Mission Plan:
Primary Mission : None Alternate Mission: N/A Future Mission(s): Possible Lagrangian mission on Friday with aircraft takeoff at 1500 UTC 30 Nov (0200LDT Friday, 1 Dec) ATTENTION: The 1100 LDT Mission Selection Meeting on Thursday 30 Nov) will be held at the Bureau of Meteorology Office on Macquarie St. in Hobart. International flight will use Hobart Terminal from approx.10AM to 12 noon on Thurs.Aircraft Operations
Take-off Time: N/A Pre-flight Weather Briefing Time: N/A Updates: N/A Airborne Mission Scientist: N/A Mission Scientist: N/AShip Operations
Discoverer: Discoverer located at 41 17'S 143 11'E this evening. It will be departing this evening heading south in anticipation of a Lagrangian mission beginning near 46S. ISS soundings continue every 6 hours. See catalog reference below for detailed instrument status. Discoverer Lead Scientist: Tim Bates Southern Surveyor: Southern Surveyor position at 0600 UTC 29/11 is approaching station trans-P4 50S 145.5E. Measurements are being completed at Trans-T6 and T7. 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
GASP trajectory analysis is here
Synoptic Situaton at 00Z Wednesday 29/11/95
Deep low of 965 hPa near 54S 134E moving SSE at 10 knots forecast to be near 56S 139E at 00z tomorrow and near 58S 142E at 12z tomorrow night.
A cold front is developing south of Western Australia near 44S 116E and at 00z tomorrow is forecast to be near a line 35S 130E/43S 140E/50S 148E then into the low mentioned above. Some doubt exists as to the position and nature of this front. See "prognoses" below.
Developing cold front near 43S 130E/47S140E wrapping around a 976 hPa low near 49S 139E. Low moving SE at 50 knots. Front moving E about 35 knots but is embedded in a strong northwesterly airstream. Front likely to be near 43S 140E/50S 142E at 12z tonight and 50S 150E/low near 56S 139E at 00z tomorrow.
The broad northwest to southwest airstream around the lows S of 50S, persist over the ACE area.
Prognosies: 0-24 hours: The numerical models appear to be having difficulty resolving the development of a low pressure area in a cloud mass currently south of Western Australia. The high resolution EC prog has developed the system into a 996 hPa low near 43S 145E at 12z tomorrow night, whereas the other models have not developed anything anywhere near as significant. The GASP/US and UK models are indicating a trough through the area with some hint of further development to take place, however, the local RASP model (nested in GASP) is not showing any development at all and is significantly slower in the movement of the system. The slow movement is unlikely given the current mobility of systms in the area and the presence of a strong jet stream over SW Aust.
24-72 hours: Another weak front is likely to follow tomorrow's front on Friday, however this is unlikely to survive east of about 135E as the subsidnce in the ridge flattens it out. The ridge is not likely to be terribly strong however, traversing the ACE area on Friday, ahead of the next front on Saturday. The low around 55S 140E is expected to weaken slowly and move SE'wards, with another low developing around 55S and moving E from around 85E at 12z tonight to 115E at 12z Friday night.
FORECASTS: Cape Grim: Weather: A shower or two this evening increasing for a period overnight and again later tomorrow. Winds: Northwest winds 25/30 knots easing to 15/25 knots overnight then restrengthening tomorrow afternoon ahead of a west to southwest change of similar strength late tomorrow night.
Macquarie Island: Weather: A few light showers this evening then mostly dry tomorrow until some light showers or drizzle develop later in the day. Winds: North to northwest winds 15/25 knots increasing to 20/30 knots tomorrow and possibly reaching 35 knots tomorrow night.
R/V Discoverer Weather: A shower or two increasing for a period tonight and again later tomorrow. Winds: Chiefly northwest winds 25/35 knots easing to 20/30 knots early tomorrow morning. Winds easing as the low moves over or past you tomorrow night , and possibly tending southeast to southerly at 10/20 knots, assuming the low forms north of your track. If it forms to the south of you, northwesterlies may increase to 35 knots ahead of a west to southwest change of 25/35 knots tomorrow night. 3 to 4 metre seas, decreasing to 2 to 3 metres overnight, but increasing again later tomorrow if you are north of the low. West to northwest swell 4 to 5 metres.
R/V Southern Surveyor Weather: Showers increasing shortly (if they haven't already) and persisting tomorrow, although easing slightly during the afternoon. Winds: North to northwest winds 25/35 knots, possibly reaching 40 knots at times overnight and again tomorrow evening if you are well south of 50S. 3 to 4 metre seas rising to 5 metres at times tonight. 5 to 6 metres northwest swells.
