Northern Spring Research Articles

Investigating the Condensation of Benzene (C6H6) in Titan’s South Polar Cloud System with a Combination of Laboratory, Observational, and Modeling Tools

Abstract We have combined laboratory, modeling, and observational efforts to investigate the chemical and microphysical processes leading to the formation of the cloud system that formed at an unusually high altitude (>250 km) over Titan’s south pole after the northern spring equinox. We present here a study focused on the formation of C6H6 ice clouds at 87°S. As the first step of our synergistic approach, we have measured, for the first time, the equilibrium vapor pressure of pure crystalline C6H6 at low temperatures (134–158 K) representative of Titan’s atmosphere. Our laboratory data indicate that the experimental vapor pressure values are larger than those predicted by extrapolations found in the literature calculated from higher-temperature laboratory measurements. We have used our experimental results along with temperature profiles and C6H6 mixing ratios derived from observational data acquired by the Cassini Composite Infrared Spectrometer (CIRS) as input parameters in the coupled microphysics radiative transfer Community Aerosol and Radiation Model for Atmospheres (CARMA). CARMA simulations constrained by these input parameters were conducted to derive C6H6 ice particle size distribution, gas volume mixing ratios, gas relative humidity, and cloud altitudes. The impact of the vapor pressure on the CIRS data analysis and in the CARMA simulations was investigated and resulted in both cases in benzene condensation occurring at lower altitude in the stratosphere than previously thought. In addition, the stratospheric C6H6 gas abundances predicted with the new saturation relationship are ∼1000× higher than previous calculations between 150–200 km, which results in larger particle sizes.

Photochemistry of benzene (C6H6) hydrogen cyanide (HCN) co-condensed ices part 1: A source of solid-state production of volatile nitrile compounds in Titan's stratosphere

Since 2015, during northern spring, a massive “noxious” stratospheric cloud has been detected at 250 km of altitude at the south pole of Titan, which persisted until the last targeted Cassini's flybys in July 2016. Its chemical composition seems to be the result of a co-condensation process of benzene and hydrogen cyanide in a 4:1 mixing ratio. Since, its altitude of detection allows to undergo long-UV solar radiations known to trigger photochemical aging processes, we experimentally simulated its evolution under stratospheric-like radiation conditions. The ice photo-processing (λ > 200 nm) led to the detection of nitriles by infrared spectroscopy such as acetonitrile (CH3CN), benzonitrile (C6H5CN) as well as a partial identification of propionitrile (CH3CH2CN) and acrylonitrile (C2H3CN). Gas chromatography coupled to mass spectrometry (GC–MS) analyses of the volatile fraction released in the gas phase during the warming of the photo-processed ice have been confirmed by previous assignments and provided the detection of several other hydrocarbons ranging from C3 to C8. These experimental results are of prime interest in the context of the future Dragonfly mission. They provide a list of nitrile derivatives that can be produced from this stratospheric cloud. Indeed, they may contribute at the end to the organic layer that recovers Titan's surface and would be analyzed by the mass spectrometer (Dra-MS) of this space mission.

Combining ability and genetic diversity under low-temperature conditions at germination stage of maize (Zea mays L.)

Low temperatures are important for the production of spring maize in northern China. While the low-temperature tolerance of maize seeds can be improved by coating them, this can result in environmental pollution, high costs, and instability. Therefore, identifying new varieties of maize is the most effective method of improving the ability of maize crops to withstand low temperatures. In this experiment, four low-temperature tolerant maize inbred lines (DNF266, Zhong 451, B73, Dan 340) and four low-temperature sensitive maize inbred lines (Luyuan 92, Ji 853, Huangzaosi, Si 144) were selected from the northern spring maize area. The griffing double-row hybridization design method was used to prepare 28 hybrid combinations. After analysing the general combining ability and the special combining ability of each combination, we found that the indoor low-temperature index and low-temperature seedings were extremely similar for all combinations. The hybridization and parental inbred lines were subjected to low-temperature treatments under both laboratory conditions and in the field. Several low-temperature indexes were assessed to identify what results could be produced from combining them. Under both treatments, the inbred line DNF266 had a higher general combining ability and the Zhong 451 × Dan 340 hybrid combination had a higher special combining ability. These results provide technical support for breeding new low-temperature varieties of maize.

