Precipitation frequency in Med-CORDEX and EURO-CORDEX ensembles from 0.44° to convection-permitting resolution: impact of model resolution and convection representation

Recent studies using convection-permitting (CP) climate simulations have demonstrated a step-change in the representation of heavy rainfall and rainfall characteristics (frequency-intensity) compared to coarser resolution Global and Regional climate models. The goal of this study is to better understand what explains the weaker frequency of precipitation in the CP ensemble by assessing the triggering process of precipitation in the different ensembles of regional climate simulations available over Europe. We focus on the statistical relationship between tropospheric temperature, humidity and precipitation to understand how the frequency of precipitation over Europe and the Mediterranean is impacted by model resolution and the representation of convection (parameterized vs. explicit). We employ a multi-model data-set with three different resolutions (0.44°, 0.11° and 0.0275°) produced in the context of the MED-CORDEX, EURO-CORDEX and the CORDEX Flagship Pilot Study "Convective Phenomena over Europe and the Mediterranean" (FPSCONV). The multi-variate approach is applied to all model ensembles, and to several surface stations where the integrated water vapor (IWV) is derived from Global Positioning System (GPS) measurements. The results show that all model ensembles capture the temperature dependence of the critical value of IWV (IWVcv), above which an increase in precipitation frequency occurs, but the differences between the models in terms of the value of IWVcv, and the probability of its being exceeded, can be large at higher temperatures. The lower frequency of precipitation in convection-permitting simulations is not only explained by higher temperatures but also by a higher IWVcv necessary to trigger precipitation at similar temperatures, and a lower probability to exceed this critical value. The spread between models in simulating IWVcv and the probability of exceeding IWVcv is reduced over land in the ensemble of models with explicit convection, especially at high temperatures, when the convective fraction of total precipitation becomes more important and the influence of the representation of entrainment in models thus becomes more important. Over lowlands, both model resolution and convection representation affect precipitation triggering while over mountainous areas, resolution has the highest impact due to orography-induced triggering processes. Over the sea, since lifting is produced by large-scale convergence, the probability to exceed IWVcv does not depend on temperature, and the model resolution does not have a clear impact on the results

Investigating the representation of heatwaves from an ensemble of km-scale regional climate simulations within CORDEX-FPS convection

Heatwaves (HWs) are high-impact phenomena stressing both societies and ecosystems. Their intensity and frequency are expected to increase in a warmer climate over many regions of the world. While these impacts can be wide-ranging, they are potentially influenced by local to regional features such as topography, land cover, and urbanization. Here, we leverage recent advances in the very high-resolution modelling required to elucidate the impacts of heatwaves at these fine scales. Further, we aim to understand how the new generation of km-scale regional climate models (RCMs) modulates the representation of heatwaves over a well-known climate change hot spot. We analyze an ensemble of 15 convection-permitting regional climate model (CPRCM, ~ 2–4 km grid spacing) simulations and their driving, convection-parameterized regional climate model (RCM, ~ 12–15 km grid spacing) simulations from the CORDEX Flagship Pilot Study on Convection. The focus is on the evaluation experiments (2000–2009) and three subdomains with a range of climatic characteristics. During HWs, and generally in the summer season, CPRCMs exhibit warmer and drier conditions than their driving RCMs. Higher maximum temperatures arise due to an altered heat flux partitioning, with daily peaks up to ~ 150 W/m$^{2}$ larger latent heat in RCMs compared to the CPRCMs. This is driven by a 5–25% lower soil moisture content in the CPRCMs, which is in turn related to longer dry spell length (up to double). It is challenging to ascertain whether these differences represent an improvement. However, a point-scale distribution-based maximum temperature evaluation, suggests that this CPRCMs warmer/drier tendency is likely more realistic compared to the RCMs, with ~ 70% of reference sites indicating an added value compared to the driving RCMs, increasing to 95% when only the distribution right tail is considered. Conversely, a CPRCMs slight detrimental effect is found according to the upscaled grid-to-grid approach over flat areas. Certainly, CPRCMs enhance dry conditions, with knock-on implications for summer season temperature overestimation. Whether this improved physical representation of HWs also has implications for future changes is under investigation

The first multi-model ensemble of regional climate simulations at kilometer-scale resolution. Part I: Evaluation of precipitation

