Comment on wcd-2023-10

<strong class="journal-contentHeaderColor">Abstract.</strong> Strong winds associated with extratropical cyclones are one of the most dangerous natural hazards in Europe. These high winds are mostly associated with five mesoscale dynamical features: the warm (conveyor belt) jet (WJ); the cold (conveyor belt) jet (CJ); cold frontal convection (CFC); strong cold-sector winds (CS); and, in some cases, the sting jet (SJ). The timing within the cyclone's life cycle, the location relative to the cyclone core and further characteristics differ between these features and, hence, likely also their associated forecast errors. In Part 1 of this study (Eisenstein et al., 2022b), we introduced the objective and flexible identification tool RAMEFI (RAndom-forest-based MEsoscale wind Feature Identification), which distinguishes between WJ, CFC and CS as well as CJ and SJ combined. RAMEFI is based on a probabilistic random forest trained on station observations of 12 storm cases over Europe. Being independent of spatial distribution, RAMEFI can also be applied to gridded data. Here, we use RAMEFI to compile a climatology over 19 extended winter seasons (October&ndash;March, 2000&ndash;2019) based on high-resolution regional reanalyses of the German Consortium for Small-scale Modelling (COSMO) model over Europe. This allows the first-ever long-term objective statistical analysis of the mesoscale wind features, their occurrence frequency, geographical distribution and characteristics. For Western and Central Europe, we demonstrate that the CS is prominent in most winter storms, while CFC is the least common cause of high winds, both in terms of frequency and affected area. However, probably due to convective momentum transport, CFC is on average the cause of the highest gusts after the CJ, and has the highest gust factor. As expected, CFC high-wind areas show high levels of humidity and overcast conditions. In contrast, CS is characterised by sunnier conditions interspersed by patchy cumulus clouds leading to a broader cloud cover distribution than for other features. The WJ produces the weakest winds on average, but affects a larger area than CJ. Central Europe is more strongly affected by WJ and CFC winds, while the CJ usually occurs farther north over the North and Baltic Seas, northern Germany, Denmark and southern Scandinavia. System-relative composites show that WJ and CFC tend to occur earlier in the cyclone life cycle than CJ and CS. Consistently, CS is the most common cause of high winds over Eastern Europe, where cyclones tend to occlude, represented by a narrowing warm sector and weakening cold front. The WJ mostly occurs within the southeastern quadrant of a cyclone bordering with the narrow CFC in the west. However, the location of CFC varies greatly between cases. The CS occurs in the southwestern quadrant, while the CJ appears closer to the cyclone centre, sometimes stretching into the southeastern quadrant. This objective climatology largely confirms previous, more subjective investigations but puts these into climatological context. It allows a more detailed analysis of feature properties, and provides a solid foundation for model assessment and forecast evaluation in future studies.

&amp;lt;p&amp;gt;Strong winds associated with extratropical cyclones are one of the most dangerous natural hazards in Europe. These high winds are mostly connected with five mesoscale dynamical features, namely the warm (conveyor belt) jet (WJ), the cold (conveyor belt) jet (CJ), (post) cold-frontal convective gusts (CFC), strong cold sector winds (CS) and &amp;amp;#8211; at least in some storms &amp;amp;#8211; the sting jet (SJ). While all these have strong winds in common, the timing, location and some further characteristics tend to differ and hence likely also the forecast errors occurring in association with them.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Here we present a novel objective identification approach for the features listed above, based on a probabilistic random forest using each feature&amp;amp;#8217;s most important characteristics in wind, rainfall, pressure and temperature evolution. However, as CJ and SJ turn out to be difficult to distinguish in surface observations alone, we decided to consider the two features together. This identification can then be used to generate a climatology for Central Europe, to analyse forecast errors specific to individual features, and to ultimately improve forecasts of high wind events through feature-dependent statistical post-processing. To achieve this, we strive to identify the features in irregularly spaced surface observations and in gridded analyses and forecasts in a consistent way, thus making it independent of spatial dependencies and gradients.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;To train the probabilistic random forest, we subjectively identify the four storm features in twelve winter storm cases between 2015 and 2020 in both hourly surface observations and high-resolution reanalyses of the German COSMO model over Europe, using an interactive data analysis and visualisation tool. Results show that mean sea-level pressure (tendency), potential temperature, precipitation amount and wind direction are most important for the distinction between the features. From the random forest we get occurrence probabilities for each feature at every station, which can be converted into areal information using Kriging.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The results show a satisfactory identification for all features, especially for WJ and CFC. We encounter, however, some difficulties to clearly distinguish the CJ and CS, which are dynamically similar. A climatology is currently being compiled for both surface observations and the reanalyses over a period of around 20 years using the trained probabilistic random forests and further for high-resolution COSMO ensemble forecasts, for which we want to analyse forecast errors and develop feature-dependent postprocessing procedures.&amp;lt;/p&amp;gt;

