Top Of Boundary Layer Research Articles

Aerosol and cloud properties over a coastal area from aircraft observations in Zhejiang, China

Using in-situ aircraft observations from six flights over Zhejiang on Sep. 1 and Sep. 4, 2016, this study investigates differences in aerosol and cloud properties between daytime and nighttime. The samples were divided into marine type and continental type based on the backward air mass trajectories and aerosol characteristics. The results show that the aerosol number concentration (Na) near the ground during daytime is higher than that at nighttime. During daytime, Na has a significant decreasing trend near the top of the planetary boundary layer (PBL), which is not obvious during nighttime. There may be still a relative high concentration of aerosols remaining in the transition zone between the PBL and the free troposphere. Under similar liquid water content (LWC) conditions, the cloud droplet number concentration (Nc) at night is lower, and the cloud droplet effective diameter (cloud ED) is larger. The total Na of marine type aerosols is generally lower than that of continental type aerosols, but for aerosols with particle diameters greater than 1 μm, the marine type aerosols are higher. The study shows a strong negative Na-cloud ED relationship for marine type aerosols, but no obvious Na-cloud ED relationship for continental type aerosols. The number of cloud condensation nuclei (CCN) is higher under high-Na conditions; the ratio of CCN to Na reveals that the activation efficiency of marine type aerosols is higher than that of continental type aerosols. There is no obvious difference in activation efficiency between day and night.

Tropical Cyclone Intensification Simulated in the Ooyama-type Three-layer Model with a Multilevel Boundary Layer

AbstractThe first successful simulation of tropical cyclone (TC) intensification was achieved with a three-layer model, often named the Ooyama-type three-layer model, which consists of a slab boundary layer and two shallow water layers above. Later studies showed that the use of a slab boundary layer would produce unrealistic boundary layer wind structure and too strong eyewall updraft at the top of TC boundary layer and thus simulate unrealistically rapid intensification compared to the use of a height-parameterized boundary layer. To fully consider the highly height-dependent boundary layer dynamics in the Ooyama-type three-layer model, this study replaced the slab boundary layer with a multilevel boundary layer in the Ooyama-type model and used it to conduct simulations of TC intensification and also compared the simulation with that from the model version with a slab boundary layer. Results show that compared with the simulation with a slab boundary layer, the use of a multilevel boundary layer can greatly improve simulations of the boundary-layer wind structure and the strength and radial location of eyewall updraft, and thus more realistic intensification rate due to better treatments of the surface layer processes and the nonlinear advection terms in the boundary layer. Sensitivity of the simulated TCs to the model configuration and to both horizontal and vertical mixing lengths, sea surface temperature, the Coriolis parameter, and the initial TC vortex structure are also examined. The results demonstrate that this new model can reproduce various sensitivities comparable to those found in previous studies using fully physics models.

Understanding the Roles of Convective Trigger Functions in the Diurnal Cycle of Precipitation in the NCAR CAM5

AbstractThe wrong diurnal cycle of precipitation is a common weakness of current global climate models (GCMs). To improve the simulation of the diurnal cycle of precipitation and understand what physical processes control it, we test a convective trigger function described in Xie et al. with additional optimizations in the NCAR Community Atmosphere Model version 5 (CAM5). The revised trigger function consists of three modifications: 1) replacing the convective available potential energy (CAPE) trigger with a dynamic CAPE (dCAPE) trigger, 2) allowing convection to originate above the top of planetary boundary layer [i.e., the unrestricted air parcel launch level (ULL)], and 3) optimizing the entrainment rate and threshold value of the dynamic CAPE generation rate for convection onset based on observations. Results from 1° resolution simulations show that the revised trigger can alleviate the long-standing GCM problem of too early maximum precipitation during the day and missing the nocturnal precipitation peak that is observed in many regions, including the U.S. southern Great Plains (SGP). The revised trigger also improves the simulation of the propagation of precipitation systems downstream of the Rockies and the Amazon region. A further composite analysis over the SGP unravels the mechanisms through which the revised trigger affects convection. Additional sensitivity tests show that both the peak time and the amplitude of the diurnal cycle of precipitation are sensitive to the entrainment rate and dCAPE threshold values.

