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


15 June
at 10:00

Link to recording:

Impact of stochastic physics and model resolution on the simulation of Tropical Cyclones in climate GCMs

Speaker: Prof Pier Luigi Vidale (University of Reading)


The role of model resolution in simulating geophysical vortices with the characteristics of realistic tropical cyclones (TCs) is well established. The push for increasing resolution continues, with general circulation models (GCMs) starting to use sub-10-km grid spacing. In the same context it has been suggested that the use of stochastic physics (SP) may act as a surrogate for high resolution, providing some of the benefits at a fraction of the cost. Either technique can reduce model uncertainty, and enhance reliability, by providing a more dynamic environment for initial synoptic disturbances to be spawned and to grow into TCs. We present results from a systematic comparison of the role of model resolution and SP in the simulation of TCs, using EC-Earth simulations from project Climate-SPHINX, in large ensemble mode, spanning five different resolutions. All tropical cyclonic systems, including TCs, were tracked explicitly. As in previous studies, the number of simulated TCs increases with the use of higher resolution, but SP further enhances TC frequencies by ~30%, in a strikingly similar way. The use of SP is beneficial for removing systematic climate biases, albeit not consistently so for interannual variability; conversely, the use of SP improves the simulation of the seasonal cycle of TC frequency. An investigation of the mechanisms behind this response indicates that SP generates both higher TC (and TC seed) genesis rates, and more suitable environmental conditions, enabling a more efficient transition of TC seeds into TCs. These results were confirmed by the use of equivalent simulations with the HadGEM3-GC31 GCM.

20 April
at 10:30




The ERA5 Reanalysis

Speaker: Hans Hersbach


The C3S ERA5 climate reanalysis provides detailed hourly snapshots of the Earth’s atmosphere, land surface and ocean waves from 1950 with timely updates with a latency of 5 days. It is a highly popular product on the Climate Data Store (CDS) and is used for a wide range of applications. To date there are over (ERA5-Land included) 46,000 users worldwide and around 400 Terabyte is downloaded every single week.

ERA5 uses a version of the ECMWF Numerical Weather Prediction forecast model and data assimilation system from 2016 (Cy41r2) to assimilate both in-situ and satellite observations, many of which stem from reprocessed data records. This presentation provides a concise overview of the ERA5 system and a basic evaluation of characteristics and performance.

Special focus will be on the ERA5 back extension, the segment from 1950 to 1978 that was made available in autumn 2020 and supplements the previously published segment covering 1979-present. It features the assimilation of many conventional observations, as well as improved use of early satellite data. The fidelity of the extension is illustrated by the accurate depiction of the North Sea Storm of 1953, and the events leading to the first discovery of Sudden Stratospheric Warmings in 1952. Time series of ERA5 global surface temperature anomalies show temperatures to be relatively stable from 1950 until the late 1970s, in agreement with the other contemporary full-input reanalyses covering this period and with independent datasets, although there are significant differences in the accuracy of representing specific regions. The evolution of upper air temperatures, humidities and winds show smoothly varying behaviour, including tropospheric warming and stratospheric cooling, modulated by volcanic eruptions. The Quasi Biennial Oscillation is well represented throughout.

Despite these good characteristics, the ERA5 back extension did use historical observations for tropical cyclones in a sub-optimal way, which, given their sparsity is a challenging subject in itself. As a result, a number of tropical cyclones are far too intense. Although this has an occasional local impact, it does affect the consistency of extreme events and ocean waves on larger scales. For these reasons it was decided to publish the back extension as a separate, preliminary data set in the CDS, while preparations for an improved version of the back extension have been taking place.

9 April
at 10:30





Summarising ensembles using a mean and a reasonable worst-case

Speaker: Steve Jewson, weather and climate risk consultant


For some applications of ensembles it may not be possible to process every ensemble member. One approach is to reduce the ensemble down to just the mean and a reasonable worst-case before processing. I describe a simple statistical methodology for creating the worst-case, and apply it to EURO-CORDEX rainfall projections and ECMWF medium range temperature forecasts.

