Mountain Meteorology

The effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and seasonality. Over the ocean, small rain and large sea spray droplets co-exist in the same diameter size class (0.072 to 1000 mm); hence, sea spray creates uncertainty when seeking to characterize the drop size distribution (DSD) of rain droplets over the ocean. We measured droplet sizes at a marine tower using a state-of-the-art optical disdrometer, a tipping-bucket rain gauge, a wind anemometer, and a time-lapse camera, over a period that included typhoon Krosa of 2019. The number of rain droplets of diameter less than 1 mm increased monotonically as the horizontal wind speed became stronger. Thus, the shape parameter μ of the Ulbrich distribution decreased. This decreasing trend can be ...

0h-5h), NW durante a manhã (6h-11h), S durante a tarde(12h-17h) e SW durante a noite (18h-23h). 2-Os ventos foram predominantemente fracos. A velocidade predominate oscilou entre 1 e 3kt (50,6%), sendo que as máximas atingiram valores superiores a 10kt. Os valores mais elevados ocorreram no período noturno, onde atingiram seu pico as 18h. Os ventos foram mais intensos no início da época chuvosa (setembro e outubro). 3-As chuvas a cada hora são predominantemente fracas(44%), ocorrendo com maior frequências no período da tarde(60%), com pico entre as 15-16h.

A deep snow pack, remote locations, no external power supply and very low temperatures are often the main ingredients when it comes to the deployment of meteorological stations in mountainous terrain. The accurate position of the sensor related to the snow surface is normally not known. A new device called METLIFT overcomes the problems. WMO recommends a height between 1.2 m and 2 m above ground level for the measurement of air temperature and humidity. The height above ground level is specified to take care of the possible strong vertical temperature and humidity gradients at the lowest layers in the atmosphere. Especially in snow rich and remote locations it may be hardly possible to follow this advice. Therefore most of the meteorological stations in mountainous terrain are situated at mountain tops where strong winds will blow off the snow or in valleys where a daily inspection of the sensors is possible. In other unpopulated mountainous areas, e.g. basins, plateaus, the distanc...

The interaction of katahatic winds with ambient winds has been investigated for an idealized valley using Clark's nonhydrostatic model. Ambient ridgetop wind speeds ranged from 0.5 to 6 m/s. and made angles with the valley axis rangin, 0 from 0" to 90": cooling of the valley was based on measured values of sensible heat fluxes taken from observations in Colorado's Brush Creek Valley. The depth and strength of the down-valley winds decreased with increasing ambient wind speeds but showed relatively little sensitivity to wind directions in the range of 10" to 6O" from the valley axis. An observed inverse linear decrease of drainage depth with wind speed in a 100 m thick layer above the ridgetops was also found in the simulations for parts of the valley but not near the valley mouth. Vertical motions over the valley showed marked patchiness, and implications of this structure on valley flow dynamics are discussed.

High resolution meteorological fields have been found potentially useful for hydrological and agricultural applications and mitigation of hydro-meteorological hazards such as landslide and snow avalanches. These meteorological fields are being generated for Himalaya using Weather Research and Forecast (WRF) model with spatial resolution up to 3 km. However, gridded meteorological data of sub-kilometer resolution is not available for the Himalayan region. In the present study, Numerical Weather Prediction model-WRF has been configured for NorthWest (N-W) Himalayan region with spatial resolution of 2 km and run in hind cast mode to generate meteorological data of 11 winters (2009-19). Artificial neural networks (ANNs) have been developed for post-processing of maximum temperature, minimum temperature, wind speed, relative humidity, snow depth and snowfall in 24h generated by the WRF model using observed surface weather data of five different locations in Chowkibal-Tangdhar (C-T) region. Post-processed WRF output has been spatially interpolated to a grid resolution of 90 m using quasi-physical relations and inverse distance weighing scheme. The ultra-high resolution meteorological fields generated over the C-T domain have been validated at five locations in the C-T region for two winters (2017-19). For all five stations, the Nash-Sutcliffe Efficiency (NSE) scores of the model for maximum and minimum temperature, relative humidity and snow depth has been found at "very good" level (> 0.75) with considerably high Heidke Skill Score (HSS) (> 0.4). A comparison of observed and simulated cumulative snowfall during major snow storms during 2017-19 has also been discussed.

High resolution meteorological fields have been found potentially useful for hydrological and agricultural applications and mitigation of hydro-meteorological hazards such as landslide and snow avalanches. These meteorological fields are being generated for Himalaya using Weather Research and Forecast (WRF) model with spatial resolution up to 3 km. However, gridded meteorological data of sub-kilometer resolution is not available for the Himalayan region. In the present study, Numerical Weather Prediction model-WRF has been configured for North-West (N-W) Himalayan region with spatial resolution of 2 km and run in hind cast mode to generate meteorological data of 11 winters (2009-19). Artificial neural networks (ANNs) have been developed for post-processing of maximum temperature, minimum temperature, wind speed, relative humidity, snow depth and snowfall in 24h generated by the WRF model using observed surface weather data of five different locations in Chowkibal-Tangdhar (C-T) regi...

