TIME (UTC) REMARKS
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1929 Takeoff Hobart, climb to 18,000'
1950:50-2058:30 Level at 18,000' (1958 moved to 500 mb, 18,500')
2024:00 Turned westbound at 45:10 S 145 E
2025 Disco 45:18 S 145 E, moving to 45:33 S
2037 Passsed into cloudfree air ~45:10 S 143:54 E
2048:30-2058:30 Lidar leg northbound at 500 mb (18,500')
1000 fpm descent to 750 mb
2109:53-2119:53 Lidar leg southbound at 750 mbar (8200')
BL top 2700' north end, 2300' south end, aerosol layers ~4000'
2119:53-2134:31 Sounding 1000 fpm to 5000', then 500 fpm to 100'
2123 Lots of particles at 4800'
First Stack
2134:31-2204:31 CW 30 min Lenschow circle at 100'
Start 45:25 143:09
90/270 climb to 500'
2207:25-2237:25 CCW 30 min Lenschow circle at 500'
End 45:26 143:11
90/270 climb to 1000'
2240:43-2310:43 CW 30 min Lenschow circle at 1000'
End 45:27 143:22
2255 Disco 45:33 144:46
90/270 climb to 1500'
2313:36-2343:36 CCW 30 min Lenschow circle at 1500'
End 45:28 143:26
90/270 climb to 3000'
2346:22-0016:22 CW 30 min Lenschow circle at 3000'
2354 Disco 45:33 144:29
0008 Acquired signal from Balloon #8
0017:30-0027:30 Northbound porpoise across circle
0027:30-0038:50 Southbound sounding to 100' at 500 fpm
Second Stack
0040:50-0110:50 CCW 30 min Lenschow circle at 100'
Start 45:26 143:47
0044 Disco 45:33 144:18
0047 #8 at 45:36 144:39
0113:54-0143:54 CW 30 min Lenschow circle at 500'
Start 45:28 143:54
0118 Disco 45:33 144:11
90/270 climb to 3000'
0146:38-0216:38 CCW 30 min Lenschow circle at 3000'
Start 45:28 144:02
0147 Disco 45:33 144:07
0151 #8 at 45:39 144:55, 327 m
0154 #0 at 45:33 144:07, 361 m
0216:38-0227:00 Porpoise leg northbound across diameter
Start 45:30 144:11
0218 #0 at 45:35 144:14
0227:00-0235:15 500 fpm descent to 100'
Reregister to balloon #0
Third Stack
0238:36-0308:36 CW 30 min Lenschow circle at 100'
Start 45:29 144:19
0238 #0 at 45:36 144:20
0236 #8 at 45:42 145:06
0251 #6 at 45:33 144:06
90/270 climb to 500'
0311:13-0341:13 CCW 30 min Lenschow circle at 500'
Start 45:34 144:21
0313 #0 at 45:40 144:31 595m
End 45:36 144:29
0344 #0 at 45:43 144:38
0341:13 Climbout directly toward Hobart
0352-0417 Level at 15,000'
1059 Descent into Hobart
0437 Landed Hobart
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The pre-Lagrangian flight confirmed that a substantial clear patch existed behind the front we had been watching for several days. The general agreement between several meteorological models, forecast trajectories from them, the BoM forecasters, and the movement of the patch in satellite images gave us confidence that we could position Disco and the C-130 in the same clear patch in mid-morning, when the photochemistry would be reaching its maximum rate. About the time of our takeoff, Disco was at 45:18 145:00 to prepare for the balloon launch. We directed the C-130 to 45:10 145:00 and headed directly west to intercept the clear air behind the front.
When we passed the cloud edge at 45:10, two things were apparent: the front was sloping strongly NW to SE, so that Disco would encounter clear air long before our study patch (to their north) reached the ship. Furthermore, a huge clear patch was located a bit to our south, with much greater amounts of broken cloud to our north. We elected to begin the study in the more southerly clear air at 45:25 143:09, since there was enough time for Disco to relocate a few miles to 45:33 145. The study area had only a few very light broken clouds at the northern edge of the circle. It was rather hazy, but otherwise sunny and cloud-free. We began with lidar legs at 500 mb and 750 mb over the area, then profiled at 500 fpm to our initial 100' leg.
