Low-Level Jets

The lowest wildfire activity in Bolivia was in April and the highest in September, with a strong west-to-east AOD gradient. • Smoke impacted Santa Cruz due to its proximity to fire foci and lower altitude, exceeding WHO daily PM 10 limit in Jun-Sept. • Lowland wildfires had little impact on La Paz and Cochabamba; WHO daily PM 10 exceedances (36-76% of the time) were mainly local.

There is a growing trend toward applying remote sensing equipment to investigate the Planetary Boundary Layer (PBL) characteristics. In this work, a Doppler lidar was employed to study the Low Level Jets (LLJs) at Ipero, Sao Paulo countryside, Brazil. Previous works have shown that the LLJs are a common feature at Ipero. The LLJs were rstly recognized on the Great Plains of the United States, but have now been identied in many other locations and nearly all continents. LLJs cause economical and social impacts, which includes: pollutants transport and dispersion, moisture transport, forest re propagation, ight safety and wind power production. Despite their importance, the LLJ simulation has a high computational cost, a common PBL feature due to its typical temporal and spatial scales. The one-year experimental campaign with the Doppler lidar generated an extensive dataset of the vertical wind prole at Ipero. This dataset allowed to investigate the LLJ features such as seasonality, frequency and intensity. It was possible to apply methods that have been recently proposed for the assesment of other properties, like the turbulent kinetic energy (TKE) and the TKE dissipation rate. It was found that there is TKE above the LLJ level and that the local dissipation is not a proper representation during LLJ events. For the Case Study, a LLJ formed near the surface and with a long life cycle was selected. Continuous observational data allowed to monitor the temporal evolution of this event and the impacts on transport and atmospheric dispersion simulations.

This study was accomplished using radiosonde, surface and L-Band Doppler radar data, in Serpong-Indonesia (6° 24' S-106° 42' E), during the dry season of 1993. The structure of the ABL (Atmospheric Boundary Layer) was interpreted through the radar echo (wind), observed 24 hours a day during the whole study period. The more evident characteristic of the ABL is the presence of a diurnal ML (Mixed Layer) that reaches altitudes greater than 0,3 km in the morning and a reaches 3 to 5 km in the afternoon, observing a diurnal cycle of heating and cooling. The information obtained by the BLR (Boundary Layer Radar) shows the existence of pronounced diurnal variations in the ABL, during clear days. It was also verified that the diurnal variation of the ABL was affected by sea breeze circulation, confirmed by the BLR. As an example, on the 12/10/93 the breeze intensified at 14 LT and increasing rapidly (about 15 LT) up to a depth of 1.5 to 2 km. The validation of the radar data presented here has shown significant results, proving that the radar observations should be an important method in the study sea breeze in equatorial atmosphere.

The central Great Plains region in North America has a nocturnal maximum in warm-season precipitation. Much of this precipitation comes from organized mesoscale convective systems (MCSs). This nocturnal maximum is counterintuitive in the sense that convective activity over the Great Plains is out of phase with the local generation of CAPE by solar heating of the surface. The lower troposphere in this nocturnal environment is typically characterized by a low-level jet (LLJ) just above a stable boundary layer (SBL), and convective available potential energy (CAPE) values that peak above the SBL, resulting in convection that may be elevated, with source air decoupled from the surface. Nocturnal MCS-induced cold pools often trigger undular bores and solitary waves within the SBL. A full understanding of the nocturnal precipitation maximum remains elusive, although it appears that bore-induced lifting and the LLJ may be instrumental to convection initiation and the maintenance of MCSs at...

During the Sea State cruise in the fall of 2015, in the Chukchi/Beaufort Sea region, there were five strong (>10 m s−1) surface wind events associated with low‐level atmospheric jets. These jets were analyzed using rawinsonde observations, ship measurements, and a numerical forecast model. The jets occurred when easterly winds aligned with the ice edge, generating low‐level baroclinicity in a direction favorable for increasing the geostrophic wind speed toward the surface. The maximum wind speed usually occurred at the top of the atmospheric boundary layer with wind speeds greater than 8 m s−1 extending through the capping inversion to 2,000–3,000 m elevation, with winds decreasing toward the surface in the boundary layer due to friction. The width (crosswind) dimensions of the jets were 250–400 km and they existed downwind for as long as the winds remained generally parallel to the ice edges, typically several hundred kilometers. Thermal winds calculated from crosswind‐oriented ...

