scholarly journals Formation and Maintenance Mechanisms of the Stable Layer over the Po Valley during MAP IOP-8

2006 ◽  
Vol 134 (11) ◽  
pp. 3336-3354 ◽  
Author(s):  
Allison M. Hoggarth ◽  
Heather Dawn Reeves ◽  
Yuh-Lang Lin
Keyword(s):  
Numerical Simulations ◽  
Western Alps ◽  
Reanalysis Data ◽  
Lower Atmosphere ◽  
Stable Layer ◽  
Ligurian Sea ◽  
Air Mass ◽  
Po Valley ◽  
Sensitivity Experiments ◽  
The Alps

Abstract During intensive observation period 8 (IOP-8) of the Mesoscale Alpine Program, a strong stable layer formed over Italy’s Po Valley and the northern Ligurian Sea. This stable layer has been shown in previous research to be important for the formation of convection over the Ligurian Sea and the lack thereof over the Po Valley and southern slopes of the Alps. The purpose of this study is to investigate the mechanisms that acted to form and maintain the stable layer during IOP-8. This aim is accomplished through inspection of observed data as well as numerical simulations and sensitivity experiments. Observations and reanalysis data show that starting on 17 October 1999, a relatively cool, stable air mass was advected around the eastern side of the Alps into the lower atmosphere of the Po Valley. Both observational data and model output show this air mass as being blocked as it encountered the western Alps, thus resulting in an accumulation of cool, stable air at low levels in the Po Valley during the ensuing 60 h. When southerly flow approached northern Italy beginning on 20 October 1999, both the western Alps and the northern Alps appeared to help retain the low-level, cool, stable air over the Po Valley. A trajectory and sounding analysis shows that warmer, less stable air originating from over the southern Mediterranean Sea was advected atop the low-lying stable layer within the Po Valley. It is hypothesized that this differential advection, as well as blocking by the western and northern flanks of the Alps, were responsible for the longevity of the stable layer. A series of numerical simulations and sensitivity experiments were performed to test the above hypotheses. These tests support the hypotheses. Other mechanisms were also considered, including blocking of solar radiation by clouds, friction, and evaporative cooling. These simulations revealed that all three processes were critical for the longevity of the stable layer and point to the importance of accurate model representation of subgrid-scale processes.

scholarly journals Formation Mechanisms for Convection over the Ligurian Sea during MAP IOP-8

2005 ◽  
Vol 133 (8) ◽  
pp. 2227-2245 ◽  
Author(s):  
Yuh-Lang Lin ◽  
Heather Dawn Reeves ◽  
Shu-Yun Chen ◽  
Sen Chiao
Keyword(s):  
Potential Temperature ◽  
Leading Edge ◽  
Moisture Flux ◽  
Material Surface ◽  
Formation Mechanisms ◽  
The South ◽  
Stable Layer ◽  
Ligurian Sea ◽  
Air Mass ◽  
Po Valley

Abstract The dynamical impacts of an unusually strong stable layer that developed over the Po Valley and northern Ligurian Sea during Mesoscale Alpine Program (MAP) intensive observation period 8 (IOP-8) on the formation of convection over the Ligurian Sea are explored. Based on numerically simulated equivalent potential temperature, wind vectors, and by a trajectory analysis of parcels both beneath and above the stable layer, it is shown that the stable layer behaved as a material surface or “effective mountain” to the airstreams impinging on it from the south. Additional analyses show that the leading edge of the stable layer was collocated with maxima in upward motion and a strong positive moisture flux. Hence, it was further argued and demonstrated through inspection of soundings upstream of the cold dome and trajectory analyses that lifting by the stable layer enhanced convective activities over the Ligurian Sea. Finally, processes contributing to the maintenance of the stable layer during IOP-8 were explored. It was found that the differential advection of a warm, less stable air mass on top of a cooler, more stable air mass helped maintain the stable layer. The Ligurian Apennines made a secondary contribution to the stagnation of the cool air in the Po Valley by partially blocking this air mass from exiting the valley to the south.

