AWS Data: Characteristics of Snow Megadunes and Their Potential Effect on Ice Core Interpretation

Summary

The Antarctic megadune research was conducted during two field seasons, one in November 2002 and the other during the period of December 2003 through January 2004. The megadune field site is located on the East Antarctic Plateau, southeast of Vostok station. The objectives of this multi-facetted research are 1) to determine the physical characteristics of the firn across the dunes including typical climate indicators such as stable isotopes and major chemical species and 2) to install instruments to measure the time variation of near-surface wind and temperature with depth, to test and refine hypotheses for megadune formation. It is important to improve our current understanding of the megadunes because of their extreme nature, their broad extent, and their potential impact on the climate record. Megadunes are a manifestation of an extreme terrestrial climate and may provide insight on the past terrestrial climate or on processes active on other planets.

Snow megadunes are undulating variations in accumulation and surface texture with wavelengths of 2 to 5 km and amplitudes up to 5 meters. The features cover 500,000 km² of the East Antarctic plateau, occurring in areas of moderate regional slope and low accumulation on the flanks of the ice sheet between 2500 and 3800 meters elevation. Landsat images and aerial photography indicate the dunes consist of alternating surfaces of glaze and rough sastrugi, with gradational boundaries. This pattern is oriented perpendicular to the mean wind direction, as modeled in katabatic wind studies. Glazed surfaces cover the leeward faces and troughs; rough sastrugi cover the windward faces and crests.  The megadune pattern is crossed by smooth to eroded wind-parallel longitudinal dunes. Wind-eroded longitudinal dunes form spectacular 1-meter-high sastrugi in nearby areas.

This data set contains automated weather station (AWS) data from two sites. The Mac site was oriented on the rough sastrugi-covered windward face and the Zoe site was on the glazed leeward face. The AWSs collected data throughout the year from 16 January 2004 to 17 November 2004. Investigators received data from the two field sites via the ARGOS Satellite System (http://www.argosinc.com/). Data are provided in space-delimited ASCII text format and are available via FTP.

Citing These Data

Fahnestock, M., T. Scambos, T. Haran, and R. Bauer. 2006. AWS data: characteristics of snow megadunes and their potential effect on ice core interpretation. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5K935F3.

Overview Table

Category	Description
Data format	Data are provided as space-delimited ASCII text files.
Spatial coverage and resolution	Southernmost Latitude: 80.79008° S Northernmost Latitude: 80.77546° S Westernmost Longitude: 124.43450° E Easternmost Longitude: 124.52668° E
Temporal coverage and resolution	16 January 2004 through 17 November 2004
Tools for accessing data	text editor
File Information	File names follow the convention SssAWS_blk#_2004_all.txt, where Sss represents the Mac or Zoe site and blk# represents Block 1 or Block 2 data.
Parameters	Data collected by the AWS include snow/firn temperature measurements from the surface to 10.0 meters below the surface, air temperature measurements, air pressure measurements, and wind speed and direction measurements.
Procedures for obtaining data	Data are available via FTP.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigators

Mark Fahnestock
Institute for the Study of Earth, Oceans, and Space
University of New Hampshire
39 College Road
Durham, NH 03824-3525

Ted Scambos
National Snow and Ice Data Center
449 UCB, University of Colorado
Boulder, CO 80309-0449

Terry Haran
National Snow and Ice Data Center
449 UCB, University of Colorado
Boulder, CO 80309-0449

Rob Bauer
National Snow and Ice Data Center
449 UCB, University of Colorado
Boulder, CO 80309-0449

Technical Contact

Acknowledgements

This research was supported by the National Science Foundation (NSF) Office of Polar Programs (OPP) awards OPP-0225992 to Mark Fahnestock and OPP-0125570 to Ted Scambos.

2. Detailed Data Description

Format

AWS data are in space-delimited ASCII text format.

File Information

Investigators received the data in two blocks from each AWS. Data collected by the AWS include snow/firn temperature measurements from the surface to 10.0 meters below the surface, air temperature measurements, air pressure measurements, and wind speed and direction measurements.