Nocturnal low-level jets (LLJs) have been documented at many places around the world, particularly across the Great Plains of the United States. Nocturnal LLJs significantly affect the regional weather and climate, as well as several industrial activities. While the LLJ has been extensively studied, little attention has been paid to the relationship between the evolution of the LLJ, its properties, and the boundary-layer structure. Here, observations collected in northern Oklahoma, USA are used to analyze the characteristics and evolution of the LLJ during conditions of weak and strong turbulence, respectively, coinciding with strongly and weakly stable nocturnal boundary layers. Additionally, the relationship between the LLJ and the temperature profile under these different conditions is examined. Three case studies are used during conditions of weak and strong turbulence, followed by statistics computed from a larger dataset of LLJs. When turbulence is weak, the LLJ is shown to reach peak intensity later near sunrise, while a maximum in the intensity is reached about six hours after sunset in the highly turbulent boundary layer. Furthermore, the LLJ tends to stay constant with height when turbulence is maintained throughout the night, while the LLJ tends to follow isentropic surfaces when vertical mixing is suppressed. When the LLJ follows isentropic surfaces, changes in the wind speed are related to the stability modification. Keywords Doppler lidar • Low-level jet • Stable boundary layer • Turbulence 1 Background The low-level jet (LLJ) is a local wind-speed maximum typically observed at night in the lowest kilometre of the atmosphere when a stable boundary layer (SBL) develops. It is a prominent feature over the Great Plains of the United States (Bonner 1968). Several boundarylayer processes interact to produce the LLJ. The inertial oscillation contributes to the flow acceleration commencing around sunset; radiational cooling near the surface quells turbulent B Timothy A. Bonin

The Lower Atmospheric Boundary Layer Experiment (LABLE) included two measurement campaigns conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma during 2012 and 2013. LABLE was designed as a multi-phase, low-cost collaboration among the University of Oklahoma, the National Severe Storms Laboratory, Lawrence Livermore National Laboratory, and the ARM program. A unique aspect was the role of graduate students in LABLE. They served as principal investigators and took the lead in designing and conducting experiments using different sampling strategies to best resolve boundary-layer phenomena.

Observations from three nights of the Plains Elevated Convection at Night (PECAN) field campaign were used in conjunction with Rapid Refresh model forecasts to find the cause of north–south lines of convection, which initiated away from obvious surface boundaries. Such pristine convection initiation (CI) is relatively common during the warm season over the Great Plains of the United States. The observations and model forecasts revealed that all three nights had horizontally heterogeneous and veering-with-height low-level jets (LLJs) of nonuniform depth. The veering and heterogeneity were associated with convergence at the top-eastern edge of the LLJ, where moisture advection was also occurring. As time progressed, this upper region became saturated and, due to its placement above the capping inversion, formed moist absolutely unstable layers, from which the convergence helped initiate elevated convection. The structure of the LLJs on the CI nights was likely influenced by nonuniform...

The central Great Plains region in North America has a nocturnal maximum in warm-season precipitation. Much of this precipitation comes from organized mesoscale convective systems (MCSs). This nocturnal maximum is counterintuitive in the sense that convective activity over the Great Plains is out of phase with the local generation of CAPE by solar heating of the surface. The lower troposphere in this nocturnal environment is typically characterized by a low-level jet (LLJ) just above a stable boundary layer (SBL), and convective available potential energy (CAPE) values that peak above the SBL, resulting in convection that may be elevated, with source air decoupled from the surface. Nocturnal MCS-induced cold pools often trigger undular bores and solitary waves within the SBL. A full understanding of the nocturnal precipitation maximum remains elusive, although it appears that bore-induced lifting and the LLJ may be instrumental to convection initiation and the maintenance of MCSs at...

Simultaneous measurements of CT2 and CV2 have been made using the Penn State Doppler sodar system and comprehensively instrumented research aircraft. In each experiment the aircraft was vectored using air-ground ratio to the altitude (ranging from ≃ 150 to 600 m) zone of interest on the basis of the received sodar signals. Measurements have been made in both “layers” (with and without detectable turbulence and “waves”), and in convective “plumes”. CT2, and CV2 have been derived both from the calibrated monostatic-bistatic Doppler sodar and airborne sensors. In addition to the normal complement of sensors for state parameters, winds, and position, the aircraft was equipped with special, spaced (at sodar λ/2) hot-wire probes capable of measuring turbulent temperature and velocity fluctuations to about 2.5-cm resolution. Using the combined sodar, turbulence, and meteorological measurements both the turbulent and larger-scale characteristics of the atmosphere in the sounder volume were ...

Low-level jets (LLJ) are important for turbulence in the stably stratified atmospheric boundary layer, but their occurrence, properties, and generation mechanisms in the Arctic are not well known. We analysed LLJs over the central Arctic Ocean in spring and summer 2007 on the basis of data collected in the drifting ice station Tara. Instead of traditional radiosonde soundings, data from tethersonde soundings with a high vertical resolution were used. The Tara results showed a lower occurrence of LLJs (46 ± 8 %) than many previous studies over polar sea ice. Strong jet core winds contributed to growth of the turbulent layer. Complex relationships between the jet core height and the temperature inversion top height were detected: substantial correlation (r = 0.72; p < 0.01) occurred when the jet core was above the turbulent layer, but when inside the turbulent layer there was no correlation. The most important forcing mechanism for LLJs was baroclinicity, which was responsible for the generation of strong and warm LLJs, which on average occurred at lower altitudes than other jets. Baroclinic jets were mostly associated with transient cyclones instead of the climatological air temperature gradients. Besides baroclinicity, cases related to inertial oscillations and gusts were detected. As many as 49 % of the LLJs observed were associated with a frontal passage, which provides favourable conditions for baroclinicity, inertial oscillations, and gusts. Further research needs on LLJs in the Arctic include investigation of low-level jet streams and their effects on the sea ice drift and atmospheric moisture transport.