This study is focused on the sensitivity of simulated severe windstorms downstream of the Snæfellsnes mountain range in West-Iceland to various choices of the planetary boundary layer (PBL) and cloud parameterizations that are available in the PSU/NCAR MM5 model and the Advanced Research WRF model. Both MM5 and AR-WRF are run on a 1 km horizontal grid with two different PBL schemes, the classical ETA/MYJ scheme and a modified version of it (a 2-equation scheme), along with all the available microphysical schemes in AR-WRF. The results from the study show that the simulated surface wind speed downstream of the mountain range and close to the mountain foot (location Bláfeldur), is greater in AR-WRF than in MM5 and in better agreement with observations, regardless what combination of PBL and cloud parameterizations is used. The simulated surface winds using the 2-equation PBL scheme are slightly greater than those simulated using the ETA/MYJ scheme. The simulated winds show little sens...

The three dimensional structure of the Red Sea Low Level Jet (RSLLJ) that occurs over the southern Red Sea during the winter season is examined using the Weather Research and Forecasting (WRF) model. The causes of the jet formation are investigated, and the simulations confirm that the jet is a terrain-induced phenomenon. It initiates as a gap flow as the jet forms north of the strait of Bab el-Mandab as a result of a hydraulic effect when a stably stratified cool layer is channeled through the mountainous gap at low levels over the strait into the southern Red Sea. The jet intensity is enhanced by the Red Sea trough over the southern Red Sea. The cool dense air mass south of the strait is supported by a generally persistent synoptic regime that includes a high-pressure system This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

The state and composition of the lowest part of the planetary boundary layer (PBL), i.e., the atmospheric surface layer (SL), reflects the interactions of external forcing, land surface, vegetation, human influence and the atmosphere. Vertical profiles of atmospheric variables in the SL at high spatial and temporal resolution increase our understanding of these interactions, but are still challenging to measure appropriately. Traditional ground-based observations include towers that often cover only few measurement heights on a fixed location. At the same time, remote sensing techniques and aircraft measurements are challenged to achieve sufficient detail close to the ground. Vertical and horizontal sounding of the PBL can be complemented by unmanned aerial vehicles (UAV). Our aim in this case study is to assess the use of a multicopter-type UAV to simultaneously support the spatial sampling of air and the sensing of meteorological variables for the study of the surface exchange pro...

Springerlink.com conditions. Frozen and snow-covered soils at high elevations are likely to have played an important role in generating record streamflows. Results point to a doubling of surface runoff due to the frozen conditions, while 25 % of the modelled runoff originated from snowmelt. The estimated return time of the 3-day precipitation event exceeds 50 years over a large region, and an increase in the occurrence of similar extreme precipitation events is projected by the end of the 21st century. Event attribution analysis suggests that greenhouse gas increases may have increased 1-day and 3-day return levels of May-June precipitation with respect to pre-industrial climate conditions. However, no anthropogenic influence can be detected for 1-day and 3-day surface runoff, as increases in extreme precipitation in the present-day climate are offset by decreased snow cover and lower frozen water content in soils during the May-June transition months, compared to pre-industrial climate.

(FRONT-PORCH) experiment is an investigation of meteorological and hydrological processes that are important to accurately predict the timing, location and intensity of orographic and convective precipitation and its hydrological response in complex terrain. The multi-organizational FRONT-PORCH experiment in the summer of 2013 will provide critical insight into a comprehensive range of processes contributing to convective and orographic precipitation over the mountains, foothills and plains in the FRONT domain. This scientific proposal will accomplish this by executing the following four principle research tasks: Task 1-Physcial Process Studies: Conduct hydrometeorological process research into the controls on warm season convection initiation, evolution and its hydrological responses in complex terrain Task 2-Radar Retrieval Research: Perform basic research with multi-parameter microwave radar systems on the spatially and temporally continuous retrieval of precipitation, wind, humidity and hydrometeor structures Task 3-Real-time Demonstrations: Demonstrate real-time, end-to-end, hydrometeorological (e.g., precipitation and streamflow) nowcasting capabilities through assimilation of high resolution data into both NWP-based and extrapolation-based prediction systems Task 4-Collection of Radar Data Sets for Classroom Use: Obtain radar data sets which will serve as the basis of web-accessible modules designed to illustrate key mesoscale storm structures for upper level undergraduate and graduate students. Essential in addressing the research objectives in FRONT-PORCH is the usage of the FRONT radar network (i.e., NCAR S-PolKa, CSU-CHILL and CSU-Pawnee) in conjunction with numerous other deployable assets described in the adjacent proposal. Intellectual merit: Accurate prediction of the timing, location and amount of precipitation over complex terrain continues to be a grand meteorological challenge as it depends on complex, multi-scale processes ranging from orographic airflow dynamics to atmospheric thermodynamics to cloud microphysics. The proposed measurements in FRONT-PORCH are the first in the western U.S. to track both meteorological and hydrological connections between the 'outputs' (location and amount of precipitation and hydrological runoff) and the 'inputs' (upwind flow, humidity, temperature and surface fluxes) of the hydrometeorological regime through study of the intermediate transformational steps (orographic flow modification and formation of precipitation). By integrating data from multiple observation systems with data assimilation and modeling systems we will create a unique opportunity to evaluate existing hypotheses on orographic-convective processes and will be able to quantify principal sources of error in the hydrometeorological prediction chain. These discoveries will help answer the fundamental question: "What is the predictability of the timing, location and amount of convectiveorographic precipitation and hydrologic responses over complex terrain of the Colorado Front Range?" Broader Impacts: Improving the ability to predict the timing, location and amount of convectiveorographic precipitation will have a direct impact on flood prediction skill and on a wide range of human activities. One of the most important scientific impacts will be on hydrological modeling and forecasting since uncertainty in the location and amount of precipitation is one of the greatest sources of error in hydrological predictions. The societal threats imposed by severe convection in the Colorado Front Range (CFR) region are endemic in many other mountain front regions around the world such as the southern Alps in Europe, the southern fronts of the Himalaya and the Hindu-Kush in south Asia, and the Sierra Madre Occidental and Oriental in Mexico. Using the CFR as a natural laboratory for such hydrometeorological regimes, the FRONT-PORCH project will make significant, transferrable discoveries in fundamental earth system processes while also making significant strides in improving the accuracy and timeliness of hazardous weather impacts predictions. Furthermore, the proposed education plan will offer educators and students a unique, hands-on experience in conducting field research in hydrometeorology.

