Andreas Rauchöcker

FS 3.512

Turbulent Exchange over varying terrain and ecosystem characteristics

Details

Full Title
FS 3.512: Turbulent Exchange over varying terrain and ecosystem characteristics
Scheduled
TBA
Location
TBA
Convener
Andreas Rauchöcker
Co-Conveners
Judith Schmack,
Assigned to Synthesis Workshop
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Thematic Focus
No focus defined
Keywords
Boundary Layer, Mountain Meteorology, Canopy flows, Turbulent exchange

Description

Turbulent transport is a key mechanism for the exchange of mass, momentum and heat in the atmospheric boundary layer. While reasonably well understood over homogeneous surfaces, turbulent exchange becomes more complex in mountain regions due to factors like thermally-driven wind systems, terrain-induced pressure gradients and the influence of surface roughness. Across different terrain features and ecosystems, turbulent exchange is influenced by terrain shape and heterogeneity associated with topography, land cover and vegetation type, which has impacts on the exchange of heat and momentum as well as on the emission and dispersion of trace gases. Especially the latter has important implications for the atmospheric composition and air quality interactions between atmosphere and biosphere. This session invites researchers to discuss challenges and strategies in measuring and modelling of turbulent flows and biogenic fluxes across complex surfaces and ecosystems while also covering wide-spread measurement techniques such as the eddy covariance method.

Submitted Abstracts

ID: 3.10250

Assessment of Atmospheric Dispersion Processes in a Mountain Valley for Effective Implementation of Vehicle Emission Reduction Policies.

Ahmed Njimongbet

Abstract/Description

Atmospheric dispersion processes behave differently on flat terrain compared to complex terrain. Orography plays a crucial role in atmospheric dynamics in mountainous areas by influencing air mass movement, which affects pollutant dispersion within or beyond the valley. This research project focuses on analyzing atmospheric dynamics, pollutant dispersion processes, and the impact of vehicle emissions on air quality in the Adige Valley. The objectives include studying meteorological conditions that influence pollutant dispersion, quantifying spatial and temporal variations in pollutant concentrations, and developing and validating modeling tools in the context of planning and implementing vehicle emission reduction policies. The expected outcomes include a comprehensive understanding of the factors influencing pollutant dispersion in mountainous areas, the identification of pollution hotspots, the evaluation of policies, and recommendations for improving air quality. Verification and evaluation methods will ensure the reliability of the results. By combining data analysis, atmospheric modeling, and policy evaluation, this study aims to provide valuable insights for the effective implementation of vehicle emission reduction policies in complex terrain.

ID: 3.10287

In the sunshine and the shadow: how local topography affects temperatures and life in mountain lakes?

Adam Janto
Svitok, Marek; Hamerlík, Ladislav; Bitušík, Peter; Novikmec, Milan

Abstract/Description

Due to their elevation, catchment characteristics, and simple structure, mountain lakes react sensitively to climate change. However, local topography – one of the prominent features of mountain landscapes – may profoundly affect the climate change signal by reducing the insolation of topographically shaded lakes. Our objective was to quantify the “sun umbrella” effect of local topography on the temperatures and communities of littoral invertebrates of Tatra Mountain lakes (Slovakia). We analyzed data on lake surface water temperature (LSWT) and littoral benthic communities of 18 mountain lakes distributed along a 500-m altitudinal gradient and characterized by differing topographic shading levels: unshaded lakes and shaded lakes (years 2010 – 2011). Further, we compared these temperature data with our recent data from 2021-2023 to address the role of local topography in the modulation of climate change signals on LSWT over time. Shaded lakes were significantly colder and local topography affected the composition of littoral invertebrates. Investigated lake groups supported distinct communities in lower altitudes and shaded lakes were characterized by higher abundances of cold-stenothermal species. However, the community composition of both lake groups converged towards higher altitudes in communities typical for a greater abundance of cold-stenotherms. The proportion of cold-stenothermal species increased with increasing altitude in shaded lakes and was notably greater than that in unshaded lakes along the studied altitudinal gradient. Most of the studied lakes became warmer during ca. 10-year period (on average +0,87°C). Local topography had a marginally significant (p = 0.076) effect on the temperature changes over time. Our results suggest that local topography profoundly affects the temperature and benthic communities of the mountain lakes. Topographically shaded lakes may perhaps provide refuge for cold-stenothermal communities threatened by ongoing global warming. However, the role of local topography in the modulation of climate change signals on mountain lakes requires further research.