During the Sea State cruise in the fall of 2015, in the Chukchi/Beaufort Sea region, there were five strong (&gt;10 m s−1) surface wind events associated with low‐level atmospheric jets. These jets were analyzed using rawinsonde observations, ship measurements, and a numerical forecast model. The jets occurred when easterly winds aligned with the ice edge, generating low‐level baroclinicity in a direction favorable for increasing the geostrophic wind speed toward the surface. The maximum wind speed usually occurred at the top of the atmospheric boundary layer with wind speeds greater than 8 m s−1 extending through the capping inversion to 2,000–3,000 m elevation, with winds decreasing toward the surface in the boundary layer due to friction. The width (crosswind) dimensions of the jets were 250–400 km and they existed downwind for as long as the winds remained generally parallel to the ice edges, typically several hundred kilometers. Thermal winds calculated from crosswind‐oriented ...

We have analyzed long-term wind speed time-series from five field sites up to a height of 300 m from the ground. Structure function-based scaling analysis has revealed that the scaling exponents in the mesoscale regime systematically depend on height. This anomalous behavior is likely caused by the buoyancy effects. In the framework of the extended self-similarity, the relative scaling exponents portray quasi-universal behavior.

The winter wind regime of Go Èteborg, located on the West coast of Sweden, is composed of three different wind systems besides the ambient wind; a nocturnal low level jet (NLLJ), a winter land breeze (WLB) and an urban heat island circulation (UHIC). An inversion divides the air column into two layers, one between 10±50 m and one between 50±100 m. The UHIC is located in the lower layer, the WLB in the top layer and the NLLJ above the top layer. The intensity of the interacting processes depends on the stability of each layer as calculated from the bulk Richardson number BRi low and BRi high using continuous data collected during four years (1991±94) from two sites (one within and one outside the urban area) and sampled at three levels. In the evening the WLB develops from the ground level and increases in height until after midnight. At about the same time an UHIC develops in the urban area, below the WLB and causing an uplift of the latter. However, at both sites the WLB does not exceed the 100 m level. At this time BRi in both layers are below one resulting in continuous coupling between the WLB, the UHIC layers and the regional wind. Consequently, the exchange of momentum is still effective between all layers and this is highlighted by a change in the wind direction and a regulation of wind-speed to more constant levels. When BRi high ! 1, the layers become frictionally decoupled, as indicated by a return in the wind direction in the top level to the regional wind, and an acceleration of the top wind. The top level then becomes incorporated in to a nocturnal lowlevel jet (NLLJ) system. The normally acknowledged development of the NLLJ, with a start around sunset, is in this case delayed for several hours at the top level. The reason for this is that there are meso-scale/local wind systems present in layers beneath the jet causing an interaction between the layers. In the morning, when the layers are again coupled the top layer wind is once more in¯uenced by the WLB and therefore changes direction and speed. The local and meso-scale wind systems thus delay the current nocturnal wind development.

The purpose of the Mesoscale-Microscale Coupling (MMC) Project is to develop, verify, and validate physical models and modeling techniques that bridge the most important atmospheric scales that determine wind plant performance and reliability. Without appropriate larger scale forcing, microscale models cannot correctly capture the meteorologically dependent flow details required to optimize siting, operations, controls, and the integration of wind-generated electricity. Incorporating meteorological forcing into wind plant simulation tools, on the other hand, will significantly improve viability of wind power to meet the emerging domestic and global demands for reliable, efficient, and cost-competitive energy sources. As part of the U.S. Department of Energy's Atmosphere to Electrons (A2e) program, the MMC project seeks to create a new predictive numerical simulation capability that is able to represent the full range of atmospheric flow conditions impacting wind plant performance. vii

O presente estudo apresenta uma aplicação do modelo de mesoescala WRF à simulação de um episódio de vento intenso e persistente que ocorre com frequência irregular no reservatório de Guapé, MG. Tal evento altera a rotina da população na região, fazendo com que, por exemplo, a embarcação que faz a travessia entre as cidades de Guapé e Capitólio interrompa o serviço. Durante um destes episódios, ocorrido em 22 de setembro de 2016, foram realizadas medidas utilizando um LIDAR Zephir ZP300 e uma torre anemométrica, e estes dados foram posteriormente utilizados para validar as simulações. Para a avaliação dos resultados, foram comparadas pressão, temperatura, umidade e velocidade do vento simuladas e observadas. A análise dos perfis verticais de velocidade simulados sugere a presença de um jato de baixos níveis, posicionado em torno de 500 m acima da superfície, gerado por um gradiente de temperatura pós-frontal, cuja parte inferior teria sido acelerada pelo relevo e pela variação de rugosidade superficial terra-água. Mais estudos encontram-se atualmente em andamento para que se possa sugerir à população e às autoridades locais algum tipo de ação preventiva. Palavras-chave: jatos de baixos níveis, reservatórios de centrais hidroelétricas, relevo complexo, modelo WRF.