Resumo Neste trabalho é apresentada uma revisão sobre métodos para cálculo do desvio padrão da direção do vento horizontal (σθ). Três diferentes métodos clássicos encontrados na literatura [Verral e Williams, 1982 (VW), Ackermann, 1983 (ACK), e Yamartino, 1984 (YM)] são avaliados a partir de intercomparação entre eles utilizando-se dados de vento obtidos por radiossondagens. Estas medidas foram realizadas a cada seis horas durante um período de 11 dias do mês de setembro de 2008 (estação seca da região Norte do NE do Brasil, com ventos alísios intensos). Os cálculos mostraram que o método de YM apresentou-se o mais confiável, sendo que os resultados de VW foram muito próximos de YM. Comparando os métodos dois a dois, as máximas diferenças foram de 29 graus entre ACK e YM e 26,3 graus entre ACK e VW, enquanto que entre YM e VW a máxima diferença foi de apenas 2,6 graus. Segundo a literatura revisada, YM é o método mais estável ao longo da variação de σθ, com erro de, no máximo, 2%.

A three-dimensional, non-hydrostatic, terrain-following numerical model was used to investigate the Adelaide gully wind of South Australia. It reproduced most features of this downslope wind. Results showed that the onset and strength of the Adelaide gully wind are critically dependent on the upstream wind and potential temperature profiles, and that thl appearance of this local wind is also strongly influenced by the complicated threedimensional effect of the real topography. The results also suggesi ttrat the production of the Adelaide gully wind can be explained by either-the wave-resoiant amplification mechanism or the hydraulic amplification mechanism. A sensitivity-study of the numerical model showed that a grid size of Ax : Ay : I km is desirable for resolving the fine structures of the Adelaide gully wind, including regions ofreversed wind flow at the surface.

Heavy precipitation plays a significant role in arid and semi-arid regions of Iran. In order to understand the effect of blocking high system on rainfalls in northwest Iran during 25 - 28 October 2008, meteorological conditions including pressure, wind fields and temperature at multiple levels of the atmosphere were analyzed. Sea level pressure, the 1000-500 hPa thickness, perceptible water, relative humidity, temperature, u and v components of wind at 850 hPa, geopotential height at 500 hPa  and relative vorticity of u and v were obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis dataset. Location and displacement of the atmospheric systems such as cyclones, anticyclones, fronts and wind fields were identified using synoptic charts. Daily rainfall data obtained over 50 weather stations. Results indicate that the existence of a blocking high over the northern portion of the Caspian Sea caused the activity ...

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Global change has triggered several transformations, such as alterations in climate, land productivity, water resources, and atmospheric chemistry, with far reaching impacts on ecosystem functions and services. Finding solutions to climate and land cover change-driven impacts on our terrestrial environment is one of the most important scientific challenges of the 21st century, with farreaching interlinkages to the socio-economy. The setup of the German Terrestrial Environmental Observatories (TERENO) Pre-Alpine Observatory was motivated by the fact that mountain areas, such as the pre-alpine region in southern Germany, have been exposed to more intense warming compared with the global average trend and to higher frequencies of extreme hydrological events, such as droughts and intense rainfall. Scientific research questions in the TERENO Pre-Alpine Observatory focus on improved process understanding and closing of combined energy, water, C, and N cycles at site to regional scales. The main long-term objectives of the TERENO Pre-Alpine Observatory include the characterization and quantification of climate change and land cover-management effects on terrestrial hydrology and biogeochemical processes at site and regional scales by joint measuring and modeling approaches. Here we present a detailed climatic and biogeophysical characterization of the TERENO Pre-Alpine Observatory and a summary of novel scientific findings from observations and projects. Finally, we reflect on future directions of climate impact research in this particularly vulnerable region of Germany.

