The exchange of heat, momentum, and mass in the atmosphere over mountainous terrain is controlled by synoptic-scale dynamics, thermally driven mesoscale circulations, turbulence. This article reviews key challenges relevant to understanding processes mountain boundary layer outlines possible research priorities for future. review describes limitations experimental study turbulent complex terrain, impact slope valley breezes on structure convective layer, role intermittent mixing...

Monin-Obukhov similarity theory (MOST) forms the basis for parametrizations of turbulent exchange in virtually all numerical models atmospheric flows. Yet, its limitations to flat and horizontally homogeneous terrain have plagued since inception. Here we present a first generalized extension MOST based on inclusion turbulence anisotropy as an additional nondimensional term. This novel developed unprecedented ensemble complex datasets covering mountainous terrain, is shown be valid conditions...

The theoretical treatment of turbulence is largely based on the assumption horizontally homogeneous and flat underlying surfaces. Correspondingly, approaches developed over years to measure statistics in order test this understanding or provide model input, are also same terrain. Here we discuss aspects measurements that require special attention mountainous We especially emphasize importance data quality (flux corrections, assessment, uncertainty estimates) address issues coordinate systems...

The role of the atmospheric boundary layer (ABL) in atmosphere-climate system is exchange heat, mass and momentum between 'the earth's surface' atmosphere. Traditionally, it understood that turbulent transport responsible for this hence understanding physical description turbulence structure key to assess effectiveness earth-atmosphere exchange. This rooted (implicit) assumption a scale separation or spectral gap mean motions, which turn leads horizontally homogeneous flat (HHF) surface as...

Abstract The flow and turbulence structure in the atmospheric boundary layer over complex mountainous terrain determines Earth–atmosphere interaction, that is, exchange of energy, mass, momentum between surface such free atmosphere. Numerical models for weather climate, even when operated at high or very grid resolution, are known to be deficient, leading inaccurate local forecasts (weather) scenarios (climate). nature reasons these deficiencies, however, difficult assess because systematic...

Turbulence data from the CASES-99 field experiment, over comparatively horizontally homogeneous and flat terrain, are separated based on anisotropy of Reynolds stress tensor (into isotropic, two-component axisymmetric one-component turbulence) flux-variance similarity scaling relations tested. Results illustrate that different states correspond to relations, especially under unstable stratification. Experimental with close isotropic turbulence match relationships well. On other hand, very...

Abstract The correct simulation of the atmospheric boundary layer (ABL) is crucial for reliable weather forecasts in truly complex terrain. However, common assumptions model parametrizations are only valid horizontally homogeneous and flat Here, we evaluate turbulence parametrization numerical prediction COSMO with a horizontal grid spacing $$\Delta x = 1.1\,\hbox {km}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>x</mml:mi>...

The development of a unified similarity scaling has so far failed over complex surfaces, as studies show large deviations from the empirical formulations developed flat and horizontally homogeneous terrain well between different data sets. However, recent study turbulence anisotropy for shown that separating according to limiting states (isotropic, two-component axisymmetric one-component turbulence) improves near-surface scaling. In this paper we explore whether finding can be extended...

Abstract The near-surface boundary layer above patchy snow cover in mountainous terrain is characterized by a highly complex interplay of various flows on multiple scales. In this study, we present data from comprehensive field campaign that period 21 days the ablation season an alpine valley, continuous until complete melt out. We recorded eddy covariance at different heights and investigated spectral decompositions. topographic setting led to categorisation into up down valley flows, with...

Numerical simulations of flow over steep terrain using 11 different nonhydrostatic numerical models are compared and analyzed. A basic benchmark five other test cases simulated in a two-dimensional framework the same initial state, which is based on conditions during Intensive Observation Period (IOP) 6 Terrain-Induced Rotor Experiment (T-REX), intense mountain-wave activity was observed. All use an identical horizontal resolution 1 km vertical resolution. The six various heights: 100-m...

Abstract We present the first direct comparison of turbulence conditions measured simultaneously over exposed ice and a 0.08 m thick supraglacial debris cover on Suldenferner, small glacier in Italian Alps. Surface roughness, sensible heat fluxes (~20–50 W −2 ), latent (~2–10 topology scale are similar both surface types during katabatic synoptically disturbed conditions. Exceptions sunny days when buoyant convection becomes significant debris-covered (sensible flux ~ −100 ; −30 ) prevailing...

Abstract The mass balance of mountain glaciers is interest for several applications (e.g., local hydrology or climate projections), and turbulent fluxes can be an important contributor to glacier surface during strong melting events. underlying complex terrain leads spatial heterogeneity non‐stationarity fluxes. Owing the contribution thermally induced flows gravity waves, exchange mechanisms are fully three‐dimensional, instead only vertical. Additionally, have their own distinct...

