Supercooled Liquid Water Detection Capabilities from Ka-Band Doppler Profiling Radars: Moment-Based Algorithm Formulation and Assessment

The occurrence of supercooled liquid water in mixed-phase cloud (MPC) affects their cloud microphysical and radiative properties. The prevalence of MPCs in the mid- and high latitudes translates these effects to significant contributions to Earth’s radiative balance and hydrological cycle. The current study develops and assesses a radar-only, moment-based phase partition technique for the demarcation of supercooled liquid water volumes in arctic, MPC conditions. The study utilizes observations from the Ka band profiling radar, the collocated high spectral resolution lidar, and ambient temperature profiles from radio sounding deployments following a statistical analysis of 5.5 years of data (January 2014–May 2019) from the Atmospheric Radiation Measurement observatory at the North Slope of Alaska. The ice/liquid phase partition occurs via a per-pixel, neighborhood-dependent algorithm based on the premise that the partitioning can be deduced by examining the mean values of locally sampled probability distributions of radar-based observables and then compare those against the means of climatologically derived, per-phase probability distributions. Analyzed radar observables include linear depolarization ratio (LDR), spectral width, and vertical gradients of reflectivity factor and radial velocity corrected for vertical air motion. Results highlight that the optimal supercooled liquid water detection skill levels are realized for the radar variable combination of spectral width and reflectivity vertical gradient, suggesting that radar-based polarimetry, in the absence of full LDR spectra, is not as critical as Doppler capabilities. The cloud phase masking technique is proven particularly reliable when applied to cloud tops with an Equitable Threat Score (ETS) of 65%; the detection of embedded supercooled layers remains much more uncertain (ETS = 27%)

Highly supercooled riming and unusual triple-frequency radar signatures over Antarctica

Riming of ice crystals by supercooled water droplets is an efficient ice growth process, but its basic properties are still poorly known. While it has been shown to contribute significantly to surface precipitation at mid-latitudes, little is known about its occurrence at high latitudes. In Antarctica, two competing effects can influence the occurrence of riming: the scarcity of supercooled liquid water clouds due to the extremely low tropospheric temperatures and the low aerosol concentration, which may lead to the formation of fewer and larger supercooled drops potentially resulting in an enhanced riming efficiency. In this work, by exploiting the deployment of an unprecedented number of multi-wavelength active and passive remote sensing systems (including triple-frequency radar measurements) in West Antarctica, during the Atmospheric Radiation Measurements West Antarctic Radiation Experiment (AWARE) field campaign, we evaluate the importance of riming incidence in Antarctica and find that riming occurs at much lower temperatures compared to the mid-latitudes. We then focus on a case study featuring a persistent layer of unexpectedly pronounced triple-frequency radar signatures but only a relatively modest amount of supercooled liquid water. In-depth analysis of the radar observations suggests that such signatures can only be explained by the combined effects of moderately rimed aggregates or similarly shaped florid polycrystals and a narrow particle size distribution (PSD). Simulations of this case study performed with a 1D bin model %by introducing an additional class corresponding to rimed ice indicate that similar triple frequency radar observations can be reproduced when narrow PSDs are simulated. Such narrow PSDs can in turn be explained by two key factors: (i) the presence of a shallow homogeneous droplet or humidified aerosol freezing layer aloft seeding an underlying supercooled liquid layer, and (ii) the absence of turbulent mixing throughout a stable polar atmosphere that sustains narrow PSDs, as hydrometeors grow from the nucleation region aloft to several millimeter ice particles, by vapor deposition and then riming

Ice microphysics from multifrequency suites of active and passive remote sensing instruments