Evaluation and Applications of Multi-Instrument Boundary-Layer Thermodynamic Retrievals

Recent reports have highlighted the need for improved observations of the atmosphere boundary layer. In this study, we explore the combination of ground-based active and passive remote sensors deployed for thermodynamic profiling to analyze various boundary-layer observation strategies. Optimal-estimation retrievals of thermodynamic profiles from Atmospheric Emitted Radiance Interferometer (AERI) observed spectral radiance are compared with and without the addition of active sensor observations from a May–June 2017 observation period at the Atmospheric Radiation Measurement Southern Great Plains site. In all, three separate thermodynamic retrievals are considered here: retrievals including AERI data only, retrievals including AERI data and Vaisala water vapour differential-absorption lidar data, and retrievals including AERI data and Raman lidar data. First, the three retrievals are compared to each other and to reference radiosonde data over the full observation period to obtain a bulk understanding of their differences and characterize the impact of clouds on these retrieved profiles. These analyses show that the most significant differences are in the water vapour field, where the active sensors are better able to represent the moisture gradient in the entrainment zone near the boundary-layer top. We also explore how differences in retrievals may affect results of applied analyses including land–atmosphere coupling, convection indices, and severe storm environmental characterization. Overall, adding active sensors to the optimal-estimation retrieval shows some added information, particularly in the moisture field. Given the costs of such platforms, the value of that added information must be weighed for the application at hand.

Using mobile surface in situ and remote sensing and airborne remote sensing to derive emissions from a producing central California oil field in complex terrain

In this study, we demonstrate how under certain wind conditions, a mobile surface in situ platform, Truck MObile trace Gas (TMOG) Surveyor, that includes a ceilometer to derive boundary layer height (BL) can derive emissions. Field in situ and airborne thermal infrared imaging spectroscopy data were acquired by the thermal infrared imaging spectrometer, Mako, for three adjacent, central California producing oil fields (Kern River, Kern Front, Poso Creek) on 14 Sept. 2018. Derived methane (CH4) and carbon dioxide (CO2) emissions from TMOG data were 46.6 ± 15 Mg dy−1 (17 ± 5.6 Gg yr−1) and 3.12 ± 1.02 Mg dy−1 (1140 ± 230 Gg yr−1), respectively, with about half the CH4 from near-field point-source plumes and half from a well-mixed far field plume. Uncertainty was 33 % from the Monte Carlo simulations. Mako data confirmed that emissions were in the far field and there were no strong, buoyant plumes. The survey vertically profiled a nearby mountain to measure winds at the boundary layer top and validate BL using in situ data.The CH4 to CO2 emissions ratio for plume matched reservoir composition to better than 10 %. The plume anomaly CH4 to ethane emissions ratio suggested ethane emissions of around 200 kg dy−1 (74 Mg yr−1). Mako data in 2015 and concurrent data in 2018 confirmed that most emissions were from distant plumes in the Poso Creek and Kern Front fields.

Observational Evidence of Lightning‐Generated Ultrafine Aerosols

AbstractHigh temperature and pressure during lightning can quickly trigger multiple chemical reactions in the air, resulting in considerable impacts on aerosols, atmospheric chemistry, and air quality. Here, new particle formation (NPF) events motivated by lightning flashes were captured during an observation at Mt. Tai in summer 2017 for the first time. Numerous ultrafine particles were formed during the lightning events, leading to increases in nucleation and Aitken mode aerosols by 18.9 and 5.6 times, respectively. The formation rate (FR) and growth rate (GR) during lightning‐generated NPF were 67.1 cm−3·s−1 and 20.1 nm·h−1, which were 61 and 1.7 times higher than the averaged daytime NPF. Moreover, chemical composition of aerosols was strongly influenced by lightning NOx. Nitrate aerosol (NO2− and NO3−) signals intensified significantly (by 11.9% and 12.4%, respectively) during the lightning‐generated NPF, which contrasted with the sulfate aerosols measured in previous studies (non‐lightning NPF). Meanwhile, lightning contributed noticeably to surface NO2 concentrations. Accompanying the uplifting airflows before rainfall, surface air pollutants (SO2, NH3, and NOx, etc.) can be transported above the top of the planet boundary layer, which plays an important role in NPF. The NPF in the hot lightning channels resulted from pollution NOx and lightning NOx, with the latter dominating. Finally, lightning‐generated pollutants, including NOx and aerosols, were delivered down to the surface with descending airflows.

