Soil ice in land-atmosphere coupling over the United States

Ahmed B Tawfik & Allison L Steiner

Mathew Taormina - Aviation

Why dirt water can be important during that 4-5 month dead period we

called winter. And super computers.Mathew Taormina

Schedule of events

• Introduction of the study• Methods• Results• Summary• Q & A (more Q , less A)

The Study

The question:

What is the impact of soil moisture and its

phase in land-atmosphere coupling,

during winter?

The Study

Why this question? Aren’t there more

interesting questions to ask about

climatological feedback mechanisms?

The Study

Almost certainly!

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.

The Study

Surface energy balance:

Incoming shortwave + Incoming longwave =

Reflected shortwave + Emitted longwave + Latent

heat flux + Sensible heat flux + Subsurface

conduction

The Study

Sensible Heat Flux:

SH = Cd Cp V (Tsfc - Tair)

Latent Heat Flux:

LH = Cd L V (qsfc - qair)

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?

Next…

• Introduction of the study• Methods• Results• Summary• Q & A (mostly Q , less A)

You are here

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!

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.

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.

Methods

Changes in atmospheric variables are

caused by changes in soil moisture.

Standard deviation difference is used to

measure coupling:

Methods

Next…

• Introduction of the study• Methods• Results• Summary• Q & A

You are here

ResultsGreater coupling strength is found in October-April than in the summer months. These areas “migrate” with the freezing line.

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

What does this mean???

ResultsStefan-Boltzmann Law?

Liquid soil moisture is key to controlling ground temperature variability.

Results

Next…

• Introduction of the study• Methods• Results• Summary• Q & A

You are here

SummaryThe impact of winter soil moisture in land-atmosphere feedback coupling is the ability for soil water phase to control surface fluxes.

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).

Summary

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?