One of the firmest conclusions of the Nagoya meeting is that ACE-Asia should be a much broader experiment than the brief intensive land, ship, and aircraft experiments of ACE-1. A two-year observing period (probably including calendar years 2000 and 2001) would allow interannual time-series observations at a network of surface sites. The potential to record seasonal changes in the spatial distributions of aerosols and their precursors is a truly exciting one. By activating a relatively dense set of surface sites in China, Korea, Japan and a series of islands (and then supplementing this with occasional ship and aircraft observations) we could generate a data set that would be an excellent challenge for chemical transport and aerosol dynamics models. The two-year observation period would also allow for shipborne and airborne experiments to take place in several seasons, with emphasis on the springtime in both years for studying the nature and extent of aerosol and aerosol-precursor outflow from Asia. The two main foci of the experiment will be industrial and mineral aerosol and their evolution over the Pacific.
Goals and Objectives: We reaffirmed that the goals of ACE-Asia are to
determine and understand the properties and controlling factors of the
aerosol in the anthropogenically modified atmosphere of Eastern Asia and
the Northwest Pacific and to assess their relevance for radiative forcing.
To achieve this goal, ACE-Asia will pursue these specific objectives:
The discussions about carbonaceous aerosols were particularly stimulating. The recent Tarfox results, in which more than half of the FT aerosol mass in North American outflow was found to be carbonaceous, make it clear that we must do a much better job of characterizing organics than has been done in most previous experiments. Kawamura's efforts to quantify the molecular composition of lipids and oxygenated species opened up a new range of potential analytical methods for consideration. Cahill and Perry offered to organize an organic intercomparison workshop.
Springtime Kosa events, in which eastern Asia is blanketed with mineral aerosol, are one of the most obvious impacts of Asian aerosol. These events have long been known to deliver dust to the central Pacific, potentially providing an important fraction of biologically-important iron to the north Pacific. Recently these aerosols have generated additional interest because of their absorption of radiation: they tend to cool over low-albedo surfaces (such as the oceans) but have a warming effect over snow and clouds. The evolution of these aerosols as they pass from source regions is of particular interest, since the adsorption of soot and sulfate from polluted air and seasalt from marine air should change their radiative properties as well as their tendency to form cloud droplets and to be scavenged by precipitation.
The modeling group, under the leadership of John Seinfeld, is already helping to design the experiment to make it the most useful test of a variety of model types. It is envisioned that hemispheric-scale chemical transport models with fairly complete aerosol dynamics will be available by the 2001 time frame. Both the intensive and network observations will be directed toward improving aerosol process, radiative transfer, and regional and global climate models.
Lagrangian experiments may have to take a different form from those in ACE-1 and ACE-2. The airspace over the Yellow Sea is full of military warning zones, which makes it impossible to ensure access by research aircraft when meteorological conditions happen to be ideal for following an airmass. We could follow air east from Japan, though. And we could follow some air masses that come from the Yangtse River industrial region and the deserts. We could also do some Lagrangian observations from (mostly) ground sites, in which we identify after the fact the airmasses that passed first over one observation site and then another on a different landmass. Karsten Suhre, in part as a result of the trajectory modeling he has undertaken in the region, has proposed a Qindao - Cheju-Island - Southern Japan pseudo-Lagrangian experiment of this type. His letter suggesting this idea can be found on our web site at: http://saga.pmel.noaa.gov/aceasia/
It might be possible to do this in 2000 and 2001. Those of us who are hoping to operate from mobile platforms in 2001 might try to put extra equipment at surface sites or on ships or aircraft in spring 2000, which would also help us to standardize our protocols and try methods that might be used during the 2001 intensive observing period (IOP). In 2001 both NSF and NASA aircraft and a NOAA/UNOLS ship might support radiative closure, Lagrangian evolution, photochemical, and removal experimental designs. The two targets for understanding are the evolution of urban/industrial emissions and Kosa events.
Surface Measurement Network
A network of surface sites will form the backbone of ACE-Asia. The potential sites are listed below in the Potential Platforms section. Most of these sites have been or are being used for some other sampling programs. The old Searex sites, for instance, would need to be reactivated, while active sites may need only to add a few new instruments to their existing activities. Since the extent of the dust impact is observed every spring as far away as the Aleutians and Hawaii, it was decided that these should form the northern and eastern boundaries of the network. The western boundary would be near the Chinese deserts (the dust source regions) and the southern boundary would be around 20-30 N, to avoid the trade winds and focus on outflow.
For these network measurements to be useful, at least one common measurement needs to be made at each site. One simple possibility would be a daily filter sample, using the same substrate at every site, with an omnidirectional inlet of known cut size (maybe 1 µm). As long as this were sufficiently inexpensive, it could be replicated at all the surface sites, so that one observation would be directly comparable between them. If some sites only operate a part of the year, they would limit this filter sampling to the times they were active. Alongside this sampler each site would continue with their usual measurement protocols, so the remainder of the instruments at each site might be quite diverse. Intercomparison of instruments from multiple sites will be an important part of the network's quality control.
Defendable, comparable measurements of both organic and mineral aerosols from surface and airborne platforms will be critical for achieving a number of our objectives. An organics task force, led by Cahill and Kawamura, is starting to talk about observing methods and intercomparison experiments. The mineral aerosol group will likewise need to settle on a set of observational strategies that offer enough commonality of inlet efficiency and accuracy that differences between sites can be attributed to sources, processing, and sinks, rather than experimental uncertainty.