Implementing a New Formulation in WRF-LES for Buoyant Plume Simulations: bPlume-WRF-LES Model

AbstractA new formulation—bPlume-WRF-LES model—was implemented within the Weather Research and Forecasting (WRF) Model to simulate the two-way coupling between the atmospheric boundary layer (ABL) and gas plume (denser and lighter) released into the atmosphere. The existing WRF large-eddy simulation (WRF-LES) modeling system was modified by coupling an additional transport equation for the plume gas mixture and by accounting for the buoyant production term in the turbulence kinetic energy equation. The focus of the work was to understand the effect of atmospheric forcings on plume rise, plume mixing, and plume dynamics during the early stages of plume development. For this purpose, the bPlume-WRF-LES model was used to simulate the release of buoyant plumes from a large area source into different atmospheric conditions with varying stratification and mean wind forcing values. Plumes released in a convective ABL background rise according to the 2/3 power law with time before reaching the boundary layer top and spreading laterally. The convective ABL eddy turnover time scale () dictates the rate at which plume mixes with the ambient air inside the convective boundary layer (CBL) and the plume dilution rate scales as . Both the stratification and wind forcing enhance the plume mixing from the early plume development stage, and dilute the plume much faster. An increase in the mean winds within the CBL contributes to uniform mixing and greater bent-over plume behavior at a shorter downwind distance from the source.

Sensitivity of PM2.5 and O3 pollution episodes to meteorological factors over the North China Plain

The Comprehensive Air-quality Model with extensions (CAMx) was used to explore the sensitivity of PM2.5 and O3 concentrations to four selected meteorological factors: wind speed, temperature, water vapor mixing ratio (Q), and planetary boundary layer height (PBLH) during two pollution episodes over the North China Plain (NCP). We also investigated the impact pathways of different meteorological factors on the formation of PM2.5 and O3. It is found that PM2.5 was more sensitive to the selected meteorological factors in the southeastern NCP, where high anthropogenic emissions and severe air pollution occur. Large variations were observed along the Taihang Mountains, where the height of the terrain changes dramatically. The sensitivity of O3 to wind speed, PBLH, temperature, and Q was mainly determined by the inhibition effects of PM2.5 in winter, while in summer, the complex chemical reactions were dominant. Significant diurnal variations of process analysis (PA) results were observed under various meteorological conditions. Higher temperature generally enhance heterogeneous chemistry and transport of NO3− through the top boundary layer during night-time in winter, however, in summer, the heterogeneous chemistry of NO3− and NH4+ during daytime were the major pathways to the increased PM2.5 due to increased temperature. Moreover, temperature alter PM2.5 concentrations through affecting vertical diffusivity and relative humidity, and alter O3 concentrations by affecting the gas phase chemistry and mass fluxes through the top boundary layer. Q mainly affects the rate of chemical reactions of PM2.5 and O3. The different impact pathways suggest that it is essential to consider variations in meteorological factors, in addition to the direct impacts of wind speed and PBLH, more attention should be paid to the complex impacts of temperature and Q, when developing emission control strategies.

