Mission Plan:
Primary Mission : Ship Intercomparison and Stratocumulus Cloud Alternate Mission: Clear Air Closure Future Mission(s): Possible Intercomparison at Macquarie Island on Sunday, 26 Nov. 1995Aircraft Operations
Take-off Time: N/A Flight #15: 1000 LDT(Sat, 25 Nov); 2300 UTC (24 Nov) Pre-flight Weather Briefing Time: Flight #15: 0800 LDT (Sat 25 Nov; 2100 UTC (24 Nov) Updates: none Airborne Mission Scientist: Flight #15: Lenschow Mission Scientist: Flight #15: HuebertShip Operations
Discoverer: Discoverer continued to move downwind following Lagrangian mission. The balloon transponders were lost late yesterday afternoon. Ship position at 2100 UTC 23/11 was approx.47.26S, 140.26E. Ship will continue toward rendezvous with the Southern Surveyor. Soundings are taken every six hours after 1200 23/11.Detailed measurement values available on status page accessed below on catalog. Discoverer Lead Scientist: Tim Bates Southern Surveyor: Southern Surveyor position at 0000 UTC 24/11 is 46 34', 144 10'. They will be on station at Trans-P3 (45S 145 27'E) at approx 1400 UTC 24/11. They will remain there for 30 hours. Soundings are being taken every 12 hours. Six hourly soundings were taken through 1200 UTC 23 Nov in support of the Lagrangian experiment. 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 Friday 24/11/95
994 hPa Low near 45S 146E moving east about 10/15 knots, forecast to be near 45S 151E at 12z tonight, 44S 156E at 00z tomorrow and peripheral to a large 988 hPa low near NZ by 12z tomorrow night.
1022 hPa high near 40S 130E moving E at 20 knots forecast to be near 43S 141E at 00z tomorrow and near 46S 145E at 12z with another centre developing near 38S 138E. A ridge extends SE from the high towards 50S 140E and this ridge should move eastwards tomorrow to be near 50S 142E by 00Z and 50S 149E at 12z.
A cold front is forecast to approach the western parts of the ACE area (around 130E) at 12z tomorrow night.
Small low near Macquarie moving rapidly SE. A cold front to also move through the area tonight.
Prognoses: 0-24 hours: The progs are still not resolving the low near Tas very well and the EC is the preferred model. However, the latest run of the local RASP model has picked up the low to a certain extent so can be used with some confidence. (More than yesterday anyway!) The ridge is expected to move into the Southern Surveyor/Discoverer area later tomorrow, so the southerly stream through the area should finally ease.
24-72 hours: The ridge should continue moving across the ACE area, across Tasmania and even extend south as far as Macquarie late in the weekend. A front is forecast to move through the ACE area during the weekend, preceeded by a strong northerly airstream. Small lows may form on this front as it moves eastwards towards Tasmania. A significant low with central pressure below 970 hPa (as low as 945 hPa on the EC prog) is forecast to develop near 50S 110E at 12z Saturday night and progress E at 15/20 knots to be near 53S 125E on Monday night.
FORECASTS:
Cape Grim: Weather: Showers gradually easing overnight and clearing during the morning to a fine afternoon. Breaks in the cloud developing during the morning. Winds: Southwest winds 30/40 knots easing to 20 to 30 knots overnight and 10/20 knots tomorrow morning. South to southwest winds 10/15 knots tomorrow afternoon.
Macquarie Island: Weather: Periods of rain or drizzle easing to showers this evening with showers persisting tomorrow, possibly of sleet or hail at times. Wind: Northwest winds 15/20 knots turning west/southwesterly 20/30 knots overnight and tomorrow morning. Southwest winds moderating slightly late tomorrow.
R/V Discoverer Weather: A few light showers or drizzle patches overnight and tomorrow morning but fine most of the time. Wind: South to southwest winds 20/30 knots easing to 15/25 knots this evening and 10/20 knots tomorrow. Seas to 3 metres decreasing to 1 to 2 metres tomorrow. Southwest swell around 3 metres.
