2,091 research outputs found
Observing relationships between lightning and cloud profiles by means of a satellite-borne cloud radar
Abstract. Cloud electrification and related lightning activity in thunderstorms have their origin in the charge separation and resulting distribution of charged iced particles within the cloud. So far, the ice distribution within convective clouds has been investigated mainly by means of ground-based meteorological radars. In this paper we show how the products from Cloud Profiling Radar (CPR) on board CloudSat, a polar satellite of NASA's Earth System Science Pathfinder (ESSP), can be used to obtain information from space on the vertical distribution of ice particles and ice content and relate them to the lightning activity. The analysis has been carried out, focusing on 12 convective events over Italy that crossed CloudSat overpasses during significant lightning activity. The CPR products considered here are the vertical profiles of cloud ice water content (IWC) and the effective radius (ER) of ice particles, which are compared with the number of strokes as measured by a ground lightning network (LINET). Results show a strong correlation between the number of strokes and the vertical distribution of ice particles as depicted by the 94âŻGHz CPR products: in particular, cloud upper and middle levels, high IWC content and relatively high ER seem to be favourable contributory causes for CG (cloud to ground) stroke occurrence
Analysis of Thunderstorms Producing Terrestrial Gamma Ray Flashes With the Meteosat Second Generation
Up to now, only few works focused on the meteorological context leading to the production of Terrestrial Gamma ray Flashes (TGFs). In this study, we carry out, for the first time, an analysis on large scale of the meteorological scenario linked to 278 TGFs detected by RHESSI, AGILE, and Fermi, by using the Meteosat Second Generation geostationary satellites. These satellites are useful as they continuously monitor the same geographic region in time, allowing investigations on thunderstorms' development; moreover, they are endowed with channels and products that provide information about the meteorological context under analysis, such as the cloud top temperature and altitude, the cloud extension, the drop effective radius and the cloud phase. Our work confirms what previously found in other studies about the TGFâassociated thunderstorms, by using a different approach and by using for the first time the Meteosat satellites: we find TGFs mostly linked to the development phase of deep convective thunderstorm systems, exhibiting typical characteristics of tropical storms, and providing a first picture on large scale of the TGFâassociated thunderstorm systems.publishedVersio
A luminosity distribution for kilonovae based on short gamma-ray burst afterglows
The combined detection of a gravitational-wave signal, kilonova, and short
gamma-ray burst (sGRB) from GW170817 marked a scientific breakthrough in the
field of multi-messenger astronomy. But even before GW170817, there have been a
number of sGRBs with possible associated kilonova detections. In this work, we
re-examine these "historical" sGRB afterglows with a combination of
state-of-the-art afterglow and kilonova models. This allows us to include
optical/near-infrared synchrotron emission produced by the sGRB as well as
ultraviolet/optical/near-infrared emission powered by the radioactive decay of
-process elements (i.e., the kilonova). Fitting the lightcurves, we derive
the velocity and the mass distribution as well as the composition of the
ejected material. The posteriors on kilonova parameters obtained from the fit
were turned into distributions for the peak magnitude of the kilonova emission
in different bands and the time at which this peak occurs. From the sGRB with
an associated kilonova, we found that the peak magnitude in H bands falls in
the range [-16.2, -13.1] ( of confidence) and occurs within after the sGRB prompt emission. In g band instead we obtain a peak
magnitude in range [-16.8, -12.3] occurring within the first after
the sGRB prompt. From the luminosity distributions of GW170817/AT2017gfo,
kilonova candidates GRB130603B, GRB050709 and GRB060614 (with the possible
inclusion of GRB150101B) and the upper limits from all the other sGRBs not
associated with any kilonova detection we obtain for the first time a kilonova
luminosity function in different bands.Comment: Published in MNRAS, 24 pages, 14 figure
Pyrgi. Analysis of possible climatic effects on a coastal archaeological site
This work refers to an interdisciplinary study on the archaeological site of
Pyrgi, an Etruscan harbour still under excavation, located on the Lazioâs coast in Santa
Severa, in the province of Rome. The site in question is subject to frequent flooding which
compromises its accessibility and delays the archaeological excavation operations. The
study is based on the combined use of geomatic technologies, meteorological and climatic
models, and hydrogeological knowledge of the examined site, to have a global view of the
hazard to which it is exposed. Different geomatic techniques at different scales are used in the
analysis. Large scale surveys are carried out to define the water networks and to monitor
the site using satellite images. On a small scale, drone photogrammetry techniques are used
to assess the morphology of the territory and eventual protection from natural hazards present
in the site. Using these images, a detailed digital surface model (DSM) has been generated.
