The MIT group will emphasize the physical processes controlling
atmospheric trace constituents in the PEM-Tropics B region in
February-March 1999. These processes will be studied from large scale
meteorological fields found using global analyses derived from actual and
forecast ECMWF or NCEP data during the mission, and probably from ECMWF
data after the mission. Rotational and divergent wind components will be
used to study motions, mass balance and conceive region boundaries. The
divergent components will also be used to estimate the vertical mass
transport. The pattern of upward transport by deep convection in the
western South Pacific in this season and downward transport in the eastern
South Pacific leads us to suggest that the eastern sector may be a sink
for pollution injected into the airstreams in the west, such as the
biomass burning noted extensively in PEM-Tropics A. The subsidence could
also carry downwards pollution injected into the atmosphere over South
America, and perhaps even some pollution injected over the Asian
continent, then carried into the Southern Hemisphere over the central
Pacific. Overall, the eastern South Pacific region may act as a pollution
sink. We propose to examine this possibility using chemical tracers and
meteorological tracer such as potential vorticity. Before the mission, we
will work on the possibility of forecasting regions where substantial
layering occurs, and we will work with the Science Team during the mission
to get some horizontal samples within the layers themselves. We suggest
that such sampling could be performed at two levels while the P-3B is at
Christmas Island and the DC-8 is at Hilo. Such sampling would also be
valuable to check the difference in gradient across the ITCZ, which will
be much closer to Christmas Island than to Hilo in this season. Attempts
will be made to quantitatively assess the vertical and horizontal fluxes
of chemical components associated with the different types of layers seen.
The layers work and separate independent work with MLS data suggests much dry air is introduced into the tropical tropospheric region from the lower stratosphere in middle latitudes. It would be valuable to measure atmospheric composition with the DC-8 and P3-B separately at< points separated in space but on the same isentropic surface. The convective motions in the ITCZ to the north of Christmas Island will be accompanied by subsidence to the north of the ITCZ and to the south of Christmas Island. The upper levels of these regions could be monitored by the DC-8 especially now it will be measuring H2O as well as O3 and aerosol - while the P3-B can sample the lower regions of the sinking motion on both sides of the ITCZ. These experiments will have great value in considering the climatic impact of ITCZ structure.
The PI will be one of the Mission Meteorologists. This will entail flying on the P-3B aircraft, preparing daily forecasts during the mission, contributing to designing flight plans before the mission in conjunction with the Science Team members and attempting to maximize information available on both chemical and physical processes. While the P-3B is at Christmas Island, Dr. Cho of MIT will operate the NOAA radar systems to provide fine scale wind data supporting the planned sulphur cycle experiment and the possible ITCZ circulation exploration experiments. He would also monitor the radar scatter for signs of tropopause weakening associated with stratosphere-troposphere exchange.