recreates real-world conditions (among them atmospheric and aerosol profiles, light sources with complex geometries at the ground and in the sky, terrain obstructions). It has been successfully tested at mid-latitudes where sky emissions are of weak intensity. We show a series of comparisons between POMEROL predictions and polarisation measurements during two field campaigns in the auroral zone, in both quiet and active conditions. These comparisons show the strength of the model to assess the aerosol characteristics in the lower atmosphere by using a mesospheric line. They also show that three main upper atmosphere emissions must be polarised: the green atomic oxygen line at 557.7 nm and the 1st N2+ negative band at 391.4 nm (purple) and 427.8 nm (blue). This polarisation can be either created directly at the radiative de-excitation or may occur when the non-polarised emission crosses the ionospheric currents. We provide some of the potentialities it offers in the frame of space weather. These require refinements of the preliminary modeling approach considered in the present study

The polarisation of auroral emissions: A tracer of the E region ionospheric currents

International audienceIt is now established that auroral emissions as measured from the ground are polarised. The question of the information given by this polarisation is still to be explored. This article shows the results of a coordinated campaign between an optical polarimeter and several ground-based instruments, including magnetometers, the EISCAT VHF radar, and complementary luminance meters in the visible domain (Ninox). We show that in the E region, the polarisation is a potential indicator of the ionospheric currents, velocity, and dynamics

On the nightglow polarisation for space weather exploration

International audienceWe present here observations of the polarisation of four auroral lines in the auroral oval and in the polar cusp using a new ground polarimeter called Petit Cru. Our results confirm the already known polarisation of the red line, and show for the first time that the three other lines observed here (namely 557.7 nm, 391.4 nm and 427.8 nm) are polarised as well up to a few percent. We show that in several circumstances, this polarisation is linked to the local magnetic activity and to the state of the ionosphere through the electron density measured with EISCAT. However, we also show that the contribution of light pollution from nearby cities via scattering can not be ignored and can play an important role in polarisation measurements. This series of observations questions the geophysical origin of the polarisation. It also leaves open its relation to the magnetic field orientation and to the state of both the upper atmosphere and the troposphere

Cx36 makes channels coupling human pancreatic β-cells, and correlates with insulin expression

Previous studies have documented that the insulin-producing β-cells of laboratory rodents are coupled by gap junction channels made solely of the connexin36 (Cx36) protein, and have shown that loss of this protein desynchronizes β-cells, leading to secretory defects reminiscent of those observed in type 2 diabetes. Since human islets differ in several respects from those of laboratory rodents, we have now screened human pancreas, and islets isolated thereof, for expression of a variety of connexin genes, tested whether the cognate proteins form functional channels for islet cell exchanges, and assessed whether this expression changes with β-cell function in islets of control and type 2 diabetics. Here, we show that (i) different connexin isoforms are differentially distributed in the exocrine and endocrine parts of the human pancreas; (ii) human islets express at the transcript level different connexin isoforms; (iii) the membrane of β-cells harbors detectable levels of gap junctions made of Cx36; (iv) this protein is concentrated in lipid raft domains of the β-cell membrane where it forms gap junctions; (v) Cx36 channels allow for the preferential exchange of cationic molecules between human β-cells; (vi) the levels of Cx36 mRNA correlated with the expression of the insulin gene in the islets of both control and type 2 diabetics. The data show that Cx36 is a native protein of human pancreatic islets, which mediates the coupling of the insulin-producing β-cells, and contributes to control β-cell function by modulating gene expression

Thrombotic and hemorrhagic complications of COVID-19 in adults hospitalized in high-income countries compared with those in adults hospitalized in low- and middle-income countries in an international registry

Background: COVID-19 has been associated with a broad range of thromboembolic, ischemic, and hemorrhagic complications (coagulopathy complications). Most studies have focused on patients with severe disease from high-income countries (HICs). Objectives: The main aims were to compare the frequency of coagulopathy complications in developing countries (low- and middle-income countries [LMICs]) with those in HICs, delineate the frequency across a range of treatment levels, and determine associations with in-hospital mortality. Methods: Adult patients enrolled in an observational, multinational registry, the International Severe Acute Respiratory and Emerging Infections COVID-19 study, between January 1, 2020, and September 15, 2021, met inclusion criteria, including admission to a hospital for laboratory-confirmed, acute COVID-19 and data on complications and survival. The advanced-treatment cohort received care, such as admission to the intensive care unit, mechanical ventilation, or inotropes or vasopressors; the basic-treatment cohort did not receive any of these interventions. Results: The study population included 495,682 patients from 52 countries, with 63% from LMICs and 85% in the basic treatment cohort. The frequency of coagulopathy complications was higher in HICs (0.76%-3.4%) than in LMICs (0.09%-1.22%). Complications were more frequent in the advanced-treatment cohort than in the basic-treatment cohort. Coagulopathy complications were associated with increased in-hospital mortality (odds ratio, 1.58; 95% CI, 1.52-1.64). The increased mortality associated with these complications was higher in LMICs (58.5%) than in HICs (35.4%). After controlling for coagulopathy complications, treatment intensity, and multiple other factors, the mortality was higher among patients in LMICs than among patients in HICs (odds ratio, 1.45; 95% CI, 1.39-1.51). Conclusion: In a large, international registry of patients hospitalized for COVID-19, coagulopathy complications were more frequent in HICs than in LMICs (developing countries). Increased mortality associated with coagulopathy complications was of a greater magnitude among patients in LMICs. Additional research is needed regarding timely diagnosis of and intervention for coagulation derangements associated with COVID-19, particularly for limited-resource settings