The following paragraphs summarize new deliverables which have been divided into two additional work packages, WP6 and WP7, to be added onto the end of the existing contract. Following are tables which break down the contents of each work package and a diagram illustrating the proposed timeline.
In the previous phase of the contract, the possible extension of the model top up to 120 km has been investigated in some detail. In particular, a way of introducing some non-LTE effects in the infra-red part of the radiative transfer code has been derived and the parameterization for the visible part of the spectrum has been improved.
A good prediction of the atmospheric thermal structure in this altitude range is taking an increasing importance since it appears that aero-breaking or aero-capture will be systematically used for future missions to Mars.
However, a major difficulty has arisen. First results have shown that the radiative cooling rates can reach values of several hundred K per day above 100 km. This make the use of the existing radiative transfer code inpracticable. In fact, the radiative transfer code -- which has been adapted from the ``state-of-the-art'' terrestrial code used at the European Centre for Medium Range Weather Forecasts -- is much too costly to be computed more than about 50 times a day in current configurations. Moreover, the cost of this code increases as the square of the number of vertical layers. Both reasons require a complete rethinking and rewriting of the radiative code. The methodology is presently under development and should be ready for the beginning of the extension of the contract.
In addition, the transmission functions were fitted for pressure range corresponding to altitudes below 80 km. This particular point will require additional work and validation.
[LMD to take primary responsibility.]
The work proposed above for modifications to the radiative transfer code is necessary with or without non-LTE effects. Additional non-LTE effects will be included in the new radiative code. The first approach to the treatment of non-LTE problems, under current development in preparation for WP5 of the present phase of the contract, needs to be improved and further validated for the model with a top at 120 km to be accurate over its full domain. With the involvement of the group at IAA and the use of their non-LTE 1-dimensional radiative code, it will be possible to test the initial schemes for correcting the cooling rates for the effecs of non-LTE at any altitude with a greater degree of precision. An important novelty has come to light from the recent data collected during the descent of the Mars Pathfinder through the Martian upper atmosphere. The mesospheric thermal structure has shown a large variability in time, when compared with the Viking lander entry profiles taken at a different local time of day. We consider it necessary to study in detail the effects that wave-like structures and diurnally-varying temperatures, as observed, may have on the infrared cooling rates in the region where non-LTE effects are important. The design of fast parameterizations should take these characteristics into account and be able to reproduce them. An important element of the new phase of this project will therefore be to carry out an investigation of new fast and accurate parameterizations of the infrared cooling rates with the aid of the full 1-dimensional non-LTE model, and to incorporate validated results in the model radiative code up to the highest accessible altitudes on Mars.
[IAA/AOPP to take primary responsibility.]
A version of the GCM including interactive dust lifting and transport has been developed at LMD and should be operational at the end of 1998. Similar extensions will be implemented in the AOPP model. In the spirit of the present complementary modelling approach the AOPP GCM will employ a different dust transport scheme, though treatments of dust sources and sinks will be parameterized similarly.
We propose to use this tool to improve the representation of the temporal and spatial distribution of dust in the model scenarios that will be used to compile the new version of the climate database. Indeed, it has been shown that the thermal structure and general circulation of the atmosphere strongly depends on the highly variable dust distribution, but few observations are currently available. In practice, the dust transport and lifting model will be carefully used to extrapolate from the available data. For instance, we could improve the current representation of the vertical extension of the dust or take into account a possible decrease of the dust mixing ratio at high latitudes. The full, interactive dust model will be used for at least one scenario to be incorporated into the climate database.
[LMD to take primary responsibility.]
In 1999 the Mars Global Surveyor Laser Altimeter data should become available which will provide a definitive topographic dataset. This was expected to be available before the end of WP5 in the previous extension, but, unfortunately, the Mars Global Surveyor spacecraft encountered problems during the aero-braking phase of the mission and will enter its scientific mapping orbit at least one year behind schedule. This data will be processed and included in the model used to compile the improved climate database at the end of the contract. The new topographic dataset will not only be used for the large-scale topography resolved by the model, but will also be used to re-tune the small-scale topographic and gravity wave drag parameterizations used in the model.
Similarly, improved thermal inertia, surface emissivity and albedo fields derived from the TES instrument aboard Mars Global Surveyor and improved dust properties from the Mars Pathfinder camera may become available in 1999. If available in time, we will adapt these data to the GCM and possibly use them to compile the new database.
[LMD to take primary responsibility for introduction of new data to the Mars GCM.]
[AOPP to take primary responsibility for updates to database and tuning of gravity wave drag parameterization.]
The GCMs used to compile the Mars Climate Database have been calibrated using a few direct observations of the Martian atmosphere; mainly measurements made by the Mariner 9 and Viking spacecraft. However, current and forthcoming missions (including Mars Global Surveyor and Mars Climate Orbiter) will provide much new atmospheric data against which the models may be tested. In addition to the improved topographic, thermal inertia and albedo fields and increased knowledge of the Martian dust properties and distribution, which will be incorporated in the improved models, there will be remotely sounded measurements, of temperature structure in particular, with much better spatial and temporal coverage than any currently available. The models will be tested directly against such observations. Work has already begun on a direct comparison made between the Oxford model and the in-situ observations of temperature, wind and pressure from Mars Pathfinder. This has so far found good agreement in many respects; most differences may be ascribed to lack of knowledge of the topography and surface properties and to the scales of motion which the global model is able to represent. However, the Pathfinder data is limited to a few tens of days of observations at one site made during the mid-summer season when there was little day-to-day variability observed or predicted. The more complete horizontal, vertical and seasonal coverage which will become available from the orbiting spacecraft will provide a more comprehensive test of the models. A report will be written comparing the model and database output with whatever new observations are available by the end of the contract.
[AOPP to take primary responsibility.]
A new version of the Mars Climate Database will be generated. This will have been compiled employing the model with an extended vertical range to at least 120 km, as developed under this contract extension, as well as the latest topography and other model parameters as derived from current spacecraft data wherever possible and the extended two-dimensional EOF variability model as used in version 2 of the database. The current dust scenarios will be improved and extended by the introduction of results from model experiments with interactive dust transport and an interactive dust transport scenario.
All documentation for the database will be updated and a new critical review comparing it to the latest observations will be written.
[AOPP to take primary responsibility.]
Some of the work which will have been conducted under this contract for Mars is also applicable to the atmosphere of Venus. This group will be in a unique position to determine the aspects which may be carried directly over and where further model development and database design will be required to produce a possible Venus Climate Database in the future. This is because of the presence of many of the European experts on the atmosphere of Venus within the collaborating groups and the wealth of experience already accumulated in planetary atmospheric circulation modelling and database design.
A technical report will be written briefly reviewing the current state of knowledge of the atmosphere of Venus, in particular its thermal structure, clouds and winds. It will outline those areas where there is insufficient knowledge, especially to meet the requirements of possible future Venus missions such as the ESA Venus Sample Return proposal. It will also describe the main features which need to be represented in a realistic model and discuss how the methodology already developed for Mars of compiling a climate database from results produced by a GCM might be extended in future to cover the atmosphere of Venus.
[AOPP to take primary responsibility for observational background.]
[LMD to take primary responsibility for aspects related to model development.]
[IAA to contribute on non-LTE aspects.]
The delivery of the final report shall take place as part of WP7 under the extended contract.
[LMD to take primary responsibility.]