O objetivo deste estudo é fazer uma análise do comportamento do perfil vertical do vento, utilizando dados de radiossondagem no Centro de Lançamento de Alcântara (CLA), por meio do uso da técnica estatística multivariada da Análise das Componentes Principais (ACP), verificar se há presença de fluxos no perfil vertical do vento. Estes fluxos podem caracterizar circulações locais e estar associados com circulações do tipo brisa marítima, e também pode estar associado a circulações ao nível de mesoescala sinótica, tais como os Jatos de Baixos Níveis (JBN). Os resultados mostraram que nas três primeiras componentes no período noturno há presença de JBN, com 85% da variância explicada. A ocorrência dos JBN apresentou alturas típicas nas componentes, sendo a primeira com altura de 800 metros (direção média 60 a 70 graus), a segunda com altura de 400 metros (direção média 40 a 50 graus) e a terceira com 200 metros (direção média 50 a 60 graus). Tais JBN encontrados podem estar associados a processos relacionados a Camada Limite Planetária (CLP) no período noturno, como por exemplo o vento máximo de inversão e brisas.

The purpose of the Mesoscale-Microscale Coupling (MMC) Project is to develop, verify, and validate physical models and modeling techniques that bridge the most important atmospheric scales that determine wind plant performance and reliability. Without appropriate larger scale forcing, microscale models cannot correctly capture the meteorologically dependent flow details required to optimize siting, operations, controls, and the integration of wind-generated electricity. Incorporating meteorological forcing into wind plant simulation tools, on the other hand, will significantly improve viability of wind power to meet the emerging domestic and global demands for reliable, efficient, and cost-competitive energy sources. As part of the U.S. Department of Energy's Atmosphere to Electrons (A2e) program, the MMC project seeks to create a new predictive numerical simulation capability that is able to represent the full range of atmospheric flow conditions impacting wind plant performance. vii

During the 2015 Plains Elevated Convection at Night (PECAN) field campaign, several nocturnal low-level jets (NLLJs) were observed with integrated boundary layer profiling systems at multiple sites. This paper gives an overview of selected PECAN NLLJ cases and presents a comparison of high-resolution observations with numerical simulations using the Weather Research and Forecasting (WRF) Model. Analyses suggest that simulated NLLJs typically form earlier than the observed NLLJs. They are stronger than the observed counterparts early in the event, but weaker than the observed NLLJs later in the night. However, sudden variations in the boundary layer winds, height of the NLLJ maximum and core region, and potential temperature fields are well captured by the WRF Model. Simulated three-dimensional fields are used for a more focused analysis of PECAN NLLJ cases. While previous studies often related changes in the thermal structure of the nocturnal boundary layer and sudden mixing events ...

Atmospheric lump structures were observed at Rome during two nights in the summer of 1994 by a triaxial Doppler sodar operating in monosmtic mode. They appeared on sodar facsimile records at height ranges between 300 and 800 m for several hours each night. The vertical velocities within the lump structures ranged around _+2 m/sec. Their occurrence was found to increase as the nights progressed. A Raman lidar, which was also simultaneously operated, provided high-resolution water vapor profiles. The sodar-derived wind profiles confirmed the presence of sea breeze during both nights while the water vapor mixing ratio showed steep gradients at the height of lump structures. The analysis of the two dam sets provided evidence that the lumps had originated, in an otherwise neutral atmosphere, from small-scale temperature fluctuations generated in isolated regions due to thermodynamical processes of water vapor by way of condensation and re-evaporation.

During field experiments using surface weather stations and a Sodar-RASS (radio acoustic sounding system) combination, low-level jets were observed in the Colima Valley of central western Mexico. These low-level jet events have not been previously observed in this part of the tropics. The present study focuses on events from one specific field period from December 2011 to April 2013 performed at a specific location. From this dataset, it was found that these phenomena typically develop at night at around 0300 local time and they reach their maximum speed 20 min after sunrise and end at 1100 local time. For the considered period, low-level jet events occurred during 88 % of nights, and most of these events were fully characterized; thus, 73 % of the nights presented with categorized lowlevel jets following the classical literature on this mesoscale phenomenon in other parts of the world. The low-level wind maxima occurred with events ranging from category sub-zero to category 3. The strongest category 3 events are around 25 m s −1 and the longest event was 57.5 h, but they are more typical of category 1. Their average speed is 11.7 m s −1 and their height distribution is bimodal, with a group of events occurring at lower levels, with an average height of 190 m; higher levels have a mean height of 480 m. The higher cases are more typical of the rainy season. During all seasons, their direction is predominantly from the north-northwest to north-northeast with some dispersion occurring during the rainy season. The region of study is typically considered to have low wind speeds in the atmospheric boundary layer, making these events super-geostrophic. Keywords Land-sea contrasts • Low-level wind maxima • Low-level jet • Radio acoustic sounding system (RASS) • Sodar • Stable boundary layer • Tropical boundary layer

