91 research outputs found
The Potential Importance of Non-Local, Deep Transport on the Energetics, Momentum, Chemistry, and Aerosol Distributions in the Atmospheres of Earth, Mars and Titan
A review of non-local, deep transport mechanisms in the atmosphere of Earth
provides a good foundation for examining whether similar mechanisms are
operating in the atmospheres of Mars and Titan. On Earth, deep convective
clouds in the tropics constitute the upward branch of the Hadley Cell and
provide a conduit through which energy, moisture, momentum, aerosols and
chemical species are moved from the boundary layer to the upper troposphere and
lower stratosphere. This transport produces mid-tropospheric minima in
quantities such as water vapor and moist static energy and maxima where the
clouds detrain. Analogs to this terrestrial transport are found in the strong
and deep thermal circulations associated with topography on Mars and with Mars
dust storms. Observations of elevated dust layers on Mars further support the
notion that non-local deep transport is an important mechanism in the
atmosphere of Mars. On Titan, the presence of deep convective clouds almost
assures that non-local, deep transport is occurring and these clouds may play a
role in global cycling of energy, momentum, and methane. Based on the potential
importance of non-local deep transport in Earth's atmosphere and supported by
evidence for such transport in the atmospheres of Mars and Titan, greater
attention to this mechanism in extraterrestrial atmospheres is warranted.Comment: 25 pages, no figures, no table
Atmospheric risk assessment for the Mars Science Laboratory entry, descent, and landing system
In 2012, the Mars Science Laboratory (MSL) mission will pioneer the next generation of robotic Entry, Descent, and Landing (EDL) systems, by delivering the largest and most capable rover to date to the surface of Mars. As with previous Mars landers, atmospheric conditions during entry, descent, and landing directly impact the performance of MSL's EDL system. While the vehicle's novel guided entry system allows it to "fly out" a range of atmospheric uncertainties, its trajectory through the atmosphere creates a variety of atmospheric sensitivities not present on previous Mars entry systems and landers. Given the mission's stringent landing capability requirements, understanding the atmosphere state and spacecraft sensitivities takes on heightened importance. MSL's guided entry trajectory differs significantly from recent Mars landers and includes events that generate different atmospheric sensitivities than past missions. The existence of these sensitivities and general advancement in the state of Mars atmospheric knowledge has led the MSL team to employ new atmosphere modeling techniques in addition to past practices. A joint EDL engineering and Mars atmosphere science and modeling team has been created to identify the key system sensitivities, gather available atmospheric data sets, develop relevant atmosphere models, and formulate methods to integrate atmosphere information into EDL performance assessments. The team consists of EDL engineers, project science staff, and Mars atmospheric scientists from a variety of institutions. This paper provides an overview of the system performance sensitivities that have driven the atmosphere modeling approach, discusses the atmosphere data sets and models employed by the team as a result of the identified sensitivities, and introduces the tools used to translate atmospheric knowledge into quantitative EDL performance assessments
Dependence of the Martian radiation environment on atmospheric depth: Modeling and measurement
The energetic particle environment on the Martian surface is influenced by
solar and heliospheric modulation and changes in the local atmospheric pressure
(or column depth). The Radiation Assessment Detector (RAD) on board the Mars
Science Laboratory rover Curiosity on the surface of Mars has been measuring
this effect for over four Earth years (about two Martian years). The
anticorrelation between the recorded surface Galactic Cosmic Ray-induced dose
rates and pressure changes has been investigated by Rafkin et al. (2014) and
the long-term solar modulation has also been empirically analyzed and modeled
by Guo et al. (2015). This paper employs the newly updated HZETRN2015 code to
model the Martian atmospheric shielding effect on the accumulated dose rates
and the change of this effect under different solar modulation and atmospheric
conditions. The modeled results are compared with the most up-to-date (from 14
August 2012 to 29 June 2016) observations of the RAD instrument on the surface
of Mars. Both model and measurements agree reasonably well and show the
atmospheric shielding effect under weak solar modulation conditions and the
decline of this effect as solar modulation becomes stronger. This result is
important for better risk estimations of future human explorations to Mars
under different heliospheric and Martian atmospheric conditions
The impact of lake shape and size on lake breezes and air-lake exchanges on Titan
Titan, the largest moon of Saturn, has many lakes on its surface, formed
mainly of liquid methane. Like water lakes on Earth, these methane lakes on
Titan likely profoundly affect the local climate. Previous studies (Rafkin and
Soto 2020, Chatain et al 2022) showed that Titan's lakes create lake breeze
circulations with characteristic dimensions similar to the ones observed on
Earth. However, such studies used a model in two dimensions; this work
investigates the consequences of the addition of a third dimension to the
model. Our results show that 2D simulations tend to overestimate the extension
