Towards development of a Regional Arctic Climate System Model ---

Coupling WRF with the Variable Infiltration Capacity land model via a flux couplerChunmei Zhu1, Dennis Lettenmaier1, Juanxiong He2, Tony Craig3, Wieslaw Maslowski4

1Department of Civil and Environmental Engineering, Box 352700, University of Washington, Seattle, WA 981952International Arctic Research Center, Fairbanks, AK; 3National Center for Atmospheric Research; 4Naval Postgraduate School

Coupling Guideline

Intensified warming of the Arctic region is expected to affect not only global climate

but also change the climate and hydrology of the constituent land areas. Hence, understanding the functioning of the Arctic climate system is important both for its contribution to, and response from global change. To address these issues, a state-of-the-art Regional Arctic Climate system Model (RACM) is being constructed which includes high-resolution atmosphere, ocean, sea ice, and land hydrology components. As part of the RACM development, we have successfully coupled the macroscale Variable Infiltration Capacity (VIC) hydrology model with the Weather Research and Forecasting (WRF) regional climate model through the new Community Climate System Model (CCSM) flux coupling architecture CPL7. At present, the WRF/VIC coupled system has been run over the Arctic region in the wr50a grid for more than 3 months with ocean and sea ice conditions prescribed (“data model”) and is ready for long-time simulation. The ability of the WRF/VIC in RACM to reproduce hydrological processes will be preliminarily evaluated by comparing model simulations with .precipitation and temperature observations. We have conducted preliminary investigations of the impact of sea ice on the land surface hydrological cycle by performing a set of experiments with prescribed, partially, and fully ice-free ocean. These efforts will later be part of the foundation to explore the complex interactions and feedbacks among the components of the Arctic climate system that contribute to observed and predicted changes in Arctic climate.

1 Introduction

Model Description2

3

4

Surface Temperature Field (Feb. 2001)6

In the Sea Ice Full run, snow occurs in parts of Africa and South America that don’t presently experience snow, however decreases occur over the Arctic region. Precipitation decreases over most regions globally. The Sea Ice Free run is similar to the control in terms of .precipitation and snow depth.

Comparison of WRF/VIC with Observation (Feb. 2001)

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• The macroscale hydrology model VIC has been successfully coupled with WRF through CCSM4 flux coupler CPL7.

• WRF/VIC successfully runs more than 3

months over Arctic in wr50a grid with

ocean and sea ice as a data model.

• Currently WRF/VIC is basically ready

for long-time (multi-year) simulation

since VIC has restart function and also

is able to produce its own output.

• Currently WRF/VIC produces wetter

climate over most regions globally, and

capture temperature pattern well.

• The impact of sea ice on the global

hydrological cycle has

been .investigated.

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Model features:

• multiple vegetation classes in each cell

• energy and water budget closure at each time step

• subgrid infiltration and runoff variability

• non-linear baseflow generation

• critical elements relevant to high latitude implementations: a snow model, a frozen soil algorithm, a lake/wetland model, and a blowing snow model.

In CCSM4, the communication process is separated from the component integration process. All communication processes are performed by Cpl7 and the components run by themselves. Our coding work therefore is mainly focused on replacing CLM with VIC. Most of the coding doesn’t involve Cpl7 directly. Key aspects of the work include:

● Extract VIC as it runs in an existing MM5-VIC coupling system for interaction with the flux coupler (because VIC in MM5 is in image mode, i.e., runs at all space for a given time step, as contrasted with point mode, which runs all time steps at a given grid node before proceeding to the next grid node). ● Current versions of VIC don’t have the capacity for parallel operation.● VIC and the flux coupler exchange fields hourly (the time step at which VIC runs). This allows WRF and VIC to run at different time steps.

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Experiment Design

Surface Air Temperature Surface Skin Temperature

Precipitation and Snow Field (Feb. 2001)

Snow Depth Precipitation

Latent Heat and Sensible Heat (Feb 2001)

Implement VIC routing model into RACM

9 Arctic WRF/VIC run (Mar. 2003)

Future Work

Parrellizing VIC land model in CCSM .to improve computing performance.

Summary

Latent Heat Sensible Heat

Latent heat is greatly reduced in the Sea Ice Full run globally as a result of .colder land (in section 6), while sensible heat .globally approaches zero. The Sea Ice Free run reverses the sign of sensible heat over southern Africa and South America

WRF/VIC

Sea Ice Free

Sea Ice Full

WRF/VIC

Sea Ice Free

Sea Ice Full

WRF/VIC

Sea Ice Free

Sea Ice Full

Temperature

Precip. 2m Air T

Precipitation

WRF/VIC Observation

Sensible Latent

Snow Depth Temperature

Generally, WRF/VIC exhibits much wetter climate globally than observation. The spatial pattern of surface air temperature is captured very well.

As expected the Sea Ice Full run produces a much colder land surface globally than does Sea Ice Free. On the other hand, the Sea Ice Free run isn’t much different from the control run over most regions.

Sea Ice Free

Sea Ice Full

ControlSea ice area fraction is prescribed at

Sea Ice Free Sea Ice Full

AprMarFeb

Sea Ice Fraction prescribedJan 1, 2001

Performing multi-year simulation to evaluate the model performance