The data and supplementary files available via the FTP site are as follows:

File Name	Approximate File Size	Description
MacAWS_blk1_2004_all.txt	440 KB	Block 1 data from the Mac AWS site
MacAWS_blk2_2004_all.txt	410 KB	Block 2 data from the Mac AWS site
ZoeAWS_blk1_2004_all.txt	328 KB	Block 1 data from the Zoe AWS site
ZoeAWS_blk2_2004_all.txt	303 KB	Block 2 data from the Zoe AWS site
aws_block_diagram.pdf	24 KB	Investigator-provided schematic for Mac and Zoe AWS sites
B_DUNES_CR10X_RUN_1.CSI	11 KB	LoggerNet program for the Mac AWS site
C_DUNES_CR10X_RUN_1.CSI	11 KB	LoggerNet program for the Zoe AWS site

Spatial Coverage

Southernmost Latitude: 80.79008° S
Northernmost Latitude: 80.77546° S
Westernmost Longitude: 124.43450° E
Easternmost Longitude: 124.52668° E

Mac site (MGD 160 AWS, ARGOS ID 2516):

Latitude: 80.79008° S
Longitude: 124.43450° E
Elevation: 2884 meters above WGS84 ellipsoid

Zoe site (N1 360 AWS, ARGOS ID 2769):

Latitude: 80.77546° S
Longitude: 124.52668° E
Elevation: 2881 meters above WGS84 ellipsoid

Click on the thumbnail to view the full resolution (~481 KB, JPEG) images.

Spatial Resolution

Data are included from two sites, approximately 2.4 km apart. Data from both sites include temperature measurements taken at the surface; 1.0 m and 2.5 m above the surface; and 0.1 m, 0.2 m, 0.35 m, 0.5 m, 0.75 m, 1.0 m, 1.5 m, 2.0 m, 3.0 m, 4.0 m, 5.5 m, 7.0 m, and 10.0 m below the surface.

Temporal Coverage

Data were collected starting on 16 January 2004 and ending on 17 November 2004. Investigators recorded multiple readings each day.

Parameter or Variable

Parameter Description

Data collected by the AWS include snow and firn temperature measurements from the surface to 10.0 meters below the surface, air temperature and pressure measurements, and wind speed and direction measurements.

Block 1 Parameters

Column Header	Description
jd	fractional julian day of year 2004 when block was acquired by ARGOS
tsurf	snow temperature at 0.0 m depth (°C)
t0_1	snow temperature at 0.1 m depth (°C)
t0_2	snow temperature at 0.2 m depth (°C)
t0_35	snow temperature at 0.35 m depth (°C)
t0_5	snow temperature at 0.5 m depth (°C)
t0_75	snow temperature at 0.75 m depth (°C)
t1_0	snow/firn temperature at 1.0 m depth (°C)
t1_5	snow/firn temperature at 1.5 m depth (°C)
t2_0	snow/firn temperature at 2.0 m depth (°C)
t3_0	firn temperature at 3.0 m depth (°C)
t4_0	firn temperature at 4.0 m depth (°C)
t5_5	firn temperature at 5.5 m depth (°C)
t7_0	firn temperature at 7.0 m depth (°C)

Block 2 Parameters

Column Header	Description
jd_blk2	fractional julian day of year 2004 when block was acquired by ARGOS
t10_0	firn temperature at 10.0 m depth (°C)
tair1_0	air temperature at 1.0 m (°C)
tair2_5	air temperature at 2.5 m (°C)
tbb_top	temperature at the top of the battery box (°C)
v_bat	battery system voltage (volts)
P	barometric pressure (mbar)
wdir7	wind direction at 7 m (degrees clockwise from true north)
wspeed7	mean wind speed at 7 m over the previous 10 minutes (m/sec)
wspsd7	standard deviation wind speed at 7 m over the previous 10 minutes (m/sec)
wspmin7	minimum wind speed at 7 m over the previous 10 minutes (m/sec)
wspmax7	maximum wind speed at 7 m over the previous 10 minutes (m/sec)
wspeed1	mean wind speed at 1 m over the previous 10 minutes (m/sec)
wspsd1	standard deviation wind speed at 1 m over the previous 10 minutes (m/sec)
wspmin1	minimum wind speed at 1 m over the previous 10 minutes (m/sec)
wspmax1	maximum wind speed at 1 m over the previous 10 minutes (m/sec)

Sample Data Record

These data are from the MacAWS_blk1_2004_all.txt data file.

