Energetic electron depletions are a notable feature of the nightside Martian upper atmosphere. In this study, we investigate systematically the variations of the occurrence of depletions with both ...internal and external conditions, using the extensive Solar Wind Electron Analyzer measurements made on board the Mars Atmosphere and Volatile Evolution. In addition to the known trends of increasing occurrence with decreasing altitude and increasing magnetic field intensity, our analysis reveals that depletions are more easily observed in regions with near horizontal magnetic fields and under low solar wind (SW) dynamic pressures. We also find that below 160 km, the occurrence increases with increasing CO2 density, a trend mostly visible in weakly magnetized regions. These observations have important implications on the formation of electron depletions: (1) Near strong magnetic anomalies, closed magnetic loops preferentially form and shield the atmosphere from direct access of SW electrons, a process that is modulated by the upstream SW condition; and (2) in weakly magnetized regions, SW electrons precipitate into the atmosphere unhindered, but at sufficiently low altitudes, they are either “absorbed” due to inelastic collisions with ambient neutrals or shielded again in response to a change in magnetic connectivity from open to closed. Our analysis further reveals that both the ionospheric plasma content and thermal electron temperature are reduced in regions with depletions compared to regions without, supporting SW electron precipitation as an important source of external energy driving the variability in the deep nightside Martian upper atmosphere and ionosphere.
Key Points
Electron depletions in the nightside Martian ionosphere are more easily observed in regions with near horizontal magnetic fields
Electron depletions are more easily observed under low solar wind dynamic pressures
Substantially reduced ionospheric plasma content and thermal electron temperature are observed in regions with depletions
Context.
Jeans escape is believed to dominate atmospheric escape for most outer Solar System bodies. However, non-thermal mechanisms, particularly atmospheric and ionospheric chemistry, are likely to ...contribute substantially to neutral escape on Triton.
Aims.
This study is devoted to evaluating the role of the chemically induced escape of H, H
2
, C, N, O, N
2
, and CO on Triton via a variety of processes. Here, we also aim to identify the dominant processes for these species.
Methods.
We used the background atmospheric and ionospheric structures from available model calculations. We constructed a test particle Monte Carlo model to determine the escape probability profiles of various species released from 35 channels. Species-dependent and energy-dependent cross sections were adopted in our calculations, along with a strongly forward-scattering angle distribution, all constrained by the available laboratory measurements.
Results.
The chemical escape rates on Triton are derived as 4.5 × 10
24
s
−1
for total H, 6.9 × 10
22
s
−1
for total C, 8.0 × 10
24
s
−1
for total N, and 1.4 × 10
23
s
−1
for total O.
Conclusions.
Based on a comparison with the respective Jeans escape rates, our calculations indicate that atmospheric and ionospheric chemistry make small but non-negligible contributions to both H and C escape on Triton, whereas its contributions to N and O escape are significant.
Abstract
In the absence of solar radiation, precipitating electrons from the solar wind (SW) are generally thought to be the dominant source of energy deposition in the nightside Martian upper ...atmosphere, creating a patchy ionosphere and possibly also affecting the nightside thermal budget of various neutral and ionized species. Previous model calculations have not taken into account in situ heating via SW electron impact. In the present study, we utilize extensive measurements made by several instruments on board the Mars Atmosphere and Volatile Evolution spacecraft, in order to perform data-driven computations of the nightside neutral, ion, and electron heating rates. Considering the large range of energetic electron intensity observed on the nightside of Mars, we divide the entire data set into two subsamples, either with or without energetic electron depletion, a notable feature of the nightside Martian ionosphere. Our calculations indicate that in situ nightside neutral heating is dominated by exothermic chemistry and Maxwell interaction with thermal ions for regions with depletion, and by direct SW impact for regions without. Collisional quenching of excited state species produced from a variety of channels, such as electron impact excitation, dissociation, and ionization, as well as
dissociative recombination, makes a substantial contribution to neutral heating, except during depletion. For comparison, nightside ion heating is mainly driven by energetic ion production under all circumstances, which occurs mainly via ion-neutral reaction O
+
+ CO
2
and CO
2
+
predissociation.
The effect of surface wettability on condensation heat transfer in a nanochannel is studied with the molecular dynamics simulations. Different from the conventional size, the results show that the ...filmwise mode leads to more efficient heat transfer than the dropwise mode, which is attributed to a lower interfacial thermal resistance between the hydrophilic surface and the condensed water compared with the hydrophobic case. The observed temperature jump at the solid-liquid surface confirms that the hydrophilic properties of the solid surface can suppress the interfacial thermal resistance and improve the condensation heat transfer performance effectively.