High-latitude processes and polar cloud microphysics envelop research areas the furtherance of which in the more accurate description of the arctic energy budget, climate variability, and feedbacks is essential. This study develops and assesses a multifrequency and Doppler-inclusive, ice particle size distribution retrieval technique for mean mass-weighted diameter and ice water content, and additionally proposes a radaronly, moment-based phase partition scheme tailored to polar regions. The technique is applied to datasets collected by the ARM research facility at the North Slope of Alaska and two ARM Mobile Facility 2 campaigns (BAECC, AWARE) that comprise a gamut of ground-based profiling sensors including radars at X, Ka, and W bands, lidar, and microwave radiometer. The microphysical retrieval is a multi-instrument task; firstly, a Ka-band -based, reflectivity-velocity power-law scheme estimates an ice sedimentation velocity corrected for the vertical wind component. An attenuation correction is then applied for the estimation of effective reflectivities. Both reflectivity and sedimentation velocity are integrated in a Bayesian scheme that compares observations against lookup- tables in both backscattering and hydrodynamic ice-particle properties. The radar only, phase partitioning is proven reliable in detecting cloud-top supercooled liquid water layers. Aggregate statistics are computed based on BAECC data. The combined utilization of radar reflectivity in a dual- or triple-frequency forward modeling in conjunction with sedimentation velocity, demonstrates that Doppler observations can assist in microphysical characterizations because connections across observations and simulations of both ice scattering and hydrodynamic properties are less ambiguous compared to scattering-only. Results demonstrate less retrieval spread among X / Ka / W / Doppler or Ka / W / Doppler retrieval scenarios as opposed to X / Ka / W. Lastly, the inclusion of a lower frequency (10-15 GHz) is advocated due to its significance in signal mitigation (attenuation, cross-calibration) and in the retrieval forward modeling ambiguity constraining.</div

Μικροφυσική παγοκρυστάλλων βάσει παρατηρησιακών συστημάτων πολλών συχνοτήτων ενεργών και παθητικών αισθητήρων

