Mesoscale simulations with MRAMS of atmospheric response to chaos formation
Do Hesperian plateau channel networks record local or global climate conditions?
Edwin Kite (UC Berkeley) Collaborators: Scot Rafkin & Tim Michaels (SwRI) Michael Manga (UC Berkeley)
Outline Channels on the Valles Marineris plateau:
formed by chaos storms? The Mars Regional Atmospheric Modeling
System (MRAMS) Boundary conditions Results
Plateau channel networks• Remarkably late in Martian
history– Overlie Late Hesperian lavas– Main epoch of valley network
formation tightly constrained to Late Noachian – Early Hesperian (Fassett & Head, JGR, 2008)
• Associated with opal, ‘jarosite’ bearing light-toned layered deposits
• Sometimes inverted relief• No HiRISE-resolved clasts• Multiple periods of flow; in
places, flow direction changed over time
• Strong evidence for precipitation, not groundwater– Drainage density, branching order,
tributaries extend to near ridges– Phase (rain vs. snow) not clear
• Local, regional or global climate change?
Williams et al., LPSC, 2005Milliken et al., GRL, 2008; Weitz et al., GRL, 2008
Bishop et al., JGR, 2009; Weitz et al., Icarus, in press
MO
C N
A R
08-0
2129
2
1.5km
Localized, chaos-induced precipitation?
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.
Test
loca
tion:
Juve
ntae
Flooding level
Forced by present-day (Ames) GCMPressure 2x present-dayFixed lake surface temperature and elevationSurface albedo -> 0.75 when water ice landsFlooded to -1000m, just below spillway elevationGrid resolution 8.33 km (finest grid)approx. 40 CPU-days 50km
-1000 mcontour
spillway
Area of inverted channels Area of LLD
from Weitz et al., Icarus, in press
crater
OUTFLOW
CHANNEL
Hypothesis test with MRAMS
Mars Regional Atmospheric Modeling System (Rafkin et al., Icarus, 2001)
Non-hydrostatic mesoscale modelUsed in landing-site downselect for MER, PHX, MSLBoundary conditions supplied by GCMNested 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 parameterizationModified to include ITS-90 saturation vapor pressure
Hypothesis: Given a chaos region filled to spillway with water at 5 deg C,
(1)Precipitation location matches mapped light-toned layered deposits(2)Precipitation magnitude can move sediment through mapped inverted channels.
Atmospheric response
460 km
42 k
m
FloodedJuventae Chasmafloor
Observed layereddeposits
X-Zsection
ALL RESULTSARE PRELIMINARY
peak ~ 1.4%
MGCM, 1.25 days water release:Ls = 270°, PCO2 = 2 x PAL
Steady state zone of precipitation has been established1.25 days
640 km
Rates in inverted-channel area are steady
Precipitation
SnowPeak value:3.96 g/cm^2 in 1.25 daysIn 1 Earth year, 1200 g/cm^2
Strong precip on chasm walls expected ALL RESULTSARE PRELIMINARY
Mean ice precip rate in mm/hr
W-directed winds + promontory effect + rapid rainout
Area of channels Area of LLD
from Weitz et al., Icarus, in press
Precipitation is highly localized
At 2 x PAL CO2, conditions on the plateau permit melting of precipitated water ice
Max. air temp from control run Max. surface temp from control run (K)
With albedo 0.7, temperatures are always less than 273.15K.
Modeled precipitation rates are sufficient to move gravel through mapped channels
Perron et al., JGR, 2006
PS
P_0
0372
4_17
55
dd =1.33 km-1
Outstanding issues / Next steps1) Physics:
Sensitivity tests show a trend of reduced vapor release with reduced grid spacing in z; The model has an inadequately-resolved water vapor concentration boundary layer.
Treat water vapor as a bulk constituent of the atmosphere - Pressure & virtual temperature effects of H2Ov (pressure source; different molecular mass)
Self-consistent lake thermodynamicsWind-dependent lake surface roughness parameterization from Shieh et al., 1979New locations: Echus & Ganges
2) Geology:
Are modelled precipitation rates sufficient to initiate observed channel network?
Look for additional inverted channels/layered deposits around chaos rims.
Search for opal or jarosite bearing deposits on the plateau far from candidate paleolakes(would disprove the localized-precipitation hypothesis).
SummaryAtmospheric 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
Backup slides
What is the range of acceptable lake surface temperatures?
• Vapor -> atm. will be small unless freezing of top of lake can be delayed -- 4.18 K for fresh water
• In model, evaporative cooling ~ 2 KW/m2 -- Sensible heat cooling < 1% of total cooling
• Heat sources– fracturing mixes reservoirs
that are isolated by low permeability
– Shear heating– Clathrate decomposition (?)– Most important: volcanic
heating – Warmest (deepest) water will
arrive last (Andrews-Hanna & Phillips, 2007).
McKenzie & Nimmo, Nature, 1999