Aim
To gain deeper insights into the clostridial community dynamics and chemical transformations during the ensiling of alfalfa.
Methods and Results
Direct‐cut alfalfa silage (with the dry matter ...content of 240 g kg−1) was prepared with or without the addition of a lactic acid bacterial inoculant and sucrose. Silages were sampled at 0, 3, 7, 14, 28 and 56 days after ensiling and their bacterial community was determined using high‐throughput sequencing with a special focus on the clostridial community. A clostridial fermentation occurred in the control silage, with high contents of acetic acid, butyric acid and ammonia nitrogen and Clostridia counts; while the inoculated silage was well preserved, with low pH and high lactic acid content. Lactic acid bacteria dominated the bacterial community during the ensiling process. In the control silage, Weissella confusa, Lactobacillus brevis, Enterococcus mundtii and Pediococcus acidilactici were identified at the beginning of the fermentation. Thereafter, W. confusa, Lactobacillus helsingborgensis and Bifidobacterium asteroides appeared and quickly prevailed. In the inoculated silage, Lactobacillus plantarum dominated the whole ensiling process. The genus Clostridium dominated the clostridial community, and was depressed with the inoculated treatment. Clostridium perfringens, Garciella sp. and Clostridium baratii were the main initiators of the clostridial fermentation of the control silage, while Clostridium tyrobutyricum became the most abundant Clostridia with prolonged ensiling. Overall in the inoculated silage, little changes in the clostridial community were observed throughout the ensiling period. Treating alfalfa silage with a homolactic acid‐based bacterial inoculant prevented a clostridial fermentation resulting in more efficient fermentation.
Conclusion
Distinct changes in the bacterial community with a special focus on the clostridial community were associated with the development of the clostridial fermentation during the ensiling of alfalfa.
Significance and Impact of the Study
High‐throughput sequencing based on a novel Clostridia‐specific primer set proved a potentially useful tool to study the clostridial community dynamics, and could aid to elucidate the mechanism by which the clostridial fermentation develops during the ensiling of alfalfa.
The neutral heating efficiency is commonly defined as the fraction of the solar extreme ultraviolet and X-ray energy absorbed by a planetary atmosphere that ends up as local heat. It is a crucial ...parameter that determines the upper atmospheric temperature and, consequently, the thermal escape rate on both solar system bodies and exoplanets. Combining the Mars Atmosphere and Volatile Evolution measurements of a variety of atmospheric parameters, we calculate the neutral heating efficiency in the dayside Martian upper atmosphere based on a complicated network of microscopic processes, including photon and photoelectron impact processes, as well as exothermic chemical reactions. Our calculations indicate that neutral heating is mainly contributed by photon impact at low altitudes, of which the bulk occurs via CO2 photodissociation, and exothermic chemistry at high altitudes, of which the bulk occurs via and dissociative recombination. Collisional quenching of metastable neutrals and ions, which is of great interest in the literature, contributes to local heating by no more than 10% at all altitudes. In the dayside median sense, the neutral heating efficiency remains roughly constant at 20% from 150 to 200 km and increases steadily to 32% near 250 km. The heating efficiency at 150-200 km shows a weak correlation with solar zenith angle, increases modestly with increasing solar activity, and is clearly enhanced over strong crustal magnetic anomalies. Throughout the study, strict local heating is assumed, but nonlocal heating does not affect our results near or below 200 km.
The Neutral Gas and Ion Mass Spectrometer of the Mars Atmosphere and Volatile Evolution provides a large data set to explore the ion composition and structure of the Martian ionosphere. Here, the ...dayside measurements are used to investigate the minor ion density profiles with distinctive peaks above 150 km, revealing a systematic trend of decreasing peak altitude with increasing ion mass. We specifically focus on a subset of species including O+, N
2+/CO+, C+, N+, He+, and O++, all of which are mainly produced via direct photoionization of parent neutrals. Our analysis reveals weak or no variation with solar zenith angle (SZA) in both peak density and altitude, which is an expected result because these ion peaks are located within the optically thin regions subject to the same level of solar irradiance independent of SZA. In contrast, the solar cycle variations of peak density and altitude increase considerably with increasing solar activity, as a result of enhanced photoionization frequency and atmospheric expansion at high solar activities. He+ serves as an exception in that its peak density increases toward large SZA and meanwhile shows no systematic variation with solar activity. The thermospheric He distribution on Mars should play an important role in determining these observed variations. Finally, the peak altitudes for all species are elevated by at least several km within the weakly magnetized regions, possibly attributable to the suppression of vertical diffusion by preferentially horizontal magnetic fields in these regions.