&amp;lt;p&amp;gt;Prediction of numerical weather prediction and climate models are the basis for informed decision making and increased resilience to hydrometeorological extremes in many of today&amp;amp;#8217;s resource management challenges e.g. in the agricultural sector. Coupled multi-compartment models are capable of reproducing interactions and feedbacks in the geosystem, and have thereby demonstrated versatile tools in a variety of applications. The Terrestrial Systems Modelling Platform (TSMP, https://www.terrsysmp.org) is an integrated regional Earth system model that simulates processes from groundwater across the land surface to the top of the atmosphere on multiple spatio-temporal scales. TSMP consists of the atmospheric model COSMO (Consortium for Small-scale Modeling), the CLM (Community Land Model), and the ParFlow hydrologic model, coupled through OASIS3-MCT. This work presents an evaluation of daily deterministic 10-day forecasts of the atmospheric, surface, and groundwater states and fluxes for a heterogeneous mid mountain-ranges area in the German and Belgium Eifel-Ardennes region in Central Europe from TSMP in a monitoring setup. TSMP runs at convection-permitting resolution of 1km (atmosphere) and 0.5km (sub- and land surface) over an area of 150km x 150km, driven by ECMWF HRES forecasts through a one-way double nest. Data from the densely instrumented Eifel/Lower Rhine Valley observational network of Terrestrial Environmental Observatories (TERENO, https://www.tereno.net) is used for evaluation of the TSMP simulations. TSMP forecasts from July 2019 to July 2021 covering an agricultural and hydrological drought and the transition back to the climatological mean state are analyzed in detail. Despite the complex terrain and the free running TSMP, meteorological and hydrological station data are generally well represented while a certain overestimation of daily precipitation is observed.&amp;lt;/p&amp;gt;

&amp;lt;p&amp;gt;In many of today&amp;amp;#8217;s resource management and climate change adaptation challenges, versatile and&amp;amp;#160; reliable numerical model simulations are the basis for informed decision making. The integration of multiple compartmental&amp;amp;#160; models into simulation platforms allows us to reproduce interacting geosystem processes and thereby solve a wide range of problems in a variety of applications. The Terrestrial System Modelling Platform (TSMP, https://www.terrsysmp.org) is an integrated regional Earth system model that simulates processes from the groundwater across the land surface to the top of the atmosphere on multiple spatio-temporal scales. TSMP consists of the COSMO (Consortium for Small-scale Modeling) atmospheric model, the CLM (Community Land Model), and the hydrologic model ParFlo, coupled through OASIS3-MCT. TSMP is used in various studies from climate change simulations to near-real time forecasting and monitoring. Here we present the results of the evaluation of the TSMP in a monitoring setup, providing daily forecasts with a lead time of 10days of the atmospheric, surface, and groundwater states and fluxes for a heterogeneous mid mountain-ranges area in Western Germany. The model domain covers an area of 150km x 150km at 1km (atmosphere) and 0.5km (land surface and subsurface) resolution. The simulated data is compared with observations from the TERENO (Terrestrial Environmental Observatories, https://www.tereno.net) Eifel/Lower Rhine Valley network. This TERENO observatory comprises a total area of 2354 km&amp;amp;#178; and provides data from a very dense measurement network of 12 climate stations, 6 eddy covariance stations, 6 lysimeter stations, and 13 cosmic-ray neutron stations. To assess the quality and suitability of the TSMP as a monitoring system of the geosystem&amp;amp;#8217;s state and evolution with agricultural applications in mind,&amp;amp;#160; forecasts from July 2019 to October 2020 are analyzed with reference to the observations. Results show that the TSMP can well represent the main subsurface hydrological and relevant meteorological features.&amp;lt;/p&amp;gt;