This work stems from the idea of improving the capability to measure the atmospheric boundary layer height (ABLH) in variable or unstable weather conditions or in the presence of turbulence and precipitation events. A new approach based on the use of rotational and roto-vibrational Raman lidar signals is considered and tested. The traditional gradient approach based on the elastic signals at wavelength 532 nm is also considered. Lidar data collected by the University of Basilicata Raman lidar (BASIL) within the Special Observation Period 1 (SOP 1) in Cardillargues (Ceveninnes–CV supersite) during the Hydrological Cycle in the Mediterranean Experiment (HyMeX) were used. Our attention was specifically focused on the data collected during the period 16–21 October 2012. ABLH estimates from the Raman lidar were compared against other innovative methods, such as the recently established Morphological Image Processing Approach (MIPA) and the temperature gradient technique applied to potent...

During winter season, large amount of precipitation is received in the Northwestern part of India due to eastward moving low pressure synoptic weather systems called western disturbances (WDs). These WD's disturbs the life in Northern India with heavy precipitation, cold wave and fog. The objective of the present study is to examine model sensitivity of different physical parameterization schemes incorporated in the weather research and forecasting model and to identify a combination of the best physics options suited for this region during the passage of a western disturbance. Four cases of intense western disturbances 13-17 January 2002 (case-1), 5-8 February 2002 (case-2), 16-19 January 2013 (case-3) and 4-7 February 2013 (case-4) which affected the northwest India has been simulated with different physics configurations in the model. The model simulation from different physics configurations are validated with the observational datasets and error statistics are presented. It is found that, the performance of the combination of National Severe Storms Laboratory one moment, Kain-Fritsch, Yonsei University, rapid radiative transfer model and Dudhia schemes as a microphysics, cumulus, planetary boundary layer, longwave radiation and shortwave radiation parameterization schemes respectively gives a better simulation of the weather during WD's over this region. It is found that, in all WD cases intensity and movement of the precipitation, circulation and low pressure area (geopotential height) over the region is well predicted by the model.

The development and tropical transition (TT) of a subsynoptic-scale cyclone in the Gulf of Genoa during the Mesoscale Alpine Project (MAP) demonstration of probabilistic hydrological and atmospheric simulation of flood events in the alpine region (D-PHASE) project is investigated using analyses and model simulations. Cyclogenesis occurs in association with the passage of a synoptic-scale trough and attendant surface cold front across the Alps on 15 November 2007. An embedded coherent tropopause disturbance (CTD) plays an important role in promoting the initial development of the lower-level vortex by simultaneously providing quasigeostrophic forcing for ascent and reducing the bulk column stability over warm Mediterranean waters. Persistent convection thereafter erodes the CTD as the storm transitions into a hurricane-like vortex. In addition to this upper-level forcing, a pair of diabatically generated lower-level cyclonic potential vorticity (PV) features associated with distinct flow regimes is potentially important to the cyclogenetic process in this case. The first, a warm surface potential temperature anomaly, is generated during cross-barrier flow by prefrontal upslope precipitation on the Alpine northside, followed by parcel descent in the lee. The second PV feature is a mountain-scale PV banner that extends southward from the southwestern tip of the Alps as the flow is deflected around the mountain chain. Numerical guidance for this case is evaluated on its ability to accurately depict the development and evolution of the cyclone. Comparison of a triply nested integration (grid spacings of 33, 10, and 2.5 km) with observations and analyses demonstrates that the model is capable of simulating the salient features of the event. Combining reliable guidance from high-resolution modeling systems with the paradigms of lee cyclone development and the emerging concepts of TT promotes an improved understanding of these potentially high-impact events.

In 2021, a group of seven Italian institutions decided to bring together their know-how, experience, and instruments for measuring the drop size distribution (DSD) of atmospheric precipitation, giving birth to the Italian Group of Disdrometry (in Italian named Gruppo Italiano Disdrometria, GID, https://www.gid-net.it/, last access: 16 May 2023). GID has made freely available a database of 1 min records of DSD collected by the disdrometer network along the Italian peninsula. At the time of writing, the disdrometer network was composed of eight laser disdrometers belonging to six different Italian institutions (including research centres, universities, and environmental regional agencies). This work aims to document the technical aspects of the Italian DSD database consisting of 1 min sampling data from 2012 to 2021 in a uniform standard format defined within GID. Although not all the disdrometers have the same data record length, the DSD data collection effort is the first of its kind in Italy, and from here onwards, it opens up new opportunities in the surface characterization of microphysical properties of precipitation in the perspective of climate records and beyond. The Version 01 GID database can be downloaded at https://doi.org/10.5281/zenodo.6875801 (Adirosi et al., 2022), while Version 02 can be downloaded at https://doi.org/10.5281/zenodo.7708563 (Adirosi et al., 2023). The difference among the two versions is the diameter-fall velocity relation used for the DSD computation.

Introduction  Objective  Study Area and Experimental Campaigns  Multiscale system  Model descriptions o Meteorological mesoscale model o Traffic emission model o CFD model  Results o Evaluation of meteorological results o Evaluation of particulate matter concentrations  Conclusions

Urban air quality is one of the main environmental concerns. The interaction between atmosphere and buildings induces complex flows within the streets and squares. This fact joint with the traffic emissions produce a heterogeneous distribution of pollutants with high gradients of concentration. The main objective of this work is to obtain high resolution maps of particle matter concentration using a CFD model so as to analyze air quality and population exposure. This study is focused on a heavily trafficked roundabout in Madrid (Fernandez Ladreda square). To achieve this objective, CFD modelling coupled with detailed emissions of PM10 and PM2.5 and outputs from WRF meteorological mesoscale model is performed. Emissions from vehicle exhaust and particle resuspension are considered with a resolution of 5 m x 5 m. The simulated mesoscale vertical profiles of wind velocity and turbulent kinetic energy, previously checked with onsite meteorological measurements, are used as boundary cond...