Super Sites for Advancing Understanding of the Oceanic and Atmospheric Boundary Layers

Abstract Air‐sea interactions are critical to large-scale weather and climate predictions because of the ocean's ability to absorb excess atmospheric heat and carbon and regulate exchanges of momentum, water vapor, and other greenhouse gases. These exchanges are controlled by molecular, turbulent, and wave-driven processes in the atmospheric and oceanic boundary layers. Improved understanding and representation of these processes in models are key for increasing Earth system prediction skill, particularly for subseasonal to decadal time scales. Our understanding and ability to model these processes within this coupled system is presently inadequate due in large part to a lack of data: contemporaneous long-term observations from the top of the marine atmospheric boundary layer (MABL) to the base of the oceanic mixing layer.We propose the concept of “Super Sites” to provide multi-year suites of measurements at specific locations to simultaneously characterize physical and biogeochemical processes within the coupled boundary layers at high spatial and temporal resolution. Measurements will be made from floating platforms, buoys, towers, and autonomous vehicles, utilizing both in-situ and remote sensors. The engineering challenges and level of coordination, integration, and interoperability required to develop these coupled ocean‐atmosphere Super Sites place them in an “Ocean Shot” class.

A study of the effect of aerosols on surface ozone through meteorology feedbacks over China

Abstract. Interactions between aerosols and gases in the atmosphere have been the focus of an increasing number of studies in recent years. Here, we focus on aerosol effects on tropospheric ozone that involve meteorological feedbacks induced by aerosol–radiation interactions. Specifically, we study the effects that involve aerosol influences on the transport of gaseous pollutants and on atmospheric moisture, both of which can impact ozone chemistry. For this purpose, we use the UK Earth System Model (UKESM1), with which we performed sensitivity simulations including and excluding the aerosol direct radiative effect (ADE) on atmospheric chemistry, and focused our analysis on an area with a high aerosol presence, namely China. By comparing the simulations, we found that ADE reduced shortwave radiation by 11 % in China and consequently led to lower turbulent kinetic energy, weaker horizontal winds and a shallower boundary layer (with a maximum of 102.28 m reduction in north China). On the one hand, the suppressed boundary layer limited the export and diffusion of pollutants and increased the concentration of CO, SO2, NO, NO2, PM2.5 and PM10 in the aerosol-rich regions. The NO/NO2 ratio generally increased and led to more ozone depletion. On the other hand, the boundary layer top acted as a barrier that trapped moisture at lower altitudes and reduced the moisture at higher altitudes (the specific humidity was reduced by 1.69 % at 1493 m on average in China). Due to reduced water vapour, fewer clouds were formed and more sunlight reached the surface, so the photolytical production of ozone increased. Under the combined effect of the two meteorology feedback methods, the annual average ozone concentration in China declined by 2.01 ppb (6.2 %), which was found to bring the model into closer agreement with surface ozone measurements from different parts of China.

The generalized Ekman model for the tropical cyclone boundary layer revisited: Addendum

AbstractMotivated by prior research examining the myth of inertial stability as a radial restoring force in the tropical cyclone boundary layer, we explore factors determining the vertical velocity at the top of the linear vortex boundary layer. Possible applications of these findings to mature tropical cyclone vortices are discussed briefly.

Symmetry-breaking-induced rare fluctuations in a time-delay dynamic system.

Inspired by the experimental and numerical findings, we study the dynamic instabilities of two coupled nonlinear delay differential equations that are used to describe the coherent oscillations between the top and bottom boundary layers in turbulent Rayleigh–Bénard convection. By introducing two sensitivity parameters for the instabilities of the top and bottom boundary layers, we find three different types of solutions, namely in-phase single-period oscillations, multi-period oscillations and chaos. The chaos solution contains rare but large amplitude fluctuations. The statistical properties of these fluctuations are consistent with those observed in the experiment for the massive eruption of thermal plumes, which causes random reversals of the large-scale circulation in turbulent Rayleigh–Bénard convection. Our study thus provides new insights into the origin of rare massive eruptions and sudden changes of large-scale flow pattern that are often observed in convection systems of geophysical and astrophysical scales.

