2. Surface In-Situ Measurements• Prior ADG deployments by AWS project in Greenland successful

o First deployment in 1992 (Stearns & Weidner, 1993)

• ADG Units (Figure 1)o Measures snow depth with a series of sound pulseso Time from transit to return is basis for obtaining distanceo Speed of sound varies with temperature so requires temperature measuremento Provide ground truth measurements of snow accumulation

• ADGs placed onboard AWS unitso AWS units measure temperatureo AWSs already deployed in several areas around Ross Island/Ross Ice Shelf Regiono AWS measure wind speed, which helps determine if blowing snow

• Visual Stratigraphyo 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

• Deploymento ADG deployed at Williams Field on Ross Island in 2004 (Figure 2)o Joins two others – C-16 and B-15A iceberg siteso B-15A has malfunctioned, so data is only collected from other two

• Issueso ADGs cannot determine if accumulation is precipitation or blowing snowo Will need storms to provide the precipitation, but also brings higher windso Web cam located at Williams Field and C-16 sites

Will provide visual guidance for storms

o ADG measurements combined with AWS measurements will determine whether or not blowing snow (at least in part) Figure 3 represents snow depths and temperatures at Williams Field from February through mid-May 2004 Several instances where snow depth decreased from winds – one particular storm was on 14 April 2004

Precipitation Measurements on the Ross Ice Shelf and Ross Island, AntarcticaShelley L. Knuth1, Gregory J. Tripoli2, and Charles R. Stearns1

1Automatic Weather Stations Project, Antarctic Meteorological Research Center2Department of Atmospheric and Oceanic Sciences

University of Wisconsin

1. Introduction

• Precipitation difficult to detect in Antarcticao Relative scarcity of surface measurementso Difficult to resolve falling snow over snow at the surface (similar emissivities)o Hard to detect difference between blowing and falling snow

• To overcome difficulties, use variety of data sources o In-Situ Measurements

Acoustic Depth Gauge (ADG) measurements for snow depth Antarctic Automatic Weather Station measurements (temperature, wind speed, wind direction, and pressure)

o Satellite Data Advanced Microwave Scanning Radiometer - EOS (AMSR-E) Visible, infrared, and water vapor imagery

o Model Output• University of Wisconsin - Nonhydrostatic Modeling System (UW-NMS)

3. Satellite Data • Microwave Data

o Shows true location of storm systemso Can possibly determine precipitation rate over polar regionso Primary satellite data for this study

• Visible, Infrared, and Water Vapor Imageryo Gives multi-channel, higher resolution look at storm systemso Also shows true location of stormso Cannot predict precipitation

 • Issues Studying Precipitation

o Falling snow and snow on ground have roughly same emissivity

Difficult to see difference between brightness temperatureso However, falling snow should have slightly higher emissivity than snow already at surface

Figure 4 shows brightness temperatures during 14 April 2004 storm which might indicate precipitation

Figure 4. AMSR-E microwave image from 14 April 2004 at 10:14Z depicting the Ross Ice Shelf region. Brightness temperatures greater than 200K are highlighted.

Figure 3. Plot of temperatures (K) and snow depth (m) for Williams Field, Antarctica, from February to mid-May 2004.

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.

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.

4. Model Output

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.

5. Future Work

• Additional ADGs will be deployed during 2004-05 season

o Ferrell site, due to its accessibility and long climate record

o Windless Bight, due to its higher precipitation levels and low wind speeds

 • Snow Pits – 2004-05 field season

o Visual stratigraphy will be performed at ADG sites at Williams Field and the C-16 iceberg

 • Continued analysis of case studies

Figure 2. Map of Automatic Weather Stations across Antarctica, including Ferrell, Williams Field, and Windless Bight sites.

Williams Field Acoustic Depth Gauge Measurements Displaying Temperature and Snow Depth

200

210

220

230

240

250

260

270

280

Date

Te

mp

era

ture

(C

)

1.3

1.35

1.4

1.45

1.5

1.55

Sn

ow

De

pth

(m

)

air temp snow depth

Figure 1. Example of ADG mounted on AWS. Picture from B-15A site in October 2003.

Figure 5. Output from the UW-NMS showing wind speeds over the Ross Ice Shelf on 14 April 2004 at 17Z.

• Will compare model output from UW-NMS to in-situ and satellite data

• UW-NMS (Tripoli, 1992)o Cloud resolving modelo Determine different forms of hydrometeors in clouds

Can determine form of precipitation falling as well as rate

o Estimate location of stormso Simulate wind speeds and precipitation accumulation

Can compare this data to real time measurements

• 14 April 2004o Wind speeds over Ross Island are high, indicating that blowing snow is a factor (Figure 5)o 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