REVIEW OF PREVIOUS DAY'S FORECASTS: The prognoses did fairly well for today, correctly predicting the continuation of the broad NW/SW airstream over the ACE area. The forecasts for the platforms reflected this, although the rain and drizzle at Macquarie was somewhat less than forecast and Cape Grim somehow missed out on recording any rain, after the radar showed an extensive band moving through Tas's west coast and nearby Marrawah recorded 1mm in the 6 hours to 3pm. Winds on the Discoverer and the Southern Surveyor look to be on track at this stage, although the latest data available is 00z today. The Discoverer had stronger squalls with the weak front I mentioned on yesterday's forecast, but these appear to have been reasonably short lived.
Reporter: Barry Huebert
We are examining an opportunity to start a Lagrangian experiment in the predawn hours of Friday, 1 December. A weak frontal system is moving our way very rapidly, with the potential for clear air and westerly trajectories behind it. Accordingly, we are starting the preparations for a series of flights that would begin at 0200 local on Friday.
This would be a two- or three-flight Lagrangian series. The system is still developing, and may not be ready to fly until it is almost due south of Tasmania Thursday night or Friday morning. Since the Disco has been working near Cape Grim and has to move into position to start the experiment, we cannot get them far enough west to start it far in advance of the air's arrival near Tasmania, anyway. The system is moving at 35-40 knots, and will cover a very large range in the 12 hours before our planned sunrise flight. This extra westbound 4-500 nmi is 36 hours steam for the Disco under good conditions, and the 4-5 m existing swell makes moving that far upstream completely impractical. If we started farther west, we would need to also go farther south, to avoid hitting Tasmania.
Although it may seem unfortunate that we cannot get in one flight while the air is upstream of Tasmania, it in fact has a great benefit: While the Lagrangian sequence will only be two or three flights, the first two flights will have very long times on station, because operating just south of Tasmania greatly reduces our ferry times to the parcel under study. We might well have 6 or 7 hours on station (2 before sunrise and 4 or 5 after) for the first flight, and 4-6 hours for the subsequent afternoon/sunset flight. Since the system is forecast to slow down, we may well get a third flight in, but that remains to be seen. It seems desirable to do a third flight, even if the station time is only 2 1/2-3 hours, to get a look at how the chemistry and microphysics have evolved in a second diurnal cycle. We should, however, have long enough station times to do two complete stacks of circles on the first two flights.
The reason for wanting to position the first flight around sunrise concerns the potential that chlorine radicals might be important oxidants of DMS and hydrocarbons. Since the time evolution of hydrocarbons, DMS, and OH will all be measured as the sun comes up, it will be possible to see whether the loss of hydrocarbons agrees with the well-known rate constants for attack by OH. If a greater loss rate is observed, then it is likely that chlorine radicals are produced shortly after sunrise and contribute to the DMS loss rate. Since they would also have a predictable effect on DMS concentrations, that then specifies the DMS loss rate.
Of course, a lot of other interesting chemistry turns on at sunrise. SO2 will react with OH to produce sulfuric acid vapor, as we saw in the Kilauea plume. As condensible material is formed, it will begin to cause particle growth, although we may need more than the 7 hours we could be on station to observe it in the boundary layer. During the subsequent flight in the late afternoon and sunset, we will observe the minimum DMS and maximum SO2 levels, which will further constrain models of sulfur chemistry.
We are in a very tricky predictive situation, since we need to 1) get the balloons into a relatively small clear area, 2) with a trajectory that we can follow, 3) which we can hit not far downwind of the ship, 4) at less than 2 hours before sunrise. The fact that this has to be predicted using models which frequently don't even acknowledge the existence of these small features makes it even harder. Fortunately, the ECMWF model has picked up the small low which threatens to complicate the frontal passage, so we plan to get some trajectories from that. Steve Businger is running forward trajectories using the ECMWF model runs, and will help us pick a starting point tomorrow.
It is by no means clear that this will be a desirable Lagrangian trajectory, but we will be prepared to fly it if it develops suitably. If we do not fly it, however, there may be a clear patch of air west of Tasmania in which we could still conduct the cross-sunrise flight. In view of the importance of achieving this objective, we will keep open the option of flying at 0200 local Friday morning, whether the Lagrangian patch pans out or not. Meanwhile, the Disco is moving soutward to make a Friday morning start possible, and the Southern Surveyor is keeping its schedule flexible so it could follow the latter part of the track if the opportunity arises.
