1. University of Colorado – Boulder
Characteristics of the Ross Ice Shelf Air Stream Based On AWS Observations
Mark W. Seefeldt
John J. Cassano
University of Colorado – Boulder
PAOS / CIRES

2. Overview: Ross Ice Shelf surface wind field
The Past – AWS wind rose analysis
Annual, Seasonal, Selected Events
The Current AWS sites
The Future – proposed site locations

3. Ross Ice Shelf Surface Wind Field
Katabatic wind regime result of drainage flows through the glaciers in the Transantarctic mountains and the confluence zone of Siple Coast
Regional topography highly influences the direction and channeling of winds in the Ross Island region
Synoptic scale cyclones enhance the controlling pressure gradient force driving the surface wind flow

4. Ross Ice Shelf Air Stream (RAS)
The corridor of transport of mass, heat, and momentum due to this surface wind field is referred to as the Ross Ice Shelf air stream
(Carrasco and Bromwich 1993)

5. Analysis of RAS Using AWS Observations
Wind rose plots for the Ross Ice Shelf
Only sites with greater than 50% valid observations were plotted
Plots from 1996
Annual, Feb.-Mar.-Apr, May-Jun.-Jul., Aug.-Sep.-Oct., Nov.-Dec Jan.-1997
Based on 3 hourly data
Selected events:
July 2001, June 28-July 1, 1988
Based on 10 minute data
Plot from 2004

6. Wind Rose Plots Direction is indicated by wind blowing from
16 sector plots
Each ring represents a 5% frequency of occurrence
The colors indicate the frequency of the wind speed

7. Wind Rose Analysis – 1996 - Annual
Katabatic drainage through the glacier valleys
Wind flow is primarily southerly near the edge of the ice shelf (Ferrell and Linda)
The topography in the Ross Island region redirects the flow

8. Wind Rose Analysis – 1996 – Feb.-Mar.-Apr.
More defined wind flow in the Austral fall

9. Wind Rose Analysis – 1996 – May-Jun.-Jul.

10. Wind Rose Analysis – 1996 – Aug.-Sep.-Oct.

11. Wind Rose Analysis – Nov.-Dec.-1996 - Jan.-1997
Minimal katabatic drainage
Less defined surface wind flow

12. Selected Event – July
Mean streamlines of 10-m winds from July 2001 daily MM5 simulations (60 km grid)
A pronounced southerly flow off of the Ross Ice Shelf

13. Wind Rose Analysis – May-Jun.-Jul. - Comparison
1996
2001
A slightly stronger katabatic flow is observed down the glaciers
The flow is more southerly at Ferrell in 2001 than in 1996

14. Wind Rose Analysis – 2001 – July
The strong southerly flow is observed at Ferrell and Laurie 2
The east-west components of the surface wind field is not represented in the MM5 10-m winds

15. Wind Rose Analysis – 1988 – June 28-July 1
Parish and Bromwich 1988
Large scale katabatic drainage amplified by intense cyclonic activity.
Pressure decreases up to 20 hPa over the Antarctic continent
(wind rose rings are increments of 10%)

16. 2003-04 AWS Sites -installed in support of RAS studies
Emilia
78.5ºS
173.1ºE
50 m
Vito
78.5ºS
177.7ºE
58 m

17. Wind Rose Analysis – 2004 – Feb.-Mar.-Apr.
Emilia – Vito:
An west-east component of the wind is still observable
A larger variability in wind direction
The channeling of the wind due to the Ross Island region is still noticed

18. Proposed AWS Sites

19. Future Research and Analysis
Continue to implement the data from the new AWS sites
Clearly define the different wind regimes which make up the RAS
Perform climatologically analysis on the prevalence of the different RAS wind regimes
Analyze the characteristics and features of the different RAS wind regimes
Isolate specific events which can be used to typify and understand the RAS