OpenIFS 2019: Programme

Mark Rodwell

ECMWF, UK

Some days, the atmosphere is less predictable than on average. This is partly because the rate of growth of certainty (the result of Chaos) is dependent on the atmospheric flow itself. For example, moist processes are almost always implicated during investigations of very poor forecasts for Europe (so-called "forecast busts"). These moist processes might be associated with, for example, warm conveyor-belts along the cold-fronts of a cyclonic systems, meso-scale convective situations, or the extra-tropical transition of tropical cyclones.

Such moist situations also present a particular challenge for data assimilation. For example, satellite observation operators are highly non-linear in cloudy situations. The result is that the ensemble distribution of initial conditions is less constrained by the available observations.

Furthermore, these moist situations present challenges for the model. For example, the model's parametrized "deterministic physics" is very active in these situations, and biases are likely to have a large impact on the forecast. In order to maintain the "spread-error" relationship of the ensemble, additional "stochastic physics" is required to adequately represent the effects of sub-grid-scale uncertainty in these moist processes.

Hence such moist situations represent, almost literally, a "perfect storm" for forecasting. Progress can be made on some aspects, but the inherent large uncertainty growth-rates will remain.

This talk will illustrate these various aspects with some emphasis on the case-study of the transition of tropical cyclone Karl, which was well observed during the recent NAWDEX field campaign.

Keith Williams

Met Office, UK

This presentation will discuss the sensitivity of weather forecasts to parametrizations, with a focus on moist processes. A range of examples from the Met Office Unified Model will be given including discussion of the role of convection, cloud and boundary layer processes. Diagnostic techniques to identify the likely source of sensitivity will also be discussed. Global examples of the Impacts on both the large scale circulation and local weather will be presented.

Victoria Sinclair¹, Helen Dacre²

¹University of Helsinki, Finland
²University of Reading, UK

Extra-tropical cyclones are known to be responsible for a large proportion of the poleward moisture transport in the mid-latitudes. However, not all cyclones are equal; some transport significantly more moisture polewards than others. The aim of the work presented here is to identify which cyclone characteristic (genesis latitude, maximum vorticity and poleward propagation speed), leads to the greatest variability in meridional moisture transport per cyclone. We use ERA-Interim reanalysis combined with an objective cyclone tracking algorithm (TRACK), a cyclone masking method and cyclone composites. Interestingly, the results show that cyclone intensity, quantified by maximum vorticity, has a weaker influence on how much moisture a cyclone can transport than other cyclone characteristics. This result suggests that studies considering how extra-tropical cyclones will change in the future should focus on cyclone track as well as cyclone intensity and number.

Heini Wernli

ETH, Switzerland

The prediction of the track, intensity and structure of extratropical cyclones is of key importance for accurately forecasting surface weather and its extremes. In addition to classical baroclinic instability typically induced by an upper-level cyclonic potential vorticity (PV) anomaly, moist diabatic processes that occur in saturated ascending airstreams are essential for the evolution of cyclones, the associated surface weather, and the downstream flow evolution. Results from studies that are mainly based on the analysis of IFS analyses and forecasts, will be shown to illustrate that (i) the diabatic PV production in the low troposphere is essential for the formation of intense extratropical cyclones, (ii) diabatic processes are particularly intense in so-called warm conveyor belts, i.e., in moist ascending airstreams associated with extratropical cyclones, (iii) different microphysical processes in and below clouds contribute to the diabatic formation of PV anomalies in cyclones, and (iv) exceptionally poor global model medium-range weather forecasts (so-called forecast busts) in Europe are often associated with errors in the representation of warm conveyor belts. The presentation will also provide a selection of first results from the recent field experiment NAWDEX, which was dedicated to observing diabatic processes in mid-latitude weather systems.

