Seminars

Seminars / Informal seminars / Lectures by ECMWF Staff and Invited Lecturers

Seminars contribute to our ongoing educational programme and are tailored to the interests of the ECMWF scientific community.

Informal seminars are held throughout the year on a range of topics. Seminars vary in their duration, depending on the area covered, and are given by subject specialists. As with the annual seminar, this may be an ECMWF staff member or an invited lecturer.

The following is a listing of seminars/lectures that have been given this year on topics of interest to the ECMWF scientific community.  See also our past informal seminars

2020

20 October
at 11:00

Virtual

http://tiny.cc/ECMWF_Grazzini

Classification and dynamical precursors of extreme precipitation events over Northern Italy

Speaker: Federico Grazzini

Abstract

In this work, we investigate a vast number of extreme precipitation events (EPEs) occurring between 1979 and 2015 in northern-central Italy. Through the optimal blending of ERA5 dataset and high resolution gridded daily precipitation observational analysis (ARCIS), we classify, via a simple machine learning approach, EPEs into three categories (Cat1, Cat2, Cat3) according to thermo-dynamic conditions over the affected region. The three categories do not only differ locally but also in the evolution of precursor Rossby wave packet (RWP) associated with the trough responsible for the precipitation. The apparent seasonality of the flow cannot solely explain these differences; therefore, the relevant physical processes in the RWP propagation of each case are further investigated. In particular, we show that RWPs associated with the strongest EPEs, namely the ones falling in Cat2, undergo a substantial amplification over the western N. Atlantic due to anomalous ridge-building two days before the event; arguably due to diabatic heating sources. A greater understanding of flow dynamics and water vapour transport pathways leading to EPEs not only helps evaluate the predictability of regional precipitation extremes but could also clarify the response of local hydrogeological cycle to a warming climate.

30 September at 14:15

 

Using the power of data assimilation to model the COVID-19 pandemic

Speaker: Geir Evensen (NORCE and NERSC Bergen)

Abstract

The onset of the SARS-COV-2 Pandemic led to a complete lockdown of society in many countries. So here I was, an applied mathematician, in confinement, following the news coverage of extreme situations at hospitals in Italy and New York, and at the same time hearing confusing and contradictory statements from politicians and leaders in various countries. This situation motivated me to contribute with knowledge-based information to support decision-makers. So, in my home office, I started developing an epidemic model and gather data on the COVID-19 decease and related hospitalizations and deaths in Norway. I coupled the model to my data-assimilation library, and end of March, after about two weeks of work, I was able to model and predict the SARS-COV-2 pandemic evolution in Norway.  I used the data-assimilation system to calibrate model parameters, including the time-dependent effective-reproductive-number, R. I then provided reports with model predictions to the Norwegian authorities to explain the unstable situation and the pandemic's dependency on R.  

On April 10th, I invited an international group of colleagues working in data assimilation to use the model system on data from their respective countries. Nearly everyone jumped at the opportunity, and from then, we have worked together as an international team.  We modeled the SARS-COV-2 pandemic in the four European countries Norway, England, The Netherlands, and France; the province of Quebec in Canada; the South American countries Argentina and Brazil; and the four US states Alabama, North Carolina, California, and New York. These countries and states all have vastly different developments of the epidemic, and we could accurately model the SARS-CoV-2 outbreak in all of them.

The joint work led to significant learnings regarding the use of data assimilation in epidemic modeling. We compiled the results into a large manuscript and submitted it to the journal "Fundamentals of Data Science," where we are currently finalizing the revisions.  We also made the paper available from MedRxiv

(https://www.medrxiv.org/content/10.1101/2020.06.11.20128777v1).

In this seminar, I will present results from this paper. I will introduce and justify the choice of model used, i.e., an SEIR model with age-classes and compartments of sick, hospitalized, and dead. I will introduce and demonstrate the ESMDA data-assimilation technique used, and I will discuss some of the benefits of using this system.

This work demonstrates how it is possible to use iterative ensemble smoothers to estimate an SEIR model's parameters. The data assimilated are the daily numbers of accumulated deaths and the number of hospitalized. Also, it is possible to condition on the number of cases obtained from testing.

We start from a wide prior distribution representing the model parameters; then, the ensemble conditioning leads to a posterior ensemble of estimated parameters leading to model predictions in close agreement with the observations. The updated ensemble of model simulations has predictive capabilities and include uncertainty estimates.

We estimate the effective-reproductive-number as a function of time, and we can assess the impact of different intervention measures. By starting from the updated set of model parameters, we can make accurate short-term predictions of the epidemic development given knowledge of the future effective-reproductive-number. Also, the model system allows for the computation of long-term scenarios of the epidemic under different assumptions.

The model system is freely available from Github (https://github.com/geirev/EnKF_seir).

 We realize that more complex models, e.g., with regional compartments, may be desirable, and we suggest that the approach used here should be applicable also for these models. I have recently upgraded the model system to include multiple regions or countries with specified interactions between them. This new model formulation allows for simulating the pandemic development for, e.g., the countries in Europe or the states in the US.