During 2–3 December 2012, the Black Sea and east coast of Romania were affected by a rapidly deepening Mediterranean cyclone. The cyclone developed a bent-back front along which short-lived (2–4 h) strong winds up to 38 m s−1 were recorded equatorward of the cyclone center. A mesoscale model simulation was used to analyze the evolution of the wind field, to investigate the physical processes that were responsible for the strong winds and their acceleration, and to investigate the relative importance of the stability of the boundary layer to those strong winds. The origin of the air in the wind maximum equatorward of the cyclone center was twofold. The first was associated with a sting jet, a descending airstream from the midlevels of the cloud head and the lower part of the cyclonic branch of the warm conveyor belt. The sting jet started to descend west of the cyclone center, ending at the frontolytic tip of the bent-back front. The second was a low-level airstream associated with the cold conveyor belt that originated northeast of the cyclone center and traveled below 900 hPa along the cold side of the bent-back front, ending behind the cold front. Both airstreams were accelerated by the along-flow pressure gradient force, with the largest accelerations acting on the sting-jet air before entering into the near-surface strong-wind area. The sensible heat fluxes destabilized the boundary layer to near-neutral conditions south of the cyclone center, facilitating downward mixing and allowing the descending air to reach the surface. Mesoscale instabilities appeared to be unimportant in the sting-jet formation.

Extra-tropical windstorms are one of the costliest natural hazards affecting Europe, and windstorms that develop a sting jet are extremely damaging. A sting jet is a mesoscale core of very high wind speeds that occurs in Shapiro–Keyser type cyclones, and high-resolution models are required to adequately model sting jets. Here, we develop a low-cost methodology to automatically detect sting jets, using the characteristic warm seclusion of Shapiro–Keyser cyclones and the slantwise descent of high wind speeds, within pan-European 2.2 km convection-permitting climate model (CPM) simulations. The representation of wind gusts is improved with respect to ERA-Interim reanalysis data compared to observations; this is linked to better representation of cold conveyor belts and sting jets in the CPM. Our analysis indicates that Shapiro–Keyser cyclones, and those that develop sting jets, are the most damaging windstorms in present and future climates. The frequency of extreme windstorms is projected to increase by 2100 and a large contribution comes from sting jet storms. Furthermore, extreme wind speeds and their future changes are underestimated in the global climate model (GCM) compared to the CPM. We conclude that the CPM adds value in the representation of extreme winds and surface wind gusts and can provide improved input for impact models compared to coarser resolution models.

Abstract. Anthropogenic aerosol particles remain a significant air quality concern in central Europe, particularly during winter months. This study employs the chemistry transport model COSMO–MUSCAT (COnsortium for Small scale MOdelling coupled with the MUltiScale Chemistry Aerosol Transport) to investigate particulate matter sources, with a focus on emissions from residential heating. The model results are compared with winter measurements from one site in Germany and two sites in the Czech Republic, where solid fuels are commonly used for heating. A non-reactive tagging method tracking primary organic matter (OM) reveals a high contribution from residential heating. Although the magnitude and temporal changes of the model results mostly agree with total OM values at two measuring stations, it appears to underestimate measurements at a site in the central Czech Republic. This underestimation is partly attributed to the inadequate representation of secondary organic aerosol (SOA) emitted from wood combustion. The study highlights the impact of anthropogenic volatile organic compounds (AVOCs) on SOA formation, which are currently underrepresented in air quality models. Sensitivity tests adjusting SOA yields and AVOC emissions increase OM concentrations by up to 40 % at the measurement sites. These findings emphasise the need for accurate parameterisation of AVOC-derived SOA formation and residential heating emissions to better tackle wintertime air quality challenges in central Europe.