jd	tsurf	t0_1	t0_2	t0_35	t0_5	t0_75	t1_0	t1_5	t2_0	t3_0	t4_0	t5_5	t7_0
16.058	-28.08	-28.37	-28.34	-28.91	-29.71	-31.32	-32.8	-35.73	-38.59	-43.84	-47.06	-49.19	-49.91
16.128	-27.64	-28.2	-28.39	-28.91	-29.75	-31.31	-32.8	-35.73	-38.6	-43.9	-47.03	-49.24	-49.93
16.202	-26.87	-27.85	-28.28	-28.98	-29.75	-31.36	-32.84	-35.36	-38.62	-43.86	-47.07	-49.21	-49.92
16.272	-26.15	-27.53	-28.15	-28.97	-29.74	-31.3	-32.86	-35.75	-38.59	-43.88	-47.06	-49.22	-49.96

These data are from the MacAWS_blk2_2004_all.txt data file.

jd_blk2	t10_0	tair1_0	tair2_5	tbb_top	v_bat	P	wdir7	wspeed7	wspsd7	wspmin7	wspmax7	wspeed1	wspsd1	wspmin1	wspmax1
16.055	-49.45	-26.5	-26.62	-25.05	14.97	678	222.2	8.15	0.197	7.85	8.39	6.437	0.175	6.2	6.65
16.13	-49.45	-26.14	-25.64	-19.78	14.89	677.8	216	8.22	0.109	8.08	8.35	6.625	0.168	6.4	6.85
16.2	-49.47	-25.45	-24.97	-17.95	14.82	678.1	217.5	7.98	0.63	7.13	8.62	6.425	0.462	5.7	6.85
16.27	-49.47	-25.03	-25.03	-17.61	14.79	678.1	209.8	7.34	0.218	7.1	7.69	6.062	0.156	5.8	6.2

Quality Assessment

The 10 meter firn temperature reading did not work much of the time at the Zoe site (mostly not a number (NAN) values). Not all ARGOS satellite passes caught both a Block 1 and a Block 2 corresponding to the same set of measurements, so they are not coincident measurements unless their julian day values match to within about 0.007 days (about 10 minutes). There are a few spurious points because of the communication link: sometimes the data logger and satellite transmitter would get out of sync, and values ended up in the wrong columns, etc. Investigators filtered out the obvious spurious values, but a few still exist in the data.

Investigators estimated the wind direction margin of error at the Mac site to be ±1 degree clockwise from true north with no measurable offset. They estimated wind direction margin of error at the Zoe site to be ± 4 degrees clockwise from true north, but believe the measurements appeared to be approximately 4 degrees too high.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The entire data set is 1.48 MB.

Software and Tools

Data can be viewed with a text editor.

See Also

• Antarctic Megadunes: Research at the Edge of the Earth
• GPS and GPR Data: Characteristics of Snow Megadunes and Their Potential Effect on Ice Core Interpretation

4. Data Acquisition and Processing

Theory of Measurements

See the following instrument descriptions and refer to the investigator-provided block diagram (PDF file, ~24 KB).

Sensor or Instrument Description

Instrument	Quantity	Description
Campbell Scientific CR10X Data Logger	1 unit	View instrument description.
Campbell Scientific SM16M Storage Module	1 unit	View instrument description.
Campbell Scientific AM16/32 Relay Multiplexer	1 unit	View instrument description.
Campbell Scientific 4WPB1K PRT Bridge Terminal Input Modules	2 units	View instrument description.
Honeywell HEL-705-U-0-12-00 1000 ohm Platinum Resistance Thermometers	17 units	View instrument description.
Campbell Scientific SAT ARGOS Platform Transmitter Terminal	1 unit	View instrument description.
Campbell Scientific 13904 ARGOS Omni-directional, ½ Wave Antenna	1 unit	View instrument description.
Campbell Scientific 03101-5 R.M. Young Wind Sentry Anemometer	1 unit	View instrument description.
Campbell Scientific 05103 R.M. Young Wind Monitor	1 unit	View instrument description.
Campbell Scientific CS105 Barometric Pressure Sensor	1 unit	View instrument description.

