On the Insignificance of Photochemical Hydrocarbon Aerosols in the Atmospheres of Close-in Extrasolar Giant Planets

The close-in extrasolar giant planets (CEGPs) reside in irradiated environments much more intense than that of the giant planets in our solar system. The high UV irradiance strongly influences their photochemistry and the general current view believed that this high UV flux will greatly enhance photochemical production of hydrocarbon aerosols. In this letter, we investigate hydrocarbon aerosol formation in the atmospheres of CEGPs. We find that the abundances of hydrocarbons in the atmospheres of CEGPs are significantly less than that of Jupiter except for models in which the CH$_4$ abundance is unreasonably high (as high as CO) for the hot (effective temperatures $\gtrsim 1000$ K) atmospheres. Moreover, the hydrocarbons will be condensed out to form aerosols only when the temperature-pressure profiles of the species intersect with the saturation profiles--a case almost certainly not realized in the hot CEGPs atmospheres. Hence our models show that photochemical hydrocarbon aerosols are insignificant in the atmospheres of CEGPs. In contrast, Jupiter and Saturn have a much higher abundance of hydrocarbon aerosols in their atmospheres which are responsible for strong absorption shortward of 600 nm. Thus the insignificance of photochemical hydrocarbon aerosols in the atmospheres of CEGPs rules out one class of models with low albedos and featureless spectra shortward of 600 nm.Comment: ApJL accepte

Quasi-biennial oscillation and quasi-biennial oscillation--annual beat in the tropical total column ozone: A two-dimensional model simulation

The National Centers for Environmental Prediction–Department of Energy Reanalysis 2 data are used to calculate the monthly mean meridional circulation and eddy diffusivity from 1979 to 2002 for use in the California Institute of Technology–Jet Propulsion Laboratory two-dimensional (2-D) chemistry and transport model (CTM). This allows for an investigation of the impact of dynamics on the interannual variability of the tropical total column ozone for all years for which the Total Ozone Mapping Spectrometer and the Solar Backscatter Ultraviolet merged total ozone data are available. The first two empirical orthogonal functions (EOFs) of the deseasonalized and detrended stratospheric stream function capture 88% of the total variance on interannual timescales. The first EOF, accounting for over 70% of the interannual variance, is related to the quasi-biennial oscillation (QBO) and its interaction with annual cycles, the QBO-annual beat (QBO-AB). The 2-D CTM provides realistic simulations of the seasonal and interannual variability of ozone in the tropics. The equatorial ozone anomaly from the model is close to that derived from the observations. The phase and amplitude of the QBO are well captured by the model. The magnitude of the QBO signal is somewhat larger in the model than it is in the data. The QBO-AB found in the simulated ozone agrees well with that in the observed data

Methanol on Enceladus

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95284/1/grl26203.pd

Photolysis of sulphuric acid as the source of sulphur oxides in the mesosphere of Venus

The sulphur cycle plays fundamental roles in the chemistry and climate of Venus. Thermodynamic equilibrium chemistry at the surface of Venus favours the production of carbonyl sulphide and to a lesser extent sulphur dioxide. These gases are transported to the middle atmosphere by the Hadley circulation cell. Above the cloud top, a sulphur oxidation cycle involves conversion of carbonyl sulphide into sulphur dioxide, which is then transported further upwards. A significant fraction of this sulphur dioxide is subsequently oxidized to sulphur trioxide and eventually reacts with water to form sulphuric acid. Because the vapour pressure of sulphuric acid is low, it readily condenses and forms an upper cloud layer at altitudes of 60–70 km, and an upper haze layer above 70 km (ref. 9), which effectively sequesters sulphur oxides from photochemical reactions. Here we present simulations of the fate of sulphuric acid in the Venusian mesosphere based on the Caltech/JPL kinetics model, but including the photolysis of sulphuric acid. Our model suggests that the mixing ratios of sulphur oxides are at least five times higher above 90 km when the photolysis of sulphuric acid is included. Our results are inconsistent with the previous model results but in agreement with the recent observations using ground-based microwave spectroscopy and by Venus Express

Methanol on Enceladus

Near infrared spectra of the surface of Enceladus returned by Cassini show the presence of an absorption feature at 3.53 μm, ascribed by Brown et al. (2006) to “short chain organics,” and by Newman et al. (2007) to hydrogen peroxide. We assign this feature tentatively to methanol. Variations in the peak position of the feature suggest that methanol in the “tiger stripes” region may be segregated from the water ice, and not homogeneously distributed in the ice matrix. The photolytic destruction of methanol implies that methane or methanol itself must be continually deposited on the surface. On Enceladus, methanol may be generated photochemically from a mixed methane/water ice, or deposited from the plume itself. The variation in the concentration of methanol over the surface could be used to distinguish between these two processes

