First Science Team Meeting
Notes from Discussion Group C:
Surface, In Situ, and Field Experiments: Validation and Constraints
Moderator: Brent N. Holben ; Rapporteur: John A. Ogren
Surface and in-situ aerosol measurements made locally, regionally or globally
during GACP's proposed twenty-year retrospective time frame are largely
disorganized and incomplete, particularly as we move back in time. The focus
of the Within Atmosphere Measurement (WAM) working group was to raise issues
related to:
-
Approach for WAM retrospective inventory.
-
Strategies for combined use of satellite and field measurements.
-
- constraints versus validation versus uncertainties
-
- statistical and scaling issues
-
- radiative versus climate forcing
-
Suggestions for new measurement programs.
The WAM data set is largely to be organized to constrain, validate and impose
error bars on the satellite and model generated aerosol climatology. The group
emphasized the importance of separating the WAM data used to constrain the
aerosol models employed in satellite aerosol retrievals from the WAM data used
to validate the retrievals. Additionally, WAM data will be used to validate
derived aerosol forcing from chemical transport and radiative transfer models.
Closure experiments from various intensive field programs (IFP) are designed to
establish uncertainties in 'critical' parameters.
The specifications for the WAM data base must be developed jointly by the
measurement community (satellite and WAM) and modelers (transport and GCM), and
should address the resolution (both spatial and temporal) and types of aerosol
regimes needed. A clear specification of criteria for choice of WAM parameters
and their acceptable uncertainties for inclusion in the WAM data base is
required. Several broad measurement categories were identified:
1. In-situ (chemical composition, radiative properties, and microphysical
properties)
2. Passive remote sensing systems, including spectral and broadband radiative
fluxes, optical depth, and sky radiance.
3. Active remote sensing (LIDAR).
Each of these categories includes measurements made both at the surface and
from aircraft.
Several strategies for integration of WAM data into GACP were discussed.
Closure experiments, from IFP's, test the combined ability of models and
measurements to quantify key aerosol properties. Intercomparisons of long-term
WAM data, satellite-derived aerosol properties, and results from chemical
transport models can address questions related to scaling of point measurements
to larger spatial scales and longer temporal scales. Calculating radiative
fluxes from radiances is another method for integrating different types of WAM
data.
Although the parameters from the retrospective data base have not been fully
identified new measurements and programs were suggested to enhance the utility
of WAM to the GACP team.
|
Parameter
|
Systems
|
Programs
|
Single scattering albedo,
as function of wavelength and
relative humidity
|
Improved/coordinated
LIDAR
|
Asian Dust
|
|
Particle shape & size
|
Repeat airborne
measurement systems
|
EOS validation
|
|
DMS fluxes
|
Enhanced co-location of
WAM systems
|
|
Sulfur speciation
| |
|
|
Aerosol composition aloft
| |
|
The group emphasized the need for co-location of long term measurement systems
-particularly surface radiation budget, aerosol optical depth, LIDAR profiles
of aerosol backscattering and extinction, and in-situ aerosol chemical,
radiative, and microphysical properties - and for establishing criteria for
choosing sites and coordination with existing measurement programs.
The WAM working group ended with several action items and recommendations
listed as follows:
- 1. Develop task-oriented working groups to cover the following topics:
- a. Aerosol optical depth and related products.
- b. Long-term, in-situ aerosol measurements
- c. Radiative fluxes
- d. IFP's.
- e. LIDAR measurements.
-
2. Establish a time frame for the inventory
-
3. Develop, in collaboration with the entire GACP team, the critical parameters
for inclusion into the retrospective data base.
-
4. Identify comprehensive supersites, such as the ARM CART site, where
long-term WAM data are available for multiple parameters.
-
5. Develop a data inventory questionnaire as a possible follow-on to step 3 and
4.
The retrospective data sets archived will follow the development of current
technology. This will require geocoding with adequate meta data for retrieval
from web based browser systems. The group concurred with other sessions that
an infrastructure needs to be established to facilitate communication and
collaboration between team members, including web-based systems.