The relationship between springtime mid-latitude cyclones and background ozone (O3) is explored using a combination of observational and reanalysis data sets. First, the relationship between surface O3 observations at two rural monitoring sites on the west coast of Europe - Mace Head, Ireland and Monte Velho, Portugal - and cyclone track frequency in the surrounding regions is examined. Second, detailed case study examination of four individual mid-latitude cyclones and the influence of the associated frontal passage on surface O3 is performed. Cyclone tracks have a greater influence on the O3 measurements at the more northern coastal European station, Mace Head, located within the main North Atlantic (NA) storm track. In particular, when cyclones track north of 53° N, there is a significant relationship with high levels of surface O3 (> 75th percentile). The further away a cyclone is from the NA storm track, the more likely it will be associated with both high and low (< 25th percentile) levels of O3 at the observation site during the cyclone's life cycle. The results of the four case studies demonstrate a) the importance of the passage of a cyclone's cold front in relation to surface O3 measurements, b) the ability of mid-latitude cyclones to bring down high levels of O3 from the stratosphere and c) that accompanying surface high pressure systems and their associated transport pathways play an important role in the temporal variability of surface O3. The main source of high O3 to these two sites in springtime is from the stratosphere, either from direct injection into the cyclone or associated with aged airstreams from decaying downstream cyclones that can become entrained and descend toward the surface within new cyclones over the NA region.

AimTo understand the role and significance of the reindeer, Rangifer tarandus (Linnaeus, 1758), as a specific indicator in terms of late Quaternary biogeography and to determine the effects of global climate change on its range and local extinction dynamics at the end of the Ice Age.LocationLate Pleistocene/early Holocene range of reindeer over all of central and western Europe, including southern Scandinavia and northern Iberia, but excluding Russia, Belarus and the Ukraine.MethodsRadiocarbon‐dated subfossil records of R. tarandus from both archaeological and natural deposits younger than 25,000 years were assembled in a database. The distribution area was divided into six representative regions. The 14C dates were calibrated and plotted chronologically in maps in order to compare presence and absence and regional extinction patterns from one region to another.ResultsAfter the Last Glacial Maximum, R. tarandus disappeared from south‐eastern Central Europe but survived in the south‐west until the Younger Dryas period. The ‘Allerød warming’ did not result in complete extirpation of reindeer in Central Europe. Reindeer probably disappeared c. 11,250 years ago in the North European Plain and c. 11,000 years ago in the British Isles. In southern Scandinavia the species survived until c. 10,300 years ago.Main conclusionsThe late Quaternary record for reindeer in Europe during the last 25 kyr shows a climate‐driven dispersal and retreat in response to climate change, with regional variations. The collapse of the mammoth steppe biome did not lead to the local extinction in Europe, as in the case of other megafaunal species. Rangifer tarandus co‐existed for about 3000 years during the Late Glacial and early Holocene with typical temperate species such as red deer and roe deer in non‐analogue faunal communities. The regional extinction at the end of the Pleistocene coincides with the transition from light open birch/pine forests to pine/deciduous forests.

VIRVELINĖS KERAMIKOS KULTŪRA LIETUVOJE 2800–2400 cal BC

For the period of 1990 to 2000, atmospheric particulate mass concentrations have decreased in Central Europe. Simultaneously, the amount of shortwave radiation reaching the ground increased during clear sky conditions. The aerosol indirect effect has not been seen as clearly, as the radiation reaching the ground during overcast conditions has not increased as much as might be expected. Here we show that this may be caused by the condensation kinetics of water during cloud droplet formation. The decrease in the particulate mass led to a clear decrease in the number concentration of cloud condensation nuclei (CCN). However, in urban areas a relatively larger decrease in the number of particles in the upper end of the accumulation mode has led to slower condensation of water. As a result, a higher maximum supersaturation is reached during the cloud droplet formation. This compensates for the effect of decreased CCN concentrations. For example in Erfurt between 1991 and 1996, the aerosol properties changed so that aerosol optical depth decreased by 58% and CCN concentration decreased by 25 to 50%. These led to a 4 to 12% reduction in cloud droplet number concentration (CDNC) and less than a 2 Wm−2 increase in shortwave radiation during overcast conditions. These results demonstrate that locally the aerosol direct effect can be much larger than the aerosol indirect effect. Furthermore, even though AOD appears to be a valid proxy for CCN, the correlation between AOD and CDNC is not straightforward and thus AOD cannot be used as a proxy for CDNC.