Synconvergent and coherent (ultra)high-pressure crustal rock exhumation

2021 ◽  
Author(s):  
Lorenzo G. Candioti ◽  
Joshua D. Vaughan-Hammon ◽  
Thibault Duretz ◽  
Stefan M. Schmalholz
Keyword(s):  
Numerical Models ◽  
A Priori ◽  
Western Alps ◽  
Ultrahigh Pressure ◽  
Plate Motion ◽  
Crustal Rock ◽  
Plate Boundaries ◽  
Crustal Rocks ◽  
Natural Data ◽  
The Alps

<p>Ultrahigh-pressure (UHP) continental crustal rocks were first discovered in the Western Alps in 1984 and have since then been observed at many convergent plate boundaries worldwide. Unveiling the processes leading to the formation and exhumation of (U)HP metamorphic crustal rocks is key to understand the geodynamic evolution of orogens such as the Alps.</p><p> </p><p>Previous numerical studies investigating (U)HP rock exhumation in the Alps predicted deep (>80 km) subduction of crustal rocks and rapid buoyancy-driven exhumation of mainly incoherent (U)HP units, involving significant tectonic mixing forming so-called mélanges. Furthermore, these predictions often rely on excessive erosion or periods of divergent plate motion as important exhumation mechanism. Inconsistent with field observations and natural data, application of these models to the Western Alps was recently criticised.</p><p> </p><p>Here, we present models with continuous plate convergence, which exhibit local tectonic-driven upper plate extension enabling compressive- and buoyancy-driven exhumation of coherent (U)HP units along the subduction interface, involving feasible erosion.</p><p> </p><p>The two-dimensional petrological-thermo-mechanical numerical models presented here predict both subduction initiation and serpentinite channel formation without any a priori prescription of these two features. The (U)HP units are exhumed coherently, without significant internal deformation. Modelled pressure and temperature trajectories and exhumation velocities of selected crustal units agree with estimates for the Western Alps. The presented models support previous hypotheses of synconvergent exhumation, but do not rely on excessive erosion or divergent plate motion. Thus, our predictions provide new insights into processes leading to the exhumation of coherent (U)HP crustal units consistent with observations and natural data from the Western Alps.</p>

scholarly journals Using spectra characteristics to identify ice nucleating particle populations during winter storms in the Alps

2018 ◽  
Author(s):  
Jessie M. Creamean ◽  
Claudia Mignani ◽  
Nicolas Bukowiecki ◽  
Franz Conen
Keyword(s):  
Spectral Characteristics ◽  
Research Station ◽  
Winter Storms ◽  
Air Mass ◽  
Airborne Measurements ◽  
The Alps ◽  
Cloud Environments ◽  
Freezing Temperatures ◽  
Cloud Ice ◽  
Viable Method

Abstract. One of the least understood cloud processes is modulation of their microphysics by aerosols, specifically of cloud ice by ice nucleating particles (INPs). To investigate INP impacts on cloud ice and subsequent precipitation formation, measurements in cloud environments are necessary but difficult given the logistical challenges associated with airborne measurements and separating interstitial aerosol from cloud residues. Additionally, determining the sources of INPs is important given the dependency of glaciation temperatures on the mineral or biological components and diversity of such INP populations. Here, we present results from a comparison of INP spectral characteristics in air, cloud rime, and fresh fallen snow for storm days at the High-Altitude Research Station, Jungfraujoch. The goal of the study was two-fold: (1) to assess variability in wintertime INP populations found in-cloud based on air mass direction during snowfall and (2) to evaluate INPs between different sample types using normalized differential INP spectra. INP freezing temperatures and concentrations were consistently higher on average from the southeast as compared to the northwest for rime, snow and especially aerosol samples which is likely a result of air mass influence from boundary layer terrestrial and marine sources in Southern Europe, the Mediterranean, and North Africa. For all three sample types combined, average onset freezing temperatures were −7.7 and −12 °C for southeasterly and northwesterly days, respectively, while INP concentrations were 3 to 20 times higher when winds arrived from the southeast. Southeasterly aerosol samples typically had bimodal freezing spectra – indicating a putative influence from biological sources – while bimodality of the rime and snow varied depending on meteorological context. Evaluating normalized differential INP spectra exhibited variable modality and shape – depending on the types of INPs present – and may serve as a viable method for comparing different sampling substances and assessing the possible mixed mineral and biological versus only biological contributions to INP sample populations.

