The Influence of Topographically Trapped Waves on the Ross Ice

Shelf Air Stream Manda Adams

University of Wisconsin-Madison

Ross Ice Shelf Air Stream (RAS)

Siple Dome

Ross Island

Siple Coast

Transantarctic Mountains

University of Wisconsin-Madison Nonhydrostatic Modeling System (UW-

NMS)• Quasi-Compressible, enstrophy conserving

model in non-Boussinesq framework• Fully Scaleable• Multiple two-way nested grids• Five categories of precipitating hydrometeors

– Rain, pristine crystals, rimed mature crystals, aggregate crystals, graupel

• Cloud active long and short wave radiation• TKE based turbulence closure• Variable Step Topography

Slope limited to 1 vertical grid increment per horizontal grid increment or else face stability problems.

Must step discretely in one vertical grid interval, which makes subtle topography nearly impossible to represent.

Both steep and subtle topography can be represented

University of Wisconsin-Madison Nonhydrostatic Modeling System (UW-

NMS)

Surges in the RAS

May 20-21, 2003

Surges in the RAS

Was that an isolated event?

May 15-16, 2004 April 23-24, 2004

Surges in the RAS

AWS Locations

Siple Dome

Elizabeth

Brianna

Lettau

Marilyn

Pressure at 5km(10mb increment)

What does the vertical structure look like?

Potential Vorticity

Why are some events stronger?

Are these events due to topographically trapped waves?

Are these events due to topographically trapped waves?

2/11

gHf

R

R=233km

R=190km

R=165km

HgC

Are these events due to topographically trapped waves?

2/11

gHf

R

HgC

R=170 km

Conclusions

• Surges within the RAS simulated by the UW-NMS are a robust feature associated with the movement of a large scale trough onto the Siple Coast– Surges associated with wind speeds in excess of

30ms-1 temperature drops in excess of 20oC/hr– Cold air surge generated by deepening of the cold air

as it dams up along the Transantarctic Mountains– Consistent with a topographically trapped internal

Kelvin Wave– Numerical Simulations of this feature are consistent

with the limited available observations

Future Work

• Look at the AMPS archive to get an idea of the climatology of surges in the RAS due to topographically trapped waves

Questions?