PLA Logistics and Sustainment: PLA Conference 2022

The US Army War College People’s Liberation Army Conference (PLA) Conference was held March 31 to April 2, 2022, at Carlisle Barracks, Pennsylvania. The conference focused on PLA logistics and sustainment. As the PLA continues to build and modernize its combat forces, it is important to examine if the capabilities meant to support combat operations are also being developed. Specific topics included: 1) China’s national-level logistics, including how China mobilizes national resources for the military and how it provides joint logistics support to the PLA Theater Commands; 2) the logistics capabilities of the different PLA services, especially the Army, Navy, and Air Forces; 3) PLA logistics in China’s remote regions, such as airpower projection in the Western Theater Command along the Indian border; and, 4) the PLA’s ability to sustain overseas operations at its base in Djibouti. Despite notable potential shortfalls and points of friction, the PLA has successfully sustained counterpiracy maritime operations for many years and conducted noncombatant evacuation operations well-distant from China. It is increasingly able to move forces across the vast distances of China and conduct large training exercises. Far more must be known about PLA sustainment and logistics before the hard questions about PLA operational reach and endurance can be answered.https://press.armywarcollege.edu/monographs/1954/thumbnail.jp

Excitatory Motor Neurons are Local Central Pattern Generators in an Anatomically Compressed Motor Circuit for Reverse Locomotion [preprint]

Central pattern generators are cell- or network-driven oscillators that underlie motor rhythmicity. The existence and identity of C. elegans CPGs remain unknown. Through cell ablation, electrophysiology, and calcium imaging, we identified oscillators for reverse locomotion. We show that the cholinergic and excitatory class A motor neurons exhibit intrinsic and oscillatory activity, and such an activity can drive reverse locomotion without premotor interneurons. Regulation of their oscillatory activity, either through effecting an endogenous constituent of oscillation, the P/Q/N high voltage-activated calcium channel UNC-2, or, via dual regulation, inhibition and activation, by the descending premotor interneurons AVA, determines the propensity, velocity, and sustention of reverse locomotion. Thus, the reversal motor executors themselves serve as oscillators; regulation of their intrinsic activity controls the reversal motor state. These findings exemplify anatomic and functional compression: motor executors integrate the role of rhythm generation in a locomotor network that is constrained by small cell numbers

Excitatory motor neurons are local oscillators for backward locomotion

Cell- or network-driven oscillators underlie motor rhythmicity. The identity of C. elegans oscillators remains unknown. Through cell ablation, electrophysiology, and calcium imaging, we show: (1) forward and backward locomotion is driven by different oscillators; (2) the cholinergic and excitatory A-class motor neurons exhibit intrinsic and oscillatory activity that is sufficient to drive backward locomotion in the absence of premotor interneurons; (3) the UNC-2 P/Q/N high-voltage-activated calcium current underlies A motor neuron\u27s oscillation; (4) descending premotor interneurons AVA, via an evolutionarily conserved, mixed gap junction and chemical synapse configuration, exert state-dependent inhibition and potentiation of A motor neuron\u27s intrinsic activity to regulate backward locomotion. Thus, motor neurons themselves derive rhythms, which are dually regulated by the descending interneurons to control the reversal motor state. These and previous findings exemplify compression: essential circuit properties are conserved but executed by fewer numbers and layers of neurons in a small locomotor network

Habitat change mediates the response of coral reef fish populations to terrestrial run-off

Coastal fish populations are typically threatened by multiple human activities, including fishing pressure and run-off of terrestrial pollution. Linking multiple threats to their impacts on fish populations is challenging because the threats may influence a species directly, or indirectly, via its habitats and its interactions with other species. Here we examine spatial variation in abundance of coral reef fish across gradients of fishing pressure and turbidity in Fiji. We explicitly account for multiple pathways of influence to test the alternative hypotheses that (1) habitat moderates predation by providing shelter, so habitat loss only affects prey fish populations if there are abundant predators, (2) habitat change co-drives biomass of both prey and predator functional groups. We examined responses of 7 fish functional groups and found that habitat change co-drives both predator and prey responses to turbidity. Abundances of all functional groups were associated with changes in habitat cover; however, the responses of their habitats to turbidity were mixed. Planktivore and piscivore abundance were lower in areas of high turbidity, because cover of their preferred habitats was lower. Invertivore, browser and grazer abundance did not change strongly over the turbidity gradient, because different components of their habitats exhibited both increases and decreases with turbidity. The effects of turbidity on fish populations were minor in areas where fish populations were already depleted by fishing. These findings suggest that terrestrial run-off modifies the composition of reef fish communities indirectly by affecting the benthic habitats that reef fish use