Foehn Research Articles

Experimental evaluation of concrete shrinkage deformation under the influence of foehn wind in vietnam

Foehn wind or foehn effect is a hot dry wind type blowing down from the mountains. It appears in the middle of Vietnam from early April to mid-September every year. The foehn effect has characteristic humidity drops deeply while the temperature rises. This has affected the concrete shrinkage deformation in the work construction. This paper presented an experimental study to evaluate the concrete shrinkage deformation under the influence of the Foehn wind in Vietnam. The experiment was performed in a simulated environment with temperatures high and humidity down, which is intended to simulate the phenomenon of foehn wind and climate change in the middle of Vietnam. The datasets obtained from this experiment were tested with previous results, it was highly accurate and reliable. The research obtained results have reflected that the concrete shrinkage deformation in foehn wind conditions has a significant effect compared to normal conditions in both the value and speed. In addition, this test also shows that the concrete shrinkage deformation with Ca(OH)2 added to in the mixture is smaller than concrete without Ca(OH)2.

The surface energy balance during foehn events at Joyce Glacier, McMurdo Dry Valleys, Antarctica

Abstract. The McMurdo Dry Valleys (MDV) are a polar desert, where glacial melt is the main source of water to streams and the ecosystem. Summer air temperatures are typically close to zero, and therefore foehn events can have a large impact on the meltwater production. A 14-month record of automatic weather station (AWS) data on Joyce Glacier is used to force a 1D surface energy balance model to study the impact of foehn events on the energy balance. AWS data and output of the Antarctic Mesoscale Prediction System (AMPS) on a 1.7 km grid are used to detect foehn events at the AWS site. Foehn events at Joyce Glacier occur under the presence of cyclones over the Ross Sea. The location of Joyce Glacier on the leeward side of the Royal Society Range during these synoptic events causes foehn warming through isentropic drawdown. This mechanism differs from the foehn warming through gap flow that was earlier found for other regions in the MDV and highlights the complex interaction of synoptic flow with local topography of the MDV. Shortwave radiation is the primary control on melt at Joyce Glacier, and melt often occurs with subzero air temperatures. During foehn events, melt rates are enhanced, contributing to 23 % of the total annual melt. Foehn winds cause a switch from a diurnal stability regime in the atmospheric surface layer to a continuous energy input from sensible heat flux throughout the day. The sensible heating during foehn, through an increase in turbulent mixing resulting from gustier and warmer wind conditions, is largely compensated for by extra heat losses through sublimation. Melt rates are enhanced through an additional energy surplus from a reduced albedo during foehn.

A Comparative Analysis of Characteristics and Synoptic Backgrounds of Extreme Heat Events over Two Urban Agglomerations in Southeast China

Based on high-resolution surface observation and reanalysis data, this paper analyzes the extreme heat events (EHEs) over two densely populated urban agglomerations in southeast China, namely the Yangtze River Delta (YRD) and the Pearl River Delta (PRD), including the spatial–temporal distribution of heatwaves and warm nights and the synoptic backgrounds for regional heatwaves. The results show that the occurrence frequency of EHEs is modulated significantly by local underlying features (i.e., land–sea contrast, terrain), and the strong nocturnal urban heat island effects make warm nights much more likely to occur in cities than rural areas during heatwaves. About 80% of the YRD regional heatwaves occur from 15 July to 15 August, while a lower fraction (53%) of the PRD heatwaves is found during this mid-summer period, which partially explains the warm-season average intensity of the former being 2–3 times the latter. A persistent, profound subtropical high is the dominant synoptic system responsible for the mid-summer YRD heatwaves, which forces significant descending motion leading to long-duration sunny weather. The mid-summer PRD heatwaves involve both high-pressure systems and tropical cyclones (TCs). A TC is present to the east of the PRD region on most (about 72%) PRD heatwave days. The organized northerly winds in the planetary boundary layer in the outer circulation of the TC transport the inland warm air, which is heated by the foehn effect at the lee side of the Nanling Mountains and possibly also the surface sensible heat flux, towards the PRD region, leading to the occurrence of the extremely high temperatures.

