Characteristics of the Ross Ice Shelf Air Stream Based On

AWS ObservationsMark W. Seefeldt

John J. Cassano

University of Colorado – BoulderPAOS / CIRES

Overview:• Ross Ice Shelf surface wind field

• The Past – AWS wind rose analysis– Annual, Seasonal, Selected Events

• The Current - 2004 AWS sites

• The Future – proposed site locations

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

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)

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.-1996-Jan.-1997

– Based on 3 hourly data

• Selected events:– July 2001, June 28-July 1, 1988 – Based on 10 minute data

• Plot from 2004

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

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

Wind Rose Analysis – 1996 – Feb.-Mar.-Apr.

• More defined wind flow in the Austral fall

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

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

Wind Rose Analysis – Nov.-Dec.-1996 - Jan.-1997

• Minimal katabatic drainage

• Less defined surface wind flow

Selected Event – 2001 - 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

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

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

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%)

2003-04 AWS Sites-installed in support of RAS studies

Emilia

78.5ºS

173.1ºE

50 m

Vito

78.5ºS

177.7ºE

58 m

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

2004-05 Proposed AWS Sites

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