The World Climate Research Programme identifies critical gaps in understanding and modeling orographic precipitation. This includes characterizing pre-convective environmental conditions and understanding how they lead to precipitation onset. To address these knowledge gaps, we introduce a field campaign initiative supported by the IDEA-S4S network under the GPEX working group. As part of the TEAMx summer extensive observation period, two identical measurement sites equipped with one scanning microwave radiometer (MWR), one micro rain radar, and one disdrometer were deployed along an altitudinal transect in the Alps at approximately 1200 m and 2100 m a.s.l. on the slope of Corno del Renon, Bolzano, Italy. These two sites are embedded within a broader ground-based remote sensing network surrounding the mountain, facilitating monitoring of valley and mountain flows at larger scales. Additionally, a third MWR was installed at the KITcube supersite on the valley floor at 250 m a.s.l..
Building on these measurements, we present insights from multisensor analysis of convective events observed between May and September 2025. Specifically, we investigate boundary-layer conditions for convective initiation, focusing on water vapor variability and its temporal evolution across sites, as well as precipitation variability across space and elevation. In parallel, we apply a self-supervised learning (SSL) framework to long-term geostationary satellite data to characterize convective cloud structures and their transitions, estimate growth rates of key cloud variables, and relate these findings to observed climatology. By leveraging the synergy of the campaign's multisensor observations, we advance our understanding of orographic convective processes, thereby addressing the critical gaps initially highlighted.
How to cite: Acquistapace, C., Corradini, D., Oertel, A., Cattani, E., Pospichal, B., and Marke, T.: Insights into convection over the Alps exploiting multisensor multiplatform observations and deep learning methods, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-206, https://doi.org/10.5194/ems2026-206, 2026.
The Inn Valley in the European Alps frequently exhibits thermally driven along-valley flows under clear, high-pressure conditions. During nighttime, a pronounced down-valley jet can develop near the valley exit and extend into the Bavarian foreland, commonly referred to as the Inn Valley exit jet. While its occurrence has been documented in previous studies, detailed observations of its structure, variability, and governing dynamics remain limited.
During the summer 2025 Intensive Observation Period of the TEAMx field program, three exit-jet events were captured using a coordinated multi-platform observational strategy. Measurements included a network of five automatic weather stations, a Doppler wind lidar, repeated radiosonde launches, and observations from meteorological drones. This combination of platforms provides a comprehensive view of both the temporal evolution and vertical structure of the flow across the valley exit region and into the adjacent foreland.
The exit-jet events were identified and analyzed with respect to their onset characteristics, synoptic forcing, and spatial and temporal extent. The events exhibit substantial variability, particularly in the timing and intensity of near-surface wind acceleration. Exit jet wind speed maxima ranged between 13 and 17 m s⁻¹ at heights between 150 and 200 m above ground. Despite this variability, all events share a consistent nocturnal intensification and a coherent low-level jet structure in the valley exit region.
Turbulence characteristics were examined using bulk estimates of the gradient Richardson number and Froude number, providing constraints on flow stability and dynamical regime. Across the observed cases, the diagnosed flow conditions indicate the absence of a supercritical flow regime. This finding is robust across events despite their variability in intensity and spatial extent.
These observations provide new insights on the dynamics of valley-exit flows and highlight the importance of coordinated multi-platform measurements for capturing their temporal and vertical structure. The results offer a valuable benchmark for evaluating high-resolution numerical simulations and improving the representation of thermally driven flows in complex terrain.
How to cite: De Wekker, S. F. J., Kossmann, M., Sedlmeier, K., and Kalthoff, N.: Multi-platform Observations of Nocturnal Exit-Jet Events in the Inn Valley Exit Area: Insights from the TEAMx Summer 2025 Campaign, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-505, https://doi.org/10.5194/ems2026-505, 2026.
The surface energy balance (SEB) is a fundamental physical framework describing the distribution
of energy between the Earth’s surface and the lowest layer of the atmosphere. Its
understanding is essential not only for characterizing meteorological and climatological conditions
within the atmospheric boundary layer, but also for a wide range of applications, including
weather and climate modeling, agricultural and forest management, air quality studies, ecosystem
carbon budgeting, and biological processes. All these applications inherently rely on the
assumption of a closed energy balance. However, even under flat and horizontally homogeneous
conditions, closure of the SEB is rarely achieved.
For an idealized, massless surface layer, the SEB is expressed as the balance between net radiation
and the sum of sensible heat, latent heat, and ground heat fluxes (Rn = H + LE + G).