Methodologies to improve disdrometer processing, loosely based on mathematical techniques common to the field of particle flow and fluid mechanics, are examined and tested. The inclusion of advection and vertical wind field estimates appears to produce significantly improved results in a Lagrangian hydrometeor trajectory model, in spite of very strict assumptions of noninteracting hydrometeors, constant vertical air velocity, and time independent advection during a radar scan time interval. Wind field data can be extracted from each radar elevation scan by plotting and analyzing reflectivity contours over the disdrometer site and by collecting the radar radial velocity data to obtain estimates of advection. Specific regions of disdrometer spectra (drop size versus time) often exhibit strong gravitational sorting signatures, from which estimates of vertical velocity can be extracted. These independent wind field estimates can be used as initial conditions to the Lagrangian trajectory simulation of falling hydrometeors.

In this work local circulation patterns are investigated for the year of 2010 in the Sobradinho Lake region, at the 25 m and 50 m levels. The hodographs illustrate the local wind variation in the four quadrants of the wind rose, in the majority of the months. The local time (LT) and magnitude of the maxima and minima intensities depend on the time of the year. A negative vertical shear in the local wind during the late night-early morning (night) is more evident in the period from May to September (October to February). The local wind, at times of maximum intensity, represents up to 60% of the observed wind speed and, in the remaining of the twenty four hours of the day, between 10 and 30%. This ratio decreases with height in the twelve months of 2010, and is more evident in the periods 4-6 LT and 17-20 LT, with exception of March and June, respectively. The local circulations may be associated with coupling between the land (lake) breeze and the catabatic (anabatic) winds during th...

The diurnal hourly dynamics of the kinetic energy flux density vector, called the Umov vector, and the mean and turbulent components of the kinetic energy are estimated from minisodar measurements of wind vector components and their variances in the lower 200 m layer of the atmosphere. During a 24 h period of continuous minisodar observations, it was established that the mean kinetic energy density dominated in the surface atmospheric layer at altitudes below ~50 m. At altitudes from 50 to 100 m, the relative contributions of the mean and turbulent wind kinetic energy densities depended on the time of the day and the sounding altitude. At altitudes below 100 m, the contribution of the turbulent kinetic energy component is small, and the ratio of the turbulent to mean wind kinetic energy components was in the range 0.01–10. At altitudes above 100 m, the turbulent kinetic energy density sharply increased, and the ratio reached its maximum equal to 100–1000 at altitudes of 150–200 m. A...

An attempt is made to examine the role of Anatolian and Caucasus mountain ranges in the precipitation distribution over the Black Sea region and to clarify the dynamical and physical mechanisms responsible for precipitation distribution over the region. Existence of a complex topography in the southern and eastern part of the Black Sea region makes it an important region for cyclogenesis. In this study the effect of Anatolian and Caucasus Mountains on the precipitating synoptic systems forming over the Black Sea are investigated. To this end, the Weather Research and Forecasting (WRF) model at 15-km horizontal grid spacing has been used to evaluate the lifetime of a low pressure system that was accompanied with heavy precipitation on 14 March 2009 over the coastal region of the Black Sea. Two experiments were conducted. In the control experiment (CTL), the topographical features of the region were retained. In the sensitivity experiment (EXP), the Anatolian and Caucasus mountain ranges were removed. It is found that in the EXP, some fields including vertical motion, relative vorticity, humidity, geopotential height in low level, cloud water content and precipitation distribution in the region undergo significant changes. As such, in the EXP, the vorticity, and the cutoff low system over the Black Sea intensified. It is also seen that, under favorable conditions for precipitation occurrence, the precipitation intensity in the south and east coasts of the Black Sea decreased and the region of maximum precipitation shifted toward the "Sea of Azov" region, in the direction of the surface southerly winds.

During the Greenland Flow Distortion experiment, barrier flow was observed by an instrumented aircraft on 1, 2, 5 and 6 March 2007 off southeastern Greenland. During this time period the barrier flow increased from a narrow jet, ∼15 m s −1 , to a jet filling almost the whole of the Denmark Strait with maximum wind speed exceeding 40 m s −1. Dropsonde observations show that the barrier flow was capped by a sharp temperature inversion below mountain height. Below the inversion was a cold and dry jet, with a larger northerly wind component than that of the flow above, which was also warmer and more moist. Thus, the observations indicate two air masses below mountain height: a cold and dry barrier jet of northern origin and, above this, a warmer and moister air mass that was of cyclonic origin. Numerical simulations emphasize the non-stationarity of the Greenland barrier flow and its dependence on the synoptic situation in the Greenland-Iceland region. They show that the barrier jet originated north of the Denmark Strait and was drawn southward by a synoptic-scale cyclone, with the strength and location of the maximum winds highly dependent on the location of the cyclone relative to the orography of Greenland. Experiments without Greenland's orography suggest a ∼20 m s −1 enhancement of the low-level peak wind speeds due to the presence of the barrier. Thus, the Greenland barrier flows are not classic geostrophically balanced barrier flows but have a significant ageostrophic component and are precisely controlled by synoptic-scale systems.

