AIDJEX Bulletin #40 - Polar Science Center - University of Washington

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APPROACH A baseline simulation 0-f the conditions of interest in winter, performed as part of the OCSEAP program (Pritchard et al., 19771, shows that when sufficiently accurate barometric pressure fields and boundary motions are available the ice model predicts ice motions and behavior remarkably well. Deformations and stress are also simulated with physical reality, although these have not been as thoroughly tested for accuracy as has the motion. The purpose of the present work is to learn how badly the accuracy of the simulation of ice response is degraded if driving forces are not as accurate as those available for hindcasting during the AIDJEX main experiment. We have not made a thorough evaluation of the accuracy of weather prediction. Walsh (1977), using a statistical evaluation of many comparisons, concludes that weather predictions degrade seriously at 72 hours. We, on the other hand, have taken a representative case in which accurate driving forces are known and ice motions have been accurately predicted. Using this case and a set of weather predictions during this time, we make a sensitivity study which will serve as a first check on the influence on ice behavior of such errors in the weather predictions. We have chosen the period 27 January through 3 February 1976, because accurate winds and ice motions are available and because the drifting buoys and NOAA-4 satellite images show interesting ice behavior in the nearshore Beaufort Sea. In this work we show how errors in the barometric pressure field are transmitted into errors in the ice motion, deformation, and stress for the observed conditions. It is necessary not only to determine barometric pressure fields accurately so that wind stress may be found, but also to provide boundary data for accurate forecasting of ice behavior. We have integrated the model equations in time over a portion of the Beaufort Sea approximately 800 X 1200 km in size. On the landward parts of the boundary of this region we set the velocity to zero to represent the lack of motion of the land mass. Since the plasticity model admits discontinuous velocity behavior along these boundaries, this method provides a satisfactory approach even in cases in which the ice is moving very near the shore. One late the possible alternative for providing ice response throughout the Arctic boundary motion would be to simu- Basin. Then the former boundary 15 7
conditions could be used everywhere. However, this approach appears to be unnecessary and rather brutish and subject to large errors in winds far from the region of interest. In the present simulations and in all previous ones we have drifting buoys located at the northern edge of our region of interest. Since we are performing hindcasts, it is satisfactory to drive the model with these observed buoy motions. However, to use the model in a forecast mode requires that either the boundary motion or the boundary traction be predicted. There appear to be several possible schemes for predicting the boundary motion. We have not yet evaluated them. The most direct that we have thought of are (1) free drift, (2) a viscous solution in an infinite space, (3) persistence, and (4) nesting the calculation inside a larger grid. Free drift has been shown to give reasonable motions much of the time during the summer (McPhee, 1977). However, Coon et al. (1977) show it to be a poor representation of ice motion at other times. Free drift has been modified by Pritchard (1977) based on the fact that if all terms in the momentum equation are averaged over a large area, the effect of the ice strength will decay with gauge length. These large-scale free-drift results have wider application than local free drift. The second technique could use solutions developed by Hibler and Tucker (1977). Although the viscous model is inadequate for describing deformation or stress and does not represent variations observed in the nearshore velocity, it is plausible that adequate far-field boundary motions could be derived by such solutions. Both of these techniques for predicting boundary motions depend on area-wide weather patterns, including the pressure field outside the region of interest. The case for persistence is well known. It is the basis for many ice forecasting schemes. A review of ice forecasting services may be found in Wittmann and Burkhart (1973, 1974). The nesting of the grid in a larger region has been used in other geophysical problems to represent far-field effects. However, such a scheme requires a sequence of simulations in which the first one determines motion in a large region with a coarse grid and subsequent simulations use these motions as boundary input with a finer grid. 15 8
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DATA BUOYS AIDJEX BULLETIN No. 40 J
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NOTE TO FRIENDS, AND BYSTANDERS . .
