Mission Plan:
Primary Mission : Photochemical Sunrise (Flight #21) Flux Intercomparison (wi Disco.)(Flight #22) Alternate Mission: Clear Air Column Closure (Flight #22 only) Future Mission(s): Possible stratocumulus flight on Wednesday (6 Dec). Potential Lagrangian conditions late Thursday and Friday (7-8 Dec)Aircraft Operations
Take-off Time: Flight #21: 0230 LDT, 5 Dec (1530 UTC, 4 Dec) Flight #22: 1330 LDT, 5 Dec (0230 UTC, 5 Dec) Alternate: same as #22 Pre-flight Weather Briefing Time: Flight #21: 0030 LDT, 5 Dec (1330 UTC, 4 Dec) Flight #22: 1130 LDT, 5 Dec (0030 UTC, 5 Dec) Updates: None before pre-flight briefings Airborne Mission Scientist: Flight #21, Bandy Flight #22, Huebert Alternate Flight #22, Clarke Mission Scientist: Flight #21, Huebert Flight #22, DurkeeShip Operations
Discoverer: Discoverer located at approx 44 40'S 141 17'E at 1200 LDT 4 Dec (0100 UTC 4 Dec). They are now headed North bound toward vicinity of 42S to find higher seawater DMS concentrations and intercompare with C130 tomorrow. Soundings have resumed the 6 hourly launch sequence. See catalog reference below for detailed instrument status. Discoverer Lead Scientist: Tim Bates Southern Surveyor: Southern Surveyor position at 0000 UTC 4 Dec is 47 37'S 150E. They have begun a 30 hour process station at this location. Soundings will 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
GASP trajectory analysis is here
Synoptic Situaton at 00Z Monday 4/12/95:
Cold front lies over the eastern ACE area from 40S 150E/50S 162E into a 980 hPa low southwest of Macquarie Is. Low to move southeastwards and away from Macquarie overnight.
A 1028 hPa low well west of the ACE area to move eastwards quickly during the next 24 hours to be near 36S 130E at 00z tomorrow, extending a strong ridge southeastwards towards 50S 160E and east of Macquarie. High to move only very slowly eastwards for the following 48 hours, with the ridge edging close to Tasmania on Wednesday morning.
A cold front to the far southwest forecast to reach 50S 130E/60S 140E by 00z tomorrow and be near 43S 130E/50S 138E/a 965 hPa low near 58S 128E at 12z tomorrow night.
Prognoses:
0-24 hours: The strong high currently southwest of Australia is already riding in strongly across the ACE area in the wake of the front which crossed Tas and Macquarie last night, directing a dry southwest stream over the Discoverer's area. The thermal trough following the front is still between 140/150E however, and this is generating a large area of cumuliform cloud west of Tasmania's longitudes. As the ridge becomes stronger, convection will gradually become more supressed and with the dry air showing up on the progs at all levels, hopefully, cloud free areas will open up west of Tas during tomorrow, ahead of the next front and its associated cloud.
24-72 hours: The following front will traverse the ACE area on Tuesday night/Wednesday, but pass south of the high over the Bight. The high is then likely to re-establish a ridge southwards to the west of Tasmania, possibly generating a reasonable area of stratocumulus. Yet another front is forecast to cross the area on Thursday, with a signifcant ridge developing in its wake in the Tas/Maquarie area on Friday, offering a potential Lagrangian experiment situation.
FORECASTS FOR TONIGHT AND TUESDAY:
Cape Grim: Weather: Fine with sunny breaks. Wind: South to southwest winds 20/30 knots easing to 15/25 knots overnight and tending southwest to southeasterly at 10/20 knots tomorrow morning.
Macquarie Island: Weather: Showers, heavy at times with the chance of some hail or sleet at times tonight and tomorrow morning. Showers easing tomorrow morning and tending to drizzle later in the day. Wind: Winds turning west to southwesterly at 15/25 knots this evening, but returning to the northwest tomorrow morning and strengthening to 25/30 knots during the afternoon and 30/40 knots by tomorrow evening.
R/V Discoverer Weather: A shower or two overnight but becoming fine tomorrow. Wind: Chiefly south to southwest winds 10/15 knots, possibly decreasing to below 10 knots for a period tomorrow in the middle of the ridge. Winds returning to the northwest tomorrow evening but still remaining below 15 knots.1 to 2 metre seas decreasing to below 1.5 metres tomorrow. Southwest swell 2 to 3 metres decreasing slowly.
R/V Southern Surveyor Weather: Showers, increasing overnight then mostly clearing tomorrow morning. Some drizzle redeveloping during the evening. Wind: Westerly winds 20/30 knots turning southwesterly tonight and gradually easing to 10/20 knots tomorrow morning. Winds turning west to northwesterly tomorrow afternoon and increasing to 20/25 knots during the evening. 2 to 3 metre seas decreasing to 1 to 2 metres for a period tomorrow morning. 3 to 4 metre west to southwest swell slowly decreasing.
