bluuebunny/crossref_metadata_2025 huggingface dataset:
Weather and Climate Services in Africa as Digital Public Goods
Authors: Jeuring Jelmer , Sivle Anders , Futsæter Håvard , Bønes Vegard , Gjesdal Kristine , Melchior David , Kolstad Erik
Published: June 2021

The global digitalization of societies is arguably one of the most influential  drivers of change in the development, implementation and dissemination of weather and climate information. From observations and measurements, to communication of weather warnings, the value chain of Weather & Climate Services (WCS) is increasingly characterized by digital interactions. Yet, digitalization occurs at different paces across regions, depending on a wide range of (local) socio-economic factors. Access to digital information is an important indicator of socio-economic development, and as such strongly embedded in the UN’s Sustainable Development Goals. Particularly in the context of objectives to provide equal access to information, education and knowledge, open weather data can provide significant benefits in developing countries, and contribute to meeting various SDGs. 

Many NMHSs, including the Norwegian Meteorological Institute, currently provide access to weather data under open access licences. One of its most important open data data services is MET Norway Weather API, a global location based time-series forecast service. Recently this api has formally been recognized as a Digital Public Good. 

Open weather data can provide opportunities to improve the forecasting capacity of African NMHSs and improve the quality of weather and climate information in African countries. With the objective to provide leading examples of the potential of open weather data as Digital Public Good, the Norwegian Meteorological Institute has been funded by NORAD to explore this potential in a pilot project together with African NMHSs. We present insights and experiences from the pilot phase of our collaboration with NMA in Ethiopia, and DCCMS in Malawi. We reflect on the challenges and successes of the first phase of this project. Also, we present an overview of key factors that need consideration when aiming to transform open weather data into value-added services that meet user-oriented criteria of Digital Public Goods. Finally, we provide an overview of next steps to move beyond the pilot phase.
URBan environments and Regional Climate Change (URB-RCC) – new CORDEX FPS on Urbanization
Authors: Halenka Tomas , Langendijk Gaby
Published: June 2021

Cities play a fundamental role on climate at local to regional scales through modification of heat and moisture fluxes, as well as affecting local atmospheric chemistry and composition, alongside air-pollution dispersion. Vice versa, regional climate change impacts urban areas and is expected to increasingly affect cities and their citizens in the upcoming decades. Simultaneously, the share of the population living in urban areas is growing, and is projected to reach about 70% of the world population up to 2050. Thus, cities are becoming one of the most vulnerable environments under climate change. This is especially critical in connection to extreme events, for instance heat waves with extremely high temperatures exacerbated by the urban heat island effect, in particular during night-time, with significant consequences for human health.

This is clearly a problem of regional to local scales and local impacts, which cannot be addressed by GCMs and till now are not included commonly in regional simulations. Already in 2013, the CORDEX community identified cities to be one of the prime scientific challenges. Therefore, we proposed this topic to become an activity at CORDEX platform, within the framework of so called flagship pilot studies, which was accepted and the FPS URB-RCC activity has been started in May this year. The proposed activity relies on specific data, for the land-use parameterization and observations, which are available from previous campaigns, to perform the expected simulations and to validate them. This FPS action is connected to the certain extent to SDGs (Sustainable Development Goals) on sustainable cities (#11), climate action (#13) and health (#3), providing information for risk management in these aspects to urban stakeholders. Moreover, urbanization is important for many groups participating in CORDEX activities and goes across CORDEX domains as big cities appear in each of them. Clearly, careful selection of targeted coordinated simulations are going to be performed.

The main goal of this FPS is to understand the effect of urban areas on the regional climate, as well as the impact of regional climate change on cities, with the help of coordinated experiments with urbanized RCMs. While the urban climate with all the complex processes has been studied for decades, there is a significant gap to incorporate this knowledge into RCMs. This FPS aims to bridge this gap, leading the way to include urban parameterization schemes as a standard component in RCM simulations, especially at  high resolutions
Drought in a changing climate – a pan-European view
Authors: Tallaksen Lena M.
Published: June 2021