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SUMMARY OF TECHNICAL DEVELOPMENTS I
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milestones, kept the vendor working
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The scene during deployment of HF-N
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The initial AIDJEX scientific plan
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poizr-orbiting satellite, which is
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t@ the spacecraft during each orbit
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BUOY NAHE COMMUN. COMMANDS FIXES TA
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L( 0 I 2 3 4 3 Radial error, kilome
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The buoy will be subjected to tempe
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nics occupy about 12 feet of the 17
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Ill -- - KEY AIUJEX WIN WW AEBa 0 4
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event that a melt pond should form
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chute supplied by Paranetics Inc. i
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6'" IqORGANIC LITHIUM BP.TTEI?Y IMP
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OM (AD RAMS) UREMEN~ \ AIRDROP N m
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provides a grid from which geostrop
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words; a four-bit air temperature w
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PERFORMANCE OF MET/OCEAN BUOYS IN A
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Sensor samples were taken every thr
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strengths are known, were used with
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the ice (causing reduced shear). An
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(McPhee, Mangum, and Martin) , TABL
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70°N 75'N n 3 P 17OOW (D Y 170°W
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12OOW * U Station 25. Xeasurements
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(McPhee , Mangum, and Martin) 2701
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(McPhee, Mangum, and Martin) a 0 a
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"i BUOY 4 I 43 360- 309- 257 206 15
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a30gl 251 I 60 511 r 43 BUOY 4 I
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n 4, (McPhee, Mangum, and Martin) 8
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(McPhee, Mangum, and Martin) 33 W c
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. '-,..I.. . B A R R O W W I N D S
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:
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I 25 23 t h--:!li[ NCI PiHCEl4l 22
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.5 .4 .3 0 A R 2 R 0 W J - 0 B U -
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9 1.5 1.0 c 8 w .5 R 930 $ 565 1000
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Clock corrections were applied rout
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Q) u o z z i 4- 4- Z + + z f n 9 Ef
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TABLE 1 DIFFERENCES IN DAILY TEMPER
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Laboratory calibration of the ADRAM
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3.20- - 1 t W o? 2 3.051 ...:-.;..
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POSITION MEASUREMENTS OF AIDJEX MAN
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some redundancy. Four points were u
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75.5 75.: - E75.1 LLI % y75.c - 1 1
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The translocation principle removes
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POSITION ACCURACY To evaluate the q
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TABLE 1 STAND-ALONE ACCURACY 68th P
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Az i mu t h s When both receivers a
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DATA PROCESSING Following the field
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model ice motion in the statistical
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FREC 1 INCY / DOPPLER / FREQUENCY /
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35 30 25 v) > 0 2 20 LL 0 r= E m 15
Page 108 and 109: An example of a large-scale buoy ar
Page 110 and 111: observations are needed in remote a
Page 112 and 113: useful for determining how various
Page 114 and 115: as well as velocity fields, we must
Page 116 and 117: Since small changes in the yield su
Page 118 and 119: The transformation of the system of
Page 120 and 121: e able to judge how well such a mod
Page 122 and 123: then the flow rule becomes Q = +A -
Page 124 and 125: [-B' -F Finally, we eliminate Carte
Page 126 and 127: differential equation. 2. Discontin
Page 128 and 129: Substituting (36) and (37) into (34
Page 130 and 131: arbitrarily assign the values of 1
Page 132 and 133: The special case when advection can
Page 134 and 135: TABLE 1 STRETCHING, STRESS, ASP CHA
Page 136 and 137: ate of deformation, we have normali
Page 138 and 139: CHARACTERISTIC EQUATIONS The ordina
Page 140 and 141: One way to circumvent the problems
Page 142 and 143: The equations governing solutions a
Page 144 and 145: It is readily seen that when body f
Page 146 and 147: which may be substituted into equat
Page 148 and 149: a the stress derivative dCldS remai
Page 150 and 151: Although we have not studied in thi
Page 152 and 153: Courant, R., and D. Hilbert. 1962.
Page 154 and 155: A RESEARCH PLAN TO TEST THE AIDJEX
Page 156 and 157: the barges managed to reach their d
Page 160 and 161: SENSITIVITY OF ICE RESPONSE TO DIFF
Page 162 and 163: Since free drift of ice is computed
Page 164 and 165: and what is observed becomes less i
Page 166 and 167: stresses appear to be relatively un
Page 168 and 169: ehavior is directly related to accu
Page 170 and 171: TABLE 1 COMPARISON OF ESTIMATED ERR
Page 172 and 173: a) Base line b) 24-hour prediction
Page 174 and 175: \ / a) Base line b) 24- hour predi
Page 176 and 177: a) Base line b) 24- hour predi ct i
Page 180 and 181: \ / a) Base line b) 24-hour predict
Page 182 and 183: .. a) Base line b) 24- hour predict
Page 184 and 185: J2 a) Base line b) 24-hour predicti
Page 186 and 187: ) 24-hour prediction c) 36-hour pre
Page 190 and 191: 8 Figure 17. AIDJEX surface pressur
Page 192 and 193: APPENDIX 1 AIDJEX DATA FILES 1. Pos
Page 194 and 195: 9A. Surface-1 eve1 ai r pressure (d
Page 196 and 197: 19. Surface pressure (Val i dated)
Page 198 and 199: APPENDIX 2 AIDJEX DATA TRANSFERRED
Page 200 and 201: I -7-71327GEO A Cards (continued) 7
Page 202: B Cards (continued) 201
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AIDJEX Bulletin #40 - Polar Science Center - University of Washington

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