- When are the results due?
- How is the cloud defined?
- What about sedimentation?
- My cloud disappears!
- What form do you want the output in?
- The units in the radiative flux expression are inconsistent!
- What is the correct value for the Divergence?
- How do we know if you change the web page?
- The overview document is not consistent with the web page, which is right?
- What about 1-D models?
- How should I define z_i for the purposes of radiation?
- What value should I take for the Coriolis Parameter?
- What parameterization should we use for interactive surface fluxes?
- To what extent can I modify the initial conditions/spin-up to insure a reasonable cloud deck?
- Why are there no advective forcings?
- How come the radiative term is missing a factor of Theta/T?
- Are the units for kappa correct in table three of the overview document?
- What should the radiative forcing be?
- How was the case revised subsequent to the Broomfield workshop?
- What are common mistakes in the submission of output statistics?
- When are the results due?
- To be included in the intercomparison I must receive your results before September 30, 2003.
- How is cloud defined when computing cloud base, etc.?
- Here this is any column where the total water mixing ratio exceeds the saturation mixing ratio at the column temperature.
- What about drop sedimentation or drizzle?
- This is neglected in the base cases but such effects would be of interest for sensitivity studies.
- My model is not maintaining the cloud very well, is this usual?
- Perhaps, this is proving to be a difficult case to simulate and is very sensitive to vertical resolution in my model. Too much entrainment tends to be associated with evidence of ""decoupling"" as evidenced by a cloud base minimum in the vertical velocity variance profile.
- What form should model output be provided in?
- NetCDF. Templates will be made available on the output page in due course.
- The units seem incorrect in the expression for the radiative flux above cloud.
- Here the confusion arises because we assumed Tl ~ (z-zi)1/3, in reality a constant with value of unity should have been included to carry the units, but because it was unity it was dropped, leading to confusion with regard to the units.
- D takes on two different values in the overview, which is correct?
- The factor of 10-6 was accidentally dropped in Table 3, but it should be there, i.e., the correct value is D=3.75e-6 s-1.
- How will we know if pages have been updated?
- A list of updates will be posted to the calendar on the logistics page. When updates to the case are made they will also be sent by email to the participating scientists, to be on the list of participating scientists please send me an email.
- The overview document and the web page disagree, which is correct?
- Please contact me if you see any conflicts. The web page will be maintained more regularly and will be the definitive source, changes will be noted on the logistic page. For instance, in the first release the output page asked for different data than what was specified in the initial pdf release of the case, these discrepancies have since been reconciled by correcting the web page.
- Will 1-Dimensional models be incorporated into the intercomparison?
- Yes. Instructions are being prepared in collaboration with Martin Koehler of the ECMWF.
- For the last term in the expression of the radiative flux, should we assume that zi is the averaged zi as defined from the 295 K contour?
- No. Here it was intended that zi denote the local cloud top height as this is more consistent with the radiative parameterization.
- What should we use for the Coriolis parameter?
- Use a value of 7.6 e-5 s-1 as appropriate for 31.5 deg Latitude. Note that with the specified geostrophic winds and this value of f the boundary layer winds will not equilibrate to their observed value. This is not particularly meaningful as the value of geostrophic winds were only roughly estimated for the purposes of this cases definition. Those interested in a more accurate coupling of the momentum and thermodynamic budgets should revisit the measurements to make better estimates of the geostrophic winds,
- When we allow the surface fluxes to be freely determined, what parameterization should we use?
- Whatever you feel is best, i.e., this is not specified.
- How freely am I allowed to change the initial conditions in order to produce a reasonable cloud deck?
- This is a bit of an open question. At the minimum one simulation from each case should be provided which more or less confirms the initial specifications. However, one of the interesting questions is how far do we need to depart from our best guess of the initial state in order to represent the observed cloud evolution? By letting different groups explore different strategies we may stand a better chance of stumbling on a reasonable strategy. This in effect can be thought of as one of the motivating scientific questions for the workshop.
- Why are there no advective forcings?
- We are taking a Lagrangian point of view and assuming that the change in surface temperatures are such that they maintain a constant flux, and that the change in the properties of the atmosphere above the inversion are negligible.
- The radiative term is not energetically consistent. It should be multiplied by a factor of theta/T.
- This was considered to be negligible, and hence was not included.
- Are the units of Kappa correct in table three of the overview document?
- No. These should have been m2 kg-1, they have been since updated through the addition of a table three to the set up page, but remain incorrect in the pdf description of the case.
What should the radiative forcing be?
For step 1 the net forcing should be 48 Wm-2 all introduced through the F0 term in the radiative transfer equation. That is the second and third terms should be zeroed. For step 2 the F1 term is introduced and for step three the full equation is used with the values of constants specified in Table 3.
How was the case revised subsequent to the October Workshop?
- The temperature of the free troposphere was reduced by 1.5 K to be in better accord with the observations. So now the initial value for theta (z > zi) is set to theta = 297.5 + (z-zi)1/3 K.
- The surface friction velocity (u*) was changed to a prescribed value of 0.25 ms-1 for steps 1-3.
- The definition of the inversion was identified with the 8.0 gkg-1 isoline of qt for both the output statistics and for the purpose of calculating the radiative cooling in the free troposphere.
- Participation in the intercomparison was made contingent on providing clean output (conforming to the NetCDF templates) for Step 3 prior to December 15, 2003.
- Cloud fraction was given in percent instead of as a fraction
- Dissipation was defined as negative (we want positive dissipations)
- Only 8 time records were given for the profile statistics, i.e., initial time profiles were omitted.