Radio Acoustic Sounding System Research Articles

Sensitivity of thermodynamic profiles retrieved from ground-based microwave and infrared observations to additional input data from active remote sensing instruments and numerical weather prediction models

Abstract. Accurate and continuous estimates of the thermodynamic structure of the lower atmosphere are highly beneficial to meteorological process understanding and its applications, such as weather forecasting. In this study, the Tropospheric Remotely Observed Profiling via Optimal Estimation (TROPoe) physical retrieval is used to retrieve temperature and humidity profiles from various combinations of input data collected by passive and active remote sensing instruments, in situ surface platforms, and numerical weather prediction models. Among the employed instruments are microwave radiometers (MWRs), infrared spectrometers (IRSs), radio acoustic sounding systems (RASSs), ceilometers, and surface sensors. TROPoe uses brightness temperatures and/or radiances from MWRs and IRSs, as well as other observational inputs (virtual temperature from the RASS, cloud-base height from the ceilometer, pressure, temperature, and humidity from the surface sensors) in a physical iterative retrieval approach. This starts from a climatologically reasonable profile of temperature and water vapor, with the radiative transfer model iteratively adjusting the assumed temperature and humidity profiles until the derived brightness temperatures and radiances match those observed by the MWR and/or IRS instruments within a specified uncertainty, as well as within the uncertainties of the other observations, if used as input. In this study, due to the uniqueness of the dataset that includes all the abovementioned sensors, TROPoe is tested with different observational input combinations, some of which also include information higher than 4 km above ground level (a.g.l.) from the operational Rapid Refresh numerical weather prediction model. These temperature and humidity retrievals are assessed against independent collocated radiosonde profiles under non-cloudy conditions to assess the sensitivity of the TROPoe retrievals to different input combinations.

Method for adapting radioacoustic sounding systems of the atmosphere

Stations of radioacoustic sounding (RAS) of the atmosphere are a promising means of obtaining information about the altitudinal distribution of meteorological parameters in the Earth's atmosphere used in the process of solving current scientific and applied tasks to ensure aircraft flights, weather forecasting, etc. However, the effectiveness of the existing radio-acoustic means is insufficient, and there are practical needs for the development of appropriate prospective structures and algorithms, which will be implemented during the construction of specific stations designed to solve actual applied tasks. The article presents the synthesis of the RAS systems algorithm adaptation performed by changing the frequency of the sounding radio signal to fulfill the Bragg condition when the emitted acoustic pulse signal moves along the sounding path from the standpoint of optimal control theory. Since in the problem of synthesizing the algorithm for controlling the frequency of a radio signal, the disturbing and leading to violations of the Bragg condition during the propagation of an acoustic packet along the sounding path, as well as the process causing measurement errors, are considered as random, this problem is considered as a problem of stochastic optimal control. It is shown that in accordance with the separation theorem, known from the theory of optimal stochastic control, the method of controlling the frequency of a sounding radio signal should include sequentially peformed operations of forming estimates of the information parameter of the scattered radio signal, optimal linear filtering of the obtained estimates, and deterministic control of the frequency of the sounding radio signal.

Wind Profiler for Understanding of Meiyu at Dongshan

Abstract: To understand the Meiyu Boundary layer evolutionand vertical structure of precipitating cloud systems over Dongshan, special observational campaigns have been conducted downstream of the Yangtze River during June and July in the years 2001 and 2002. We deployed a Lower Atmospheric Wind Profiler (LAWP) with Radio Acoustic Sounding System (RASS) at the Meteorological Observatory, Dongshan within a mesoscale network that consists of three X-band Doppler radars, three AWS, and Micro rain radar to observe the inner structure of precipitating cloud systems seen frequently in the observational area. The LAWP provides vertical profiles of three-dimensional wind, vertical structure of the precipitating cloud system, convective boundary layer (CBL), and temperature from the (RASS) lower atmosphere with a height resolution of 60 m to 200 m and a time resolution of about 1 to 60 minutes. LAWP had been operated in two modes: low mode and high mode up to 4 km and 11 km height during non-rainy and rain conditions, respectively. A study was carried out during an intensive observational period (IOP-2001 and IOP-2002) to understand the pre-convective environments in the boundary layer during pre-Meiyu and Meiyu convective days to find out whether there is any precursor before the convection triggering. Further in Meiyu precipitating cloud systems, the reflectivity vertical structure can be used to identify the range of precipitation processes from the young, dynamically vigorous cells to the mature, bright band resolved stratiform rain.