Flows in horizontal thermohaline convection with differential diffusion

Oceanographers use the term “differential diffusion” to express a greater value of bulk turbulent diffusivity of temperature within the ocean than the value of bulk diffusivity of salinity, the ratio quantified by Lewis number. Investigation of horizontal thermohaline convection at Prandtl number 1 and infinity over the range reveals a variety of new flow patterns. The chamber has a linearly changing temperature T and salinity S along the top extending from the cold, fresh “polar” end to the hot, salty “tropics” end. It has an aspect ratio of 8 and sides and bottom are insulated and impermeable. Five transition flow patterns occur with little hysteresis for a fixed salinity Rayleigh number Ras of order 105 as Rayleigh number Ra changes from 3.2 × 106 down to 1. They are: 1. A steady T-cell with sinking at the cold end flowing into a bottom flow that feeds up into a top thermal boundary layer. 2. Salty blobs in the boundary layer that amplify and move from the hot to cold end. Each cold end arrival triggers a sudden increase in overturning velocity. 3. A “stripes” pattern where top to bottom cells (alternating T and S cells) move toward the cold end. 4. An S-cell that is a mirror image of the T-cell near the top along with small T-cells lying at the bottom that move toward the cold end 5. A steady S-cell. Each pattern has a distinct volumetric signature in a T-S diagram. Ranges of Ra with various patterns are sizeable at Ras=7.5 × 105 if Le >4/3 but insensitive to Pr. Balanced convection at Ra = Ras >106 adopts a large unsteady supercell containing smaller T and S cells. Exact ranges of the supercell are unknown. Since differential diffusion produces a large collection of flows compared to thermal convection alone, it might produce unexpected new results if added into numerical models of the ocean.

Updates to the Oxford Space Environment Goniometer to measure visible wavelength bidirectional reflectance distribution functions in ambient conditions.

Understanding how the surfaces of airless planetary bodies-such as the Moon-scatter visible light enables constraints to be placed on their surface properties and top boundary layer inputs to be set within thermal models. Remote sensing instruments-such as Diviner onboard the Lunar Reconnaissance Orbiter-measure thermal emission and visible light scattering functions across visible (∼0.38-0.7 µm) to thermal infrared (TIR) wavelengths (∼0.7-350 μm). To provide ground support measurements for such instruments, the Oxford Space Environment Goniometer (OSEG) was built. Initially, the OSEG focused on measuring TIR directional emissivity functions for regolith and regolith simulant samples in a simulated space environment, but it has recently been modified to measure visible wavelength Bidirectional Reflectance Distribution Functions (BRDFs) of samples in ambient conditions. Laboratory-measured BRDFs can be used (1) to test and to help interpret models-such as the Hapke photometric model-and (2) as visible scattering function inputs for thermal models. This paper describes the modifications to and initial calibration measurements taken by the Visible Oxford Space Environment Goniometer with a 532nm laser, and details how this setup can be used to measure BRDFs of regolith and regolith simulant samples of airless planetary bodies.

Impacts of Nocturnal Cloud Top Radiative Cooling on Surface O3 in Sichuan Basin, Southwestern China

AbstractNighttime ozone (O3) reserved over the stable boundary layer (SBL) could contribute significantly to surface O3 levels. While many studies have revealed that daytime convective eddies and turbulence induced by nighttime low‐level jets can mix O3‐rich air over the SBL down to the surface, increasing nocturnal surface O3 within the cloud topped boundary layer has rarely been examined. In this study, we used measurements and a single‐column photochemistry model to investigate O3 variations within the nighttime cloud topped boundary layer over the Sichuan Basin, which is the cloudiest region in southwest China. The Santa Barbara Distort Atmospheric Radiative Transfer radiation model was coupled into the single‐column photochemistry model to investigate the nighttime radiative effects of clouds. The results showed that the nocturnal cloud top radiative cooling generated turbulence and enhanced vertical mixing below the cloud top layer. The cloud‐driven turbulent eddies even penetrated through the SBL to the surface. Consequently, it weakened the decoupling of the SBL from the residual layer. O3‐rich air over the SBL was entrained downwards to the surface, decreasing O3 aloft and increasing surface O3 at nighttime. The cloud top radiative cooling rates were enhanced with the increase in the cloud liquid water path. Higher cooling rates produced stronger turbulent transport of O3, leading to higher nocturnal surface O3 levels. The turbulent transport of O3 induced by cloud top radiative cooling is revealed as an important mechanism of vertical transport of O3 within a cloud topped boundary layer, contributing to the maximum nocturnal surface O3, which has great implications for understanding atmospheric O3 variation.

