Comment on egusphere-2023-347

We present here a new heuristic framework for the variability of the atmospheric boundary layer (ABL) height h based on an extended concept of the similarity theory retaining non-local effects. Based on several sets of well-known data (Wangara, JASIN, ICE-77), the locus of variability of h in the phase-space determined from this similarity framework points to a new combination for the most relevant scales affecting the ABL height. We show that the most likely length scales to explain the variability of the ABL height are the classical MoninObukhov length L and the background static stratification scale LfluJN, where U, is the friction velocity and N the Brunt-Vaisala frequency above the ABL. This concept is applied to a new set of data obtained above a hgh-latitude forested site, i.e., very different from the above mentioned field experiments. The correlation between the heuristic model and observed values of h reaches high values. This model can be applied to a wide range of quasi-stationary situations, so that relatively simple point measurements can be used to implement the model without calling for prognostic model equations and calculations.

The atmospheric boundary layer (ABL) height defines the volume of air within which heat, moisture and pollutants released at the Earth’s surface are rapidly diluted. Despite the importance for air quality interpretation, numerical weather prediction, greenhouse gas assessment and renewable energy applications, amongst others, quantitative knowledge on the temporal and spatial variation in ABL height is still scarce. With continuous profiling of the entire ABL vertical extent at high temporal and vertical resolution now increasingly possible due to recent advances in ground-based remote sensing measurement technology and algorithm development, there are also dense measurement networks emerging across Europe and other parts of the world. To effectively monitor the spatial and temporal evolution of the ABL continuously at continent-scale, harmonised operations and data processing are key. Autonomous ground-based remote sensing instruments, such as microwave radiometers, radar wind profilers, Doppler wind lidars or automatic lidars and ceilometers, each offer different capabilities. The overarching objective of this review is to emphasize how these instruments are best exploited with informed network design, algorithm implementation, and data interpretation. A summary of the capability and limitations of each instrument type is provided together with a review of the vast number of retrieval methods developed for ABL height detection from different atmospheric quantities (temperature, humidity, wind, turbulence, aerosol). It is outlined how the diurnal evolution of the ABL can be monitored effectively with a combination of methods, highlighting where instrument or methodological synergy promise to be particularly valuable. To demonstrate the vast potential of increased ABL monitoring efforts, long-term observational studies are reviewed summarising our current understanding of ABL height variations. The review emphasizes that harmonised data acquisition and careful data processing are key to obtaining high-quality products, which are essential to capture the spatial and temporal complexity of the lowest part of the atmosphere in which we live and breathe.

The lack of sounding observations in the western Tibetan Plateau (TP), the highest terrain in the world, has resulted in few efforts to evaluate the quality of the atmospheric reanalysis results in this region. Using the sounding observations from the Third Tibetan Plateau Atmospheric Scientific Experiment during 2013–2015, the NCEP and ERA-Interim reanalysis temperature and humidity fields in the TP are evaluated and the characteristics of the reanalysis Atmospheric Boundary Layer (ABL) height are utilized to explain the reasons for the differences in temperature and humidity between the western and eastern TP. The results show that the NCEP and ERA-Interim reanalysis temperature and humidity products generally have larger errors at low level (such as 500 hPa) in the western TP (WTP) than in the eastern one (ETP) at 12:00 UTC. However, this difference is small at 00:00 UTC. Further analysis reveals that the temporal and spatial variations of temperature and humidity errors at low level are closely associated with the differences in the terrain and ABL between the western and eastern TP. In the early morning when the ABL height is low over the TP, the 500 hPa pressure level in both the WTP and ETP is significantly above the top of ABL, with weak spatial variations of temperature and humidity errors. However, in the late afternoon when there is a larger increase in ABL height over the WTP than over the ETP, the 500 hPa pressure level is located inside the ABL in the WTP and is still above the ABL in the ETP, which causes significant regional differences in these errors.