Midsummer Atmospheric Changes in Saturn’s Northern Hemisphere from the Hubble OPAL Program

Abstract Using the Hubble Space Telescope, Saturn was observed in 2018, 2019, and 2020, just after the northern hemisphere summer solstice. Analysis of multispectral imaging data reveals three years of cloud changes associated with a 70° N storm that began in 2018. Additionally, there is an increase in equatorial brightness and perhaps haze optical depth at 0° to 7° N. There are small midsummer changes at the north pole, with a thin blue feature near the polar hexagon’s outer edge disappearing between 2019 and 2020 and increasingly reddish polar haze. Zonal winds at most latitudes remain close to values obtained by the Cassini mission with a slight increase of winds in the equatorial zone. Yearly cloud changes, while noticeable, are small compared with the changes observed between the Voyager (northern spring) and Cassini (southern summer to northern spring) eras, but further observations will provide a longer baseline for comparison.

Characteristic features of water ice clouds over Olympus and Arsia Mons using MOM and MRO observations

The present study used the observations from Mars Color Camera (MCC) onboard Mars Orbiter Mission, from the two instruments onboard Mars Reconnaissance Orbiter, i.e., Mars Climate Sounder (MCS) and Mars Color Imager (MARCI), for investigating the water ice cloud appearance over two Martian volcanos, Olympus Mons and Arsia Mons. Indeed, these regions offer an opportunity to explore the dynamical effects related to the orographic clouds and give an idea about their interactions with atmospheric transport. Also, the long-term MCS profile observations are much useful to emphasize the sub-seasonal, seasonal, and interannual variability of clouds at different altitudes. The MCC and MARCI images show a cloud patch over Olympus Mons within the aphelion and a thin cloud trails over Arsia Mons within the perihelion of Mars years. Night-time MCS observations suggest an appearance of thick low altitude clouds within 15–32 ​km height during LS ​= ​35–150° and thin high-altitude clouds within 30–50 ​km height during LS ​= ​225–315°. The profile observations over both the volcanic regions show that the atmospheric temperature variations more strongly control the water ice cloud distribution at lower altitudes during northern hemispheric spring and summer. In contrast, the high altitude thin clouds during southern hemispheric spring and summer are found to be more associated with the elevated dustiness and vertical advection of dust-laden mountain induced regional circulation, as suggested by MarsWRF simulated wind. The appearance of the consistent thick followed by thin clouds during aphelion and perihelion season shows a nearly constant cloud water content of ~0.2 and ~0.05 pr μm. The high or low magnitude of cloud water content could be distinguished from the peak water ice extinction within the column, as observed in the inter-annual variations. However, irrespective of low cloud water content during the second half of the year, the presence of high altitude thin clouds leads to an overall cloud vertical depth (≥30 ​km) higher (mostly visible during the night) than the first half of the year. Comparison of the nighttime appearance of thick clouds (centered at ~20 ​km) during the first half and thin clouds (centered at ~40 ​km) during the second half of the year over two volcanos indicates the suitable atmospheric conditions in the case of the Olympus Mons for the former type clouds and over Arsia Mons for the later. Also, the appearance of thick clouds mostly resembles the consistent and stable aphelion cloud cycle. In contrast, the thin high altitude clouds are more variable and influenced by the vertical advection during the perihelion season. Besides, these high altitude clouds drive the more prominent east-west asymmetry in the cloud abundance over the Arsia Mons region during the perihelion period.

Observation of aphelion cloud belt over Martian tropics, its evolution, and associated dust distribution from MCS data

