Mission Plan:
Primary Mission : Langrangian Alternate Mission: Sunrise photochemistry in clear air Future Mission(s): Continuation of up to three more flights on the Lagrangian mission, possibly extending through 1130 UTC Sunday 3 December ( 2230 LDT, 3 Dec).Aircraft Operations
Take-off Time: Flight #18. 0230 LDT, Saturday 2 Dec (1530 UTC, 1 Dec) Flight #19. 1330 LDT, Saturday 2 Dec (0230 UTC, 2 Dec) Flight #20. 0230 LDT, Sunday 3 Dec (1530 UTC, 2 Dec) Flight #21. 1330 LDT, Sunday 3 Dec (0230 UTC, 3 Dec) Alternate mission, same as Flight #18. Pre-flight Weather Briefing Time: Flight #18. 0030 LDT, Saturday 2 Dec (1330 UTC, 1 Dec) Flight #19. 1200 LDT, Saturday 2 Dec (0100 UTC, 2 Dec) Flight #20, 0030 LDT, Sunday 3 Dec (1330 UTC, 2 Dec) Flight #21, 1130 LDT, Sunday 3 Dec (0030 UTC, 3 Dec) Alternate mission, same as Flight #18. Updates: Lagrangian decision update 2130 LDT, 1 Dec (1030 UTC, 1 Dec) Updates on position for Southern Surveyor(if changed) and balloon launch times will be transmitted at approximately 2200 LDT (1100 UTC). Airborne Mission Scientist: Flight #18, Lenschow Flight #19, Huebert Flight #20, Wang Flight #21, Huebert Mission Scientist: Flight #18, Huebert Flight #19, Durkee Flight #20, Huebert Flight #21, DurkeeShip Operations
Discoverer: Discoverer located at 45 28'S 141 27'E this evening. It will be in the vicinity of 45S 141S by approx 0900 UTC this evening. ISS soundings continue every 6 hours. Three hourly launches in support of the Lagrangian mission will be begin at 0900 UTC this evening. See catalog reference below for detailed instrument status. Discoverer Lead Scientist: Tim Bates Southern Surveyor: Southern Surveyor position at 0600 UTC 01/12 is at station trans-P4 50S 145.5E. They will begin moving toward 47S 148E by approx. 0800UTC today. Transit time is estimated at 20 hours. Soundings continue every 12 hours. See catalog reference below for detailed instrument status. Southern Surveyor Lead Scientist: Bronte Tilbrook
48 hour MSL P Prognosis is here
72 hour MSL P Prognosis is here
Latest Visible Sat Picture is here
Surface Wind 24-h forecast is here
BMRC Hysplit trajectories are here
GASP trajectory analysis is here
Synoptic Situaton at 00Z Friday 1/12/95
Deep low below 980 hPa near 60S 146E moving SE.
High 1018 hPa near 35S 130E moving E at 10 knots, forecast to be near 36S 135E at 00z tomorrow and extending a ridge east to another centre near 38S 154E.
Cold fornt near 37S 120E/41S 130E/50S 134E/wrapping into a 986 hPa low near 53S 127E, moving E at 35 knots, forecast to be near 43S 142E/50S 144E at 12z, and east of Macquarie Island by 12z tomorrow night. The following ridge is about 5 to8 degrees behind the front and forecast to weaken during the next 24 hours.
Another front is near 45S 113E and moving E at 35 knots, forecast to be near 40S 120E/42S 130E/50S 139E to a 972 hPa low near 56S 126E at 00Z tomorrow. Front to be near eastern Tas to a low near 52S 145E at 12z tomorrow night.
Prognoses: 0-24 hours: The latest RASP model run shows the front just to the west of Tas to be slowing down and not crossing the Disco's area until about 12z tonight. On current satpics this looks a little slow with the front likely to move through 45S 140E about 08z. The "mostly" cloud free air behind the front is about 8 hours wide, however this may be even larger if a weak front near 48S 130E weakens further. The progs are quite consistent however, in weakening tonight's front southeast of Tas by tomorrow night. The weak ridging may persist until later tomorrow though.
24-72 hours: The following cold front is moving in very quickly and is likely to cross the Disco and Southern Surveyor Saturday night.with the low moving into the area around 55S 140E with central pressure about 975 hPa. This low is expected to move slowly eastwards on Sunday, pushing a cold front through Tasmania early Monday morning with an upstream ridge directing a fresh/strong and cold southwest stream over the ships and Tasmania during the day. The SW stream is likely to be convective, however this will stabilise on Tuesday as the ridge move across the ACE area.
FORECASTS FOR TONIGHT AND TOMORROW:
Cape Grim: Weather: A few showers with the front overnight clearing during the morning to a fine afternoon. Winds West to northwest 15/20 knots occasionally reaching 25 knots this evening ahead of a 15/20 knots westerly change. Winds returning to the northwest tomorrow at 15/20 knots.
Macquarie Island: Weather: Occasional light showers increasing late tomorrow as the front nears you. Winds North to northwest winds 15/25 knots reaching 30 knots at times later tomorrow ahead of a late northwest to westerly change of similar strength.
