Characteristics of the Ross Ice Shelf Air Stream Based On AWS Observations

1
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 - 2004 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.-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

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 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

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
2004-05 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