Here we present the first multi-model ensemble of regional climate simulations at kilometer-scale horizontal grid spacing over a decade long period. A total of 23 simulations run with a horizontal grid spacing of ∼ 3 km, driven by ERA-Interim reanalysis, and performed by 22 European research groups are analysed. Six different regional climate models (RCMs) are represented in the ensemble. The simulations are compared against available high-resolution precipitation observations and coarse resolution (∼ 12 km) RCMs with parameterized convection. The model simulations and observations are compared with respect to mean precipitation, precipitation intensity and frequency, and heavy precipitation on daily and hourly timescales in different seasons. The results show that kilometer-scale models produce a more realistic representation of precipitation than the coarse resolution RCMs. The most significant improvements are found for heavy precipitation and precipitation frequency on both daily and hourly time scales in the summer season. In general, kilometer-scale models tend to produce more intense precipitation and reduced wet-hour frequency compared to coarse resolution models. On average, the multi-model mean shows a reduction of bias from ∼ −40 at 12 km to ∼ −3 at 3 km for heavy hourly precipitation in summer. Furthermore, the uncertainty ranges i.e. the variability between the models for wet hour frequency is reduced by half with the use of kilometer-scale models. Although differences between the model simulations at the kilometer-scale and observations still exist, it is evident that these simulations are superior to the coarse-resolution RCM simulations in the representing precipitation in the present-day climate, and thus offer a promising way forward for investigations of climate and climate change at local to regional scales. © 2021, The Author(s)

The first multi-model ensemble of regional climate simulations at kilometer-scale resolution, part I: evaluation of precipitation

Here we present the first multi-model ensemble of regional climate simulations at kilometer-scale horizontal grid spacing over a decade long period. A total of 23 simulations run with a horizontal grid spacing of ∼3 km, driven by ERA-Interim reanalysis, and performed by 22 European research groups are analysed. Six different regional climate models (RCMs) are represented in the ensemble. The simulations are compared against available high-resolution precipitation observations and coarse resolution (∼ 12 km) RCMs with parameterized convection. The model simulations and observations are compared with respect to mean precipitation, precipitation intensity and frequency, and heavy precipitation on daily and hourly timescales in different seasons. The results show that kilometer-scale models produce a more realistic representation of precipitation than the coarse resolution RCMs. The most significant improvements are found for heavy precipitation and precipitation frequency on both daily and hourly time scales in the summer season. In general, kilometer-scale models tend to produce more intense precipitation and reduced wet-hour frequency compared to coarse resolution models. On average, the multi-model mean shows a reduction of bias from ∼ −40% at 12 km to ∼ −3% at 3 km for heavy hourly precipitation in summer. Furthermore, the uncertainty ranges i.e. the variability between the models for wet hour frequency is reduced by half with the use of kilometer-scale models. Although differences between the model simulations at the kilometer-scale and observations still exist, it is evident that these simulations are superior to the coarse-resolution RCM simulations in the representing precipitation in the present-day climate, and thus offer a promising way forward for investigations of climate and climate change at local to regional scales

Internal arc testing of medium voltage switchgear

Text in Russia

Novi trendovi u oplemenjivanju uljanih kupusnjača

Po potrosnji biljnog ulja u svetu uljana repica (Brassica napus L.) se nalazi na trecem mestu, iza palme i soje. Koristi se u ishrani ljudi, Zivotinja, proizvodnyi biodizela. Kao posledica velike potraznje na trzistu, primetan je trend povecanja povrsina, prinosa t kvaliteta uljane repice u svetskim razmerama. Mendelova pravila predstavijaju osnovu svih metoda oplemenjivanja sorti t hibrida uljanih i krmnih kupusnjaca. Linije se testiraju u vise godina i lokaliteta, a zadatak oplemenjivanja na kvalitet je da se primenom konvencionalnth i metoda biotehnologije stvore nove sorte i hibridi visokog i stabilnog prinosa, sa poboljsanom nutritivaom vrednoscu semena. Seme dobrih sorti uljane repice sadrzi oko 45% ulja sa 60% oleinske kiseline i 23% proteina. Razvijene su sorte uljane repice kanola tipa kao i visokooleinski tipovi sa vecom Stabilnoscu na visokim temperaturama. Najznacajnije antinuiritivne materije u semenu uljane repice su glukozinolati. Znacajan napredak u oplemenjivanju ucinjen je primenom savremenih metoda biotehnologie. Tokom tri decenije oplemenjivanja uljane repice u Institutu za ratarstvo | povrtarstvo u Novem Sadu stvoreno je 13 sorti ozime uljane repice, dve sorte jare repice i tri ozima hibrida. Od oplemenjivanja se ocekuje dalje povecanje prinosa, pri istovremenom poboljsanju njegove sigurnosti, odnosno rezistentnosti na bolesti i tolerancije na stres

