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This 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. Plain Language Summary: Mars has a peculiar tendency, in one in every three Martian year, the entire planet is covered by dust suspended in the atmosphere. These events are referred as Global Dust Storms (GDS). The dust is lifted by fierce winds from the ground up to 80 km high. The mixture of water ice crystals and dust particle in the air of Mars change how the incoming Sun light warms the atmosphere. It is then of a crucial importance to properly characterize the nature and size of the aerosols, especially during a GDS, to better understand the dynamics of the Martian atmosphere. The spacecraft (ESA/Roscosmos) ExoMars Trace Gas Orbiter has been studying the Martian atmosphere since April 2018 and observed a GDS but also other and less intense dust storms. These data help us distinguish the aerosols nature (dust and water ice) and sizes during these distinct types of dust events. Our study confirms that, globally, the particles of dust and water ice are quite small, close to 1 μm or even less. Their distribution varies a lot, meaning that one may find a lot of different particle sizes or lot of similar sized particles. Key Points: MY 34 C‐Storm aerosol effective size and vertical structure is similar to MY 34 Global Dust Storm (GDS)MY 35 early dust event aerosol shows similar effective size and vertical structure as MY 34 GDSMY 34 GDS leads to more intense C‐Storm and an unusual early storm at the start of MY 35 [ABSTRACT FROM AUTHOR]

Since 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. Plain Language Summary: Mars' atmosphere is filled with dust and water ice particles carried by the winds. These aerosols affect the way sunlight is distributed in the atmosphere and on the surface, and this directly affects temperature. In addition, approximately every three Martian years, Mars experiences what is known as a "global dust storm." This type of dust storm covers the entire red planet in dust. It affects the temperature and water vapor content of the Martian atmosphere. Determining and assessing aerosol properties, number, size and mass during and after a global dust storm is of crucial importance to understanding its underlying mechanisms. Here, we develop an analysis scheme to study the size, nature, number and distribution of Martian aerosols. Our study confirms that, overall, dust and water ice particles are quite small, close to 1 μm or even smaller, and that a global dust storm affects the intensity of other storms that follow. Key Points: Retrieval of Martian aerosols key properties from NOMAD‐SO data during the MY 34 GDSMesospheric dust and water ice reff are mainly ∼1 μm and ≤0.5 μm respectively during the MY 34 GDS and its decay phaseDuring the MY 34 GDS, the effective variance shows a slight N/S asymmetry and values mainly ≤0.2 [ABSTRACT FROM AUTHOR]

Measurements of CO2, Ar and N2 densities from the Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatile Evolution Mission (MAVEN) between 150 and 200 km altitude during 2015–2022 are analyzed to reveal diurnal (DW1), semidiurnal (SW2) and terdiurnal (TW3) solar‐synchronous tides in Mars thermosphere. Multi‐year‐mean tidal perturbations on a diurnal‐ and zonal‐mean background, corrected for solar flux variations, are reported as a function of latitude (48°S–48°N), altitude and solar longitude (Ls). The DW1, SW2 and TW3 amplitudes at for example, 180 km altitude are of order 90%–120%, 15%–20%, and ≲10% for CO2 and Ar, and roughly 2/3 these values for N2, the latter presumably due to the difference in molecular weight from the other species. Through examination of vertical phase progressions, DW1 is concluded to be mainly excited in situ, but SW2 and TW3 contain significant contributions from tides propagating upward from lower altitudes. By analogy with studies for Earth's thermosphere, the DW1 amplitudes and phases are thought to reflect the combined influences of thermal expansion and vertical winds. Points of agreement and disagreement with DW1, SW2, and TW3 amplitudes and phases derived from the Mars Climate Database are noted and interpreted. Key Points: Global‐scale solar‐synchronous tides are derived from Mars Atmosphere and Volatile Evolution Mission/Neutral Gas and Ion Mass Spectrometer measurements of CO2, Ar, and N2 at Mars, 150–200 kmThe diurnal tide originates mainly in situ; semidiurnal and terdiurnal tides show evidence of upward propagation from belowPoints of agreement and disagreement with the Mars Climate Database are noted and interpreted [ABSTRACT FROM AUTHOR]