Previous studies attribute the persistent lack of closure either to measurement uncertainties or
to neglected processes. In practice, fluxes are not measured exactly at the surface interface but
at some distance above (for Rn, H, and LE) or below the ground (for G), implying that they
are representative of a volume rather than a surface. Accordingly, the storage of heat in the air
volume below the measurement height and the heat storage in the soil layer above the heat flux
plate have been identified as contributors to the SEB residual. More recently, non-turbulent
advective fluxes associated with surface heterogeneity have been recognized as a major driver
of SEB non-closure.
In this study, we investigate the role of additional three-dimensional terms (heat storage, vertical
advection, and horizontal advection) in the SEB using observational data from selected
complex terrain sites in the Inn Valley (Austria), including measurements collected during the
TEAMx Extended Observation Periods (EOPs). The magnitude of these fluxes is quantified
to assess their relative importance within the SEB. Furthermore, the SEB residual is evaluated
by incorporating all available terms and characterized under different environmental and
atmospheric conditions.
How to cite: Destro, M., Rotach, M. W., and Lehner, M.: Surface Energy Balance in Complex Terrain: Accountingfor Three-Dimensional Fluxes, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-806, https://doi.org/10.5194/ems2026-806, 2026.
Forecasting in mountainous regions is particularly challenging due to the influence of their complex topography and the associated weather events that occur on different temporal and spatial scales. Interactions within the Mountainous Boundary Layer (MoBL) are governed by a variety of thermodynamic and dynamic processes. High-resolution models offer the ability to investigate how these complex atmospheric circulations evolve and how they impact the weather situation in complex terrain. However, a fundamental question pertains to whether current NWP models do adequately represent small-scale thermally driven circulations, given that the underlying turbulence parametrizations were not developed with such high-resolution applications in mind.
Cold air pools are a common occurrence in complex orographic terrain, where cold air accumulates in the valleys and causes a temperature inversion. The PIANO (Penetration and Interruption of Alpine Föhn) campaign examined how Föhn events erode cold air pools in the Innsbruck region of Austria in autumn and early winter of 2017. This case study focuses on the night between 15 and 16 October 2017, when the combination of a clear sky, weak south-westerly synoptic flow and the absence of a Föhn interruption favored the development of a persistent cold air pool in the Inn Valley.
We investigate how the representation of this event is affected by model resolution and refined initial conditions. For this purpose, we compare three experiments with different initial and boundary conditions: the IFS forecast, ICON-DREAM, our global reanalysis, and ICON-FORCE, our regional reanalysis. All of the experiments use a one-way nesting approach, beginning with the operational ICON-D2 domain, which has a horizontal grid spacing of 2 km and covers the entire Alpine region. Within this domain, three nests are configured with horizontal grid spacings of 1 km, 0.5 km, and 0.25 km. We find that all simulations consistently benefit from increased resolution, and that a grid spacing of 0.25 km already yields a reasonably well-represented cold air pool and intermittent jet. As expected, ICON-FORCE produces the closest agreement with the observations. However, the differences in boundary conditions are smaller than those resulting from changes to the horizontal grid spacing. Finally, the ICON model in its NWP configuration is able to capture the dynamics of the cold air pool when initial conditions are refined and the simulation is conducted at sub-kilometre resolution.
How to cite: Littmann, D.-C., de Lozar, A., Marsigli, C., Zängl, G., and Schlemmer, L.: The Study of Thermally Driven Circulations during the Formation of a Cold Air Pool in the Inn Valley using High-resolution Modelling, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-389, https://doi.org/10.5194/ems2026-389, 2026.
The development of summertime convection is sensitive to mesoscale atmospheric conditions, which, in particular in complex terrain, are not well captured by conventional observation systems. Here, we investigate whether the assimilation of substantial additional observations of lower-tropospheric thermodynamic and dynamic variables at high resolution has the potential to improve the resulting analysis used for forecast initialization, and ultimately the predictability of convective events.
The high-resolution observations used here have been obtained during the ‘Swabian MOSES 2023’ campaign, conducted in June, July and August 2023 in the southwest German mountain ranges, a region that is particularly prone to hailstorms. A key component was an unprecedented network of 12 Doppler wind lidars (DWL), a configuration never used before in data assimilation experiments. We adopted the regional forecasting system of Deutscher Wetterdienst, the ICON model at 2 km resolution (ICON-D2) coupled to the Kilometer Scale Ensemble Data Assimilation system (KENDA) based on the Local Ensemble Transform Kalman Filter (LETKF) with an hourly assimilation step to produce a campaign and a control reanalysis. The campaign reanalysis uses, in addition to all operationally available observations used in the control reanalysis, (i) DWL-retrieved vertical profiles of the horizontal wind components, (ii) X-band radar reflectivity, (iii) targeted radiosoundings from two sites during intensive observation periods, (iv) ground-based zenith path-delay data from a domain-wide Global Navigation Satellite Systems receiver network, and (v) 2m-temperature and relative humidity from meteorological masts at the campaign sites.