Hydro-climatic extremes occur on different spatial and temporal scales, ranging from local, short term events, such as heavy storms and flash floods, to large-scale (regional to continental scale), long duration (weeks to years) events, such as drought and heat waves. Extremes affect every aspect of our society and to meet the societal need for preparedness and hazard management, the research community is challenged by underlying, critical science questions, including the need for improved knowledge on governing processes in a changing climate. In 2018, northern and parts of central Europe experienced a severe summer drought and record-breaking, persistent high temperatures led to severe impacts across a wide range of sectors. Wild ﬁres destroyed vast areas in northern Europe, and the drought led to significant impacts on agricultural production and terrestrial ecosystems. Record low river levels disrupted inland waterways and low groundwater levels led to regional water restrictions. As illustrated by the 2018 event, drought effects all components of the hydrological cycle as it propagates from its origin as a meteorological anomaly, to a deficit in soil moisture and finally - if sustained - to below normal streamflow and groundwater levels (hydrological drought). Furthermore, a drying soil affects the partitioning of latent and sensible heat at the land surface, leading to higher air temperatures and thus, a reinforcement of the warming signal (positive feedback). Due to the diverse nature of drought, a large number of drought indicators exists, representing different time scales and type of drought. Simple indices may not be sufficient when applied to the complex and cumulative nature of drought. Often it is a combination of variables or events that leads to extreme drought impacts (compound event). A better understanding of the links between physical drought indicators and key drivers of drought is vital for drought prediction, whereas a better understanding of the links between physical indicators and drought impacts is critical to improve drought preparedness and support drought mitigation. This presentation highlights key achievements in drought research with a special emphasis on the identification of drought events, detection of recent changes, and our ability to model drought, including their spatial and temporal footprint. Focus is on Europe, and it will start introducing some recent extreme drought events – their main drivers, key characteristics, and wider environmental and societal impacts, and will close with an assessment of what the future may bring.
Studying tropospheric turbulence with GNSS
Authors: Schön Steffen , Kermarrec Gaël
Published: June 2021

Long-term variations of the tropospheric refractive index delay the carrier phase measurements from Global Navigation Satellite System (GNSS). This information is now operationally integrated in Weather prediction models. Random fluctuations of the refractive index correlate the phase measurements and induces non-stationary noise processes. The correlation structure and spectral properties of observation residuals from GNSS relative positioning provide a unique opportunity to study specific properties of the turbulent atmosphere. In this contribution, we will give a short overview on turbulent processes and their impact on GNSS carrier phase measurements. We will discuss our data analysis concepts to separate the tropospheric fluctuations from other temporally varying error sources such as GNSS receiver clock errors or multipath. The analysis is based on the power spectrum of single or double differences of carrier phase measurements. This approach enables a determination of the cut-off frequencies of the atmospheric noise and the associated power law processes with their typical slopes. The obtained values are compared with theoretical expectations. We will show results for GPS from the Seewinkel network (Austria), as well as from a small network at Physikalisch-Technische Bundesanstalt (PTB, Germany) where all receivers are connected to a common highly stable atomic clock. We show that (i) a two slopes power spectrum can be reliably determined and (ii) that the outer scale length can be taken to a constant value, close to the physically expected one and in relation with the size of the eddies at tropospheric height. The study of their dependencies with the satellite geometry, the Day of the Year (DOY) or the time of the day provides a new insight on the two- and three-dimensional atmospheric turbulence in the free atmosphere.
Impact of climate change on hydropower production in the Upper Danube
Authors: Martin Santos Ignacio , Herrnegger Mathew , Holzmann Hubert
Published: June 2021

In the last two decades, different climate downscaling initiatives provided climate scenarios for Europe. The most recent initiative, CORDEX, provides Regional Climate Model (RCM) data for Europe with a spatial resolution of 12.5 km, while the previous initiative, ENSEMBLES, had a spatial resolution of 25 km. They are based on different emission scenarios, Representative Concentration Pathways (RCPs) and Special Report on Emission Scenarios (SRES) respectively.

A study carried out by Stanzel et al. (2018) explored the hydrological impact and discharge projections for the Danube basin upstream of Vienna when using either CORDEX and ENSEMBLES data. This basin covers an area of 101.810km2 with a mean annual discharge of 1923 m3/s at the basin outlet. The basin is dominated by the Alps, large gradients and is characterized by high annual precipitations sums which provides valuable water resources available along the basin. Hydropower therefore plays an important role and accounts for more than half of the installed power generating capacity for this area. The estimation of hydropower generation under climate change is an important task for planning the future electricity supply, also considering the on-going EU efforts and the “Green Deal” initiative.

Taking as input the results from Stanzel et al. (2018), we use transfer functions derived from historical discharge and hydropower generation data, to estimate potential changes for the future. The impact of climate change projections of ENSEMBLE and CORDEX in respect to hydropower generation for each basin within the study area is determined. In addition, an assessment of the impact on basins dominated by runoff river plants versus basins dominated by storage plants is considered.

The good correlation between discharge and hydropower generation found in the historical data suggests that discharge projection characteristics directly affect the future expected hydropower generation. Large uncertainties exist and stem from the ensembles of climate runs, but also from the potential operation modes of the (storage) hydropower plants in the future.