ID: 3.10810

Ecosystem CO2 exchange in complex terrain

Alexander Platter
Hammerle, Albin; Wohlfahrt, Georg

Abstract/Description

Eddy covariance measurements are the backbone of in-situ ecosystem CO2 budget estimations, serving as the primary means to understand and quantify the terrestrial CO2 sink’s role in the global carbon cycle. Conventionally, this technique relies on an above-canopy eddy covariance setup to quantify vertical turbulent flux divergence, often supplemented by a profile system for estimating changes in CO2 storage. However, the complete CO2 mass balance for an ecosystem includes several additional exchange terms, including advection, horizontal flux divergence, and dispersive fluxes. The common practice is to assume these terms are negligible. However, it has been recognized that this assumption is flawed, particularly during stable, nighttime conditions. This assumption may be even less valid for complex terrain, where persistent thermally induced flows in combination with surface heterogeneities can lead to significant contributions from advection or dispersive fluxes. In the absence of a suitable and practical measurement technique for the unmeasured terms, engineering-type filtering methods are applied to measurements, without knowing the true biosphere-atmosphere exchange or the contributions of single components. High-resolution numerical modeling of the atmospheric flow can be a promising method to investigate the exchange processes at the ecosystem scale.
Here these problems in the context of complex situations of mountainous terrain and forests are summarized, and limitations and implications of current approaches to derive in-situ ecosystem CO2 estimations are highlighted. Furthermore, I am giving an outlook to my upcoming work, where Large Eddy Simulations will be used to gain insights into the CO2 exchange on an ecosystem scale.

ID: 3.10853

The impact of drought on carbonyl sulfide and CO2 fluxes in P. sylvestris and J. communis

Anna De Vries
Spielmann, Felix; Wohlfahrt, Georg; Schmack, Judith; Jud, Werner; Karl, Thomas; Schnitzler, Jörg-Peter; Winkler, Jana Barbro

Abstract/Description

Gross primary productivity (GPP) is a key driver of the current net land carbon sink. However, climate change—along with the increasing frequency of extreme events—may significantly alter GPP, particularly in mountain regions, which are very vulnerable to extreme events like drought. Understanding how the GPP responds to droughts in mountain regions is therefore crucial. Since GPP cannot be measured directly, it must be inferred via proxies or modelling, introducing substantial uncertainties, which limit the ability to predict GPP responses to climate change driven stressors such as drought. A promising proxy of GPP are measurements of carbonyl sulfide (COS) fluxes, as COS is taken up by plants in parallel to CO2 but in contrast to the latter generally not emitted. In this study, we measured COS and CO₂ fluxes of two woody mountain species, Pinus sylvestris and Juniperus communis, under controlled and varying drought conditions (soil water content ranging from 40 % to 2 %). As water stress intensified, the uptake of both COS and CO₂ declined due to reductions in stomatal conductance. These flux responses to drought were of greater magnitude in P. sylvestris than in J. communis. Interestingly, diurnal variations in GPP and autotrophic respiration were more pronounced in semi-stressed plants, which regulated stomatal conductance and closure following an optimality principle, compared to heavily stressed or control groups. The CO₂ uptake velocity decreased more rapidly than COS uptake under increasing stress in both species due to the increasing biochemical limitations of photosynthesis. The main driver of the diurnal cycle of the COS and CO2 exchange was PAR in both species and all stress levels but with increasing light saturation points as drought intensified. Daily means were mostly driven by the water availability. This study provides valuable insights into how mountain species respond to drought stress, improving our understanding of GPP dynamics under extreme conditions, essential for refining carbon cycle models and improving predictions on the impacts of climate change on terrestrial carbon sinks.