High sulfuric acid and ozone were noted at 13,000' during the first part of our descent. This was apparently the same layer in which high SO2 was noted the night before. Its origin is not clear, but the long-range transport of biomass burning smoke is one possibility, which is consistent with the lack of UCN and the presence of nonvolatile cores in many of the CN. The lidar got a strong return from the mixed layer, with its top at 2600-2800' at the north end and 2300' at the south end. An aerosol layer was evident at 4300-4600', sloping in a different direction than the mixed-layer top. The presence of this layer was confirmed in situ during our profile, since we encountered high particle concentrations and RH at 4800'. Ten nm particles were the smallest reported, suggesting this was not a new aerosol. Since the nephelometer didn't note much of a change when we entered this layer, it may be that the clear lidar signature was largely due to the high RH in the layer.
The attached soundings show that while theta-v suggests there is a well-mixed surface layer below 2000' and ozone looks well-mixed to 3000', the mixing ratio of water does not look well-mixed. The air dries almost continuously with altitude, with bigger drops at 2200' and 5500'. We elected to fly at 100', 500', 1000', and 1500' in the surface mixed layer and 3000' in the layer immediately above it. We completed 10 circles in all, repeating the 100' and 500' levels three times.
Once we began our 100' circle, we found that the winds in the mixed layer were only 8-9 knots. While this is desirable for keeping the study air accessible for three flights, it meant that our patterns in the clear patch would not reach Disco (over 70 miles away) for roughly 8 hours, long after we had returned to Hobart. Disco then began steaming westward to launch their three balloons in the vicinity of our patterns. Between their steaming west and our slightly faster advection at higher altitudes, we closed on one another in just over two hours. It is ironic that in this situation, the 15 knot ship became more mobil than the 200 knot aircraft, which was constrained to drift with the clear patch. (It is also interesting to note that this is one of the few times I have ever found English units to be easier to use than metric: the ship and balloon locations were reported to me in degrees and minutes. One minute of latitude is 1 mile, and 1 minute of longitude here is about 2/3 mile, so no conversion was required to change location reports into distances between platforms.)
The first balloon, #8, was launched midway through our first 3000' circle, at about 0000z. We acquired its signal at 0008, and lost it only during our lowest-level legs, when our receiving antenna was very close to the surface. The balloon was roughly 35 miles downwind of the southern start point of our circle at the time of launch. We moved a few miles closer to it throughout the day, due to our more rapid advection during our 3000' legs, but did not intentionally adjust our position to move closer to balloon #8. Once we selected the study airmass, we advected with it until the start of our third stack.
The second balloon, #0, was launched by 0151z, during our second 3000' circle. We actually acquired its signal while it was still on deck of Disco at 0139, and kept it the remainder of the flight. At the time of launch it was almost exactly 5 miles due south of the (advecting) southern start point of our pattern. We had hoped to locate the patterns between 4 and 10 miles to the north of the balloons, so we took this balloon to be the official marker of the study airmass. After completing the 3000' leg, a porpoise across the circle and a slow descent back to the south, we reregistered our next 100' circle to balloon #0. Our protocol was to advect each pattern with the winds, and only realign to the balloon(s) at the start of each new stack. When we started the third stack, we were 7 miles north and <1 mile west of #0. At the end of the 500' leg, one hour later, we were 7 miles north and 6 miles west of #0, apparently due to wind-shear and the imperfections in our circles.
It should be noted that this sort of realignment relative to a moving target would not be possible without the aid of RAF's highly skilled pilots, whose experience was critical to our success.
The last balloon, #6, was launched about an hour later, and we acquired its signal at 0251. When we left the study area, the three balloons were all transmitting their locations. The lead balloon, #8, was roughly 30 miles ahead of #0, while the trailing one, #6, was about 13 miles behind.