Meeting Preparations (Updated 23 June 2006)

Dear Colleagues,

Our meeting is quickly approaching, and we would like to focus on a few issues before we meet. In addition to assessing the state of current cloud climatologies and trying to attach errors to the properties, we ask that you consider the following.

1. At this point, a number of different intercomparison efforts are ongoing. It would be extremely helpful if each group would contact their session chair (and us) with a brief summary of their findings. Specifically, each group can list a number of issues, some larger than others, that are thought to be causing differences. Some might be algorithmic, or due to ancillary data, or the treatment of orbital drift, and so forth. We think that it would be quite useful for us to have a summary of the major issues/thoughts before we meet so that the chairs can better guide the discussion.

2. One of our goals is to be able to both list the issues outstanding and also to prioritize them in order of importance. Some problems, while easily identified, may not be addressed without considerable effort, while others may be more straightforward to resolve. Please give some thought towards dealing with the various issues from a practical point of view. At the end, we feel that the community would be well served by having a community assessment of what the problems are with some priority attached to them in terms of importance.

3. The agenda is under revision due to some feedback we have been receiving. Some people are beginning to contact each other so that they can combine their presentations - this will lead to more of a community presentation rather than a series of individual presentations. If you are comfortable doing this, please consider this option.

On to more practical matters. Could you prepare a short description (1 -2 pages) of your dataset(s) (cloud detection, inversion, observation times, spatial resolution and sampling etc) and its validation and make it available for out GEWEX web site? This way, the presenters will not have to spend time addressing this in their talks and can more quickly get to the results of their analyses.

Our discussions should lead to answers on the following questions:

1) What are the present results on cloud properties and their associated uncertainties and biases (depending certainly on the cloud type)?

2) Which results need further understanding and interpretation?

3) What are the current issues in order of importance and priority?

As already written in an earlier mail (8 June 2006), the next meeting should give us the opportunity to prepare a WMO report on cloud assessment (and perhaps a BAMS article summarizing).

Here are some suggested topics for a comprehensive report:

- Brief description of participating datasets

- How useful are ground networks for comparison with global satellite data sets?

- How do we summarize the algorithms and their accuracies and error sources?

- summarize the methodology used to intercalibrate the various satellite imagers.

- Climatological averages: global, ocean, land, regional (latitude bands) and seasonal (just a table)

- Seasonal and regional variability

- Trend anomalies and their interpretation

- What are some strategies for using geostationary and polar-orbiting satellite data:

- merge the datasets like ISCCP?

- use geostationary data to gain information on the diurnal cycle and apply to LEO data?

- other strategies

- Explanation of how datasets were intercompared (e.g., EOF analysis or linear statistical analysis with anomaly plots and correlations) as well as some interpretation of the intercomparison results.

- Do we need to develop a set of protocols for the use of active sensors (ground, aircraft, satellite) in comparison to satellite-derived properties? With such a set of protocols, the community would use the active sensor data the exact same way, which would remove one area of uncertainty in the comparisons.

Again, please think about these issues and send a summary of your results from the intercomparison effort to your session chairs, as well as us. It will help us prepare for a more productive meeting.

Thank you very much for your input.

Bryan and Claudia