Christian M. Grams

Karlsruher Institut für Technologie, Germany

The large-scale extratropical circulation is dominated by Rossby wave activity along the upper-level midlatitude wave guide. Recent research revealed that moist processes can be as important in the evolution of Rossby wave packets as dry dynamics. This is primarily due to latent heat release in ascending air streams, i.e. warm conveyor belts (WCBs). Thereby moist warm air is transported poleward and ascends slantwise along the midlatitude baroclinic zone. Latent heat release due to condensation enhances this ascent and results in a net transport of air mass into the upper troposphere. This so-called diabatic outflow deflects the wave guide poleward, accelerates the jet stream, and an upper-level ridge builds or amplifies that might ultimately become a blocking anticyclone. Rossby wave activity in the Atlantic-European region often occurs in preferred quasi-stationary, persistent, and recurrent states called weather regimes. These explain most of the atmospheric variability on sub-seasonal time scales. However, current numerical weather prediction models struggle in correctly predicting weather regime life cycles.

This presentation will focus on the role of diabatic outflow in the life cycle of Atlantic-European weather regimes and how diabatic outflow affects predictability of the large-scale extratropical circulation. In the period prior to the onset of regimes characterized by blocking important changes of the location and frequency of WCBs occur. WCB activity increases significantly upstream of the incipient blocking anticyclone even before blocking is detectable. Diabatic outflow persists over the blocked region later. Thus diabatic outflow is key for the onset and maintenance of blocked regimes in the Atlantic-European region. The misrepresentation of WCB activity and associated diabatic outflow can result in severe forecast busts due to upscale error growth. Thereby the physical processes within a WCB might communicate and amplify small initial condition error to the large-scale extratropical circulation. This is exemplified for recent cases of regime onset.

Further reading:

Ferranti, L., S. Corti, M. Janousek, 2015: Flow-dependent verification of the ECMWF ensemble over the Euro-Atlantic sector. Q.J.R. Meteorol. Soc., 141, 916–924, https://doi.org/10.1002/qj.2411.

Grams, C.M., H.M. Archambault, 2016: The key role of diabatic outflow in amplifying the midlatitude flow: a representative case study of weather systems surrounding western North Pacific extratropical transition. Mon. Wea. Rev., 144, 3847–3869, https://doi.org/10.1175/MWR-D-15-0419.1.

Grams, C.M., R. Beerli, S. Pfenninger, I. Staffell, H. Wernli, 2017: Balancing Europe’s wind-power output through spatial deployment informed by weather regimes. Nature Climate Change, 7, 557–562, https://doi.org/10.1038/nclimate3338.

Joos, H., H. Wernli, 2012: Influence of microphysical processes on the potential vorticity development in a warm conveyor belt: a case-study with the limited-area model COSMO. Q.J.R. Meteorol. Soc., 138, 407–418, https://doi.org/10.1002/qj.934.

Martínez-Alvarado, O., E. Madonna, S.L. Gray, H. Joos, 2016: A route to systematic error in forecasts of Rossby waves. Q.J.R. Meteorol. Soc., 142, 196–210, https://doi.org/10.1002/qj.2645.

Michel, C., G. Rivière, 2011: The link between Rossby wave breakings and weather regime transitions. J. Atmos. Sci., 68, 1730–1748, https://doi.org/10.1175/2011JAS3635.1.

Pfahl, S., C. Schwierz, M. Croci-Maspoli, C.M. Grams, H. Wernli, 2015: Importance of latent heat release in ascending air streams for atmospheric blocking. Nature Geosci, 8, 610–614, https://doi.org/10.1038/ngeo2487.

Vautard, R., 1990: Multiple weather regimes over the North Atlantic: analysis of precursors and successors. Mon. Wea. Rev., 118, 2056–2081, https://doi.org/10.1175/1520-0493(1990)118<2056:MWROTN>2.0.CO;2.

