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IntroductionThis page describes two studies of convection exhibiting different characteristics; one over N. America associated with the formation of severe tornadoes, the other over central Africa. The N.America case has strong large scale forcing whereas the central African case is driven by the diurnal cycle. The role of convection in these cases is quite different. Both cases use a forecast from the same date/time (initial conditions). In these case studies, you will carry out a control forecast, followed by any number of suggested sensitivity experiments. Info |
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These cases were used in the 2014 OpenIFS user workshop at the University of Stockholm. A Linux 'virtual machine' with a complete copy of the Stockholm workshop exercises is available on request from openifs-support@ecmwf.int. For more details and copies of handouts, please see the workshop page. |
US Tornado convection case (Arkansas) On the 27 April 7pm local time (00UTC 28 April), tornadoes hit towns north and west of Little Rock, Arkansas killing approx 17 people (see http://edition.cnn.com/2014/04/28/us/severe-weather/index.html?hpt=hp_c2). On the evening on the 28 April fatal tornadoes occurred over Mississippi ( see: http://www.bbc.co.uk/news/world-us-canada-27199071). This case study will look at the role of convection and the large scale in these events.
More information can also be found on the ECMWF Severe Event Catalogue 201404 - Convection - Arkansas U.S. Panel |
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African diurnal deep convection (Central Africa)Over tropical land masses, incoming radiation strongly heats the surface leading to the development of deep convection and precipitation. Observations show that convective activity and precipitation peak in the late afternoon or early evening. Until very recently, numerical weather prediction models struggled to reproduce this diurnal cycle, often predicting convective activity to peak too early in the day. In this case study, aspects of the convective parameterization scheme can be altered to see how the intensity and the diurnal cycle of convection responds. |
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Note that if using OpenIFS version 38r1 some additional code is needed for the diurnal correction of convection case study. Please retrieve the modified source code in the file 'src38r1-conv.tgz' from the same directory as the initial conditions as described below. |
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Initial conditions
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Note: The initial conditions data for the case studies described here are available for OpenIFS 40r1. Please contact OpenIFS Support if you require initial experiment data for more recent model version. |
Case study initial conditions for this case study are provided on the OpenIFS ftp site.
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We recommend that the initial files from the 27th April are used for a 30hr forecast for these exercises. The initial files from the 22nd are provided for interest in examining a longer forecast lead-time for the N.American case. |
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T159L62 | g4a5 | 2014/04/22 at 00Z | t159l62_g4a5_2014042200.tgz | 19Mb |
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| 2014/04/27 at 00Z | t159l62_g4a5_2014042700.tgz | 19Mb | T255L62 | g4a4 | 2014/04/22 at 00Z | t255l62_g4a4_2014042200.tgz | 51Mb |
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| 2014/04/27 at 00Z | t255l62_g4a4_2014042700.tgz | 51Mb | T255L91 | g455 | 2014/0427 at 00Z | t255l91_g455_2014042700.tgz | 76Mb | T511L62 | gflf | 20140422 at 00Z | t511l62_gflf_2014042200.tgz | 190Mb |
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| 20140427 at 00Z | t511l62_gflf_2014042700.tgz | 190Mb | T799L62 | gflg | 20140422 at 00Z | t799l62_gflg_2014042200.tgz | 441Mb |
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| 20140427 at 00Z | t799l62_gflg_2014042700.tgz | 441Mb | T1279L62 | gflh | 20140422 at 00Z | t1279l62_gflh_2014042200.tgz | 1.1Gb | |
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| 20140427 at 00Z | t1279l62_gflh_2014042700.tgz | 1.1Gb |
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To unpack files with .tgz, either use: tar zxf T159_1999122412_fqar.tgz
or if your tar command does not support compression: mv T159_1999122412_fqar.tgz T159_1999122412_fqar.tar.gz gunzip T159_1999122412_fqar.tar.gz tar xf T159_1999122412_fqar.tar
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We suggest starting with horizontal resolution of T255 for these exercises. Higher resolutions can be used for comparison. |
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Case study: N.America deep convection
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title | Key questions and tasks using the control forecast |
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- Understand the weather situation over Africa.
- What is the role of large scale in this case (compare with N.America case).
- Look at the diurnal variation of key parameters (2m temperature, surface heat fluxes, precipitation, outgoing-longwave-radiation) for location 0N,25E.
Perhaps plot hourly area average precipitation [-20S to 10N, 10-40E] (can also do this for the sensitivity experiments). - Compare differences in convection profiles between Central Africa and (i) open ocean, and (ii) Amazonia.
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Further reading
Journal publications
- Bechtold, P. et al, 2014, Representing Equilibrium and Nonequilibrium Convection in Large-Scale Models. J. Atmos. Sci., 71, 734–753. http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-13-0163.1
- Bechtold, P. et al, 2008, Advances in simulating atmospheric variability with the ECMWF model: From synoptic to decadal timescales, QRMS, 134, DOI: 10.1002/qj.289
- Petch, J. C. et al , 2002: The impact of horizontal resolution on the simulations of convective development over land. Quart. J. Roy. Meteor. Soc., 28, 2031–2044. DOI: 10.1256/003590002320603511
Other online material
The forecasting system at ECMWF makes use of "ensembles" of forecasts to account for errors in the initial state. In reality, the forecast depends on the initial state in a much more complex way than just the model resolution or starting date. At ECMWF many initial states are created for the same starting time by use of "singular vectors" and "ensemble data assimilation" techniques which change the vertical structure of the initial perturbations.
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We are especially grateful to Peter Bechtold for suggesting these case studies, assisting in their preparation and for his support during the OpenIFS workshop. We also give a special thanks to: Glenn Carver, Filip Vana and Sandor Kertesz in preparing the material for the OpenIFS user workshop in Stockholm 2014, from which most of the material on this page is derived. We also thank the forecast department for their material on the ECMWF Severe Event Catalogue that was used in preparing these cases. We also thank the participants of the OpenIFS user workshop in Stockholm for their participation and enthusiasm.
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