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Do Hesperian plateau channel networks record local or global climate conditions?. Mesoscale simulations with MRAMS of atmospheric response to chaos formation. Edwin Kite (UC Berkeley) Collaborators: Scot Rafkin & Tim Michaels (SwRI) Michael Manga (UC Berkeley). Outline.
Do Hesperian plateau channel networks record local or global climate conditions?
Scot Rafkin & Tim Michaels (SwRI)
Michael Manga (UC Berkeley)
Channels on the Valles Marineris plateau:
formed by chaos storms?
The Mars Regional Atmospheric Modeling
MOC NA R08-021292
Williams et al., LPSC, 2005
Milliken et al., GRL, 2008; Weitz et al., GRL, 2008
Bishop et al., JGR, 2009; Weitz et al., Icarus, in press
MEGAOUTFLO hypothesis: Vapor release to atmosphere by chaos outflows produces transient global greenhouse.
- Baker et al., Nature, 1991; Baker, Nature, 2001.
But hydrologic models suggest individual chaos-forming events were small.
- Andrews-Hanna & Phillips, JGR, 2007
Harrison & Grimm, JGR, 2008.
Therefore, a localized response to chaos formation might be expected – mesoscale, not global.
- e.g., Mangold et al., 2008.
Area of LLD
from Weitz et al., Icarus, in press
Forced by present-day (Ames) GCM
Pressure 2x present-day
Fixed lake surface temperature and elevation
Surface albedo -> 0.75 when water ice lands
Flooded to -1000m, just below spillway elevation
Grid resolution 8.33 km (finest grid)
approx. 40 CPU-days
Hypothesis: Given a chaos region filled to spillway with water at 5 deg C,
Mars Regional Atmospheric Modeling System (Rafkin et al., Icarus, 2001)
Non-hydrostatic mesoscale model
Used in landing-site downselect for MER, PHX, MSL
Boundary conditions supplied by GCM
Nested grids (8 km resolution on finest grid)
Water vapor treated as a trace gas
CARMA-derived ice and dust aerosol microphysics
Monin-Obukhov surface flux parameterization
Modified to include ITS-90 saturation vapor pressure
Steady state zone of precipitation has been established
Rates in inverted-
channel area are steady
Max. surface temp from control run (K)
With albedo 0.7, temperatures are always less than 273.15K.
Perron et al., JGR, 2006
dd =1.33 km-1
Atmospheric response is “hurricane-like”
- Water vapor mass ratio reaches 0.3 (>> trace)
Juventae channels correspond to a local maximum in water-ice precipitation
- No channels in available (CTX) images of the south chasm wall
Water-ice precipitation is highly localized
- Inverted channels on the Valles Marineris plateau far from paleolakes would disprove the localized-precipitation hypothesis
Chaos storms can mobilize sand and perhaps gravel but not boulders.
- Detection of HiRISE-resolvable clasts would be a severe
challenge for the localized-precipitation hypothesis
-- 4.18 K for fresh water
-- Sensible heat cooling < 1% of total cooling
McKenzie & Nimmo, Nature, 1999