A case‐study is presented of a south foehn emanating from the Wipp Valley, Austria, which encountered a cold‐air pool (CAP) in the Inn Valley near the city of Innsbruck. The analysis is based on data ...collected during the second Intensive Observation Period of the Penetration and Interruption of Alpine Foehn (PIANO) field experiment. Foehn was initiated on 3 November 2017 by an eastward moving trough and terminated in the afternoon of 5 November 2017 by a cold front passage. On two occasions, reversed foehn flow deflected at the mountain ridge north of Innsbruck penetrated to the bottom of the Inn Valley. The first breakthrough occurred in the afternoon of 4 November 2017. It was transient and locally limited to the northwest of the city. The second (final) breakthrough occurred in the morning of 5 November 2017 and was recorded by all surface stations in the vicinity of Innsbruck. It started with a foehn air intrusion to the northeast of Innsbruck and continued with the westward propagation of the foehn–CAP boundary along the valley. Subsequently observed northerly winds above the city were caused by an atmospheric rotor. A few hours later and prior to the cold front passage, the CAP pushed back and lifted the foehn air from the ground. During both nights, shear flow instabilities formed at the foehn–CAP interface, which resulted in turbulent heating of the CAP and cooling of the foehn. However, this turbulent heating/cooling was partly compensated by other mechanisms. Especially in the presence of strong spatial CAP heterogeneity during the second night, heating in the CAP was most likely overcompensated by negative horizontal temperature advection.
A case‐study is presented of a south foehn emanating from the Wipp Valley, Austria, which encountered a cold‐air pool in the Inn Valley near the city of Innsbruck. The goal is to investigate small‐scale processes that govern the breakthrough of foehn in the valley based on observations collected during the PIANO field experiment. The study evaluates the contribution of shear flow instabilities (illustrated in the figure) and temperature advection to the heat budget of the cold‐air pool.
Processes of cold‐air pool (CAP) erosion in an Alpine valley during south foehn are investigated based on a real‐case large‐eddy simulation (LES). The event occurred during the second Intensive ...Observation Period (IOP 2) of the PIANO field experiment in the Inn Valley, Austria, near the city of Innsbruck. The goal is to clarify the role of advective versus turbulent heating, the latter often being misrepresented in mesoscale models. It was found that the LES of the first day of IOP 2 outperforms a mesoscale simulation, is not yet perfect, but is able to reproduce the CAP evolution and structure observed on the second day of IOP 2. The CAP exhibits strong heterogeneity in the along‐valley direction. It is weaker in the east than in the west of the city with a local depression above the city. This heterogeneity results from different relative contributions and magnitudes of turbulent and advective heating/cooling, which mostly act against each other. Turbulent heating is important for faster CAP erosion in the east and advective cooling is important for CAP maintenance to the west of Innsbruck. The spatial heterogeneity in turbulent erosion is linked to splitting of the foehn into two branches at the mountain range north of the city, with a stronger eastward deflected branch. Intensification of the western branch at a later stage leads to complete CAP erosion also to the west of Innsbruck. Above the city centre, turbulent heating is strongest, and so is advective cooling by enhanced pre‐foehn westerlies. These local winds are the result of CAP heterogeneity and gravity‐wave asymmetry. This study emphasizes the importance of shear‐flow instability for CAP erosion. It also highlights the large magnitudes of advective and turbulent heating compared to their net effect, which is even more pronounced for individual spatial components.
Turbulent erosion of a cold‐air pool in the Austrian Inn Valley during foehn is investigated based on a large‐eddy simulation and a comprehensive heat budget analysis. It is found that cold‐pool erosion is governed by a complicated interplay between turbulent and advective heating/cooling that is strongly variable in time and space. The figure illustrates turbulent cold‐pool erosion by shear‐flow instability induced by the foehn flow.
Numerical simulations are performed to assess the influence of horizontal and vertical model resolution on the turbulent erosion of a cold-air pool (CAP) by foehn winds in an Alpine valley near ...Innsbruck, Austria. Strong wind shear in the transition zone from the CAP to the overlying foehn generates turbulence by shear-flow instability and contributes to the CAP erosion. The sensitivity of this process to grid resolution in the "grey zone" of turbulence is studied with the Weather Research and Forecasting model in large-eddy simulation (LES) mode with a horizontal grid spacing of 200, 40, and 13.33 m and in mesoscale mode with a grid spacing of 1 km. Moreover, two different vertical resolutions are tested. The mesoscale simulation exhibits deficiencies in the CAP development and is neither able to resolve nor parametrize the effect of Kelvin-Helmholtz (K-H) instability. In contrast, the LES with the coarsest horizontal grid spacing begins to explicitly permit K-H instability, albeit individual K-H waves are not completely resolved, and thereby greatly improves the stability and wind profile of the foehn. Refining the LES grid spacing leads to a more explicit and realistic representation of turbulence, but surprisingly has little impact on mean quantities. An increase in the vertical resolution shows the greatest benefit in the turbulent upper part of the foehn jet, whereas an increase in the horizontal resolution improves the turbulence characteristics, especially at the foehn-CAP interface. However, spectral analysis indicates that even a horizontal grid spacing of 40 m does not fully capture the energy cascade in the inertial subrange. Eddies remain too large and foehn-CAP interaction is too vigorous compared with the simulation with 13.33 m grid spacing. Nevertheless, results illustrate the potential benefit of an
(100 m) model resolution for improving numerical weather predictions in complex terrain.