John Methven¹, Ben Harvey¹, Andreas Schäfler¹, Suzanne Gray¹, Leo Saffin², Maarten Ambaum¹

¹University of Reading, UK
²University of Oxford, UK

The jet stream has a major influence on the development of weather systems across the North Atlantic and weather across Europe. Forecast busts in Europe have been associated with a particular precursor configuration of waves on the jet stream linked with active weather systems over the eastern USA 5 days beforehand. It has been conjectured that misrepresentation of cloud processes and latent heat release in those systems is responsible for the poor forecasts downstream. However, is it true? How might these diabatic processes influence the jet stream structure, Rossby wave disturbances and the dynamics of weather systems? The North Atlantic Waveguide and Downstream Impacts Experiment set out to answer these questions by making new high resolution measurements exploring jet stream structure and influences on development. One finding was that the tropopause potential vorticity gradient and the peak jet stream winds are much sharper than represented in global analyses and furthermore the gradient decreases with forecast lead time. Evidence for diabatic processes acting to increase the PV contrast across the tropopause is presented, and the consequences for Rossby wave propagation and forecasts are explored.

1. Jake Bland (University of Reading, UK)

2. Yun Chen (National Meteorological Center of China)

3. Guokun Dai (Fudan University, China)

4. Mokhliss El-azaar (EHTP, Morocco)

5. Jian-Feng Gu (University of Reading, UK)

6. Ben Harvey (University of Reading)

7. Sam Hatfield (University of Oxford, UK)

8. Ying Li (Chinese Academy of Meteorological Sciences)

9. Federico Serva (CNR-ISMAR, Italy)

10. Lorenzo Silvestri (CIRIAF-CRC, University of Perugia, Italy)

11. Irina Statnaia (University of Helsinki, Finnish Meteorological Institute)

12. Lauri Tuppi (University of Helsinki, Finland)

13. Jun Xu (National Meteorological Center of China)

14. Sophia Schäfer (Deutscher Wetterdienst, Germany)

Helen Dacre

University of Reading, UK

Extreme precipitation associated with extratropical cyclones can lead to flooding if cyclones track over land. However, the dynamical mechanisms by which moist air is transported into cyclones is poorly understood. We analyse airflows within a climatology of cyclones in order to understand how cyclones redistribute moisture stored in the atmosphere. This analysis shows that within a cyclones' warm sector the cyclone-relative airflow is rearwards relative to the cyclone propagation direction. This low-level airflow (termed the feeder airstream) slows down when it reaches the cold front resulting in moisture flux convergence and the formation of a band of high moisture content. One branch of the feeder airstream turns towards the cyclone centre supplying moisture to the base of the warm conveyor belt where it ascends and precipitation forms. The other branch turns away from the cyclone centre exporting moisture from the cyclone. As the cyclone travels, this export results in a filament of high moisture content marking the track of the cyclone (often used to identify atmospheric rivers). We find that both cyclone precipitation and water vapour transport increase when moisture in the feeder airstream increases, thus explaining the link between atmospheric rivers and the precipitation associated with warm conveyor belt ascent. Atmospheric moisture budgets calculated as cyclones pass over fixed domains relative to the cyclone tracks, show that continuous evaporation of moisture in the pre-cyclone environment moistens the feeder airstream. Evaporation behind the cold front acts to moisten the atmosphere in the wake of the cyclone passage, potentially preconditioning the environment for subsequent cyclone development.

Mika Rantanen, Jouni Räisänen, Victoria Sinclair, Heikki Järvinen

University of Helsinki, Finland

Hurricane Ophelia was a category 3 hurricane which underwent an extratropical transition and made landfall in Europe as an exceptionally strong post-tropical cyclone in October 2017. In Ireland, for instance, Ophelia was the worst storm in 50 years and resulted in significant damage and loss of life.

In this study, the different physical processes affecting Ophelia’s transformation from a hurricane to a mid-latitude cyclone are studied. For this purpose, we have developed software which uses OpenIFS model output and a system consisting of a generalized omega equation and vorticity equation. By using these two equations, the atmospheric vertical motion and vorticity tendency are separated into the contributions from different physical processes: vorticity advection, thermal advection, friction, diabatic heating, and the imbalance between the temperature and vorticity tendencies.

Vorticity advection, which is often considered an important forcing for the development of mid-latitude cyclones, is shown to play a small role in the re-intensification of Ophelia as an extratropical storm. This is because the effects of divergent and non-divergent components of vorticity advection mainly cancelled each other out, resulting in a net effect close to zero. However, our results show that diabatic heating was the dominate forcing in both the tropical and extratropical phases of Ophelia.