Variation of virtual temperature and wind in the atmospheric boundary layer over the pearl river estuary during 2011–2020

Most studies of the effects of urbanisation on local climate have been based on ground observation data. In contrast, we used observation data from a boundary layer radar wind profiler, radio-acoustic sounding system, and automatic meteorological station located at Shenzhen Bao’an International Airport to analyse changes in wind and virtual temperature in the upper level atmosphere, with a top height of 1,200 m, over the Pearl River Estuary between 2011 and 2020. Our results show that during the decade evaluated, the wind speed and virtual temperature of the upper level atmosphere over the Pearl River Estuary changed very significantly and faster than the changes observed at ground level. During the study period, the linear warming rate of the virtual temperature of the upper level atmosphere reached 0.24°C/a, whereas that on the land surface was 0.17°C/a. The mean decreases in the upper level atmosphere and land surface wind speeds were −0.12 and −0.05 m/s·a, respectively. Additionally, the rate of change in the upper level climate was faster in winter than in summer for both wind speed and virtual temperature. These changes in the climate of the upper level atmosphere over the Pearl River Estuary may be related to the rapid increase in the number of high-rise buildings in the region during that decade, which generally negatively affected the atmospheric environment.

The impacts of wildfires on ozone production and boundary layer dynamics in California's Central Valley

Abstract. We investigate the role of wildfire smoke on ozone photochemical production (P(O3)) and atmospheric boundary layer (ABL) dynamics in California's Central Valley during June–September from 2016 to 2020. Wildfire events are identified by the Hazard Mapping System (HMS) and the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT). Air quality and meteorological data are analyzed from 10 monitoring sites operated by the California Air Resources Board (CARB) across the Central Valley. On average, wildfires were found to influence air quality in the Central Valley on about 20 % of the total summer days of the study. During wildfire-influenced periods, maximum daily 8 h averaged (MDA8) O3 was enhanced by about 5.5 ppb or 10 % of the median MDA8 (once corrected for the slightly warmer temperatures) over the entire valley. Overall, nearly half of the total exceedances of the National Ambient Air Quality Standards (NAAQS) where MDA8 O3 > 70 ppb occur under the influence of wildfires, and approximately 10 % of those were in exceedance by 5 ppb or less indicating circumstances that would have been in compliance with the NAAQS were it not for wildfire emissions. The photochemical ozone production rate calculated from the modified Leighton relationship was also found to be higher by 50 % on average compared with non-fire periods despite the average diminution of j(NO2) by ∼ 7 % due to the shading effect of the wildfire smoke plumes. Surface heat flux measurements from two AmeriFlux sites in the northern San Joaquin Valley show midday surface buoyancy fluxes decrease by 30 % on average when influenced by wildfire smoke. Similarly, afternoon peak ABL heights measured from a radio acoustic sounding system (RASS) located in Visalia in the southern San Joaquin Valley were found to decrease on average by 80 m (∼ 15 %) with a concomitant reduction of downwelling shortwave radiation of 54 Wm−2, consistent with past observations of the dependence of boundary layer heights on insolation.