29 September
at 14:00

VIRTUAL

 

Cubesats for monitoring atmospheric processes (CubeMAP): a constellation mission to study the middle atmosphere

Speaker: Damien Weidmann (Rutherford Appleton Laboratory, UK)

Abstract

Earth is changing at an unprecedented pace. Understanding and quantifying the processes driving the change and particularly the role played by the atmosphere is necessary, and the CubeMAP mission has been designed to address this need. The CubeMAP mission has been selected as a finalist for the new ESA SCOUT mission programme. It consists of a constellation of three identical CubeSats, each equipped with three high resolution spectrometers and one hyperspectral solar disk imager. The overall mission goal is to study, understand, and quantify processes in the tropical Upper Troposphere and Stratosphere (UTS), study its variability, and contribute to trends analysis in its composition and its effects on climate and vice-versa. The UTS composition plays a significant role in controlling the Earth’s climate, with still poorly explored feedbacks within the Earth System. This region of the atmosphere is coupled to the surface and the free troposphere both dynamically and radiatively. Its composition is determined by anthropogenic emissions of greenhouse gases and pollution precursors and is subject to changes via radiative, dynamical, and chemical processes. The ultra-miniature, while high spectral resolution, spectrometers selected for the payload are integrated thermal infrared laser heterodyne spectro-radiometer probing narrow spectral windows in limb solar occultation. For aerosol and oxygen measurements, an innovative, co-registered, solar disk imager using a multispectral CMOS sensor ensures both pointing knowledge accuracy and a large spectral channel diversity in the visible and near infrared, together with a small form factor. The platform selected for the mission is based on the GomSpace 12U CubeSat form factor which can accommodate the payloads while also keeping volume, mass and cost at a manageable level. The system design is to a high degree based on proven GomSpace COTS products with demonstrable flight heritage, hence lowering the mission risk. The mission contributes to developing a novel observation model: it offers a high level of deployment flexibility and system modularity, as well as economy of scale, through the use of identical payloads and platforms functionalized to specific Earth observation goals. The constellation approach also obviates the traditional limited coverage of limb solar occultation mission, whilst benefiting from the high accuracy this sounding mode brings. CubeMAP is also highly complementary to the nadir sounding infrastructure and contributes to enhancing its outputs and exploitation. It also addresses the forthcoming gap in solar occultation sounding capabilities.

24 September
at 10:00

VIRTUAL

 

Joint ECMWF/UoR seminar on GloFAS-ERA5 river discharge trends

Speaker: Ervin Zsoter

Abstract

The main objective of this study is to analyse the GloFAS-ERA5 river discharge reanalysis for any noticeable change (including gradual trends or discontinuities) in the annual mean time series across the 1979-2018 (40-year) period, and to evaluate how realistic these are compared with available observed river discharge time series. 

These variabilities are quantified by linear regression in order to highlight any concerning features in the GloFAS-ERA5 time series. 

This work is particularly important for GloFAS, as large trends, discontinuities or other similar features could have a major consequence on the GloFAS flood thresholds in around 50% of catchments, which are based on GloFAS-ERA5, and thus subsequently on the issuing of flood warnings. 

In addition, this study also contributes to the understanding of the water cycle variable behaviour in ERA5 (driver of GloFAS-ERA5) and ERA5-Land (higher resolution land reanalysis forced by ERA5, produced offline) by exploring the linear trends in river discharge and related hydrological variables. In exploring the stability of the time series in ERA5, we seek to trigger potential further discussions and research studies, which subsequently should help with the planning and development for the next generation ECMWF reanalysis, ERA6. 

18 June
at 10:30

VIRTUAL

 

“ecPoint” - a Post-processing Tool that improves Forecasts and highlights Systematic Model Errors

Speaker: Timothy Hewson

Abstract

In April 2019 ECMWF introduced a new, experimental, “point rainfall” forecast product onto its ecCharts web display platform, based on the post-processing package “ecPoint”, to give site-specific forecasts for everywhere in the world up to day 10. Prior to this development forecasters had access to just raw ensemble output in ecCharts, which provides gridbox average totals. ecPoint aims to incorporate probabilistically the expected sub-grid variability, and simultaneously apply gridscale bias corrections. Both these adjustments depend critically on “gridbox-weather-type”.

This presentation will describe the meteorology-based calibration rationale that underpins ecPoint, how this is different to pre-existing post-processing methods, and how it can also be applied to other surface variables such as 2m temperature. Numerous benefits will be highlighted.

The conditional verification concepts underpinning the calibration allow one to identify weather-situation-dependent gridscale biases. Examples will illustrate the diagnostic power of this approach, showing where and when rainfall is typically under- and over-forecast, providing pointers for future model improvements. And using an open source GUI one can apply the calibration code to data from other models, and thereby intercompare performance in different weather situations.

