UP3.6 | Global and regional reanalyses
Global and regional reanalyses
Convener: Frank Kaspar | Co-conveners: Eric Bazile, Jan Keller
| Tue, 05 Sep, 11:00–13:00 (CEST)|Lecture room B1.04
Tue, 11:00
Improved reanalyses of past weather can be obtained by retrospectively assimilating reprocessed observational datasets ranging from surface stations and satellites with a up-to-date Numerical Weather Prediction (NWP) model. The resulting time series of the atmospheric state is both dynamically consistent and close to observations. The interest in extracting climate information from reanalysis is rising and creating a request for reanalysis uncertainty estimation at various temporal-spatial scales.
These research questions have been addressed in EU-funded research projects (e.g.ERA-CLIM, EURO4M and UERRA). Regional reanalyses are now available for Europe and specific sub-domains, e.g. produced by national meteorological services. Global and regional reanalyses are also an important element of the Copernicus Climate Change Services.

This session invites papers that:
• Explore and demonstrate the capability of global and regional reanalysis data for climate applications
• Compare different reanalysis (global, regional) with each other and/or observations
• Improve recovery, quality control and uncertainty estimation of related observations
• Analyse the uncertainty budget of the reanalyses and relate to user applications

Orals: Tue, 5 Sep | Lecture room B1.04

Chairpersons: Frank Kaspar, Eric Bazile
Onsite presentation
Frank Kaspar, Jaqueline Drücke, Franziska Bär, Michael Borsche, Alexander Kelbch, and Thomas Spangehl

Germany’s national meteorological service (Deutscher Wetterdienst, DWD) has initiated the development of a regional reanalysis more than a decade ago by establishing the Hans Ertel Centre for Weather Research (HErZ), which has one focus on climate monitoring. The development of a reanalysis system is the major tool for that focus activity. The development was carried outat the meteorological institutes of the Universities of Bonn and Cologne. Based on the numerical weather prediction model COSMO of DWD, regional reanalysis datasets have been developed with grid spacing of up to 2 km (Bollmeyer et al., 2015; Wahl et al., 2017). Esp. COSMO-REA6, a reanalysis for the EURO-CORDEX domain with 6 km spatial resolution has been made available under an open-data policy and has been used in a number of applications, esp. related to renewable energies (Kaspar et al., 2019). As the production relied on ERA-Interim boundary conditions, the production ended in 2019, but a second generation (“R6G2”, with boundary conditions from ERA5) is currently produced. Also, a reanalysis based on DWD’s new NWP system ICON is being prepared.

Electricity generation with wind and solar is weather-dependent and the shift towards increased use of renewable energy leads to an increased need towards high quality meteorological data. In order to support the usage of DWD’s reanalysis data in energy-related applications, the project MEDAILLON has been started together with partners with specialized expertise in energy system analysis (MEDAILLON: “Generierung eines offenen meteorologischen Datensatzes mit zeitlich und räumlich hoher Auflösung für die Energiesystemanalyse und -wirtschaft”, coordinated by Fraunhofer IEE: https://www.iee.fraunhofer.de/de/projekte/suche/2023/medaillon.html). The aim is to better understand the user requirements and to provide optimized user-oriented products for energy applications. This includes an assessment of the quality of the relevant parameters. Previous experience has shown that users are especially interested in wind parameters from the reanalysis datasets. For solar radiation, also satellite-based products are an alternative, as e.g. the new version of the CM SAF-SARAH-dataset (also produced at DWD, most recent version is 3.0).

The datasets are also applied in climate services of DWD, as e.g. in support of offshore wind planning in Germany’s Exclusive Economic Zone or in studies related to the potential of renewable energies alongside the German transportation infrastructure.

In the presentation, we will summarize the current status of reanalysis activities at DWD and present the approach of MEDAILLON to derive user-friendly products.

How to cite: Kaspar, F., Drücke, J., Bär, F., Borsche, M., Kelbch, A., and Spangehl, T.: Progress in regional reanalyses of DWD and their use in energy applications, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-623, https://doi.org/10.5194/ems2023-623, 2023.

Onsite presentation
Alexander Kelbch, Arianna Valmassoi, Thomas Spangehl, Michael Borsche, and Florian Imbery

The development of regional reanalyses aims at the provision of high-resolution data sets that are suitable for climate applications and climate services. As the desired high-resolution information can barely be provided by either synoptic or remote sensing observation data, a growing interest in high-quality regional reanalyses is recognisable. Particular demand arises from the renewable energy sector. Further quality gains are expected by using an ensemble approach, e.g. by making available the desired uncertainty information when moving towards higher resolution. Within the framework of the Innovation Programme for applied Researches and Developments (IAFE) at Germany's national meteorological service (DWD) our project aims to develop and evaluate an operational ensemble-based regional reanalysis system incorporating the current NWP model of DWD (ICON). One final goal of the project is to provide a basic framework for user-oriented verification.  

