Seminars/Lectures by ECMWF Staff and Invited Lecturers

Piotr K. Smolarkiewicz (NCAR, Boulder, CO)

Sound-proof simulations of atmospheric wave phenomena

We investigate the performance of several sound-proof models, including the anelastic Lipps-Hemler and the pseudo-incompressible Durran nonhydrostatic equations. Physics wise, our primary interests are with the dynamics of inertia-gravity waves, an important element of weather and climate. Our numerical developments are based on a class of non-oscillatory forward-in-time methods and are applicable to global and limited area models. Challenging simulations of atmospheric wave phenomena involve structured-grid and unstructured-mesh discretizations.

Tim Palmer (ECMWF and University Oxford)

Reflections on the past 25 years - and some speculations on the next

15:30 Lecture Theatre

Internal Seminar

Anders Persson

A new layout for the Daily Report?

The layout of the Met Ops Section's Daily Report has not changed significantly since its introduction in 1992. A suggestion for a new layout will be presented where the contents is organized in five parts. The first and the last (Operational status and Additional comments) will remain. The other three will address "NOW", "FUTURE" and "HISTORY" i.e. all problems with the definition of the initial state, the forecast performance and verifications (both for the deterministic and ensemble system, including e-suites). When deciding on the new layout we need feedback from the RD-staff about which parameters or problems they think the Daily Report should focus on. A preliminary version will be tested 7-11 November.

Peter Webster and Subbiah Arjunapermal (School of Earth and Atmospheric Sciences, Georgia Tech)
The Regional Integrated Multi-Hazard Early Warning System for Africa and Asia (RIMES): The Third Way

Christel Prudhomme and Tanya Warnaars (Centre for Ecology & Hydrology)
WATCH and WaterMIP Global Hydrological Models: inter-model comparison for hydrological extremes of Europe

Within the WATCH project, a new methodology for assessing the ability of gridded global hydrological models (GHM) to reproduce large-scale hydrological high and low flow events (as a proxy for hydrological extremes) was developed and applied in Europe. It was first applied to develop a European catalogues of historical droughts (using the Regional Deficiency Index, RDI) and high flows (Regional High Flow Index, RHFI) previously derived from river flow measurements across Europe.  Using the same methods, total runoff simulated by seven global hydrological models from WaterMIP run with the same meteorological input (Watch Forcing Data) at the same spatial 0.5º grid was used to calculate simulated RDI and RHFI for the period 1963-2001 in the same European regions, directly comparable with the observed catalogues.  Results show that GHMs can broadly reproduce the spatio-temporal evolution of hydrological extremes in Europe to varying degrees, but the length and strength of the spatial coherence of events can vary significantly between GHMs.  The same method was also applied to total runoff generated using GCM driving climate for both baseline and future time slices. Results then show that GHMs have different sensitivity to the climate, and that GHM uncertainty can be as large (or larger for some regions) than climate model (GCM) uncertainty. Overall, the study has demonstrated that RDI and RHFI are powerful tools which can be used to assess how well large-scale hydrological models reproduce large-scale hydrological extremes - an exercise rarely undertaken in model inter-comparisons. It also showed that global hydrological model uncertainty can be large and should be accounted for hydrological extreme simulation and climate change impact assessments.

Prashant. D. Sardeshmukh (University of Colorado, Boulder and NOAA)
Need for Caution in Interpreting Extreme Weather Statistics

Roel Stappers and Jan Barkmeijer (KNMI)
Variational data assimilation without nonlinear models

Abstract: The use of tangent linear and, in particular, adjoint models has been very useful in several applications in numerical weather prediction. For example, at ECMWF these linear models play a crucial role in the computation of initial condition perturbations used in the ensemble prediction system and in their 4D-VAR data assimilation system. The greatest limitation to the application of linear models is that the results are useful only when the linear approximation is valid. As a result the usage of tangent linear and adjoint models is restricted to 'short' time spans.

In this presentation we show that by linearizing the tangent linear model around an ensemble of trajectories the nonlinear growth of perturbations can be described exactly by the tangent linear model. We show that in a three level quasi geostrophic model the tangent linear model can be used for more than 200 days (with increments much larger than typical analysis increments, using only a single linearization trajectory).