The influence of mountainous relief on the vertical gradient of precipitation and pluvial zoning in the central slope of the Gulf of Mexico

Although variation of air temperature with respect to terrain altitude is widely understood, less is known about the altitudinal behaviour of precipitation. The eastern slope of Mexico is the most contrasting physiographic province of the country due to its relief. This area is also one of the most important regions of Mexico and of the intertropical region of America because of its biodiversity. Due to the vital and ecosystemic value of precipitation, this work seeks to analyse the altitudinal distribution of precipitation as a function of the relief. Our main methodology consisted of analysing the climatological normal of 86 weather stations to determine accumulated precipitation during rainy, dry and annual periods. Precipitation was correlated with the altitude of the relief, which allowed the study area to be divided into groups relative to the degree of accumulated rainfall throughout the year, as well as by the gradient of variation according to the elevation of the terrain. The results indicated that during the year, precipitation was favoured by the humidity of the Gulf of Mexico and decreased at a rate of ‐3.7 mm/m in coastal areas. Subsequently, precipitation increased with the altitude of the relief at a rate of 0.7 mm/m, between ~700 and ~ 1500 masl, which is where the greatest accumulation of rainfall was concentrated. Thereafter, it decreased by ‐0.9 mm/m until it reached the highest volcanic watershed. Crossing this watershed, the foehn effect caused rainfall rates to be much lower than on the windward slope, where the central plateau of the country begins.

Foehn Winds at Pine Island Glacier and their role in Ice Shelf Sublimation and Surface Melt

Foehn Winds at Pine Island Glacier and their role in Ice Shelf Sublimation and Surface Melt

Foehn winds at Pine Island Glacier and their role in ice shelf sublimation and surface melt

Foehn winds at Pine Island Glacier and their role in ice shelf sublimation and surface melt

Future changes of the extreme high‐temperature events influenced by foehn winds in Niigata, Japan

AbstractThis study quantifies the future changes in extreme high‐temperature events (ETE) influenced by foehn winds in Niigata, Japan, using numerical and sensitivity experiments based on regional climate modelling. Numerical simulations suggest that the contribution of foehn winds to ETEs is approximately 3.5°C in both the baseline (past) and future climate, and hence it remains unaffected by future climate change; however, the frequency of ETEs is influenced by foehn winds may increase by a factor of 1.5. This is due to the fact that the pressure gradient between land and sea (i.e., the pressure gradient driving the sea breezes) is expected to decrease during the daytime in the future, making it easier for foehn winds to reach Niigata; it also suggests that foehn winds, due to their high‐pressure pattern, which is easily affected by the weakening of the sea breezes, may increase in the future. Overall, to evaluate the regional effects of climate change, it is necessary to understand how future changes in local circulation will impact future changes in the regional climate.

Machine learning-based prediction of Alpine foehn events using GNSS troposphere products: first results for Altdorf, Switzerland

Abstract. Remote sensing of water vapour using the Global Navigation Satellite System (GNSS) is a well-established technique and reliable data source for numerical weather prediction (NWP). However, one of the phenomena rarely studied using GNSS are foehn winds. Since foehn winds are associated with significant humidity gradients between two sides of a mountain range, tropospheric estimates from GNSS are also affected by their occurrence. Time series reveal characteristic features like distinctive minima and maxima as well as a significant decrease in the correlation between the stations. However, detecting such signals becomes increasingly difficult for large datasets. Therefore, we suggest the application of machine learning algorithms for the detection and prediction of foehn events by means of GNSS troposphere products. This initial study develops a new, machine learning-based method for detection and prediction of foehn events at the Swiss station Altdorf by utilising long-term time series of high-quality GNSS troposphere products. Data from the Automated GNSS Network Switzerland (AGNES) and various GNSS sites from neighbouring countries as well as records of an operational foehn index are used to investigate the performance of several different classification algorithms based on appropriate statistical metrics. The two best-performing algorithms are fine tuned and tested in four dedicated experiments using different feature setups. The results are promising, especially when reprocessed GNSS products are utilised and the most dense station setup is used. Detection- and alarm-based measures reach levels between 66 %–80 % for both tested algorithms and thus are comparable to those from studies using data from meteorological stations and NWP. For operational prediction, limitations due to the availability and quality of GNSS products in near-real time (NRT) exist. However, they might be mitigated to a significant extent by provision of additional NRT products and improved data processing in the future. Results also outline benefits for the results when including geographically relevant stations (e.g. high-altitude stations) in the utilised datasets.