The objective of the research is to assess the main cause of the floods and the time
the water stays in the site and to determine if the floods are periodic phenomena over time
or random events. The study was conducted using images captured by Sentinel 2 satellites
processed at level 2-A. These images enabled the identification of the flooding periods of
the site for the years of monitoring. The study was conducted by comparing the captured
images with rainfall data, paying attention to extreme weather phenomena that occurred
from 2012 to date. The rainfall data are provided by the National Department of Civil
Protection to CNR-ISAC by an agreement between the two institutions. The same images
have been compared with the wind data recorded by the anemometer located in the
Civitavecchia harbour and the wave height data available from ERA5 reanalysis.
Knowledge of the main cause of the floods and a possible periodicity will allow to plan
correct conservation of the site through specific protection measures designed according to
the hazards to which it is exposed
Chapter Pyrgi: analysis of possible climatic effects on a coastal archaeological site
This work refers to an interdisciplinary study on the archaeological site of Pyrgi, an Etruscan harbour still under excavation, located on the Lazioâs coast in Santa Severa, in the province of Rome. The objective of the research is to assess the main cause of the floods and the time the water stays in the site to determine if the floods are periodic phenomena over time or random events for guarantee a correct conservation of the site . The study is based on the combined use of geomatic technologies, meteorological and climatic models, and hydrogeological knowledge
Flavor Dependence of the S-parameter
We extend the results of [arXiv:1006.0207 [hep-lat]] by computing the
S-parameter at two loops in the perturbative region of the conformal window.
Consistently using the expression for the location of the infra-red fixed point
at the two-loop order we express the S-parameter in terms of the number of
flavors, colors and matter representation. We show that S, normalized to the
number of flavors, increases as we decrease the number of flavors. Our findings
support the conjecture presented in [arXiv:1006.0207 [hep-lat]] according to
which the normalized value of the S-parameter at the upper end of the conformal
window constitutes the lower bound across the entire phase diagram for the
given underlying asymptotically free gauge theory. We also show that the
non-trivial dependence on the number of flavors merges naturally with the
non-perturbative estimate of the S-parameter close to the lower end of the
conformal window obtained using gauge duality [arXiv:1007.0254 [hep-ph]]. Our
results are natural benchmarks for lattice computations of the S-parameter for
vector-like gauge theories.Comment: Version to match the one published in Phys. Lett. B. The file is
prepared in the 2-columns RevTeX format has 9 pages, 4 figures and one tabl
Time evolution of storms producing terrestrial gamma-ray flashes using era5 reanalysis data, gps, lightning and geo-stationary satellite observations
In this article, we report the first investigation over time of the atmospheric conditions around terrestrial gamma-ray flash (TGF) occurrences, using GPS sensors in combination with geostationary satellite observations and ERA5 reanalysis data. The goal is to understand which characteristics are favorable to the development of these events and to investigate if any precursor signals can be expected. A total of 9 TGFs, occurring at a distance lower than 45 km from a GPS sensor, were analyzed and two of them are shown here as an example analysis. Moreover, the lightning activity, collected by the World Wide Lightning Location Network (WWLLN), was used in order to identify any links and correlations with TGF occurrence and precipitable water vapor (PWV) trends. The combined use of GPS and the stroke rate trends identified, for all cases, a recurring pattern in which an increase in PWV is observed on a timescale of about two hours before the TGF occurrence that can be placed within the lightning peak. The temporal relation between the PWV trend and TGF occurrence is strictly related to the position of GPS sensors in relation to TGF coordinates. The life cycle of these storms observed by geostationary sensors described TGF-producing clouds as intense with a wide range of extensions and, in all cases, the TGF is located at the edge of the convective cell. Furthermore, the satellite data provide an added value in associating the GPS water vapor trend to the convective cell generating the TGF. The investigation with ERA5 reanalysis data showed that TGFs mainly occur in convective environments with unexceptional values with respect to the monthly average value of parameters measured at the same location. Moreover, the analysis showed the strong potential of the use of GPS data for the troposphere characterization in areas with complex territorial morphologies. This study provides indications on the dynamics of con-vective systems linked to TGFs and will certainly help refine our understanding of their production, as well as highlighting a potential approach through the use of GPS data to explore the lightning activity trend and TGF occurrences.publishedVersio
SLALOM: An all-surface snow water path retrieval algorithm for the GPM microwave imager
