Requested Diagnostics


The following is a first draft recommendation from Francois Lott:

Here is a table of diagnostics, which include the diagnostics requested by the ISSI group initiated by Joan Alexander a couple of years ago, and from which I started. What I remember from our discussions during the QBOi workshop, is that each group makes a simulation with its best QBO (not necessarily a version suited to CMIP6), and over 30 years (more maybe for histograms and spread?) store at pressure levels as near as they can be from the model levels and between 0.01 and 1000hPa, monthly-mean zonal mean data of:

u,  du/dt, T, v*, w*, F_phi, F_z, divF, G_ogw, G_ngw


Here the time derivative of the mean velocity (dynamical tendency) is to try to make the difference between the advective terms we can deduce from the TEM equations, and the advective plus forcing terms due to explicit/numerical diffusions which are sometimes difficult to extract from models. Also, we nead the EPF divergence (EPFD), and the tendencies due to the orographic and non-orographic gravity waves G_ogw, G_ngw

Also, it is useful to have the eastward and westward component of the non-orographic GWs momentum fluxes, rho_0*\bar{u'w'}_egw, rho_0*\bar{u'w'}_wgw


We could repeat this in 2XCO2+2K SST and 4XCO2+4K SST to see how our QBOs respond to climate change: there seems to be large spread amoing models.

Now, from the QBOi workshop I remember that we need to no know if our models simulate the QBO for the right (or the same reasons) and in particular the fraction of the resolved waves in each models. For this, the EPFD may not be sufficient, and the EPF themselves can include large opposing balance so we have to calculate time-wavenumber spectra of EPF, and this request storage of instantaneous values of u, w, v, and T at pressure levels, every three hours (to be discussed, 1hr?) and during at least one QBO period (for instance over three years). In my opinion, this needs to be done over a good number of levels in the QBO regions, above and below, for instance (to be discussed):

200hPa,150hPa,100hPa,70hPa,50hPa,30hPa,20hPa,15hPa,10hPa,5hPa,2hPa,1hPa
Why many levels: 1) to make better than the spectra in Horinoushi et al.~(2003) on top of the fact that we now all have a QBO (which was not the case in the 2003, paper); 2) A big question is to know how fast the equatorial waves dissipate in the vertical in the QBO region, 3) understand the behaviour around the TTL and in the SAO region. Differences between vertical levels may also help reduce the contribution of the tidal signals in the time-lon spectra, something that can be problematic at sub-diurnal periods (true?).


My rough estimate for one model is almost 500GB if we stay on netcdf format. But this opens the debate (3years of u,v,w,T at 12 vertical levels, 160x90 horizontal levels, every 3hrs).

Also, we would need a good deal of 2D fields, like precipitation, convective prec, OLR, etc. Information on the vertical structure of the tropical heating would be useful also, but I have no especially precise idea right now of about this should be done.

All diagnostics are done according to the TEM formalism as described in, Middle atmosphere dynamics. By D. G. Andrews, J. R. Holton and C. B. Leovy. Academic Press, San Diego, 1987 

Horinouchi, T., S. Pawson, K. Shibata, E. Manzini, M.A. Giorgetta, F. Sassi, R. J. Wilson, K.
Hamilton, J. DeGrandpe and A.A. Scaife, 2003: Tropical cumulus convection and upward propagating waves in middle-atmospheric GCMs, J. Atmos. Sci. , 60, 2765—2782.

Some spectra/composites from CMIP5 models are in:


Lott, F. S. Denvil , N. Butchart, C. Cagnazzo , M. Giorgetta, S. Hardiman, E. Manzini, T. T. Krishmer , J.-P. Duvel, P. Maury, J. Scinocca, S. Watanabe, S. Yukimoto, 2014: Kelvin and Rossby gravity wave packets in the lower stratosphere of some high-top CMIP5 models, J. Geophys. Res., 119, 5, 2156-2173, DOI: 10.1002/2013JD020797

Additional Experiment - Dynamical Cores

These experiments investigate the sensitivity of QBO-like variability in GCM dynamical cores to changes/representations of numerics and resolution.

A first draft for this experiment  is being prepared by Christiane Jablonowski and will appear here shortly. At this time wider discussion will be encouraged to best facilitate wider participation within the group.

Additional Experiment - Nudging to Specifiy Dynamics

The following experiments are suggested for interested groups. These investigate the role of feedbacks in maintaining the QBO. The general idea would be to alter model physics or numerics while maintaining the zonal mean state. This technique will isolate the resolved wave response without feedbacks from the changing zonal men state. Possible experiments might include:

  • nudging zonal-mean conditions in the tropical stratosphere
  • nudging aspects of the tropical troposphere
A first draft for this experiment  is being prepared by Kevin Hamilton and will appear here shortly. At this time wider discussion will be encouraged to best facilitate wider participation within the group.