Resumo Este artigo é uma contribuição do Projeto “uso de VANT para prospecção eólica em sistemas aquáticos”, que consistiu num esforço multi-instrumental e multi-institucional para estudar a camada limite atmosférica influenciada por extensos corpos d’água e pelas feições do entorno como colinas, rampas e mudanças abruptas de rugosidade. O trabalho apresenta o resultado de um experimento específico, realizado em novembro de 2016, que visou estudar a camada limite atmosférica (CLA) influenciada por colinas. Durante os experimentos foram levantados perfis verticais do vento a partir de um VANT, utilizado pela primeira vez no Brasil, para esta finalidade. O escoamento do vento, no topo da colina, apresentou forte intensificação a 20 m de altura. Os resultados foram comparados com um modelo analítico baseado na teoria linear aplicado a um terreno real.

Experimentos numéricos realizados com o RAMS e análises de dados meteorológicos e hidrológicos são usados para avaliar o impacto da variação no nível do reservatório de Sobradinho sobre os processos meteorológicos e variáveis climáticas na região do lago. A represa tem capacidade de armazenar 34,1 bilhões de metros cúbicos de água, mas pode operar com apenas 35% do seu volume útil. Periodicamente, extensas faixas de terra anteriormente submersas são expostas em torno do lago. Um conjunto de fatores é responsável pelo comportamento climatológico na área da represa. Excluída a influência do escoamento de grande escala, uma combinação de fatores tais como a geometria do vale, a configuração das margens do reservatório, o relevo e a diversidade no uso da terra em torno do lago são responsáveis pela geração de um sistema de circulações complexo que inclui ventos de vale-montanha, anabáticos-catabáticos e brisas lacustres e terrestres. Os resultados mostram que a variação no nível do lago e conseqüente contração e expansão da área alagada produz variações espaciais significantes na direção e intensidade do vento, temperatura e umidade atmosféricas.

We use two series of eight-month UHF radar observations collected during the dry and wet seasons of AMMA field campaign. The ultimate goal is to do preliminary work to know whether the lowest layers are suitable for wind energy applications. Surface wind is usually weak in West Africa, but the regular occurrence of a nocturnal low level jet (NLLJ) could provide interesting conditions for wind energy. This work is two-fold: it first aims at improving our knowledge about the NLLJ in West Africa regarding its structure and its variability during the year. Then, special attention is paid to the first 200 m agl, to study the possibility to use the sub-jet wind as a source of energy. A set of enhanced radio-soundings is taken to help to understand the dynamics and thermodynamics and to find a way to extrapolate the wind at low level, where the UHF radars do not provide data.

Foram comparados perfis do vento horizontal medidos por radiossondagens e por um equipamento SODAR durante experimento DRYTOWET-AMC/LBA. em 2002, no Estado de Rondônia. As análises foram feitas para três camadas, a saber: da superfície até 500 m, de 500 m até 1000 m e de 1000 m até 1500 m. Na primeira camada os campos apresentaram boa concordância, porém, a correlação entre as medidas diminuiu de forma significativa nas outras duas camadas. Os resultados sugerem que os dados do SODAR poderiam ser mais bem aproveitados se na instalação do instrumento fosse dada prioridade a uma camada menos profunda (até 500 m) e com uma resolução vertical maior.

During field experiments using surface weather stations and a Sodar-RASS (radio acoustic sounding system) combination, low-level jets were observed in the Colima Valley of central western Mexico. These low-level jet events have not been previously observed in this part of the tropics. The present study focuses on events from one specific field period from December 2011 to April 2013 performed at a specific location. From this dataset, it was found that these phenomena typically develop at night at around 0300 local time and they reach their maximum speed 20 min after sunrise and end at 1100 local time. For the considered period, low-level jet events occurred during 88 % of nights, and most of these events were fully characterized; thus, 73 % of the nights presented with categorized lowlevel jets following the classical literature on this mesoscale phenomenon in other parts of the world. The low-level wind maxima occurred with events ranging from category sub-zero to category 3. The strongest category 3 events are around 25 m s −1 and the longest event was 57.5 h, but they are more typical of category 1. Their average speed is 11.7 m s −1 and their height distribution is bimodal, with a group of events occurring at lower levels, with an average height of 190 m; higher levels have a mean height of 480 m. The higher cases are more typical of the rainy season. During all seasons, their direction is predominantly from the north-northwest to north-northeast with some dispersion occurring during the rainy season. The region of study is typically considered to have low wind speeds in the atmospheric boundary layer, making these events super-geostrophic. Keywords Land-sea contrasts • Low-level wind maxima • Low-level jet • Radio acoustic sounding system (RASS) • Sodar • Stable boundary layer • Tropical boundary layer