This paper describes a new algorithm that is able to detect snowfall and retrieve the associated snow water path (SWP), for any surface type, using the Global Precipitation Measurement (GPM) Microwave Imager (GMI). The algorithm is tuned and evaluated against coincident observations of the Cloud Profiling Radar (CPR) onboard CloudSat. It is composed of three modules for (i) snowfall detection, (ii) supercooled droplet detection and (iii) SWP retrieval. This algorithm takes into account environmental conditions to retrieve SWP and does not rely on any surface classification scheme. The snowfall detection module is able to detect 83% of snowfall events including light SWP (down to 1 Ă 10â3 kg·mâ2) with a false alarm ratio of 0.12. The supercooled detection module detects 97% of events, with a false alarm ratio of 0.05. The SWP estimates show a relative bias of â11%, a correlation of 0.84 and a root mean square error of 0.04 kg·mâ2. Several applications of the algorithm are highlighted: Three case studies of snowfall events are investigated, and a 2-year high resolution 70°Sâ70°N snowfall occurrence distribution is presented. These results illustrate the high potential of this algorithm for snowfall detection and SWP retrieval using GMI
Tramadol/dexketoprofen (TRAM/DKP) compared with tramadol/paracetamol in moderate to severe acute pain: results of a randomised, double-blind, placebo and active-controlled, parallel group trial in the impacted third molar extraction pain model (DAVID study)
Objectives: To compare efficacy/safety of oral tramadol 75 mg/dexketoprofen 25 mg (TRAM/DKP) and TRAM 75 mg/paracetamol 650 mg (TRAM/paracetamol) in moderate to severe pain following surgical removal of impacted lower third molar. Design: Multicentre, randomised, double-blind, placebo-controlled, phase IIIb study. Participants: Healthy adult patients scheduled for surgical extraction of at least one fully/partially impacted lower third molar requiring bone manipulation. 654 patients were randomised and 653 were eligible for analysis. Interventions: Surgery was performed under local anaesthetic. No sedation was permitted. Patients rated pain intensity (PI) using an 11-Numerical Rating Scale (NRS) (0 no pain; 10 worst pain). Participants experiencing moderate/severe pain (â„4) within 4 hours of surgery were randomised (2:2:1 ratio) to a single oral dose of TRAM/DKP 75/25 mg, TRAM/paracetamol 75/650 mg or placebo. Main outcome measures: Efficacy was based patients' electronic diaries. Analgesia and pain were recorded as follows: pain relief (PAR) on a 5-point Verbal Rating Scale (0='no relief', 1='a little (perceptible) relief', 2='some (meaningful) relief', 3='lot of relief', 4='complete relief') at the predefined postdose time points t15 min, t30 min, t1 hour, t1.5 hour, t2 hour, t4 hour, t6 hour and t8 hour and PI on the 11-point NRS at t0 and at the same predefined postdose time points. Onset of analgesia documented using double stopwatch method over a 2-hour period. Primary endpoint was total pain relief over 6 hours (TOTPAR6). Rescue medication was available during the treatment period. Results: TRAM/DKP was superior to TRAM/paracetamol and placebo at the primary endpoint TOTPAR6 (p<0.0001). Mean (SD) TOTPAR6 in the TRAM/DKP group was 13 (6.97), while those in the active control and placebo groups were 9.2 (7.65) and 1.9 (3.89), respectively. Superiority of TRAM/DKP over active comparator and placebo was observed at all secondary endpoints. Incidence of adverse events was comparable between active groups. Conclusions: TRAM/DKP (75/25 mg) is effective and superior to TRAM/paracetamol (75/650 mg) in relieving moderate to severe acute pain following surgical removal of impacted lower third molar, with a faster onset of action, greater and durable analgesia, together with a favourable safety profile
Keck and ESO-VLT View of the Symmetry of the Ejecta of the XRF/SN 2006aj
Nebular-phase spectra of SN 2006aj, which was discovered in coincidence with
X-ray flash 060218, were obtained with Keck in 2006 July and the Very Large
Telescope in 2006 September. At the latter epoch spectropolarimetry was also
attempted, yielding an upper limit of ~ 2% for the polarization. The spectra
show strong emission lines of [OI] and MgI], as expected from a Type Ic
supernova, but weak CaII lines. The [FeII] lines that were strong in the
spectra of SN 1998bw are much weaker in SN 2006aj, consistent with the lower
luminosity of this SN. The outer velocity of the line-emitting ejecta is ~ 8000
km/s in July and ~ 7400 km/s in September, consistent with the relatively low
kinetic energy of expansion of SN 2006aj. All emission lines have similar
width, and the profiles are symmetric, indicating that no major asymmetries are
present in the ejecta at the velocities sampled by the nebular lines (v < 8000
km/s), except perhaps in the innermost part. The spectra were modelled with a
non-LTE code. The mass of 56Ni required to power the emission spectrum is ~
0.20 Msun, in excellent agreement with the results of early light curve
modelling. The oxygen mass is ~ 1.5 Msun, again much less than in SN 1998bw but
larger by ~ 0.7 Msun than the value derived from the early-time modelling. The
total ejected mass is ~ 2 Msun below 8000 km/s. This confirms that SN 2006aj
was only slightly more massive and energetic than the prototypical Type Ic SN
1994I, but also indicates the presence of a dense inner core, containing ~ 1
Msun of mostly oxygen and carbon. The presence of such a core is inferred for
all broad-lined SNe Ic. This core may have the form of an equatorial
oxygen-dominated region, but it is too deep to affect the early light curve and
too small to affect the late polarization spectrum.Comment: 20 pages, 6 figures. Accepted for publication in the Astrophysical
Journa
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