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

2017

8 June at 13:00-18:00

Symposium on dynamic meteorology and numerical weather prediction

Speakers:

  • Raymond T. Pierrehumbert (Halley Professor of Physics at the University of Oxford)
  • Nedjeljka Žagar (Associate Professor of Meteorology at the University of Ljubljana)
  • Hans Huang (Head of Weather Modelling and Prediction at the Centre for Climate Research Singapore)
  • Stephen Belcher (Chief Scientist at the UK Met Office)
  • David Burridge (Director of ECMWF 1991–2004)
  • Erland Källén (Director of Research at ECMWF)
  • Florence Rabier (Director-General of ECMWF)

Abstract: Raymond Pierrehumbert

Raymond Pierrehumbert will speak on multiple equilibria, bifurcations and climate regimes. Professor Pierrehumbert’s research on climate has spanned timescales from billions of years in the past to billions of years in the future. His work on atmospheric dynamics has included contributions to theories of weather regimes and blocking, baroclinic instability, stratified flow (with applications to mountain meteorology), atmospheric mixing problems and dynamical control of atmospheric humidity.

Abstract: Nedjeljka Žagar

Nedjeljka Žagar will talk about data assimilation in the context of tropical dynamics. Professor Žagar’s research interests range from modelling mid-latitude mesoscale weather to large-scale tropical variability and data assimilation. Her research has highlighted the role of large-scale equatorial waves in tropical data assimilation. She applies normal modes for the scale-dependent evaluation of the global unbalanced circulation and the growth of forecast uncertainties in ensemble prediction.

Abstract: Hans Huang

Hans Huang’s lecture will be devoted to high-resolution forecast modelling in the context of tropical dynamics. Dr Huang has extensive experience of data assimilation research, observation system design and assessment, and NWP system development. He was the lead scientist for data assimilation in the forecast system developed by the European HIRLAM programme, and the manager of the US-based Weather Research and Forecasting (WRF) Model data assimilation system.

Abstract: Stephen Belcher

Stephen Belcher will talk about climate change. Since 1990, Professor Belcher has published over 100 peer-reviewed papers on the fluid dynamics of atmospheric and oceanic turbulence. Between 2007 and 2010, he was the Head of the School of Mathematical and Physical Sciences at the University of Reading. In 2012, he joined the Met Office as Director of the Met Office Hadley Centre for Climate Science and Services before becoming the Met Office Chief Scientist in November 2016.

Abstract: David Burridge

David Burridge will speak on the past evolution of numerical weather prediction at ECMWF. Dr Burridge was the Head of Research at ECMWF from 1982 to 1991 and the Centre’s Director from 1991 to 2004. Subsequently he shaped and steered the implementation of THORPEX, a ten-year international research and development programme set up by the World Meteorological Organization to improve one-day to two-week forecasts of high-impact weather.

Abstract: Erland Källén

Erland Källén’s lecture will be about the Centre’s research and operations today. Between 1983 and 2009, Professor Källén was first an associate professor and later professor in dynamic meteorology at Stockholm University. His research areas are large-scale dynamics of the atmosphere, NWP and climate modelling. He has worked as a project leader for the HIRLAM programme and was responsible for initiating and heading the first Swedish climate modelling programme in the 1990s.

Abstract: Florence Rabier

Florence Rabier will talk about what the future holds for numerical weather prediction and related services at ECMWF. Dr Rabier has greatly contributed to delivering major operational changes at ECMWF and Météo-France. She is especially well known within the meteorological community for her key role in implementing a new data assimilation method (4DVar) in 1997. She was ECMWF’s Director of Forecasts before she became the Centre’s Director-General in January 2016.

26 April
at 10.30

Room: LT

Compatible finite element methods for numerical weather prediction

Speaker: Jemma Shipton (Imperial College, UK)

Abstract

We present recent work on developing a compatible finite element model for numerical weather prediction. This work has been motivated by the requirement for numerical discretisations that are stable and accurate on nonorthogonal grids (such as icosahedral or equiangular cubed sphere grids) without sacrificing properties of conservation, balance and wave propagation that are important for accurate atmosphere modelling on the scales relevant to weather and climate (Staniforth et. al. 2012).

Compatible finite element methods are a type of mixed finite element method (where different finite element spaces are used for different fields) where the divergence of the velocity space maps on to the pressure space. This necessitates the use of div-conforming finite element spaces for velocity, such as Raviart-Thomas and Brezzi-Douglas-Marini, and discontinuous finite element spaces for pressure. The main reason for choosing compatible finite element spaces is that they have a discrete Helmholtz decomposition of the velocity space; this means that there is a clean separation between divergence-free and rotational velocity fields. Cotter and Shipton (2012) used this decomposition to demonstrate that compatible finite element discretisations for the linear shallow water equations satisfy the basic conservation, balance and wave propagation properties listed in Staniforth and Thuburn (2012).