6 April at 16:00


Compressing atmospheric data into its real information content

Speaker: Milan Kloewer (University of Oxford)


Hundreds of petabytes of data are produced annually at weather and climate forecast centres worldwide. Compression is inevitable to reduce storage and to facilitate data sharing. Current techniques do not exploit the spatio-temporal correlation in climate variables nor is only the real information in floating-point numbers compressed. Here, the bitwise real information content is calculated for data from the Copernicus Atmospheric Monitoring Service (CAMS). Most variables contain less than 7 bits of real information per value, which are also highly compressible due to spatio-temporal correlation. Identifying information-less bits with this technique is widely applicable to geoscientific variables. Rounding information-less bits to 0 facilitates available lossless compression algorithms, while bounding various error norms. Variables from the CAMS data set can consequently be compressed by a factor of 20-50x, relative to 64-bit floats. In comparison, the 24-bit linear quantisation currently used for storing CAMS data has a fixed compression factor of 2.7x. While most lossless compression algorithms act in one dimension only, the potential of multi-dimensional correlation can be exploited using modern compression libraries such as zfp. Our information-preserving approach is generalised to 4-dimensional space-time compression with zfp, achieving compression factors beyond 100x, without an impact on forecast skill scores. Widely-used modern data formats such as netCDF and HDF5 support this multi-dimensional and information-preserving compression, providing the basis to compress large climate data archives without a loss of real information.

 26 February
at 10:30


Link to recording:


The role of latent heating in atmospheric blocking

Speaker: Daniel Steinfeld (ETH-Zurich)


Recent studies have pointed to an important role of latent heating for the formation and maintenance of prolonged anticyclonic circulation anomalies, denoted as atmospheric blocking. However, the effect of latent heating on blocking is not yet well understood.

This presentation will provide an overview of the role of latent heating in atmospheric blocking dynamics with two different approaches: (i) a global climatological analysis based on air parcel trajectory calculation with ERA-Interim reanalysis and (ii) numerical sensitivity experiments with modified upstream latent heating for five selected blocking events with the global weather prediction model IFS.

The results show a strong influence of latent heating on blocking and the midlatitude flow due to the injection of air masses with low potential vorticity (PV) into the upper troposphere in strongly ascending “warm conveyor belt” airstreams and the interaction of the associated divergent outflow with the upper-level PV structure.

29 January
at 10:30


Link to recording:


Atmospheric blocking in seasonal forecast: where are we now? 

Speaker: Paolo Davini (CNR, Torino)


Proper simulation of atmospheric blocking is a tough challenge for numerical modelling, both from the weather and the climate point of view. We here investigate blocking representation in GCMs on a less studied time window, i.e. the seasonal timescale. We assess the simulation and prediction of the winter Northern Hemisphere atmospheric blocking in the ECMWF seasonal prediction systems: blocking statistics from the operational November-initialised seasonal hindcasts are evaluated in three generations of models - System3, System4 and System5 (SEAS5) - and in a series of complementary sensitivity experiments. 

Overall, we observe improvements in the climatological representation of blocking in the most recent model configurations, with reduced bias over North Pacific and Greenland. However, as seen in many GCMs, minor progress is recorded over the European sector.

Interannual variability is also underestimated and is found to be proportional to the climatological frequency, highlighting that a negative bias in blocking frequency implies an underestimation of the interannual variance. 

Predictive skill and signal-to-noise ratio remain low - also in SEAS5 - but interesting significant results are found over Western and Central Europe. Complementary experiments show that the statistics of blocking are improved following atmospheric and oceanic resolution increase. On the other hand, the implementation of stochastic parametrizations tends to displace blocking activity equatorward.

Finally, by comparing seasonal hindcasts with non-initialised climate runs (based on the same model) we highlight that the largest contributor to the chronic underestimation of blocking are persistent errors in the atmospheric model. It is also shown that the SST errors have a larger impact on blocking bias in climate runs than in seasonal runs, and that increased ocean model resolution contributes to improved blocking more effectively in climate runs.

We conclude that - although the predictive skill is still weak - seasonal forecasts can thus be considered a suitable test-bed for model development targeting blocking improvement in climate models.

26 January
at 15:30



Assessing Predictability and Prediction Skill of the MJO in ECMWF S2S Reforecast

Speaker: Shu-Yi Chen (Department of Atmospheric Sciences, U Washington)


The Madden-Julian Oscillation (MJO) has been recognized as a source of predictability of the global weather on the subseasonal-to-seasonal (S2S) time scales. However, the MJO initiation and eastward propagation of its the large-scale convection and precipitation over the Indo-Pacific warm pool remain to be difficult to evaluate quantitatively in NWP and climate models. This study aims to better understand the predictability and model prediction skill of the MJO using a new Large-scale Precipitation Tracking (LPT) method developed by Kerns and Chen (2016, 2020) based on the 20-year TRMM-GPM precipitation data and the ECMWF S2S reforecast from 1998-2018.  The advantage of LPT is its explicit representation of the MJO precipitation in terms of both zonal and meridional structure and variability in time and space. The S2S reforecast reproduced the observed MJO climatology in terms of the total number of the MJO events and seasonal variability very well. However, the timing and location of the MJO precipitation, especially over the tropical Indian Ocean, is less well predicted. In addition to the MJO, general characteristics of multiscale precipitation in the S2S reforecast compared with the TRMM-GPM observation will be discussed.

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