 

 

References:

Stanzel, P., Kling, H., 2018. From ENSEMBLES to CORDEX: Evolving climate change projections for Upper Danube River flow. J. Hydrol. 563, 987–999. https://doi.org/10.1016/j.jhydrol.2018.06.057

 
Updated gridded datasets version 2020 provided by the Global Precipitation Climatology Centre (GPCC)
Authors: Rustemeier Elke , Schneider Udo , Ziese Markus , Finger Peter , Becker Andreas
Published: June 2021

Since its founding in 1989, the Global Precipitation Climatology Centre (GPCC) has been producing global precipitation analyses based on land surface in-situ measurements. In the now over 30 years the underlying database has been continuously expanded and includes a high station density and large temporal coverage. Due to the semi-automatic quality control routinely performed on the incoming station data, the GPCC database has a very high quality. Today, the GPCC holds data from more than 123,000 stations, about three quarters of them having long time series.

The core of the analyses is formed by data from the global meteorological and hydrological services, which provided their records to the GPCC, as well as national meteorological and hydrological services from all over the world.  In addition, the GPCC receives SYNOP and CLIMAT reports via the WMO-GTS. These form a supplement for the high quality precipitation analyses and the basis for the near real-time evaluations.

Quality control activities include cross-referencing stations from different sources, flagging of data errors, and correcting temporally or spatially offset data. This data then forms the basis for the following interpolation and product generation.

In near real time, the 'First Guess Monthly', 'First Guess Daily', 'Monitoring Product', ‘Provisional Daily Precipitation Analysis’ and the 'GPCC Drought Index' are generated. These are based on WMO-GTS data and monthly data generated by the CPC (NOAA).

With a 2-3 year update cycle, the high quality data products are generated with intensive quality control and built on the entire GPCC data base. These non-real time products consist of the 'Full Data Monthly', 'Full Data Daily', 'Climatology', and 'HOMPRA-Europe' and are now available in the 2020 version.

All gridded datasets presented in this paper are freely available in netcdf format on the GPCC website https://gpcc.dwd.de and referenced by a digital object identifier (DOI). The site also provides an overview of all datasets, as well as a detailed description and further references for each dataset.
Communicating warnings for extreme events: use-case of a high-speed shutdown warning system for a system operator with high wind power penetration
Authors: Möhrlen Corinna
Published: June 2021

In the world meteorological organization's (WMO) guidelines on ensemble prediction, the WMO warns about ignoring uncertainty in forecasts, even if an end-user receives a deterministic forecasts. The WMO argues that “...if a forecaster issues a deterministic forecast the underlying uncertainty is still there, and the forecaster has to make a best guess at the likely outcome. Unless the forecaster fully understands the decision that the user is going to make based on the forecast, and the impact of different outcomes, the forecaster's best guess may not be well tuned to the real needs of the user”.

It is this gap in the basic understanding of uncertainty inherent in forecasts that lead to wrong assumptions among end-users with little or no experience in basic meteorology or atmospheric science. Mistrust in forecasts and forecasting methods including uncertainty methodologies often stem from a wrong expectation on the quality of forecasts for a specific problem. If uncertainty forecasts should find their way into the power industry's weather related decision making, a deeper understanding of weather uncertainty, the way weather services produce uncertainty of weather forecasts, and how such forecasts are to be translated into end-user applications is required.

In order to shed some light into the gaps and pitfalls of uncertainty forecasts in the energy sector we want to present a use-case and highlight some of the many advantages of applying uncertainty forecasts in power system applications.

The use case is a probabilistic warning system for a system operator in an area with high penetration of wind power, where regular high wind speeds (> 20m/s) lead to shutdown of wind turbines over large areas of the transmission grid, causing large costs due to reserve requirements, if such events are not predicted a number of days in advance.

The high-speed shutdown warning system will be explained and practical experience from the evaluation of high-speed shutdown events will be discussed. The alert system provided to a transmission system operator showed that it is absolutely crucial for the end-user to understand the alerts,  receive the information in different ways (text and graphics) in order to be capable of relating the warnings to the impact it may have on their grid planning. The impact of a false alarm needs to be evaluated carefully, decided upon and documented in the design phase, so that the end-users have a clear reference system to relate an alert to. Technically, the frequency of the alert generation is easy to adjust, but difficult to design efficiently from a human perspective. It is crucial to not overload end-users with warnings.

The many technical and behavioural communication aspects that need consideration in such a design and our experience with a real application will be described and discussed.
Numerical simulation of urban thermal plume merging
Authors: Mei Shuojun , Yuan Chao , He Wenhui , Talwar Tanya
Published: June 2021