Striking differences in lithospheric structure between the north- and south-western Alps: insights from receiver functions along the Cifalps profiles and a new Vs model

2021 ◽  
Author(s):  
Anne Paul ◽  
Ahmed Nouibat ◽  
Liang Zhao ◽  
Stefano Solarino ◽  
Stéphane Schwartz ◽  
...  
Keyword(s):  
Receiver Function ◽  
Negative Polarity ◽  
Western Alps ◽  
Lithospheric Structure ◽  
Seismic Stations ◽  
Continental Subduction ◽  
The North ◽  
Ligurian Alps ◽  
The Alps ◽  
Converted Waves

<p>The CIFALPS receiver-function (RF) profile in the southwestern Alps provided the first seismological evidence of continental subduction in the Alps, with the detection of waves converted on the European Moho at 75-80 km depth beneath the western edge of the Po basin (Zhao et al., 2015). To complement the CIFALPS profile and enhance our knowledge of the lithospheric structure of the Western Alps, we installed CIFALPS2, a temporary network of 55 broadband seismic stations that operated for ~14 months (2018-2019) across the North-Western Alps (Zhao et al., 2018). The CIFALPS2 line runs from the Eastern Massif Central to the Ligurian coast, across the Mont-Blanc and Gran Paradiso massifs and the Ligurian Alps. Seismic stations were installed along a quasi-linear profile with a spacing of 7-10 km.</p><p>We will show 2 receiver-function CCP (common-conversion point) depth-migrated sections along the CIFALPS2 profile, the first one across the Alps, and the second one across the Ligurian Alps and the Po basin. The time-to-depth migration of RF data is based on the new 3-D Vs model of the Greater Alpine region derived by Nouibat et al. (2021) using transdimensional ambient noise tomography on a large dataset including the AlpArray seismic network. Depth sections across the Vs model are also useful for interpreting the RF CCP sections as they have striking similarities.</p><p>The images of the lithospheric structure of the NW Alps along CIFALPS2 are surprisingly different from those of the SW Alps along CIFALPS. The deepest P-to-S converted phases on the European Moho are detected at 60-65 km depth beneath the Ivrea-Verbano zone, that is 15 km less than on CIFALPS. The negative polarity converted phase interpreted as the base of the Ivrea body mantle flake on the CIFALPS section is still visible on CIFALPS2, but with a lower amplitude. The RF section confirms the existence of a jump of the European Moho of ~10 km amplitude in less than 10 km distance, which is located within a few km from the western boundary of the Mont Blanc external crystalline massif. All these observations are confirmed by the Vs model that also displays a less deep continental subduction than on CIFALPS, weaker S-wave velocities in the Ivrea body wedge, and the jump of the European Moho.</p><p>The Moho beneath the Ligurian Alps is detected at 25-30 km depth both on the RF and on the Vs depth sections. Moving northwards, this Ligurian Moho is separated from the Adriatic Moho by a puzzling S-dipping set of P-to-S converted waves with negative polarity. The crust of the Ligurian Alps is characterized by a set of north-dipping negative-polarity converted waves at 10 to 20 km depth beneath the Valosio massif, which is a small internal crystalline massif of (U)HP metamorphic rocks located north of Voltri. The similarity of this set of negative-polarity conversions to the one observed beneath the Dora Maira massif on the CIFALPS profile suggests that it may be a relic of the Alpine structure overprinted by the opening of the Ligurian sea.</p>

The arc of the Western Alps : understanding its kinematics and formation mechanisms based on new structural and paleomagnetic datas, and thermo-mechanical modelling.

2021 ◽  
Author(s):  
Quentin Brunsmann ◽  
Claudio Rosenberg ◽  
Nicolas Bellahsen ◽  
Laetitia Le Pourhiet
Keyword(s):  
Western Alps ◽  
Strike Slip ◽  
Rheological Parameters ◽  
The South ◽  
Adriatic Plate ◽  
The North ◽  
Field Evidence ◽  
Internal Zone ◽  
The Alps ◽  
East West