of the lake breeze over the land, and underestimate the strength of the
subsidence over the lake, due to divergence/convergence geometrical effects in
the mass conservation equations. In addition, 3D simulations including a large
scale background wind show the formation of a pocket of accelerated wind behind
the lake, which did not form in 2D simulations. An investigation of the effect
of shoreline concavity on the resulting air circulation shows the formation of
wind currents over peninsulas. Simulations with several lakes can either result
in the formation of several individual lake breeze cells (during the day), or
the emergence of a large merged cell with internal wind currents between lakes
(during the night). Simulations of several real-shaped lakes located at a
latitude of 74{\deg}N on Titan at the spring equinox show that larger lakes
trigger stronger winds, and that some sections of lakes might accumulate enough
methane vapor to form a thin fog. The addition of a third dimension, along with
adjustments in the parametrizations of turbulence and subsurface land
temperature, results in a reduction in the magnitude of the average lake
evaporate rate, namely to ~6 cm/Earth year.Comment: Submitted to Icarus on 2023-07-21. Dataset available at the DOI:
10.5281/zenodo.817227
Atmosphere Assessment for MARS Science Laboratory Entry, Descent and Landing Operations
On August 6, 2012, the Mars Science Laboratory rover, Curiosity, successfully landed on the surface of Mars. The Entry, Descent and Landing (EDL) sequence was designed using atmospheric conditions estimated from mesoscale numerical models. The models, developed by two independent organizations (Oregon State University and the Southwest Research Institute), were validated against observations at Mars from three prior years. In the weeks and days before entry, the MSL "Council of Atmospheres" (CoA), a group of atmospheric scientists and modelers, instrument experts and EDL simulation engineers, evaluated the latest Mars data from orbiting assets including the Mars Reconnaissance Orbiter's Mars Color Imager (MARCI) and Mars Climate Sounder (MCS), as well as Mars Odyssey's Thermal Emission Imaging System (THEMIS). The observations were compared to the mesoscale models developed for EDL performance simulation to determine if a spacecraft parameter update was necessary prior to entry. This paper summarizes the daily atmosphere observations and comparison to the performance simulation atmosphere models. Options to modify the atmosphere model in the simulation to compensate for atmosphere effects are also presented. Finally, a summary of the CoA decisions and recommendations to the MSL project in the days leading up to EDL is provided
Modeling the variations of Dose Rate measured by RAD during the first MSL Martian year: 2012-2014
The Radiation Assessment Detector (RAD), on board Mars Science Laboratory's
(MSL) rover Curiosity, measures the {energy spectra} of both energetic charged
and neutral particles along with the radiation dose rate at the surface of
Mars. With these first-ever measurements on the Martian surface, RAD observed
several effects influencing the galactic cosmic ray (GCR) induced surface
radiation dose concurrently: [a] short-term diurnal variations of the Martian
atmospheric pressure caused by daily thermal tides, [b] long-term seasonal
pressure changes in the Martian atmosphere, and [c] the modulation of the
primary GCR flux by the heliospheric magnetic field, which correlates with
long-term solar activity and the rotation of the Sun. The RAD surface dose
measurements, along with the surface pressure data and the solar modulation
factor, are analysed and fitted to empirical models which quantitatively
demonstrate} how the long-term influences ([b] and [c]) are related to the
measured dose rates. {Correspondingly we can estimate dose rate and dose
equivalents under different solar modulations and different atmospheric
conditions, thus allowing empirical predictions of the Martian surface
radiation environment
Oxidant Enhancement in Martian Dust Devils and Storms: Implications for Life and Habitability
We investigate a new mechanism for producing oxidants, especially hydrogen peroxide (H2O2), on Mars. Large-scale electrostatic fields generated by charged sand and dust in the martian dust devils and storms, as well as during normal saltation, can induce chemical changes near and above the surface of Mars. The most dramatic effect is found in the production of H2O2 whose atmospheric abundance in the "vapor" phase can exceed 200 times that produced by photochemistry alone. With large electric fields, H2O2 abundance gets large enough for condensation to occur, followed by precipitation out of the atmosphere. Large quantities of H2O2 would then be adsorbed into the regolith, either as solid H2O2 "dust" or as re-evaporated vapor if the solid does not survive as it diffuses from its production region close to the surface. We suggest that this H2O2, or another superoxide processed from it in the surface, may be responsible for scavenging organic material from Mars. The presence of H2O2 in the surface could also accelerate the loss of methane from the atmosphere, thus requiring a larger source for maintaining a steady-state abundance of methane on Mars. The surface oxidants, together with storm electric fields and the harmful ultraviolet radiation that readily passes through the thin martian atmosphere, are likely to render the surface of Mars inhospitable to life as we know it.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63211/1/ast.2006.6.439.pd
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