In this essay, we highlight some challenges the atmospheric community is facing concerning adequate treatment of flows over mountains and their implications for numerical weather prediction (NWP), climate simulations, and impact modeling. With recent increases in computing power (and hence model resolution) numerical models start to face new limitations (such as numerical instability over steep terrain). At the same time there is a growing need for sufficiently reliable NWP model output to drive various impact models (for hydrology, air pollution, agriculture, etc.). The input information for these impact models is largely produced by the boundary layer (BL) parameterizations of NWP models. All known BL parameterizations assume flat and horizontally homogeneous surface conditions, and their performance and interaction with resolved flows is massively understudied over mountains—hence their output may be accidentally acceptable at best. We therefore advocate the systematic investigat...

Este estudo identificou e analisou o comportamento de circulações locais induzidas pela topografia no Vale do Paraíba e na Serra da Mantiqueira, entre os dias 16 e 22 de agosto de 2010, por meio de uma simulação numérica com o modelo WRF. O modelo foi dirigido com as saídas do GFS-FNL e a simulação validada com dados de estações meteorológicas. Os maiores valores de correlação entre simulação e observação foram obtidos para a temperatura do ar e menores para a intensidade e direção dos ventos. Mesmo assim, o WRF foi capaz de representar as mudanças no sentido do vento associadas à circulação de brisa vale e montanha. O modelo simulou durante o dia a brisa de vale e durante à noite, a brisa de montanha. A brisa de vale iniciou-se aproximadamente entre 10 UTC e 14 UTC e a de montanha às 22 UTC, sendo que a fase de transição entre a brisa de montanha para a de vale ocorreu entre as 16 e 20 UTC. Os resultados obtidos também são apresentados por meio de seções verticais das células de ci...

Raco is the local name given to a strong (gusts up to 17 m s−1), warm, and dry down-valley wind observed at the exit of the Maipo River Canyon in central Chile. Its climatology is documented based on eight years of surface measurements near the canyon exit together with a more complete characterization of its structure during an intensive observational period (IOP) carried out in July 2018. Raco winds occur in the cold season under well-defined synoptic conditions, beginning abruptly at any time during the night, reaching maximum hourly averages around 10 m s−1, and terminating around noon with the onset of afternoon westerly up-valley winds. About 25% of the days in May–August have more than six raco hours between 0100 and 1200 LT, and raco episodes last typically 1–2 days. The sudden appearance of raco winds at the surface can be accompanied by conspicuous warming (up to 10°C) and drying (up to 3 g kg−1). Raco winds are associated with a strong along-canyon pressure gradient, a re...

The near-surface wind and temperature regime at three points in the Atacama Desert of northern Chile is described using two years of multilevel measurements from 80-m towers located in an altitude range between 2100 and 2700 m MSL. The data reveal the frequent development of strong nocturnal drainage flows at all sites. Down-valley, nose-shaped wind speed profiles are observed, with maximum values occurring at heights between 20 and 60 m AGL. The flow intensity shows considerable interdaily variability and a seasonal modulation of maximum speeds, which in the cold season can attain hourly average values of more than 20 m s−1. Turbulent mixing appears to be important over the full tower layer, affecting the curvature of the nighttime temperature profile and possibly explaining the observed increase of surface temperatures in the down-valley direction. Nocturnal valley winds and temperatures are weakly controlled by upper-air conditions observed at the nearest aerological station. Est...

Raco is the local name given to a strong (gusts up to 17 m s−1), warm, and dry down-valley wind observed at the exit of the Maipo River Canyon in central Chile. Its climatology is documented based on eight years of surface measurements near the canyon exit together with a more complete characterization of its structure during an intensive observational period (IOP) carried out in July 2018. Raco winds occur in the cold season under well-defined synoptic conditions, beginning abruptly at any time during the night, reaching maximum hourly averages around 10 m s−1, and terminating around noon with the onset of afternoon westerly up-valley winds. About 25% of the days in May–August have more than six raco hours between 0100 and 1200 LT, and raco episodes last typically 1–2 days. The sudden appearance of raco winds at the surface can be accompanied by conspicuous warming (up to 10°C) and drying (up to 3 g kg−1). Raco winds are associated with a strong along-canyon pressure gradient, a re...

ScaleX is a collaborative measurement campaign, collocated with a long-term environmental observatory of the German Terrestrial Environmental Observatories (TERENO) network in the mountainous terrain of the Bavarian Prealps, Germany. The aims of both TERENO and ScaleX include the measurement and modeling of land surface–atmosphere interactions of energy, water, and greenhouse gases. ScaleX is motivated by the recognition that long-term intensive observational research over years or decades must be based on well-proven, mostly automated measurement systems, concentrated in a small number of locations. In contrast, short-term intensive campaigns offer the opportunity to assess spatial distributions and gradients by concentrated instrument deployments, and by mobile sensors (ground and/or airborne) to obtain transects and three-dimensional patterns of atmospheric, surface, or soil variables and processes. Moreover, intensive campaigns are ideal proving grounds for innovative instrument...

