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  author = {{Turbet}, M. and {Gillmann}, C. and {Forget}, F. and {Baudin}, B. and 
	{Palumbo}, A. and {Head}, J. and {Karatekin}, O.},
  title = {{The environmental effects of very large bolide impacts on early Mars explored with a hierarchy of numerical models}},
  journal = {\icarus},
  archiveprefix = {arXiv},
  eprint = {1902.07666},
  primaryclass = {astro-ph.EP},
  year = 2020,
  volume = 335,
  eid = {113419},
  pages = {113419},
  abstract = {{The origin of the presence of geological and mineralogical evidence that
liquid water flowed on the surface of early Mars is now a 50-year-old
mystery. It has been proposed (Segura et al., 2002, 2008, 2012) that
bolide impacts could have triggered a long-term climate change,
producing precipitation and runoff that may have altered the surface of
Mars in a way that could explain (at least part of) this evidence. Here
we use a hierarchy of numerical models (a 3-D Global Climate Model, a
1-D radiative-convective model and a 2-D Mantle Dynamics model) to test
that hypothesis and more generally explore the environmental effects of
very large bolide impacts (D$_{impactor}$ $\gt$ 100 km, or
D$_{crater}$ $\gt$ 600 km) on the atmosphere, surface and interior
of early Mars.

Using a combination of 1-D and 3-D climate simulations, we show that the
environmental effects of the largest impact events recorded on Mars are
characterized by: (i) a short impact-induced warm period (several tens
of Earth years for the surface and atmosphere to be back to ambient
conditions after very large impact events); (ii) a low amount of
hydrological cycling of water (because the evaporation of precipitation
that reached the ground is extremely limited). The total cumulative
amount of precipitation (rainfall) can be reasonably well approximated
by the initial post-impact atmospheric reservoir of water vapour (coming
from the impactor, the impacted terrain and from the sublimation of
permanent ice reservoirs heated by the hot ejecta layer); (iii)
deluge-style precipitation ({\sim}2.6 m Global Equivalent Layer of
surface precipitation per Earth year for our reference simulation,
quantitatively in agreement with previous 1-D cloud free climate
calculations of Segura et al., 2002), and (iv) precipitation patterns
that are uncorrelated with the observed regions of valley networks.

However, we show that the impact-induced stable runaway greenhouse state
predicted by Segura et al. (2012) should not be achievable if convection
and water vapour condensation processes are considered. We nevertheless
confirm the results of Segura et al. (2008) and Urata and Toon (2013)
that water ice clouds could in theory significantly extend the duration
of the post-impact warm period, and even for cloud coverage
significantly lower than predicted in Ramirez and Kasting (2017).
However, the range of cloud microphysical properties for which this
scenario works is very narrow.

Using 2-D Mantle Dynamics simulations we find that large bolide impacts
can produce a strong thermal anomaly in the mantle of Mars that can
survive and propagate for tens of millions of years. This thermal
anomaly could raise the near-surface internal heat flux up to several
hundreds of mW/m$^{2}$ (i.e. up to {\sim}10 times the ambient flux)
for several millions years at the edges of the impact crater. However,
such internal heat flux is largely insufficient to keep the martian
surface above the melting point of water.

