162 research outputs found
Mechanical properties of magnesium alloy for medical applications after deformation treatment
Get PDFComposition and size of Martian aerosols as seen in the IR from solar occultation measurements by NOMAD onboard TGO
Get PDF&lt;p&gt;&lt;strong&gt;Introduction&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;The nature, size and content of aerosols in the atmosphere affect the energy budget on all planets, hence the atmospheric dynamic of the planet. Mars exhibits three types of atmospheric aerosol. Mineral dust, water ice and carbon dioxide ice. Martian aerosols nature and size distribution were observed using many different methods and experiments, from rovers to satellites. Exhaustive review scan be found in [1] and in [2]. Usually, dust effective radius, r&lt;sub&gt;eff&lt;/sub&gt;, ranges from 1 to 2 &amp;#956;m and its effective variance, &amp;#957;&lt;sub&gt;eff&lt;/sub&gt;, from 0.2 to 0.4. H&lt;sub&gt;2&lt;/sub&gt;O ice r&lt;sub&gt;eff&lt;/sub&gt; ranges from 1 to 5 &amp;#956;m and its &amp;#957;&lt;sub&gt;eff&lt;/sub&gt; from 0.1 to 0.4. However, these two parameters and their variability are poorly constraint in the vertical to date. ExoMars TGO mission (ESA/Roscosmos) was primarily designed to study trace gases, thermal structure and aerosol content in Mars atmosphere with unprecedented vertical resolution [3]. &lt;/p&gt;&lt;p&gt;&lt;strong&gt;NOMAD-SO Data processing&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;NOMAD (Nadir and Occultation for MArs Discovery) is suite of two infrared spectrometers onboard the ExoMars 2016 Trace Gas Orbiter (TGO) orbiter, covering the spectral range of 0.2 to 4.3 &amp;#956;m [4]. An Acousto-Optical Tunable Filter (AOTF) is used to select different spectral windows. The sampling of this channel is approximately of 1 second, allowing a vertical sampling about 1km. the SO channel is able to observe the atmosphere at a given altitude with 6 different diffraction orders. For this study, we selected a configuration of 5 diffraction orders (121,134,149,168,190) effectively spanning the overall spectral range of NOMAD.&lt;/p&gt;&lt;p&gt;In order to evaluate the local extinction due to aerosols, we use an inversion program called Retrieval Control Program (RCP). It is a multi-parameter non-linear least squares fitting of measured and modelled spectra [5]. Its forward model, KOPRA, was recently adapted to limb emissions on Mars [6] and for solar occultation data on Mars for the first time. RCP solves iteratively the inverse problem [7] and is described in details in [8]. The regularization matrix is build from Tikhonov-type terms of different orders which can be combined to obtain a custom-tailored regularization for any particular retrieval problem.&lt;/p&gt;&lt;p&gt;An example of the retrieved extinction profile is shown in Fig 1. The retrieved extinctions differs from previous work on aerosols using ACS data [9,10]&amp;#160; using the Onion-peeling or Abel's transform method since this global fit is less affected by the large error propagation to low altitudes typical of those methods, and the lower Martian atmosphere is precisely where aerosols are particular relevant.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.9dee3cb4b48268814682561/sdaolpUECMynit/2202CSPE&amp;app=m&amp;a=0&amp;c=c3ce34094b99922ae3b0d1b323aad8d3&amp;ct=x&amp;pn=gnp.elif&amp;d=1&quot; alt=&quot;&quot; width=&quot;486&quot; height=&quot;468&quot;&gt;&lt;/p&gt;&lt;p&gt;Fig 1.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Mean extinction cross-section ratio modelling&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;In order to model the optical behavior of the Martian aerosol we chose the log-normal distribution which is widely used in atmospheric sciences. It is a function of two parameters (r&lt;sub&gt;g&lt;/sub&gt;, &amp;#963;&lt;sub&gt;g&lt;/sub&gt;). In optics, we change those parameters to more suitable ones, the effective radius, r&lt;sub&gt;eff &lt;/sub&gt;and its corresponding effective variance &amp;#957;&lt;sub&gt;eff&lt;/sub&gt;. For any aerosol size distribution, the extinction k is km&lt;sup&gt;-1&lt;/sup&gt;&amp;#160;is k(&amp;#955;) = N . &amp;#963;&lt;sub&gt;ext&lt;/sub&gt;&amp;#160;(&amp;#955;r&lt;sub&gt;eff&lt;/sub&gt;,&amp;#957;&lt;sub&gt;eff&lt;/sub&gt;). N is the aerosol number density and &amp;#963;&lt;sub&gt;ext&lt;/sub&gt; (&amp;#955;,r&lt;sub&gt;eff&lt;/sub&gt;,&amp;#957;&lt;sub&gt;eff&lt;/sub&gt;) is the mean average extinction cross-section at a wavelength &amp;#955;, a specific aerosol distribution defined by (r&lt;sub&gt;eff&lt;/sub&gt;,&amp;#957;&lt;sub&gt;eff&lt;/sub&gt;). We build a look-up table of dust and water ice &amp;#963;&lt;sub&gt;ext&lt;/sub&gt; at the selected NOMAD order's wavelengths for different sets of (r&lt;sub&gt;eff&lt;/sub&gt;,&amp;#957;&lt;sub&gt;eff&lt;/sub&gt;). The extinction are evaluated with a Lorenz-Mie code for polydisperse spherical particle from [11].