REVIEW OF PREVIOUS DAY's FORECASTS:
The cold front which moved through the eastern ACE area yesterday evening did not cause quite as significant weather as was predicted on the Discoverer, however weather at Cape Grim, the Southern Surveyor and Macquarie Island did live up to expectations today. The winds also came up to nearly gale force on the Southern Surveyor last night as was expected, but not at the Discoverer where winds were slightly lighter than forecast. Winds were also a little lighter than forecast at Macquarie Island.
Reporter: Barry Huebert
We hope to achieve two high-priority objectives tomorrow, in a pair of clear-air flights. A ridge developing west of Tasmania offers probably the best potential yet for clear, clean air. Since some of our objectives require clear air and since we haven't seen very much of it while in Hobart, we are planning flights both in the morning and afternoon to take advantage of it.
The morning flight is aimed at studying photochemistry across sunrise. This is the same flight we tried to start the last Lagrangian with, but it turned out to be far too cloudy to see the conversion of DMS to SO2. The flight would be on station about an hour or two before sunrise, to characterise the concentrations before photochemistry begins. It will be able to stay on station until about 10:45 AM, roughly 5 hours after the sun came up. The major objectives are to study the DMS to SO2 conversion, evaluate the importance of Cl in this conversion, observe the production of H2SO4 in clear air, and watch the evolution of particles as photochemistry occurs.
If the clear patch is large enough, we will fly Lenschow circles, just like the start of the last Lagrangian. This gives us the ability to compute the surface and entrainment fluxes of several species. But if the patches are very small, we might fly linear legs to stay in sunny air. If we can coordinate this flight with Disco, we will do so. That coordination would take the form of starting the pre-sunrise pattern far enough upwind that the study air would be near Disco at 2:30 or 3:00 PM for a flight that _must_ take place near Disco. (We will look at trajectories, but something like 44 S 141 E is a likely morning start point.) However, if that upwind location is not cloud-free, the flight will be flown in the clearest clean air that we can reach quickly.
After the morning flight, we will turn the C-130 around in 2 hours and depart at 1:30 PM for a flux intercomparison flight with Disco. The flight will evaluate threee independent approaches to estimating DMS and other surface fluxes: the thin-film approach (seawater concentrations and transfer coefficients), the Lenschow micrometeorological gradient/circle approach, and a photochemical-loss method. The major concern with this plan is that the windspeeds may be so low that the seawater/transfer coefficient approach may not be in its optimum range.
An additional benefit of this flight is that it will fly across the late-afternoon DMS minimum, thereby completing the sulfur photochemistry picture. If it can be flown in the same air that was studied in the morning, the conclusions will be that much stronger. The plan here is to start and end with lidar legs, fly two sets of four circles, and fly an above-inversion circle after each.
The schedule, then, in UTC, is:
1330 Power on C-130
Weather briefing
1515 Decision about location, from 1450 high-resolution image
1530 C-130 T/O Hobart for Sunrise Photochemistry flight
1645 C-130 on station, begin 500' circle
~1745 Sunrise
2315 Begin ferry to Hobart
0030 C-130 Land Hobart
Weather briefing for next flight
0230 C-130 T/O Hobart for Flux Intercomparison flight
0345 C-130 arrive near Disco to beging Lenschow circles.
1015 Begin ferry to Hobart
1130 Land Hobart
There is a possibility of a stratocumulus flight on Wednesday and another Lagrangian Thursday night. If the Lagrangian potential looks good during the Tuesday flights, however, we may need a down day Wednesday to tune instruments and ensure that we are ready for the Thursday Lagrangian opportunity. With 10 more days in Hobart, we are likely to get more stratocumulus opportunities than Lagrangian ones, and the relationship between subcloud aerosol and stratoQ properties (see S&I Plan description) may be adequately observed in the next Lagrangian experiment.
Early next week looks good for cold air in a nearby convective region, which would be desirable for a convective cloud/aerosol nucleation flight.
We learned today that RAF's previous accounting for flight hours was high by about 8 hours! We now have just 66.5 hours left in Hobart. This essentially means that we have one less flight than we believed we did a day ago. This morning I had assumed that the following could be achieved: 4 Lagrangian flights 1 Sunrise photochemistry flight 1 Flux intercomparison flight 1 Aerosol nucleation/convective outflow flight 1 Stratocumulus flight 1/2 Column closure flight Clearly this is not now possible on 9 hour independent flights. We have decided to continue with our plans for tomorrow's flights, since clear air is so rare that we need to take the opportunity when it presents itself. We hope that we can meet the last two objectives either tomorrow (clear column closure) or on the Lagrangian (stratoQ), or that the Lagrangian would be only three flights, leaving another free for the unmet objective. We are still planning for a 4-flight Lagrangian, however, and the northward-curving trajectory that is likely for Thursday's start would tend to give us longer access to clear air.
We are at the point in the experiment where it becomes evident that we may not be able to achieve every objective. The earlier arithmetic error by RAF certainly lead us to believe we were in better shape than we thought. As we work our way down to the last few flights, we encourage comment on which of these objectives to favor over others. This will have to be a community decision.