Furthermore, we calculated in more detail the diabatic heating contributions from different model parameterizations. We find that the temperature tendency due to the convection scheme was the dominant forcing for vorticity tendency during the hurricane phase, but as Ophelia transformed into a mid-latitude cyclone, the microphysics temperature tendency gradually increased becoming the dominant forcing once the transition was complete.

• Semi-implicit, semi-Lagrangian schemes
• New octahedral grid & implications
• Stratospheric improvements

Sarah Sparrow¹, Antje Weisheimer^1,2, Andy Bowery¹, Glenn Carver², Gabriella Szépszó², Marcus Köhler², Florian Pappenberger², David Wallom¹

¹University of Oxford, UK
²ECMWF, UK

Weather forecasts rely heavily on general circulation models of the atmosphere and other components of the Earth system. National meteorological and hydrological services and intergovernmental organisations, like ECMWF, provide routine operational forecasts on a range of spatio-temporal scales, by running these models on state-of-the-art high-performance computing systems. Such operational forecasts are very demanding in terms of computing resources. To facilitate the use of a weather forecast model for research and training purposes outside the operational environment, ECMWF provides a portable version of its numerical weather forecast model, called OpenIFS, for use by universities and other research institutes on their own computing systems.

In this contribution, we describe a new project (OpenIFS@home) that combines OpenIFS with a citizen science approach to involve the general public in helping conduct scientific experiments. We will be using volunteers from across the world to run OpenIFS on their computers at home. The infrastructure of such distributed computing experiments will be based on our experience and expertise with the climateprediction.net and weather@home systems, that successfully use versions of the Met Office Hadley Centre model for weather and climate change simulations.

In OpenIFS@home, the enormous computing resource by volunteers will be utilised to study the predictability of weather forecasts. Interesting past weather and climate events will be explored by re-running them and testing sensitivities to physical parameter choices in the model. Large ensemble simulations will be possible that will help study probabilistic forecasts in a chaotic atmospheric flow and reduce uncertainties due to nonlinear interactions. It is also planned for a later stage, to adopt the system for performing climate change experiments. It is expected that OpenIFS@home will become a valuable additional contribution to the existing range of distributed computing modelling experiments for weather impacts and climate attribution research.

Nedjeljka Žagar

University of Hamburg, Germany

Global numerical weather prediction (NWP) models are characterized by significant uncertainties in their initial state in the tropics. Furthermore, the largest simulated uncertainties of the global ensemble forecasts in the short range is also found in the tropics. This applies to all zonal wavenumbers and the larger the scale, the greater the uncertainty. My lecture will present evidence of these facts using the data from the ECMWF deterministic and ensemble prediction system to illustrate how these properties have evolved in recent years.

Moist processes in the tropics generate the spectrum of waves that propagate horizontally and vertically. For example, the short-term response to tropical heating anomalies resembling MJO projects predominantly on the inertio-gravity (IG) waves, especially the Kelvin wave. The equatorial IG waves make a large part of tropical variance on all scales and their role in the initial state for NWP is still not clear. This is related to complex moist dynamics, a lack of wind observations and assumptions made in data assimilation modelling. I will demonstrate that uncertainties in the forecasted IG spectra associated with moist convection are less successfully reduced on all scales than uncertainties associated with Rossby waves.

In order to explain some observed features of the NWP models and to investigate possible remedies, simplified models can be used provided they are still complex enough to capture the main dynamical and physical aspects of the phenomena of interest. I will introduce such a model for moist processes and data assimilation in the tropics and present its results that explain some observed features of full-scale NWP systems.

Klaus Wyser

Swedish Meteorological and Hydrological Institute

The 6th phase of the Coupled Model Intercomparison (CMIP6) has started and the EC-Earth community has started making pre-industrial, historical and future scenario experiments with the EC-Earth3 model. The data are uploaded to ESG data nodes and shared with the climate modeling community. In my talk I will briefly describe the development from the coupled IFS-NEMO model to the CMIP6 version of EC-Earth3, the tuning of the coupled model, and present an analysis of the first results from our CMIP6 simulations. The results will be put in context to other CMIP6 models in a common evaluation that will focus on the role of clouds for the climate.

