Modelling Slope Microclimates in the Mars Planetary Climate Model

A large number of surface phenomena (e.g., frost and ice deposits, gullies, slope streaks, recurring slope lineae) are observed on Martian slopes. Their formation is associated with specific microclimates on these slopes that have been mostly studied with one-dimensional radiative balance models to date. We demonstrate here that any Martian slope can be thermally represented by a poleward or equatorward slope, i.e., the daily average, minimum, and maximum surface temperatures depend on the North-South component of the slope. Based on this observation, we propose here a subgrid-scale parameterization to represent slope microclimates in coarse-resolution global climate models. We implement this parameterization in the Mars Planetary Climate Model and validate it through comparisons with surface temperature measurements and frost detections on sloped terrains. With this new model, we show that these slope microclimates do not have a significant impact on the seasonal CO2 and H2O cycle. Our model also simulates for the first time the heating of the atmosphere by warm plains surrounding slopes. Active gullies are mostly found where our model predicts CO$_2$ frost, suggesting that the formation of gullies is mostly related to processes involving CO2 ice. However, the low thicknesses predicted there rule out mechanisms involving large amounts of ice. This model opens the way to new studies on surface-atmosphere interactions in present and past climates

A Reappraisal of Near-Tropical Ice Stability on Mars

Two arguments have suggested the presence of subsurface water ice at latitudes lower than 30\textdegree~on Mars. First, the absence of CO2 frost on pole-facing slopes was explained by the presence of subsurface ice. Second, models suggested that subsurface ice could be stable underneath these slopes. We revisit these arguments with a new slope microclimate model. Our model shows that below 30{\deg} latitude, slopes are warmer than previously estimated as the air above is heated by warm surrounding plains. This additional heat prevents the formation of CO2 and subsurface water ice for most slopes. Higher than 30{\deg}S, our model suggests the presence of subsurface water ice. In sparse cases (steep dusty slopes), subsurface ice may exist down to 25{\deg}S. While hypothetical unstable ice deposits cannot be excluded by our model, our results suggest that water ice is rarer than previously thought in the +- 30{\deg} latitude range considered for human exploration

Eruptions at Lone Star Geyser, Yellowstone National Park, USA: 1. Energetics and eruption dynamics

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 118 (2013): 4048–4062, doi:10.1002/jgrb.50251.Geysers provide a natural laboratory to study multiphase eruptive processes. We present results from a 4 day experiment at Lone Star Geyser in Yellowstone National Park, USA. We simultaneously measured water discharge, acoustic emissions, infrared intensity, and visible and infrared video to quantify the energetics and dynamics of eruptions, occurring approximately every 3 h. We define four phases in the eruption cycle (1) a 28±3 min phase with liquid and steam fountaining, with maximum jet velocities of 16–28 m s−1, steam mass fraction of less than ∼0.01. Intermittently choked flow and flow oscillations with periods increasing from 20 to 40 s are coincident with a decrease in jet velocity and an increase of steam fraction; (2) a 26±8 min posteruption relaxation phase with no discharge from the vent, infrared (IR), and acoustic power oscillations gliding between 30 and 40 s; (3) a 59±13 min recharge period during which the geyser is quiescent and progressively refills, and (4) a 69±14 min preplay period characterized by a series of 5–10 min long pulses of steam, small volumes of liquid water discharge, and 50–70 s flow oscillations. The erupted waters ascend from a 160–170°C reservoir, and the volume discharged during the entire eruptive cycle is 20.8±4.1 m3. Assuming isentropic expansion, we calculate a heat output from the geyser of 1.4–1.5 MW, which is <0.1% of the total heat output from Yellowstone Caldera.Support comes from NSF (L. Karlstrom, M. Manga), the USGS Volcano Hazards program (S. Hurwitz, F. Murphy, M.J.S. Johnston, and R.B. McCleskey), and WHOI (R. Sohn).2014-02-1

Challenges in Mars climate modelling with the LMD Mars Global Climate Model, now called the Mars “Planetary Climate Model” (PCM)