&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Aerosol composition and size distribution evaluation&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;We will detail the process of evaluating the aerosol composition and size distribution that consists of a mix of non-linear least square and brute force in order to evaluate the best set of parameters (r&lt;sub&gt;eff&lt;/sub&gt;,&amp;#957;&lt;sub&gt;eff&lt;/sub&gt; ,&amp;#947;) where &amp;#947; represent a mixture of dust and H&lt;sub&gt;2&lt;/sub&gt;O ice&lt;sub&gt;.&lt;/sub&gt; The NLSQ algorithm is provided by the SciPy Python package [12]. To assess the robustness and limitations of our evaluation procedure, we will present results against synthetic extinction signal. We will discuss our main results, especially for the period covering the Global Dust Storm of MY34 (Fig 2.).&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.a8e3e9d4b48267124682561/sdaolpUECMynit/2202CSPE&amp;app=m&amp;a=0&amp;c=2a5bd4f384692b29ec745b0c68ef1ecb&amp;ct=x&amp;pn=gnp.elif&amp;d=1&quot; alt=&quot;&quot; width=&quot;801&quot; height=&quot;570&quot;&gt;&lt;/p&gt;&lt;p&gt;Fig 2.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgments&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the \emph{&quot;Center of Excellence Severo Ochoa&quot;} award for the Instituto de Astrof&amp;#237;sica de Andaluc&amp;#237;a (SEV-2017-0709) and funding by grant PGC2018-101836-B-100 (MCIU/AEI/FEDER, EU). ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;[1] Robert M. Haberle et al., eds. The Atmosphere and Climate of Mars. Cambridge University Press, 2017.&lt;/p&gt;&lt;p&gt;[2] R. Todd Clancy et al. &amp;#8220;The distribution, composition, and particle properties of Mars meso-spheric aerosols: An analysis of CRISM visible/near-IR limb spectra with context from near-coincident MCS and MARCI observations&amp;#8221;. Icarus 328 (2019).&lt;/p&gt;&lt;p&gt;[3] J. Vago et al. &amp;#8220;ESA ExoMars program: The next step in exploring Mars&amp;#8221;. SSR 49.7 (2015).&lt;/p&gt;&lt;p&gt;[4] A. C. Vandaele et al. &amp;#8220;NOMAD, an Integrated Suite of Three Spectrometers for the ExoMarsTrace Gas Mission: Technical Description, Science Objectives and Expected Performance&amp;#8221;. SSR 214.5 (2018).&lt;/p&gt;&lt;p&gt;[5] T. von Clarmann et al. &amp;#8220;Retrieval of temperature and tangent altitude pointing from limb emission spectra recorded from space by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)&amp;#8221;. JGR: Atmospheres 108.D23 (2003).&lt;/p&gt;&lt;p&gt;[6] Sergio Jim&amp;#233;nez-Monferrer et al. &amp;#8220;CO2 retrievals in the Mars daylight thermosphere from its 4.3&amp;#956;m limb emission measured by OMEGA/MEx&amp;#8221;. Icarus 353 (2021).&lt;/p&gt;&lt;p&gt;[7] Clive D Rodgers. Inverse Methods for Atmospheric Sounding. WORLD SCIENTIFIC, 2000.&lt;/p&gt;&lt;p&gt;[8] Jurado Navarro et al. Retrieval of CO2 and collisional parameters from the MIPAS spectra in the Earth atmosphere. Universidad de Granada, 2016.&lt;/p&gt;&lt;p&gt;[9] M. Luginin et al. &amp;#8220;Properties of Water Ice and Dust Particles in the Atmosphere of Mars During the 2018 Global Dust Storm as Inferred From the Atmospheric Chemistry Suite&amp;#8221;. JGR: Planets 125.11 (2020).&lt;/p&gt;&lt;p&gt;[10] A. Stcherbinine et al. &amp;#8220;Martian Water Ice Clouds During the 2018 Global Dust Storm as Observed by the ACS-MIR Channel Onboard the Trace Gas Orbiter&amp;#8221;. JGR: Planets 125.3 (2020).&lt;/p&gt;&lt;p&gt;[11] Michael I Mishchenko et al. Scattering, absorption, and emission of light by small particles. Cambridge university press, 2002.&lt;/p&gt;&lt;p&gt;[12] Pauli Virtanen et al. &amp;#8220;SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python&amp;#8221;. Nature Methods 17 (2020).&lt;/p&gt;</jats:p
Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements: 1. Methodology and Application to the MY 34 Global Dust Storm
Get PDFSince the beginning of the Trace Gas Orbiter (TGO) science operations in April 2018, its instrument ?Nadir and Occultation for MArs Discovery? (NOMAD) supplies detailed observations of the IR spectrums of the Martian atmosphere. We developed a procedure that allows us to evaluate the composition and distribution's parameters of the atmospheric Martian aerosols. We use a retrieval program (RCP) in conjunction with a radiative forward model (KOPRA) to evaluate the vertical profile of aerosol extinction from NOMAD measurements. We then apply a model/data fitting strategy of the aerosol extinction. In this first article, we describe the method used to evaluate the parameters representing the Martian aerosol