Solving a Deconvolution Problem in Photon Spectrometry Aleksandrov, D.; Alme, J.; Basmanov, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2010, Letnik:
620, Številka:
2
Journal Article
Recenzirano
We solve numerically a deconvolution problem to extract the undisturbed spectrum from the measured distribution contaminated by the finite resolution of the measuring device. A problem of this kind ...emerges when one wants to infer the momentum distribution of the neutral pions by detecting the
π
0
decay photons using the photon spectrometer of the ALICE LHC experiment at CERN
1. The underlying integral equation connecting the sought for pion spectrum and the measured gamma spectrum has been discretized and subsequently reduced to a system of linear algebraic equations. The latter system, however, is known to be ill-posed and must be regularized to obtain a stable solution. This task has been accomplished here by means of the Tikhonov regularization scheme combined with the L-curve method. The resulting pion spectrum is in an excellent quantitative agreement with the pion spectrum obtained from a Monte Carlo simulation.
It is demonstrated that a realistic quasi‐biennial oscillation (QBO) of the zonally averaged zonal winds in the tropical stratosphere can be retrieved from a monthly mean GNSS radio occultation ...(GNSS‐RO) geopotential height climatology via equatorial thermal wind balance. The retrieved GNSS‐RO zonal winds are compared with a zonal wind climatology from radiosonde measurements at Singapore, and the ERA5 atmospheric reanalysis. Simplified low‐resolution reanalysis experiments also show that assimilating just reprocessed GNSS‐RO bending angles and AMSU‐A channel 14 radiances produces a reasonable QBO. Further, it is demonstrated that the ERA5 and ERA‐Interim tropical zonal winds at 30 and 10 hPa are more consistent after the assimilation of COSMIC GNSS‐RO measurements in 2006.
The ERA5 monthly mean, zonally averaged zonal winds on pressure levels, for the period January 2007 to December 2018. The zonal averaging is between ±5° latitude.
The ALICE experiment at CERN will propose unprecedented requirements for
event building and data recording. New technologies will be adopted as well as
ad-hoc frameworks, from the acquisition of ...experimental data up to the transfer
onto permanent media and its later access. These issues justify a careful,
in-depth planning and preparation. The ALICE Data Challenge is a very important
step of this development process where simulated detector data is moved from
dummy data sources up to the recording media using processing elements and
data-paths as realistic as possible. We will review herein the current status
of past, present and future ALICE Data Challenges, with particular reference to
the sessions held in 2002 when - for the first time - streams worth one week of
ALICE data were recorded onto tape media at sustained rates exceeding 300 MB/s.
A reanalysis data set produced by the Copernicus Atmosphere Monitoring service (CAMS reanalysis, 2003 to present day) augmented by ERA5 data for the years before 2003 is used to describe the ...evolution of the 2020 Arctic ozone season and to compare it with years back to 1979. Ozone columns over large parts of the Arctic reached record low values in March and April 2020 because of an exceptionally strong, cold, and persistent Arctic polar vortex. Minimum ozone columns were below 250 DU for most of March and the first half of April, with the lowest values of 211 DU in the CAMS reanalysis found on 18 March. Such low values are extremely unusual for the Arctic. The previous years with similarly strong Arctic ozone depletion were 2011 and 1997 with minimum values of 232 and 217 DU, respectively. The performance of the CAMS ozone analysis is assessed by comparison with ozonesonde data and found to agree well with the independent observations. We find a clear sign of chemical ozone destruction with ozone severely depleted in a layer between 80 and 50 hPa in late March and early April when partial pressure values below 2 mPa were observed. Profiles from the limb sounders Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer (ACE‐FTS) and Microwave Limb Sounder (MLS) show clear signs of chlorine activation and the presence of polar stratospheric clouds. Monthly mean ozone columns in March 2020 were up to 180 DU or 40% lower than the CAMS climatology (2003–2019) while values for 2011 and 1997 were lower by 31% and 35%, respectively.
Plain Language Summary
The stratosphere is the layer of the atmosphere between about 15 and 50 km where most of the ozone resides. Usually, Arctic ozone reaches maximum values in the stratosphere during boreal spring. However, in spring 2020 the Arctic stratosphere was exceptionally cold, and ozone transport from the midlatitudes was inhibited. Because of the low temperatures, polar stratospheric clouds could form over the Arctic region and lead to stratospheric ozone destruction. This led to record low ozone columns in the Arctic at the end of March and the beginning of April 2020, with minimum values of 211 DU. This is lower than in 1997 and 2011, the previous two years that had exceptionally low ozone columns over the Arctic during spring. In spring 2020, the Arctic ozone layer showed clear signs of chemical ozone depletion with ozone almost completely destroyed in a layer around 18 km in a way that is usually only seen over the Antarctic during the austral spring, when the ozone hole forms.