Data Acquisition Methods

Both the Mac and Zoe AWS sites used a dedicated CR10X Data Logger to control the acquisition of data from the various scientific instruments. The data loggers enable investigators to store data locally in non-volatile memory using a SM16M Storage Module (SM) and transmit data to the ARGOS satellite system using a SAT ARGOS Platform Transmitter Terminal (PTT). The CR10X at each site contained a LoggerNet program (See Campbell Scientific: Product Information - LoggerNet 3.x.) consisting of CR10X commands to perform these functions. The Mac program, B_DUNES_CR10X_RUN_1.CSI, and the Zoe program, C_DUNES_CR10X_RUN_1.CSI, are basically identical but have the following notable differences:

1. The 16 temperature offset constants corresponding to each of the calibrated 16 HEL-705-U-0-12-00 1000 ohm Platinum Resistance Thermometers (PRTs), which were used to measure air and snow/firn temperatures at each site, varied. (A 17th PRT that was not calibrated, and thus had an offset of 0, was used to measure the box temperature at each site.)
2. A unique Array ID was used for each SM, namely 420 for the Mac site and 430 for the Zoe site.

Once every 30 seconds, the CR10X program performs the following tasks:

1. Determine the average wind speed over the previous 30 seconds for the 03101-5 cup anemometer.
2. Determine the average wind speed over the previous 30 seconds for the 5103 propeller anemometer.
3. Accumulate values for computing the mean, standard deviation, minimum, and maximum value for both wind speed sensors.

Once every 10 minutes, the CR10X program performs the following tasks:

1. Set output flag 0 high. This action converts the accumulated wind speed values to the final mean, standard deviation, minimum, and maximum values and zeros out accumulated values.
2. Set Active Storage Area to Final Storage Area 1 and Array ID to 420 for the Mac site or 430 for the Zoe site.
3. Read the current year, day of year, hour, and minute.
4. Read the 16 calibrated temperature sensors using the AM16/32 Multiplexer.
5. Apply the 16 calibration offset values to the 16 calibrated temperature values.
6. Read the 17th uncalibrated temperature sensor inside the top of the battery box.
7. Convert all 17 temperature values to Celsius.
8. Read the battery voltage.
9. Read the CS105 Barometric Sensor. The pressure was stored as mbars−600.
10. Read the 5103 propeller wind direction.
11. Send all final data (that is, two data blocks) to the SAT ARGOS PTT satellite transmitter.
12. Send all final data to the SM16M Storage Module.

The SAT ARGOS PTT satellite transmitter for each site was configured prior to installation in the field with a unique ARGOS ID number:

1. ARGOS ID 2516 for the Mac site.
2. ARGOS ID 2769 for the Zoe site.

Furthermore, each PTT was configured to transmit one of two data blocks every 200 seconds; that is, every 200 seconds the PTT transmitted either block 1 or block 2 of the most recently computed 10 minutes of data. Each data block consisted of 16 data values, and each data value was a 16-bit number in Campbell Scientific's LO Resolution Binary Final Storage Format (see section C.2 in the CR10X Measurement and Control Module Operator's Manual). Even though all data values collected by the CR10X were transmitted, inspection of the final data files indicates that only about 20 two-block sets or about 14% of the transmitted data were received and processed by the ARGOS system. This is mainly due to the intermittent nature of the ARGOS satellite passes over the field sites.

In addition to transmitting data to the ARGOS satellite system, the CR10X stored the same data in non-volatile memory in a SM16M Storage Module at each site. Each storage module should contain about 144 unique sets of 10 minute data for each day that the CR10X was operating. According to the Campbell Scientific SM4M/SM16M Storage Module Instruction Manual, each storage module can retain data in non-volatile flash EEPROM memory for approximately 10 years. As of this writing, the storage modules have not been retrieved from the field.

Derivation Techniques and Algorithms

The CR10X computes the standard deviation of each wind speed sensor as:

S = ((ΣX_i² − (ΣX_i)² / N) / N)^1/2

where X_i is the ith measurement and N is the number of samples (typically 20).

Processing Steps

Individual blocks of AWS data were transmitted from the two sites, received by the ARGOS satellites, and re-transmitted to the ARGOS Satellite System. Each individual block was then sent via email to an account at the University of New Hampshire where investigators performed the following processing:

1. Tagged each block of data with the UTC date and time of acquisition by the ARGOS satellite and converted the date/times to fractional day of the year 2004 values
2. Converted the pressure values to millibars (mbars) by adding 600 to them
3. Converted all values to ASCII and stored sequentially in a separate data file for each site (Mac and Zoe) for each data block type (1 or 2)
4. Deleted duplicate records (that is, those from the same site having the same fractional day value)
5. Manually inspected the resulting data files for obviously bad data records and deleted those that qualified
6. Sent the final data files to NSIDC for posting on the distribution FTP site

5. References and Related Publications

Albert, M. R., C. A. Shuman, Z. R. Courville, R. Bauer, M. A. Fahnestock, and T. A. Scambos. 2004. Extreme firn metamorphism: impact of decades of vapor transport on near-surface firn at a low-accumulation glazed site on the East Antarctic Plateau. Annals of Glaciology 39: 73-78.