Based on this result we introduce a new incremental 4D-VAR method that 1) Does not require the nonlinear model to update the linearization trajectory in the outer loops (these updates are responsible for a significant fraction of the computational cost in the current ECMWF implementation).
2) Does not modify the innovation vector in the outer loops. To demonstrate the advantage of this we derive the exact equations for adjoint based observation impact including the effect of using multiple outer loops in 4D-VAR.
3) Does not require the strict distinction between inner/outer loops. The linearization trajectory can be updated in the inner loops at no additional computational cost.

Annarita Mariotti, NOAA, USA
Decadal climate variability and change in the Mediterranean region

Abstract: The Mediterranean region is among the “Hot Spots”  projected to experience major climatic changes in the twenty-first century as a
result of the global increase in greenhouse gas (GHG) concentrations.
However  the way in which these changes may initially become manifest in
the Mediterranean will also depend on internal decadal variability and
its impacts on climate in this region.  Here, we present an analysis of
the main decadal climate variations that have influenced past climatic
conditions in the Mediterranean/South Europe region since the
mid-nineteenth century. Decadal variability is discussed in the context
of forced climatic changes from increased GHG.
Results point to significant connections between Mediterranean climate
and decadal and multi-decadal variability in the Atlantic. Namely, a
significant influence of the North Atlantic Oscillation on Mediterranean
precipitation and a relationship between regional temperatures and the
Atlantic Multi-decadal Oscillation which may imply a certain degree of
decadal regional predictability. CMIP3 projections indicate that in the
longer term “forced” regional climatic changes from GHG increases would
bring significantly drier conditions over land and major changes in
Mediterranean Sea water cycle.

Klaus Arpe
Impact of the European Russia drought in 2010 on the Caspian Sea Level

Abstract

K. Arpe(1), S. A. G. Leroy(2), H. Lahijani(3) and V. Khan(4)
[1] Max Plank Institute for Meteorology, Hamburg, Germany
[2] Institute for the Environment, Brunel University, Uxbridge, UK
[3] Iranian National Institute for Oceanography (INIO), Tehran, Iran
[4] Hydrometeorological Research Center of the Russian Federation, Moscow, Russia

The Caspian Sea (CS) basin has no outlet to the oceans. The inflow from rivers, mainly the Volga River is compensated by evaporation over the Caspian Sea itself, imbalances lead to changes in the CS Level (CSL). It is therefore an ideal test area for investigating the water budget of an area using a variety of observational and reanalysis data. The period 1993 to 2010 was investigated with emphasis on summer 2010 when a severe drought developed over European Russia, the catchment of the Volga River. Precipitation and evaporation from the ECMWF interim analysis are compared with Volga River discharge and the CSL observations.
A drop in precipitation over the Volga basin (VB) in July 2010 occurs simultaneously with a decrease in evaporation for the same area, an increase of evaporation over the CS itself and a drop of the CSL. The drop in the precipitation over the VB cannot have led to an instantaneous drop of the CSL because the precipitated water needs some months to reach the CS. However, the evaporation over the CS itself is considered to be responsible for a simultaneous drop of the CSL in July to September 2010. The impact on the CSL from the precipitation deficit over the VB occurs in the months following the drought. The water deficit for June to September 2010 calculated from the anomalous precipitation minus evaporation over the VB would decrease the CSL by 22 cm, of which only 2.5 cm had been observed until end of September (observed Volga River discharge anomaly), 7 cm from October to the end of 2010 and another 5 cm to the end of May 2011. The remaining 7 cm may be compensated by excessive precipitation from October to February. In previous studies the precipitation over the VB has been identified as the main cause for CSL changes, but here a 10 cm drop from beginning of July to end of September can be directly assigned to the enhanced evaporation over the CS itself (6 cm) and due to reduced precipitation over the CS (2cm).
Further periods with strong changes of the CSL are investigated as well which provide some estimates concerning the accuracy of the data.
The consistency between the different components of the water budget over the Caspian Sea basin based on independent data gives a high confidence in the quality of the ERA interim data.
This investigation provides some scope for making forecasts of the CSL few months ahead to allow for mitigating societal impacts.

