Arctic Field Campaign Data and Instrument Performance Reviewed at Workshop

 
Published: 31 December 2008
Both wings of the Canadian National Research Council’s Convair-580 aircraft were equipped with numerous cloud and aerosol probes during ISDAC.
Both wings of the Canadian National Research Council’s Convair-580 aircraft were equipped with numerous cloud and aerosol probes during ISDAC.

In April 2008, the month-long Indirect and Semi-Direct Aerosol Campaign (ISDAC) obtained cloud and aerosol data from above, within, and below clouds in the vicinity of the ARM site in Barrow, Alaska. In mid-November, about 50 members of the ISDAC science team gathered in Lansdowne, Maryland, for a 1-day workshop to review and assess data quality and instrument performance from the various probes and instruments on the different ISDAC flight days, and to identify cases for future analysis. Led by the campaign’s principle investigators Greg McFarquhar and Steve Ghan, the workshop discussions identified 30 different journal articles to be prepared using ISDAC data.

Preliminary analyses of the data indicated April 8 and 26 as two golden days for process studies of single-layer stratocumulus clouds, as well as April 19 due to measurements obtained in polluted conditions. During the workshop, instrument leads described the data they collected on these days, compared data quality for different flights, and identified the flights most suitable for accomplishing their scientific goals. Several scientists also presented preliminary analyses and findings.

Alexi Korolev presented data from the golden days suggesting that dynamic forcing plays an important role in the maintenance and longevity of the mixed-phase layers.  McFarquhar and Paul Lawson presented probe intercomparisons that showed shattering of ice crystals on probe inlets can affect the measurements of smaller and larger ice crystals – impacts that must be taken into account when comparing observations against model results.  Alla Zelenyuk concluded that the counterflow virtual impactor used to isolate aerosol particles from the cloud particles that formed on them did not produce artifacts of the gold and stainless steel on the surface of the impactor, thus permitting the identification of dust as the most common composition of ice nuclei.

Representing the of ISDAC science team, Ghan then attended the annual ARM Cloud Modeling Working Group meeting, held in Princeton, New Jersey, the following week. He presented a shortened version of the findings from the workshop to gain feedback on the direction for future case studies. The consensus of the cloud modelers was that the ISDAC golden days represent excellent opportunities to test cloud microphysics hypotheses regarding the influence of aerosols on clouds. The ISDAC science team is tentatively planning to present findings during a session at the 2009 AGU fall meeting.