Densely packed urban buildings trap outgoing long-wave radiation, leading to reduced surface cooling and increased building surface temperature. In calm conditions, poor natural ventilation causes both thermal comfort and air quality issue. The buoyancy flow generated by heated urban surfaces is the main driving of the urban flow and pollutant dispersion. A 3D numerical modelling is conducted to investigate the thermal plumes merging and buoyancy-driven airflow in urban areas. The performances of four different turbulence models, i.e., two URANS (Unsteady Reynolds-averaged Navier–Stokes equations) models and two LES (Large-Eddy Simulation) models are evaluated by comparing the velocity field with previous water tank measurements. Validation results show that all four turbulence models can capture the bending of thermal plumes toward the centre, and LES models provide a better prediction on the vertical velocity profiles, while both URANS models show underestimation. The plume merging mechanism is analysed with the high accuracy LES results. Both pressure difference and swaying motion caused by mean flow and turbulence are important for plume merging. The turbulence coherent structure of plume merging is analysed by a quadrant analysis, which shows ejection and sweep events could significantly change with the building density. A case study with complex urban geometry is conducted to show the impact of thermal plumes merging in the real high-density urban areas. The convergence airflow at the pedestrian level is estimated to 2 m/s under a surface-air temperature difference of 5 °C, which is comparable to wind-driven ventilation and beneficial to thermal comfort and air quality.
Experience gained from running the KNMI Climate Explorer (est. 1999)
Authors: van Oldenborgh Geert Jan
Published: June 2021

This is the EMS Technology Achievement Award Lecture 2021.
Information on the awardee at https://www.emetsoc.org/ems-technology-award-2021-for-geert-jan-van-oldenborgh/
Boundary-layer remote-sensing observations and modeling of foehn in the Dead Sea valley
Authors: Rostkier-Edelstein Dorita , Kunin Pavel , Alpert Pinhas
Published: June 2021

The atmospheric dynamics in the Dead Sea (DS) Valley has been studied for decades. However, the studies relied mostly on surface observations and simple coarse-model simulations, insufficient to elucidate the complex flow in the area.  I will present a first study using high resolution (temporal and spatial) and sophisticate both, measurements and modeling tools. We focused on afternoon hours during summer time, when the Mediterranean Sea (MS) breeze penetrates into the DS Valley and sudden changes of wind, temperature and humidity occur in the valley.

An intense observations period , including ground-based remote sensing and in-situ observations, took place during August and November 2014. The measurements were conducted as part of the Virtual Institute DEad SEa Research Venue (DESERVE) project using the KITcube profiling instruments (wind lidars, radiometer and soundings) along with surface Energy Balance Station. These observations enabled analysis of the vertical profile of the atmosphere at one single location at the foothills of Masada, about 1 km west of the DS shore.

High resolution (1.1 km grid size) model simulations were conducted using the WRF model. The simulations enabled analysis of the 3D flow at the DS Valley, information not provided by the observations at a single location. Sensitivity tests were run to determine the best model configuration for this study.

Our study shows that foehn develops in the lee side of the Judean Mountains and DS Valley in the afternoon hours when the MS breeze reaches the area. The characteristics of the MS breeze penetration into the valley and of the foehn (e.g. their depth) and the impact they have on the boundary layer flow in the DS Valley (e.g. the changes in temperature, humidity and wind) are conditioned to the daily synoptic and mesosocale conditions. In the synoptic scale, the depth of the seasonal trough at sea level and the height of inversion layers play a significant role in determining the breeze and foehn characteristics. In the mesoscale, the intensity of the DS breeze and the humidity brought by it determines the outcomes at the time of MS breeze penetration and foehn development. Dynamically, the foehn is associated with a hydraulic jump.

Hypothetical model simulations with modified terrain and with warmer MS surface temperature were conducted to reveal the relative contribution of each of these factors and of their synergism on the observed phenomena. The information provided by the factor separation study can be useful in future climate projections, when a warmer MS is expected.

The forecasting feasibility of foehn and the sudden changes in the DS valley 24 hours in advance using WRF is suggested following the present study. These forecasts can be most valuable for the region affected by pollution penetration from the metropolitan coastal zone.
Stochastic Rain Generator Based on Disaggregation of Precipitation into Convective and Stratiform for Climate Change Studies
Authors: Martinkova Marta
Published: June 2021

The outputs from regional climate models (RCMs) have to be further downscaled. This is usually done via a bias correction method.  This study presents a novel approach to statistical downscaling of outputs from RCMs. The novelty lies primarily in distinguishing the convective and stratiform precipitation by rain generator operating in 6-hour time step. For this purpose, the technique based on determination of threshold rainfall intensity is used, built on the observation that the convective precipitation amounts follow exponential distribution.

The resulting rain generator operates in the following steps: disaggregation of 6-hour cumulative precipitation into convective and stratiform types, fitting of the first order 3-state discrete time Markov chain to the data, and simulation of long time series of precipitation. Then the mixture of log-normal and Generalized Pareto distribution is fitted to stratiform events and the Generalized extreme value distribution to convective events.

The impact of climate change on precipitation is represented by change factors that are identified for precipitation occurrence (by comparing the transition matrices for the future and control period) and for precipitation amounts (by comparing the scale and location parameters of distributions fitted for the future and control period). The observational data are then altered with the obtained change factors.