composition and size distribution. MY 34 GDS showed a peak intensity from LS 190° to 210°. During this period, the aerosol content rises multiple scale height, reaching altitudes up to 100 km. The lowermost altitude of aerosol's detection during NOMAD observation rises up to 30 km. Dust aerosols reff were observed to be close to 1 ?m and its ?eff lower than 0.2. Water ice aerosols reff were observed to be submicron with a ?eff lower than 0.2. The vertical aerosol structure can be divided in two parts. The lower layers are represented by higher reff than the upper layers. The change between the lower and upper layers is very steep, taking only few kilometers. The decaying phase of the GDS, LS 210°?260°, shows a decrease in altitude of the aerosol content but no meaningful difference in the observed aerosol's size distribution parameters
Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements: 1. Methodology and Application to the MY 34 Global Dust Storm
Get PDFSince the beginning of the Trace Gas Orbiter (TGO) science operations in April 2018, its instrument “Nadir and Occultation for MArs Discovery” (NOMAD) supplies detailed observations of the IR spectrums of the Martian atmosphere. We developed a procedure that allows us to evaluate the composition and distribution\u27s parameters of the atmospheric Martian aerosols. We use a retrieval program (RCP) in conjunction with a radiative forward model (KOPRA) to evaluate the vertical profile of aerosol extinction from NOMAD measurements. We then apply a model/data fitting strategy of the aerosol extinction. In this first article, we describe the method used to evaluate the parameters representing the Martian aerosol composition and size distribution. MY 34 GDS showed a peak intensity from L 190° to 210°. During this period, the aerosol content rises multiple scale height, reaching altitudes up to 100 km. The lowermost altitude of aerosol\u27s detection during NOMAD observation rises up to 30 km. Dust aerosols r were observed to be close to 1 μm and its ν lower than 0.2. Water ice aerosols r were observed to be submicron with a ν lower than 0.2. The vertical aerosol structure can be divided in two parts. The lower layers are represented by higher r than the upper layers. The change between the lower and upper layers is very steep, taking only few kilometers. The decaying phase of the GDS, LS 210°–260°, shows a decrease in altitude of the aerosol content but no meaningful difference in the observed aerosol\u27s size distribution parameters
Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements: 2. Extended Results, End of MY 34 and First Half of MY 35
Get PDFThis is the second part of Stolzenbach et al. (2023, https://doi.org/10.1029/2022JE007276), named hereafter Paper I, extends the period to the end of MY 34 and the first half of MY 35. This encompasses the end phase of the MY 34 Global Dust Storm (GDS), the MY 34 C-Storm, the Aphelion Cloud Belt (ACB) season of MY 35, and an unusual early dust event of MY 35 from L 30° to L 55°. The end of MY 34 overall aerosol size distribution shows the same parameters for dust and water ice to what was seen during the MY 34 GDS. Interestingly, the layered water ice vertical structure of MY 34 GDS disappears. The MY 34 C-Storm maintains condition like the MY 34 GDS. A high latitude layer of bigger water ice particles, close to 1 μm, is seen from 50 to 60 km. This layered structure is linked to an enhanced meridional transport characteristic of high intensity dust event which put the MY 34 C-Storm as particularly intense compared to non-GDS years C-Storms as previously suggested by Holmes et al. (2021, https://doi.org/10.1016/j.epsl.2021.117109). Surprisingly, MY 35 began with an unusually large dust event (Kass et al., 2020, https://ui.adsabs.harvard.edu/abs/2020AGUFMP039…01K) found in the Northern hemisphere during L 35° to L 50°. During this dust event, the altitude of aerosol first detection is roughly equal to 20 km. This is close to the values encountered during the MY 34 GDS, its decay phase and the C-Storm of the same year. Nonetheless, no vertical layered structure was observed
Forecasting auroras from regional and global magnetic field measurements