Key Points
Arctic ozone columns in spring 2020 were the lowest since 1979 because the Arctic polar vortex was unusually strong, cold, and long lasting
We see evidence of chlorine activation and the presence of polar stratospheric clouds over the Arctic in March 2020
The CAMS reanalysis captures the 2020 Arctic stratospheric ozone well
The ALICE experiment at CERN will propose unprecedented requirements for event building and data recording. New technologies will be adopted as well as ad-hoc frameworks, from the acquisition of ...experimental data up to the transfer onto permanent media and its later access. These issues justify a careful, in-depth planning and preparation. The ALICE Data Challenge is a very important step of this development process where simulated detector data is moved from dummy data sources up to the recording media using processing elements and data-paths as realistic as possible. We will review herein the current status of past, present and future ALICE Data Challenges, with particular reference to the sessions held in 2002 when - for the first time - streams worth one week of ALICE data were recorded onto tape media at sustained rates exceeding 300 MB/s.
Numerical weather forecast systems like the ECMWF IFS
(European Centre for Medium-Range Weather Forecasts – Integrated
Forecasting System) are known to be affected by a moist bias in the
...extratropical lowermost stratosphere (LMS) which results in a systematic
cold bias there. We use high-spatial-resolution water vapor measurements by the airborne infrared limb-imager GLORIA (Gimballed Limb Observer for
Radiance Imaging of the Atmosphere) during the PGS
(POLSTRACC/GW-LCYCLE-II/SALSA) campaign to study the LMS moist bias in ECMWF analyses and 12 h forecasts from January to March 2016. Thereby, we
exploit the two-dimensional observational capabilities of GLORIA, when
compared to in situ observations, and the higher vertical and horizontal
resolution, when compared to satellite observations. Using GLORIA
observations taken during five flights in the polar sub-vortex region around Scandinavia and Greenland, we diagnose a systematic moist bias in the LMS exceeding +50 % (January) to +30 % (March) at potential vorticity levels from 10 PVU (∼ highest level accessed with suitable
coverage) to 7 PVU. In the diagnosed time period, the moist bias decreases at the highest and driest air masses observed but clearly persists at lower levels until mid-March. Sensitivity experiments with more frequent temporal output, and lower or higher horizontal and vertical resolution, show the short-term forecasts to be practically insensitive to these parameters on timescales of < 12 h. Our results confirm that the diagnosed
moist bias is already present in the initial conditions (i.e., the analysis)
and thus support the hypothesis that the cold bias develops as a result of
forecast initialization. The moist bias in the analysis might be explained
by a model bias together with the lack of water vapor observations suitable
for assimilation above the tropopause.
We have implemented a new stratospheric ozone model in the European Centre for Medium-Range Weather
Forecasts (ECMWF) system and tested its performance for different timescales to assess the impact
...of stratospheric ozone on meteorological fields.
We have used the new ozone model to provide prognostic ozone in medium-range and long-range (seasonal) experiments,
showing the feasibility of this ozone scheme for a seamless numerical weather prediction (NWP) modelling approach.
We find that the stratospheric ozone distribution provided by the new scheme in ECMWF forecast experiments
is in very good agreement with observations, even for unusual meteorological conditions such as Arctic stratospheric
sudden warmings (SSWs) and Antarctic polar vortex events like the vortex split of year 2002.
To assess the impact it has on meteorological variables, we have performed experiments in which the
prognostic ozone is interactive with radiation. The new scheme provides a realistic ozone field able to
improve the description of the stratosphere in the ECMWF system, as we find clear reductions of biases in the stratospheric
forecast temperature. The seasonality of the Southern Hemisphere polar vortex is also significantly improved
when using the new ozone model.
In medium-range simulations we also find improvements in high-latitude tropospheric winds during the SSW
event considered in this study. In long-range simulations, the use of the new ozone model leads to
an increase in the correlation of the winter North Atlantic Oscillation (NAO) index with respect to ERA-Interim and an increase in the
signal-to-noise ratio over the North Atlantic sector. In our study we show that by improving the description
of the stratospheric ozone in the ECMWF system, the stratosphere–troposphere coupling improves.
