Mission Plan:
Primary Mission : Lagranagian Experiment Alternate Mission: Column Closure Experiment Future Mission(s): If Primary Mission, continue with Lagrangian Flights. **Special Notice** A meeting will be held at 9:30 p.m. LDT 22 Nov 1995 (1030 UTC 22 Nov 1995) to update weather, discuss details of the Lagrangian series of flights, and finalize Discoverer position for operations.Aircraft Operations
Take-off Time: N/A Flight #13:11:30 A LDT(Thu, 23 Nov); 0030 UTC (Thu, 23 Nov) Flight #14:01:45 A LDT(Fri, 24 Nov); 1445 UTC (Thu, 23 Nov) Flight #15:01:45 P LDT(Fri, 24 Nov); 0245 UTC (Fri, 24 Nov) Flight #16:01:45 A LDT(Sat, 25 Nov); 1445 UTC (Fri, 24 Nov) Pre-flight Weather Briefing Time: Flight #13: 09:30 a LDT (Thurs. 23 Nov); 2230 UTC (Wed 22 Nov) Updates: 09:30 pm LDT (Wed 22 Nov); 2230 UTC (Tues 21 Nov) Airborne Mission Scientist: Flight #13: Huebert Flight #14: Lenschow Flight #15: Huebert Flight #16: Lenschow Mission Scientist: Flight #13: Lenschow Flight #14: Huebert Flight #15: Lenschow Flight #16: HuebertShip Operations
Discoverer: Discoverer is on station for Lagrangian at 50S 135E. 1900 UTC 11/21 position was 48S 138E. Detailed measurement values available on status page accessed below on catalog. Discoverer Lead Scientist: Tim Bates Southern Surveyor: Southern Surveyor is on station at Trans-P2 (45S 143E). They will remain there for 30 hours Soundings being taken 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
GASP trajectory analysis is here
ACE-1 FORECAST
Synoptic Situaton at 00Z Wednesday 22/11/95:
High 1023 hPa near 43S 161E moving steadily eastwards.
Low 1000 hPa near 43S 143E moving SE at 10/15 knots forecast to be near 45S 147E at 12Z tonight, 48S 150E at 00Z tomorrow and near 52S 152E at 12Z tomorrow night.
Weak cold front near 51S 140E/45S 134E/41S 130E moving northeast at 15 knots forecast to dissipate east of 140E after 12z tonight.
Next cold front near 50S 120E/40S 112E moving ESE at 40 knots forecast to be near 52S 138E/46S 135E/40S 130E at 00Z, 55S 150E/46S 142E/40S 139E at 12Z tomorrow night.
The front is slowing as it moves through the area and small lows are likely to form along the front, with one between 45S/50S a distinct possiblity for 00z tomorrow.
. Prognoses:
0-24:Most interest centres on the position of the second cold front as it moves into the ACE area and the possiblities of a Lagrangian experiment commencing. On current timing, the progs look good for the front to cross the Discoverer's area at about 00z tomorrow and slow to about 25/30 knots during the day. Small lows may form on the frontal surface overnight and tomorrow, however the consensus between the models is that they'll form around 50S or slightly further north.
48-72: Significant variations still exist between the models with the EC and US both generating lows on the front north of 45S, the GASP maintaining a front with no lows on it and the latest RASP (nested in GASP) showing a low developing 52.5S 142E tomorrow night. The RASP low location I feel is the least likely, with the US/GASP the most probable at this stage. The resulting trajectories origninating from the Discoverer would then take the parcel south of Tasmania, but it is VERY close! The following high is likely to be a reasonably strong system, ridging quite strongly over the ACE area late in the week. A deep low pressure system is forecast to move into the far western parts of the ACE area late in the week and this will be monitored closely.
FORECASTS:
Cape Grim:
Weather: Showers increasing for a period this evening then easing tomorrow morning and mostly clearing during the afternoon. Wind: Winds shifting southwest at 20/30 knots this evening and possibly 35 knots for a period following the change, easing to 15/20 knots tomorow morning . Winds returning to the west later tomorrow. For CSIRO sampling: The trajectories ENDING 06Z tomorrow show the track to be near 41S 143E at 00z and 41.2S 141E at 18z tomorrow morning (5am local). Parcel moving at about 15kts.
Macquarie Island:
Weather: Occasional light showers or drizzle.
Wind: Northwest winds 15 to 20 knots tending north to northeasterly tomorrow.
R/V Discoverer
Weather: Light rain developing this evening and gradually increasing until the front reaches you around 00z tomorrow. Rain easing to showers with the front and even clearing for a period an hour or 2 following the change, then showers redeveloping in the colder air later tomorrow afternoon.
Wind: Northwest winds increasing to 20/30 knots overnight and possibly reaching 35 knots just ahead of the front tomorrow morning. Winds backing west to southwest at 25/30 knots with the front. Seas rising 3 to 4 metres tonight. West to northwest swell 2 metres tending west to southwesterly with the front and increasing to 3 to 4 metres later tomorrow. The deep low mentioned above (central pressure around 960 hPa) is not expected to move east of 110E until Sunday. We'll keep you posted on the movement and wind strengths expected in your area.
R/V Southern Surveyor
Weather: (No obs received since 22z) Showers gradually clearing tonight then remaining mostly fine tomorrow until the front nears you tomorrow night, when some rain may develop.