The present study uses five Martian years of observations from Mars Climate Sounder onboard Mars Reconnaissance Orbiter for investigating the Aphelion Cloud Belt (ACB) over the tropics. Analysis of zonal mean water ice column opacity suggests that the spatial extension of the ACB is mainly confined over the tropics and mid-latitudes (-20 – 40°N) during LS ~ 45 – 135° (LS = 0° signifies northern spring equinox). The ACB is seen primarily in the nighttime only due to the truncation of the daytime profile observations at significantly higher altitudes (at ~30 km). Zonal mean ice extinction profiles show ACB’s altitudinal range within ~10 – 40 km, and the existence of a thin cloud band in the absence of a thick ACB during aphelion season. Three phases of the ACB could be identified as the formation phase during LS = 45 – 75° (phase 1), the peak phase during LS = 76 – 105° (phase 2), and the decaying phase during LS = 106 – 135° (phase 3). Observation of the cloud latitude belt shows a northward movement starting from phase 2, prominent over regions nearby Lunae Planum and Xanthe Terra. During this phase, the top level of thick clouds within the ACB decreases to ~20 km in the southern hemisphere, while it increases a little over the northern hemisphere (NH). The decreasing tendency continues in phase 3 over the entire region −10 – 10°N, and the thick cloud base moves higher over the NH, though the vertical depth of it becomes narrower than phase 2. Temperature profiles do not show any noticeable influence on the northward evolution of the ACB. However, the study at a regional level indicates a possible association of upper tropospheric dustiness with the ACB’s evolution. The mechanism is evident in the correlation analysis mostly at an altitude range of ~18 – 35 km. The migrating semidiurnal tide (SMD) as a proxy of dust or water ice forcing, and the calculated upper tropospheric dust radiative heating, shows an apparent northward movement of their peak amplitude within the three phases of the ACB. This match between the spatiotemporal variations of the SMD and the water ice was not observed previously. However, the correlating behavior seems to be prominent in the areas nearby Lunae Planum and Xanthe Terra and the upper-tropospheric region of the atmosphere.

The hole truth

Arctic Ozone Ozone loss in the Arctic stratosphere has never been as severe as that in the Antarctic ozone hole, but during the past year, it declined to a level a bit closer to that of its southern counterpart. Wohltmann et al. report that during the northern spring of 2020, Arctic stratospheric ozone levels fell to near zero in some places. This unprecedented depletion, caused by unusually cold and stable conditions in the Arctic stratosphere, could become more frequent or extensive if the recent trend toward colder Arctic winters continues. Geophys. Res Lett. 10.1029/2020GL089547 (2020).

Seasonal Dependence of the Magnetospheric Drag Torque on Saturn's Northern and Southern Polar Thermospheres and its Relation to the Periods of Planetary Period Oscillations

AbstractWe calculate the magnetospheric drag torques on Saturn's northern and southern polar thermospheres during late southern summer in 2008 and northern spring in 2012–2013 using previously derived profiles of ionospheric meridional coupling currents determined from high‐latitude Cassini magnetic field data. We show that the drag torques in the “winter” and “summer” auroral regions are near equal at ~2.3 × 1016 N m, contrary to the recent discussion of Brooks et al. (2019, https://doi.org/10.1002/2019JA026870) who suggest that significant seasonal differences should occur in these regions. Instead, seasonally dependent torques occur in the adjacent polar open field regions, where the “winter” and “summer” torques are ~0.3 × 1016 and ~1.8 × 1016 N m, respectively. We derive a simple rotating disc model of the polar thermosphere and estimate the speed of the poleward flow from midlatitudes required to balance these torques in steady state, finding values of tens of m s−1 consistent with previous numerical modeling. Comparison of the calculated torques with concurrent periods of the northern and southern planetary period oscillations (PPOs) does not suggest a direct connection between these quantities as proposed by Brooks et al., 2019, showing at the least that significant additional factors must be involved. We further note some issues with their scenario for dual modulation of radio emissions, previous observations having shown that the principal oscillatory PPO field‐aligned currents that modulate the emissions rotate in the auroral region with periods ~10.7 ± 0.1 hr, propagating through the more slowly rotating ~15–20 hr period outer magnetospheric plasma, with implications for the proposed “atmospheric flywheel” picture.

Temperature and chemical species distributions in the middle atmosphere observed during Titan’s late northern spring to early summer