From evaluation of observational data it stems that the average volume of a convective event is higher for the western region than the eastern region of the Czech Republic. Additionally, statistically significant trends in the number and volume of convective events were identified for the western region. The analysis of the RCM simulations shows that even though the overall precipitation is projected to be lower in future, the proportion of convective events (versus stratiform ones) would be higher. In a future climate, the number of convective events is projected to be lower while the mean volume of a convective event to be larger.
Spatial analysis of hourly precipitation combining observations and ensemble forecasts
Authors: Lussana Cristian , Nipen Thomas N. , Seierstad Ivar A. , Elo Christoffer A.
Published: June 2021

Hourly precipitation is often simultaneously simulated by numerical models and observed by multiple data sources. Accurate precipitation fields based on all available information are valuable input for numerous applications and a critical aspect of climate monitoring. 

Inverse problem theory offers an ideal framework for the combination of observations with a numerical model background. In particular, we have considered a modified ensemble optimal interpolation scheme. The deviations between background and observations are used to adjust for deficiencies in the ensemble. A data transformation based on Gaussian anamorphosis has been used to optimally exploit the potential of the spatial analysis, given that precipitation is approximated with a gamma distribution and the spatial analysis requires normally distributed variables. For each point, the spatial analysis returns the shape and rate parameters of its gamma distribution. 

The ensemble-based statistical interpolation scheme with Gaussian anamorphosis for precipitation (EnSI-GAP) is implemented in a way that the covariance matrices are locally stationary, and the background error covariance matrix undergoes a localization process. Concepts and methods that are usually found in data assimilation are here applied to spatial analysis, where they have been adapted in an original way to represent precipitation at finer spatial scales than those resolved by the background, at least where the observational network is dense enough.

The EnSI-GAP setup requires the specification of a restricted number of parameters, and specifically, the explicit values of the error variances are not needed, since they are inferred from the available data. 

The examples of applications presented over Norway provide a better understanding of EnSI-GAP. The data sources considered are those typically used at national meteorological services, such as local area models, weather radars, and in situ observations. For this last data source, measurements from both traditional and opportunistic sensors have been considered.
Introduction and validation of a simplistic method to represent vehicle-induced turbulence in high-resolution large-eddy simulations
Authors: Motisi Giovanna , Maronga Björn
Published: June 2021

Vehicle-induced effects (VIE) and exhaust fumes interacting with turbulent flow has become known to be a critical factor when investigating the wind flow and the transport of pollutants in urban street canyons. Up to now, mainly the Reynolds-Averaged-Navier-Stokes (RANS) technique has been applied for CFD studies of the processes within urban street canyons; research studies using turbulence-resolving Large-Eddy Simulations (LES), however, were rather rare. As LES models explicitly resolve the dominant turbulent motions, whose knowledge is needed to fully understand the processes, the incorporation of moving objects into a turbulence-resolving model is essential for the accurate simulation of pollutant dispersion in urban environments. In this paper we outline our effort to account for VIE in the LES model PALM. For this purpose, an innovative and easy to implement method was realised to represent a common car shape within the environmental LES setup: the so-called air-block method. Its concept is based on an object (representing the vehicle) in which a fixed velocity is prescribed to the objects grid volumes that equals the driving speed of the vehicle. Control of its movement, however, is achieved via a Lagrangian particle located at its center of gravity. This approach is significantly different from conventional consideration of solid objects as obstacles, since the air-block representation assumes that frictional drag is much smaller (and can thus be neglected) than form drag. By the same token the implementation is much easier to achieve in a complex LES model such as PALM.

In this talk we will outline the newly-developed simplistic method to represent driving vehicles in an LES model and show its performance based on a validation study for the turbulent wake flow and dispersion of exhaust fumes. For this purpose we employ existing wind tunnel data and comparative PALM simulations using the conventional solid-obstacle approach (Carpentieri et al. 2012, Atmospheric Environment, 62:9-25, DOI:10.1016/j.atmosenv.2012.08.019; Kastner-Klein et al. 2001, J. Wind Eng Ind Aerodyn, 89:849-861, DOI:10.1016/S0167-6105(01)00074-5). 
Uncertainties in ERA-5 and UERRA reanalyses detected by adjusted radar precipitation - a regional study for the Czech Republic
Authors: Bližňák Vojtěch , Pokorná Lucie , Rulfová Zuzana
Published: June 2021

Regional reanalysis constitute of potentially attractive new data source for many applications. They can offer added value benefiting from their higher spatial and temporal resolution. On the other hand, similarly as other data sources in regular network, reanalysis comes with uncertainties especially in the case of extremes.