The atmospheric circulation of the Tapajós River region has unique characteristics due to influences of forests, agricultural fields, rivers and urban areas. The study with regard to the wind field in two different points in National Forest Tapajós (FNT) shows that there are significant differences in wind direction at those points. Identifying and quantify of the North and South canalization, and westerly winds, give important indications for studying the influence of different areas on the FNT. The results show that the occurrences of drains and west winds are more present during the rainy season and occur more during the day. Furthermore, in Jamaraquá station nearest to the River, the influence of channeling and west winds are greater, which can be due not only proximity of river but also the topographical features.

A low-level jet (LLJ) event observed during a frontal passage in the 2001 Coupled Boundary Layers and Air–Sea Transfer Experiment in Low Winds campaign was simulated using the Weather Research and Forecasting model (WRF). The sensitivity of the modeled LLJ characteristics, such as formation time, height and the strength of the LLJ core, to the choice of initial and boundary conditions, planetary boundary layer (PBL) schemes and vertical resolution was evaluated with a suite of diagnostic tools. The model simulations were compared against available soundings from the campaign observations as well as with surface observations from the Automated Surface Observing Systems. The simulation initialized with ERA-interim reanalysis and using the Mellor–Yamada–Nakanishi–Niino PBL scheme gave the best mix of diagnostic scores for surface temperature and wind speed predictions. The choice of boundary conditions introduced a stronger variability in the LLJ characteristics than the changes in PBL...

h i g h l i g h t s < We identify 16 significant Asian dust events to Taiwan from 2002 to 2008. < We further classified into dry and wet types according to atmospheric conditions. < Mean mass fractions of major aerosol species in the PM 10 and PM 2.5 were discussed. < Meteorological and air quality models were employed to study the transport mechanism.

A study of the possibIe impIications of the substitution of the Amazonian forest for pasture in the State ofRondônia, with reIation to the thermodynamic processes that govern the Atmospheric Boundary Layer (ABL) was carried out. In this study, di verse important parameters in the development ofthe CLA have been compared, on the basis of col Iected data campaigns of RBLE (Rondonia Boundary Layer Experiment) Project, conducted during the dry station of 1994. Measures of altitude with the aid ofradiossonds and tethered balloons and ofsurface in are as ofForest (F) and Pasture (P) habe been perfomed. The results showed evidence of important differences between the ABL on the two types of vegetation. In the area deforested (pasture), dut;ing the day, the growth rate is practically the double, the CLA is 2,7K hotter and 3.0gkg-1 drier and its thickness can be 1000m Iager. During the night the humidity difference starts to be the double of that registered during the day. On the other hand,...

The Level Low Jet (LLJ) observed in the Porto Alegre metropolitan region, Rio Grande do Sul State, Brazil, was analyzed using 1989-2003 at 00:00 and 12:00 UTC upper-air observations. The LLJ classification criteria proposed by Bonner (1968) and modified by Whiteman et al. (1997) were applied to determine the LLJ occurrence. Afterwards was selected a LLJ event, that was one of the most intense observed in the summer (01/27/2002 at 12:00 UTC), during the study period. In this study were used as tools: atmospheric soundings, GOES-8 satellite images, and wind, temperature and specific humidity fields from GLOBAL, ETA and BRAMS models. Based on the numerical analysis was possible to verify that the three models overestimated the specific humidity and potential temperature values, at LLJ time occurrence. The wind speed was underestimated by the models. It was observed in the study region, at 12:00 UTC (LLJ detected hour in the Porto Alegre region), by three models, warm and wet air from north, generating conditions to Mesoscale Convective System (MCS) formation and intensification.

The atmospheric circulation of the Tapajós River region has unique characteristics due to influences of forests, agricultural fields, rivers and urban areas. The study with regard to the wind field in two different points in National Forest Tapajós (FNT) shows that there are significant differences in wind direction at those points. Identifying and quantify of the North and South canalization, and westerly winds, give important indications for studying the influence of different areas on the FNT. The results show that the occurrences of drains and west winds are more present during the rainy season and occur more during the day. Furthermore, in Jamaraquá station nearest to the River, the influence of channeling and west winds are greater, which can be due not only proximity of river but also the topographical features.

The primary goal of the Second Wind Forecast Improvement Project (WFIP2) is to advance the state-of-the-art of wind energy forecasting in complex terrain. To achieve this goal, a comprehensive 18-month field measurement campaign was conducted in the region of the Columbia River basin. The observations were used to diagnose and quantify systematic forecast errors in the operational High-Resolution Rapid Refresh (HRRR) model during weather events of particular concern to wind energy forecasting. Examples of such events are cold pools, gap flows, thermal troughs/marine pushes, mountain waves, and topographic wakes. WFIP2 model development has focused on the boundary layer and surface-layer schemes, cloud–radiation interaction, the representation of drag associated with subgrid-scale topography, and the representation of wind farms in the HRRR. Additionally, refinements to numerical methods have helped to improve some of the common forecast error modes, especially the high wind speed bi...