In addition to the poor temporal correlation between the formation of
the largest basins and valley networks (Fassett and Head, 2011), these
arguments indicate that the largest impact events are unlikely to be the
direct cause of formation of the Noachian valley networks. Our numerical
results support instead the prediction of Palumbo and Head (2018) that
very large impact-induced rainfall could have caused degradation of
large craters, erased small craters, and formed smooth plains,
potentially erasing much of the previously visible morphological surface
history. Such hot rainfalls may have also led to the formation of
aqueous alteration products on Noachian-aged terrains, which is
consistent with the timing of formation of clays.
  doi = {10.1016/j.icarus.2019.113419},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Spiga}, A. and {Guerlet}, S. and {Millour}, E. and {Indurain}, M. and 
	{Meurdesoif}, Y. and {Cabanes}, S. and {Dubos}, T. and {Leconte}, J. and 
	{Boissinot}, A. and {Lebonnois}, S. and {Sylvestre}, M. and 
	{Fouchet}, T.},
  title = {{Global climate modeling of Saturn's atmosphere. Part II: Multi-annual high-resolution dynamical simulations}},
  journal = {\icarus},
  archiveprefix = {arXiv},
  eprint = {1811.01250},
  primaryclass = {astro-ph.EP},
  year = 2020,
  volume = 335,
  eid = {113377},
  pages = {113377},
  abstract = {{The Cassini mission unveiled the intense and diverse activity in
Saturn's atmosphere: banded jets, waves, vortices, equatorial
oscillations. To set the path towards a better understanding of those
phenomena, we performed high-resolution multi-annual numerical
simulations of Saturn's atmospheric dynamics. We built a new Global
Climate Model [GCM] for Saturn, named the Saturn DYNAMICO GCM, by
combining a radiative-seasonal model tailored for Saturn to a
hydrodynamical solver based on an icosahedral grid suitable for
massively-parallel architectures. The impact of numerical dissipation,
and the conservation of angular momentum, are examined in the model
before a reference simulation employing the Saturn DYNAMICO GCM with a
1/2{\deg} latitude-longitude resolution is considered for analysis.
Mid-latitude banded jets showing similarity with observations are
reproduced by our model. Those jets are accelerated and maintained by
eddy momentum transfers to the mean flow, with the magnitude of momentum
fluxes compliant with the observed values. The eddy activity is not
regularly distributed with time, but appears as bursts; both barotropic
and baroclinic instabilities could play a role in the eddy activity. The
steady-state latitude of occurrence of jets is controlled by poleward
migration during the spin-up of our model. At the equator, a
weakly-superrotating tropospheric jet and vertically-stacked alternating
stratospheric jets are obtained in our GCM simulations. The model
produces Yanai (Rossby-gravity), Rossby and Kelvin waves at the equator,
as well as extratropical Rossby waves, and large-scale vortices in polar
regions. Challenges remain to reproduce Saturn's powerful superrotating
jet and hexagon-shaped circumpolar jet in the troposphere, and
downward-propagating equatorial oscillation in the stratosphere.
  doi = {10.1016/j.icarus.2019.07.011},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Lefèvre}, M. and {Spiga}, A. and {Lebonnois}, S.},
  title = {{Mesoscale modeling of Venus' bow-shape waves}},
  journal = {\icarus},
  archiveprefix = {arXiv},
  eprint = {1902.07010},
  primaryclass = {astro-ph.EP},
  year = 2020,
  volume = 335,
  eid = {113376},
  pages = {113376},
  abstract = {{The Akatsuki instrument LIR measured an unprecedented wave feature at
the top of Venusian cloud layer. Stationary bow-shape waves of thousands
of kilometers large lasting several Earth days have been observed over
the main equatorial mountains. Here we use for the first time a
mesoscale model of the Venus's atmosphere with high-resolution
topography and fully coupled interactive radiative transfer
computations. Mountain waves resolved by the model form large-scale bow
shape waves with an amplitude of about 1.5 K and a size up to several
decades of latitude similar to the ones measured by the Akatsuki
spacecraft. The maximum amplitude of the waves appears in the afternoon
due to an increase of the near-surface stability. Propagating vertically
the waves encounter two regions of low static stability, the mixed layer
between approximately 18 and 30 km and the convective layer between 50
and 55 km. Some part of the wave energy can pass through these regions
via wave tunneling. These two layers act as wave filter, especially the
deep atmosphere layer. The encounter with these layers generates trapped
lee waves propagating horizontally. No stationary waves is resolved at
cloud top over the polar regions because of strong circumpolar transient
waves, and a thicker deep atmosphere mixed layer that filters most of
the mountain waves.
  doi = {10.1016/j.icarus.2019.07.010},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}