Improving thermodynamic profile retrievals from microwave radiometers by including radio acoustic sounding system (RASS) observations

Abstract. Thermodynamic profiles are often retrieved from the multi-wavelength brightness temperature observations made by microwave radiometers (MWRs) using regression methods (linear, quadratic approaches), artificial intelligence (neural networks), or physical iterative methods. Regression and neural network methods are tuned to mean conditions derived from a climatological dataset of thermodynamic profiles collected nearby. In contrast, physical iterative retrievals use a radiative transfer model starting from a climatologically reasonable profile of temperature and water vapor, with the model running iteratively until the derived brightness temperatures match those observed by the MWR within a specified uncertainty. In this study, a physical iterative approach is used to retrieve temperature and humidity profiles from data collected during XPIA (eXperimental Planetary boundary layer Instrument Assessment), a field campaign held from March to May 2015 at NOAA's Boulder Atmospheric Observatory (BAO) facility. During the campaign, several passive and active remote sensing instruments as well as in situ platforms were deployed and evaluated to determine their suitability for the verification and validation of meteorological processes. Among the deployed remote sensing instruments were a multi-channel MWR as well as two radio acoustic sounding systems (RASSs) associated with 915 and 449 MHz wind profiling radars. In this study the physical iterative approach is tested with different observational inputs: first using data from surface sensors and the MWR in different configurations and then including data from the RASS in the retrieval with the MWR data. These temperature retrievals are assessed against co-located radiosonde profiles. Results show that the combination of the MWR and RASS observations in the retrieval allows for a more accurate characterization of low-level temperature inversions and that these retrieved temperature profiles match the radiosonde observations better than the temperature profiles retrieved from only the MWR in the layer between the surface and 3 km above ground level (a.g.l.). Specifically, in this layer of the atmosphere, both root mean square errors and standard deviations of the difference between radiosonde and retrievals that combine MWR and RASS are improved by mostly 10 %–20 % compared to the configuration that does not include RASS observations. Pearson correlation coefficients are also improved. A comparison of the temperature physical retrievals to the manufacturer-provided neural network retrievals is provided in Appendix A.

Analysis of properties of integral equations of the field in the aperture of an open coaxial probe

Acoustic sounding systems are an effective means of monitoring the lower troposphere. They find application in various fields of science and technology. The problem of developing acoustic methods and means for remote sensing of the lower atmosphere remains relevant given the importance of information on the state of the atmospheric boundary layer for the functioning of areas such as meteorology, ecology, transport, especially aviation, agriculture and others. This problem has both theoretical and technical aspects. These, for example, include solving inverse problems of sound propagation in a turbulent atmosphere, compensation for wind shear, and others. A number of companies and universities create acoustic locators – sodars and radio-acoustic sounding systems. The paper discusses their application for assessing the propagation conditions of radio waves on surface paths near the land-sea boundary. Despite the development of satellite systems for transmitting information and positioning, traditional means of communication and navigation are still in demand. They occupy their niche in the general nomenclature of radio equipment, while remaining indispensable in emergency warning systems, navigation in limited areas, in emergency situations. The effectiveness of these tools largely depends on operational information on the state of the propagation paths of radio waves. One of the most complex objects for assessing the propagation conditions of radio waves is the atmospheric boundary layer. Its condition is largely determined by the state of the underlying surface, which in turn depends on the time of day, season, rainfall and other factors. To date, only very limited theoretical models of dynamics have been created for some states of the atmospheric boundary layer despite the considerable efforts of meteorological specialists. Therefore, information is required on the spatial distribution of meteorological parameters. The most promising solution to this problem is the use of remote non-contact sensing methods based on one or another form of wave processes. Acoustic waves are significantly more sensitive to changes in air parameters than other types of radiation. The objectives of this work are to present a comprehensive methodology for using remote, non-contact sensing methods, theoretical representations of the dynamics of APS and modern software for solving problems of promptly determining the conditions of RRS on surface paths and assessing the most promising ways of developing methods and means for obtaining this information.An example of the experimental results of radio-acoustic sounding and sodar monitoring of the atmospheric boundary layer near the land-sea boundary is given. Based on these results, the spatial-temporal distribution of the index of refractive index is estimated. An analysis of the results is given. The choice of ways to develop means of acoustic sensing and processing the information received is substantiated, taking into account the progress of electronic devices and systems.