Abstract. This study evaluates methods to derive the surface mixing layer (SML) height of the Arctic atmospheric boundary layer (ABL) using in situ measurements inside the Arctic ABL during winter and the transition period to spring. An instrumental payload carried by a tethered balloon was used for the measurements between December 2019 and May 2020 during the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Vertically highly resolved (centimeter scale) in situ profile measurements of mean and turbulent parameters were obtained, reaching from the sea ice to several hundred meters above ground. Two typical conditions of the Arctic ABL over sea ice were identified: cloudless situations with a shallow surface-based inversion and cloudy conditions with an elevated inversion. Both conditions are associated with significantly different SML heights whose determination as accurately as possible is of great importance for many applications. We used the measured turbulence profile data to define a reference of the SML height. With this reference, a more precise critical bulk Richardson number of 0.12 was derived, which allows an extension of the SML height determination to regular radiosoundings. Furthermore, we have tested the applicability of the Monin–Obukhov similarity theory to derive SML heights based on measured turbulent surface fluxes. The application of the different approaches and their advantages and disadvantages are discussed.

The Atmospheric Boundary Layer (ABL) height is measured with the help of Monostatic SODAR (Sonic Detection And Ranging) System [1]. Meteorological aspects of Doppler free acoustic sounding (Mono-static SODAR system) of the atmosphere are considered [2, 3]. This instrument plays an important role in ABL studies using remote sensing techniques, where other techniques (like Radio-sonde, LIDAR, and Mast etc.) are difficult and expensive. Various features of Mono-static SODAR records with direct measurements with meteorological sensors in ABL are analysed. Some primary results regarding the statistical analysis of the ABL height, meteorological parameters, atmospheric pollutants of main physical parameter of the ABL (Atmosphere) were shown and discussed for the metropolitan city Delhi during the periods of October 2016 to February 2017. During mid-October to mid-November low height of ABL were observed due to high concentration of atmospheric pollutants and low wind speed. During the period of mid-December 2016 to mid-January 2017, fog episodes and strong low level elevated and inversions were observed most of the time.

The boundary layer height obtained by the spline numerical differentiation method using COSMIC GPS radio occultation data: A case study of the Qinghai-Tibet Plateau

Methods of estimation of the atmospheric boundary layer height according to the rawinsonde measurements are considered. Calculations based on the data obtained during observations from the Perm land-based rawinsonde station for the period 2018 to 2024. The atmospheric boundary layer height was estimated based on calculations of the bulk Richardson number and the vertical gradient of the virtual potential temperature. The critical value of the Richardson number indicates atmospheric stability and turbulence. The first point at which the value of bulk Richardson number first reached the critical value is taken as the atmospheric boundary layer height. In other words, the atmospheric boundary layer it is the most turbulent layer of the atmosphere. The article suggests using four critical values of the Richardson number RiBC = {0,1; 0,25; 0,5; 1,0} . The critical value of the Richardson number RiBC = 1,0 shows the most accurate values of the atmospheric boundary layer height. It was determined that the maximum thickness of the atmospheric boundary layer is observed during daytime in summer (1800 m), and the minimum at nighttime in summer (500 m). Moreover, during daytime there is a trend of increasing of the atmospheric boundary layer height from winter to summer, and at nighttime the atmospheric boundary layer height has maximum values in the spring and autumn. Virtual potential temperature profiles are nearly adiabatic in the atmospheric boundary layer. The first point at which the vertical gradient of the virtual potential temperature becomes non-adiabatic is taken as the height of the atmospheric boundary layer. The article shows that values of the atmospheric boundary layer height based on calculations of the vertical gradient of the virtual potential temperature are too large. The use of the considered methods allows to estimate the atmospheric boundary layer height based on the rawinsonde data without making additional measurements, and these methods can be used to study the atmospheric processes occurring in this layer.

Abstract. Accurate boundary layer structure and height are critical in the analysis of the features of air pollutants and local circulation. Although surface-based remote sensing instruments provide a high temporal resolution of the boundary layer structure, there are numerous uncertainties in terms of the accurate determination of the atmospheric boundary layer heights (ABLHs). In this study, an algorithm for an integrated system for ABLH estimation (ISABLE) was developed and applied to the vertical profile data obtained using a ceilometer and a microwave radiometer in Seoul city, Korea. A maximum of 19 ABLHs were estimated via the conventional time-variance, gradient, wavelet, and clustering methods using the backscatter coefficient from the ceilometer. Meanwhile, several stable boundary layer heights were extracted through near-surface inversion and environmental lapse rate methods using the potential temperature from the microwave radiometer. The ISABLE algorithm can find an optimal ABLH from post-processing, such as k-means clustering and density-based spatial clustering of applications with noise (DBSCAN) techniques. It was found that the ABLH determined using ISABLE exhibited more significant correlation coefficients and smaller mean bias and root mean square error between the radiosonde-derived ABLHs than those obtained using the most conventional methods. Clear skies exhibited higher daytime ABLH than cloudy skies, and the daily maximum ABLH was recorded in summer because of the more intense radiation. The ABLHs estimated by ISABLE are expected to contribute to the parameterization of vertical diffusion in the atmospheric boundary layer.