We show that the additional campaign observations have a substantial influence on the reanalysis. We focus specifically on the mesoscale flow in the Black Forest region where the dense wind lidar observations lead to systematic differences in wind speed and direction between the campaign and the reference analysis. We discuss possible sources of these differences by further stratifying the analysis increments by time of day, different flow regimes, and stability. Furthermore, we investigate the impact of additionally assimilated observations on reforecasts by comparing forecasts initialized from the campaign and control reanalysis. Our results motivate future reanalyses projects, such as a high-resolution reanalysis for the ‘Multi-scale transport and exchange processes in the atmosphere over mountains – programme and experiment’ (TEAMx) summer extensive observation period.
How to cite: Thomas, J., Reich, H., Steinert, T., Geppert, G., Stephan, K., Gasch, P., Carrassi, N. A., Keller, J., Knippertz, P., and Oertel, A.: Assimilating Doppler wind lidar observations from the ‘Swabian MOSES 2023’ campaign reveals wind biases in the ICON-D2 model, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-606, https://doi.org/10.5194/ems2026-606, 2026.
Large-eddy simulations (LES) have become one of the most important tools to study boundary layer turbulence due to the increase in computing power in recent years. Research including LES spans from idealized simulations of flow over horizontally homogeneous and flat terrain to realistic hindcasts nested in mesoscale simulations. Due to the wide range of potential applications of LES models, many different LES codes were developed. Differences between these codes include the spatial and temporal discretization, the dynamical cores, the sub-filter-scale turbulence models, and the representation of terrain. Benchmark studies comparing the outcomes of LES from different models have been performed for a variety of scenarios and weather regimes (stable boundary layer, very stable arctic boundary layer, stratocumulus, idealized convective boundary layer flows exist for flat terrain), but no such study exists for complex-terrain flows yet.
The Terrain-Flow Atmospheric Boundary Layer Large-Eddy Simulation (TABLES) Model Intercomparison Study was designed to fill this research gap and provide a benchmark for convective boundary layer flows above idealized bell-shaped hills. In this simple scenario, baroclinicity due to differential heating along sloping surfaces generates a thermally-driven circulation that exerts a profound impact on the spatial heterogeneity of turbulence in the boundary layer. The project consists of 12 research groups bringing 12 different LES codes. While all models use the same initial and boundary conditions, the models differ in the dynamical core and spatial discretization, as well as in the implementation of terrain, sub-filter-scale model and surface model. Each research group was asked to provide simulations of free convection and forced convection, both over flat terrain and over a 100-m-high ridge. In addition, research groups working with compressible models provided also one free convection and one forced convection simulation over a 1000-m-high ridge.
Preliminary analysis suggests that mean variables and turbulence statistics from the flat simulations agree remarkably well between the different models. Also, general flow structures of convective boundary layer flows above idealized ridges agree well, but differences in both the strength of these flow structures and their location across the ridge are more pronounced for terrain-induced flow cases.
How to cite: Rauchöcker, A., Serafin, S., and Stiperski, I. and the TABLES team: Introducing TABLES: First insights from the Terrain-induced Atmospheric Boundary-Layer flow: Large-Eddy Simulation model intercomparison study, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-354, https://doi.org/10.5194/ems2026-354, 2026.
Incoming surface radiation in mountainous terrain is strongly modulated by topography. Direct shortwave radiation can be blocked by shadow casting from surrounding terrain and depends on local slope and aspect. Diffuse shortwave and longwave radiation are also affected by terrain, although typically to a lesser extent. These terrain-induced effects on surface radiation influence surface energy balance components such as ground temperature and snow cover, as well as near-surface atmospheric variables including 2 m air temperature and humidity. Through land–atmosphere interactions, such impacts can propagate vertically and affect boundary-layer processes, valley wind systems, and convection.
In atmospheric models such as ICON, topographic influences on surface radiation are not explicitly resolved. The radiative transfer scheme operates in the vertical direction only and assumes horizontally aligned grid cells, thereby neglecting the influence of local and surrounding terrain on radiation. To address these limitations, ICON includes a parameterisation that accounts for terrain effects on direct shortwave radiation on the model grid scale.
At MeteoSwiss, ICON is operated for numerical weather prediction at horizontal resolutions of 1–2 km. At these scales, fine-scale topographic features present in the high-resolution input dataset, available at 30 m, are substantially smoothed and thus not considered in the grid-scale topography-surface radiation parameterisation. To capture these unresolved effects, we implemented a subgrid-scale extension of the topography–radiation parameterisation in ICON. The required static input fields are derived using a high-performance ray-tracing algorithm. The new parameterisation is verified against station observations of global radiation, sunshine duration, and 2 m air temperature. Results show clear improvements, particularly in mountainous valleys and during winter months when solar elevation angles are low. In addition, a comparison of simulated snow cover with a satellite-derived product also reveals improved performance on seasonal timescales.