Experiment Two - Initialisation Runs

The following experiment attempts to identify those conditions and processes which impact skilful prediction of the QBO. The time length of these runs are seasonal to annual (e.g. 9 months). Discussions ought to include:

  • Common initial state for all model tuns? (initialised by nudging, singular vectors etc.)
  • What relevant phase during the QBO and annual cycle? (4 QBO states? 2-4 annual cycle states?)
A first draft for the initialisation set-up  is being prepared by Tim Stockdale and will appear here shortly. At this time wider discussion will be encouraged to best facilitate wider participation within the group.

Experiment One - Climate Runs

The first set of experiments will centre around modelling the QBO subject to:
  1. historical climate forcing, 
  2. climatological forcing (interannual external forcing removed) 
  3. and a climate change scenario (e.g. +2K or x2 CO2 etc). 
The intention will be to employ AMIP SSTs and sea-ice. Other forcing fields should include representations of: aerosol, ozone, GHGs, solar variability etc.

A first draft of the experimental set-up  is been prepared by John Scinocca and will appear here shortly. At this time wider discussion will be encouraged to best facilitate wider participation within the group.

Experiments

The objective of QBOi is to evaluate the sensitivity dependencies of tropical stratosphere variability within current global climate models. In so doing, we anticipate learning more about the modelled dynamics and variability of the tropical stratosphere. On a practical level, it is hoped this project will help improve QBO modelling in time for CMIP6.

It is commonly believed that to generate a QBO, GCMs require the right choice of: resolution (spatial and temporal), parameterisation (convection and GWs) and numerics (diffusion, numerical solvers). The choice of parameters is not completely unique: getting a QBO in one model, with one set of parameters, may not necessarily result in a QBO in another model. Having said this, one might suspect particular parameter choices being more likely to result in a QBO than others. We propose to explore these parameter settings, across a range of GCMs, to better identify robust effects.

We propose two levels of participation within QBOi. The first, QBOi-lite, assumes one or more sets of model runs with no changes in model formulation (but may include initial condition ensembles). The intention for these runs would be to compare across models i.e. an intermodel comparison. Although such an analysis is not without its problems, it is nothing different from other studies comparing different models e.g. CMIP5. A second level of participation, and more in line with the spirit of the project, is for separate runs using one model with structural changes to resolution, parameterisation etc. Differences would first be sought within a model, before then being checked across models for robustness.

It is suggested that runs should be AMIP styled (atmosphere only) and run over the recent past (1960 onwards). More specifically, it is suggested that boundary/ancillary fields used for CMIP5 should be employed. As many participating groups would have been involved in CMIP5, this would seem a natural choice.

The diagnostics which we suggest include those terms required to close the momentum budget, so include 4-daily instantaneous: u, v, Z, GW flux/tendencies. Presumably, there is flexibility for instantaneous or time-average output, but perhaps the former would be better(?). For completeness, temperature/heating terms (T, Q_sw, Q_lw) would be advantageous, but perhaps monthly mean output would be suitable. Obviously, the high frequency diagnostics would be used to derived terms in the TEM equations (e.g. EP flux) which your model may already log. However, it is recognised that model diagnostics should be openly discussed within the wider group.

But what do you think? Should experiments be more prescriptive? Should specific resolutions, parameterisations be suggested? What is the right balance of diagnostics which should be included? A number of these questions also require a discussion of the science people wish to do. If you think this is important do say so, otherwise science topics will be deferred to a separate discussion blog. Please feel free to contribute to this discussion, your thoughts are most welcome.

Update 22 March 2015 - Following the discussion coming out from the first QBOi Workshop held in Victoria, BC 16-18 March 2015, a number of experiments were endorsed. The details of these will be discussed in separate blogs found on this website.


Questionnaire

We are interested in assessing tropical stratosphere variability in past and present day global climate models. Not only are we interested in better understanding the phenomenology of a modelled QBO, but we are also interested in knowing why most GCMs can not readily reproduce it. The QBOi questionnaire is designed to identify and collate the phenomenological characteristics of QBO variability from GCMs. The survey makes no attempt to be exhaustive, but instead attempts to balance capturing as much useful information as possible, with a minimum of user calculation, to better ensure user participation.

The questions are (mostly) designed to objectively identify the observed characteristics of a modelled QBO, so that comparisons can be made with observations/reanalyses. However we may have missed out other interesting and verifiable diagnostics which would be of interest to a wider group. What questions would you have liked to have been asked? Do you think the current questions capture most of the salient features of the QBO?

Lastly, we can also arrange for your data to be uploaded to the QBOi project work-space where we can analyse the data for you. Please contact us if this is an option for you.

Please let us know your thoughts?