The Atmospheric Boundary Layer (ABL) height is a key parameter in air quality research as well as for numerical simulations and forecasts. The identification of thermally stable layers, often with radiosondes, has been a common approach for estimating ABL height, though with limited temporal coverage. Remote sensing techniques offer essentially continuous measurements. Nevertheless, ABL height retrievals from different methods can vary greatly when compared, which is particularly notable for topographically complex terrains, such as that surrounding Mexico City. This study, employing one year of data in Mexico City, reveals that the daytime convective boundary layer height (retrieved from Doppler lidar data) is typically lower than the aerosol layer height (retrieved from ceilometer data). Although both estimated heights evolved diurnally, the more elevated aerosol layer decays more slowly, suggesting that the mechanisms that elevate aerosols are not limited to convective motions. Additionally, both diurnal and seasonal variability are investigated, comparing remotely sensed-retrieved heights with thermally stable layers estimated from radiosonde data. Multiple stable layers often develop, those at higher levels have similar values to the ceilometer-retrieved heights, while stable layers at lower heights are similar to Doppler lidar height retrievals. The present research constitutes the first detailed analysis of ceilometer backscatter and Doppler lidar thresholding methods for estimating ABL height over Mexico City, and our results illustrate the complexity of mixing mechanisms on the ABL in this region of complex orography.

The atmospheric boundary layer height is important for constraining air pollution and meteorological models. This study attempted to validate the MODIS-estimated atmospheric boundary layer height (ABLH), and variation in the ABLH in Uganda was evaluated. The ABLH was estimated from MODIS data using the mixing ratio profile gradient method and compared to the ABLH estimated from radiosonde data using three different methods. Unlike in studies in other regions of the world, correlations between ABLH estimated using MODIS and radiosonde data were weak, implying limited usefulness of MODIS data for determining ABLH. However, the diurnal variation in MODIS-derived ABLH and particulate matter (PM10) was consistent with the expected inverse relationship between PM10 mass concentration and ABLH, and the mean MODIS-derived ABLH values were significantly lower during wet seasons than dry seasons, as expected.

The differences in planetary boundary layer characteristics, in particular atmospheric boundary layer height (ABLH), humidity, and local circulations in pre-monsoon and monsoon period over the Erhai Lake, were simulated by the lake-atmosphere coupled model WRF v3.7.1. No lake simulations were also conducted to investigate lake effects over complex topography. During pre-monsoon period, local circulation was fully developed under weak synoptic system. The ABLH ran up to 2300 m or so. During monsoon period, temperature difference between land and lake became smaller, resulting in weaker local circulations. The height of circulation reduced by 500 m, and ABLH ran up to 1100 m during the day. Enhanced soil moisture and low surface temperature due to monsoon rainfalls in July could be the main reason for the slightly lower ABLH over the Erhai Lake area. Specific humidity of the boundary layer increased 8.8 g kg−1 or so during monsoon period. The Erhai Lake enlarged thermal contrast between valley and mountain slope in the Dali Basin. The lake reduced air temperature by 2~3 °C during daytime and increased air temperature by nearly 2 °C in the evening. Due to its small roughness length and large thermal capacity, the Erhai Lake enlarged lake-land temperature difference and local wind speed. A cyclonic circulation was maintained by the combination of mountain breeze and land breeze in the south of the lake. The lake decreased air temperature, increased specific humidity, and reduced ABLH during daytime, whereas the opposite effect is presented at night.