How to cite: Steger, C. R., Leutwyler, D., Arpagaus, M., and Schär, C.: A Subgrid Topography–Surface Radiation Parameterisation in ICON for NWP, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-728, https://doi.org/10.5194/ems2026-728, 2026.
Surface roughness is a key control on turbulent exchange over glaciers, yet it is still commonly treated as a constant or tuning parameter in surface energy balance models. This simplification stands in contrast to the strong spatial heterogeneity and temporal evolution of glacier surfaces, particularly during the ablation season. A better understanding of how roughness varies, and how this variability translates into aerodynamic properties, is therefore essential for improving representations of surface–atmosphere exchange in mountainous terrain.
Here, we investigate glacier surface roughness using a combination of turbulence measurements from eddy covariance systems and high-resolution digital elevation models (DEMs) derived from close-range photogrammetry, acquired during recent field campaigns on Silvrettagletscher and Hintereisferner. Turbulence data are filtered to retain periods that approximately satisfy the assumptions required for applying the bulk aerodynamic method, allowing for consistent estimates of aerodynamic roughness length. In parallel, roughness length is derived from the DEMs using a microtopographic approach based on the Lettau formulation, explicitly accounting for the orientation of surface elements relative to the flow.
Both turbulence-based estimates and microtopographic analysis consistently show that roughness length depends on wind direction. In particular, lower roughness lengths are found for along-glacier (katabatic) flow compared to cross-glacier flow. This behaviour is present on both glaciers, reflecting the anisotropic structure of the glacier surface with roughness elements that tend to be aligned with the flow direction at larger scales. As a result, the effective aerodynamic roughness experienced by the flow varies with wind direction relative to the glacier flowline, and cannot be represented by a single, direction-independent parameter. In addition, a clear temporal evolution is observed over the ablation season: Roughness sharply decreases during the transition from snow-covered to ice surfaces, followed by a progressive increase as melt features such as channels and cavities develop and organize the surface.
These results show that glacier surface roughness is highly variable in space, time, and direction. This variability has direct implications for the parametrization of turbulent fluxes and suggests that commonly used approaches based on a single roughness length may be insufficient to capture the complexity of glacier–atmosphere interactions.
How to cite: Asemann, P., Cheda, A., Sesselmann, M., Dadic, R., Lehning, M., and Mott, R.: Glacier surface roughness from turbulence and microtopographic observations, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-686, https://doi.org/10.5194/ems2026-686, 2026.
Topography and cold frontal passages are key factors influencing the formation and dissipation of air pollution in east-central China. Elucidating their synergistic mechanisms is of great significance for regional air pollution prevention and control. Using multi-source data, this study analyzed the evolutionary characteristics of a regional PM₂.₅ heavy pollution event during December 16–21, 2025, in east-central China, and revealed the physical mechanisms by which the coupling of post-cold-frontal subsidence and topographic forcing drove the formation and intensification of this heavy pollution event. The results indicate that this event was characterized by a wide effect range and long duration, with heavy pollution occurring in all cities of Anhui Province and its surrounding provinces, displaying a spatial distribution of heavier pollution in the west and lighter pollution in the east. The cumulative heavy pollution duration in central and western Anhui cities generally exceeded 30 hours, with a maximum of 44 hours. Most cities experienced two explosive increases in PM₂.₅ concentrations. The formation and dissipation mechanisms can be attributed to three factors: (1) Regional transport provided the background for pollution accumulation; (2) Large-scale subsidence following two cold frontal passages directly drove the two explosive increases in surface PM₂.₅ concentrations; (3) Topographic effects enhanced the convergence and accumulation of particles on the windward side of mountains, and by altering the spatial distribution of vertical motions, aggravated pollution on the northern and western sides of the Dabie Mountains, the mountainous areas of southern Anhui, and other hilly terrains.
The findings of this study contribute to improving the forecasting and early warning capabilities for heavy pollution events in east-central China. Operationally, forecasters should pay close attention to the variations in upstream PM₂.₅ concentrations and the evolution of the continental high-pressure system, which governs shifts in wind direction and pollutant transport pathways. Notably, heavy pollution episodes tend to occur in the post-cold-frontal phase, under the control of the continental high pressure.
How to cite: Shi, C.: Formation and Dissipation Mechanisms of a Heavy Pollution Event in east-central China under the Combined Influence of Topography and Cold Fronts, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-90, https://doi.org/10.5194/ems2026-90, 2026.