The Mars atmosphere Global Climate Model (GCM) developed at the Laboratoire de Météorologie Dynamique [1] in collaboration with several teams around the world (LATMOS, the Instituto de Astrofisica de Andalucia, UAE University, University of Oxford, The Open University), and with the support of ESA and CNES is currently used for many kinds of applications. It simulates Mars from the subsurface to the top of the thermosphere and includes the cycles of dust, water and CO2 that control the current Martian climate as well as a photo-chemical/ionospheric module. The aim of this modeling is high: ultimately to build a numerical simulator based only on universal equations, yet able to consistently reproduce available observations. The goal is to create a realistic virtual planet on which all observed phenomena and climate-induced geological landforms arise naturally. Like for the other similar models in the community, this specific goal is a scientific endeavour by itself. Such a GCM can also provide useful environmental predictions that can be used to process observations or prepare space missions. For this purpose our teams have produced the Mars Climate Database (See Millour et al., this issue) which provides climatologies derived from GCM simulations completed by dedicated tools. The GCM is also used to perform meteorological data assimilation to create an optimal description of the Martian environment obtained by combining observation and model simulations (See e.g. Young et al., Read et al., Holmes et al., this issue)

A case study of resistivity and self-potential signatures of hydrothermal instabilities, Inferno Crater Lake, Waimangu, New Zealand

International audienceInferno Crater Lake, Waimangu, one of the largest hot springs in New Zealand, displays vigorous cyclic behavior in lake level and temperature. It provides a natural small-scale laboratory for investigating the geo-electrical signature of fluid flows. We measured self-potential and electrical resistivity to see whether the huge variations of fluid volume, approximately 60,000 m3 during a mean cycle period of 40 days, could be detected. Electrical resistivity measurements revealed spectacular changes over time, with the medium becoming more conductive as the lake receded. This result is consistent with analog models, where the vapor phase is replaced by liquid at recession. The self-potential survey did not detect temporal changes related to fluid movements. This can be explained by the pH of the pore water (∼2.3), which is close to the point of zero charge of silica

Water Supersaturation for Early Mars

International audienceEvidence of past liquid water flowing on the surface of Mars has been identified since the first orbital mission to the planet. However, reconstructing the climate that would allow liquid water at the surface is still an intense area of research. Previous studies showed that an atmosphere composed only of CO2 and H2O could not sustain surface temperatures above the freezing point of water. Different solutions have been studied, ranging from events like impacts on different atmospheric compositions, or even radiative feedback of water clouds that would create a dramatic greenhouse effect. In this context, we propose to study whether the supersaturation of water could warm the planet. Strong supersaturation is observed in the present-day Martian atmosphere. On early Mars, supersaturation could enhance the greenhouse effect through strong absorption of the IR flux by water vapor or by modifying water clouds. While 1D modeling suggests a significant impact, our 3D model shows that warming the climate of early Mars requires a high supersaturation ratio, especially in the lower layers of the atmosphere. This configuration seems highly unrealistic since the level of supersaturation is higher than what would be expected in a dense atmosphere

A Reappraisal of Subtropical Subsurface Water Ice Stability on Mars

International audienceAbstract Massive reservoirs of subsurface water ice in equilibrium with atmospheric water vapor are found poleward of 45° latitude on Mars. The absence of CO 2 frost on steep pole‐facing slopes and simulations of atmospheric‐soil water exchanges suggested that water ice could be stable underneath these slopes down to 25° latitude. We revisit these arguments with a new slope microclimate model. Our model shows that below 30° latitude, slopes are warmer than previously estimated as the air above is heated by warm surrounding plains. This additional heat prevents the formation of surface CO 2 frost and subsurface water ice for most slopes. Our model suggests the presence of subsurface water ice beneath pole‐facing slopes down to 30° latitude, and possibly 25° latitude on sparse steep dusty slopes. While unstable ice deposits might be present, our results suggest that water ice is rarer than previously thought in the ±30° latitude range considered for human exploration