Internal arcing : issues related to testing and standardization

Internal arc tests are intended to verify the effectiveness of switchgear design in protecting personnel in case of an internal arc. With the IEC 62271-200 & 201 in 2003, new methods and criteria for testing metal / insulation enclosed switchgear under conditions of an internal arc have been formulated. KEMA's experiences with the new standards will be highlighted, including statistics on the failure rates (approx. 20%), differentiated to the various acceptance criteria. A comparison with experiences related to the prior standard (IEC 60298) will be presented. Various problems around certification are highlighted, among which reproducibility of results, initiation and an adequate definition of relevant design features in the stage of verification of drawings. With switchgear having an increasing rated voltage coming on the market, there is an increased tendency to perform internal arc testing with reduced voltage, because of lack of sufficient short-circuit power. With actual examples, it will be demonstrated to what extent such "reduced voltage testing" is acceptable, the main problem being the uncertainty of the arc motion inside the enclosure, and its effect on the current (asymmetry) through its arc voltage. From environmental point of view, internal arc testing in SF6 filled installations is accepted less and less, tempting to replace SF6 (in SF6 insulated MV switchgear) by air in the regular testing of SF6 insulated MV switchgear. A literature overview is presented of several earlier investigations on the differences between arcing in SF6 and air in MV switchgear. New arcing tests are presented with the arcing in an SF6 and air filled model (0.5 m3, 14 kA and arc duration of 0.5 and 1 s). Arc voltage, current and pressure measurements, as well as high-speed infrared and optical imaging are used to demonstrate the differences between arcing in SF6 and air. It is observed that internal pressure rise as a result of arcing in air proceeds significantly faster than in SF6, and reaches higher values than in SF6. After pressure relief, however, the amount of energy supplied to the environment is higher by arcing in SF6 than in air. Concluding, all experimental results suggest that when replacing SF6 (of SF6 insulated switchgear) with air for internal arc testing, the mechanical stress on the switchgear itself is too severe because of higher and faster rising pressure in air. The effects on the environment (indicators as used in testing, pressure and temperature in switchgear compartments & -room) after pressure relief are distinctly different in SF6 and air, but are not part of IEC tests. Results suggest that adequate test procedures need to be designed that should justify replacement of SF6 by air for internal arc testing

Internal arcing : issues related to testing and standardization

Internal arc tests are intended to verify the effectiveness of switchgear design in protecting personnel in case of an internal arc. With the IEC 62271-200 & 201 in 2003, new methods and criteria for testing metal / insulation enclosed switchgear under conditions of an internal arc have been formulated. KEMA's experiences with the new standards will be highlighted, including statistics on the failure rates (approx. 20%), differentiated to the various acceptance criteria. A comparison with experiences related to the prior standard (IEC 60298) will be presented. Various problems around certification are highlighted, among which reproducibility of results, initiation and an adequate definition of relevant design features in the stage of verification of drawings. With switchgear having an increasing rated voltage coming on the market, there is an increased tendency to perform internal arc testing with reduced voltage, because of lack of sufficient short-circuit power. With actual examples, it will be demonstrated to what extent such "reduced voltage testing" is acceptable, the main problem being the uncertainty of the arc motion inside the enclosure, and its effect on the current (asymmetry) through its arc voltage. From environmental point of view, internal arc testing in SF6 filled installations is accepted less and less, tempting to replace SF6 (in SF6 insulated MV switchgear) by air in the regular testing of SF6 insulated MV switchgear. A literature overview is presented of several earlier investigations on the differences between arcing in SF6 and air in MV switchgear. New arcing tests are presented with the arcing in an SF6 and air filled model (0.5 m3, 14 kA and arc duration of 0.5 and 1 s). Arc voltage, current and pressure measurements, as well as high-speed infrared and optical imaging are used to demonstrate the differences between arcing in SF6 and air. It is observed that internal pressure rise as a result of arcing in air proceeds significantly faster than in SF6, and reaches higher values than in SF6. After pressure relief, however, the amount of energy supplied to the environment is higher by arcing in SF6 than in air. Concluding, all experimental results suggest that when replacing SF6 (of SF6 insulated switchgear) with air for internal arc testing, the mechanical stress on the switchgear itself is too severe because of higher and faster rising pressure in air. The effects on the environment (indicators as used in testing, pressure and temperature in switchgear compartments & -room) after pressure relief are distinctly different in SF6 and air, but are not part of IEC tests. Results suggest that adequate test procedures need to be designed that should justify replacement of SF6 by air for internal arc testing