284 research outputs found

    Quality assessment of ground-based microwave measurements of chlorine monoxide, ozone, and nitrogen dioxide from the NDSC radiometer at the Plateau de Bure

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    A ground-based microwave radiometer dedicated to chlorine monoxide (ClO) measurements around 278GHz has been in operation from December 1993-June 1996 at the Plateau de Bure, France (45° N, 5.9° E, 2500m altitude). It belongs to the international Network for the Detection of Stratospheric Change. A detailed study of both measurements and retrieval schemes has been undertaken. Although dedicated to the measurements of ClO, simultaneous profiles of O<sub>3</sub>, ClO and NO<sub>2</sub>, together with information about the instrumental baseline, have been retrieved using the optimal estimation method. The vertical profiles have been compared with other ground-based microwave data, satellite-borne data and model results. Data quality shows: 1) the weak sensitivity of the instrument that obliges to make time averages over several hours; 2) the site location where measurements of good opacities are possible for only a few days per year; 3) the baseline undulation affecting all the spectra, an issue common to all the microwave instruments; 4) the slow drift of some components affecting frequencies by 3-4MHz within a couple of months. Nevertheless, when temporally averaging data over a few days, ClO temporal variations (diurnal and over several weeks in winter 1995) from 35-50km are consistent with model results and satellite data, particularly at the peak altitude around 40km, although temporal coincidences are infrequent in winter 1995. In addition to ClO, it is possible to obtain O<sub>3</sub> information from 30-60km whilst the instrument is not optimized at all for this molecule. Retrievals of O<sub>3</sub> are reasonable when compared with model and another ground-based data set, although the lowermost layers are affected by the contamination of baseline remnants. Monthly-averaged diurnal variations of NO<sub>2</sub> are detected at 40km and appear in agreement with photochemical model results and satellite zonally-averaged data, although the amplitude is weaker than the other data sets. This NO<sub>2</sub> result highlights the great potential of the retrieval scheme used

    Femmes, argent et pouvoir aux Etats-Unis

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    Mid-latitude ozone changes: studies with a 3-D CTM forced by ERA-40 analyses

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    International audienceWe have used an off-line three-dimensional (3-D) chemical transport model (CTM) to study long-term changes in stratospheric O3. The model was run from 1977?2004 and forced by ECMWF ERA-40 and operational analyses. Model runs were performed to examine the impact of increasing halogens and additional stratospheric bromine from short-lived source gases. The analyses capture much of the observed interannual variability in column ozone, but there are also unrealistic features. In particular the ERA-40 analyses cause a large positive anomaly in northern hemisphere (NH) column O3 in the late 1980s. Also, the change from ERA-40 to operational winds at the start of 2002 introduces abrupt changes in some model fields which affect analysis of trends. The model reproduces the observed column increase in NH mid-latitudes from the mid 1990s. Analysis of a run with fixed halogens shows that this increase is not due to a significant decrease in halogen-induced loss, i.e. is not an indication of recovery. The model predicts only a small decrease in halogen-induced loss after 1999. In the upper stratosphere, despite the modelled turnover of chlorine around 1999, O3 does not increase to the effects of increasing ECMWF temperatures, decreasing modelled CH4 at this altitude, and abrupt changes to the SH temperatures at the end of the ERA-40 period. The impact of an additional 5 pptv stratospheric bromine from short-lived species decreases mid-latitude column O3 by about 10 DU. However, the impact on the modelled relative O3 anomaly is generally small except during periods of large volcanic loading

    Ice injected into the tropopause by deep convection - Part 2: Over the Maritime Continent