Key Points
The peak density and altitude for most minor ion species produced via direct photoionization show weak or no SZA variation
The minor ion peak density and altitude tend to increase significantly with increasing solar activity
The minor ion peak density and altitude show clear and consistent difference between the strongly and weakly magnetized regions
Context.
Atmospheric escape has an appreciable impact on the long-term climate evolution on terrestrial planets. Exothermic chemistry serves as an important mechanism driving atmospheric escape and ...the role of such a mechanism is of great interest for Titan due to its extremely complicated atmospheric and ionospheric composition.
Aims.
This study is devoted to a detailed investigation of neutral N and C escape on the dayside of Titan, which is driven by exothermic neutral–neutral, ion–neutral, and dissociative recombination (DR) reactions. It was carried out based on the extensive measurements of Titan’s upper atmospheric structure by a number of instruments on board
Cassini
, along with an improved understanding of the chemical network involved.
Methods.
A total number of 14 C- and N-containing species are investigated based on 146 exothermic chemical reactions that release hot neutrals with nascent energies above their respective local escape energies. For each species and each chemical channel, the hot neutral production rate profile is calculated, which provides an estimate of the corresponding escape rate when combined with the appropriate escape probability profile obtained from a test particle Monte Carlo model.
Results.
Our calculations suggest a total N escape rate of 9.0 × 10
23
s
−1
and a total C escape rate of 4.2 × 10
23
s
−1
, driven by exothermic chemistry and appropriate for the dayside of Titan. The former is primarily contributed by neutral-neutral reactions, whereas the latter is dominated by ion–neutral reactions; however, contributions from neutral–neutral and DR reactions to the latter cannot be ignored either. Our calculations further reveal that the bulk of N escape is driven by hot N(
4
S) production from the collisional quenching of N(
2
D) by ambient N
2
, while C escape is mainly driven by hot CH
3
and CH
4
production via a number of important ion–neutral and neutral–neutral reactions.
Conclusions.
Considered in the context of prior investigations of other known escape mechanisms, we suggest that exothermic chemistry is likely to contribute appreciably to non-thermal C escape on the dayside of Titan, although it plays an insignificant role in N escape.
Recovery of both latent heat and condensate from boiler flue gas is significant for improving boiler efficiency and water conservation. The condensation experiments are carried out to investigate the ...simultaneous heat and mass transfer across the nanoporous ceramic membranes (NPCMs) which are treated to be hydrophilic and hydrophobic surfaces using the semicontinuous supercritical reactions. The effects of typical parameters including coolant flow rate, vapor/nitrogen gas mixture temperature, water vapor volume fraction and transmembrane pressure on heat and mass transfer performance are studied. The experimental results show that the hydrophilic NPCM exhibits higher performances of condensation heat transfer and condensate recovery. However, the hydrophobic modification results in remarkable degradation of heat and condensate recovery from the mixture. Molecular dynamics simulations are conducted to establish a hydrophilic/hydrophobic nanopore/water liquid system, and the infiltration characteristics of the single hydrophilic/hydrophobic nanopore is revealed.
In this paper a stochastic robust optimization problem of residential micro-grid energy management is presented. Combined cooling, heating and electricity technology (CCHP) is introduced to satisfy ...various energy demands. Two-stage programming is utilized to find the optimal installed capacity investment and operation control of CCHP (combined cooling heating and power). Moreover, interval programming and robust stochastic optimization methods are exploited to gain interval robust solutions under different robustness levels which are feasible for uncertain data. The obtained results can help micro-grid managers minimizing the investment and operation cost with lower system failure risk when facing fluctuant energy market and uncertain technology parameters. The different robustness levels reflect the risk preference of micro-grid manager. The proposed approach is applied to residential area energy management in North China. Detailed computational results under different robustness level are presented and analyzed for providing investment decision and operation strategies.
•An inexact two-stage stochastic robust programming model for CCHP management.•The energy market and technical parameters uncertainties were considered.•Investment decision, operation cost, and system safety were analyzed.•Uncertainties expressed as discrete intervals and probability distributions.
PDF