In the talk we will show the progress we have made towards extending this approach to the fully 3D equations via a vertical slice model. Many current atmospheric models use a staggered Charney Phillips grid in the vertical to ensure a good representation of hydrostatic balance. In the finite element context the equivalent staggering requires the temperature field to be discontinuous in the horizontal direction but continuous in the vertical. We present a stable and accurate advection scheme for this field. The success of this approach is illustrated by benchmarking results from our model, implemented in Firedrake (www.firedrake.org).

21 April
at 10.30

Room: LT

SODA3 (Simple Ocean Data Assimilation ocean/sea ice reanalysis) and a step toward a coupled reanalysis?

Speaker: James Carton (Univ. Maryland, USA)

Abstract

Atmospheric reanalyses produce surface fluxes as a residual of their update cycle. These fluxes should be consistent with estimates of ocean heat and freshwater storage and divergence of transports.  Here we compare the ERA-Int, MERRA2, and JRA-55 fluxes with the imbalances apparent in the increments produced by the SODA3 ocean reanalysis system during the data-rich eight year period 2007-2014.   The heat flux comparison reveals that the regional imbalance falls in the range of 10-30 W/m2 in time mean with even larger imbalances on seasonal time scales.  In the vertical the corresponding temperature imbalances are concentrated in the mixed layer.  We argue that in the interior gyres these imbalances are the result of seasonal errors in the atmospheric reanalysis representation of surface heat and freshwater fluxes (the problem is the atmosphere).  In other regions such as the Gulf Stream we show evidence of substantial ocean model error. Elsewhere errors in momentum fluxes appear to dominate the temperature and salinity increments.  We also examine the impact on fluxes of the choice of bulk parameterization used to calculate surface fluxes from atmospheric state variables.

In the second part of the talk we present a strategy for correcting surface fluxes based on the ocean observations and we then discuss the results of experiments testing this strategy.  Examination of the results confirms that in the interior gyres our bias-correction strategy reduces the seasonal error in surface heat flux to less than 5 W/m2.  We conclude with a discussion of the changes that are needed to address biases at high latitude.

23 March
at 10:30

Room: MR1

Uncertainties in simulated evapotranspiration from land surface models over a 15-year Mediterranean crop succession

Speaker: Sebastien Garrigues (CEH/UoR/INRA)

Abstract

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6 March
at 14:00

Room: LT

Water Information in Australia - The Post Millennium Drought Experience

Speaker: Dr Dasarath Jayasuriya (BoM, Australia)

Abstract

Water data and information are needed for planning, managing and meeting the sustainable development goals related to water resources taking into account climate changes, population growth and other drivers impacting supply security. The Australian National Plan for Water Security (2007) postulated that better water information was essential for providing water security during Australia's periodic droughts. After the Millennium Drought which lasted from 1996 to 2007, the Government and the policy bureaucracy understood that they were facing a water crisis, but had no nationally consistent and accessible data to make informed decisions. Water data were held by approximately 200 organisations across state and local governments with no standardisation, transparency, and accessibility. Parochial interests often led to ‘gaming’.

The presentation lays out the Australian experience and its response to the water data and information challenge and shares the Government’s Water Information Program initiative over the last 10 years. Highlights relate to socialising the universal availability of water data, water information products and water forecasting services. Collectively they provide water intelligence to Bureau’s stakeholders including Government, industry and community.

Dr Dasarath Jayasuriya

23 February
at 10:30

Room: LT

Subseasonal forecasting – a battle between damped persistence and tropical forcing?

Speaker: Warwick Norton (CUMULUS, UK)

Abstract

Cumulus
 
We review some of the forecast performance across the 2016/17 winter where the seasonal forecasts expected a negative NAO state yet this not really played out. Rather there has been significant forecast volatility, with no forecast skill past week 2 for Europe (or in forecasting the NAO). In the southern hemisphere Australia has experienced an extremely hot summer which was also poorly forecast in the subseasonal range. We discuss sources of forecast error particularly associated with underestimating maritime continent convection but also other factors that may have led to poor forecast skill this year such as lack of MJO activity. 
 
We examine what could be predicted with perfect knowledge of the tropics from relaxation experiments. We compare this year to other recent years where skill in predicting the NAO has been higher. Results based on Rossby wave source analysis suggest that tropical teleconnections are too weak in the ECMWF model - this can lead to periods of under confidence in forecasting predictable extratropical signals. We conjecture that current subseasonal models contain too much damped persistence of the initial conditions and not enough forcing from the tropics.

