Form Approved
REPORT DOCUMENTATION PAGE
OMB No. 0704-0188
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1. AGENCY USE ONLY (Leave blank)
2. REPORT DATE
3. REPORT TYPE AND DATES COVERED
July 1995
4. TITLE AND SUBTITLE
5. FUNDING NUMBERS
A Physically Based Model of the Form Drag
OPP-90-24544
Associated with Sastrugi
OPP-93-12642
PR: 4A161102AT24
6. AUTHORS
Edgar L Andreas
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
8. PERFORMING ORGANIZATION
REPORT NUMBER
U.S. Army Cold Regions Research and Engineering Laboratory
72 Lyme Road
CRREL Report 95-16
Hanover, New Hampshire 03755-1290
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
Office of Polar Programs
Office of the Chief of Engineers
National Science Foundation
Washington, DC 20314-1000
Arlington, Virginia
11. SUPPLEMENTARY NOTES
12a. DISTRIBUTION/AVAILABILITY STATEMENT
12b. DISTRIBUTION CODE
Approved for public release; distribution is unlimited.
Available from NTIS, Springfield, Virginia 22161.
13. ABSTRACT (Maximum 200 words)
On Ice Station Weddell, some characteristics of the neutral-stability airice drag coefficient at a reference
height of 10 m (CDN10) were observed that had not been documented before. The main finding was that wind-
driven snow continually alters the sea ice surface; the resulting snowdrifts determine how large CDN10 is. In
particular, this report describes three observations and attempts to explain them: 1) CDN10 is near 1.5 103
when the wind is well aligned with the drifted snow; 2) CDN10 is near 2.5 103 when the wind makes a large
angle with the dominant orientation of the snowdrifts; 3) CDN10 can increase by 20% if, after being well aligned
with the drift patterns, the mean wind direction shifts by as little as 20. To investigate this behavior of CDN10,
this report adapts a model developed by Raupach that partitions the total surface stress into contributions
from form drag and skin friction. With reasonable choices for free model parameters and with little fine-tun-
ing, this physically based model can reproduce the three main observations. In other words, the model seems
to include the basic physics of airice momentum exchange. This modeling implies that 10-cm-high sastrugi-
like roughness elements, rather than pressure ridges, sustain most of the form drag over compact sea ice in the
western Weddell Sea. Lastly, the report speculates on what the observations and this model say about how to
parameterize CDN10 over snow-covered sea ice.
14. SUBJECT TERMS
15. NUMBER OF PAGES
14
Airseaice interaction
Form drag
Drag coefficient
Snow drifts
16. PRICE CODE
Drifting snow
Weddell Sea
17. SECURITY CLASSIFICATION
18. SECURITY CLASSIFICATION
19. SECURITY CLASSIFICATION
20. LIMITATION OF ABSTRACT
OF REPORT
OF THIS PAGE
OF ABSTRACT
UNCLASSIFIED
UNCLASSIFIED
UNCLASSIFIED
UL
Standard Form 298 (Rev. 2-89)
NSN 7540-01-280-5500
Prescribed by ANSI Std. Z39-18
298-102
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