We present CO density profiles up to about 100 km in the Martian atmosphere obtained for the first time from retrievals of solar occultation measurements by the Nadir and Occultation for Mars Discovery (NOMAD) onboard ExoMars Trace Gas Orbiter (TGO). CO is an important trace gas on Mars, as it is controlled by CO2 photolysis, chemical reaction with the OH radicals, and the global dynamics. However, the measurements of CO vertical profiles have been elusive until the arrival of TGO. We show how the NOMAD CO variations describe very well the Mars general circulation. We observe a depletion of CO in the upper troposphere and mesosphere during the peak period, LS = 190°–200°, more pronounced over the northern latitudes, confirming a similar result recently reported by Atmospheric Chemistry Suite onboard TGO. However, in the lower troposphere around 20 km, and at least at high latitudes of the S. hemisphere, NOMAD CO mixing ratios increase over 1,500 ppmv during the GDS (Global Dust Storm) onset. This might be related to the downwelling branch of the Hadley circulation. A subsequent increase in tropospheric CO is observed during the decay phase of the GDS around LS = 210°–250° when the dust loading is still high. This could be associated with a reduction in the amount of OH radicals in the lower atmosphere due to lack of solar insolation. Once the GDS is over, CO steadily decreases globally during the southern summer season. A couple of distinct CO patterns associated with the Summer solstice and equinox circulation are reported and discussed. Plain Language Summary: CO is an extremely interesting trace species in the Martian atmosphere. It has been used for both dynamical and photochemical studies of the atmosphere. But its vertical distribution has not been systematically measured until the arrival of the Exomars Trace Gas Orbiter (TGO). We use observations of the NOMAD (Nadir and Occultation for Mars Discovery) spectrometer onboard TGO to retrieve full profiles of mixing ratios of CO up to 100 km with a good vertical resolution. The retrievals cover two Martian seasons during which a global dust storm event occurred. We have found the behavior of CO during this event to be governed by local chemistry as well as by the long range transport. During the dust storm, CO mixing ratios are depleted all over the globe while over the southern high latitudes, we discover an increase in CO due to transport from low latitudes during the end of the southern winter. The dynamical effect of global transport is found in the vertical distribution of CO during the southern summer. Another important result, where the local chemistry might be at play is the increase of CO in the low altitudes over low and midlatitudes during the decay phase of the GDS. Key Points: Global map of CO profiles from Nadir and Occultation for Mars Discovery solar occultation observations during the first year of Trace Gas Orbiter operations is presented for the first timeDuring the onset of the 2018 global dust storm (GDS), the CO volume mixing ratios (VMRs) are found to be depleted by 28% at 50 km compared to the average CO VMR valuesHigh CO abundance at tropospheric altitudes is observed over NH during decay of the GDS when the atmospheric dust loading is high [ABSTRACT FROM AUTHOR]

We present vertical profiles of temperature and density from solar occultation (SO) observations by the "Nadir and Occultation for Mars Discovery" (NOMAD) spectrometer on board the Trace Gas Orbiter during its first operational year, which covered the second half of Mars Year 34. We used calibrated transmittance spectra in 380 scans, and apply an in‐house pre‐processing to clean data systematics. Temperature and CO2 profiles up to about 90 km, with consistent hydrostatic adjustment, are obtained, after adapting an Earth‐tested retrieval scheme to Mars conditions. Both pre‐processing and retrieval are discussed to illustrate their performance and robustness. Our results reveal the large impact of the MY34 Global Dust Storm (GDS), which warmed the atmosphere at all altitudes. The large GDS aerosols opacity limited the sounding of tropospheric layers. The retrieved temperatures agree well with global climate models (GCM) at tropospheric altitudes, but NOMAD mesospheric temperatures are wavier and globally colder by 10 K in the perihelion season, particularly during the GDS and its decay phase. We observe a warm layer around 80 km during the Southern Spring, especially in the Northern Hemisphere morning terminator, associated to large thermal tides, significantly stronger than in the GCM. Cold mesospheric pockets, close to CO2 condensation temperatures, are more frequently observed than in the GCM. NOMAD CO2 densities show oscillations upon a seasonal trend that track well the latitudinal variations expected. Results uncertainties and suggestions to improve future data re‐analysis are briefly discussed. Plain Language Summary: The detailed variation of temperature and density with altitude is of paramount importance to characterize the atmospheric state and to constrain the chemistry and dynamics as a whole. The Nadir and Occultation for Mars Discovery (NOMAD) instrument on board the Trace Gas Orbiter (TGO) has among its key targets the characterization of the thermal state with unprecedented vertical resolution. This is the target of this work, where we analyzed transmittance spectra obtained from the NOMAD solar occultation channel, with a state‐of‐the‐art retrieval scheme, adapted from Earth to Mars conditions and geometry. We applied it to the first year of TGO observations, which covered the last two Mars seasons of Mars Year 34. The results permit to study the temperature structure up to 90 km and its seasonal and latitudinal variations, revealing the impact of the MY34 Global Dust Storm, a warm layer at mesospheric altitudes not present in climate models, more frequent cold pockets than in current global climate models, and generally, colder temperature at those altitudes, all of which can be of importance for the validation of these climate models. Key Points: Temperature and density profiles up to 90 km are retrieved from Nadir and Occultation for Mars Discovery (NOMAD) first year of solar occultations, covering two seasons of Mars Year 34NOMAD temperatures agree well with climate model predictions below 50 km but are wavier and globally colder by about 10 K at high altitudesWe report large thermal tides producing warm layers at 80 km in the morning terminator. Also strong warming by the 2018 global dust storm [ABSTRACT FROM AUTHOR]