Aircraft-based observation of gaseous pollutants in the lower troposphere over the Beijing-Tianjin-Hebei region

To investigate the spatial and vertical distribution of atmospheric pollutants (SO2, NOx, CO and O3), aircraft-based measurements (model: Yun-12, 12 flights, 27 h total flight time) were conducted from near the surface up to 2400 m over the Beijing-Tianjin-Hebei (BTH) region between June 17th and July 22nd 2016. The results showed that high concentrations of primary gaseous pollutants (SO2, NOx, CO) were generally present in Beijing, Tianjin, Langfang and Tangshan areas, while high values of O3 frequently appeared in areas far from the city. The flights at noon and dusk measured higher O3 concentrations at 600 m and lower O3 concentrations at higher altitudes, implying a strong influence by photochemical production. Back trajectory analysis suggested that the high levels of gaseous pollutants, especially at 600 m, were associated with pollution sources transported from the southerly direction during the observation period. The first simultaneous vertical distribution measurements using aircraft and tethered balloon were conducted in Gaocun (a rural site between Beijing and Tianjin) on June 17th. The results indicated that an inversion layer at the top of the planetary boundary layer (PBL) significantly suppressed vertical exchange through the PBL and resulted in a “two-layer” vertical distribution of pollutants above and below the PBL. Additionally, a residual high O3 layer (79.9 ± 2.5 ppb, 500–1000 m) was observed above the PBL, and it contributed to the surface peak O3 level at noon through downward transport along with the opening up of the PBL. These results indicate that coupled effects of horizontal and vertical transport should be investigated in future studies to improve the chemical transport models used to study the vertical distribution and regional transport over the BTH region.

Optical and hygroscopic properties of black carbon influenced by particle microphysics at the top of the anthropogenically polluted boundary layer

Abstract. Aerosols at the top of the planetary boundary layer (PBL) could modify its atmospheric dynamics by redistributing the solar radiation and start to be activated to form low-level cloud at this layer. Black carbon (BC), as an aerosol component efficiently absorbing solar radiation, can introduce heating and positive radiative effects at this sensitive layer, especially in the polluted PBL over the continent. This study presents continuous measurements of detailed BC properties at a mountain site located at the top of the polluted PBL over the North China Plain, during seasons (3 and 4 weeks of data during winter and summer, respectively) with contrasting emission structure and meteorology. The pollution level was persistently influenced by local surface anthropogenic emission on a daily basis through daytime convective mixing, but the concentration was also enhanced or diluted depending on air mass direction, defined as a neutral, polluted and diluted PBL, respectively. Winter was observed to have a higher BC mass fraction (4 %–8 %) than summer (2 %–7 %). By resolving the detailed particle size-resolved mixing state of BC in optical and hygroscopic models, we found an enhanced BC mass absorption cross section (MACBC) for the polluted PBL (up to 13 m2 g−1 at λ = 550 nm), which was 5 % higher during summer than winter due to a smaller BC core size. The higher BC mass fraction in winter corresponded to a lower single-scattering albedo by 0.03–0.09 than summer, especially the lowest for the diluted winter PBL (0.86 ± 0.02). The water supersaturation (SS) required to activate half the number of BC decreased from 0.21 % ± 0.08 % to 0.1 % ± 0.03 % for the winter diluted and polluted PBL and from 0.22 % ± 0.06 % to 0.17 % ± 0.05 % for summer. Notably, at the top of the anthropogenically polluted PBL in both seasons, the enlarged BC with enhanced absorption capacity could also be efficiently droplet activated; e.g. winter (summer) BC with an MAC of 9.84 ± 1.2 (10.7 ± 1) m2 g−1 could be half activated at SS = 0.13 % ± 0.06 % (0.18 % ± 0.05 %). This BC at the top of the PBL can more directly interact with the free troposphere and be transported to a wider region, exerting important direct and indirect radiative impacts.