The monitoring capability of reanalysis is essential for their usage as the reference datasets for climate model validation as well as for hydrological models. In this contribution, we evaluate the agreement of precipitation between modern reanalysis products (Era5, Era5 Land, Harmonie and Mescan-Surfex; with resolution between 5.5 and 32 km) and observed data at different time scales, from annual to subdaily. Studied characteristics of precipitation are for instance annual cycle of precipitation amount and the number of wet days, diurnal cycle of precipitation, and extremes. The common period for all datasets is 2002 – 2018.

Observed data used in this study are represented by adjusted radar-derived precipitation totals in 1km raster over the Czech Republic. The adjusted radar-derived precipitation totals are gained as follows. First, the radar-derived rain field is spatially adjusted to measurements from the rain gauges as a whole. For each day, the ratio between the mean 1-day precipitation total calculated from all rain gauges and the mean 1-day precipitation total estimated from the corresponding radar pixels is determined and used for a multiplication of radar-derived precipitation in every pixel of the radar domain. Second, the spatially adjusted radar-derived rain rates are locally adjusted in individual pixels based on the distance from the closest rain gauge, whereas the weight of the observed precipitation is decreasing with increasing distance to the given pixel. Adjusted daily precipitation total is then divided according to 10 min radar-derived estimates, from which the precipitation accumulations of longer duration are calculated.
Linkages between Arctic and Mid-Latitude Weather and Climate: Unraveling the Impact of Changing Sea Ice and Sea Surface Temperatures
Authors: Jaiser Ralf , Akperov Mirseid , Timazhev Alexander , Romanowsky Erik , Handorf Dörthe , Mokhov Igor
Published: June 2021

The study addresses the question, if Arctic sea ice decline is the main driver of observed changes in terms of Arctic-midlatitude linkages during winter. We discuss, if the increase of global sea surface temperatures plays an additional role. A set of four model sensitivity experiments with different sea ice and sea surface temperature boundary conditions is analyzed and compared to observed changes in reanalysis data. A detection of atmospheric circulation regimes is performed. These regimes are evaluated for their cyclone and blocking characteristics and their changes in frequency during winter to reveal tropospheric changes induced by the change of boundary conditions. Furthermore, the impacts on the large-scale circulation up into the stratosphere are investigated. The results show that the impact from sea surface temperature changes is generally stronger than the impact of sea ice concentration changes alone. However, in particular in terms of the startospheric pathway, the combined impact of sea ice and sea surface temperature changes reproduces findings from the reanalysis best.

For early winter, the observed increase in atmospheric blocking in the region between Scandinavia and the Ural are primarily induced by the changes in sea surface temperatures. Nevertheless, the impacts on the stratospheric circulation in terms of a weakened polar vortex, are only observed if sea ice is reduced and sea surface temperatures are increased. Late winter impacts are more inconsistent in the model sensitivity study, but slightly improved when both components of forcing are changed. In this context, we further identify a discrepancy in the model to reproduce the weakening of the stratospheric polar vortex through blocking induced upward propagation of planetary waves.
Study on the role of Black Carbon aerosols in cloud droplets during the dissipation of a fog.
Authors: Al Asmar Lea , Musson-Genon Luc , Dupont Eric , Sartelet Karine
Published: June 2021

Cloud condensation nuclei (CCN) are the subset of aerosol particles able to form cloud droplets. CNN activation is influenced by the size distribution, chemical composition and number of particles. They consequently impact the cloud microstructure, which affects the radiative properties of clouds, atmospheric circulation and thermodynamics, as well as radiative budgets. By influencing the single scattering albedos of clouds, some particles lead to an increase of the solar irradiation absorption and solar heating in the cloud layers. A good example of these absorbing particles is those made of black carbon (BC), which is emitted during the combustion of various types of fuel and non-exhaust traffic-related processes. The present study deals with the role of BC in a solar radiative scheme and its interaction with clouds during a well-documented case of a fog that evolves into a low stratus cloud. To do so, the solar scheme of the computational fluid dynamic model Code Saturne is used for the estimation of fluxes and heating rates in the atmosphere. It is based on the two-stream parameterization with calculations done in the ultraviolet-visible (UV-Vis) and solar infrared (SIR) bands.

A special attention is given on the impact of BC on the dissipation of the fog. As expected, the introduction of BC in cloud droplets accentuates the heating in the layers at the top of the cloud where water liquid content is maximum. In the SIR band, there is an increase of approximatively 80 %. In the UV-Vis band, where absorption of solar irradiance by ozone is minor, the heating rate is now 10 times higher. The contribution of the UV-Vis band becomes more important. The augmentation of solar heating leads to a reduction of the liquid water content and, consecutively, to a faster dissipation of the fog and the stratus. Therefore, direct surface fluxes are also increased.