<p>The Alps have an overall East-West orientation, which changes radically in their western termination, where they rotate southward into a N-S strike, and then eastward into an E-W strike, forming the arc of the Western Alps. This arc is commonly inferred to have formed during collision, due to indentation of the Adriatic plate into the European continental margin. Several models attempted to provide a kinematic explanation for the formation of this arched, lateral end of the Alps. Indeed, the radial nature of the transport directions observed along the arc of the Western Alps cannot be explained by a classic convergence model.<br>For more than 50 years the formation of this arc was been associated to westward-directed indentation of Adria, accommodated along East-West oriented strike-slip faults, a sinistral one in the South of the arc and a dextral one in the North. The dextral one correspond to the Insubric Fault. The sinistral strike-slip zone, inferred to be localized along the «Stura corridor» (Piedmont, Italy) would correspond to a displacement of 100 to 150 km according to palaeogeographical, and geometric analyses. However, field evidence is scarce and barely documented in the literature.<br>Vertical axis rotations of the Adriatic indenter also inferred to be syn-collisional could have influenced the acquisition of the morphology of the arc. Paleomagnetic analyses carried out in the Internal Zone and in the Po plain suggest a southward increading amount of counter-clockwise rotation of the Adriatic plate and the Internal Zone, varying from 20°-25° in the North to nearly 120° in the South.<br>Dextral shear zones possibly accommodating this rotation in some conceptual models is observed in several places below the Penninic Front and affect the Argentera massif to the south. However, the measured displacement quantities do not appear to be equivalent to those induced by such rotations.<br>The present study aims to constrain the kinematic evolution of the arc of the Western Alps through a multidisciplinary approach. The first aspect of this project is the structural analysis of the area (Stura corridor) inferred to accommodate large sinistral displacements allowing for the westward indentation of the Adriatic indenter. We discuss the general lack of field evidence supporting sinistral strike-slip movements, in contrast to large-scale compilation of structures suggesting the possible occurrence of such displacement. The second part consists of a palaeomagnetic study, in which new data are integred with a compilation of already existing data. This compilation shows that several parts of the arc in the External Zone did not suffer any Cenozoic rotations, hence suggesting that a proto-arc already axisted at the onset collision, as suggested by independent evidence of some paleogeographic reconstruction. Finally, 2D and 3D thermo-mechanical modeling in using the pTatin3D code is used to test which structural (geometrical), and rheological parameters affected the first-order morphology of the Western Alpin arc and its kinematics. The synthesis of these different approaches allows us to propose a new model explaining the kinematics and the mechanisms of formation of the Western Alps arc.</p>

Numerical Simulations of the Formation of Melting-Layer Cloud

2008 ◽  
Vol 136 (1) ◽  
pp. 223-241 ◽  
Author(s):  
Kazuaki Yasunaga ◽  
Akihiro Hashimoto ◽  
Masanori Yoshizaki
Keyword(s):  
Numerical Simulations ◽  
Temperature Profile ◽  
Initial Temperature ◽  
Critical Role ◽  
Middle Level ◽  
Squall Line ◽  
Two Dimensional ◽  
Stable Layer ◽  
Cloud Coverage ◽  
Thin Cloud

Abstract A number of previously published observational studies have reported the common occurrence of cloudy layers at around 5-km elevation in the tropics. There are two candidate processes that are able to explain the occurrence of cloudy layers in the middle level: cloud detrainment promoted by the stable layer and enhanced condensation to compensate for melting cooling. In the present study, the authors used a cloud-resolving nonhydrostatic model and conducted numerical simulations of a squall line to clarify the process responsible for the formation of midlevel thin cloud, especially the cloud at the 0°C level. In a two-dimensional control experiment thin cloud was simulated in the middle level, and cloud coverage showed a notable peak just below the 0°C level for environments without a stable layer in the initial temperature profile. Enhanced and weakened stability layers simultaneously appeared above and below the peak level of the cloud coverage. The formation of midlevel thin cloud is associated with intensified condensation to compensate for strong cooling due to the melting of ice particles. The enhancement of condensation continues until ice is no longer provided to the cloud at the melting level. This means that the cloud survives for a longer period than cloud at other levels. To investigate the influence of the commonly observed tropical stable layer on the occurrence of midlevel thin cloud, the authors performed three sensitivity tests in which a warm rain microphysics scheme was employed and/or the initial temperature profile had enhanced and weakened stability layers in the middle level. Comparisons among the control and sensitivity experiments revealed that intensified condensation related to melting cooling plays a critical role in the formation of midlevel thin cloud, although the stable layer is associated with the inhibition of convection growth in the middle level. A three-dimensional experiment under more realistic conditions simulated cloud formation at the 0°C level, although the peak of the cloud coverage was less prominent than those in the two-dimensional experiments.