Identification and Characterization of Persistent Cold Pool Events from Temperature and Wind Profilers in the Columbia River Basin

AbstractCold pool events occur when deep layers of stable, cold air remain trapped in a valley or basin for multiple days, without mixing out from daytime heating. With large impacts on air quality, freezing events, and especially on wind energy production, they are often poorly forecast by modern mesoscale numerical weather prediction (NWP) models. Understanding the characteristics of cold pools is, therefore, important to provide more accurate forecasts. This study analyzes cold pool characteristics with data collected during the Second Wind Forecast Improvement Project (WFIP2), which took place in the Columbia River basin and Gorge of Oregon and Washington from fall 2015 until spring 2017. A subset of the instrumentation included three microwave radiometer profilers, six radar wind profilers with radio acoustic sounding systems, and seven sodars, which together provided seven sites with collocated vertical profiles of temperature, humidity, wind speed, and wind direction. Using these collocated observations, we developed a set of criteria to determine if a cold pool was present based on stability, wind speed, direction, and temporal continuity, and then developed an automated algorithm based on these criteria to identify all cold pool events over the 18 months of the field project. Characteristics of these events are described, including statistics of the wind speed distributions and profiles, stability conditions, cold pool depths, and descent rates of the cold pool top. The goal of this study is a better understanding of these characteristics and their processes to ultimately lead to improved physical parameterizations in NWP models, and consequently improve forecasts of cold pool events in the study region as well at other locations that experiences similar events.

Application of parametric speakers to radio acoustic sounding system

Abstract. In this study, a wind profiler with a radio acoustic sounding system (RASS) and operational radiosonde measurements were used to investigate the technical practicability and reliability of using parametric speakers to measure the vertical profile of virtual temperature. Characteristics of parametric speakers include high directivity and very low side lobes, which are preferable for RASS, especially those operating in urban areas. The experiments were conducted on fine days with light winds to mitigate the effects of the horizontal and vertical components of wind on acoustic waves used for RASS. The results of this study indicated that, although parametric speaker RASS is susceptible to horizontal winds due to the narrower acoustic beam, bias and standard deviation of parametric speaker RASS versus radiosonde virtual temperature difference (0.1 ∘C, 0.4 ∘C) were close to those from acoustic speakers (0.0 ∘C, 0.4 ∘C). In addition, when compared with acoustic speaker RASS, the values for the parametric speaker RASS were even smaller (0.1 ∘C, 0.2 ∘C). Based on these results, it is concluded that the parametric speaker RASS has accuracy and precision comparable with acoustic speaker RASS despite its high directivity of sound.

Residual layer ozone, mixing, and the nocturnal jet in California's San Joaquin Valley