ID: 3.12296

The Ice Cliff Boundary Layer

Marie Schroeder

Abstract/Description

Land-terminating ice cliffs present a unique challenge for understanding boundary layer dynamics over complex terrain. Their vertical structure disrupts conventional boundary layer assumptions, altering turbulent fluxes of heat and moisture that drive melt processes. Unlike homogeneous and flat surfaces, ice cliffs are subject to pronounced flow separation, recirculation zones, and localized turbulence effects, complicating the characterization of turbulent transport. Our research examines boundary layer flows over ice cliffs in two distinct environments: northern Greenland and Kilimanjaro. The Greenland site provides long-term low-frequency temperature and humidity measurements, capturing microclimatic variability at a polar ice cliff. The Kilimanjaro dataset, collected during a 40-hour campaign, includes high-frequency turbulence data from 3D sonic anemometers positioned on and in front of the cliff. This allows for detailed analysis of turbulence characteristics, including flux partitioning, mean flow direction, and coordinate rotation challenges over vertical surfaces. By comparing these two datasets, we investigate whether low-frequency measurements can adequately capture turbulent exchange and assess the implications for modeling ice cliff melt. Our findings contribute to the broader understanding of turbulent transport over steep and heterogeneous terrain, highlighting the complexities introduced by vertical ice faces. This work provides insight into boundary layer processes at ice cliffs and informs strategies for measuring and modeling turbulence in similarly complex environments.

ID: 3.21207

Modeling the Impact of Deforestation on Cloud Immersion and Hydrology in Monteverde’s Cloud Forest

Ellinor Krämer
Sauter, Tobias

Abstract/Description

Tropical montane cloud forests (TMCFs) are ecosystems critically dependent on persistent cloud immersion, which shapes their hydrology, biodiversity, and ecological function. Due to their occurrence only at specific altitudinal and climatic thresholds, TMCFs are highly fragmented, biologically unique, and exceptionally sensitive to environmental changes. As such, they are considered prime indicators of global climate change impacts.

Climate projections suggest significant shifts in temperature and precipitation patterns, with tropical montane ecotones expected to migrate upward by over 100 meters under elevated CO₂ scenarios. This alone suggests complete replacement of many narrow-altitude TMCFs by other ecosystems, as well as the eviction of peak-range TMCFs.

Additionally, land-use and land-cover changes (LULCC), particularly deforestation for agriculture, have been shown to reduce cloud formation, especially during dry seasons. Large scale conversion of forest to agriculture alters surface-atmosphere interactions, as well as the timing and extent of energy fluxes, and ultimately the water balance. In Costa Rica’s Monteverde Cloud Forest Reserve, remote sensing data reveal a decline in dry season cloud cover over areas deforested for pineapple cultivation, whereas forested regions maintain consistent cloud formation.

This study investigates the interactions between LULCC (focusing on pineapple cultivation), vegetation cover, and local climate in the Monteverde Reserve, particularly how these factors influence water recycling and cloud immersion. Using high-resolution simulations from the ICON (Icosahedral Nonhydrostatic) model, for numerical weather prediction, validated with remote sensing data, this research analyzes LULCC impacts on precipitation, evapotranspiration, and atmospheric humidity. Despite challenges in modeling complex mountain climates, such analyses provide valuable insights into altered surface-atmosphere feedbacks. These interactions may exhibit nonlinear behaviors, potentially triggering abrupt local climate transitions and, thus putting pressure on the ecosystem.

Addressing these dynamics requires interdisciplinary collaboration, with contributions from climate science, remote sensing, forest ecology, and hydrology to improve our understanding and management of these vulnerable ecosystems.

FS 3.237: Open Poster Session

FS 3.238: Transdisciplinary collaborations, methodologies, and ethical considerations in international mountain research

#IMC: September 14 - 18 2025

FS 3.512

Turbulent Exchange over varying terrain and ecosystem characteristics

Details

Full Title

Scheduled

Location

Convener

Co-Conveners

Assigned to Synthesis Workshop

Thematic Focus

Keywords

Description

Submitted Abstracts

Abstract/Description

Abstract/Description

Abstract/Description

Abstract/Description

Abstract/Description

Abstract/Description

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