We present a study of the seasonal evolution of Titan’s thermal field and distributions of haze, C2H2, C2H4, C2H6, CH3C2H, C3H8, C4H2, C6H6, HCN, and HC3N from March 2015 (Ls = 66°) to September 2017 (Ls = 93°) (i.e., from the last third of northern spring to early summer). We analyzed thermal emission of Titan’s atmosphere acquired by the Cassini Composite Infrared Spectrometer with limb and nadir geometry to retrieve the stratospheric and mesospheric temperature and mixing ratios pole-to-pole meridional cross sections from 5 mbar to 50 μbar (120–650 km). The southern stratopause varied in a complex way and showed a global temperature increase from 2015 to 2017 at high-southern latitudes. Stratospheric southern polar temperatures, which were observed to be as low as 120 K in early 2015 due to the polar night, showed a 30 K increase (at 0.5 mbar) from March 2015 to May 2017 due to adiabatic heating in the subsiding branch of the global overturning circulation. All photochemical compounds were enriched at the south pole by this subsidence. Polar cross sections of these enhanced species, which are good tracers of the global dynamics, highlighted changes in the structure of the southern polar vortex. These high enhancements combined with the unusually low temperatures (<120 K) of the deep stratosphere resulted in condensation at the south pole between 0.1 and 0.03 mbar (240–280 km) of HCN, HC3N, C6H6 and possibly C4H2 in March 2015 (Ls = 66°). These molecules were observed to condense deeper with increasing distance from the south pole. At high-northern latitudes, stratospheric enrichments remaining from the winter were observed below 300 km between 2015 and May 2017 (Ls = 90°) for all chemical compounds and up to September 2017 (Ls = 93°) for C2H2, C2H4, CH3C2H, C3H8, and C4H2. In September 2017, these local enhancements were less pronounced than earlier for C2H2, C4H2, CH3C2H, HC3N, and HCN, and were no longer observed for C2H6 and C6 H6, which suggests a change in the northern polar dynamics near the summer solstice. These enhancements observed during the entire spring may be due to confinement of this enriched air by a small remaining winter circulation cell that persisted in the low stratosphere up to the northern summer solstice, according to predictions of the Institut Pierre Simon Laplace Titan Global Climate Model (IPSL Titan GCM). In the mesosphere we derived a depleted layer in C2H2, HCN, and C2H6 from the north pole to mid-southern latitudes, while C4H2, C3H4, C2H4, and HC3N seem to have been enriched in the same region. In the deep stratosphere, all molecules except C2H4 were depleted due to their condensation sink located deeper than 5 mbar outside the southern polar vortex. HCN, C4H2, and CH3C2H volume mixing ratio cross section contours showed steep slopes near the mid-latitudes or close to the equator, which can be explained by upwelling air in this region. Upwelling is also supported by the cross section of the C2H4 (the only molecule not condensing among those studied here) volume mixing ratio observed in the northern hemisphere. We derived the zonal wind velocity up to mesospheric levels from the retrieved thermal field. We show that zonal winds were faster and more confined around the south pole in 2015 (Ls = 67−72°) than later. In 2016, the polar zonal wind speed decreased while the fastest winds had migrated toward low-southern latitudes.

Stratospheric impact on the Northern Hemisphere winter and spring ozone interannual variability in the troposphere

Abstract. In this study we use ozone and stratospheric ozone tracer simulations from the high-resolution (0.5∘×0.5∘) Goddard Earth Observing System, Version 5 (GEOS-5), in a replay mode to study the impact of stratospheric ozone on tropospheric ozone interannual variability (IAV). We use these simulations in conjunction with ozonesonde measurements from 1990 to 2016 during the winter and spring seasons. The simulations include a stratospheric ozone tracer (StratO3) to aid in the evaluation of the impact of stratospheric ozone IAV on the IAV of tropospheric ozone at different altitudes and locations. The model is in good agreement with the observed interannual variation in tropospheric ozone, except for the post-Pinatubo period (1992–1994) over the region of North America. Ozonesonde data show a negative ozone anomaly in 1992–1994 following the Pinatubo eruption, with recovery thereafter. The simulated anomaly is only half the magnitude of that observed. Our analysis suggests that the simulated stratosphere–troposphere exchange (STE) flux deduced from the analysis might be too strong over the North American (50–70∘ N) region after the Mt. Pinatubo eruption in the early 1990s, masking the impact of lower stratospheric ozone concentration on tropospheric ozone. European ozonesonde measurements show a similar but weaker ozone depletion after the Mt. Pinatubo eruption, which is fully reproduced by the model. Analysis based on the stratospheric ozone tracer identifies differences in strength and vertical extent of stratospheric ozone impact on the tropospheric ozone interannual variation (IAV) between North America and Europe. Over North American stations, the StratO3 IAV has a significant impact on tropospheric ozone from the upper to lower troposphere and explains about 60 % and 66 % of the simulated ozone IAV at 400 hPa and ∼11 % and 34 % at 700 hPa in winter and spring, respectively. Over European stations, the influence is limited to the middle to upper troposphere and becomes much smaller at 700 hPa. The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), assimilated fields exhibit strong longitudinal variations over Northern Hemisphere (NH) mid-high latitudes, with lower tropopause height and lower geopotential height over North America than over Europe. These variations associated with the relevant variations in the location of tropospheric jet flows are responsible for the longitudinal differences in the stratospheric ozone impact, with stronger effects over North America than over Europe.

