Soil ice in land-atmosphere coupling over the United States
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Soil ice in land-atmosphere coupling over the United States
Ahmed B Tawfik & Allison L Steiner
Mathew Taormina - Aviation
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Why dirt water can be important during that 4-5 month dead period we
called winter. And super computers.Mathew Taormina
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Schedule of events
• Introduction of the study• Methods• Results• Summary• Q & A (more Q , less A)
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The Study
The question:
What is the impact of soil moisture and its
phase in land-atmosphere coupling,
during winter?
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The Study
Why this question? Aren’t there more
interesting questions to ask about
climatological feedback mechanisms?
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The Study
Almost certainly!
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The Study
But…
The soil moisture has an important role in
surface energy balance and the
subsequent magnitude of the Sensible
Heat and Latent Heat fluxes.
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The Study
Surface energy balance:
Incoming shortwave + Incoming longwave =
Reflected shortwave + Emitted longwave + Latent
heat flux + Sensible heat flux + Subsurface
conduction
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The Study
Sensible Heat Flux:
SH = Cd Cp V (Tsfc - Tair)
Latent Heat Flux:
LH = Cd L V (qsfc - qair)
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The Study
This mechanism has been documented
during boreal summer, but is often
neglected during winter (too weak).
How do these interactions differ when soil
moisture becomes ice?
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Next…
• Introduction of the study• Methods• Results• Summary• Q & A (mostly Q , less A)
You are here
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Methods
Models:
• The Abdus Salaa, International Center
for Theoretical Physics (ICTP) Regional
Climate model (RegCM)
• National Center for Atmospheric
Research (NCAR) Community Land
Model (CLM) version 3.5
CLM 3.5 ?!? THAT’S MY FAVORITE
VERSION!
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Methods
• Two 23-year simulations were run from
1982-2004.
• RunI allows the surface to interact
freely as per atmospheric update cycle.
• RunC uses climatological surface
moisture to represent an uncoupled
land surface.
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Methods
• The Northern Great Planes were a
strong area of focus due to stronger
coupling and clear seasonal transition.
• RunC was restricted to climatological
averages from RunI.
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Methods
Changes in atmospheric variables are
caused by changes in soil moisture.
Standard deviation difference is used to
measure coupling:
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Methods
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Next…
• Introduction of the study• Methods• Results• Summary• Q & A
You are here
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ResultsGreater coupling strength is found in October-April than in the summer months. These areas “migrate” with the freezing line.
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ResultsThe snow albedo feedback was expected to enhance colder surface temperatures and have a greater affect on available surface energy.
However, there was no substantial difference in absorbed solar radiation between RunI and RunC, but there were observed differences in longwave emission
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What does this mean???
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ResultsStefan-Boltzmann Law?
Liquid soil moisture is key to controlling ground temperature variability.
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Results
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Next…
• Introduction of the study• Methods• Results• Summary• Q & A
You are here
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SummaryThe impact of winter soil moisture in land-atmosphere feedback coupling is the ability for soil water phase to control surface fluxes.
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SummaryThe feedbacks from these fluxes are rooted from ground temperature (which is a function of percentage liquid moisture).
These temperature differences influence available surface energy and can affect the vertical structure of the atmosphere in excess of 700mb during transition months (MSE, large scale precipitation, convective precipitation).
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Summary
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SummarySoil moisture phase seems more relevant than temperature during winter months.
Ensembles need to be ran. Model biases are minimized but they may enhance or dampen coupling strength.
What do we do with this observed feedback?
Questions?
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