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.