High-latitude processes and polar cloud microphysics envelop research areas the furtherance of which in the more accurate description of the arctic energy budget, climate variability, and feedbacks is essential. This study develops and assesses a multi-frequency and Doppler-inclusive, ice particle size distribution retrieval technique for mean mass-weighted diameter and ice water content, and additionally proposes a radar-only, moment-based phase partition scheme tailored to polar regions. The technique is applied to datasets collected by the ARM research facility at the North Slope of Alaska and two ARM Mobile Facility 2 campaigns (BAECC, AWARE) that comprise a gamut of ground-based profiling sensors including radars at X, Ka, and W bands, lidar, and microwave radiometer. The microphysical retrieval is a multi-instrument task; firstly, a Ka-band -based, reflectivity-velocity power-law scheme estimates an ice sedimentation velocity corrected for the vertical wind component. An attenuation correction is then applied for the estimation of effective reflectivities. Both reflectivity and sedimentation velocity are integrated in a Bayesian scheme that compares observations against lookup-tables in both backscattering and hydrodynamic ice-particle properties. The radar-only, phase partitioning is proven reliable in detecting cloud-top supercooled liquid water layers. Aggregate statistics are computed based on BAECC data. The combined utilization of radar reflectivity in a dual- or triple-frequency forward modeling in conjunction with sedimentation velocity, demonstrates that Doppler observations can assist in microphysical characterizations because connections across observations and simulations of both ice scattering and hydrodynamic properties are less ambiguous compared to scattering-only. Results demonstrate less retrieval spread among X/Ka/W/Doppler or Ka/W/Doppler retrieval scenarios as opposed to X/Ka/W. Lastly, the inclusion of a lower frequency (10-15 GHz) is advocated due to its significance in signal mitigation (attenuation, cross-calibration) and in the retrieval forward modeling ambiguity constraining.Οι φυσικές διεργασίες σε μεγάλα γεωγραφικά πλάτη και η μικροφυσική των πολικών νεφών συνιστούν πεδία έρευνας η περεταίρω μελέτη των οποίων καθίσταται επιβεβλημένη για την πιο ακριβή περιγραφή του αρκτικού ενεργειακού κύκλου, της κλιματικής μεταβλητότητας, και των μηχανισμών ανάδρασης. Η εργασία αναπτύσσει και εκτιμά μια τεχνική ανάκτησης παραμέτρων κατανομών μεγέθους παγοκρυστάλλων για μέση διάμετρο σταθμισμένη-δια-της-μάζας και κυβικής πυκνότητας πάγου, εδραζόμενη σε παρατηρήσεις πολλών συχνοτήτων και ταχυτήτων Doppler, καθώς επίσης προτείνει ένα σχήμα διαχωρισμού φάσεως υδρομετεώρων για πολικές περιοχές βασισμένο σε ανάλυση ροπών μεγεθών από παρατηρήσεις ραντάρ. Η τεχνική εφαρμόζεται σε βάσεις δεδομένων από την ερευνητική εγκατάσταση του προγράμματος ARM στη Βόρεια Κλίση της Αλάσκα και από δύο αναπτύξεις της Φορητής Εγκατάστασης 2 του ιδίου προγράμματος (BAECC, AWARE) οι οποίες συνιστούν ένα σύνολο κάθετης παρατήρησης από το έδαφος, αισθητήρων ραντάρ σε συχνότητες X, Ka, και W, lidar, και ραδιομέτρων μικροκυμάτων. Η ανάκτηση μικροφυσικών παραμέτρων επαφίεται σε παρατηρήσεις πολλών συχνοτήτων: αρχικά, ένα σχήμα παλινδρόμησης παρατηρήσεων ανακλαστικότητας-ταχήτητας σε Ka- εύρος συχνοτήτων εκτιμά ταχύτητα κατακρήμνισης παγοκρυστάλλων υποκείμενο σε διόρθωση κατακόρυφης συνιστώσας του ανέμου. Κατόπιν, ενεργές ανακλαστικότητες υπολογίζονται βάσει διόρθωσης εξασθένησης σήματος λόγω ατμοσφαιρικής διάδοσης. Οι ανακλαστικότητες και οι ταχύτητες κατακρήμνισης ενσωματώνονται σε Μπαεσιανό στατιστικό σχήμα το οποίο αντιπαραβάλλει παρατηρήσεις έναντι προϋπολογισμένων ηλεκτρομαγνητικών ενεργών διατομών σκέδασης και υδροδυναμικών ιδιοτήτων παγοκρυστάλλων. Ο διαχωρισμός φάσεως βάσει ραντάρ αποδεικνύεται αξιόπιστος στον εντοπισμό στρωμάτων μετασταθούς υγρού νερού επί κορυφών των νεφών. Συγκεντρωτικές στατιστικές υπολογίζονται βάσει των δεδομένων BAECC. Η συνδυαστική υλοποίηση ανακλαστικότητας ραντάρ με ταχύτητες κατακρήμνισης σε σχήμα αντιστροφής δύο- ή τριών- συχνοτήτων, επιδεικνύει το ότι οι παρατηρήσεις Doppler είναι σε θέση να επιχορηγήσουν το μικροφυσικό χαρακτηρισμό μειώνοντας την αβεβαιότητα των αντιστροφών, εξ’ αιτίας της σύνδεσης παρατηρήσεων και προσομοιώσεων ηλεκτρομαγνητικών και υδροδυναμικών ιδιοτήτων ατμοσφαιρικού πάγου έναντι μεθόδων που υλοποιούν μόνο ηλεκτρομαγνητικές ιδιότητες. Τα αποτελέσματα καταδεικνύουν μικρότερες αποκλίσεις των αντιστροφών μεταξύ σεναρίων υλοποίησης X/Ka/W/Doppler ή Ka/W/Doppler έναντι X/Ka/W. Κλείνοντας, η συμπερίληψη παρατηρήσεων χαμηλότερων συχνοτήτων (10-15 GHz) προτείνεται για την καλύτερη διόρθωση σήματος (απορρόφηση, βαθμονόμηση) και περεταίρω περιορισμού της αβεβαιότητας αριθμητικών σχημάτων ατμοσφαιρικών αντιστροφών

Highly supercooled riming and unusual triple-frequency radar signatures over McMurdo Station, Antarctica