Modelling the impacts of climate change and crop management measures on soybean phenology in China

Climate change and crop management measures affect crop growth. But their combined and relative impacts on soybean phenology are still not clear. Based on the first-difference method, we discriminated and quantified the impacts of climate change and crop management measures on soybean phenology using observational data from 51 agro-meteorological stations in China’s major soybean planting areas from 1992 to 2011. Results showed that (1) vegetative, reproductive and whole growth periods of northern spring soybean were shortened whereas those of summer soybean were prolonged. Reproductive and whole growth periods of southern spring soybean were also prolonged. (2) Climate change independently prolonged the vegetative growth periods of northern spring soybean, summer soybean, and southern spring soybean by 0.3, 0.52, and 0.3 days/decade, respectively, and shortened the whole growth periods by 1.43, 0.74, and 6.3 days/decade, respectively. Increasing temperature advanced the soybean phenology and shortened key growth stages. (3) Crop management measures contributed more to the observed trends of phenology and growth stages than climate change. Temperature and sunshine duration dominated the impact of climate change on soybean phenology and growth stages. (4) Shifting sowing date and selecting soybean cultivars with high temperature resistance, high thermal requirements and long growth periods are effective strategies to adapt to climate change. The findings could contribute to providing appropriate adaptation and mitigation strategies to facilitate sustainable soybean production.

The establishment of a pelagic Sargassum population in the tropical Atlantic: Biological consequences of a basin-scale long distance dispersal event

Starting in 2011, coastal areas of the Caribbean Sea and tropical Atlantic Ocean began to experience extraordinary yearly accumulations of pelagic Sargassum brown alga. Historical reports place large quantities of Sargassum only in the North Atlantic (mostly in the Gulf of Mexico and the Sargasso Sea). Accumulations of Sargassum in the tropical Atlantic have continued. We used a numerical particle-tracking system, wind and current reanalysis data, drifting buoy trajectories, and satellite imagery to determine the origin of the Sargassum that is now found persistently in the tropical Atlantic. Our analyses suggest that during the extreme negative phase of the winter 2009–2010 North Atlantic Oscillation (NAO), unusually strong and southward-shifted westerly winds explain the transport of Sargassum from the Sargasso Sea (∼20–40°N, 80–20°W) into the far eastern North Atlantic. Our hindcast Sargassum distributions agree with surface current simulations with the inclusion of “windage”. Windage is the additional, wind-induced drift of material floating at the free surface resulting from direct wind forcing on the sea surface, as well as on floating or partially-submerged objects. In our simulations, windage is included as an added vector (speed and direction) to the model-computed surface ocean currents equivalent to 1% of surface wind velocities. Lagrangian analysis of the regional circulation suggests that (1) part of the Sargassum subsequently drifted to the southwest in the North Equatorial Current (NEC) and entered the central tropical Atlantic, arriving in the Caribbean by the spring of 2011, with (2) another portion continuing southward along the coast of Africa in the Canary Current, eventually joining the seasonally-varying system of tropical Atlantic currents and thereby delivering a large Sargassum population to the tropical Atlantic. Since then, Sargassum patches aggregate from March to September in massive windrows along the Inter-Tropical Convergence Zone (ITCZ) under the action of converging winds. The windrows follow the ITCZ in its seasonal northward migration in the central tropical Atlantic. They are stretched across the central tropical Atlantic as the ITCZ crosses the latitude of the seasonal formation of the North Equatorial Counter Current (NECC). These patches and windrows are exposed to high sunlight and open-ocean upward flux of nutrients due to eddy and wind-driven mixing in the central tropical Atlantic. During the northern spring and summer, as the Sargassum drifts farther north with the ITCZ, large portions of the population are advected into the eastern Caribbean Sea. Some of these patches remain dispersed as the ITCZ migrates southward, and re-aggregate into new windrows as the ITCZ intensifies the following March-April. If wind mixing is strong and the mixed layer is deeper than about 50–60 m in the southern tropical Atlantic at this time, the Sargassum will bloom and form a massive windrow. Otherwise, the bloom will be inhibited. The extreme 2009–2010 NAO wind anomaly could be considered as triggering a biosphere “tipping point” that caused important ocean-scale ecosystem changes in the tropical Atlantic, with significant recurrent social and economic consequences. Understanding whether this new expanded geographic range of massive Sargassum blooms is temporary or whether it will revert to its pre-2009 distribution requires sustained monitoring and research.

Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017

The Cassini/Composite InfraRed Spectrometer (CIRS) instrument has been observing the middle atmosphere of Titan over almost half a Saturnian year. We used the CIRS dataset processed through the up-to-date calibration pipeline to characterize seasonal changes of temperature and abundance profiles in the middle atmosphere of Titan, from mid-northern winter to early northern summer all around the satellite. We used limb spectra from 590 to 1500 cm−1 at 0.5-cm−1 spectral resolution, which allows us to probe different altitudes. We averaged the limb spectra recorded during each flyby on a fixed altitude grid to increase the signal-to-noise ratio. These thermal infrared data were analyzed by means of a radiative transfer code coupled with an inversion algorithm, in order to retrieve vertical temperature and abundance profiles. These profiles cover an altitude range of approximately 100 to 600 km, at 10- or 40-km vertical resolution (depending on the observation). Strong changes in temperature and composition occur in both polar regions where a vortex is in place during the winter. At this season, we observe a global enrichment in photochemical compounds in the mesosphere and stratosphere and a hot stratopause located around 0.01 mbar, both linked to downwelling in a pole-to-pole circulation cell. After the northern spring equinox, between December 2009 and April 2010, a stronger enhancement of photochemical compounds occurred at the north pole above the 0.01-mbar region, likely due to combined photochemical and dynamical effects. During the southern autumn in 2015, above the South pole, we also observed a strong enrichment in photochemical compounds that contributed to the cooling of the stratosphere above 0.2 mbar (∼300 km). Close to the northern spring equinox, in December 2009, the thermal profile at 74°N exhibits an oscillation that we interpret in terms of an inertia-gravity wave.

Tracking seasonal activity of the western blacklegged tick across California

Abstract Understanding seasonal patterns of activity, or phenology, of vector species is fundamental to determining seasonality of disease risk and epidemics of vector‐borne disease. Spatiotemporal variation in abiotic conditions can influence variation in phenological patterns and life history events, which can dramatically influence the ecological role and human impact of a species. For arthropod vectors of human diseases such as ticks, these phenological patterns determine human exposure risk, yet how abiotic conditions interact to determine suitable conditions for host‐seeking of vector species is difficult to disentangle. Here, we use MaxEnt to model spatial patterns and differences in host‐seeking phenology of the western blacklegged tick (Ixodes pacificus) in California using spatially and temporally refined adult tick occurrence data and similarly refined climate and environmental data. We empirically validate the model using phenological data from field studies conducted at sites across California's latitudinal gradient. We find adult tick host‐seeking activity varies substantially throughout the year, as well as across the large latitudinal gradient in the state. Suitable conditions for host‐seeking are found earlier in fall and later in the spring in northern than in southern California. These seasonal patterns are primarily associated with monthly precipitation, minimum winter temperature, and winter precipitation, with maximum monthly temperature possibly playing a more prominent role in limiting host‐seeking activity earlier in the spring in southern than northern California. Synthesis and applications. Modelling the seasonal activity of the western blacklegged tick, we find both a longer window for host‐feeding and more protracted risk of human exposure to this vector species in northern than southern California. We further identify key environmental factors associated with these patterns, including precipitation and temperature that are otherwise challenging to elucidate in field and laboratory studies over large spatial scales. Moreover, we illustrate how species distribution models, in combination with temporally refined species occurrence and environmental data, can be used to investigate environmental factors predictive of geographic variation in seasonality or phenology of vector species. This produces not only novel ecological insight, but key information for public health practitioners in managing vector‐borne disease transmission and targeting public outreach and interventions.