This highlights the potential benefits of this new ozone model to exploit stratospheric sources of
predictability and improve weather predictions over Europe on a range of timescales.
The stratosphere can be a source of predictability for surface weather on timescales of several weeks to months. However, the potential predictive skill gained from stratospheric variability can be ...limited by biases in the representation of stratospheric processes and the coupling of the stratosphere with surface climate in forecast systems. This study provides a first systematic identification of model biases in the stratosphere across a wide range of subseasonal forecast systems. It is found that many of the forecast systems considered exhibit warm global-mean temperature biases from the lower to middle stratosphere, too strong/cold wintertime polar vortices, and too cold extratropical upper-troposphere/lower-stratosphere regions. Furthermore, tropical stratospheric anomalies associated with the Quasi-Biennial Oscillation tend to decay toward each system's climatology with lead time. In the Northern Hemisphere (NH), most systems do not capture the seasonal cycle of extreme-vortex-event probabilities, with an underestimation of sudden stratospheric warming events and an overestimation of strong vortex events in January. In the Southern Hemisphere (SH), springtime interannual variability in the polar vortex is generally underestimated, but the timing of the final breakdown of the polar vortex often happens too early in many of the prediction systems. These stratospheric biases tend to be considerably worse in systems with lower model lid heights. In both hemispheres, most systems with low-top atmospheric models also consistently underestimate the upward wave driving that affects the strength of the stratospheric polar vortex. We expect that the biases identified here will help guide model development for subseasonal-to-seasonal forecast systems and further our understanding of the role of the stratosphere in predictive skill in the troposphere.
The EChO science case Drossart, Pierre; Ribas, Ignasi; Cockell, Charles ...
Experimental astronomy,
12/2015, Letnik:
40, Številka:
2-3
Journal Article, Web Resource
Recenzirano
Odprti dostop
The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, ...and new populations of planets with masses between that of the Earth and Neptune—all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore:
What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System
? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10
−4
relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength coverage of at least 0.55 to 11 μm with a goal of covering from 0.4 to 16 μm. Only modest spectral resolving power is needed, with R ~ 300 for wavelengths less than 5 μm and R ~ 30 for wavelengths greater than this. The transit spectroscopy technique means that no spatial resolution is required. A telescope collecting area of about 1 m
2
is sufficiently large to achieve the necessary spectro-photometric precision: for the Phase A study a 1.13 m
2
telescope, diffraction limited at 3 μm has been adopted. Placing the satellite at L2 provides a cold and stable thermal environment as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. EChO has been conceived to achieve a single goal: exoplanet spectroscopy. The spectral coverage and signal-to-noise to be achieved by EChO, thanks to its high stability and dedicated design, would be a game changer by allowing atmospheric composition to be measured with unparalleled exactness: at least a factor 10 more precise and a factor 10 to 1000 more accurate than current observations. This would enable the detection of molecular abundances three orders of magnitude lower than currently possible and a fourfold increase from the handful of molecules detected to date. Combining these data with estimates of planetary bulk compositions from accurate measurements of their radii and masses would allow degeneracies associated with planetary interior modelling to be broken, giving unique insight into the interior structure and elemental abundances of these alien worlds. EChO would allow scientists to study exoplanets both as a population and as individuals. The mission can target super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300–3000 K) of F to M-type host stars. The EChO core science would be delivered by a three-tier survey. The EChO
Chemical Census
: This is a broad survey of a few-hundred exoplanets, which allows us to explore the spectroscopic and chemical diversity of the exoplanet population as a whole. The EChO
Origin
: This is a deep survey of a subsample of tens of exoplanets for which significantly higher signal to noise and spectral resolution spectra can be obtained to explain the origin of the exoplanet diversity (such as formation mechanisms, chemical processes, atmospheric escape). The EChO
Rosetta Stones
: This is an ultra-high accuracy survey targeting a subsample of select exoplanets. These will be the bright “benchmark” cases for which a large number of measurements would be taken to explore temporal variations, and to obtain two and three dimensional spatial information on the atmospheric conditions through eclipse-mapping techniques. If EChO were launched today, the exoplanets currently observed are sufficient to provide a large and diverse sample. The Chemical Census survey would consist of > 160 exoplanets with a range of planetary sizes, temperatures, orbital parameters and stellar host properties. Additionally, over the next 10 years, several new ground- and space-based transit photometric surveys and missions will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO’s launch and enable the atmospheric characterisation of hundreds of planets.
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