For 20 years the biennial symposia organized by the International Society for Acoustic Remote Sensing of the Atmosphere and Oceans and Associated Techniques (ISARS) have been held in different countries. The original papers collected in the proceedings of the symposia reflect the development of ideas, equipment, and methods, plus results obtained in the area. The spectrum of themes discussed at the symposia is broad. More than 60% of the papers were devoted to the role of SODARs in atmospheric boundary-layer research. This paper presents an overview of the development of SODAR technique as elucidated in the proceedings of 11 ISARS symposia. Topics include (1) instrumentation, (2) methods of measuring different meteorological quantities and their turbulence characteristics, and (3) validating the methods by comparison of SODAR data with in situ measurements.

⎯Results of acoustic sounding of the lower troposphere with the aid of detonation generators of acoustic pulses are given. This sounding method is based on a partial reflection of acoustic pulses with shock fronts from vertical wind-velocity and temperature gradients continuously varying with height in the troposphere and on the penetration of reflected signals into the region of acoustic shadow. Experiments on tropospheric sounding were carried out on the ground of the Barva Innovation Scientific and Technical Center (Talin, Armenia) in September 2015. In these experiments, an antihail acoustic system was first used as a generator of acoustic pulses. Experimental results have been compared with data obtained earlier in similar experiments carried out in the vicinity of Zvenigorod with the use of a special detonation generator of acoustic pulses. Due to the high resolution (in height) of the sounding method, which reaches 1 m in the stably stratified lower troposphere within a height range of 250-600 m, the vertical profiles of layered effective sound speed inhomogeneities with vertical scales from a few to a few tens of meters have been retrieved. The influence of these fluctuations on the form and amplitude of acoustic signals at a long distance from their pulsed source has been studied.

The studies conducted in 1991-2004 by scientists of the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, and the Karpov Institute of Physical Chemistry yielded data on the structures of the surface air layer (to a height of 20 m) and both subinversion and inversion layers (to heights of from 800 m to 1 km), where arid aerosol is transported. One of the main objectives of the 2007 experiment was to record the space-vortex structures within a layer of 30-700 m that directly provide the removal and longrange transport of fine-dispersed (<5 µ m) desert aerosol. This paper describes the organization of the Khar-Gzyr 2007 experiment (Black Lands, 2007) to study the convective removal of arid aerosol from desertificated lands, and it presents some data obtained from the remote sensing of the atmospheric boundary layer with a sodar network in the course of this experiment. The sodar network, which was developed to study a spatial structure of coherent vortices, included three identical minisodars (with carrier frequencies of 3.8 kHz) located at the apices of a triangle, each side of which was about 3.5 km, and a sodar (with a carrier frequency of 1.7 kHz). The vertical profiles of the three wind-velocity components and the characteristics of air temperature fluctuations were determined. The procedure of identifying coherent vortex structures is described. The variations in the vertical and horizontal wind-velocity components and the scales characteristic of such structures are estimated.

Resumo Este artigo é uma contribuição do Projeto “uso de VANT para prospecção eólica em sistemas aquáticos”, que consistiu num esforço multi-instrumental e multi-institucional para estudar a camada limite atmosférica influenciada por extensos corpos d’água e pelas feições do entorno como colinas, rampas e mudanças abruptas de rugosidade. O trabalho apresenta o resultado de um experimento específico, realizado em novembro de 2016, que visou estudar a camada limite atmosférica (CLA) influenciada por colinas. Durante os experimentos foram levantados perfis verticais do vento a partir de um VANT, utilizado pela primeira vez no Brasil, para esta finalidade. O escoamento do vento, no topo da colina, apresentou forte intensificação a 20 m de altura. Os resultados foram comparados com um modelo analítico baseado na teoria linear aplicado a um terreno real.

As linhas de instabilidade (LI) são tempestades multicelulares e é bem conhecido que fatores como o cisalhamento vertical do vento podem agir para organizar a convecção, porém há poucos indícios de como jatos de médios e baixos níveis podem alterar os processos de nuvens e, por sua vez, interferir na intensidade, duração e propagação desses sistemas. Este trabalho tenta mostrar esse papel utilizando um caso de LI amazônica simulada a partir de um perfil atmosférico do vento em Belém - PA às 12:00 UTC do dia 30 de maio de 2008. Para isso, uma série de 8 experimentos numéricos, alterando-se o perfil do vento e utilizando-se o BRAMS, foi realizada. Os resultados mostraram que com a ocorrência de um jato profundo e intenso até os médios níveis pode haver uma maior ventilação nas nuvens, implicando em mais evaporação e secagem, ou seja, maior entranhamento. O entranhamento sendo maior pode interferir nas correntes descendentes, nas piscinas frias, na convergência à frente do sistema e na...