For our new reanalysis system we plan to use observation data sets or subsets of the ECMWF ERA5 reanalysis. Thus, a converter has been developed providing the ERA5 observation data (odb files) to the operational DWD data assimilation scheme. Numerous test experiments have been performed to 1) assess the specifications for our future reanalysis system and 2) evaluate the performance of the observation data assimilation. For testing we use the Basic Cycling Environment (BACY) being characterized by its modularity, robustness, user-friendlyness and high complexity. Here we present the resulting set of "frozen" BACY specifications such as model resolution, number of ensemble members, domain size, choice of output variables as well as results of the assimilation experiments.

How to cite: Kelbch, A., Valmassoi, A., Spangehl, T., Borsche, M., and Imbery, F.: Ensemble-based regional reanalysis system for Central Europe: Observation data converter, setup, test results and outlook, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-578, https://doi.org/10.5194/ems2023-578, 2023.

Onsite presentation
Thomas Spangehl, Michael Borsche, Deborah Niermann, and Franziska Bär

Global reanalyses are known for more than 25 years and are widely used for monitoring climate variability and change, for academic purposes and commercial applications. Meanwhile, they are a fundamental part of operational climate services such as the Copernicus Climate Change Service (C3S). Recently, also regional reanalyses that provide higher spatial and temporal resolution became popular. Examples of exploitation of regional reanalyses include applications in the energy sector. Of special interest are variables such as wind speed at hub heights of modern wind turbines (offshore and onshore), near surface temperature and surface solar irradiance. Moreover, regional reanalyses are potentially useful for climate applications dealing with extremes such as wind storms, regional temperature anomalies including heat waves and droughts.

Here we show results from an evaluation approach that is used for monitoring the production process of the regional reanalysis COSMO-REA6 Generation 2 (R6G2), currently produced by Germany’s national meteorological Service (Deutscher Wetterdienst, DWD). Numerous datasets are used as observational reference, based either on in-situ measurements from stations and towers or satellite-borne remote sensing technology. Different products such as ERA5, COSMO-REA6 and HoKliSim-De are used as benchmark. The technical infrastructure for the standardised evaluation and monitoring is provided by the MAVIS system which builds on Freva (Free Evaluation System Framework, https://doi.org/10.5334/jors.253).

One user requirement is the availability of uncertainty information. There has been evidence that ensemble information is required for the representation of individual extreme events such as wind storms. The capability of the MAVIS system and requirements for application of the evaluation framework to ensemble-based regional reanalyses will be discussed.


How to cite: Spangehl, T., Borsche, M., Niermann, D., and Bär, F.: User-oriented evaluation framework for regional reanalyses, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-580, https://doi.org/10.5194/ems2023-580, 2023.

Onsite presentation
Francesco Cavalleri, Francesca Viterbo, Michele Brunetti, Riccardo Bonanno, Veronica Manara, Cristian Lussana, and Maurizio Maugeri

Since its release in 2019 by ECMWF, ERA5 has represented the state-of-the-art for global reanalysis, also providing initial and boundary conditions for many regional reanalysis products. These latter have been developed using parametrizations optimized for specific locations and observations not used in ERA5, to resolve physical processes which occur at smaller scales and thus better describe the atmospheric variables at finer resolutions than the 31 km of ECMWF global reanalysis. In this study, we investigate the capability of different reanalysis products to reproduce the characteristic atmospheric processes of the Italian peninsula. For example, a dynamical downscaling of ERA5 to higher resolutions can be an asset in studying the occurrence of extreme events, where the small scales play an important role, because of the Italian complex orography and coastal-sea interactions. For these reasons, inter-comparison and validation of different reanalysis products over Italy are carried on in this study, comparing the ERA5, ERA5-Land (9 km resolution), the MEteorological Reanalysis Italian Dataset (MERIDA, 7 km), the Copernicus European Regional ReAnalysis (CERRA, 5.5 km) and the Very High-Resolution dynamical downscaling of ERA5 REAnalysis over ITaly (VHR-REA_IT, 2.2 km). 

