Group 9. Macquarie Island measurements (Kreidenweis)


S. Kreidenweis
F. Brechtel
S. Whittlestone
N. Tindale
J. Seymour
M. Harvey
J. Gras
C. Dick

The objectives of the experiments performed on the Macquarie Island platform during ACE-1 were threefold. First, the measurements were to be used to provide a regional context for data interpretation and modeling. That is, measurements were to be compared with those made at other ACE-1 sites to establish whether regional gradients in key parameters were present, and to help establish regionally-representative values of these key parameters. Second, the Macquarie Island observations were to be compared with historical data records from the site, in part to determine the extent to which conditions during the ACE-1 study period reflected average conditions during the same season. Finally, a number of self-contained studies were also planned.

The group met to discuss progress to date on each of these objectives, and to discuss plans for further work. To address objectives one and two, a first step was to separate observations into clean marine and continentally-influenced subsets. These divisions were based upon radon, wind direction, and back trajectory criteria. Whittlestone, Brechtel and Kreidenweis reported progress in this area, and the divisions proposed were generally agreed upon. With respect to the first objective, Brechtel and Kreidenweis reported results of initial analyses of the aerosol number concentration, [CN], and size distribution measurements at the three surface sites (Macquarie Island, Cape Grim, and Discoverer), performed in collaboration with CG and Disco PIs. There was generally good agreement between clean marine average values of [CN] and size distribution shape, suggesting some degree of homogeneity in the ACE-1 region. The Macquarie Island values were also within reported ranges for historical [CN] data for Cape Grim baseline conditions and from coastal Antarctica sites, for the spring/summer seasons. A [CN] data set from about 1986 to the present exists for the Macquarie Island site, but has not yet been analyzed; this will be done by Gras, Dick and Whittlestone in the coming months.

With respect to the third objective, four studies were identified. The first involves comparing Harvey's CCN measurements with predicted [CCN] computed from measured size distributions and chemistry. For this, Tindale's chemical measurements are needed; the analyses of his samples is planned. The second study involves comparing single-particle chemistry at Macquarie Island (Tindale, Seymour, Kreidenweis and Brechtel) with that from other sites. The third involves extension of the particle size classification into sizes larger than those measured by the DMPS system, using Harvey's ASASP-X data. The fourth study is in conjunction with the C-130 team, to assist in their analyses of the new particle production event observed during their Macquarie Island fly-over. Aerosol data from the surface will be compared with aircraft data. Weber reported good agreement between surface [CN] and [CN] measured from the C-130 at lowest altitudes. Clarke and Li's C-130 size distributions generally compared well with those measured at the surface, although these need to be looked at more closely.

Several action items were identified by the group. First, the Macquarie Island meteorological analyses performed thus far should be folded into the discussion of regional meteorology being prepared at CSIRO. We will continue to discuss the air mass categorizations to converge on a set of clean marine times. Whittlestone will examine the historical Macquarie Island radon measurements, to be compared with the ACE-1 radon measurements. Gras, Dick and Whittlestone will process the historical [CN] measurements. Harvey will complete analysis of the CCN and ASASP-X data, needed for several of the studies identified. Tindale will complete analyses of the chemical data. These persons will continue the communications begun at the workshop and will define future collaborative efforts based upon the outcome of this work. To address regional aerosol issues, Wiedensohler is leading an intercomparison analysis of clean marine aerosol characteristics at the three surface sites, which will be completed later this year. Finally, Weber is leading the C-130 case study interpretation, and will be in communication with the Macquarie Island investigators to request additional information needed for that work.

Planned papers (special issue only; from list provided by T. Bates):