O vento é variável meteorológica relevante em vários aspectos da interação superfície-atmosfera e de grande influência em processos naturais e atividades humanas na atmosfera inferior. O regime de ventos numa dada região tipicamente baseia-se na análise de séries temporais do vento horizontal em termos de velocidade média e direção predominante. Essa análise é feita no presente estudo para a localidade de Cruz das Almas, Bahia (12º40’ S, 39º06’ W, 225 m anm) a partir de dados diários de velocidade e direção do vento medido por um anemógrafo universal a 10 m de altura no período 1973-2001 (29 anos). Utilizou-se a base de dados do Instituto Nacional de Meteorologia (INMET) como fonte das informações. Em Cruz das Almas, o regime de ventos é fortemente influenciado por centros de alta pressão no Atlântico Sul. A velocidade média diária do vento a 10 m de altura foi de 2,7 m s-1 com 70,4% das observações concentradas no intervalo de 1,6 m s-1 a 3,3 m s-1, correspondendo este à classe bri...

Both numerical modeling and laboratory experiments document the possibility of a raindrop size distribution (DSD) to evolve to an equilibrium stage (EDSD), where all the principal processes occur at steady rates. The aim of this work is to observe the temporal behavior of the DSD and to directly investigate the conditions favorable to the onset of the EDSD in natural rain. We exploited a large disdrometer dataset collected in the framework of the Ground Validation activities related to the NASA Global Precipitation Measurement mission. More than 200,000 one-minute data of two-dimensional video disdrometer (2DVD) are collected over USA to represent a wide range of precipitation types. The original data are averaged over 2 minutes and an automatic algorithm is used on a selected subset to identify samples with EDSD. Results show that the EDSD occurs mainly in convective events and lasts for very short time intervals (2 to 4 minutes). It is more frequent for rain rate between 20 and 40 mm h-1 and it mostly occurs during sharp increase of precipitation rates.

This paper describes the results of an analysis of extreme rainfall events in the central plateau of Iran. To study the extreme events, daily records of eighteen stations' rainfalls in the region for different initial dates up to 2005 gathered from the bureau of meteorology. Then, the extreme rainfall threshold was calculated for each individual station using the statistical index of Gamble type I. Lastly, 22 mm was determined as the extreme rainfall value for the entire stations, and eventually 17 out of 169 extreme precipitation events were extracted in accordance with three factors including a) days with precipitation in not less than 50% of the stations, b) maximum rainfall is 22 mm or more in at least one of the stations, and c) mean precipitation of the basin is more than 3 mm. In the next step to analyze the synoptic features, the relevant meteorological data i.e. relative vorticity, geopotential height, sea level pressure, u and v wind components, relative humidity, vertical velocity, and precipitable water content at multiple levels of the atmosphere were examined from the NCEP/NCAR reanalysis dataset. The synoptic findings indicate that two patterns of deep trough and high ridge of the eastern Mediterranean were responsible for making the heavy precipitation events over the central plateau of Iran. The most and severest rainfall events occurred via deep tough pattern, which covered 76% of days with extreme precipitations during the examined period. Furthermore, the results suggest that the main moisture resources, which identified by HYSPLIT model's outputs and moisture convergence/divergence zones for the rainy systems in the first pattern (deep trough) including Persian Gulf, Oman Sea, Indian Ocean, and Red Sea, while for the second pattern (high ridge) Persian Gulf and Red Sea play a significant role in feeding the storms in the central regions of Iran. Moreover, the southward movement of Polar Vortex is also considered as those important factors to produce extreme precipitation events over the central plateau of Iran. In general, the HYSPLIT trajectories model's outputs confirmed the * Corresponding author. I. Rousta et al. 298 observed synoptic features in particular for the systems' moisture feeding discussed in the patterns.

In 2021, a group of seven italian institutions decided to bring together their know-how, experience, and instruments for measuring the drop size distribution (DSD) of atmospheric precipitation giving birth to the Italian Group of Disdrometry (in Italian named: Gruppo Italiano Disdrometria, GID, https://www.gid-net.it/). The GID has made freely available a database of 1-minute records of DSD collected by the disdrometer network along the Italian peninsula. At the time of writing, the disdrometer network is composed of eight laser disdrometers belonging to six different Italian institutions (including research centers, universities and environmental regional agencies). This work aims to document the technical aspects of the italian DSD database consisting of 1-minute sampling data from 2012 to 2021 in a uniform standard format defined within GID. Although not all the disdrometers have the same length of the data record, the DSD data collection effort is the first of its kind in Italy, and from here onwards, it opens new opportunities in the surface characterization of microphysical properties of precipitation in the

