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

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SENSITIVITY OF ICE RESPONSE TO DIFFERENCES IN AIR STRESS The report on the baseline simulation of ice dynamics in winter (Pritchard et al., 1977) includes a complete description of the AIDJEX model and all parameters used. The baseline results are obtained from the Run 3C calculation with a yield strength of 10' dyn cm-'. The accuracy of the barometric pressure field and corresponding geostrophic winds has been analyzed, and ocean currents evaluated. Ice motion during the period (27 January-3 February 1976) was strongly affected by the stress. During the first two days there was no motion; when it began, it was to the west. Even while the ice was motionless, the winds were moderately strong. Ice in the eastern portion of the Beaufort Sea responded later than in other areas. Vast ice regions in the nearshore were separated from the moving pack by a discontinuity. These conditions have been verified by NOAA-4 satellite images and data from drifting buoys and AIDJEX camps. The satellite images were also useful in identifying and locating a flaw lead that was an important feature of the ice dynamics. Using these data in a test of the simulated response of the ice pack, it was found that the motion was represented accurately throughout the region of interest, especially in the nearshore where the velocity discontinuity occurred. In this work we have chosen to recalculate ice behavior for three days in the period: 27 January, 30 January, and 2 February. Ice motion on these days represents a full range of response seen during the whole period: on 27 January, no motion even though there are winds; on 30 January, strong motion of the entire region to the west at about 20 cm per second, and strong winds; and on 2 February, the motion reversed, with the ice blown toward the east and Banks Island. We have chosen to use the predicted barometric pressure maps with verifying times at 1200 GMT for each of the three days as driving forces for the model. No other changes were made in the simulations so that we could isolate the effect of the errors in the predicted air stress. We have taken 24-, 36-, and 48-hour weather predictions for the study; the 72-hour predictions we would have preferred were not available. To clarify our terminology, a 24-hour prediction for 27 January means that our verifying time is 1200 GMT on 27 January and is predicted from conditions one day preceding. 15 9
Figures 1-3 show the baseline air stress fields (derived from NWS analyses of surface barometric pressure which were augmented by all AIDJEX data; see Appendix) compared with NWS predictions made 24, 36, and 48 hours preceding the day in each figure. We have chosen to present the driving force using the predicted air stress. It can be seen that the conditions are quite different for the three days. On 27 and 30 January the general features of the actual air stress field are represented. On the 30th it appears that the low pressure moving into the area is displaced, and so the air stress does not yet appear within the region of interest; on 27 January the features observed appear even at the 48-hour prediction level, although the magnitude in the northern part of the region is not modeled correctly. On 30 January, when high winds were noted throughout the area, the predicted winds show the correct pattern everywhere, and the 48-hour prediction is actually better than either the 24- or the 36-hour prediction. This, of course, is chance and not proof of a more reliable prediction. In general, although the main features of the air stress field are represented in these predictions, many of the details within the region are approximated poorly. To demonstrate the effect of these errors in air stress on the simulated ice response, we performed the &mulation with each of the predicted air stress fields. These calculations provide us with a direct means of seeing how the input errors are transmitted to the simulated ice response. Before turning to those results, we note that if these driving forces were observed during times when ice conditions were light enough that ice stress had no effect on the ice response (a time that occurs often in the summer), it would be meaningful to learn, by means of a free-drift model, how the errors were transmitted to the ice response. We have used such a model with a set of driving forces and computed the free-drift or winddriven ice velocities during the three days of interest. The results are presented in Figures 4-6. In the past we have noted (Pritchard et al., 1977) that free drift provides a poor prediction of the ice response during this eight-day period. However, this example is not aimed at evaluating the accuracy of the free-drift response, but at estimating the effect of errors in the air stress during conditions when ice stress is unimportant. 160
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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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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
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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 158 and 159: APPROACH A baseline simulation 0-f
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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