Terhi Laurila¹, Victoria Sinclair², Hilppa Gregow¹

¹Finnish Meteorological Institute
²University of Helsinki, Finland

On 22 September 1982, an intense windstorm Mauri led to extensive wind damage in northern Finland. Mauri was potentially related to the extratropical transition of Hurricane Debby which is an uncommon origin for a windstorm in Fenno-Scandinavia. In this study, we analyze the synoptic-dynamic evolution of Mauri to investigate the role of Debby in its development, and we examine the physical reasons for strong wind gusts over Finland. A brief synoptic overview was conducted based on ERA-Interim and a more detailed analysis was performed based on multiple OpenIFS simulations with different initialization times. We found that Debby did not immediately re-intensify when it reached the mid-latitudes due to lack of upper-level support. However, ex-Debby was able to self-maintain itself as a diabatic Rossby wave while traveling rapidly across the Atlantic. Near the UK, ex-Debby rapidly re-intensified when it interacted with an upper-level potential vorticity anomaly of another extratropical cyclone. This intensification was not captured in OpenIFS simulations initialized on 17 and 19 September since the phasing of upper and lower-level anomalies was incorrectly simulated. In the simulation from 21 September, the re-intensification of ex-Debby was captured and the wind gusts over northern Finland were stronger than in the other simulations. Strong pressure gradients caused the strong wind speeds and the wind gusts were further enhanced behind the cold front due to turbulent mixing and in the warm sector due to convectively driven downdrafts. In conclusion, Mauri was connected to Hurricane Debby but the interaction with another extratropical cyclone over the UK was critical for ex-Debby to re-develop into an intense windstorm over Finland.

Bethan Harris, Remi Tailleux, Christopher Holloway, Pier Luigi Vidale

University of Reading, UK

Investigating the evolution of Available Potential Energy (APE) in a tropical cyclone (TC) offers the opportunity to gain greater physical insight into the effects of diabatic processes on TC intensification and maintenance. For example, when TC processes are considered in terms of entropy, irreversible processes are by definition a source of entropy and therefore reduce the efficiency of the TC heat engine; local APE theory shows that in fact irreversible processes may be either a source or sink of APE and so they could in some situations promote intensification. We present a budget of APE for the idealised axisymmetric TC model of Rotunno and Emanuel [1987], with Craig’s modified microphysics scheme. The APE density is defined for each moist air parcel as the work released when the parcel moves from its initial position to its level of neutral buoyancy with respect to a reference state. A discretised APE density and APE production efficiencies are constructed to match the model equations. In the mature stage, the chief source of APE in the TC is the advection of APE along the near-surface radial inflow, with significant additional contributions from local APE production due to surface fluxes and the microphysics scheme. The intensification phase is characterised by increasing APE production efficiencies as well as changes in diabatic forcings. We outline the link between the APE budget and TC intensification in terms of the kinetic energy budget, and question whether the choice of APE reference state affects the interpretation of diabatic processes as sources or sinks of APE. We discuss how the components of the APE budget may be useful as process-oriented diagnostics for studying the role of moisture-convection coupling in TC intensification in NWP and climate models.

Joakim Kjellsson, Wonsun Park, Mojib Latif

GEOMAR, Germany

We study the variations in air-sea interactions across different horizontal length scales using a climate model, FOCI, run at various resolutions. At higher horizontal and vertical resolution, the atmosphere model is capable of capturing short-lived, localised extremes in precipitation and wind speed, which impacts the air-sea exchange of momentum and freshwater. Furthermore, studies suggest that increasing the horizontal resolution of the ocean component leads to more intense air-sea fluxes of heat and freshwater.

The FOCI-OIFS v1.0 climate model is based on OpenIFS cy40r1 and NEMO/LIM v3.6 run at 1.125° and 0.5° resolution respectively, with the possibility to increase ocean resolution to 0.1° regionally using AGRIF two-way nesting. OpenIFS can be run at a variety of horizontal resolution. The development and set up of this model will be presented as discussed.