Precipitation is a key factor in High Mountain Asia’s hydrological cycle. It
remains elusive due to a significant lack of observational data at high altitude,
and the spatial heterogeneity of the extreme topography, which requires a model resolution
much finer than most gridded precipitation products provide. In this study we
use glacier mass balance to infer high-altitude precipitation patterns and assess
the biases of commonly used gridded precipitation products. We use a satellite-
derived glacier mass balance dataset of all individual glaciers with an area >
2km2, and temperature fields from downscaled ERA5 gridded reanalysis data.
These data were bias-corrected, and used to estimate five-year average melt rates
per glacier using a simple melt model. The melt was then added to the glacier
mass balance to infer the average 20-year precipitation over the glacier surface.
We show that there is much more precipitation falling at high altitude than
current precipitation products suggest, in line with previous studies performed
on a smaller scale in the Hunza Basin in Pakistan and the Upper Indus Basin.
We also show that there are clear spatial patterns in the estimated precipitation
bias. We hypothesize that these patterns can be explained by specific weather
patterns (e.g., the Indian Summer Monsoon and westerly disturbances). The
precipitation biases found using our approach confirm that our understanding
of high-altitude precipitation is far from complete, while it is one of the key
drivers of the mountain water cycle. Future studies could use this data to
further untangle the precipitation processes occurring at high altitude and the
complex interplay between atmosphere and topography. We hypothesize that
to fully understand the spatial and temporal variability of precipitation in this
region, atmospheric model simulations at a very high resolution (< 1 km2) are
required.
How to cite: van den Acker, R., Kraaijenbrink, P., Wijngaard, R., and Immerzeel, W.: Glacier Mass Balance as a Precipitation Proxy for High Mountain Asia, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-76, https://doi.org/10.5194/ems2026-76, 2026.
The summer rainfall over the southeastern Tibetan Plateau (SETP) is crucial to the hydrological cycle of both the SETP and nearby regions. However, it remains unclear why the rainfall over the SETP mostly occurs at night due to limited observations. This study aims to investigate the role of thermally driven winds in diurnal rainfall during summer (June–August) over the SETP, using high-resolution reanalysis data and surface rain-gauge observations. The results show that the strong upward motions and low-level upslope winds of the thermally forced mountain-valley wind systems (MVWS) between the SETP and the lowlands (Sichuan Basin and Yunnan–Guizhou Plateau) help to trigger the precipitation and transport moisture in the afternoon. After sunset, thermally forced circulations, including the east–west continental-scale thermal circulation between the Asian continent and its adjacent ocean, the north–south large-scale MVWS between the Yunnan–Guizhou Plateau and its southern plain, and the north–south small-scale MVWS between the SETP and its southern slope, help maintain horizontal winds from the rainy lowlands, transporting abundant moisture to facilitate the rainfall over the SETP at night. Furthermore, the diurnal cycle of gauge precipitation over the southeastern Tibetan Plateau varies markedly among stations because of small-scale topographic forcing. This variability is closely linked to local mountain–valley wind systems in north–south-oriented valleys, which suppress daytime rainfall but maintain intense nocturnal rainfall with a peak around sunset. Vertical profile observations show that daytime rainfall is inhibited by compensating subsidence induced by upslope winds perpendicular to the valley axis, despite warm, moist advection by deep up-valley winds. In contrast, nighttime downslope winds favor deep ascent and enhanced rainfall, accompanied by higher water vapor, lower lifting condensation level, and greater convective available potential energy within the valley.
How to cite: Wang, J.: Impact of Thermally Forced Circulations on the Diurnal Cycle of Summer Precipitation Over the Southeastern Tibetan Plateau, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-119, https://doi.org/10.5194/ems2026-119, 2026.
Radiative convective equilibrium (RCE) critically constrains tropical climates but its applicability to elevated terrains like the Tibetan Plateau (TP) remains unknown. Based on 23 years (2001-2023) of multiple observational datasets, our study provides the first comprehensive observational assessment of RCE applicability over the TP. We find that the TP exhibits a pronounced annual-mean energy imbalance of -15.9 W/m² and this state is characterized by strong seasonal asymmetry. Summers show intense positive energy imbalance of +56.0 W/m² that is driven by latent heating from precipitation while winters show extreme radiative cooling of -71.8 W/m². Transitional months including April and September alone achieve transient energy balance across the entire plateau region. The TP manifests four energy imbalance regimes that are categorized by specific precipitation intensity and radiative cooling thresholds. These regimes transition seasonally with Strong Precipitation-Weak Cooling dominating the summer monsoonal regions of the TP and Weak Precipitation-Strong Cooling prevailing in the winter and autumn periods of the plateau. Daily near-RCE conditions occur transiently with only 5–10% frequency across all spatiotemporal scales and this feature contrasts sharply with tropical regions where equilibrium naturally emerges through spatial aggregation. Analysis of extreme events reveals that intense latent heating drives positive imbalance during summer heating events and this imbalance is compensated primarily by enhanced vertical dry static energy divergence. Persistent radiative cooling creates sustained negative imbalance during winter cooling events and this deficit is countered by vertical divergence of dry static energy flux and meridional cold air advection. These results challenge the direct application of tropical RCE paradigms to TP region and they highlight the need for a skewed RCE framework that explicitly incorporates the TP’s unique thermal forcing effects shaped by its elevated terrain and distinct atmospheric processes.