When increasing the volume fraction of black carbon in cloud droplets, the water liquid content is furthermore reduced leading to a faster dissipation of the fog. However, this impact is small, because the fog is formed in the morning. At this time, the cooling rate due to thermal radiation is higher than the solar heating at the top of the cloud. We expect the impact of black carbon in cloud droplets to be higher for more persistent clouds or for a fog in the boundary layer of the urban atmosphere, where the fraction of BC in particles is higher.
Evaluation of analog-based post-processing in Croatia for the wind gust NWP
Authors: Vujec Ivan , Odak Plenković Iris
Published: June 2021

The potential goal of weather forecast verification is to quantify the quality of given forecasts to determine the best possible setup available for the predictand tested in a certain area. Such procedure is performed to adequately select the wind gust forecasts at a 10 m height for different geographical and topographical areas of the Republic of Croatia using data from 61 stations in 2018. In addition to the raw ALADIN numerical model forecast, 3 additional forecasts based on the analog post-processing method are verified: a simple AnEn forecast, an AnEn forecast with predictor weight optimization, AnEnT, and a forecast with an additional correction for the high wind speed AnEnK.

In the analysis of wind gust as a continuous variable, the raw ALADIN forecast is the least successful in the coastal group of stations, while the analysis of wind as a categorical variable shows the deficiencies of the raw forecast in the continental group of stations. It is shown that predictions obtained by the analog method improve the predictions overall, compared to the raw ALADIN forecast. The largest improvements are achieved in the coastal group of stations, while the improvements in the continental group of stations are not as emphasized. For the climatologically more common wind gust speeds, there is a noticeable improvement made with the analog-based post-processing over the raw ALADIN NWP. The same result is shown even for the extreme events, except for the continental group of stations.

The results presented in this work suggest that all the forecasts considered are more suited to predict the bora than the sirocco wind. Overall, better post-processing results are achieved in the northern Adriatic than in the southern Adriatic. However, the relative improvement gained by the analog method is more pronounced in the southern Adriatic, where the occurrence of the sirocco wind is more frequent.

Among the forecasts obtained by the analog method, the AnEnK variant could be singled out as the best one, especially for high wind gust speed. However, the differences in performance between the three variants of the analog method are often very small.
How to teach lightning activities to spark student curiosity?
Authors: Takátsné Lucz Ildikó , Tasnádi Péter
Published: June 2021

Last year a new National Curriculum was introduced in Hungary. Its framework not only restructured physics teaching but also have brought some changes in its content. In addition to the traditional chapters some new topics (such as the process of lightning activities, the issues of lightning-protection and the proper behaviour in lightning-hazardous situations) have emerged into the Curriculum. The aim of this study is to create and share teaching resources for secondary school students and their teachers which concern lightning strikes and damages caused by them. Thunderstorms and lightning activities are very complex and exciting phenomena which stimulate the students’ curiosity and consequently may increase their physics engagement and motivation. Furthermore, studying this topic provides students with excellent opportunities to develop their scientific thinking and deepen their science knowledge.

Our method for the investigation was the following: In total, 55 students (16-17-years old) were chosen to participate in this study. They were asked to fill in a pre-questionnaire in order to get an overview about their prior knowledge in lightning process and lightning protection. Several questions concerned misconceptions related to the topic. We were interested in what the students thought about them. Afterwards, we analysed the students’ responses and identified the areas which should be focused on. Some teaching resources and also worksheets were created based on the book An Introduction to Lightning written by Vernon Cooray. 

Before starting our discussions about lightning flashes we briefly summarized the stages of thunderstorm build-up, the formation of thunderstorm clouds and their electrification processes. After describing how clouds gain charges we examined the birth and development of lightning bolts and the operation of the global atmospheric electric circuit. Then we focused on the physics of lightning flashes, especially the mechanism of lightning strikes, the electric and magnetic field generated by them and their consequences. It was a great challenge to give the students elementary explanations for these problems as they do not have the necessary mathematical apparatus to accurately describe the electromagnetic field produced by lightning flashes. Particular attention has been paid to the electromagnetic spectrum of the strikes, the electromagnetic radiation in radio-, optic-, and in high-frequency ranges. Finally, students gained a brief insight into the method of lightning localization and lightning protection.

Based on our experience and the students’ feedback the topic could help spark student curiosity and promote their science and critical thinking. Moreover, the results of the students’ pre- and post-tests provide evidence that our teaching resources can also be effective in supporting student independent learning.
Stochastic modeling of transient surface scalar and momentum fluxes in turbulent boundary layers
Authors: Klein Marten , Lignell David O. , Schmidt Heiko
Published: June 2021

Turbulence is ubiquitous in atmospheric boundary layers and manifests itself by transient transport processes on a range of scales. This range easily reaches down to less than a meter, which is smaller than the typical height of the first grid cell layer adjacent to the surface in numerical models for weather and climate prediction. In these models, the bulk-surface coupling plays an important role for the evolution of the atmosphere but it is not feasible to fully resolve it in applications. Hence, the overall quality of numerical weather and climate predictions crucially depends on the modeling of subfilter-scale transport processes near the surface. A standing challenge in this regard is the robust but efficient representation of transient and non-Fickian transport such as counter-gradient fluxes that arise from stratification and rotation effects.

