Mission Plan:
Primary Mission : Continuation of flights in Lagrangian series Alternate Mission: None Future Mission(s): NoneAircraft Operations
Take-off Time: Flight #26: 0630 LDT, 9 Dec (1930 UTC, 8 Dec) Pre-flight Weather Briefing Time: Flight #26: 0430 LDT, 9 Dec (1730 UTC, 8 Dec) Updates: None scheduled Airborne Mission Scientist: Flight #26: Huebert Mission Scientist: Flight #26: DurkeeShip Operations
Discoverer: Discoverer is located at approx 45 34'S, 144 02'E at 1400 LDT, 8 Dec (0300 UTC 8 Dec). They are performing time series sampling at the starting point of the Lagrangian experiment which will continue until continental air reaches the ship. At that time they will begin sampling along the Lagrangian trajectory. Soundings are being taken every 3 hours during this period. See catalog reference below for detailed instrument status. Discoverer Lead Scientist: Tim Bates Southern Surveyor: Southern Surveyor has completed its cruise and is in port in Hobart. 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
Synoptic Situaton at 00Z Friday 8/12/95:
Cold front moving through the eastern ACE area at 20/25 knots. High 1019 hPa near Cape Grim extends a ridge to another high of 1020 hPa near 37S 155E. High to consolidate as one centre of 1021 hPa near 39S 160E at 00z tomorrow and move slowly eastwards.
Cold front near 40S 120E/50S 133E/into a 984 hPa low near 57S 135E moving E at 30 knots. Front forecast to be near 45S 132E/50S 135E/55S 133E at 12z tonight, and 44S 140E/50S 142E/60S 145E at 00z tomorrow and becoming complex in nature with a series of fronts to pass through the eastern ACE area tomorrow night. The low is expected to deepen to about 975 hPa or possibly even less and move east into the area near 55S 145E by 12z tomorrow night.
Prognoses:
0-24 hours: All the progs are forecasting a strengthening northerly airstream ahead of tomorrow's front. What they don't agree on is the strength of the low that is forecast to develop on the front around 145E tomorrow afternoon. The EC and US progs have the low down to about 966 hPa whereas the later RASP has only a 985 hPa low near 50S 145E at 12z tomorrow night. A compromise will be the best answer I suspect, giving a central pressure of about 975 hPa by tomorrow night. A pre-frontal trough is likely to pass through Cape grim early afternoon.
24-72 hours: A strong, cold SW stream is forecast to develop in the wake of the low and cold front complex, with further fronts likely to develop and move through the ACE area on Saturday night and Sunday. The vigorous west to southwest stream may tend more northwesterly on Monday ahead of another front to cross the area early Tuesday, with strong, cold west to southwesterlies to follow.
FORECASTS FOR TONIGHT AND SATURDAY:
Cape Grim: Weather: The chance of a little overnight or early drizzle otherwise fine until some light rain develops tomorrow afternoon, tending to showers tomorrow night behind a colder SW change. Periods of reduced visibility in smoke if someone tries to barbeque the station again. Wind: Winds shifting E/NE'ly tonight and increasing to 20/25 knots. Winds possibly reaching 30 knots tmorrow morning before easing slightly ahead of a 15/25knots west to northwest change. Outlook Sunday: Showers and west to southwest winds 25/35 knots.
Macquarie Island: Weather: A few light showers tonight but a mainly fine day tomorrow, although low cloud may possibly lower to fog at times later. Drizzle developing tomorrow night. Wind: North to northwest winds 15/25 knots increasing to 25/30 knots tomorrow.
Outlook Sunday: Drizzle increasing to rain. North to northwest winds possibly reaching 30/40 knots.
R/V Discoverer Weather: Some light rain developing tomorrow, more likely in the afternoon if you are east of 145E. Rain increasing tomorrow night near the front. Wind: North to northwest winds increasing to 15/25 knots overnight and 25/35 knots tomorrow with a further strengthening to 35/45 knots possible late in the day ahead of a west to southwest change of similar strength tomorrow night. Strong squalls with the front. 1 to 2 metre seas increasing to 4 to 6 metres later tomorrow. West to northwest increasing to 3 to 4 metres tomorrow and possibly 4 to 6 metres tomorrow night.
Outlook Sunday: Chiefly westerly winds easing to 25/35 knots, turning southwesterly during the afternoon. Seas mostly around 4 metres. Southwest swell to 5 metres. Cold with showers, possibly of hail following the front.