During Mars dust storms, atmospheric heating and expansion moves the ionospheric peak upward. Typically, peak altitude increases by no more than 10 km, and this increase occurs simultaneously with the expansion of the dust storm. However, Felici et al. (2020), https://doi.org/10.1029/2019JA027083, using the Mars Atmosphere Volatile EvolutioN (MAVEN) Radio Occultation Science Experiment (ROSE), reported an unusually large increase of ∼20 km at southern latitudes in early October 2016 during a modest dust storm. Here, we investigate why the ionospheric peak altitude increased so much in these observations. We extend the time series of ionospheric peak altitude values beyond the limited extent of the ROSE observations by applying a one‐dimensional photochemical model, in which neutral atmospheric conditions are based on in situ MAVEN Neutral Gas Ion Mass Spectrometer observations at similar latitudes and solar zenith angles to those observed by ROSE. We find that the ionospheric peak altitude was highest throughout October 2016 yet both the local and global atmospheric dust loading were greatest 1 month earlier. We hypothesize that (a) a portion of the unusually large 20 km enhancement in peak altitude and (b) the unusual delay between the greatest dust loading and the highest peak altitude were both associated with the occurrence of perihelion, which maximizes solar heating of the atmosphere, in late October 2016. Plain Language Summary: Dust storms always cause the top of the Martian ionosphere, a weakly ionized region in the upper atmosphere, to move to higher heights, typically by ∼10 km, due to the heating and expansion of the atmosphere caused by the storm. However, during a moderate regional dust storm in 2016, the ionospheric peak height elevated by ∼20 km. This study examines the reasons for this unusual increase. Simulations using a photochemical model showed that the ionospheric peak remained elevated for the whole month of October. However, the dust storm peaked in September, roughly a month before maximum ionospheric height. This is quite unusual as the ionospheric peak usually occurs at the highest heights during the peak of storms as maximum atmospheric heating and expansion occur during this period. Thus, this time delay suggests that the dust storm event does not solely cause the atypical enhancement in the ionospheric peak altitude. We suggest that the occurrence of Martian perihelion, Mars's closest point to the Sun in its orbit, and associated enhancement in solar heating in October 2016 might have contributed significantly to the thermal expansion of the atmosphere and hence toward the observed enhancement in the ionospheric peak height. Key Points: The ionospheric peak altitudes in the southern latitudes enhanced by ∼20 km during the regional dust storm of 2016Dust loading maximized during mid‐September but ionospheric peak heights reached their maximum only in October, suggesting a time delayThe occurrence of perihelion in October 2016 might have caused the time delay and also could have contributed to the unusual enhancement [ABSTRACT FROM AUTHOR]

