We investigate the conditions that will promote explosive volcanic activity on Venus. Conduit processes were simulated using a steady-state, isothermal, homogeneous flow model in tandem with a degassing model. The response of exit pressure, exit velocity, and degree of volatile exsolution was explored over a range of volatile concentrations (H2O and CO2), magma temperatures, vent altitudes, and conduit geometries relevant to the Venusian environment. We find that the addition of CO2 to an H2O-driven eruption increases the final pressure, velocity, and volume fraction gas. Increasing vent elevation leads to a greater degree of magma fragmentation, due to the decrease in the final pressure at the vent, resulting in a greater likelihood of explosive activity. Increasing the magmatic temperature generates higher final pressures, greater velocities, and lower final volume fraction gas values with a correspondingly lower chance of explosive volcanism. Cross-sectionally smaller, and/or deeper, conduits were more conducive to explosive activity. Model runs show that for an explosive eruption to occur at Scathach Fluctus, at Venus’ mean planetary radius (MPR), 4.5% H2O or 3% H2O with 3% CO2 (from a 25 m radius conduit) would be required to initiate fragmentation; at Ma’at Mons (~9 km above MPR) only ~2% H2O is required. A buoyant plume model was used to investigate plume behaviour. It was found that it was not possible to achieve a buoyant column from a 25 m radius conduit at Scathach Fluctus, but a buoyant column reaching up to ~20 km above the vent could be generated at Ma’at Mons with an H2O concentration of 4.7% (at 1300 K) or a mixed volatile concentration of 3% H2O with 3% CO2 (at 1200 K). We also estimate the flux of volcanic gases to the lower atmosphere of Venus, should explosive volcanism occur. Model results suggest explosive activity at Scathach Fluctus would result in an H2O flux of ~107 kg s−1. Were Scathach Fluctus emplaced in a single event, our model suggests that it may have been emplaced in a period of ~15 days, supplying 1–2×104 Mt H2O to the atmosphere locally. An eruption of this scale might increase local atmospheric H2O abundance by several ppm over an area large enough to be detectable by near-infrared nightside sounding using the 1.18 µm spectral window such as that carried out by the Venus Express/VIRTIS spectrometer. Further interrogation of the VIRTIS dataset is recommended to search for ongoing volcanism on Venus
Abstract. A tethered-balloon system (TBS) has been developed and is being operated by Sandia National Laboratories (SNL) on behalf of the U.S. Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) User Facility in order to collect in situ atmospheric measurements within mixed-phase Arctic clouds. Periodic tethered-balloon flights have been conducted since 2015 within restricted airspace at ARM's Advanced Mobile Facility 3 (AMF3) in Oliktok Point, Alaska, as part of the AALCO (Aerial Assessment of Liquid in Clouds at Oliktok), ERASMUS (Evaluation of Routine Atmospheric Sounding Measurements using Unmanned Systems), and POPEYE (Profiling at Oliktok Point to Enhance YOPP Experiments) field campaigns. The tethered-balloon system uses helium-filled 34 m3 helikites and 79 and 104 m3 aerostats to suspend instrumentation that is used to measure aerosol particle size distributions, temperature, horizontal wind, pressure, relative humidity, turbulence, and cloud particle properties and to calibrate ground-based remote sensing instruments. Supercooled liquid water content (SLWC) sondes using the vibrating-wire principle, developed by Anasphere Inc., were operated at Oliktok Point at multiple altitudes on the TBS within mixed-phase clouds for over 200 h. Sonde-collected SLWC data were compared with liquid water content derived from a microwave radiometer, Ka-band ARM zenith radar, and ceilometer at the AMF3, as well as liquid water content derived from AMF3 radiosonde flights. The in situ data collected by the Anasphere sensors were also compared with data collected simultaneously by an alternative SLWC sensor developed at the University of Reading, UK; both vibrating-wire instruments were typically observed to shed their ice quickly upon exiting the cloud or reaching maximum ice loading. Temperature sensing measurements distributed with fiber optic tethered balloons were also compared with AMF3 radiosonde temperature measurements. Combined, the results indicate that TBS-distributed temperature sensing and supercooled liquid water measurements are in reasonably good agreement with remote sensing and radiosonde-based measurements of both properties. From these measurements and sensor evaluations, tethered-balloon flights are shown to offer an effective method of collecting data to inform and constrain numerical models, calibrate and validate remote sensing instruments, and characterize the flight environment of unmanned aircraft, circumventing the difficulties of in-cloud unmanned aircraft flights such as limited flight time and in-flight icing.
A new analysis of the spatial relationships between volcanic features and rifts on Venus provides new constraints on models of planetary evolution. We developed a new database of volcanic features for the Beta‐Atla‐Themis (BAT) region and used nearest neighbor measurements to determine relationships between different types of volcanic features and the rifts. Nearest neighbor analysis shows that all the dome‐type and corona‐type subpopulations tend to cluster. Rift associations were inferred from the deviation of a feature's population distribution (as a function of distance from rift) from that of a random population. Dome‐type features in general have no discernible relationship with rifts. Most corona‐type features have a strong association with rifts, with intermediate and large volcanoes also tending to occur close to or on rifts. Shield fields, on the other hand, tend to occur away from rifts. Our new evidence supports classifications of rifts on Venus into different types, possibly by age, with a shift from globally dispersed (more uniform) volcanism toward the more rift‐focused distribution, which suggests a shift in tectonic regime. Our observations are consistent with recent models proposing the evolution of Venus from a stagnant lid regime to a subcrustal spreading regime. We also present evidence for a failed rift on Venus and note that this process may be analogous, albeit on a larger scale, to a proposed model for the evolution of the East African rift system.
Charge is observed in clouds of all forms, which may influence their development and properties. In-cloud charge measurements require a wide dynamic range, extending from charge in aerosols and dusts to that present in thunderstorms. Unexpectedly large charge densities (>200 pC m) have recently been detected in layer clouds using balloon-carried linear electrometers. These, however, lead to instrument saturation if sufficient sensitivity for aerosol and droplet charge is maintained. Logarithmic electrometers provide an alternative but suffer strong non-linear thermal effects. This is a limitation for balloon-carried instruments that encounter temperature changes up to ∼100 °C, as full thermal compensation requires complexity inappropriate for disposable devices. Here, a novel hybrid system is described, combining linear and logarithmic electrometers to provide extended dynamic range (±50 pA), employing the negligible (±4%) total temperature drift of the linear device to provide in situ calibration of the logarithmic device. This combination opens up new measurement opportunities for charge in clouds, dusts, and aerosols.
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