0915-1215 Lecture Theatre

NOT OPEN TO EXTERNAL VISITORS

Training sessions on C++ object oriented programming techniques

Michael Wong (IBM)

Trends and futures of C++

Over the last decades, C++ has become one of the most widely used languages supporting object-oriented programming by making abstraction techniques affordable and manageable for mainstream projects. Using C++ as his tool, Prof. Bjarne Stroustrup pioneered the use of object-oriented and generic programming techniques in application areas where efficiency is a premium; examples include general systems programming, switching, simulation, graphics, user-interfaces, embedded systems, and scientific computation. The influence of C++ and the ideas it popularized are clearly visible far beyond the C++ community. Languages including C, C#, Java, and Fortran99 provide features pioneered for mainstream use by C++.

C++ is a general purpose programming language with a bias towards systems programming which supports multiple styles of programming. Since 1998 C++ is an ISO standard. In these days a new version of the language is about to become a new ISO standard. This seminar will start by introducing the new features of the language and showing the challenges of evolving an existing programming language with a huge code base. This will enable students to truly come to understand C++ and the foundation of its design. We will cover some language concepts but also expand to describe aspects of STL, Boost and C++0x, the next version of C++.

Effective Advanced C++

This course will focus on effective C++ design based on the last 20 years of collective wisdom of C++ gurus worldwide. It will discuss coding guidelines, as well as how C++ is implemented under the cover to help truly understand what features costs. Topics of interest will include how language features are implemented by the C++ compiler, understanding inlining, code bloat, interface-based programming, and dynamic memory management.

Warwick Norton, Cumulus Funds PCE Investors, London
Use of ensemble forecasts in predicting the supply and demand of European energy

Abstract: The use of ECMWF ensemble forecasts is illustrated from the perspective of an end user who is a risk taker in the European energy market. This involves not only forecasting temperatures which drives consumption of energy, but the growing renewables sector means there is also large weather sensitivity in the supply of energy. This includes forecasting wind, surface solar radiation, precipitation and runoff. In order to calculate future energy prices, it is necessary to have an evolving view, at daily resolution, of these weather variables. This is accomplished by combining medium range forecasts with monthly forecasts and then with reanalysis data. However decision making using ensemble forecasts is not always straightforward because of the day-to-day changes in the forecasts. Some issues in forecasting these variables is discussed as well as the general performance of the EPS system over recent months.

Hong Son Hoang (Service Hydrographique et Oceanographique de la Marine, Toulouse)
On a Gain Initialization and Optimization of Adaptive Filter by Simultaneous Perturbation Stochastic Approximation

Abstract: Initialization of the filter gain plays an important role to provide a high performance of the filter. In this work, it is shown that the error covariance matrix (ECM) of the prediction error can be well estimated using simulated samples of the dominant Schur vectors of the system dynamics. This allows to well initialize the filter gain. By an appropriate parametrization, the adaptation can be applied to minimize the prediction error of the system output. It will be demonstrated that one efficient tool to optimize the performance of an AF is the simultaneous perturbation stochastic approximation (SPSA) algorithm. The main results show that the SPSA is capable of yielding the high filter performance similar to that produced by classical optimization algorithms, with better performance for non-linear filtering problems as more and observations are assimilated. The advantage of the SPSA is that at each iteration it requires only two measurements of the objective function to approximate the gradient vector regardless of the dimension of the control vector. The SPSA approach is thus free from the need to develop a discrete adjoint of tangent linear model and offers promising perspectives on developing optimal assimilation systems encountered in the field of data assimilation in meteorology and oceanography. Numerical results on data assimilation based on MICOM and HYCOM ocean models, in academic and realistic configurations, will be given to show the efficiency of the proposed filter.