We report the first detailed study of the diurnal thermal structure of upper mesosphere/lower thermosphere (∼80 to 160 km) of Mars from stellar occultation observations by the Imaging Ultraviolet Spectrograph (IUVS) aboard the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Due to stray light contamination, analyses of this data set to date have been confined to the nighttime events. This study makes use of a revised algorithm for removal of stray light from occultation spectra to retrieve the dayside events as well. The dayside is observed to be warmer than the nightside, with the maximum day/night difference of ∼30 K in the lower thermosphere, ∼20 K around the mesopause, with little diurnal variations at lower altitudes. This is consistent with the radiative time constant which is of the order of 1 Mars day in the 3×10−4 $3\times {10}^{-4}$ to 3×10−3 $3\times {10}^{-3}$ Pa region. The data also shows that the regions at pressure less than 2×10−3 $2\times {10}^{-3}$ Pa are under strong solar control with no prominent migrating tidal signatures. In contrast, on Earth, the radiative time constant near the mesopause is ∼10 Earth days and the temperature variations due to tides are quite large. The Mars Climate Database shows a diurnal trend opposite to the data in the mesosphere, with the dayside mesopause predicted to be cooler than the nightside by ∼10 K along with signatures of a vertically propagating tide. The IUVS data set provides an unprecedented constraint on the structure of the Martian mesosphere. Plain Language Summary: The dayside Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph stellar occultation observations are often contaminated by stray light and are not processed by the current data reduction pipeline. We have developed an improved algorithm to retrieve these dayside events as well, therefore expanding the usable data set. There have been very few observations of Mars in 80–160 km altitude range, a region that is influenced by the wave perturbations from lower atmosphere and solar forcing from above, with no data set providing a complete local time coverage to study the day/night differences. Therefore, we have enabled the first detailed study of the diurnal thermal structure of Mars in this region by salvaging the dayside events. We find the dayside atmosphere to be always warmer than the nightside at these altitudes. Though it is expected but has not been established for the Martian mesosphere. In contrast, the Mars Climate Database shows an opposite diurnal trend at the mesopause, along with inconsistent tidal signatures with the data. The mesopause is controlled by the energy balance between radiative processes. These data‐model inconsistencies thus imply that our current understanding of the dynamics and structure of the Martian mesosphere is inadequate and this data set can provide important constraints on the models. Key Points: First detailed study of the diurnal thermal structure of Mars for 10−5−10−2 ${10}^{-5}-{10}^{-2}$ Pa pressure levels from 3003 stellar occultationsDayside is observed to be warmer than the nightside at these pressure levels with no detectable migrating tidal signaturesGCM predictions are inconsistent with the data and show dayside mesopause cooler than the nightside, with a vertically propagating tide [ABSTRACT FROM AUTHOR]

Using a new observational technique, the NGIMS (Neutral Gas and Ion Mass Spectrometer) instrument on the MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft has the unique capability to measure horizontal thermospheric winds. Measured along the orbit track from periapsis (∼150 km) to ∼200 km, these are the first in situ observations of thermospheric winds at Mars. Significantly, this also means that simulated winds from a global circulation model can be compared to in situ observations from this part of the Martian atmosphere for the first time. In this study, observations from five NGIMS neutral wind campaigns have been compared to simulations from the Mars Global Ionosphere‐Thermosphere Model (M‐GITM), a ground to exosphere 3‐D general circulation model. By comparing NGIMS neutral wind observations to model simulations, the processes driving the winds and their variations in the upper atmosphere are examined. These comparisons show that for certain observational periods, the M‐GITM simulated winds can generally replicate the magnitude and/or direction of the NGIMS wind observations, while in others, significant differences occur. In general, wind observations from NGIMS campaigns with large orbit‐to‐orbit variability are not well replicated by M‐GITM, while campaigns with higher observed wind speeds are better captured by the model. Additionally, using these data‐model comparisons, the relative role of normal solar forcing and corresponding differential heating in driving thermospheric winds at Mars is found to be variable, likely acting as the primary driver under some conditions and secondary to other physical processes under others. Plain Language Summary: The MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft, which is currently in orbit around Mars, has been taking monthly measurements of the speed and direction of the winds in the upper atmosphere of Mars between about 150 and 200 km above the surface. The observed wind speeds and directions change with time and location, and sometimes fluctuate quickly. These measurements are compared to simulations from a computer model of the Mars atmosphere called M‐GITM (Mars Global Ionosphere‐Thermosphere Model). This is the first comparison between direct measurements of winds in the upper atmosphere of Mars and simulated winds and is important because it can help to inform us what physical processes are acting on the observed winds. Some wind measurements have similar wind speeds or directions to those predicted by the M‐GITM model, but sometimes, there are large differences between the simulated and measured winds. The disagreements between wind observations and model simulations suggest that processes other than normal solar forcing may become relatively more important during these observations and alter the expected circulation pattern. Understanding the processes that drive the winds in the upper atmosphere of Mars provides key context for understanding how the atmosphere behaves as a whole system. Key Points: New thermospheric wind observations at Mars are compared to a global circulation model for the first timeWinds during observational campaigns with high average wind speeds and little variability were best replicated in model simulationsData‐model disagreements suggest processes other than normal solar forcing may become important and alter the expected circulation pattern [ABSTRACT FROM AUTHOR]

