The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

The 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

Aerosols in the upper haze of Venus from joint SPICAV−UV and SPICAV−IR observations

Dataset for the publication "Bimodal aerosol distribution in Venus’ upper haze from joint SPICAV-UV and -IR observations on Venus Express" by M. Luginin, A. Fedorova, D. Belyaev, F. Montmessin, O. Korablev, J.-L. Bertaux, Icarus. https://doi.org/10.1016/j.icarus.2023.115866Includes a readme file, a list of observations, and effective radius, effective variance and number density profilesfor mode 1 and mode 2 particles retrieved from the joint SPICAV−UV and SPICAV−IR observations on Venus Express. Aerosol data files are named "SPICAV_UV_IR_XXXXAYY_Z.txt",where XXXX is the decimal orbit number, Y is the observation sequence, Z is 0 if there was a single occultation during the observation, 1 or 2 if there were two occultation observations.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Aerosols from ACS during LS 255-338 of MY 34

Dataset for the publication "Martian atmospheric chemistry of HCl: implications for the lifetimeof atmospheric methane" by Taysum et al.Includes a readme file, a list of observations, and effective radius and mass loading profilesfor dust and water ice retrieved from TIRVIM and NIR observations during LS 255-338 of MY 34.Aerosol data files are named "aerosol_properties_XXXXXX_Y.txt",where XXXXXX is the decimal orbit number, Y is the ingress (I) or egress (E) occultation flag.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Aerosols from ACS during 2018 GDS

Dataset for the publication "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"by Luginin et al.Includes a readme file, a list of orbits, and effective radius, number density, effective variance, and mass loading profilesfor dust and water ice from TIRVIM and NIR observations.Data/ contains the readme file, the file with the list of orbits, and the folder with aerosol data for each orbit.Aerosol data files are named "aerosol_properties_XXXX_Y.txt",where XXXX is the decimal orbit number,Y is the ingress (I) or egress (E) occultation flag.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Scale heights and detached haze layers in the mesosphere of Venus from SPICAV IR data

International audienceSPICAV IR, one channel of SPICAV/SOIR instrument suite onboard Venus Express, performed solar occultation measurements of the atmosphere at terminators in 0.65–1.7 μm spectral range. We analyze the properties of the upper part of the Venus aerosol layer (upper haze, 70−95 km altitude) from 798 observations performed from May 2006 through November 2014. Vertical profiles of slant optical depth, extinction coefficient, effective radius, and number density of haze particles from 222 orbits were analyzed in a previous publication (Luginin et al., 2016. Icarus. 277. doi: 10.1016/j.icarus.2016.05.008); their diurnal, latitudinal, and interannual variabilities were investigated. The present paper is devoted to analysis of scale heights and properties of detached haze layers from 147 orbits at mid-to-high northern latitudes, where the best spatial resolution was obtained. Scale heights retrieved from 43 orbits were equal to 4−5.5 km at the North Pole (82°N-90°N) decreasing to 2−4 km at 60°N−80°N latitudes. As an explanation of such latitudinal variations, we propose a mechanism based on vertical transport driven by winds that are directed upwards at the North Pole and downwards at 60°N−80°N latitudes. Detached layers were detected in 93 occultations at 58°N−90°N. The detached layers are presumably formed through condensation of water vapor on droplets of sulfuric acid water solution; they were mostly seen at 80−88 km at the morning terminator, and at 84−90 km at the evening one. This difference in altitude of the detached layers can be explained by diurnal variations in thermal structure of Venusian mesosphere. The vertical optical depth of detached layers varies broadly around the mean τDL ∼ 0.8−3•10−3; no difference between the morning and the evening terminators was observed. The effective radius and number density of aerosol particles in the detached layers group around a very wide maximum at the morning terminator (0.65±0.25 μm and 0.6±0.4 cm−3) and two maxima at the evening terminator (0.4±0.1 μm and 0.85±0.15 μm; 0.3±0.2 cm−3 and 4.5±2.5 cm−3). This could be explained by differences in initial altitudes at which condensation of particles occurs

Bimodal aerosol distribution in Venus' upper haze from joint SPICAV-UV and -IR observations on Venus Express