In particular, this work focuses on the evaluation of the 1991-2020 monthly climatology of surface air temperature over the Italian territory for each reanalysis product. The climatologies obtained from the different reanalyses at their native resolution are compared with the climatology obtained from a high-density station observational network. These observations were gridded for each reanalysis over its native grid, using a methodology that specifically accounts for elevation adjustments given the elevation differences between reanalysis grid points and station locations.

The results show that ERA5 underestimates temperature over most of the Italian territory. The bias is around -1 °C on average, with peaks of -3 °C over the Alps, and a positive temperature bias of around +0.5 °C over the Po valley. ERA5-Land, MERIDA, and CERRA reflect a similar cold bias distribution over the Italian region, even if some differences in the pattern distribution can be found, with local cold bias intensification in some areas. VHR-REA_IT, on the contrary, presents a warm summer bias of about +3 °C on average over the Po valley. In addition to that, ERA5 exhibits a negative bias over the Alpine region which increases with elevation in winter. A similar gradient is also found in the other higher resolution reanalyses (ERA5-Land, MERIDA, and CERRA), with the only exception of VHR-REA_IT which, conversely, shows a positive bias increase with decreasing elevation in summer.

How to cite: Cavalleri, F., Viterbo, F., Brunetti, M., Bonanno, R., Manara, V., Lussana, C., and Maugeri, M.: Inter-comparison and validation of high-resolution surface air temperature reanalysis fields over Italy, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-141, https://doi.org/10.5194/ems2023-141, 2023.

Onsite presentation
Klaudio Peqini, Tanja Porja, and Ervin Kafexhiu

Abstract: Drought is generally defined as a high moisture deficit below some expected levels but beyond this summarized definition, drought is a complex event compared to many other natural phenomena. Without a clear definition, nor a clear entry or termination, the drought phenomenon is very specific and highly region climate dependent. Defining this phenomenon by regions or quantifying it, is a very complex issue because of many alternative definitions by diverse authors. Despite the diversity on defining it, drought is a severe natural hazard that can be manageable. Viewed as a natural hazard, drought can be managed during its occurrence by alleviating and repairing the damages and by anticipating strategies and funds. Before planning the strategies, there is a need for a better known of the drought phenomenon in a given area. Knowing as well as possible of the regional drought indicators would provide an objective picture for quantification and analysis of drought. There are more than 100 drought indicators developed by diverse authors but the importance stands on the selection of the proper indicators that presents most of the risk for the area under the study. Accepting that there is no a unique accepted drought indicator but the indicators need to be developed for a specific context, in a specific area, some important drought indicators and widely used are meteorological indicators, mainly precipitation based indicators as the main driver of drought phenomenon. Some of the main drought indices based on precipitation are the Standardized Precipitation Index (SPI), Rainfall Deciles (RD), Palmer Drought Severity Index (PDSI), etc. Besides the above indicators there is some soil moisture indicators considered as a very relevant in drought analyses but the soil measurements is not always possible because of the lack of soil monitoring.

In this study were perform detailed analyses of the above drought indicators by using the proper meteorological parameter thresholds. The derived results may be used to better manage the drought phenomenon in order to convert it in a manageable natural hazard and mitigating its negative impacts.

Keywords: local drought, precipitation index, moisture, extreme drought


How to cite: Peqini, K., Porja, T., and Kafexhiu, E.: Estimating the meteorological based drought indicators to better manage its negative impact, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-164, https://doi.org/10.5194/ems2023-164, 2023.

Onsite presentation
Juha Aalto, Mika Rantanen, Matti Kämäräinen, Pekka Niittynen, Gareth Phoenix, Jonathan Lenoir, Ilya Maclean, and Miska Luoto

Over the four decades, the Arctic has warmed three to four times faster than globally. In addition to the long-term trend in average temperatures, extreme weather events are becoming increasingly frequent causing severe disturbances to the Arctic terrestrial ecosystems. Many existing climate datasets primarily concentrate on seasonal precipitation and temperature at coarse spatial (10-100 km) and temporal (30-year average climatologies) resolutions forming the basis of current understanding of how Arctic terrestrial ecosystems will respond to climate change. Therefore, the conventional datasets likely neglect many ecologically significant aspects of the Arctic climate relevant for biological or biogeochemical processes. For instance, snow cover duration, rain-on-snow events, or extreme wind events are known to be important variables for Arctic ecology that may not be adequately represented by the more widely used climate statistics. Today, atmospheric reanalyses provide temporally and spatially comprehensive and consistent evolution on climate variables without being limited by the challenges arising from the uneven coverage of in-situ observations. 