R/V Southern Surveyor Weather: Showers easing this evening to just a few light showers tomorrow morning but becoming fine for most of the time during the day. Wind: South to southwest winds easing to 20/30 knots this evening, 15/25 knots overnight and 10/20 knots tomorrow. Seas to 3 metres decreasing to 1 to 2 metres tomorrow. Southwest swell around 3 metres.
REVIEW OF PREVIOUS DAY: One I'd rather forget!
The low developed on the front as it passed 135E yesterday and generated quite thick altostratus and cirrostratus in the lagrangian area during the afternoon and evening. Of the progs, only the EC picked any kind of low development in the area and that was not a deep system. The low generated firstly southeast winds over the Southern Surveyor as distinct from the forecast southwest winds, then gale force southerlies as the low moved away (I haven't really got it in for you!). Southwesterly winds were also stronger on the Discoverer as a result of the low, but weather remained much as forecast, as it did on Macquarie and Cape Grim. Winds at Macquarie were slightly lighter than forecast as a result of another small approaching during the afternoon.
Reporter: Barry Huebert
The primary C-130 mission for tomorrow is an intercomparison with the Discoverer, which will be located at roughly 48S 146E. This flight will do more than simply evaluate the calibration of similar instruments on the two platforms, however: we will characterise the vertical profiles of fluxes and concentrations in the boundary layer near the ship, so that our simultaneous data sets can be used to study the boundary-layer chemistry and microphysics at that time. The area is to be rather drizzly in the morning, so we plan to arrive on station at about 0100 CUT, when the precip should be stopped and a fairly good stratocumulus deck will be in place.
Our plan is to do four 30 minute circular patterns in the boundary layer (one or two will be in the clouds), a porpoise leg at the inversion (~5000'), and a 30 minute circle just above the inversion. Only the first of these legs will be flown immediately adjacent to the ship: by advecting the whole pattern with the wind, when the C-130 reaches higher altitudes it will be studying the air that was over the Disco when we started the pattern, and the patterns will give more useful fluxes. Upon completion of the pattern, however, we will return to the ship (which will have been steaming upwind at about 8 1/2 knots) for another 100' 20-30 minute instrument intercomparison leg, this time upwind past the ship, during which each platform can also photograph the other.
We are also beginning to think about ways in which we can design flight profiles to characterize the FT source of new particles. This is a question that Covert, Kapustin, Bates, and others have raised before: where did all the small particles that the Disco saw immediately behind the frontal passage come from? How and where in the free troposphere were they formed? We see layers of high UCN occasionally on ferry legs, but haven't had the time to stop and study them. Our intention on tomorrow's flight and many later ones is to add an hour or so to the ferries, so that we can profile through the layers we encounter, to determine their thickness and extent. We will also try some strategies for sampling in the layers, by following potential temperature surfaces. In this way we hope to prepare ourselves for designing a flight or two which would be dedicated to understanding the source of small particles in the FT. Nucleation is such an important objective that we feel the need to identify some new strategies for studying it in the clean FT in this region.
Presumably only a loss of major measurement systems on Disco or continuing precip would cause us to abandon the intercomparison, since Disco is nearby and we need this instrument intercomparison. The alternative mission for tomorrw would be a clear air column closure mission. Assuming that todays column closure worked well, this would reduce the priority of this mission relative to others until the results have been evaluated. There is, however, and excellent satellite overpass tomorrow around 0500 west of 140, which might contain some clear air.
The third alternate is another stratocumulus mission. Since one dedicated stratoQ flight remains, Lenschow wants to use it on a deck which is close enough to Hobart to allow a full 7 hours on station, and would start it very near dawn to watch the diurnal evolution of the system.
We are looking at the potential for a flight to Macquarie Island, since the microphysical measurements there are now operational. However, to make our intercomparison as useful as possible, we want to try to avoid precip. This is going to be difficult in a place that has only 50-60 rain-free days a year, mostly in other seasons. A cold, dry tongue of air may cross Macquarie ahead of the huge low now moving that way, so that a late Sunday or early Monday flight could be possible. One concern is that we avoid having strong headwinds on our return to Hobart, since that would shorten the station time from the maximum (2 1/2 hours) to allow enough fuel reserve to ensure our safe return. We will continue to watch that possibility.