WITHDRAWN: Climatology of the ozone vertical distribution on Mars from SPICAM/MEX UV occultations

Abstract The SPICAM/MEX ultraviolet spectrometer probed the Martian atmosphere with the occultation method from 2004 until 2014. SPICAM/MEX performed both stellar and solar occultations during in total four Martian Years with a good spatial and seasonal coverages. We have analyzed these occultations and compiled a climatology of the vertical distribution of Martian ozone, a key chemical species. The stellar occultations mostly probe the nightside atmosphere, whereas the solar occultations are acquired at the terminator (sunrise or sunset), allowing the study of the day-night transition of this photochemically active species. Comparison of the observations with a global climate model show a good overall qualitative agreement. However, quantitative differences are found in certain regions, possibly related to difficulties in correct modeling of the water cycle. In particular, at low latitudes SPICAM is detecting ozone practically throughout the Martian Year, whereas it is only predicted around aphelion in the models. The occultations probe the southern polar winter vortex, its mid-altitude ozone layer (peaking at 50 km), and the ozone layer in the lower atmosphere that shows much larger O3 column concentrations than predicted by modeling. The low- and midlatitude ozone layer forming in northern spring is mapped throughout both hemispheres and details of its structure are revealed. During the northern polar spring, SPICAM observes the lower atmosphere ozone layer, reaching from the surface up to 30 km, showing higher O3 concentrations than expected from modeling.

Large‐Amplitude Quasi‐10‐Day Waves in the Middle Atmosphere During Final Warmings

AbstractGeopotential height measurements from the Aura Microwave Limb Sounder between 9‐ and 97‐km altitudes during 2004–2018 are used to examine long‐period (3–20 days) wave activity during the Northern Hemisphere winter and spring, with the primary focus on the response of normal mode Rossby waves in the middle atmosphere to sudden stratospheric warmings (SSWs). Unusually large westward propagating waves with Zonal Wave Number 1 and period ∼10 days are observed at 55° latitude at the stratopause height (∼48 km) and above following final warmings of 2016, 2015, and 2005. In each case, large‐amplitude waves are observed for the duration of two to three wave cycles. Characteristics of the waves are in conformity with the second antisymmetric Rossby normal mode of Zonal Wave Number 1, or the quasi‐10‐day wave. The growth rate of the waves is significantly greater than the classical normal mode in the upper stratosphere (approximately 30–50 km) where instability conditions are met, indicating the amplification or excitation of the waves in that region. The response of the quasi‐10‐day wave during midwinter SSWs, and also during the spring transition without an SSW, is not as obvious as the wave response during final warmings. The results suggest that not only the occurrence of SSW but also the seasonal timing of SSW is an important factor for the transient variability of the quasi‐10‐day wave in the middle atmosphere.

Titan's neutral atmosphere seasonal variations up to the end of the Cassini mission

In this paper we report new results concerning the seasonal atmospheric evolution near Titan's poles and equator in terms of temperature and composition using nadir spectra acquired by the Cassini Composite Infrared Spectrometer (CIRS) at high spectral resolution during the last year of the Cassini mission in 2017 complementing previous investigations covering almost two Titan seasons. In recent previous papers (Coustenis et al., 2016, 2018), we have reported on monitoring of Titan's stratosphere near the poles after the mid-2009 northern spring equinox. In particular we have reported on the observed strong temperature decrease and compositional enhancement above Titan's southern polar latitudes since 2012 and until 2014 of several trace species, such as complex hydrocarbons and nitriles, which were previously observed only at high northern latitudes. This effect accompanied the transition of Titan's seasons from northern winter in 2002 to northern summer in 2017, while at that latter time, the southern hemisphere was entering winter. Our new data, acquired in 2017 and analyzed here, are important because they are the only ones recorded since 2014 close to the south pole in the mid-infrared nadir mode at high resolution. A large temperature increase in the southern polar stratosphere (by 10–50 K in the 0.1 mbar–0.01 mbar pressure range) is found associated with a change in the temperature profile's shape. The 2017 observations also show a related significant decrease in most of the southern abundances which must have started sometime between 2014 and 2017. For the north, the spectra indicate a continuation of the decrease of the abundances which we first reported to have started in 2015 and small temperature variations. We discuss comparisons with other results and with current photochemical and dynamical models which could be updated and improved by the new constraints set by the findings presented here.

