The long range transport of dust and anthropogenic aerosols
(e.g, black carbon, organics and sulfates, and air pollution from Eurasia,
across the Pacific Ocean, into North America is one of the most wide spread
and major pollution events on the planet. This plume passes through the Pacific
Ocean extra tropical cloud systems, which are important climate regulators through
their large radiative cooling effect. The effect of this mixed dust-pollution plume
on the Pacific cloud systems and the associated radiative forcing is an outstanding
problem for understanding climate change and has not been explored. The primary
reason is the lack of an airborne platform that can sample the evolution of this
plume in situ all the way across the Pacific Ocean.
The NSF/NCAR Gulfstream-V research aircraft (G-V) fills this observational gap
and opens new doors for observing this great natural/man made phenomenon.
PACDEX plans for a pilot study using Lagrangian sampling of this Eurasian-Pacific-North
American dust plume. We will observe the evolution of the
aerosol physical and chemical characteristics from the lower to the upper
troposphere, the vertical and horizontal gradients in the CCN and ice nuclei
across the Pacific, and cloud size spectra and liquid and ice water content.
This pilot experiment is designed to exploit and demonstrate the unique
capabilities of the G-V. PACDEX has the potential to open new frontiers of
science by observing human impacts on the mixed-phase and ice-phase cirrus cloud systems.
The PACDEX field campaign is planned for April-May 2007.
Scientific Objectives of PACDEX
The following objectives will be the focus of this pilot experiment:
* Identification of the principal cloud-active aerosol in the Asian plume. This will be
done using the CCN measurements and the IN measurements together with the
basic aerosol package on the G-V.
* Document the changes in the cloud hydrometeor size spectra in regions of enhanced
cloud active aerosol. This is within the limited capabilities of this early G-V
payload and is the first observational step needed to understand the impact of the
Asian plume on clouds.
* Document the solar changes in the plume vertical structure in clear air and cloudy
* Document near source and far from source changes in the plume that might affect (a),
(b) and (c). While the sampling cannot be truly Lagrangian, due to the effects of
wind shear over the depth of the plume, we can identify regions with various ages
using trajectory analysis and model simulations.
* Compare the in-situ vertical structure observed from the aircraft upwind and near the ground stations.