辐射对流平衡（RCE）对热带气候造成了关键限制，但其在青藏高原（TP）等高原地区的适用性尚不清楚。基于 23 年（2001-2023 年）的多重观测数据集，本研究首次对 RCE 在 TP 上的适用性进行了全面观察评估。我们发现 TP 表现出明显的年均能量失衡，达到-15.9 W/m²，该状态表现为强烈的季节不对称。夏季显示出强烈的正能量失衡，达到+56.0 瓦/平方米，由降水潜在加热驱动;冬季则极端辐射冷却，达到-71.8 瓦/平方米。仅包括四月和九月在内的过渡月份，就实现了整个高原地区的瞬态能量平衡。TP 表现出四种能量不平衡状态，按具体降水强度和辐射冷却阈值进行分类。这些模式随季节性转变，夏季季风区域为强降水-弱降温，高原的冬秋季为弱降水-强降水。每日接近 RCE 的条件在所有时空尺度中以短暂的频率出现，仅有 5–10%，这一特征与热带地区通过空间聚合自然形成平衡形成鲜明对比。对极端事件的分析显示，强烈的潜热在夏季供暖事件中驱动正向失衡，而这种失衡主要由增强的垂直干静能散度来补偿。持续辐射冷却在冬季冷却事件中造成持续的负平衡，这一缺口静能通量和子午线冷空气平流的垂直发散所抵消。 这些结果挑战了将热带 RCE 范式直接应用于 TP 区域的观点，并凸显了需要一个倾斜的 RCE 框架，明确纳入 TP 独特热力效应，这些效应由其高地地形和独特的大气过程塑造。
How to cite: Zuo, M., Li, J., and Yu, R.: Is Radiative Convective Equilibrium Applicable over the Tibetan Plateau?, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-99, https://doi.org/10.5194/ems2026-99, 2026.
Clarifying dominant synoptic systems is highly important for understanding precipitation over complex terrain, as the effect of topography on precipitation varies with different synoptic backgrounds. Taking Southwestern China as a representative of complex terrain, this study objectively identified the dominant synoptic systems associated with summer precipitation. The distribution and fine-scale characteristics of precipitation have been further analyzed considering the combined influence of multiscale circulation and topography. First, the dominant synoptic system must be clarified, as it determines how multiscale topography affects precipitation. Here, based on a self-organizing map, large-scale winds are categorized into anomalous-westerly types, anomalous-easterly types, and transitional types. Four synoptic-scale systems (vortex type, cold front type, tropical depression type, and weak synoptic-forcing type) dominate the summer precipitation. The vortex type occurs with strengthened large-scale westerlies, and its precipitation is distributed within the moisture convergence region. The cold front type, tropical depression type, and weak synoptic-forcing type exhibit large-scale easterly anomalies. For the cold front type, a low-level northeasterly blocked by topography shapes the northwest-southeast-oriented front zone at the upper highland slope. The precipitation frequency and intensity are high within the frontal zone, while the intensity is weak on both sides. For the tropical depression type, moist low-level easterlies uplifted by westward-rising topography anchor precipitation at the lower slope. Large precipitation for the tropical depression type is attributed to a high frequency. Large-scale horizontal winds are the weakest for the weak-synoptic-forcing type, and the local topography influences the scattered precipitation distribution. Both the frequency and intensity are high for the weak synoptic-forcing type. Overall, long-lasting nocturnal events dominate the precipitation of the four synoptic types, while large-scale easterlies favor precipitation events with shorter durations and earlier peaks. For obvious synoptic systems, large-scale topography influences precipitation via a dynamic blocking effect, while the thermodynamic role of local topography is important with a weak synoptic forcing. In addition to advancing our understanding of precipitation in Southwestern China, this study provides a reference for analyzing precipitation in other regions with complex terrains.
How to cite: Zhao, Y. and Li, J.: Dominant Synoptic Systems for Summer Precipitation over the Complex Terrain of Southwestern China, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-94, https://doi.org/10.5194/ems2026-94, 2026.
The Alpine water cycle is profoundly reshaped by anthropogenic climate change. Shifts in spatial distribution, timing and intensity of precipitation, together with rising winter temperatures, are modifying snowfall and snowmelt regimes and alter snowpack structure. Consequently, avalanche risk and regionally assessed avalanche hazard levels are likely to undergo significant changes under ongoing climate warming.