Abstract. The San Joaquin Valley of California is known for excessive ozone air pollution owing to local production combined with terrain-induced flow patterns that channel air in from the highly populated San Francisco Bay area and stagnate it against the surrounding mountains. During the summer, ozone violations of the National Ambient Air Quality Standards (NAAQS) are notoriously common, with the San Joaquin Valley having an average of 115 violations of the current 70 ppb standard each year between 2012 and 2016. Because regional photochemical production peaks with actinic radiation, most studies focus on the daytime, and consequently the nocturnal chemistry and dynamics that contribute to these summertime high-ozone events are not as well elucidated. Here we investigate the hypothesis that on nights with a strong low-level jet (LLJ), ozone in the residual layer (RL) is more effectively mixed down into the nocturnal boundary layer (NBL) where it is subject to dry deposition to the surface, the rate of which is itself enhanced by the strength of the LLJ, resulting in lower ozone levels the following day. Conversely, nights with a weaker LLJ will sustain RLs that are more decoupled from the surface, retaining more ozone overnight, and thus lead to more fumigation of ozone the following mornings, giving rise to higher ozone concentrations the following afternoon. The relative importance of this effect, however, is strongly dependent on the net chemical overnight loss of Ox (here [Ox] ≡ [O3] + [NO2]), which we show is highly uncertain, without knowing the ultimate chemical fate of the nitrate radical (NO3). We analyze aircraft data from a study sponsored by the California Air Resources Board (CARB) aimed at quantifying the role of RL ozone in the high-ozone events in this area. By formulating nocturnal scalar budgets based on pairs of consecutive flights (the first around midnight and the second just after sunrise the following day), we estimate the rate of vertical mixing between the RL and the NBL and thereby infer eddy diffusion coefficients in the top half of the NBL. The average depth of the NBL observed on the 12 pairs of flights for this study was 210(±50) m. Of the average −1.3 ppb h−1 loss of Ox in the NBL during the overnight hours from midnight to 06:00 PST, −0.2 ppb h−1 was found to be due to horizontal advection, −1.2 ppb h−1 due to dry deposition, −2.7 ppb h−1 to chemical loss via nitrate production, and +2.8 ppb h−1 from mixing into the NBL from the RL. Based on the observed gradients of Ox in the top half of the NBL, these mixing rates yield eddy diffusivity estimates ranging from 1.1 to 3.5 m2 s−1, which are found to inversely correlate with the following afternoon's ozone levels, providing support for our hypothesis. The diffusivity values are approximately an order of magnitude larger than the few others reported in the extant literature for the NBL, which further suggests that the vigorous nature of nocturnal mixing in this region, due to the LLJ, may have an important control on daytime ozone levels. Additionally, we propose that the LLJ is a branch of what is colloquially referred to as the Fresno eddy, which has been previously proposed to recirculate pollutants. However, vertical mixing from the LLJ may counteract this effect, which highlights the importance of studying the LLJ and Fresno eddy as a single interactive system. The synoptic conditions that are associated with strong LLJs are found to contain deeper troughs along the California coastline. The LLJs observed during this study had an average centerline height of 340 m, average speed of 9.9 m s−1 (σ=3.1 m s−1), and a typical peak timing around 23:00 PST. A total of 7 years of 915 MHz radioacoustic sounding system and surface air quality network data show an inverse correlation between the jet strength and ozone the following day, further suggesting that air quality models need to forecast the strength of the LLJ in order to more accurately predict ozone violations.

Atmospheric Duct Detection Using Wind Profiler Radar and RASS

AbstractA method of detecting atmospheric ducts using a wind profiler radar (WPR) and a radio acoustic sounding system (RASS) is proposed. The method uses the RASS to measure the virtual temperature profile and calculate the Brunt–Väisälä frequency; it also uses the WPR to measure the spectral width of the atmosphere and the atmospheric refractive index structure constant. Then the profile of the atmospheric refractive index gradient and modified refractivity are calculated using virtual temperature, spectral width, and the atmospheric refractive index structure constant. Finally, the height and intensity of the atmospheric duct are calculated to achieve continuous monitoring of the atmospheric duct. To verify the height and intensity of the atmospheric duct, comparison experiments between WPR-RASS and radiosondes were carried out from June 2014 to June 2015 in Dalian, Liaoning Province, China. The results show that the profile of modified refractivity by WPR-RASS has exactly the same trend as the radiosondes, the two methods have a good consistency, and the atmospheric duct value from WPR-RASS is in good agreement with that from radiosondes.