Global seasonal variations of the near-surface relative humidity levels on present-day Mars

We investigate the global seasonal variations of near-surface relative humidity and relevant attributes, like temperature and water vapor volume mixing ratio on Mars using calculations from modelled and measurement data. We focus on 2 AM local time snapshots to eliminate daily effects related to differences in insolation, and to be able to compare calculations based on modelling data from the Laboratoire de Météorologie Dynamique Mars General Circulation Model with the observations of Mars Global Surveyor Thermal Emission Spectrometer. We study the seasonal effects by examining four specific dates in the Martian year, the northern spring equinox, summer solstice, autumn equinox, and winter solstice. We identify three specific zones, where the near-surface relative humidity levels are systematically higher than in their vicinity regardless of season. We find that these areas coincide with low thermal inertia features, which control surface temperatures on the planet, and are most likely covered with unconsolidated fine dust with grain sizes smaller than ∼ 40 μm. By comparing the data of relative humidity, temperature and water vapor volume mixing ratio at three different heights (near-surface, ∼ 4 m and ∼ 23 m above the surface), we demonstrate that the thermal inertia could play an important role in determining near-surface humidity levels. We also notice that during the night the water vapor levels drop at ∼ 4 m above the surface. This, together with the temperature and thermal inertia values, shows that water vapor likely condenses in the near-surface atmosphere and on the ground during the night at the three aforementioned regions. This condensation may be in the form of brines, wettening of the fine grains by adsorption or deliquescence. This study specifies areas of interest on the surface of present day Mars for the proposed condensation, which may be examined by in-situ measurements in the future.

The martian daytime convective boundary layer: Results from radio occultation measurements and a mesoscale model

We investigate the behavior of the Martian daytime convective boundary layer (CBL) through a combination of data analysis and modeling. This study relies on two subsets of Mars Express radio occultation (RO) measurements that sounded the atmosphere in northern spring of successive Mars years. Only the first year of observations has been examined previously (Hinson et al., 2008); the second year provides complementary spatial coverage and greatly increases the total number of observations. Analysis of the RO profiles yields basic characteristics of the CBL, such as its depth D and the average potential temperature of the mixed layer θm. We also combine RO retrievals of surface pressure with surface temperatures from infrared sounding to characterize the surface forcing, expressing the result as a potential temperature θs. These observations are at local times in early afternoon for θs and late afternoon for θm and D, when each parameter is near its diurnal maximum. We use measurements at mid-to-low latitudes, which sample a wide range of θs (227–294 K), to determine the response of the lower atmosphere to spatial variations in surface forcing. The depth of the CBL ranges from less than 3 km in the midlatitude topographic basins to more than 9 km above elevated terrain in the tropics. The dependence of θm on θs is linear, with a characteristic slope of about 0.7 in both years. We gain further insight by performing a simulation with the Oregon State University Mars Mesoscale Model in a region centered on Isidis Planitia, which includes two potential landing sites for the Mars 2020 Rover. As expected from previous modeling of much smaller craters, the arc of steep topography along the western and southern margins of Isidis produces a distinctive, diurnally varying, mesoscale circulation. The simulation captures key features of the observations, such as the wide variations in θm and D — by 34 K and 9 km, respectively — that occur within this region. The model also accounts for peculiar features of RO profiles on the rim of Isidis, where the wind field strongly influences the depth and diurnal evolution of the CBL. Detailed comparisons with the observations validate the general performance of the model and confirm several aspects of the simulated wind field.

Death of the Soldier and Immortality of War in Frank Ormsby’s A "Northern Spring"

The paper analyzes the collection of the Northern Irish poet Frank Ormsby entitled A Northern Spring published in 1986. On the basis of selected poems, the author of this paper aims to examine the poet’s reflections about World War II, the lives of the soldiers, and the things that remain after a military combat, which are both physical and illusive. The poems included in the volume present the author’s reflections upon the senselessness of war and dying, short lives of the soldiers, the awareness of their own meaninglessness in comparison to the broader picture, and the contradictory and desperate need to be remembered nevertheless. They also show what is left of the soldiers and the war, as well as how life goes on, with or without them.