In 2014/2015 a one-year field campaign at the Tiksi observatory in the Laptev Sea area was carried out using Sound Detection and Ranging/Radio Acoustic Sounding System (SODAR/RASS) measurements to investigate the atmospheric boundary layer (ABL) with a focus on low-level jets (LLJ) during the winter season. In addition to SODAR/RASS-derived vertical profiles of temperature, wind speed and direction, a suite of complementary measurements at the Tiksi observatory was available. Data of a regional atmospheric model were used to put the local data into the synoptic context. Two case studies of LLJ events are presented. The statistics of LLJs for six months show that in about 23% of all profiles LLJs were present with a mean jet speed and height of about 7 m/s and 240 m, respectively. In 3.4% of all profiles LLJs exceeding 10 m/s occurred. The main driving mechanism for LLJs seems to be the baroclinicity, since no inertial oscillations were found. LLJs with heights below 200 m are likely...

The aim of the research project “Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer (ISOBAR)” is to substantially increase the understanding of the stable atmospheric boundary layer (SBL) through a combination of well-established and innovative observation methods as well as by models of different complexity. During three weeks in February 2017, a first field campaign was carried out over the sea ice of the Bothnian Bay in the vicinity of the Finnish island of Hailuoto. Observations were based on ground-based eddy-covariance (EC), automatic weather stations (AWS) and remote-sensing instrumentation as well as more than 150 flight missions by several different Unmanned Aerial Vehicles (UAVs) during mostly stable and very stable boundary layer conditions. The structure of the atmospheric boundary layer (ABL) and above could be resolved at a very high vertical resolution, especially close to the ground, by combining surface-based measurements with UAV observ...

Some determinants aspects for local circulations in the regionof National Forest of Caxiuana have been investigated using a highresolution model to simulate micro and meso-scale local processes, whichhas been executed for 24 hours. The results show a horizontal temperaturegradient upon to 1,4oC between the forest and Caxiuana Bay.

This paper uses the comparative method in order to highlight the thermal anomalies, the impact of atmospheric circulation and the air masses through specific situations. Our preliminary study employs radio sounding data from Bucharest-Băneasa weather station, and this method is applied for an altitude interval bounded by Earth&#39;s surface and the geopotential surface of 900hPa. Thus, the results have been obtained from radio soundings up to the 900 hPa level, which corresponds to an altitude of 1000 meters, because above this level, there is a tendency towards generalization due to the decreased influence of the subjacent active surface and the impact of the particularities of the general atmospheric circulation above Bucharest. The aim of the study was to explain the temperature distribution through statistical shape/form indices and to measure their degree of flattening and asymmetry. Processing the radio-soundings data complemented, when not measured, by the remote sensing data...

We have analyzed long-term wind speed time-series from five field sites up to a height of 300 m from the ground. Structure function-based scaling analysis has revealed that the scaling exponents in the mesoscale regime systematically depend on height. This anomalous behavior is likely caused by the buoyancy effects. In the framework of the extended self-similarity, the relative scaling exponents portray quasi-universal behavior.

Geostationary Operational Environmental Satellite-14 (GOES-14) 1-km visible satellite data with 1-min frequency revealed horizontally propagating internal gravity waves emanating from tropopause-penetrating deep convection on 3–4 June 2015 during the Plains Elevated Convection at Night (PECAN) field experiment. These waves had horizontal wavelengths of ~6–8 km and approximate ground-relative phase speeds of 35 m s−1. PECAN radiosonde data are used to document the environment supporting the horizontally propagating gravity waves within the 200-km-long downstream thunderstorm anvil. Comparisons among soundings within the anvil core, at the downstream anvil edge, and outside of the anvil, together with supporting high-resolution numerical simulations, establish the importance of the storm-induced upper-tropospheric/lower-stratospheric (UTLS) outflow in providing conditions allowing vertical trapping of internal gravity waves over large horizontal distances within the mesoscale anvil. T...

O principal objetivo deste trabalho foi identificar e caracterizar a evolução diária da Camada Limite Atmosférica (CLA) na Região da Grande Vitória (RGV), Estado do Espírito Santo, Brasil e na Região de Dunkerque (RD), Departamento Nord Pas-de-Calais, França, avaliando a acurácia de parametrizações usadas no modelo meteorológico Weather Research and Forecasting (WRF) em detectar a formação e atributos da Camada Limite Interna (CLI) que é formada pelas brisas marítimas. A RGV tem relevo complexo, em uma região costeira de topografia acidentada e uma cadeia de montanhas paralela à costa. A RD tem relevo simples, em uma região costeira com pequenas ondulações que não chegam a ultrapassar 150 metros, ao longo do domínio de estudos. Para avaliar os resultados dos prognósticos feitos pelo modelo, foram utilizados os resultados de duas campanhas: uma realizada na cidade de Dunkerque, no norte da França, em Julho de 2009, utilizando um sistema light detection and ranging (LIDAR), um sonic d...