We address the issues mentioned above by utilizing a stochastic one-dimensional turbulence (ODT) model. For turbulent boundary layers, ODT aims to resolve the wall-normal transport processes on all relevant scales but only along a single one-dimensional domain (column) that is aligned with the vertical. Molecular diffusion and unbalanced Coriolis forces are directly resolved, whereas effects of turbulent advection and stratification are modeled by stochastically sampled sequence of mapping (eddy) events. Each of these events instantaneously modifies the flow profiles by a permutation of fluid parcels across a selected size interval. The model is of lower order but obeys fundamental conservation principles and Richardson's 1/4 law by construction.

In this study, ODT is applied as stand-alone tool in order to investigate nondimensional control parameter dependencies of the scalar and momentum transport in turbulent channel, neutral, and stably-stratified Ekman flows up to (friction) Reynolds number Re = O(104). We demonstrate that ODT is able to capture the state-space statistics of transient surface fluxes as well as the boundary-layer structure and nondimensional control parameter dependencies of low-order flow statistics.
Very good to reasonable agreement with available reference data is obtained for various observables using fixed model set-ups. We conclude that ODT is an economical turbulence model that is able to not only capture but also predict the wall-normal transport and surface fluxes in multiphysics turbulent boundary layers.
The Sandbox: How can we help forecasters to deal with uncertainties?
Authors: Sivle Anders Doksæter , Jeuring Jelmer , Svehagen Mai-Linn Finstad , Ovhed Magnus , Hagen Berit , Gislefoss Kristian , Borander Pernille
Published: June 2021

At MET Norway, a small team - the Sandbox - are spending part of their working hours trying to improve the communication between the meteorologists and the audience. At the moment the Sandbox consists of seven forecasters, researchers, and communication advisors with backgrounds from both natural and social sciences. Over the past five years, this has been a proven format to address interdisciplinary and cross-departmental challenges. For example, the team has been working with ideas related to establishing an editorial team and a podcast. Suggestions from the Sandbox are delivered directly to the leadership who then decide what to follow up on or not.

This year, the team is working with two well-known and related challenges to the meteorological community: i) how can we help the meteorologists in the transition from mainly using deterministic model data, to mainly using probabilistic data from ensemble prediction systems?, and ii) how can we aid and develop more effective communication with respect to forecast uncertainty?

The work is set up as a one-year project, with a mix of two-day meetings working with a specific topic, and monthly two-hour follow-up meetings in between. A thematic plan related to uncertainties was agreed upon at the start of 2021 and covers a varied but coherent set of challenges, and includes a set of concrete aims and deliverables, and how to actually work together (with respect to methods as well as the Covid-19 restrictions). For the two-day meetings, the selected topics were 1. Insight into the existing mind-sets and tools/data the forecasters have, 2. Communication and language, 3. Technical insight in strengths and weaknesses of ensemble models and products, and 4. Communication and visualization. The main deliverables of the project are to provide a toolbox and a repository of knowledge regarding the operational use of ensemble data and communication of uncertainty. The toolbox and repository will be available for forecaster training and operations, as well as form a basis to develop future research and outreach activities.

At the annual EMS meeting September 2021 we will reflect on the work methods that the  Sandbox uses, and present first outcomes of the project, e.g. more concrete information about what the toolbox and repository of knowledge will look like. 
Open data for weather observations in Europe – a status review
Authors: Schulze Dennis
Published: June 2021

Weather observations are a key component in the value chain to create societal benefits in meteorology. They are not just essential input to numerical weather prediction models but also core to many other applications ranging from risk assessment for insurance applications, drought monitoring in agriculture, and integration of renewable energy into the power grids.

In order to maximize the return on public investment into measurement network infrastructure and operation of weather stations, a wide use of the generated data is essential. This has been confirmed just recently by an evaluation of the European Commission on high-value datasets.

While in recent years, operators of various national and regional grids have increasingly made their measurement data publicly available, there was no transparent monitoring in place about the evolution of open data from weather stations and the availability and distribution of data for specific parameters.

In order to assess the status of open and freely available weather observations in Europe, we have captured all freely available weather observations as made available on the opendata.dwd.de server of Deutscher Wetterdienst. These observations have been decoded and stored in a database system. We compared the availability of data from weather stations to the overall station list in the ECOMET catalogue.

We will present which countries provide comprehensive sets of their weather observations as open data and also evaluate the temporal frequency of the available measurements. We have also investigated if there has been an evolution of open data from January 2020 until recently.

Furthermore, we will show insights into availability of specific parameters, in particular hourly measurements of the amount of precipitation, wind gusts and global radiation and how this impacts the value creation in downstream services.