REVIEW OF PREVIOUS DAY's FORECASTS: A major forecast failure was detected overnight with an unforecast period of reduced visibility due to smoke observed at Cape Grim. With not even a fire weather warning current at the time, we will really have to look closely at this situation and ensure that this oversight is not repeated. For the remainder, the forecasts have held up very well, with the clear air forecast for the lagrangian experiment being even better than was forecast and winds being slightly lighter. Winds have not yet gone NE at Cape Grim as was forecast, however this is likely to occur this evening. The progs have had a fairly good day and were good guidance, particulrly the GASP diagnostics, which picked up the dry air behind the front where we are currently sampling.
Reporter: Barry Huebert
Much of the discussion today concerned what appears to be our last opportunity to conduct a Lagrangian experiment. The front which will pass 140 E late Thursday night may well be our last chance, since a deep low is developing to the southwest. We have abandoned the idea of doing a stratoQ mission on the 7th, to ensure the best chance of success with this Lagrangian experiment.
We hope to fly a total of four flights, three with the balloons. After Don Thornton expressed strong opposition to using the four flights as originally scheduled for this Lagrangian (there has not been much change in SO2 in the boundary layer flights to date, and he feels that the inability to measure DMSO and DMSO2 invalidates sulfur budget studies), we finally took a vote on the use of the remaining hours. It was overwhelmingly in favor of trying to coordinate four flights, if we can do so, with only one or two votes to the contrary among those scientists who elected to attend the meeting.
To minimize the chance that Friday's daytime flight will be in cloudy air, we have decided to do a pre-Lagrangian survey flight Thursday night in (approximately) the postfrontal air that we will be studying Friday. We will launch the balloons Friday morning into what is clear air at that time. The pre-Lagrangian flight will include a series of level legs into the frontal region, looking for high CN concentrations and mapping the dynamics, potential vorticity, and aerosol microphysics well enough (hopefully) to define the altitudes from which the high postfrontal CN concentrations come. While we don't know whether these postfrontal nuclei represent a globally-important source of particle number in the boundary layer, they certainly are a reproduceable phenomenon which Bates, Covert, Kapustin, et al. have observed and which deserve further study. Hopefully Thursday night's flight will give us an idea of their origins. Clarke and Businger will lead that flight.
Friday norning we will then tag a parcel of air and follow it for at most three flights. Our intention is to locate Disco such that the C-130 is already in the air before the balloons are launched, but that may or may not work, given the uncertainty in timing from frontal passage and clear-air passage forecasting. The nominal launch time would be 2200-2300 CUT Friday morning, with the C-130 on station doing circles slightly to the north of Disco from 2000 to 0300 Friday. We would again try to place the circles 4-5 miles to the north of the balloon track. (Once those circles are begun, it will be important that Disco not move north!) At present it loks like 45 S 145 E is a good launch point, but we hope to refine that tomorrow afternoon.
Disco would actually launch the balloons when the large clear patch arrives (whatever time that happens to be). Jim Moore explained that it is common to have a small clearing behind fronts (in which the undisturbed high CN concentrations are probably located), but that that air almost certainly clouds up prior to the onset of broader subsidence farther behind the front. Our best potential for maintaining a clear study area, then, is in the larger clear area, not where the high CN first appear. Since this launch will almost certainly be in the daytime, it seems best to have the launch time chosen in close consultation with the people making satellite observations of clear areas.
All three balloons should be used in this mission, since no other opportunities seem likely prior to the end of the experiment. The closer they can be launched to the same time, the better. We recognize that the normal fill-and-ballast time is about an hour, but any efforts that can be made to get a couple of balloons out within 15 minutes of one another will increase the value of the data. Three quite close would permit an independent computation of divergence, for comparison with the aircraft measurements. Obviously, we'll take what we can get in this regard.
On one of the flights in this series, we will fly a stack of two 60 minute circles and a stack of four 30 minute circles. This will allow a test of Lenschow's theory that larger circles can greatly reduce the uncertainty in entrainment calculations. Clearly this will put us into a slightly larger airmass than the 30 minute circles, but in the context of the uncertainty in airmass identity that we already face, it may not be too serious.
If we fly four 9 hour flights in this series, we will have 20 hours remaining. Today we also spent a fair amount of time discussing the best way to understand the apparent production of aerosols at the tops of stratoQ. Clearly the stratoQ mission needs to focus more on the air just above the inversion than we have in the past, but with continuing attention to measuring the boundary layer fluxes and entrainment rates. Since early next week may offer opportunities to study cumulus detrainment and its contribution to the production of aerosols in the free troposphere, it is likely that we will use virtually all our remaining flight hours on these last two objectives.
Tentative schedule (CUT):
Friday: 0800 C-130 T/O for second Lagrangian fight (Flt 25) 1700 Land Hobart 1930 C-130 T/O for third Lagrangian flight (Flt 26) Saturday: 0430 Land Hobart
Due to the Lagrangian flights there will be NO 11:00am meeting tomorrow. We will do the update exercise at the pre-flight briefings.
