Seminars/Lectures by ECMWF Staff and Invited Lecturers

Date

Time and place

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Angeles Hernandez and Niels Bormann

Project SimulAMV2: Using geostationary imagery from high resolution model simulations to improve the characterization of current Atmospheric Motion Vectors

Abstract: In this seminar we will present the main results of SimulAMV2, a 13-month project funded by EUMETSAT and carried out by the ECMWF and EUMETSAT, with the collaboration of CIMSS.

The overall objective of the project is to improve the characterization of Atmospheric Motion Vectors (AMVs) and their errors to improve the use of AMVs in Numerical Weather Prediction. This study approaches the analysis of AMV errors by using geostationary imagery generated from high resolution NWP model simulations. AMVs are derived from sequences of simulated images, using a derivation system similar to the one used operationally by EUMETSAT. The NWP model provides a "ground truth", which allows a detailed study of AMV errors, bypassing the usual difficulty of the scarcity of collocated observations of cloud and wind.

First, cloud structures from observed and simulated images will be compared; this is an important step, as findings from simulated imagery can be extended to observed imagery only if the cloud structures produced from model simulations are realistic. Then we will present evaluations of AMVs by comparing them to the model truth, first interpreting AMVs as point, single level observations of wind, and then as horizontal and vertical averages. We will also show results regarding horizontal, vertical and temporal correlations of errors, and finally we will discuss the role of clouds, focussing on the impact of vertical cloud profiles and cloud evolution on systematic AMV errors.

Jean-Jacques Morcrette (ECMWF)

Aerosol-Cloud-Radiation Interactions and their Impact on ECMWF/MACC forecasts

Prognostic aerosols were experimentally introduced in the ECMWF Integrated Forecasting System as part of the GEMS project in 2005. Their representation was refined as part of the MACC project, starting in 2009. Here, the MACC aerosol system is used to explore the impact of different levels of interactions between the aerosols and either the radiation and/or the cloud processes on cloudiness, radiation and precipitation fields, and on objective scores.
Ten-day forecasts including fully interactive aerosols are also compared to forecasts with aerosols specified from the analysis and kept constant thereafter.
Whereas the temporal variability of the prognostic aerosols is shown to have strong local effects on surface parameters, the impact on objective scores is much smaller.

Philippe Lopez (ECMWF)

Experimental 4D-Var assimilation of SYNOP rain gauge data at ECMWF

The potential benefits of assimilating worldwide SYNOP rain gauge 6-hour rainfall accumulations in both data-sparse reanalysis-like and high-resolution operations-like experiments have been investigated using ECMWF's 4D-Var system.

Results clearly indicate that rain gauge assimilation can lead to significant improvements in global analysis and forecast scores when the coverage in other observation types is sparse (as would be the case in early-20th-century reanalyses). In contrast, when SYNOP rain gauges are assimilated together with the full modern-day coverage of surface, radiosonde and satellite observations, their impact on analysis and forecast quality remains much more modest, as expected.

A description of the method used to assimilate rain gauge measurements will be given, which will cover the issues of screening, error specification and bias correction. Examples of the impact on analysis and forecast scores will then be presented and finally remaining issues as well as the potential for future improvements will be addressed.

Seymour Laxon (Centre for Polar Observation and Modelling, University College London)

When will the Arctic become ice free?

Changes in Arctic sea ice cover are perhaps the most visible evidence for the Earths changing climate. Satellite records have shown a 30% decrease in the September ice extent over the last 30 years and submarines have found a similar decline in thickness over limited regions. However model predictions of the date at which the Arctic might become ice free in summer vary widely. This seminar will discuss the key issues involved and present new data, in particular from the CryoSat mission, which can shed light on this question. We will also describe the fieldwork which is ongoing to validate the CryoSat measurements.

David Edwards (NCAR Earth System Laboratory, Deputy Director)

Atmospheric composition monitoring from the geostationary orbit: US plans and the international context

Virginie Guemas (IC3 - Institut Català de Ciències del Clima CFU, Climate Forecasting Unit, Barcelona, Spain)

On the North Pacific reduced skill in near-term climate predictions of sea surface temperatures

Abstract: Near-term climate prediction relies both on the predictability of the internal climate variability, by initializing climate models from estimates of the observed state, and on the externally forced predictability (by greenhouse gases, aerosols, solar activity). This exercise shows that the North Pacific region is where the current generation of climate forecasting systems performs the worst worldwide. In this presentation, we look for the major events missed by the forecasting systems and we investigate the reasons for this failure.