In this presentation, we introduce a new dataset of bioclimatic indices particularly relevant for investigating the changes of Arctic terrestrial ecosystems. The dataset, called ARCLIM, consists of several climate and event-type indices for the northern high-latitude land areas. The indices are calculated from the hourly ERA5-Land reanalysis data for 1950-2021 in a spatial grid of 0.1 degree (~9 km) resolution. We provide the indices in three subsets: (1) the annual values during 1950-2021; (2) the average conditions for the 1991-2020 climatology; and (3) temporal trends over 1951-2021. The 72-year time series of various climate and event-type indices draws a comprehensive picture of the Arctic bioclimate variability. We anticipate that the ARCLIM dataset opens new research opportunities aiming to better understand the impacts of climate change in Arctic terrestrial ecosystems.

How to cite: Aalto, J., Rantanen, M., Kämäräinen, M., Niittynen, P., Phoenix, G., Lenoir, J., Maclean, I., and Luoto, M.: ARCLIM: new bioclimatic dataset for terrestrial Arctic, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-608, https://doi.org/10.5194/ems2023-608, 2023.

Onsite presentation
Fatima Pillosu, Tim Hewson, Christel Prudhomme, and Hannah Cloke

To establish climatologies that facilitate the contextualization of extreme, high-impact weather events in relation to historical occurrences or to comprehend the influence of climate change on their intensity and frequency, an extensive collection of observations extending as far back as possible is essential. Yet, these observations exhibit inaccuracies and uneven distributions in space and time. These attributes may lead to a distorted representation of past weather and climate, particularly for variables like rainfall, which can exhibit substantial variations in space and time. 

Reanalyses and reforecasts fill the gaps in the observational records. Existing literature has demonstrated that both reanalysis and reforecast datasets offer a more accurate representation of past weather and climate, owing to their global completeness and temporal consistency. Nonetheless, reanalyses and reforecasts may not adequately depict localized and/or rare events as effectively as observational climatologies might do (provided sufficient observations are available) due to the coarse spatial resolutions of both modelled datasets. This misrepresentation is particularly pertinent for discontinuous variables, such as precipitation. 

In this presentation, we will examine the representation of point-rainfall climatologies by four distinct global model datasets: ERA5_EDA (reanalysis, 62km), ERA5 (reanalysis, 31km), ECMWF reforecasts (reforecasts, 18 km), and ERA5_ePoint (reanalysis, point-scale on a 31km grid), and compare with observed point climatologies from raingauge sites. Furthermore, we will discuss the implications of this study on future calculations of reference climatologies for localized extreme precipitation events.

How to cite: Pillosu, F., Hewson, T., Prudhomme, C., and Cloke, H.: How are observed point-rainfall climatologies represented by global models with different spatial resolutions? A comparative study., EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-610, https://doi.org/10.5194/ems2023-610, 2023.

Onsite presentation
Katarina Kosovelj and Žiga Zaplotnik

The Pacific Walker circulation (PWC) is an integral part of the tropical atmospheric circulation that influences weather patterns globally, including the global distribution of mean precipitation. It also affects the rate of global warming, sea-level rise, and the efficiency of ocean carbon absorption. Due to its importance, many indices have been used historically to quantify the PWC strength and its variability, such as indices based on surface pressure, surface zonal winds, mid-tropospheric vertical velocity and stream function, upper-tropospheric velocity potential, etc.

We reviewed and compared ten different PWC indices for the 1951-2020 period using ERA5 reanalysis data, which is verified against observations.

Our results show good agreement between the time series of normalized indices for annual-mean PWC strength. The exceptions are indices based on 200 hPa velocity potential and 500 hPa stream function. Considering their performance compared to other indices, we explored an alternative definition of the stream-function index and proposed a revised, data-adaptive velocity potential index. Generally, the correlations between the ten indices are high, with the highest correlations between indices based on closely linked physical processes. The largest disagreement between the indices occurs during the strongest El Niños. Therefore, for a robust evaluation of the PWC trends, El Niño events have to be filtered from the time series (as in L’Heureux et al., 2014) and should not coincide with the beginning or the end of the time series. Indices of PWC strength show increasing trends for 1981-2010, mostly neutral trends for the 1951-2020 period, and weak and often insignificant negative trends for the latest 2000-2020 period. PWC trends in ERA5 also hint at a possible multidecadal variability with approximately a 35-year period.

How to cite: Kosovelj, K. and Zaplotnik, Ž.: Pacific Walker circulation indices in ERA5 reanalysis, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-60, https://doi.org/10.5194/ems2023-60, 2023.