An Educational Deployment of the NCAR Mobile Integrated Sounding System

Abstract The best way to train the next wave of observational talent is through direct experience. In 2012 and again in 2014, students at St. Cloud State University (SCSU) welcomed deployments of professional atmospheric research equipment, allowing them to support and execute field projects. The Boundary Structure Experiments with Central Minnesota Profiling (BaSE CaMP) projects brought the Mobile Integrated Sounding System (MISS) from the National Center for Atmospheric Research’s (NCAR) Earth Observing Laboratory (EOL) to SCSU for a National Science Foundation–funded educational deployment. Its diverse instrumentation and ability to travel to interesting weather events and locations makes MISS extremely valuable for teaching students about both weather experiments and measurement strategies. In addition to the university project, outreach activities with MISS took place at high schools, regional conferences, and public events. MISS carries four instruments: a boundary layer wind profiler, a radio acoustic sounding system (RASS), radiosondes, and an instrumented 10-m tower. The type and time of MISS deployments were quite varied so students could participate around their class schedule, jobs, and other commitments. Each year the project had periods of fixed operations and mobile activity, where MISS was relocated to best observe current weather conditions. BaSE CaMP operations and results were incorporated into many classes in the meteorology program at SCSU. The original course request was for Radar and Satellite Meteorology, but other activities contributed to Atmospheric Dynamics, Physical Meteorology, and Meteorological Analysis Software courses.

Observation of Temperature Profiles of Kototabang (Bukittinggi-West Sumatera Indonesia) Using Radiosonde and Rain Event Identification

We recorded temperature profiles of Kototabang (West Sumatera-Indonesia) in a four days observation using Radio Acoustic Sounding System (RASS) and Radiosonde. The activity was carried out in August 2016, on a research cooperation framework of National Institute of Aeronautics and Space (LAPAN), Indonesia and Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Japan. The current article discussed the temperature profile based on 12 times launch of Radiosonde, Convective Available Potential Energy (CAPE) estimation and its relationship with rain events, while the temperature profile based on RASS was discussed in another report. CAPE is the amount of energy an air parcel would have if lifted to a certain distance vertically through the atmosphere. CAPE is effectively the positive buoyancy of an air parcel and is an indicator of atmospheric instability, related to convection clouds. If there is not enough water vapour present, there is no ability for condensation, and therefore, storms, clouds, and rain will not form. CAPE is calculated as the area of positive region in the thermodynamic diagram or through relationships with virtual temperature. On August 30, 2016, at 08 LT, the range of temperatures based on Radiosonde measurements was recorded from 294.9°K at ground level to 186.5°K at an altitude of 26.8 km. The temperature range varied with time. CAPE based on Radiosonde data ranged from 0 to 5075.2 Jkg-1 within 30 August 2016 until 2 September 2016. The maximum CAPE value occurred on August 30, 2016 at 15.34 LT. Large CAPE (> 2000 Jkg-1) was coincident with rain events.

Combination of the Equatorial Atmosphere Radar – Radio Acoustic Sounding System (EAR-RASS) in Determining a Fine Structure of Total Precipitable Water (TPW) over Kototabang, West Sumatera, Indonesia

This study is mainly concerned an application the combined of the Equatorial Atmosphere Radar (EAR) and Radio Acoustic Sounding System (RASS) in determining a fine structure of Total Precipitable Water (TPW) in the lower troposphere at Kototabang, West Sumatera (0.20°S; 100.32°E) during the CPEA I Campaign started from April 10 to May 9, 2004. It looks possible, since EAR-RASS is designed specially to detect the wind at three dimensional direction and virtual temperature with good time and spatial height resolution. By applying the Weisner technique (1970), we found a fine structure of TPW vertically during the above period. While, by applying the Cross-Correlation Function (CCF), we found an a goog agreement between TPW and Optical Rain Gauge (ORG). In the same time, we analyzed the Boundary Layer Radar (BLR) to investigate the updraft and downdraft air mass activities from surface up to 5 km. We found the consistency of BLR, RASS and radiometer data when we investigated the vertical profile of TPW. Futhermore, we found the time variation of TPW, especially on April 24 and May 5, 2005 are about 0.43 and 0.35, respectively. Detailed results of this study are discussed in this paper.