Mesoscale and local‐scale climatology of extreme temperature events in Niigata, Japan

AbstractIn this study, we analysed the characteristics of extreme temperature events (ETEs) that occurred in Niigata City, located in the coastal region of the Sea of Japan. The results show that there was a tropical cyclone (TC) in the vicinity of Japan (in the latitude range of 29.0°–45.8°N and longitude range of 123.2°–139.2°E) on 60% of the days when ETEs occurred in Niigata City (TOP10 days in the past 30 years, 0.09 percentile). Furthermore, the strong east‐southeast to southeast winds caused by the TCs and winds over the mountains reached Niigata City. These results indicate that ETEs in Niigata City are caused by southeasterly foehn winds associated with TCs. It is generally believed that ETEs in Niigata City increase the risk of heatstroke. However, the index for heatstroke risk level is not high despite the extreme temperatures. This is because the downslope winds from the mountains become strong, and humidity decreases during the ETE event. A comparison of the results of this study with those of previous studies shows that the favourable atmospheric conditions for the ETE event and the impact of the ETE on local weather and human life differ greatly between the Pacific and Sea of Japan coasts.

Modeling cloud properties over the 79 N Glacier (Nioghalvfjerdsfjorden, NE Greenland) for an intense summer melt period in 2019

AbstractLong believed to be insignificant, melt activity on the Northeast Greenland Ice Stream (NEGIS) has increased in recent years. Summertime Arctic clouds have the potential to strongly affect surface melt processes by regulating the amount of radiation received at the surface. However, the cloud effect over Greenland is spatially and temporally variable and high‐resolution information on the northeast is absent. This study aims at exploring the potential of a high‐resolution configuration of the polar‐optimized Weather Research & Forecasting Model (PWRF) in simulating cloud properties in the area of the Nioghalvfjerdsfjorden Glacier (79 N Glacier). Subsequently, the model simulations are employed to investigate the impact of Arctic clouds on the surface energy budget and on surface melting during the extensive melt event at the end of July 2019. Compared to automatic weather station (AWS) measurements and remote‐sensing data (Sentinel‐2A and the Moderate Resolution Imaging Spectroradiometer, MODIS), PWRF simulates cloud properties with sufficient accuracy. It appears that peak melt was caused by an increase in solar radiation and sensible heat flux (SHF) in response to a blocking anticyclone and foehn winds in the absence of clouds. Cloud warming over high‐albedo surfaces helped to precondition the surface and prolonged the melting as the anticyclone abated. The results are sensitive to the surface albedo and suggest spatiotemporal differences in the cloud effect as snow and ice properties change over the course of the melting season. This demonstrates the importance of including high‐resolution information on clouds in analyses of ice sheet dynamics.

Temperature and moisture transport during atmospheric blocking patterns around the Antarctic Peninsula

We assess temperature and moisture transport in and around the Antarctic Peninsula (AP) associated with atmospheric blocking over two domains, one located to the west (150–90°W, 50–70°S, Western AP (WAP)) and the other over and to the east (90–30°W, 50–70°S, Eastern AP (EAP)) of the AP. We make use of surface meteorological observations, ERA5 reanalysis data, and a state-of-the-art atmospheric river (AR) database. Observed temperature anomalies indicate that the WAP and EAP blocking patterns are characterized by significant cold and warm anomalies over the AP, respectively, particularly in austral autumn, winter and spring. Consistent with these changes, cold anomalies depicted by ERA5 are associated with the transport of cold and dry air from the Antarctic continent by southerly and southeasterly flow over the eastern flank of the WAP blocking. ERA5 results highlight the importance of blocking days over the EAP domain (largely centered over the Drake Passage) to the occurrence of warm events associated with northerly and northwesterly warm air transport. Significant increases in integrated vapor transport (IVT) and AR frequency are also evident during the EAP blocking, particularly on the windward side of the AP. During the most extreme blocking days in this domain, there exist significant increases in latent and sensible heat fluxes on the windward side of the AP and the Larsen C Ice Shelf, respectively, indicating the contribution of foehn events to warm anomalies, especially in austral autumn and winter. The co-occurrences between landfalling ARs and blocking are found to amplify foehn effect due to higher IVT and associated latent heat condensation compared to blocking days without ARs. We conclude that blocking patterns are important to understand the occurrence of extremely warm events and landfalling ARs in the AP and their potential impacts on the surface cryospheric processes.

The Impact of Foehn Wind on Mental Distress among Patients in a Swiss Psychiatric Hospital.