We would urge as many groups as possible to partake in intercomparison experiments, to get their CN counters and particle sizers tweaked up to perform similarly. While every measurement will be welcomed, those data that can be traced to intercompared instruments will be given a "quality- checked" flag in the data base. This will enable modelers to know what apparent concentration differences are the least likely to be the result of instrumental calibration variations. The value of all the data we generate will be limited in part by the extent to which we have verified its quality. Without these quality control and intercomparison exercises, simultaneous data collection from a variety of sites is of little value.
In addition to the many ways that ACE-Asia will benefit from the use of satellites, it will be very important for satellite validation: Spherical vs non-spherical model assumptions yield completely different angstrom exponent in the aerosol models used in the atmospheric correction algorithms. This implies a huge uncertainty for retrievals of dust concentrations. We need actual phase- function measurements for this purpose, and measurements of chemical composition vs size to validate them. This will also be an excellent data set against which to test land aerosol retrievals.
Indirect Effect Since the cloud dynamics off Asia (more convective and a higher cloud optical depth) will be very different from the stratocumulus cases observed in ASTEX and FIRE, the cloud radiation data will be completely new. We need to know the sensitivity of the cloud droplet number concentration to aerosol concentrations in the vicinity of China. Thus, ACE-Asia will offer an excellent opportunity to study the cloud/aerosol relationship in a new setting.
Working groups were formed to address several issues in the experiment.
In some cases these groups will focus on technique development and standardization
prior to the field phase, while others may be devoted to defining observational
strategies for achieving particular objectives. The composition of each
working group (as of the Nagoya meeting) is listed at the end of this report.
All are open to anyone who wants to participate actively: express your
interest to the designated Leader of any group to which you would like
to make a contribution.
Of course at this stage of the planning, these are all proposed sites and platforms. Only a few have firm commitments for the ACE-Asia time-frame.
Surface Sites (with at least one common measurement at each)
|China||Rental possibilities? (Gras and Ogawa are checking)|
|Russia||Rental possibilities? (Sokolik is checking)|
|Unknown, but some interest||Huang Jing (via Uematsu)|
From the standoint of ground-truthing satellites, validation campaigns will be needed for: TRMM, EOS-AM, ADEOS-2, MSG-1, DMS (lidar), Chinese FY2 & GMS, a Korean ocean color sensor, and a Taiwanese satellite.
Jim Ragni of NCAR's Research Aviation Facility briefed the meeting on aircraft operations issues. The Yellow Sea is a very difficult place to operate aircraft, because it is full of military warning zones. He emphasized the importance of early coordination with the air traffic control offices of all the neighboring countries for maximizing our ability to get access to airspace.
The heaviest logistical demands will occur during the springtime intensives. Certainly during the 2001 IFO we will need to have an Operations Center to manage planning and coordination of the aircraft and ships. Possible locations for this Ops Center include Fukuoka, Hokkaido, Nagoya, and Okinawa. Karyn Sawyer and Dick Dirks of the UCAR Joint Office of Science Support led a discussion of issues ranging from network communications in the field to shipping and customs, travel and lodging, office and meeting space, weather forecasting support, aircraft issues, and project database management. JOSS is capable of handling any subset of these issues that we elect to delegate to them.
Management Structure [As of the preparation of this report, this structure is being proposed to the IGAC SSC for approval. There are suggestions such as adding the two IGAC-SSC aerosol members to the ACE-Asia SSC, which the IGAC-SSC will need to discuss. Therefore, this management structure should be treated as a strawman at this point.]
We propose that the Scientific Steering Committee (SSC) consist of the Convenors of the IGAC Activities ACAPS, DARF, ACI, SUTA, APARE, and MAGE, plus the chair of each ACE-Asia National Committee. As various major observing platforms confirm their participation, the SSC membership would be expanded as needed to assure representation for that platform. The SSC will appoint a considerably smaller Executive Committee to manage the experiment.
An International Committee of high-ranking scientific officials will also be formed to deal with matters of funding and protocol in the various countries. The makeup of that committee is under discussion.
|Jul 1998||Publish White Paper|
|Aug 1998||FAA Meetings in Seattle to refine Plans|
|Nov 1998||PI meeting, Cheju, Korea|
|Mar 1999||S&IP Draft on Web|
|Apr 1999||PI Meeting in Asia, Site Surveys|
|Jul 1999||First Science & Impl. Plan on Web|
|Jun-Dec 1999||Instrumentation Intercomparison Workshops|
|Nov 1999||Steering Committee Meeting|
|Jan 2000-Dec 2001||Surface Network Operations|
|Mar-Apr 2000||First Intensive Field Operations Dry Run for 2nd IFO|
|Nov 2000||PI Meeting in Asia|
|Mar-Apr 2001||Second Intensive Field Operations
Major US platforms participate
|Jan 2002||Archiving, Data Workshops, etc.|
For Further Information
Refer to our web site: http://saga.pmel.noaa.gov/aceasia/ for updates and plans for future meetings. To contribute your ideas about particular scientific foci, communicate with the Leaders of the working groups below.
Antony Clarke, US
Lynn Russell, US
R. Hamilton, UK
B. Gorbunov, UK
J. Slanina, Netherlands
T. Choularton, UK
Yoko Yokouchi, Japan
Jorg Jensen, Australia
Hilton Swan, Australia
Stuart Whittlestone, Australia
Jim Galloway, US
John Maben, US
Alex Pszenny, US
Ron Prinn, US
Rolf Sander, Germany
Paul Crutzen, Germany
N V Raju, India
B Naiasimhamurthy, India
Jeff Collett, US
Herman Sievering, US
Y J Kim, Korea
Brian Toon, US
Jorg Hacker, Australia
Darren Lu, PRC
Fang Li, PRC
Mao Jeitai, PRC
Robert Rosset, France
N F Elansky, Russia
I G Granberg, Russia
Dean Hegg, US
Bob Duce, US
Mark Rood, US