International audienceSpectroscopic solar occultation measurements by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus/Solar Occultation at Infrared instrument (SPICAV/SOIR) onboard the Venus Express orbiter gave new data about upper haze aerosol properties, its vertical distribution and spatial and temporal variations. Early study with three channels of SPICAV/SOIR instrument using a few selected orbits indicated presence of two aerosol modes in particle size distribution (Wilquet et al., 2009). Analysis of aerosol properties from the SPICAV−IR spectrometer for the whole Venus Express data set obtained from May 2006 till November 2014 has proved it for some occultations (Luginin et al., 2016). In this work, we report retrieval of the upper haze (81–100 km) aerosol properties from 101 simultaneous SPICAV−UV and –IR solar occultation sessions acquired between March 2007 and January 2013. A joint analysis of the data from two spectrometers allowed us to characterize the size distribution ~10 km higher in the atmosphere compared to previous analysis and to detect bimodal distribution in ~50% of observations previously believed to be unimodal. At altitudes 81–92 km bimodality is observed in >50% of cases. Mode 2 particles are detected up to 98 km and mode 1 up to 100 km. Mean radius equals 0.14 ± 0.03 μm for mode 1 and 0.78 ± 0.18 μm for mode 2. Number density profiles for both modes of particles exponentially decrease with altitude, starting from 50 cm−3 and 0.3 cm−3 at 82 km for mode 1 and mode 2, respectively, and reaching 3 cm−3 at 98 km for mode 1 and 0.03 cm−3 at 94 km for mode 2

Unambiguous detection of mesospheric CO2 clouds on Mars using 2.7 μm absorption band from the ACS/TGO solar occultations

International audienceMesospheric CO2 clouds are one of two types of carbon dioxide clouds known on Mars. We present observations of mesospheric CO2 clouds made by Atmospheric Chemistry Suite (ACS) onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO). We analyzed 1663 solar occultation sessions of Thermal InfraRed (TIRVIM) and Middle InfraRed (MIR) channels of ACS covering more than two Martian years that contain spectra of 2.7 μm carbon dioxide ice absorption band. That allowed us to unambiguously discriminate carbon dioxide ice aerosols from mineral dust and water ice aerosols, not relying on the information of atmospheric thermal conditions. CO2 clouds were detected in eleven solar occultation observations at altitudes from 39 km to 90 km. In five cases, there were two or three layers of CO2 clouds that were vertically separated by 5–15 km gaps. Effective radius of CO2 aerosol particles is in the range of 0.1–2.2 μm. Spectra produced by the smallest particles indicate a need for a better resolved CO2 ice refractive index. Nadir optical depth of CO2 clouds is in the range 5 × 10−4–4 × 10−2 at both 2.7 μm and 0.8 μm. Asymmetrical diurnal distribution of detections observed by ACS is potentially due to local time variations of temperature induced by thermal tides. Two out of five cases of carbon dioxide cloud detections made by the TIRVIM instrument reveal the simultaneous presence of CO2 ice and H2O ice aerosols. Temperature profiles measured by the Near InfraRed (NIR) channel of ACS are used to calculate CO2 saturation ratio S at locations of carbon dioxide clouds. Supersaturation S > 1 is detected in only 6 out of 19 cases of CO2 cloud layers; extremely low values of S < 0.1 are found in 9 out of 19 cases

Martian Aerosols in the 3µm Spectral Range, During and Outside the 2018 Global Dust Event Based on the TGO/ACS-MIR Channel

International audienceWe present vertical profiles of water ice clouds in the Martian atmosphere, and the effects of the last global dust storm on them. To this end, we used the data produced by the ACS MIR channel during solar occultations that senses the atmospheric opacity in the 3 μm spectral range. We observe very rapidchanges in the aerosol profile associated with the onset of the global dust event, initiating water ice cloud layer formation above 80 km in a period of days or so, sug- gesting a sudden intensification in the circulation re- gime. More work is needed to extract more infor- mation, such as particle size, yet this preliminary study already provides some insightful data about water ice during the 2018 global dust storm

SPICAV/SOIR mesospheric aerosols observations and characterization

info:eu-repo/semantics/nonPublishe

A two-Martian years survey of the water vapor saturation state on Mars based on ACS NIR/TGO occultations

On Mars, condensation is the major factor constraining the vertical distribution of water vapor. Recent measurements of water and temperature profiles showed that water can be strongly supersaturated at and above the level where clouds form during the aphelion and perihelion seasons. Since 2018, the near-infrared spectrometer (NIR) of the Atmospheric Chemistry Suite onboard the Trace Gas Orbiter has measured H2O and temperature profiles using solar occultation in the infrared from below 10 to 100 km of altitude. Here, we provide the first long-term monitoring of the water saturation state. The survey spans 2 Martian years from Ls = 163° of MY34 to Ls = 170° of MY36. We found that water is often supersaturated above aerosol layers. In the aphelion season, the water mixing ratio above 40 km in the mid-to-high latitudes was below 3 ppmv and yet is found to be supersaturated. Around the perihelion, water is also supersaturated above 60 km with a mixing ratio of 30–50 ppmv. Stronger saturation is observed during the dusty season in MY35 compared to what was observed in MY34 during the Global Dust Storm and around the perihelion. Saturation varied between the evening and morning terminators in response to temperature modulation imparted by thermal tides. Although water vapor is more abundant in the evening, colder morning temperatures induce a daily peak of saturation. This data set establishes a new paradigm for water vapor on Mars, revealing that supersaturation is nearly ubiquitous, particularly during the dust season, thereby promoting water escape on an annual average