In this study, we investigate potential future changes in avalanche hazard levels in the Austrian Alps under the Global Warming Levels 2°C, 3°C and 4°C. Our projections are based on the latest generation of EURO-CORDEX models, analysed using a machine-learning algorithm trained on ERA5 meteorological reanalysis data. For training, we use a novel multi-year observational data set compiled from regional avalanche hazard assessments and broadcast teletext archives. Within this data set, individual mountain ranges are grouped into response units that show similar avalanche hazard responses to different weather patterns. This allows us to apply a pattern-recognition algorithm that relates circulation analogues to specific changes in avalanche hazard levels. The algorithm is first validated against long-term observations in Tyrol using the full ERA5 data record and is subsequently applied to the future climate projections.
The results of this study show when, and to what extent, the effects of human-caused climate change exceed the interannual and decadal variability of avalanche hazard over the course of the 21st century. The emergence of a climate change signal has important implications for hazard assessment and risk management in the Alpine region. It furthermore highlights critical warming thresholds beyond which current forecasting practices may require substantial revision.
How to cite: Maier, P., Jutz, M., and Formayer, H.: Future Development of Avalanche Hazard Levels in the Austrian Alps, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-160, https://doi.org/10.5194/ems2026-160, 2026.
Based on conventional L-band sounding, automatic weather station data and ERA-Interim 0.125°×0.125° 6h reanalysis data, we researched 23 heavy hail events (hail diameter ≥ 20mm ) selected according the grade of hail in China (GB/T 27957-2011) and occurring in Southern China from 2004 to 2017, mainly analyzed its characteristics of atmospheric stratifications, melting effect quantificationally, and set up a physical parameters model to distinguish heavy hail. The results are as follows: (1) vertical stratification of heavy hail events with characteristic of upper dry and lower moist is more evident than that of small hail (hail diameter ≥ 5mm and <20mm) events, and vertical potential instability is mainly triggered by upper dry and lower moist rather than upper cold and lower warm. (2) The ratio of H-/H+ (cold could/warm could) can be used to distinguish heavy hail and small hail, and the ratio above 1.6/1 is one of the conditions to forecast heavy hail. (3) Compared with small hail events, the height of maximum thermal buoyancy of heavy hail is higher than the height of -5℃, which helps hail embryo enter efficient growth layer (-10℃～-30℃), driving heavy hail growth. The maximum thermal buoyancy ≥4℃ is a key threshold to distinguish heavy hail and small hail. (4) based on statistics and comparative analysis of this paper, a physical parameters model was set up, including △Td85 ≥46℃, T-Td≥15℃ at 500hPa, the minimum T-Td≤2℃ between 700hPa and 1000hPa, H-/H+≥1.6/1, the intensity of maximum thermal buoyancy ≥ 4℃, and the height of maximum thermal buoyancy > the height of -5℃, which favor heavy hail generation.
How to cite: Chen, Y., Zeng, Z., Li, S., and Yu, C.: Characteristics of Atmospheric Stratification and Melting Effect of Severe Hail Events Over Southern China, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-42, https://doi.org/10.5194/ems2026-42, 2026.
Quantifying the exchange of mass, momentum and energy between the earth’s surface and the atmosphere is essential for understanding - and therefore modeling - weather and climate processes. Compared to flat terrain, exchange processes in complex terrain are especially efficient due to valley and slope wind circulations. The international TEAMx observational campaign (TOC) in summer 2025 focused on the observation of exchange processes on different scales in the mountain boundary layer.
The LIVAVERT(EX)2 project - linking valley flow and vertical exchange in complex terrain - is embedded in TEAMx and focuses on observing valley winds in combination with exchange processes in the Sarntal Alps region, a local hotspot of convective initiation within the Alps. As part of the project, a novel airborne Doppler lidar (ADL) was used for its first extended measurement campaign in complex terrain. The new ADL system, called AIRflows, measures profiles of 3D wind at 100 m along-track and vertical resolution, and thereby provides spatially resolved insight into valley wind systems and vertical exchange.
During TEAMx, AIRflows was used on 33 research flights onboard the TU Braunschweig Cessna F406 research aircraft. Additionally, an extensive ground-based Doppler lidar (GDL) network was established as part of a KITcube deployment in the Sarntal Alps region. The obtained GDL observations, as well as synchronized airborne in-situ measurements by a second aircraft (DLR Cessna), allow for the first real-world validation of high-resolution ADL observations in complex terrain. This contribution provides estimates of the ADL and GDL wind profiling accuracy and their spatial representativeness. In a second step, the spatially resolved ADL wind profiles are used to validate existing GDL-based volume flux estimation methods. The goal of the validation is to obtain accurate volume flux budgets in the valleys surrounding the Sarntal Alps. Combining volume flux budget and direct vertical exchange observations then allows for a more quantitative insight into valley flow and its relation to convective initiation over the surrounding mountains than ever before.