The forecast improvements that then arise will be discussed, using both long term global verification up to day 10, and illustrative case studies, with a focus on how extreme localised rainfall, that might lead to flash floods, is better handled. It will be shown how the post-processing can usefully shift the emphasis for warning issue from one region to another, when one compares with raw ensemble output.

There will be brief reference, from collaborative work, to how ecPoint output seems to compare favorably with the post-processed output of convection-resolving limited area ensembles.

The talk will conclude by discussing, in the context of ongoing and potential projects, numerous future applications of ecPoint, such as bias-corrected inputs to hydrological models, point rainfall re-analyses and tests of theories such as city impact on rainfall. Avenues for improving the methodology will also be highlighted.

28 April
at 10:00

VIRTUAL

Can approximations of the CRPS help us better understand why the skill changes?

Martin Leutbecher and Thomas Haiden

Abstract

Ensemble verification of scalar variables often involves the use of the continuous ranked probability score (CRPS). The talk looks at a Gaussian approximation of the CRPS with the aim to improve our understanding of score changes. The approximation permits to express the CRPS of an ensemble as a function of the variance of the error of the ensemble mean, the mean error of the ensemble mean and the ensemble variance. The methodology will be applied to direct model output from medium-range ensemble forecasts as well as postprocessed ensemble forecasts. We will examine how well this approximation works and whether it might be suitable to complement information we see for instance in scorecards.

14 February
at 10:30

Room: LT

Aircraft Weather Observations and their Use (current and future)

Speaker: Steve Stringer (Met Office and EUMETNET) and Siebren de Haan/Jan Sondij (KNMI and EMADDC)

Abstract

Aircraft based weather observations (ABO) have increasingly become a very valuable input into the global weather forecasting process, with some independent assessments showing their impact on NWP to be second only to that of satellite data. An international workshop on Aircraft Based-Observations (ABO) is to be hosted at ECMWF, 12th/13th February 2020, bringing together ABO data users and ABO data providers to share their experience of aircraft data use and to recommend any necessary changes to procedures in the provision or use of aircraft data in the future. The seminar will provide an overview of the current status ABO data provision, plans for the future, together with outcomes and recommendations from the ABO Workshop. An overview of European plans to implement an operational centre and service for the  delivery of quality controlled Mode-S derived aircraft observations will be also included.  (Mode-S reports are derived from air traffic management messages and provide very high resolution data, particularly winds, over parts of Europe and potentially elsewhere.  They are not yet processed at ECMWF.)  

11 February
at 14:00

Room: LT

The relationship between the circumglobal teleconnection, the Indian monsoon and European summer weather

Speaker: Jonathan Beverley (University of Reading, University of Exeter)

 Abstract

Recent research has led to improvements in European winter seasonal forecasts, however summer forecast skill remains relatively low. One potential source of predictability for Europe is the Indian summer monsoon, which can influence the weather across many parts of the northern hemisphere via a global wave train known as the “circumglobal teleconnection” (CGT). Here I assess the ability of the ECMWF coupled seasonal forecast model to represent this teleconnection mechanism. To understand how errors in its representation are related to errors in summer forecast skill over Europe, results from relaxation and thermal forcing experiments, as well as barotropic model experiments, will be presented. These experiments were designed to identify possible causes of errors in the teleconnection pathway, and to explore the impact of improving the representation of the CGT on European summer forecast skill.

23 January
at 14:00

Room: LT

Can GNSS Polarimetric Radio Occultations (GNSS  PRO) contribute to better understanding, monitoring or predicting extreme events?

Speaker: Estel Cardellach (ICE-CSIC/IEEC, Spain)

Abstract

The GNSS Polarimetric Radio Occultations (GNSS PRO) is a new measurement concept being proved aboard the PAZ satellite, operating since May 2018. The technique is based on the 'traditional' GNSS Radio Occultations (GNSS RO), widely used for atmospheric profiling of thermodynamic parameters and assimilated in operational NWP. Adding polarimetric capabilities to the RO system enables to sense hydrometeors, especially big rain droplets in heavy rain, and frozen particles. The system, thus, is the first technique with joint and synchronous sensitivity to both types of parameters: thermodynamic and hydrometeor profiling. Whereas the geophysical content of the GNSS RO signals to infer the 'traditional' products lays on the bending of the signal propagation (atmosphere acting as a lens because of its vertical gradients in T, p and q), the physical principle to sense hydrometeors is the excess propagation delay of the horizontally polarized signal with respect to the vertically polarized one. These are two independent sensing principles obtained from a single set of data.

Can GNSS PRO contribute to better understanding, monitoring or predicting extreme events? We are not ready to provide a full answer to this question, yet. But the seminar will present the technique, the facts demonstrated during the PAZ mission so far, the current identified limitations, and potential areas of interest and opportunities for scientists at ECMWF working on precipitation, micro-physics modeling and large scale convective systems -- elements towards improved understanding, monitoring and prediction of some extreme events.

   

LT = Lecture Theatre, LCR = Large Committee Room, MZR = Mezzanine Committee Room,
CC = Council Chamber