Wind: Southeast to southerky winds 15/25 knots easing to 10/20 knots tomorrow morning and tending southwesterly. Winds turning northwesterly later tomorrow morning or around midday and strengthening to 20/25 knots during the afternoon, possibly 30 knots in the evening ahead of a 20/30 knot southwest change with the front late tomorrow night. Seas 2 to 3 metres decreasing to 1 to 2 metres tomorrow morning then increasing to 3 to 4 metres late tomorrow near the front. Southeast swell 1 to 2 metres decreasing. West to southwest swell 1 to 2 metres increasing to 3 metres following the front.
REVIEW OF PREVIOUS DAY: The low just west of Tasmania intensified much more than I or the models envisaged, causing much stronger winds on the Southern Surveyor than were forecast. My apologies! Over the remainder of the ACE area, systems moved according to plan. Cloud free areas opened up to the southwst of the low near Tas and as a result, the Discoverer enjoyed more settled weather than was forecast, but Macquarie and Cape Grim was much as forecast..
We have tentatively scheduled the start of our first Lagrangian experiment for 1-2 PM Hobart time on Thursday, 23 November. At this time the forecast trajectories suggest that a 0030 CUT balloon launch at 138E 52S should put the balloons in relatively clear air immediately behind a front. This air is forecast to move east and slightly north over the next 33 hours (the farthest we can now forecast), so that it would end up east of Tasmania near the end of the 48 hour period.
This launch time is desirable, since it will allow us to be on station with the C-130 near local solar noon at the start of the experiment. However, we will delay the start of the second flight slightly, to be on station 2 hours before sunrise, so that we can watch that transition. This delay of 2 1/4 hours is seen as desirable for observing the change around sunrise, without adding significant risk of missing a fourth flight before losing the airmass at the end of the experiment. This would lock all later flights into 1:45 AM or PM takeoffs. Thus, the local flight start times would be:
1130 23 Nov (0030 CUT)
0145 24 Nov (1445 CUT)
1345 24 Nov (0245 CUT)
0145 25 Nov (1445 CUT)
The first flight would have a 2 1/2 hour ferry to the research site at 138E 52S, leaving us just 4 hours on station. During that time, we would do six 30 min circular flight patterns, at roughly 100', 0.3 Zi, 0.6 Zi, 0.9 Zi, 1.1 Zi, and 100'. We would start and end with lidar legs at 10,000' across the diameter of the circle, and would do a porpoise leg across the diameter between the 0.9 and 1.1 Zi circles. Hopefully, later flights will have 5-6 hours on station, as the air moves northerly and the ferry times decrease. Additional circles would be added to these flights.
Ideally, the "best" balloons would have been launched by Disco at around 0200 CUT, so that when the C-130 arrives they will have moved away from the ship by 50 km or so. (Winds at the site are now forecast to be 25 knots at that time.) Since all 5 balloons cannot be launched near one another (they cannot be protected from damage on deck while the others are being inflated and ballasted), we are expecting a series of launches 1 hour apart. The first should take place shortly after the change in wind direction (indicating the passage of the front), as modified by examination of the height of the frontal surface from looking at RASS data. At least 4 of the 5 should be programmed to fly at half the lowest depth expected for the boundary layer, which might be only 2000' or so. Clearly the wisest choice of altitudes will need to be made on the ship, from an examination of RASS data, wind profiler direction shifts, and a radiosonde or two which could be launched just before the most critical balloons.
If it is possible to protect one balloon on deck, it would be desirable to launch two at a separation of about 5 minutes, when the Disco seems to be well into the center of the clear patch of air. That would allow some redundancy for marking the "best" airmass. The C-130 would then interrogate Disco by HF radio concerning the numbers of the two most likely candidates. Since the C-130 will be in the air by the time of the launch, it will be important to communicate the most recent locations of the front and openings in cloud from satellite pictures. Planned updates are as follows:
9:30 PM Wed: A new trajectory forecast will be available, as will a new high-resolution IR image. A small group will examine that information, to see if Disco should be moved from 138E 52S. If no message is sent, that location is still the best one. Otherwise, a call will be placed to Disco to advise of a new location by 10:15 PM.
9:00 AM Thurs: Based on the last model runs and satellite images prior to takeoff, we will inform the Disco of the most likely times of frontal passage (fropa) and of the timing and dimensions of the clear air patch. Particularly critical will be estimates of the time (distance) between fropa and the edge and center of the clear patch. At this time, we could arrange to delay the C-130 departure by as much as an hour, if that would allow the clear patch to move slightly beyond the ship. At this same time, the Surveyor will be send a trajectory image, so they can identify the closest approach point to head for when they finish their station at mid-afternoon. (They will be roughly 24 hours steam from 50S.)
After the launch of the C-130 and the balloons, presumably most of the decisions will have been made. One that may arise, however, is how to proceed if the balloons are lost. The consensus is that we continue the mission and fly near Disco, with pretty much the same paterns we have proposed. But in view of the lack of any insitu observations in the air during the 8 hours or so between C-130 visits, we would discontinue any further Lagrangian flights after the balloons were lost.
If the good lord's willin' and the creeks don't rise, we won't have to f-ACE that situation. Just how smart is a smart balloon, anyway? Answer on Saturday.
