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

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

To follow

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

PDF icon

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