Surface InSitu Measurements

1
Precipitation Measurements on the Ross Ice Shelf
and Ross Island, Antarctica Shelley L. Knuth1,
Gregory J. Tripoli2, and Charles R.
Stearns1 1Automatic Weather Stations Project,
Antarctic Meteorological Research
Center 2Department of Atmospheric and Oceanic
Sciences University of Wisconsin

• Surface In-Situ Measurements
• Prior ADG deployments by AWS project in Greenland
  successful
• First deployment in 1992 (Stearns Weidner,
  1993)
• ADG Units (Figure 1)
• Measures snow depth with a series of sound pulses
• Time from transit to return is basis for
  obtaining distance
• Speed of sound varies with temperature so
  requires temperature measurement
• Provide ground truth measurements of snow
  accumulation
• ADGs placed onboard AWS units
• AWS units measure temperature
• AWSs already deployed in several areas around
  Ross Island/Ross Ice Shelf Region
• AWS measure wind speed, which helps determine if
  blowing snow
• Visual Stratigraphy
• In years following initial deployment, dig snow
  pits
• Dig at site of ADG
• Snow layers are analyzed for falling snow and
  snow hardened by driving wind

• 1. Introduction
• Precipitation difficult to detect in
  Antarctica
• Relative scarcity of surface measurements
• Difficult to resolve falling snow over snow at
  the surface (similar emissivities)
• Hard to detect difference between blowing and
  falling snow
• To overcome difficulties, use variety of data
  sources
• In-Situ Measurements
• Acoustic Depth Gauge (ADG) measurements for
  snow depth
• Antarctic Automatic Weather Station
  measurements (temperature, wind speed, wind
  direction, and pressure)
• Satellite Data
• Advanced Microwave Scanning Radiometer - EOS
  (AMSR-E)
• Visible, infrared, and water vapor imagery
• Model Output
• University of Wisconsin - Nonhydrostatic
  Modeling System (UW-NMS)

Figure 2. Map of Automatic Weather Stations
across Antarctica, including Ferrell, Williams
Field, and Windless Bight sites.
Figure 1. Example of ADG mounted on AWS.
Picture from B-15A site in October 2003.

• 3. Satellite Data
•  
• Microwave Data
• Shows true location of storm systems
• Can possibly determine precipitation rate
• over polar regions
• Primary satellite data for this study
• Visible, Infrared, and Water Vapor Imagery
• Gives multi-channel, higher resolution look at
  storm
• systems
• Also shows true location of storms
• Cannot predict precipitation
•  
• Issues Studying Precipitation
• Falling snow and snow on ground have roughly
• same emissivity
• Difficult to see difference between brightness
• temperatures

Acknowledgments Thanks to Jonathan Thom and
George Weidner of the AWS project for the
preparation and deployment of the ADGs. Further
acknowledgment should be giving to Amanda Adams
of the UW-NMS project for supplying the UW-NMS
images. This project is partially funded by NSF
OPP-0088058.
Figure 3. Plot of temperatures (K) and snow
depth (m) for Williams Field, Antarctica, from
February to mid-May 2004.
4. Model Output

• Future Work
• Additional ADGs will be deployed during 2004-05
  season
• Ferrell site, due to its accessibility and long
  climate record
• Windless Bight, due to its higher precipitation
  levels and low wind speeds
•  
• Snow Pits 2004-05 field season
• Visual stratigraphy will be performed at ADG
  sites at Williams Field and the C-16 iceberg
•  
• Continued analysis of case studies

•  Will compare model output from UW-NMS to in-situ
  and satellite data
• UW-NMS (Tripoli, 1992)
• Cloud resolving model
• Determine different forms of hydrometeors in
  clouds
• Can determine form of precipitation falling as
  well as rate
• Estimate location of storms
• Simulate wind speeds and precipitation
  accumulation
• Can compare this data to real time measurements
• 14 April 2004
• Wind speeds over Ross Island are high,
  indicating that blowing snow is a factor (Figure
  5)
• Precipitation accumulation were predicted to
  total between one and two inches over Ross Island
  (Figure 6)
• Comparisons between Figures 4 and 6 show some
  correlation in precipitation accumulation

Figure 4. AMSR-E microwave image from 14 April
2004 at 1014Z depicting the Ross Ice Shelf
region. Brightness temperatures greater than
200K are highlighted.
6. References Stearns, C.R. and G.A. Weidner,
1993 Greenland field report. Space Science and
Engineering Center, University of
Wisconsin-Madison. Unpublished. Available upon
request. Tripoli, G.J., 1992 A nonhydrostatic
mesoscale model designed to simulate scale
interaction. Mon. Wea. Rev., 120, 1342-1359.
Figure 6. Output from UW-NMS showing accumulated
precipitation for the past 6 hours over the Ross
Ice Shelf on 14 April 2004 at 17Z.
Figure 5. Output from the UW-NMS showing wind
speeds over the Ross Ice Shelf on 14 April 2004
at 17Z.