Get PDFWe use the connection between auroral sightings and rapid geomagnetic field variations in a concept for a Regional Auroral Forecast (RAF) service. The service is based on statistical relationships between near-real-time alerts issued by the NOAA Space Weather Prediction Center and magnetic time derivative (dB / dt) values measured by five MIRACLE magnetometer stations located in Finland at auroral and sub-auroral latitudes. Our database contains NOAA alerts and dB / dt observations from the years 2002-2012. These data are used to create a set of conditional probabilities, which tell the service user when the probability of seeing auroras exceeds the average conditions in Fennoscandia during the coming 0-12 h. Favourable conditions for auroral displays are associated with ground magnetic field time derivative values (dB / dt) exceeding certain latitude-dependent threshold values. Our statistical analyses reveal that the probabilities of recording dB / dt exceeding the thresholds stay below 50% after NOAA alerts on X-ray bursts or on energetic particle flux enhancements. Therefore, those alerts are not very useful for auroral forecasts if we want to keep the number of false alarms low. However, NOAA alerts on global geomagnetic storms (characterized with K-p values > 4) enable probability estimates of > 50% with lead times of 3-12 h. RAF forecasts thus rely heavily on the well-known fact that bright auroras appear during geomagnetic storms. The additional new piece of information which RAF brings to the previous picture is the knowledge on typical storm durations at different latitudes. For example, the service users south of the Arctic Circle will learn that after a NOAA ALTK06 issuance in night, auroral spotting should be done within 12 h after the alert, while at higher latitudes conditions can remain favourable during the next night.Peer reviewe
Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements: 2. Extended Results, End of MY 34 and First Half of MY 35
Get PDFThis is the second part of Stolzenbach et al. (2023, https://doi.org/10.1029/2022JE007276), named hereafter Paper I, extends the period to the end of MY 34 and the first half of MY 35. This encompasses the end phase of the MY 34 Global Dust Storm (GDS), the MY 34 C‐Storm, the Aphelion Cloud Belt (ACB) season of MY 35, and an unusual early dust event of MY 35 from LS 30° to LS 55°. The end of MY 34 overall aerosol size distribution shows the same parameters for dust and water ice to what was seen during the MY 34 GDS. Interestingly, the layered water ice vertical structure of MY 34 GDS disappears. The MY 34 C‐Storm maintains condition like the MY 34 GDS. A high latitude layer of bigger water ice particles, close to 1 μm, is seen from 50 to 60 km. This layered structure is linked to an enhanced meridional transport characteristic of high intensity dust event which put the MY 34 C‐Storm as particularly intense compared to non‐GDS years C‐Storms as previously suggested by Holmes et al. (2021, https://doi.org/10.1016/j.epsl.2021.117109). Surprisingly, MY 35 began with an unusually large dust event (Kass et al., 2020, https://ui.adsabs.harvard.edu/abs/2020AGUFMP039…01K) found in the Northern hemisphere during LS 35° to LS 50°. During this dust event, the altitude of aerosol first detection is roughly equal to 20 km. This is close to the values encountered during the MY 34 GDS, its decay phase and the C‐Storm of the same year. Nonetheless, no vertical layered structure was observed
The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter
Get PDFThe Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described
Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements: 1. Methodology and Application to the MY 34 Global Dust Storm
Get PDFSince the beginning of the Trace Gas Orbiter (TGO) science operations in April 2018, its instrument “Nadir and Occultation for MArs Discovery” (NOMAD) supplies detailed observations of the IR spectrums of the Martian atmosphere. We developed a procedure that allows us to evaluate the composition and distribution's parameters of the atmospheric Martian aerosols. We use a retrieval program (RCP) in conjunction with a radiative forward model (KOPRA) to evaluate the vertical profile of aerosol extinction from NOMAD measurements. We then apply a model/data fitting strategy of the aerosol extinction. In this first article, we describe the method used to evaluate the parameters representing the Martian aerosol composition and size distribution. MY 34 GDS showed a peak intensity from LS 190° to 210°. During this period, the aerosol content rises multiple scale height, reaching altitudes up to 100 km. The lowermost altitude of aerosol's detection during NOMAD observation rises up to 30 km. Dust aerosols reff were observed to be close to 1 μm and its νeff lower than 0.2. Water ice aerosols reff were observed to be submicron with a νeff lower than 0.2. The vertical aerosol structure can be divided in two parts. The lower layers are represented by higher reff than the upper layers. The change between the lower and upper layers is very steep, taking only few kilometers. The decaying phase of the GDS, LS 210°–260°, shows a decrease in altitude of the aerosol content but no meaningful difference in the observed aerosol's size distribution parameters
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