15 February
at 10:30

Room: MR1

Flood forecast sensitivity to temperature using ECMWF ensembles for 145 catchments in Norway

Speaker: Trine Jahr Hegdahl (NVE, Norway)

Abstract

The Norwegian flood forecasting service is based on a flood-forecasting model run on 145 basins. The basins are located all across Norway and differ in both size and hydrological regime. Current flood forecasting system is based on deterministic meteorological forecasts, and uses an auto-regressive procedure to achieve probabilistic forecasts. An alternative approach is to use meteorological and hydrological ensemble forecasts to quantify the uncertainty in forecasted streamflow. The aim of our study is to establish and assess the performance of both meteorological and hydrological ensembles for 145 catchments in Norway, which differ in size, elevation and hydrological regime. We identify regional differences and improvements in performance for preprocessed meteorological forecasts. A separate study further investigates the sensitivity to forecasted temperature for specific snowmelt induced floods. In Norway, snowmelt and combined rain and snowmelt floods are frequent. Hence, temperature is important for correct calculations of snowmelt. Temperature and precipitation ensembles are derived from ECMWF covering a period of nearly three years (01.03.2013 to 31.12.2015). To improve the spread and reduce bias we used standard methods provided by the Norwegian Meteorological Institute. Precipitation is corrected applying a zero-adjusted gamma distribution method (correcting the spread), and temperature is bias corrected using a quantile-quantile mapping (using Hirlam (RCM) 5 km temperature grid as a reference). Observed temperature and precipitation data are station data for all of Norway, interpolated to a 1×1 km2 grid (SeNorge.no). Streamflow observations are available from the NVE database. The hydrological model is the flood-forecasting operational HBV model, run with daily catchment average values. The results show that the methods applied to meteorological ensemble data reduce the cold bias present in the ECMWF temperature ensembles. Catchments on the western coast, having a lower initial performance, show the highest improvement by the temperature corrections, whereas some inland catchments in southeastern Norway show reduced performance. Ensemble spread for precipitation improves, but is not recognized in the discharge performance measures. Both precipitation and temperature show an east-west divide in performance. Corrected temperature ensemble lead to improved performance in discharge for some western catchments. Overall, the regional analyzes including all data, show that catchments have different sensitivity to temperature correction and will benefit from regional or catchment specific bias correction. Spring flood events, in catchments located west and southeast, showed different discharge response to temperature correction (more than 2°C). For the western catchment the increased temperature, led to higher discharge, whereas there were minor change for the southeastern catchment.

 

12 January
at 14:00

Room: LT

The global ICON Ensemble at DWD

Speakers: Michael Denhard and Cristina Primo (DWD, Germany)

Abstract

Since October 2015 DWD runs an experimental ICON ensemble suite with 40 members and approx. 40km horizontal resolution on the global scale up to +168h lead time twice a day (00/12UTC). The global grid contains a 20km two-way nested area over Europe. The ensemble is initialized by analyses from our ensemble data assimilation system (ICON EDA) which is a combination of a Local Ensemble Transform Kalman Filter (LETKF) with a hybrid ensemble/3D-Var variational system for the high-resolution deterministic model. At the time there is no stochastic physics implemented and the error growth properties of the ensemble are determined by the diverse co-variance inflation techniques in the LETKF such as multiplicative inflation factors, relaxation to the prior and stochastic SST perturbations.  Moreover, the static NMC Background error co-variances are added to the flow dependent ensemble co-variances to rescale the innovations. In the first part we show verification results for the ICON-EPS forecasts in comparison to the ECMWF-EPS and analyze the spread skill relation for both ensembles. The second part introduces techniques for predicting the error growth properties along trajectories in the state space of a model. We use the "Broyden family" methods to iterate a Broyden matrix in state space of the Lorenz63 and 95 models. During iteration the Broyden matrix gains information on the error growth properties of the dynamical system. We discuss, if the information in the Broyden matrices along a trajectory can be used as an approximation of the singular vector approach.

11 January
at 10:30

Room: LT

How good (or bad) is the circulation of the stratosphere and mesosphere in the IFS?

Speaker: Inna Polichtchouk (University of Reading, UK)

Abstract

Accurate representation of the stratospheric circulation is important for tropospheric predictability on intraseasonal timescales, because of the downward influence of the stratosphere on the troposphere.  The “downward control” principle states that the stratospheric Brewer Dobson circulation (BDC) is primarily driven by the wave breaking/saturation aloft. Thus, the stratospheric circulation in turn depends on the representation of the mesospheric momentum budget. This talk reviews the state of the middle atmosphere in the IFS, with a focus on the BDC and the semi-annual oscillation. I will compare the middle-atmosphere circulation to reference datasets and assess the impact of 1) the parametrized non-orographic gravity wave drag; 2) treatment of the sponge layer; 3) the cubic octahedral discretization; and, 4) stochastic physics.

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