Historical Land Uses and Their Changes in the European Alps

2019 ◽  
Author(s):  
Ulrike Tappeiner ◽  
Erich Tasser
Keyword(s):  
Land Use ◽  
20Th Century ◽  
Land Reclamation ◽  
Alpine Region ◽  
Ecosystem Functions ◽  
Mountain Range ◽  
European Alps ◽  
Ligurian Sea ◽  
Arable Farming ◽  
The Alps

The Alps are the highest and largest mountain range in Europe. They extend from the Ligurian Sea to the Pannonian Basin in an arc 744 miles (1,200 km) long and between 93 and 155 miles (150–250 km) wide. The settlement history of this large European landscape is closely linked to the settlement of Europe as a whole, whereby the inner Alpine region was not permanently settled until around 4500 bce because of topographical and climatic disadvantages. Dense forest cover initially made it difficult to use large grazing areas, but transhumance gradually developed in the Alpine region when the animals spent their summers high up in the mountains and their winters in the valleys. At about the same time, the Alpine self-sufficiency economy of arable farming and livestock breeding was added, which made permanent settlement possible. However, the most intensive settlement and land reclamation advance took place in the Middle Ages. In the 19th century, industrialization reached the Alpine region a little delayed, and globalization in the middle of the 20th century. This also led to a fundamental change in society. The previous agricultural society was replaced by the service society of the 20th century. Developments since the late 1950s have taken place against the background of developments in the European Union (EU) as a whole, above all the Common Agricultural Policy and the European Spatial Development Perspective (ESDP), but these developments were and still are influenced by additional agreements specific to the Alps, such as the Alpine Convention, the Alpine Protection Commission (CIPRA), and the Alpine Working Community (Arge Alp). All these factors mean that historical and current development of land use in the Alpine region has been and is always linked to developments in Europe. Many studies on land use in the Alpine region should therefore be seen in this context. Moreover, past land use often has long-lasting legacy effects on ecosystems and their development. Therefore, in this article we deal not only with historical land use but also with current and future developments and their impacts on ecosystem functions and services.

scholarly journals Climatic variability of the mean flow and stationary planetary waves in the NCEP/NCAR reanalysis data

2008 ◽  
Vol 26 (5) ◽  
pp. 1233-1241 ◽  
Author(s):  
A. Yu. Kanukhina ◽  
E. V. Suvorova ◽  
L. A. Nechaeva ◽  
E. K. Skrygina ◽  
A. I. Pogoreltsev
Keyword(s):  
Lower Stratosphere ◽  
Climatic Variability ◽  
Reanalysis Data ◽  
Planetary Waves ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Mean Flow ◽  
The Mean ◽  
The 1960S ◽  
Environmental Prediction

Abstract. NCEP/NCAR (National Center for Environmental Prediction – National Center for Atmospheric Research) data have been used to estimate the long-term variability of the mean flow, temperature, and Stationary Planetary Waves (SPW) in the troposphere and lower stratosphere. The results obtained show noticeable climatic variabilities in the intensity and position of the tropospheric jets that are caused by temperature changes in the lower atmosphere. As a result, we can expect that this variability of the mean flow will cause the changes in the SPW propagation conditions. The simulation of the SPW with zonal wave number m=1 (SPW1), performed with a linearized model using the mean flow distributions typical for the 1960s and for the beginning of 21st century, supports this assumption and shows that during the last 40 years the amplitude of the SPW1 in the stratosphere and mesosphere increased substantially. The analysis of the SPW amplitudes extracted from the geopotential height and zonal wind NCEP/NCAR data supports the results of simulation and shows that during the last years there exists an increase in the SPW1 activity in the lower stratosphere. These changes in the amplitudes are accompanied by increased interannual variability of the SPW1, as well. Analysis of the SPW2 activity shows that changes in its amplitude have a different sign in the northern winter hemisphere and at low latitudes in the southern summer hemisphere. The value of the SPW2 variability differs latitudinally and can be explained by nonlinear interference of the primary wave propagation from below and from secondary SPW2.

Description of three new species of Trichoceridae (Diptera, Nematocera) from nothern Sweden and the Alps

1976 ◽  
Vol 7 (1) ◽  
pp. 59-65 ◽  
Author(s):  
Christine Dahl
Keyword(s):  
New Species ◽  
Central Europe ◽  
Light Trap ◽  
Western Alps ◽  
Northern Sweden ◽  
The Alps ◽  
Three New Species

AbstractThree new species of the genus Trichocera are described: T.(T.) implicata n.sp., T.(T.) mendli n.sp., both from northern Sweden and the western Alps, and T.(M.) candida n.sp. from the western Alps. The descriptions are based on males only. The material comes mainly from light-trap collections and it is difficult to assign the females to the species described. Whether T. implicata and T. mendli really represent a boreo-alpine element is uncertain as practically no collections of trichocerids from the mountainous parts of Central Europe exist.

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