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    Abstract. The amount of ice injected into the tropical tropopause layer has a strong radiative impact on climate. A companion paper (Part 1) used the amplitude of the diurnal cycle of ice water content (IWC) as an estimate of ice injection by deep convection, showed that the Maritime Continent (MariCont) region provides the largest injection to the upper troposphere (UT; 146 hPa) and to the tropopause level (TL; 100 hPa). This study focuses on the MariCont region and extends that approach to assess the processes, the areas and the diurnal amount and duration of ice injected over islands and over seas during the austral convective season. The model presented in the companion paper is again used to estimate the amount of ice injected (ΔIWC) by combining ice water content (IWC) measured twice a day by the Microwave Limb Sounder (MLS; Version 4.2) from 2004 to 2017 and precipitation (Prec) measurements from the Tropical Rainfall Measurement Mission (TRMM; Version 007) binned at high temporal resolution (1 h). The horizontal distribution of ΔIWC estimated from Prec (ΔIWCPrec) is presented at 2∘×2∘ horizontal resolution over the MariCont. ΔIWC is also evaluated by using the number of lightning events (Flash) from the TRMM-LIS instrument (Lightning Imaging Sensor, from 2004 to 2015 at 1 h and 0.25∘ × 0.25∘ resolution). ΔIWCPrec and ΔIWC estimated from Flash (ΔIWCFlash) are compared to ΔIWC estimated from the ERA5 reanalyses (ΔIWCERA5) with the vertical resolution degraded to that of MLS observations (ΔIWCERA5). Our study shows that the diurnal cycles of Prec and Flash are consistent with each other in phase over land but different over offshore and coastal areas of the MariCont. The observational ΔIWC range between ΔIWCPrec and ΔIWCFlash, interpreted as the uncertainty of our model in estimating the amount of ice injected, is smaller over land (where ΔIWCPrec and ΔIWCFlash agree to within 22 %) than over ocean (where differences are up to 71 %) in the UT and TL. The impact of the MLS vertical resolution on the estimation of ΔIWC is greater in the TL (difference between ΔIWCERA5 and 〈ΔIWCERA5〉 of 32 % to 139 %, depending on the study zone) than in the UT (difference of 9 % to 33 %). Considering all the methods, in the UT, estimates of ΔIWC span 4.2 to 10.0 mg m−3 over land and 0.4 to 4.4 mg m−3 over sea, and in the TL estimates of ΔIWC span 0.5 to 3.9 mg m−3 over land and 0.1 to 0.7 mg m−3 over sea. Finally, based on IWC from MLS and ERA5, Prec and Flash, this study highlights that (1) at both levels, ΔIWC estimated over land can be more than twice that estimated over sea and (2) small islands with high topography present the largest ΔIWC (e.g., island of Java).This research has been supported by the Cen- tre National de la Recherche Scientifique-Institut National des Sci- ences de l’Univers (CNRS-INSU), Météo-France, and the Excel- lence Initiative (Idex) of Toulouse, France (grant no. 139225)

    Stripping experiments in carbon foils with heavy ions in the energy range of 0.4-0.9 mev/a

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    We studied the properties of heavy ions stripped by carbon foils. Ni, I and Au ions of 0.4 - 0.9 MeV/A were used to bombard foils of 5 - 200 μg/cm 2. In these measurements the ions were detected in a Browne-Buechner spectrometer. We measured the angular straggling of the ions and the energy straggling. We looked for the behaviour of the foils under impact of large beam densities (several μAp/cm2 on an area of 1-2 mm2). We observed the thickness variations of the foils during bombardment in a vacuum of ∼ 10-6 and 10-7 torr. We looked for the evolution of the energy straggling during exposure and conclude that this parameter does not change in an important way. This means that neither thickening nor sputtering affects the homogeneity of the foil. Results on the lifetime of the bombarded foils are reported

    A linear CO chemistry parameterization in a chemistry-transport model: evaluation and application to data assimilation

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    This paper presents an evaluation of a new linear parameterization valid for the troposphere and the stratosphere, based on a first order approximation of the carbon monoxide (CO) continuity equation. This linear scheme (hereinafter noted LINCO) has been implemented in the 3-D Chemical Transport Model (CTM) MOCAGE (MOdèle de Chimie Atmospherique Grande Echelle). First, a one and a half years of LINCO simulation has been compared to output obtained from a detailed chemical scheme output. The mean differences between both schemes are about ±25 ppbv (part per billion by volume) or 15% in the troposphere and ±10 ppbv or 100% in the stratosphere. Second, LINCO has been compared to diverse observations from satellite instruments covering the troposphere (Measurements Of Pollution In The Troposphere: MOPITT) and the stratosphere (Microwave Limb Sounder: MLS) and also from aircraft (Measurements of ozone and water vapour by Airbus in-service aircraft: MOZAIC programme) mostly flying in the upper troposphere and lower stratosphere (UTLS). In the troposphere, the LINCO seasonal variations as well as the vertical and horizontal distributions are quite close to MOPITT CO observations. However, a bias of ~−40 ppbv is observed at 700 Pa between LINCO and MOPITT. In the stratosphere, MLS and LINCO present similar large-scale patterns, except over the poles where the CO concentration is underestimated by the model. In the UTLS, LINCO presents small biases less than 2% compared to independent MOZAIC profiles. Third, we assimilated MOPITT CO using a variational 3D-FGAT (First Guess at Appropriate Time) method in conjunction with MOCAGE for a long run of one and a half years. The data assimilation greatly improves the vertical CO distribution in the troposphere from 700 to 350 hPa compared to independent MOZAIC profiles. At 146 hPa, the assimilated CO distribution is also improved compared to MLS observations by reducing the bias up to a factor of 2 in the tropics. This study confirms that the linear scheme is able to simulate reasonably well the CO distribution in the troposphere and in the lower stratosphere. Therefore, the low computing cost of the linear scheme opens new perspectives to make free runs and CO data assimilation runs at high resolution and over periods of several years