Psychiatric patients are particularly vulnerable to strong weather stimuli, such as foehn, a hot wind that occurs in the alps. However, there is a dearth of research regarding its impact on mental health. This study investigated the impact of foehn wind among patients of a psychiatric hospital located in a foehn area in the Swiss Alps. Analysis was based on anonymized datasets obtained from routine records on admission and discharge, including the Brief Symptom Checklist (BSCL) questionnaire, as well as sociodemographic parameters (age, sex, and diagnosis). Between 2013 and 2020, a total of 10,456 admission days and 10,575 discharge days were recorded. All meteorological data were extracted from the database of the Federal Office of Meteorology and Climatology of Switzerland. We estimated the effect of foehn on the BSCL items using a distributed lag model. Significant differences were found between foehn and non-foehn admissions in obsession–compulsion, interpersonal sensitivity, depression, anxiety, phobic anxiety, paranoid ideation, and general severity index (GSI) (p < 0.05). Our findings suggest that foehn wind events may negatively affect specific mental health parameters in patients. More research is needed to fully understand the impact of foehn’s events on mental health.

Ecoclimates

One of the greatest challenges to mankind is understanding the underlying principles of climate change. Over the last years, the role of forests in climate change has received increased attention. This is due to the observation that not only the atmosphere has a principal impact on vegetation growth but also that vegetation is contributing to local variations of weather resulting in diverse microclimates. The interconnection of plant ecosystems and weather is described and studied as ecoclimates. In this work we take steps towards simulating ecoclimates by modeling the feedback loops between vegetation, soil, and atmosphere. In contrast to existing methods that only describe the climate at a global scale, our model aims at simulating local variations of climate. Specifically, we model tree growth interactively in response to gradients of water, temperature and light. As a result, we are able to capture a range of ecoclimate phenomena that have not been modeled before, including geomorphic controls, forest edge effects, the Foehn effect and spatial vegetation patterning. To validate the plausibility of our method we conduct a comparative analysis to studies from ecology and climatology. Consequently, our method advances the state-of-the-art of generating highly realistic outdoor landscapes of vegetation.

Causes of the Extreme Hot Event on February 9, 2020, in Seymour Island, Antarctic Peninsula

On early February of 2020, two consecutive extreme warming events of three day interval at the similar location occurred over the Antarctic Peninsula (AP). The later event, that occurred on February 9, 2020, exhibited a second-highest temperature record of 15.5°C at Marambio station, located on Seymour Island, northeast of the AP. To understand the possible cause of the extreme warming event, we analyzed extreme warming events that occurred on Seymour Island during February over the past 40 years by using observational data from Marambio station alongside the European Center for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) data. The results revealed that the extreme warming event on February 9, 2020 occurred due to the foehn and large-scale horizontal advection. In foehn winds, radiative heating and isentropic drawdown occur simultaneously. The horizontal advection of heat, which leads to extreme warming events, is associated with the strong blocking high in the upper and lower atmosphere. Contrary to the average characteristics of extreme warming events in February over the past 40 years, the extreme warming on February 9, 2020, occurred not only in the AP but also throughout entire West Antarctica.

A 20‐Year Study of Melt Processes Over Larsen C Ice Shelf Using a High‐Resolution Regional Atmospheric Model: 1. Model Configuration and Validation

AbstractFollowing collapses of the neighboring Larsen A and B ice shelves, Larsen C has become a focus of increased attention. Determining how the prevailing meteorological conditions influence its surface melt regime is of paramount importance for understanding the dominant processes causing melt and ultimately for predicting its future. To this end, a new, high‐resolution (4 km grid spacing) Met Office Unified Model (MetUM) hindcast of atmospheric conditions and surface melt processes over the central Antarctic Peninsula is introduced. The hindcast is capable of simulating observed near‐surface meteorology and surface melt conditions over Larsen C. In contrast with previous model simulations, the MetUM captures the observed east‐west gradient in surface melting associated with foehn winds, as well as the interannual variability in melt shown in previous observational studies. As exemplars, we focus on two case studies—the months preceding the collapse of the Larsen B ice shelf in March 2002 and the high foehn, high melt period of March‐May 2016—to test the hindcast's ability to reproduce the atmospheric effects that contributed to considerable melting during those periods. The results suggest that the MetUM hindcast is a useful tool with which to explore the dominant causes of surface melting on Larsen C.

Influence of grid resolution of large-eddy simulations on foehn-cold pool interaction.

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.