Retrieval of temperature profiles using radio acoustic sounding system (RASS) with the equatorial atmosphere radar (EAR) in West Sumatra, Indonesia

The radio acoustic sounding system (RASS) with the equatorial atmosphere radar (EAR) at Koto Tabang, Indonesia was adapted to test the effects of the acoustic source location and acoustic frequency range on the continuous measurement of height profiles of temperature in the tropical troposphere. We installed the acoustic transmitting system by using six high-power horn speakers and four subwoofers. We developed a three-dimensional ray-tracing method of acoustic waves to predict the shape of acoustic wavefronts, accounting for the effects of the background winds on acoustic wave propagation. Then, we selected the appropriate antenna beam directions for EAR that satisfy the Bragg condition between the radar and acoustic wave propagation vectors. We carried out eight campaign observations in 2016, testing the performance of EAR–RASS. We found that the location and acoustic frequency range affected the RASS echoes. We also tested the compensation method of the background wind velocity with EAR to obtain the true sound speed. We intensively analyzed the RASS results from August 29 to September 3, 2016, when radiosondes were launched 12 times from the EAR site. We successfully retrieved the temperature profiles from RASS from 2 to 6–14 km with time and height resolutions of about 10 min and 150 m, respectively. Some temperature profiles were obtained up to about the tropopause at 17 km, although the observation period was short. During the RASS campaign, we detected a few interesting events regarding temperature variations as well as large perturbations in the three components of wind velocity.

EXPERIMENTAL ESTIMATION OF EFFICIENCY OF DISTRIBUTED ACOUSTIC RADIATOR APPLICATION IN THE SYSTEM OF RADIO ACOUSTIC SENSING OF THE ATMOSPHERE

An estimation of efficiency of the distributed acoustic radiator using in the radio acoustic sounding (RAS) system, when measuring meteorological quantities, is carried out experimentally. A good coincidence of results of the wind speed measurement performed with the comparative means (RAS and mast anemorombometer) for some averaging is shown, though the standard deviations of results of measurement carried out using the RAS system and the anemorombometer are markedly different due to methodological and technical factors. In addition, the use of the distributed emitter in the RAS system gives a real possibility of simultaneous recording of air humidity in the investigated atmosphere layer and also improves the accuracy of recording temperature profiles by using the maximum of the video pulses amplitude for calculations. The RAS system with the distributed acoustic radiator can be made in a mobile version for synchronous measurements of the main meteorological values: the speed and direction of the horizontal wind, temperature and humidity of air in the field.

Validation of numerically forecast vertical temperature profile with measurements for dispersion modelling

Modelling of air pollution dispersion in the immediate vicinity of industrial sources over a complex terrain requires proper meteorological input data regarding the state of the atmosphere. For this purpose, numerical weather prediction-model results, rather than direct measurements, are becoming more widely used. In order to ensure high-quality modelling of the air-pollution dispersion, the forecast meteorological input data have to be of high quality. The quality of numerically obtained data has to therefore be validated with measurements. Measurements of the vertical temperature profile, which is vital, with radio acoustic sounding system (RASS) were used in this study. The paper presents the validation of the forecast vertical temperature profile over the complex terrain of the Krsko Basin. The validation is carried out with sensor measurements from a 70 metre tall tower and remote RASS measurements. 13 months' worth of data is used for the validation study.

Assessing the accuracy of microwave radiometers and radio acoustic sounding systems for wind energy applications