R/V Discoverer Weather: A few showers ahead of and with the front this evening, then fine until the next front catches up with you late tomorrow, accompanied by further showers. Winds Northwest winds 20/30 knots backing westerly 15/25 knots with the front. Winds returning to the northwest tomorrow morning and increasing to 20/30 knots again during the afternoon ahead of a late west to southwest change of similar strength. 2 to 3 metres seas easing following the front but increasing again tomorrow afternoon. 3 to 4 metre westerly swell, possibly decreasing a little overnight.
R/V Southern Surveyor Weather: A few showers ahead of and with the front this evening, then mostly fine until the next front catches up with you late tomorrow, accompanied by further showers. Winds Northwest winds 20/30 knots backing westerly 20/30 knots with the front. Winds returning to the northwest tomorrow morning and increasing to 20/30 knots again during the afternoon and possibly reaching 35 knots ahead of a late 20/30 knot west to southwest change. 2 to 3 metres seas reaching 4 metres at times later tomorrow. 3 to 4 metre westerly swell, possibly decreasing a little overnight.
REVIEW OF PREVIOUS DAY's FORECASTS:
The forecast for the Lagrangian experiment turned out to be reasonably good guidance, with the subsidence following the thermal trough establishing an inversion over the Discoverer during the early hours of the morning. Forecasts for the other platforms appear to have been quite accurate. Showers cleared from Cape Grim and the Discoverer, with only light showers reported from Macquarie. Wind forecasts also appear to have been on track.
Reporter: Barry Huebert
One issue that we're struggling with is how to define the conditions needed to start a Lagrangian experiment. Last night, I think we defined one helpful maxim: "If you see a trajectory that's too good to be true, it probably is."
That's the essence of our experience last night and this morning. We had beautifully straight forecast trajectories that came quite close to southern Tasmania. The windspeeds were only 20 knots, which means we could almost certainly get three flights in, even starting very close to Hobart. But such straight trajectories are only likely in situations where the frontal development is extremely weak. And without that development, you cannot be certain that the post-frontal air will have the subsidence needed to generate a reliable clear patch and avoid a decoupled boundary layer.
We were unable to satisfy ourselves last night that any clear air would develop in the region of the Discoverer, nor that the boundary layer would be well-enough defined to do a Lagrangian experiment. As we watched the succession of satellite photos of the area near Disco and behind the (weakening) front, we saw an increase in patches of stratocumulus, with embedded cumulus clouds. Even the most recent sounding from Disco showed a poorly-defined boundary layer with at least two layers and the potential for venting from the top by cumulus. Several people described those condtions as similar to the decoupled boundary layers we flew throughout ASTEX; those data were extremely difficult or impossible to interpret because of the layering.
In view of those observations, we decided it was unwise to expend any of our scarce balloon resources on a Lagrangian attempt. Although the Disco experienced some clearing and a lowered boundary layer after our decision to abort the try, it is not obvious that we could have achieved our sunrise photochemistry objective of 80% clear air.
We are now planning for another opportunity, as Disco approaches 140E 45S. This front is moving much faster than the last one, but appears to have plenty of clear air behind it (perhaps 6-8 hours in the clear). It appears that Disco will be in this clear air by about 1000 CUT this evening. How long could they wait to launch balloons and still be in useable air? The concern is the approach of the following front, which is moving faster than the windspeed and could overtake the balloons, thereby messing up a late-start Lagrangian experiment.
Since we released the C-130 crews at 1430 this morning, it is not possible to fly a mission this evening. (The regulations specify a 12 hour notice, for very good reasons.) What we are planning instead is that Disco release one balloon at 1200 and one at 1400 CUT tonight, for us to pick up tomorrow morning when we depart at 1530 for a sunrise experiment in that clear air.
Our schedule is as follows:
Friday:
1000 Clear air predicted to arrive at Disco, roughly 140E 45S
Disco may in fact be east of this a bit, which would help somewhat.
1030 Meeting to examing trajectories and 2245 High REs image
1100 Advise Disco on balloon launch times
Nominal start to fill first balloon, pending advice from Ops
1200 Nominal first balloon launch. If 3-4000' BL, balloon at 500m
Saturday:
1330 Power on C-130
Weather brief
1400 Nominal second balloon launch, also at 500m
1530 T/O C-130, flight #18
1630 Nominal acquire balloons from C-130
1730 Latest time to arrive on station and begin Lenschow circles
1845 Sunrise
Again, conditions which would terminate the Lagrangian experiment include:
1. Precip or convection ruining the integrity of the BL
2. Less than 2 1/2 hours on station due to long ferries
3. Not having a balloon to follow
If we acquire both balloons, we would use trajectories and satellite
information (a high resolution image is due in at 1545 Saturday morning,
just after takeoff) to select the clearer of the two. The last launched
might be most desirable in terms of our staying with it longer, but that
air might also degrade sooner due to its proximity to the following front.
If no balloon is acquired, we will seek the best clear patch of clean air
(there should be plenty tomorrow morning) and fly a sunrise experiment in
it.