Campbell Scientific, Inc. 2002. CR10X Measurement and Control Module Operator's Manual.

Courville, Z. R., M. R. Albert, and J. Severinghaus. 2002. Firn physical characteristics and impact on interstitial convection and diffusion in the megadunes of East Antarctica. Eos. Trans. AGU 85(47). Fall Meeting Suppl., Abstract C31C-06.

Courville, Z. R., M. R. Albert, M. A. Fahnestock, and L. Cathles. 2005. Impact of accumulation rate on firn properties. Eos. Trans. AGU 86(52). Fall Meeting Suppl., Abstract C21B-1108.

Courville, Z. R., M. Albert, M. Fahnestock, L. M. Cathles. 2006. Impact of accumulation hiatus on the physical properties of firn at a low accumulation site. Journal of Geophysical Research. In review.

Fahnestock, M. A., T. A. Scambos, C. A. Shuman, et. al. 2000. Snow megadune fields on the East Antarctic Plateau: extreme atmosphere-ice interaction. Geophysical Research Letters 27(22): 3719-3722.

Fahnestock, M. A., C. A. Shuman, M. R. Albert, and T. A. Scambos. 2002. Satellite, observational, meteorological and thermal records from two sites in the Antarctic megadunes stability of atmospheric forcing, thermal cracking, and the seasonal evolution of the thermal profile. Eos. Trans. AGU 85(47). Fall Meeting Suppl., Abstract C31C-03.

Fahnestock, M. A., C. A. Shuman, T. A. Scambos, M. R. Albert, T. Haran, Z. R. Courville, and R. Bauer. 2005. Mapping Antarctic megadunes and other accumulation-related features on the East Antarctic Plateau. Eos. Trans. AGU 86(52). Fall Meeting Suppl., Abstract C13A-06.

Frezzotti, M., S. Gandolfi, F. La Marca, and S. Urbini. 2002. Snow dunes and glazed surfaces in Antarctica: new field and remote sensing data. Annals of Glaciology 34: 81-88.

Frezzotti, M., S. Gandolfi, and S. Urbini. 2002. Snow megadunes in Antarctica: sedimentary structure and genesis. Journal of Geophysical Research 107(D18), 4344: doi:10.1029/2001JD000673.

Kawamura, K., and J. P. Severinghaus. 2005. Krypton and Xenon as indicators of convective zone thickness in firn at Megadunes, Antarctica. Eos. Trans. AGU 86(52). Fall Meeting Suppl., Abstract PP33C-1590.

Scambos, T. A., M. A. Fahnestock, C. A. Shuman, and R. Bauer. 2002. Antarctic megadunes: characteristics and formation. Eos. Trans. AGU 85(47). Fall Meeting Suppl., Abstract C31C-04.

Suchdeo, V. P., C. A. Shuman, T. A. Scambos, M. A. Fahnestock, M. R. Albert, and R. Bauer. 2002. Precise elevation profiles across Antarctic megadunes. Eos. Trans. AGU 85(47). Fall Meeting Suppl., Abstract C33C-0357.

Suwa, M., and J. Severinghaus. 2002. Firn density profile at Megadunes, East Antarctica, calls for an improved densification model for low accumulation sites. Eos. Trans. AGU 85(47). Fall Meeting Suppl., Abstract C33C-0359.

6. Document Information

List of Acronyms

The following acronyms are used in this document:

ASCII: American Standard Code for Information Interchange
AWS: Automated Weather System
FTP: File Transfer Protocol
NSIDC: National Snow and Ice Data Center
NSF: National Science Foundation
OPP: Office of Polar Programs
PTT: Platform Transmitter Terminal
PRT: Platinum Resistance Thermometers
RTD: Resistance Temperature Detectors
SM: Storage Module
URL: Uniform Resource Locator

Document Creation Date

October 2006

Document URL

http://nsidc.org/data/docs/agdc/nsidc0283_fahnestock/index.html