Modelling daily air temperature at a fine spatial resolution dealing with challenging meteorological phenomena and topography in Switzerland

AbstractEpidemiological studies investigating the relationship between air temperature or heat and health, still, by and large, rely on either information from the nearest weather station or on coarse gridded temperature predictions, thereby ignoring small‐scale intra‐urban variations. Recent methodological advances show promise in achieving high spatiotemporal temperature predictions, thus improving the characterization of spatial variations in temperature and decreasing bias in health studies. Here, we applied a two‐stage approach using random forest to (a) impute missing moderate resolution imaging spectroradiometer (MODIS) land surface temperature at a 1 × 1 km resolution and (b) to use the gap‐filled MODIS data to explain spatiotemporal variation in the measured ground‐based air temperature data at a 100 × 100 m resolution across Switzerland using a range of predictor variables, including meteorological parameters, normalized difference vegetation index, impervious surface and altitude. Models presented here managed to capture temporal and spatial variations in air temperature in Switzerland from 2003 to 2018 at a fine spatial resolution of 100 × 100 m. Stage 1 models achieved an overall R2 of 0.98 and a root mean squared error (RMSE) of 1.49°C (independent validation), and the stage 2 model performed well for all years with R2 and RMSE ranging from 0.94 to 0.99 and 1.05 to 1.86°C, respectively. We were also able to capture the urban heat island effect and some typical weather phenomena caused by Switzerland's complex topography, like the foehn effect and inversion conditions. The resulting daily temperature surfaces for 2003–2018 will facilitate ongoing epidemiological research investigating the health effects of heat.

The foehn effect during easterly flow over Svalbard

Abstract. This article presents a comprehensive analysis of the foehn episode which occurred over Svalbard on 30–31 May 2017. This episode is well documented by multiplatform measurements carried out during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) and Physical feedbacks of Arctic PBL, Sea ice, Cloud And AerosoL (PASCAL) campaigns. Both orographic wind modification and foehn warming are considered here. The latter is found to be primarily produced by the isentropic drawdown, which is evident from observations and mesoscale numerical modeling. The structure of the observed foehn warming was in many aspects very similar to that for foehns over the Antarctic Peninsula. In particular, it is found that the warming was proportional to the height of the mountain ridges and propagated far downstream. Also, a strong spatial heterogeneity of the foehn warming was observed with a clear cold footprint associated with gap flows along the mountain valleys and fjords. On the downstream side, a shallow stably stratified boundary layer below a well-mixed layer formed over the snow-covered land and cold open water. The foehn warming downwind of Svalbard strengthened the north–south horizontal temperature gradient across the ice edge near the northern tip of Svalbard. This suggests that the associated baroclinicity might have strengthened the observed northern tip jet. A positive daytime radiative budget on the surface, increased by the foehn clearance, along with the downward sensible heat flux provoked accelerated snowmelt in the mountain valleys in Ny-Ålesund and Adventdalen, which suggests a potentially large effect of the frequently observed Svalbard foehns on the snow cover and the glacier heat and mass balance.

Orographic Flow Influence on Precipitation During an Atmospheric River Event at Davis, Antarctica

AbstractIntense snowfall sublimation was observed during a precipitation event over Davis in the Vestfold Hills, East Antarctica, from 08 to 10 January 2019. Radar observations and simulations from the Weather Research and Forecasting model revealed that orographic gravity waves (OGWs), generated by a north‐easterly flow impinging on the ice ridge upstream of Davis, were responsible for snowfall sublimation through a foehn effect. Despite the strong meridional moisture advection associated with an atmospheric river (AR) during this event, almost no precipitation reached the ground at Davis. We found that the direction of the synoptic flow with respect to the orography determined the intensity of OGWs over Davis, which in turn directly influenced the snowfall microphysics. We hypothesize that turbulence induced by the OGWs likely enhanced the aggregation process, as identified thanks to dual‐polarization and dual‐frequency radar observations. This study suggests that despite the intense AR, the precipitation distribution was determined by local processes tied to the orography. The mechanisms found in this case study could contribute to the extremely dry climate of the Vestfold Hills, one of the main Antarctic oases.

Modeling Thermal Environment Responses to Terrain and Urbanization of Metropolis

Thermal environment responses to terrain and urbanization of Beijing, a metropolis of China, were simulated by the Weather Research and Forecasting model (WRF) with the single-layer Urban Canopy model (UCM). Four numerical experiments were designed: (1) the control experiment (Control exp), (2) no-terrain sensitive experiment (No-Terrain exp), (3) no-urban surface sensitive experiment (No-Urban exp), and (4) real land surface sensitive experiment (LU exp). Results indicate that better near-surface air temperature simulations were obtained after using MODIS land surface type product data MCD12Q1. The foehn effect due to northwestern mountains in Beijing were simulated to intensify the high temperature intensity in the plain area. Urban heat island effect existed in this area day and night, and the heat island intensity in the nighttime was obviously greater than that in the daytime. As a result of urbanization, the nighttime temperature had risen by 1.5∼3.5 °C and the expansion range of nighttime high temperature areas was basically consistent with the urban expansion range.