Reginald E. Newell
MIT
The importance of atmospheric layered structure
has emerged from the earlier GTE PEM missions and now has been
amplified using data from the MOZAIC aircraft program. Layers
often seem to be places where air from different origins is
juxtaposed; theoretical work shows that ozone production or
destruction rates can be significantly distorted if one treats
the air from different origins as well mixed. The layers are
often in continuous evolution; for example, sinking layers
will tend to sharpen dynamically and if they are water vapor
poor will also become more stable by infrared radiative cooling.
TRACE-P will provide an excellent hunting ground for layers.
The Japan jet is a rich potential source of layers from the
stratosphere that move into the upper troposphere and descend
in the anticyclonic regions over the North Pacific. Concomitantly
there may be pollution clouds coming off the coast held down
by anticyclonic subsidence at the beginning of the TRACE-P
period and raised by convection in the later period. Some of
the material raised from the ocean surface may also be raised
by convection and spread over the region. Overall there may
be opportunities to sample interacting layers.
With the 50 layer ECMWF model now in operation
it will be possible to see when stable layers are most likely
to be found and this information can be included in our mission
forecasts. Stability cross sections. proved very helpful in
PEM Tropics A and enabled us to descend in cloud-free regions
on several occasions. As mentioned in our proposal we may be
able to track plumes of CO from MOPMT on TERRA and encourage
real time forward trajectories to be made. We also hope to
arrange some data sharing with ECMWF on an ozone product they
are now testing. Ozone and potential vorticity cross-sections
would be a valuable combination. We suggest some changes in
flight procedures whereby when a marked layer is encountered
it can be sampled in an up and down zig-zag pattern over a
reasonable range (-50 km) instead of a single pass through;
and we suggest an effort to identify the edges of layers if they are thought to be
in the mission field on a given day.
In PEM West B one of our group was stationed at
Hong Kong Observatory and collected synoptic maps which contained
all the synoptic observations being plotted for China. In the
visibility code numbers 30-34 characterize dust-storms (the
dust storm symbol is capital S), and by tracing the time evolution
from the maps it is possible to have some advance notice of
the storms. Before the mission the Observatory could be contacted
and their help obtained on this point.
The legs southwards in the South China Sea will
give an opportunity to study the chemical evolution of the
material coming off the continent. These legs will need careful
timing with respect to MOPITT, trajectories, etc.