Numerical simulations are performed to assess the influence of horizontal and vertical model resolution on the turbulent erosion of a cold‐air pool (CAP) by foehn winds in an Alpine valley near ...Innsbruck, Austria. Strong wind shear in the transition zone from the CAP to the overlying foehn generates turbulence by shear‐flow instability and contributes to the CAP erosion. The sensitivity of this process to grid resolution in the “grey zone” of turbulence is studied with the Weather Research and Forecasting model in large‐eddy simulation (LES) mode with a horizontal grid spacing of 200, 40, and 13.33 m and in mesoscale mode with a grid spacing of 1 km. Moreover, two different vertical resolutions are tested. The mesoscale simulation exhibits deficiencies in the CAP development and is neither able to resolve nor parametrize the effect of Kelvin–Helmholtz (K–H) instability. In contrast, the LES with the coarsest horizontal grid spacing begins to explicitly permit K–H instability, albeit individual K–H waves are not completely resolved, and thereby greatly improves the stability and wind profile of the foehn. Refining the LES grid spacing leads to a more explicit and realistic representation of turbulence, but surprisingly has little impact on mean quantities. An increase in the vertical resolution shows the greatest benefit in the turbulent upper part of the foehn jet, whereas an increase in the horizontal resolution improves the turbulence characteristics, especially at the foehn–CAP interface. However, spectral analysis indicates that even a horizontal grid spacing of 40 m does not fully capture the energy cascade in the inertial subrange. Eddies remain too large and foehn–CAP interaction is too vigorous compared with the simulation with 13.33 m grid spacing. Nevertheless, results illustrate the potential benefit of an 𝒪(100 m) model resolution for improving numerical weather predictions in complex terrain.
Shear‐flow instability is found to be an important process of cold‐air pool erosion by foehn winds. Compared with a large‐eddy simulation with a horizontal mesh size of 13 m, the effect of this turbulent process is much better represented at a 200 m grid size (although not fully resolved) than parametrized at a kilometre resolution. It is concluded that 𝒪(100 m) model resolution will improve numerical weather predictions in complex terrain.
Processes of cold‐air pool (CAP) erosion in an Alpine valley during south foehn are investigated based on a real‐case large‐eddy simulation (LES). The event occurred during the second Intensive ...Observation Period (IOP 2) of the PIANO field experiment in the Inn Valley, Austria, near the city of Innsbruck. The goal is to clarify the role of advective versus turbulent heating, the latter often being misrepresented in mesoscale models. It was found that the LES of the first day of IOP 2 outperforms a mesoscale simulation, is not yet perfect, but is able to reproduce the CAP evolution and structure observed on the second day of IOP 2. The CAP exhibits strong heterogeneity in the along‐valley direction. It is weaker in the east than in the west of the city with a local depression above the city. This heterogeneity results from different relative contributions and magnitudes of turbulent and advective heating/cooling, which mostly act against each other. Turbulent heating is important for faster CAP erosion in the east and advective cooling is important for CAP maintenance to the west of Innsbruck. The spatial heterogeneity in turbulent erosion is linked to splitting of the foehn into two branches at the mountain range north of the city, with a stronger eastward deflected branch. Intensification of the western branch at a later stage leads to complete CAP erosion also to the west of Innsbruck. Above the city centre, turbulent heating is strongest, and so is advective cooling by enhanced pre‐foehn westerlies. These local winds are the result of CAP heterogeneity and gravity‐wave asymmetry. This study emphasizes the importance of shear‐flow instability for CAP erosion. It also highlights the large magnitudes of advective and turbulent heating compared to their net effect, which is even more pronounced for individual spatial components.