The Cameron bands and the UV doublet are two of the most prominent emission systems in the UV in Mars dayside. Their altitude variation has been exploited in the past to derive thermospheric temperatures from measurements obtained by the Mariner 6, 7, and 9 missions, the SPICAM instrument on board Mars Express, and the IUVS instrument on board MAVEN. Here we identify and quantify possible biases in these temperature determinations. For this purpose, we use a global model able to simulate these two emission systems, and we compare the temperature derived from the simulated emission with that predicted by the model at the same location and time. We find that an exponential fit to the scale height of the UV doublet can be used to derive temperatures with an error less than 10 K at altitudes above about 170 km and for low and moderate values of the Solar Zenith Angle. The temperature derived from the Cameron bands is biased towards higher values due to the non-negligible contribution of CO to the emission. We find that, at 170 km, the difference between the temperature derived from the Cameron bands and the UV doublet can be related to the CO abundance. Our results have implications for previous temperature determinations from the Mariners, SPICAM/MEx and IUVS/MAVEN, some of them being biased by about 25 K. • Temperature derived from Cameron bands biased to high values due to CO contribution. • Temperature derived from UV doublet accurate in optically thin region, above ∼ 170 km. • The temperature difference between Cameron bands and UV doublet is linked to the CO abundance. [ABSTRACT FROM AUTHOR]

This work uses a subset of "quiet" MaRS ionospheric dayside observations (MaRS quiet , 2004–2017) and a 1-D photochemical model (IonA-2) to investigate the potential formation processes of the excess electron densities merged with the base of the main ionosphere (Mm). 42% of the investigated MaRS observations contain identified Mm, which occur in a large variety of shapes ranging from smoothly decreasing electron densities to peak structures below the base of M1. The Mm appear over the full range of accessible solar zenith angles (50° - 90°) and are found between approximately 70 and 110 km altitude. Their base is found on average deeper in the atmosphere than the base of the averaged undisturbed MaRS electron density profiles. This indicates a dependence of the Mm formation on energy sources that penetrate deep into the atmosphere. This is supported by a strong positive correlation with increasing solar activity when solar flares, coronal mass ejections, and enhanced short solar X-ray and Ly-α intensities are more common. No relationship is found between the Mm occurrence rate and the magnitude/inclination of the weak crustal crustal magnetic field in MaRS quiet. Investigations with the IonA-2 photochemical model for undisturbed and flare conditions show that the ionization of the local neutral atmosphere by solar X-ray radiation <2 nm provides a satisfying explanation for detected Mm features with smoothly decreasing electron densities below the M1 base in combination with moderate slopes of the lower Mm region α Mm and altitudes of the lower boundary h L , S. While sufficient ionization energy reaches the region of interest during flares, no Mm features with peaks below the M1 base occur in any of the model electron density profiles. This supports the conclusion that the subgroup of merged excess electron densities with peaks or intermediate features (Mi) below the M1 base must have an origin different from the sole variability of solar X-ray radiation during undisturbed and solar flare conditions. The size of the identified Mm makes an exclusive meteoric origin of the Mm peak structures unlikely. It is indicative from the IonA-2 model results that the general increase/decrease of solar X-ray <2 nm leads to a correlated response of the Mm region. The sporadic occurrence of the merged excess electron densities in the MaRS observations is therefore assumed to be a combination of observational (increased observation noise level compared to the available amount of X-ray radiation <2 nm, shift of the lower baseline by ionospheric deviations from radial symmetry) and environmental (e.g. variations in solar X-ray) factors. [ABSTRACT FROM AUTHOR]