09:15 - 12:00 Classroom

Internal Tutorial

Drasko Vasiljevic, Anne Fouilloux, Manuel Fuentes, Peter Kuchta, Mohamed Dahoui and Sandor Kertesz
Observation Handling and Monitoring Tutorial

(1) MARS Data Access (M. Fuentes and P. Kuchta)
(2) OBSTAT (M. Dahoui)
(3) METVIEW (S. Kertesz)

10:30 Lecture Theatre (N.B. modified time)

Zoltan Toth (GSD/ESRL/OAR/NOAA, Boulder, CO. and Malaquias Pena, EMC/NCEP/NWS/NOAA)
A new method for estimating analysis and forecast error variance

Abstract: Accurate estimates of error variances in numerical analyses and forecasts are critical for the evaluation of forecasting systems, the tuning of data assimilation systems, and the proper initialization of ensemble forecasts. A number of issues, however, hinder related efforts. A new approach is introduced for the unbiased estimation of analysis and forecast errors. The method is independent of any assumption or tuning parameter used in data assimilation schemes. In a functional analysis, it combines information from differences between forecast and analysis fields (“perceived errors”) with prior knowledge regarding the time evolution of (a) forecast error variance and (b) correlation between errors in analyses and different lead-time forecasts. In a simulated forecast environment, the method is demonstrated to reproduce the true analysis and forecast error within the predicted error bounds. The method is then applied to forecasts from four leading Numerical Weather Prediction centers to assess the performance of their corresponding data assimilation and modeling systems.

Prof. Paul Bates (Bristol University)
The Surface Water Ocean Topography satellite mission: prospects for climatology and hydrology science.

Abstract: In 2019 NASA and CNES will launch the Surface Water Ocean Topography satellite mission (see swot.jpl.nasa.gov) which will measure surface water height to centimetric accuracy every 10 days with complete global coverage at 1km resolution over the oceans and for all rivers above 100m wide. Over oceans, current altimeter constellations can only resolve the ocean circulation at resolutions larger than 300 km. Fundamental questions on the dynamics of ocean variability at scales shorter than 300 km, the mesoscale and submesocale processes, such as the formation, evolution, and dissipation of eddy variability (including narrow currents, fronts, and quasi-geostrophic turbulence) and its role in air-sea interaction, are to be addressed by the new observations. Over land the SWOT mission will provide measurements of water storage changes in terrestrial surface water bodies and will provide estimates of discharge in large (50 m-100 m width) rivers, globally. These data sets will provide a quantum improvement on our current understanding of surface water dynamics. Beyond improved characterization of the water cycle, meeting these measurements will enable numerous applications of great scientific, social, and political importance.

Jiandong Gong
Cloud analysis background error development

Abstract: We have added cloud condensate to the ECMWF upper air analysis, because satellite observations measuring in cloudy areas are sensitive not only to humidity, temperature, and surface, but also to cloud condensate and precipitation. Cloud condensate requires a flow dependent background error due to its high variability in space. We will describe the development of the background error including correlations with humidity and temperature errors and illustrate the results with single observation experiments.

10:30 Lecture Theatre

Internal Seminar

Carla Cardinali
Observation Impact Diagnostic: Use of Observation Influence and Forecast Sensitivity Tools (OI and FSO)

This seminar intends to illustrate the use of the sensitivity tools developed. In particular:

• how to compute OI in the analysis experiment
• how to run  FSO
• use of OBSTAT to display the observation impact in the analysis and forecast

15:30 Lecture Theatre

Robert Scheichl (University of Bath)
Scalable elliptic solvers and their application in numerical weather prediction

Abstract: Large ill-conditioned elliptic systems are at the heart of
applications in many areas of science and engineering where diffusive
processes are important. Due to the global nature of the solution
operator, any iterative solver that scales efficiently to large
problem sizes needs to incorporate not only local but also global
exchange of information. Multilevel iterative solvers provide such a
global exchange (at a negligible cost), by using a hierarchy of
auxiliary problems of lower spatial resolution. However, the robust
construction of such a hierarchy in the context of strong anisotropies
and/or coefficient variations requires some care and insight. In this
talk I will give an introduction to multilevel iterative solvers for
elliptic problems and discuss robustness issues, as well as their
application in meteorology.

Harri Auvinen
An investigation of systematic model error using a quasi-geostrophic weak-constraint 4D-Var system

Abstract: Even the most sophisticated numerical weather prediction model is not perfect. Although some errors may be entirely random, many will result from systematic misspecification of parameters, or deficiencies in parametrizations. In this work we estimate the covariance structure of systematic error a quasi-geostrophic (QG) model using the OOPS assimilation framework. We use this estimate in a Long-Window Weak-Constraint 4d-Var analysis system, and demonstrate that method is successful in taking model error into account.

Internal Seminar