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

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