Key words: TEAMx, KITcube, airborne research, Doppler lidar, validation, valley flow, volume flux budget, complex terrain, convective initiation, boundary layer meteorology
How to cite: Schaeffler, L., Gasch, P., Gohm, A., and Stiperski, I.: Novel airborne and ground-based Doppler lidar observations of mountain wind systems: Validation of volume flux estimates during TEAMx, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-59, https://doi.org/10.5194/ems2026-59, 2026.
Mountain regions are among the most sensitive to climate change and serve as important indicators of ongoing environmental change. Due to their complex topography, strong elevation gradients, and pronounced local atmospheric processes, mountainous environments often display considerable spatial variability in meteorological conditions over short distances. This makes them particularly valuable for studying climatic variability and extremes. In this context, the CroClimExtremes project initiated the first systematic measurements of air temperature and humidity on Biokovo, a coastal Croatian mountain characterised by complex relief and marked climatic contrasts.
In February 2024, a network of 22 measuring devices was installed along two mountain transects. The first transect was established on the maritime slope, extending from sea level to 1650 m a.s.l., while the second was set up on the continental slope, ranging from 602 to 1650 m a.s.l. This observational design enables a direct comparison of meteorological conditions between the seaward and landward sides of the mountain, as well as an assessment of vertical variability along both slopes.
The main objective of the measurements is to investigate the spatial and temporal characteristics of air temperature and humidity on Biokovo and to identify potential extreme weather and microclimatic conditions. Preliminary analyses reveal pronounced differences in both variables across altitude and between the continental and maritime slopes. In addition to differences in absolute values, clear variations were detected in diurnal and annual cycles, as well as in vertical gradients of temperature and absolute humidity. These patterns point to the strong influence of elevation, slope orientation, complex topography, and local meteorological processes on the observed distribution of atmospheric conditions.
The dataset collected on Biokovo represents the first of its kind for a mountainous area in Croatia. As such, it provides an important foundation for a more detailed understanding of the climatic characteristics of this topographically complex environment. The results contribute not only to improved knowledge of local-scale atmospheric processes, but also to a broader understanding of mountain climate variability in coastal and inland transition zones. This research therefore offers valuable insights into the role of topography in shaping temperature and humidity patterns and provides a basis for future studies of climatic extremes in Croatian mountain regions.
How to cite: Herceg Bulić, I., Pasarić, Z., Cokarić, L., Paar, D., Bočić, N., Mlađen, K., Protrka, K., and Škrabić, H.: Air Temperature and Humidity Variability on the Continental and Maritime Slopes of Biokovo Mountain, Croatia , EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-491, https://doi.org/10.5194/ems2026-491, 2026.
When foehn winds cross the Alps from the south, they often descend abruptly and vigorously into the valleys on the northern side. Although mountain gravity waves and hydraulic theory offer theoretical explanations for this phenomenon, the descent of the Alpine south foehn has never been systematically quantified across real-case events. This study addresses that knowledge gap using kilometer-scale numerical simulations combined with online trajectory calculations.
In the first part, we find that foehn air parcels descend primarily at distinct hotspots immediately downwind of local peaks and ridges, highlighting the anchoring role of local topography. The magnitude of descent correlates clearly with small-scale terrain elevation differences, though other factors also contribute. Since the descent is mostly dry adiabatic, the motion appears to follow downward-sloping isentropes tied to gravity waves. A minority of air parcels undergo diabatic cooling and moisture uptake, mostly south of the Alpine crest.
The second part examines factors governing descent at the local scale, focusing on a prominent hotspot along the Rätikon — a mountain range bordering the Rhine Valley — through two detailed case studies. During periods of intensified descent, gravity waves excited by local Rätikon peaks drive air parcels down into the range's northern tributaries and into the Rhine Valley. The two cases reveal different wave regimes — vertically propagating waves, breaking waves, and horizontally propagating lee waves — none of which is consistently dominant, suggesting no single regime defines foehn descent along the Rätikon. Beyond gravity waves, additional effects matter too: a topographic concavity deflects near-surface flow and promotes strong descent toward the valley floor, while in one case nocturnal cooling creates a smooth virtual topography that suppresses gravity wave development and inhibits foehn descent into the valley.
In summary, applying a Lagrangian framework to a comprehensive multi-case dataset reveals that foehn descent is inherently local, topographically anchored, and shaped by a variety of interacting wave regimes and secondary effects. This perspective not only complements but substantially extends the traditional Eulerian view of foehn dynamics.
How to cite: Sprenger, M., Jansing, L., and Papritz, L.: A Lagrangian framework for detecting and characterizing the descent of foehn from Alpine to local scales, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-609, https://doi.org/10.5194/ems2026-609, 2026.
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