This study represents the first detailed analysis of multi-year, near-surface turbulence observations for an urban area located in highly complex terrain. Using 4 years of eddy covariance ...measurements over the Alpine city of Innsbruck, Austria, the effects of the urban surface, orographic setting and mountain weather on energy and mass exchange are investigated. In terms of surface controls, the findings for Innsbruck are in accordance with previous studies at city centre sites. The available energy is partitioned mainly into net storage heat flux and sensible heat flux (each comprising about 40 % of the net radiation, Q*, during the daytime in summer). The latent heat flux is small by comparison (only about 10 % of Q*) due to the small amount of vegetation present but increases for short periods (6–12 h) following rainfall. Additional energy supplied by anthropogenic activities and heat
released from the large thermal mass of the urban surface helps to support positive sensible heat fluxes in the city all year round. Annual observed CO2 fluxes (5.1 kg C m−2 yr−1) correspond well to modelled emissions and expectations based on findings at other sites with a similar proportion of vegetation. The net CO2 exchange is dominated by anthropogenic emissions from traffic in summer and building heating in winter. In contrast to previous urban observational studies, the effect of the orography is examined here. Innsbruck's location in a steep-sided valley results in marked diurnal and seasonal patterns in flow conditions. A typical valley wind circulation is observed (in the absence of strong synoptic forcing) with moderate up-valley winds during daytime, weaker down-valley winds at night (and in winter) and near-zero wind speeds around
the times of the twice-daily wind reversal. Due to Innsbruck's location north of the main Alpine crest, southerly foehn events frequently have a marked effect on temperature, wind speed, turbulence and pollutant concentration. Warm, dry foehn air advected over the surface can lead to negative sensible
heat fluxes both inside and outside the city. Increased wind speeds and intense mixing during foehn (turbulent kinetic energy often exceeds 5 m2 s−2) help to ventilate the city, illustrated here by low CO2 mixing ratios. Radiative exchange is also affected by the orography – incoming shortwave radiation is blocked by the terrain at low solar elevation. The interpretation of the dataset is complicated by distinct temporal patterns in flow conditions and the combined influences of the urban environment, terrain and atmospheric conditions. The analysis presented here reveals how Innsbruck's mountainous setting impacts the near-surface conditions in multiple ways, highlighting the similarities with
previous studies in much flatter terrain and examining the differences in order to begin to understand interactions between urban and orographic processes.
European buckthorn (
Rhamnus cathartica), a prevalent invasive shrub in relict woodlands throughout Northeastern Illinois, alters certain soil properties in a manner that may have importance for the ...long-term conservation management of these systems. We found that soil in areas of the woodland where buckthorn dominates have higher percentage of nitrogen (N) and carbon (C), modified nitrogen mineralization rates, elevated pH, and higher soil moisture than those areas where buckthorn was not present. Although there were small C:N ratio differences at two of the three sites, there was no overall difference in C:N ratios between the sites. Since the long-term management for these systems often calls for restoration to pre-invaded conditions, the likelihood that the invasive shrub is creating a legacy effect of altered ecosystems properties may call for reassessed management strategies.
As the findings of many studies have shown,
different aspects of children's home literacy environment are related to
the development of their language competence. We designed the Home Literacy
...Environment Questionnaire (HLEQ) to evaluate the quality of different
aspects of the home literacy environment. This paper presents the development
of this instrument, including: (1) the construction of the instrument
based on the theoretical background and findings about the relation between
family environment and child language development; (2) examination of
the construct validity of the HLEQ and (3) an evaluation of its
empirical criterion validity through correlations with children's
achievements on a language development scale and their storytelling ability.
Language competence was assessed with a sample of 4-year-old
children that attended a Slovenian preschool. Using factor analysis, five HLEQ
factors were identified: Stimulation to use language, explanation
(F1), Reading books to the child, visiting the library and puppet
theater (F2), Joint activities and conversation (F3),
Interactive reading (F4) and
Zone-of-proximal-development stimulation (F5).
The findings show that some aspects of the home literacy environment (F2,
F4 and F5) are positively related to different measures of child language
development at 4 years of age and also contribute to a prediction of child
language competence. Four HLEQ factors (F1, F2, F3, and F5) were also
positively related to maternal level of education.
Many studies show that play represents an important context for the development of child's language, communication skills & competence, & is often accompanied by complex language interactions. The ...purpose of our study was to evaluate children's use of language during three different pre-school activities: free play, routine activity & guided activity. The sample included 60 preschool children, aged 4 to 5 years who attended one of 3 preschool institutions. Children's speech was recorded during each of the three daily activities in the pre-school institution. The results of the structural & functional analysis show significant differences in many of the characteristics of children's speech during each of the three activities. Children spoke significantly more, used more multi-word utterances, interrogative & negative clauses, as well as used their language more frequently in the symbolic & regulatory function during free play than during routine & guided activity. The results show no significant differences between girls & boys in their free speech during the three pre-school activities. 3 Tables, 3 Figures, 17 References. Adapted from the source document
PDF