    Effect of Application Frequency on the Fate of Azinphosmethyl in a Sugercane Field (Bulletin #863)

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    Reducing the amounts of dissolved substances in surface and ground water is of major concern nationally and within the agricultural community. The primary focus of this study was to investigate the fate of azinphosmethyl (Guthion®) in sugarcane canopy, soil and runoff water.https://digitalcommons.lsu.edu/agcenter_bulletins/1014/thumbnail.jp

    An optimally concentrated Gabor transform for localized time-frequency components

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    Gabor analysis is one of the most common instances of time-frequency signal analysis. Choosing a suitable window for the Gabor transform of a signal is often a challenge for practical applications, in particular in audio signal processing. Many time-frequency (TF) patterns of different shapes may be present in a signal and they can not all be sparsely represented in the same spectrogram. We propose several algorithms, which provide optimal windows for a user-selected TF pattern with respect to different concentration criteria. We base our optimization algorithm on lpl^p-norms as measure of TF spreading. For a given number of sampling points in the TF plane we also propose optimal lattices to be used with the obtained windows. We illustrate the potentiality of the method on selected numerical examples

    Supercooled liquid water cloud observed, analysed, and modelled at the top of the planetary boundary layer above Dome C, Antarctica

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    Abstract. A comprehensive analysis of the water budget over the Dome C (Concordia, Antarctica) station has been performed during the austral summer 2018–2019 as part of the Year of Polar Prediction (YOPP) international campaign. Thin (∼100 m deep) supercooled liquid water (SLW) clouds have been detected and analysed using remotely sensed observations at the station (tropospheric depolarization lidar, the H2O Antarctica Microwave Stratospheric and Tropospheric Radiometer (HAMSTRAD), net surface radiation from the Baseline Surface Radiation Network (BSRN)), radiosondes, and satellite observations (CALIOP, Cloud-Aerosol LIdar with Orthogonal Polarization/CALIPSO, Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) combined with a specific configuration of the numerical weather prediction model: ARPEGE-SH (Action de Recherche Petite Echelle Grande Echelle – Southern Hemisphere). The analysis shows that SLW clouds were present from November to March, with the greatest frequency occurring in December and January when ∼50 % of the days in summer time exhibited SLW clouds for at least 1 h. Two case studies are used to illustrate this phenomenon. On 24 December 2018, the atmospheric planetary boundary layer (PBL) evolved following a typical diurnal variation, which is to say with a warm and dry mixing layer at local noon thicker than the cold and dry stable layer at local midnight. Our study showed that the SLW clouds were observed at Dome C within the entrainment and the capping inversion zones at the top of the PBL. ARPEGE-SH was not able to correctly estimate the ratio between liquid and solid water inside the clouds with the liquid water path (LWP) strongly underestimated by a factor of 1000 compared to observations. The lack of simulated SLW in the model impacted the net surface radiation that was 20–30 W m−2 higher in the BSRN observations than in the ARPEGE-SH calculations, mainly attributable to the BSRN longwave downward surface radiation being 50 W m−2 greater than that of ARPEGE-SH. The second case study took place on 20 December 2018, when a warm and wet episode impacted the PBL with no clear diurnal cycle of the PBL top. SLW cloud appearance within the entrainment and capping inversion zones coincided with the warm and wet event. The amount of liquid water measured by HAMSTRAD was ∼20 times greater in this perturbed PBL than in the typical PBL. Since ARPEGE-SH was not able to accurately reproduce these SLW clouds, the discrepancy between the observed and calculated net surface radiation was even greater than in the typical PBL case, reaching +50 W m−2, mainly attributable to the downwelling longwave surface radiation from BSRN being 100 W m−2 greater than that of ARPEGE-SH. The model was then run with a new partition function favouring liquid water for temperatures below −20 down to −40 ∘C. In this test mode, ARPEGE-SH has been able to generate SLW clouds with modelled LWP and net surface radiation consistent with observations during the typical case, whereas, during the perturbed case, the modelled LWP was 10 times less than the observations and the modelled net surface radiation remained lower than the observations by ∼50 W m−2. Accurately modelling the presence of SLW clouds appears crucial to correctly simulate the surface energy budget over the Antarctic Plateau
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