By means of modern archeological research it is today possible to gain much information even from non-written material, This paper covers the late bronze age and early iron age, ca. 1000 B.C. —O. It is based on material from Denmark, the Southwest of Sweden, and the Southeast of Norway. This region formed a cultural unity since the sea bound the area together. Our main sources of knowledge of Nordic religion during this time span are votive offerings and rock-carvings. During the bronze age and early iron age the Nordic peasant population had intensive contacts with the Southeastern and Centralparts of Europe. A great quantity of imported objects bear evidence of widespread connections. The inhabitants of the Nordic area not only brought home objects, but also ideas and religious conceptions. This is clearly reflected in the iconography. The cultures with which connections were upheld and from which ideas were introduced were those of Hallstatt and La Tène. They were both Celtic iron age cultures prospering in Central Europe at the same time as the late bronze age and early iron age in the Nordic area. This means that the new symbols in the Nordic area come from a Celtic environment. Consequently, Celtic religion such as it may be found in the pre-Roman period, can clarify the meaning of the conceptions, linked with these symbols.

Effects of liming and fertilization on growth, soil chemistry and soil water chemistry in a Norway spruce plantation on a nutrient-poor soil in Denmark

The frontal structure and occlusion process in a cyclone of moderate intensity that affected the central United States in January 1995 is examined. The deep warm-frontal zone associated with this cyclone had a lateral extension to the southwest of the sea level pressure minimum that, although characterized by cold-air advection near the surface, had many of the characteristics of a warm front aloft. In fact, this feature had a structure similar to the so-called bent-back fronts previously documented only in association with explosively deepening maritime cyclones. The development of a warm-occluded structure was investigated with the aid of a numerical simulation of the event performed using the University of Wisconsin–Nonhydrostatic Modeling System. The development of the warm-occluded structure was asynchronous in the vertical; occurring first at midtropospheric levels and later near the surface, in contrast to the classical occlusion process. Near the surface, the warm-occluded front was formed as the warm front was overtaken by the frontogenetically inactive portion of the historical cold-frontal zone. At midtropospheric levels, the warm occluded structure formed as a result of the cold-frontal zone approaching, and subsequently ascending, the warm-frontal zone in accord with a component of the classical occlusion mechanism. The observed asynchronous evolution of the occluded structure is proposed to result from the vertical variation in vortex strength associated with the upper-level potential vorticity (PV) anomaly that controls the cyclogenesis. It is suggested that the occlusion process begins aloft, where the associated vortex strength is greatest, and gradually penetrates downward toward the surface during the cyclone life cycle. Additionally, a characteristic“treble clef” shape to the upper-level PV anomaly is shown to be a sufficient condition for asserting the presence of a warm-occluded structure in the underlying troposphere.

This study reviews the development of the omega equation and the relation between omega and potential vorticity (PV) advection and considers the application of PV theory to investigate the impact of large‐scale mountains on downstream weather development. A diabatic quasi‐geostrophic omega equation is introduced to reveal the feedback of diabatic heating (Q) on PV advection and vertical velocity. A challenge therein concerning the use of the diagnostic omega equation to interpret weather system development is considered from the PV‐Q perspective based on a severe weather event that occurred downstream of the Tibetan Plateau (TP) on 17–21 January 2008. Results demonstrate that owing to PV restructuring, positive PV was generated over the eastern flank of the TP, and its eastward advection triggered development of isentropic displacement vertical velocity and cyclogenesis in the lower troposphere. A converging southeasterly wind accompanied with ascending isentropic gliding vertical velocity in the lower troposphere was induced to the east of the cyclone center, which transported not only warm moist air but also negative PV from the south, contributing to developments of both local diabatic ascent and precipitation and eastward migration of the cyclone. During the cyclone life cycle, three omega components induced by different processes interacted with each other, and diabatic heating associated with precipitation exerted considerable feedback to vertical motion as well as PV advection. It is the vertical differential PV advection and feedback from diabatic heating that control the evolution of the circulation and the associated precipitation downstream of the TP.