Abstract. To assess current remote-sensing capabilities for wind energy applications, a remote-sensing system evaluation study, called XPIA (eXperimental Planetary boundary layer Instrument Assessment), was held in the spring of 2015 at NOAA's Boulder Atmospheric Observatory (BAO) facility. Several remote-sensing platforms were evaluated to determine their suitability for the verification and validation processes used to test the accuracy of numerical weather prediction models.The evaluation of these platforms was performed with respect to well-defined reference systems: the BAO's 300 m tower equipped at six levels (50, 100, 150, 200, 250, and 300 m) with 12 sonic anemometers and six temperature (T) and relative humidity (RH) sensors; and approximately 60 radiosonde launches.In this study we first employ these reference measurements to validate temperature profiles retrieved by two co-located microwave radiometers (MWRs) as well as virtual temperature (Tv) measured by co-located wind profiling radars equipped with radio acoustic sounding systems (RASSs). Results indicate a mean absolute error (MAE) in the temperature retrieved by the microwave radiometers below 1.5 K in the lowest 5 km of the atmosphere and a mean absolute error in the virtual temperature measured by the radio acoustic sounding systems below 0.8 K in the layer of the atmosphere covered by these measurements (up to approximately 1.6–2 km). We also investigated the benefit of the vertical velocity correction applied to the speed of sound before computing the virtual temperature by the radio acoustic sounding systems. We find that using this correction frequently increases the RASS error, and that it should not be routinely applied to all data.Water vapor density (WVD) profiles measured by the MWRs were also compared with similar measurements from the soundings, showing the capability of MWRs to follow the vertical profile measured by the sounding and finding a mean absolute error below 0.5 g m−3 in the lowest 5 km of the atmosphere. However, the relative humidity profiles measured by the microwave radiometer lack the high-resolution details available from radiosonde profiles. An encouraging and significant finding of this study was that the coefficient of determination between the lapse rate measured by the microwave radiometer and the tower measurements over the tower levels between 50 and 300 m ranged from 0.76 to 0.91, proving that these remote-sensing instruments can provide accurate information on atmospheric stability conditions in the lower boundary layer.

Assessing State-of-the-Art Capabilities for Probing the Atmospheric Boundary Layer: The XPIA Field Campaign

Abstract To assess current capabilities for measuring flow within the atmospheric boundary layer, including within wind farms, the U.S. Department of Energy sponsored the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) campaign at the Boulder Atmospheric Observatory (BAO) in spring 2015. Herein, we summarize the XPIA field experiment, highlight novel measurement approaches, and quantify uncertainties associated with these measurement methods. Line-of-sight velocities measured by scanning lidars and radars exhibit close agreement with tower measurements, despite differences in measurement volumes. Virtual towers of wind measurements, from multiple lidars or radars, also agree well with tower and profiling lidar measurements. Estimates of winds over volumes from scanning lidars and radars are in close agreement, enabling the assessment of spatial variability. Strengths of the radar systems used here include high scan rates, large domain coverage, and availability during most precipitation events, but they struggle at times to provide data during periods with limited atmospheric scatterers. In contrast, for the deployment geometry tested here, the lidars have slower scan rates and less range but provide more data during nonprecipitating atmospheric conditions. Microwave radiometers provide temperature profiles with approximately the same uncertainty as radio acoustic sounding systems (RASS). Using a motion platform, we assess motion-compensation algorithms for lidars to be mounted on offshore platforms. Finally, we highlight cases for validation of mesoscale or large-eddy simulations, providing information on accessing the archived dataset. We conclude that modern remote sensing systems provide a generational improvement in observational capabilities, enabling the resolution of finescale processes critical to understanding inhomogeneous boundary layer flows.

Characteristics of the Springtime Alpine Valley Atmospheric Boundary Layer Using Self-Organizing Maps

AbstractVertical profiles of wind velocity and air temperature from a sound detection and ranging (sodar) radio acoustic sounding system (RASS)-derived dataset within an alpine valley of the New Zealand Southern Alps were analyzed. The data covered the month of September 2013, and self-organizing maps (SOM; a data-clustering approach that is based on an unsupervised machine-learning algorithm) are used to detect topological relationships between profiles. The results of the SOM were shown to reflect the physical processes within the valley boundary layer by preserving valley boundary layer dynamics and its response to wind shear. By examining the temporal evolution of ridgetop wind speed and direction and SOM node transitions, the sensitivity of the valley boundary layer to ridgetop weather conditions was highlighted. The approach of using a composite variable (wind speed and potential temperature) with SOM was successful in revealing the coupling of dynamics and atmospheric stability. The results reveal the capabilities of SOM in analyzing large datasets of atmospheric boundary layer measurements and elucidating the connectivity of ridgetop wind speeds and valley boundary layers.