<title>Abstract</title> Describing the turbulent mixing of heat in stable boundary layer (SBL) has been a long-standing difficulty for similarity theory. We investigated connection between and thermal structure near-surface SBL at three sites impacted by topography using Distributed Temperature Sensing (DTS) universal decoupling parameter, which describes degree vertical coupling eddies. Three categories structures were found: logarithmic, sublayered, quasi-logarithmic profiles. The...

Monin Obukhov Similarity Theory (MOST) has long served as the basis for parameterizations of turbulence exchange between surface and atmospheric boundary layer in models weather climate prediction. Decades research, however, illuminated some limitations MOST based parameterizations, particularly when MOST's foundational assumptions flat horizontally homogeneous terrain are violated. Recent work leveraged anisotropy an additional non-dimensional term to extend generalize complex terrain. In...

TEAMx (multi-scale transport and exchange processes in the atmosphere over mountains &amp;#8211; programme experiment) is an international research program that aims at improving our understanding of complex terrain evaluating representation these numerical weather climate prediction models. As part TEAMx, a one-year long field campaign, Observational Campaign (TOC), started September 2024, with dedicated observations being conducted four target areas aligned approximate north-south cross...

Common turbulence parametrization in numerical weather prediction models and traditional boundary layer theory are predominantly designed for horizontally homogeneous flat terrain only consider vertical transport processes. However, these assumptions fail valleys, where the horizontal constrictions to flow as well prevalent surface heterogeneity mean that terms budget equations (e.g. advection, flux divergence) become important. Over a mountain glacier, addition, acceleration of katabatic...

For the past five decades, modelers have relied on Monin-Obukhov Similarity Theory (MOST) to model surface exchanges for application in atmospheric models boundary layer meteorology and weather climate prediction. During this time, studies also illuminated some of limitations MOST based parameterizations, particularly when MOST&amp;#8217;s foundational assumptions flat horizontally homogeneous terrain are violated. Recent work over groups meteorological towers from Stiperski Calaf 2023...

Reynolds stress anisotropy is one of the fundamental characteristics all wall bounded turbulent flows, especially those in atmosphere. In canonical (flat and horizontally homogeneous) boundary layers, presents a balance between processes that generate it (shear, buoyancy blocking) pressure-redistribution terms act to redistribute kinetic energy towards non-energetic velocity components. This pressure redistribution remains an area active research, stratified conditions, dominating...

Land-terminating ice cliffs are rare features of the cryosphere, displaying unique atmosphere-cryosphere interactions due to their vertical nature. Although cliff surface is small compared total glacier surface, mass balance face can play a decisive role in ablation, cliff's altered exposure radiative fluxes and modulation turbulent heat fluxes. Understanding boundary layer over these walls therefore essential for accurately modeling melt other related processes. Our research addresses this...

Mountain glaciers are a perfect laboratory to study the interaction between mountain atmosphere, including multiscale processes developing within it, and stably stratified ice surfaces. Due their setting valleys, structure of glacier boundary layers is result complex interplay surface thermal forcing, thermally dynamically driven flows larger scale flow aloft. This plays an important role in microclimates energy mass balance glaciers. However, few datasets atmospheric measurements over whole...

The scaled standard deviations of temperature and humidity are investigated in complex terrain. study area is a steep Alpine valley, with six measurement sites different slope, orientation roughness (i-Box experimental site, Inn Valley, Austria). Examined here several assumptions forming the basis Monin-Obukhov similarity theory (MOST), including constant turbulence fluxes height degree self-correlation between involved variables. Since basic for applicability MOST approach-horizontally...

Abstract Trapped lee wave interference over double bell-shaped obstacles in the presence of surface friction is examined. Idealized high-resolution numerical experiments with nonhydrostatic Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) are performed to examine influence a frictional boundary layer and nonlinearity on impact wave-induced separation formation rotors. The appearance constructive destructive interference, controlled by ratio ridge distance intrinsic horizontal...

Abstract. Within the Innsbruck Box project, a ground-based microwave radiometer (RPG-HATPRO) was operated in Inn Valley (Austria), very complex terrain, between September 2012 and May 2013 to obtain temperature humidity vertical profiles of full troposphere with specific focus on valley boundary layer. In order assess its performance deep alpine valley, obtained by different retrieval algorithms based climatologies are compared local radiosonde data. A that is improved respect one provided...

Abstract The correct simulation of the atmospheric boundary layer (ABL) in highly complex terrain is a challenge for mesoscale numerical weather prediction models. An improvement model performance possible if horizontal contributions to turbulence kinetic energy (TKE) production, such as shear are implemented model’s parameterization. However, 3D parameterizations often only have constant length scale that depends on grid spacing. This unphysical applications, because were initially...