Chris Thorncroft, Alan Brammer, Matt Janiga

University at Albany, USA

In the first part of this talk emphasis will be given to the regional differences in the vertical structure of AEWs as they move between East Africa and the East Atlantic. The vertical structure of temperature and vorticity in the AEWs are related to regional differences in the climatological and vortex‐centred diabatic heating and diabatic potential vorticity (PV) generation profiles from three reanalysis datasets (ERA-Interim, NCEP-CFSR, MERRA). The climatological diabatic heating over East Africa peaks at 450 hPa with diabatic cooling below 750 hPa. In contrast, the convectively active West African coast and the East Atlantic have increased diabatic heating in the lower troposphere. Due to these regional differences in diabatic heating, diabatic PV generation peaks near 700 hPa over the continent and below 800 hPa over the East Atlantic. Moving westwards from East Africa to the East Atlantic, AEW composites have weaker lower tropospheric cold cores and significantly increased lower tropospheric vorticity within the convectively active troughs.In the second part of this talk emphasis is given to the factors that influence the probability that a favorable-looking AEW leaving the West African coast becomes a tropical cyclone or not. The analysis shows that favorable developing waves had significantly higher moisture content in the lower troposphere to the northwest of the trough as they exited the West African coast compared to favorable non-developing waves. Trajectory analysis for all the waves revealed that as the AEWs transition over the West African coast the troughs are typically open to the environment ahead and to the northwest of the trough. For developing waves this means that moist air is ingested into the lower levels of the system, while for non-developing waves dry air is ingested. Finally, some real time monitoring and forecast products based on this work will briefly be presented.

Pirkka Ollinaho

Finnish Meteorological Institute

Probabilistic forecasts provide information on how predictions of the atmospheric evolution may differ from the traditional "best guess" solution, i.e. the deterministic forecast. Ensemble prediction systems generate this probabilistic information through assessing uncertainties in both the model initial state and the model itself. In order to open up ensemble prediction research for a wider research community, we have recreated all 50+1 operational IFS ensemble initial states for OpenIFS. The data set covers one year (December 2016 to November 2017) twice a day. A range of model resolutions are provided to cover different research needs (TL159, TL399 and TL639).

An open-source workflow manager, called OpenEPS, is used to launch ensemble forecast experiments from the perturbed initial conditions. The experiments are run with OpenIFS CY40R1 and examine all the provided resolutions. The probabilistic skill of the experiments is assessed through ensemble mean RMSE and ensemble spread, and the Continuous Ranked Probability Score (CRPS) for several forecast variables. We will furthermore discuss how many ensemble members are required for conducting meaningful research experiments. This is inspired by a recent paper by Leutbecher (2018), who explored the ensemble size impacts with IFS. Here we redo the same experiments with the OpenIFS ensembles.

We will also illustrate the research potential of running your own ensemble of forecasts through a case study of typhoon Damrey, which severely affected Vietnam in 2017.

Further reading:

Leutbecher M., 2018: Ensemble size: How suboptimal is less than infinity? Q. J. R. Meteorol. Soc. 2018, 1–22, https://doi.org/10.1002/qj.3387.

Xavier Yepes Arbós, Etienne Tourigny, Mario Acosta Cobos, Francisco Doblas-Reyes

Barcelona Supercomputing Center, Spain

Models used in weather and climate forecasts must initialize the state of the Earth system (atmosphere, ocean, land and cryosphere) from observations. Retrospective forecasts (also called hindcasts) in weather or climate prediction mode are used to evaluate the model’s performance and are typically initialized from reanalysis products (such as ERA-Interim). However, the horizontal and vertical resolution of the reanalyses can be different and additional operations are needed to fit the grid model of the hindcast.

The EC-Earth climate model used, among others, by BSC relies on atmospheric initial conditions derived from ERA-Interim. These data must be obtained for several start dates (4 each year) for the entire period covered by the reanalysis product. Until recently, these data were generated at ECMWF HPC facilities using an IFS experiment with the prepIFS infrastructure.