A mesoscale model RAMS (the Regional Atmospheric Modeling System) was used to investigate the effectiveness of the broadcast static seeding method for dispersing particles into clouds, as it is used in Israel. The model was run using three nested grids, with 500 m ϫ 500 m horizontal resolution in the finest grid. In this paper, the particles were assumed to be inert; namely, only the wind field controlled the dispersal of the tracer particles, and no interaction with cloud or precipitation particles was considered. Although the resolution of the model is good for mesoscale studies, it could not resolve individual plumes. The results, therefore, present average values of the concentrations at each level. The simulations showed that seeding particles reach altitudes at which they could become effective as ice nuclei. These cases were primarily the ones in which the updrafts developed over the seeding lines when the seeding plane was just passing underneath. In these cases only, seeding at about 1-km level (ϳ4ЊC) with 500 g h Ϫ1 of inert material (simulating AgI particles) resulted in about 1 ϫ 10 3-2 ϫ 10 3 L Ϫ1 being lifted to the Ϫ10ЊC level. Based on previous laboratory studies of the seeding agent used in Israel, out of these total concentrations, only 1-2 L Ϫ1 could form ice at Ϫ10ЊC. The simulations also suggest that in most other cases the horizontal advection diluted the particles in the air and only very low concentrations (Ͻ10 Ϫ3 L Ϫ1 , active at Ϫ10ЊC) reached the Ϫ10ЊC level. Most other released particles were transported horizontally with the winds and were later on forced down by downdrafts. Although these simulations await some experimental verification, they suggest that the broadcast seeding method used in Israel is not so effective for widespread rain enhancement operations.

O transporte de partículas entre diferentes regiões é fortemente influenciado pela atividade dos ventos, o qual pode exercer grande influência na formação das paisagens litorâneas. Com o objetivo de caracterizar a dinâmica dos ventos no extremo norte da Planície Costeira do Rio Grande do Sul (RS), foram analisados dados históricos e anuais dos ventos (velocidade e direção) de quatro estações meteorológicas localizadas na região. Os resultados demonstram que na estação de Torres os ventos provenientes das direções NE e S são mais frequentes, e que os ventos das direções W e N são raros. Na estação SBTR/Aeroporto, os ventos do quadrante N-E são os mais frequentes (32%), seguidos dos ventos provenientes das direções SW, SSW e S. Na estação da Lagoa Itapeva Central o padrão dos ventos se altera um pouco, prevalecendo as direções NE e SW, com ventos de maior intensidade provenientes da direção SW. Verificou-se uma variabilidade considerável na direção e frequência dos ventos no decorrer ...

Extreme heavy precipitation events (HPEs) pose a threat to human life but remain difficult to predict because of the lack of adequate high frequency and high-resolution water vapor (WV) observations in the low troposphere (below 3 km). To fill this observational gap, we aim at implementing an integrated prediction tool, coupling network measurements of WV profiles, and a numerical weather prediction model to precisely estimate the amount, timing, and location of rainfall associated with HPEs in southern France (struck by ~ 7 HPEs per year on average during the fall). The Water vapor Lidar Network Assimilation (WaLiNeAs) project will deploy a network of 6 autonomous Raman WV lidars around the Western Mediterranean to provide measurements with high vertical resolution and accuracy to be assimilated in the French Application of Research to Operations at Mesoscale (AROME-France) model, using a four-dimensional ensemble-variational approach with 15-min updates. This integrated prediction tool is expected to enhance the model capability for kilometer-scale prediction of HPEs over southern France up to 48 h in advance. The field campaign is scheduled to start early September 2022, to cover the period most propitious to heavy precipitation events in southern France. The Raman WV lidar network will be operated by a consortium of French, German, Italian, and Spanish research groups. This project will lead to recommendations on the lidar data processing for future operational exploitation in numerical weather prediction (NWP) systems.

This paper complements the existing studies of Bora flow properties in the Vipava valley with the study of Bora turbulence in a lower region of the troposphere. The turbulence characteristics of Bora flow were derived from high resolution Doppler wind lidar measurements during eight Bora wind episodes that occurred in November and December 2019. Based on the vertical profiles of wind velocity, from 80 to 180 m above the valley floor, the turbulence intensity related to all three spatial directions and the along-wind integral length scales related to three velocity components were evaluated and compared to the approximations given in international standards. The resulting turbulence characteristics of Bora flow in a deep mountain valley exhibited interesting behaviour, differing from the one expected and suggested by standards. The intensity of turbulence during Bora episodes was found to be quite strong, especially regarding the expected values for that particular category of terrai...

RESUMO: Considerando que a produção elétrica brasileira é alicerçada na geração hidráulica, associado à crise hídrica, o crescimento da demanda e a preocupação ambiental, fomentaram-se os estudos para encontrar mecanismos que minimizem os problemas que cercam a geração elétrica. Entre as formas de geração, está a proveniente de movimento de massas de ar, denominada eólica. Com o intuito de conhecer o potencial eólico sazonal do município de Cascavel, realizou-se um comparativo dos dados de velocidade do vento para descobrir qual estação pode render melhor aproveitamento de acordo com a velocidade média do vento local. Para tal análise, as velocidades médias do município de Cascavel foram obtidas através do Sistema Meteorológico do Paraná (SIMEPAR). Os dados foram apresentados em planilha eletrônica e analisados no programa BioEstat 5.0, onde realizaram-se testes estatísticos como o de Shapiro-Wilk e Análise de Variância ANOVA: um critério. Os testes foram aplicados objetivando a comparação das velocidades médias entre todas as estações em uma série histórica de 06 anos (2011-2016). Com as análises realizadas, pôde-se comprovar que na série histórica analisada, o inverno possui significante diferença de velocidade média sazonal, e portanto, pode proporcionar melhores condições de geração elétrica.