Abstract. Riming of ice crystals by supercooled water droplets is an efficient ice growth process, but its basic properties are still poorly known. While it has been shown to contribute significantly to surface precipitation at mid-latitudes, little is known about its occurrence at high latitudes. In Antarctica, two competing effects can influence the occurrence of riming: (i) the scarcity of supercooled liquid water clouds due to the extremely low tropospheric temperatures and (ii) the low aerosol concentration, which may lead to the formation of fewer and larger supercooled drops potentially resulting in an enhanced riming efficiency. In this work, by exploiting the deployment of an unprecedented number of multiwavelength remote sensing systems (including triple-frequency radar measurements) in West Antarctica, during the Atmospheric Radiation Measurements West Antarctic Radiation Experiment (AWARE) field campaign, we evaluate the riming incidence at McMurdo Station and find that riming occurs at much lower temperatures when compared to previous results in the mid-latitudes. This suggests the possible occurrence of a common atmospheric state over Antarctica that includes a rather stable atmosphere inhibiting turbulent mixing, and a high riming efficiency driven by large cloud droplets. We then focus on a peculiar case study featuring a persistent layer with a particularly pronounced riming signature in triple-frequency radar data but only a relatively modest amount of supercooled liquid water. In-depth analysis of the radar observations suggests that such signatures can only be explained by the combined effects of moderately rimed aggregates or similarly shaped florid polycrystals and a narrow particle size distribution (PSD). Simulations of this case study performed with a one-dimensional bin model indicate that similar triple-frequency radar observations can be reproduced when narrow PSDs are simulated. Such narrow PSDs can in turn be explained by two key factors: (i) the presence of a shallow homogeneous droplet or humidified aerosol freezing layer aloft seeding an underlying supercooled liquid layer, and (ii) the absence of turbulent mixing throughout a stable polar atmosphere that sustains narrow PSDs, as hydrometeors grow from the nucleation region aloft to ice particles of several millimeters in size, by vapor deposition and then riming

Transcatheter closure of paravalvular leak: Multicenter experience and follow-up

Background: Paravalvular leak (PVL) is a common complication following valve replacement, which leads to heart failure and hemolysis. Transcatheter PVL closure has emerged as a reliable alternative with promising results. We quote the combined three-center experience of PVL patients treated percutaneously. Methods: Consecutive patients treated percutaneously for PVL were retrospectively studied. Procedural characteristics, inhospital, and long-term clinical outcomes were assessed. Technical (successful deployment) and clinical (NYHA and/or hemolysis improvement) success were evaluated. Results: In total, 39 patients treated for PVL in either the aortic (12 patients) or the mitral (27 patients) position were studied. Amplatzer Vascular Plug III was the most commonly used device among the 45 devices totally implanted. Postprocedurally, the rates of at least moderate PVL (87.5% preprocedurally vs 10.5% at discharge) and functional status (mean NYHA class 2.8 +/- 0.7 on admission vs 1.5 +/- 0.8 at follow-up) were statistically significantly improved. Total population technical success rate was 89.7%, being comparable between patients treated for mitral or aortic valve PVLs (92.6% vs 83.3%, respectively). Clinical success was achieved in 82.1% of patient cohort without statistical difference among those with isolated aortic or mitral PVL or among those with PVL closure an indication of heart failure or hemolysis. During a mean follow-up of 33.5 months, five patients died, including one periprocedural death. Conclusions: This multicenter recorded experience confirms that percutaneous PVL closure can be performed with high technical and clinical success rates and limited complications that lead to significant PVL reduction and functional status improvement. (C) 2021 Hellenic Society of Cardiology. Publishing services by Elsevier B.V

Salivary Biomarkers for Diagnosis and Therapy Monitoring in Patients with Heart Failure. A Systematic Review

International audienceThe aim of this study was to perform a systematic review on the potential value of saliva biomarkers in the diagnosis, management and prognosis of heart failure (HF). The correlation between saliva and plasma values of these biomarkers was also studied. PubMed was searched to collect relevant literature, i.e., case-control, cross-sectional studies that either compared the values of salivary biomarkers among healthy subjects and HF patients, or investigated their role in risk stratification and prognosis in HF patients. No randomized control trials were included. The search ended on 31st of December 2020. A total of 15 studies met the inclusion criteria. 18 salivary biomarkers were analyzed and the levels of all biomarkers studied were found to be higher in HF patients compared to controls, except for amylase, sodium, and chloride that had smaller saliva concentrations in HF patients. Natriuretic peptides are the most commonly used plasma biomarkers in the management of HF. Their saliva levels show promising results, although the correlation of saliva to plasma values is weakened in higher plasma values. In most of the publications, differences in biomarker levels between HF patients and controls were found to be statistically significant. Due to the small number of patients included, larger studies need to be conducted in order to facilitate the use of saliva biomarkers in clinical practice