The procedure used is:

1. Download the reanalysis data at its native resolution using MARS requests.
2. Running IFS in mode 927 to make use of FullPos, a powerful post-processing package that performs horizontal and vertical interpolations.
3. Post-processing the result and archival on MARS.

While this procedure is robust and relatively fast, it relies on ECMWF infrastructure and support. Moreover, it is vulnerable to changes in the HPC platform used.

To overcome these shortcomings, the scripts have been simplified and adapted to run on other HPC platforms using the OpenIFS model cycle 40r1. The advantage of the new scripts is that they can be easily deployed on any machine with minimal effort by the user. Currently, the retrieval script is run on the ecgate cluster at ECMWF for efficiency and ease of implementation, relying on the MARS client, but it could be adapted to use the CDS API instead of MARS client. In addition, they are automated using the open-source Autosubmit workflow manager to minimize the user intervention as well as errors, and to optimize some processes.

The results show that the differences of the interpolated GRIB files produced by IFS on ECMWF and by OpenIFS on MareNostrum are negligible. Moreover, several configurations have been successfully interpolated, including configuration T1279L137, which takes very little time, proving that the implementation is fast.

Hannah Christensen

University of Oxford, UK

Stochastic parametrisations are used in weather and climate models to represent model error. Designing new stochastic schemes has been the target of much innovative research over the last decade, with a focus on developing physically motivated schemes. We present a technique for systematically deriving new stochastic parametrisations or for constraining existing stochastic approaches. We take a high-resolution model simulation and coarse-grain it to the desired forecast model resolution. This provides the initial conditions and forcing data needed to drive the OpenIFS Single Column Model (SCM). By comparing the SCM parametrised tendencies with the evolution of the high-resolution model, we can measure the ‘error’ in the SCM tendencies. As a case study, we use this approach to assess the physical basis of the ‘Stochastically Perturbed Parametrisation Tendencies’ (SPPT) scheme, used operationally in the ECMWF Ensemble Prediction System to represent model uncertainty. We provide justification for the multiplicative nature of SPPT, and for the large temporal and spatial scales used in the stochastic perturbations. However, we also identify issues with the SPPT scheme and motivate improvements. In particular, our results indicate that an alternative approach is needed to represent uncertainty in the convection scheme. It is hoped this new coarse-graining technique will improve both holistic and process-based approaches to stochastic parametrisation.

Further reading:

Christensen, H.M.: Constraining stochastic parametrisation schemes using high-resolution simulations. For submission to Q. J. Roy. Meteor. Soc.

Christensen, H.M., Dawson, A., Holloway, C.E., 2018: Forcing Single-Column Models Using High-Resolution Model Simulations. J. Adv. Model. Earth Syst., 10(8), 1833-1857, https://doi.org/10.1029/2017MS001189.

Emma Howard, Richard Washington

University of Oxford, UK

Precipitation underpins the lives of 150 million people in southern Africa. Shifts in rainfall can undercut agricultural production, undermine water, food and energy security, and ultimately threaten the economic viability of the region.

Tropical Lows are important rain-bearing weather systems in southern Africa, providing 33% of summer precipitation across the southern edge of the tropical rain belt. They are a means by which the ENSO signal is expressed in Southern Africa, forming less frequently and further north during the El Nino phase, which is linked to regional drought. Meanwhile, heat lows play an important role in controlling the location of the edge of the tropical rain belt in spring.

This talk will present some key findings on the synoptics of tropical lows and heat lows. The role of the steep southern African topography in the formation, maintenance and anchoring of these features will be considered by means of a novel global-regional modelling setup combining OpenIFS with WRF.

• Build the model
• Study and set the namelist
• Running on Cray (basic commands to submit a job, check the job status etc.)
• Run the T21 test
• Diagnostics
• gribapi/eccodes tools for examine GRIB files
• GRIB 2 netCDF conversion

• Case study: storm Desmond
• Short study the initial conditions
• Set the namelist
• Run the model (T255 experiment for 3 days)
• Post-processing
• Collect ERA5 data for validation
• Introduction to Metview
• Visualization of the forecast outputs and ERA5 with Metview