The differences and similarities in atmospheric boundary-layer (ABL) characteristics, in particular the ABL height, evolution and wind field, between two contrasting episodes of the Indian summer monsoon have been studied using measurements from wind profilers and an instrumented 50-m tower at Gadanki in India. The observed differences are discussed in light of various forcing mechanisms, in particular the effect of soil moisture on the surface energy balance and ABL. The differences in ABL height, its evolution and the wind field between episodes are quite pronounced. Wet episodes not only have a shallower ABL but also the growth is delayed by 1–4 h when compared with that for dry episodes. Abundant soil moisture during the wet episodes (a factor of two greater than during the dry episodes) reduces the buoyancy flux, and thereby not only limits the ABL height but also delays the commencement of ABL growth. The low-level jet (LLJ) is stronger during the dry episodes and has a larger diurnal range than during the wet episodes. The highest occurrence and magnitude of LLJ apparent at a height of 1.5 km during early morning hours shift progressively with height and time till the afternoon, following ABL evolution. The weaker LLJ during the wet episodes is attributed to its southward migration from its mean position (15 $$^{\circ }$$ N). Larger signal-to-noise ratio and spectral width values are observed during the early night to midnight, compared to noon-time, when the ABL is buoyantly turbulent.

A solar-blind lidar system is developed by using Nd:YAG laser to produce 266nm wavelength at the frequency of 10Hz as the light source to to detect the height of boundary layer in Xi'an area. The observation experiment and analysis are made.The solar background light has no 266nm wavelength and the influence of it can be ignored in the daytime, and then all day detection can be realized. It can be detected in the daytime and nighttime. The wavelength of 266nm absorbed by ozone is considered only. The absolute minimum of first derivative and second derivative of the range-squared-corrected lidar signal are employed to retrieve height of boundary layer. Based on the observation of atmosphere in daytime and nighttime, the heights of atmospheric boundary layer are 0.44km and 0.47km, and the influences of meteorological factors and human activities on the height of atmospheric boundary layer are analyzed. The results showed that the lidar can satisfied the need for detection of troposphere atmospheric aerosol particles at all time and are beneficial to offer practical and effective data for monitoring atmospheric environment in Xi'an aera.

Atmospheric turbulence is highly dynamic in both temporal and spatial aspects, so to detect it, equipment that can rapidly scan with high resolution within seconds is necessary. The Wind Lidar can complement the shortcomings of various remote sensing equipment and enable high-resolution rapid scanning, making it an optimal device for turbulence detection. With various scan modes, it can capture the three-dimensional spatial distribution of winds within seconds, making it particularly advantageous for detecting low-level winds within 600 meters over the urban area. Data were collected from the WIND3D6000 model by LEICE, which is installed near Incheon airport, and seven quality management techniques were applied and evaluated for their performance to enhance the quality. Subsequently, using the radial velocity derived from VAD scans, the eddy dissipation rate (EDR) was calculated based on Kolmogorov theory. The atmospheric boundary layer height was estimated using radiosonde. Typhoon cases provide a good choice for explaining the development and variation of the atmospheric boundary layer as meteorological variables such as temperature, humidity, wind direction, and speed change rapidly along their path. This study revealed that during clear days between 09:00 and 16:00, the EDR generally increased as the atmospheric boundary layer developed, and following boundary layer destruction, the EDR values also decreased accordingly. After typhoons made landfall, precipitation increased, hindering the development of the atmospheric boundary layer, with high EDR values primarily observed during precipitation periods. These results validate the potential of utilizing wind lidars for high-resolution wind and turbulence detection in the lower atmosphere, and through EDR calculations, they also indicate the ability to estimate the development of the atmospheric boundary layer.

A 307-m tall meteorological tower was used to evaluate meteorological observation data obtained using a rotary-wing unmanned aerial vehicle (UAV). A comparative study between the tower and UAV observations was conducted during the daytime (06:00 to 19:00 local time (LT)) in the summer of 2017 (16–18th August). Hourly vertical profiles of air temperature, relative humidity, black carbon (BC), and ozone (O3) concentrations were obtained for up to 300 m height. Statistical metrics for evaluating the accuracy of UAV observations against the tower observation showed positive (potential temperature) and negative (relative humidity) biases, which were within acceptable ranges. The daytime evolution of the lower atmospheric boundary layer (ABL) was successfully captured by the hourly UAV observations. During the early morning, a large vertical slope of potential temperature was observed between 100 and 140 m, corresponding to the stable ABL height. The large vertical slope coincided with the large differences in BC and O3 concentrations between altitudes below and above the height. The transition from stable to convective ABL was observed at 10–11 LT, indicated by the ABL height higher than 300 m in the convective ABL. Finally, we provide several recommendations to reduce uncertainties of UAV observation.