Weather radar detection of planetary boundary layer and smoke layer top of peatland fire in Central Kalimantan, Indonesia

During the dry period of August–October 2015, a C-band Doppler weather radar of the BMKG station in a fire-prone peatland area, Palangka Raya, detected echoes with reflectivity values between − 19 and + 34 dBZ at a height below 2–3 km and a slant range of 100 km. The MERRA-2/NASA atmospheric reanalysis database is used to obtain the vertical profiles of refractive index and equivalent potential temperature of the air. The temporal variation of the radar image is due to the tropical diurnal cycle of planetary boundary layer formation, which is consistent with the results of the database analysis. The echo images are discussed in terms of Bragg scattering of microwaves at the top of the planetary boundary layer. Weather radar monitoring of the fire smoke layer-top images has a potential feasibility to support real-time management of peatland fires.

Estimation of <inline-formula><tex-math id="M1">\begin{document}${\boldsymbol{C_n^2}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20211201_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20211201_M1.png"/></alternatives></inline-formula> profile of troposphere over the sea

The problem of turbulence has been puzzling relevant researchers for more than 300 years. Although some feasible solutions and models have been proposed, the turbulence still brings trouble in the foreseeable future. Turbulence is caused mainly by buoyant thermal bubbles and wind shear, which transports matter and energy between the earth surface and the atmosphere. Based on the analysis of the measured data obtained from the Sea Monsoon Experiment-II (SMEX-II), carried out on the ‘Shenkuo’ scientific research ship, the vertical spatial distribution of meteorological data overseas was explored when the air sounding balloons were released at relatively fixed times during June 2019. Through the Tatarski model, the main influencing factors of fitting turbulence profile over the sea and the turbulence evolution of boundary layer top and tropopause are discussed. Meanwhile, the effect of offshore distance of the scientific research ship on the vertical profile of optical turbulence strength is analyzed. The results show that the outer scale plays a decisive role in the distribution of turbulence over the seas. The inverse growth section between the boundary layer top and the tropopause depends on the sudden change of temperature gradient. The underlying land surface has a significant influence on the inverse growth section to the boundary layer top, while the underlying sea surface has a more pronounced influence on the inverse growth section of the tropopause. Based on the obtained data and corresponding analysis, the spatiotemporal distribution characteristics of optical turbulence overseas are grasped, which provides necessary references for selecting the astronomical observation sites, atmospheric laser transmission, and satellite remote sensing observations over the sea.

The dual-field-of-view polarization lidar technique: a new concept in monitoring aerosol effects in liquid-water clouds – case studies

Abstract. In a companion article (Jimenez et al., 2020), we introduced a new lidar method to derive microphysical properties of liquid-water clouds (cloud extinction coefficient, droplet effective radius, liquid-water content, cloud droplet number concentration Nd) at a height of 50–100 m above the cloud base together with aerosol information (aerosol extinction coefficients, cloud condensation nuclei concentration NCCN) below the cloud layer so that detailed studies of the influence of given aerosol conditions on the evolution of liquid-water cloud layers with high temporal resolution solely based on lidar observations have become possible now. The novel cloud retrieval technique makes use of lidar observations of the volume linear depolarization ratio at two different receiver field of views (FOVs). In this article, Part 2, the new dual-FOV polarization lidar technique is applied to cloud measurements in pristine marine conditions at Punta Arenas in southern Chile. A multiwavelength polarization Raman lidar, upgraded by integrating a second polarization-sensitive channel to permit depolarization ratio observations at two FOVs, was used for these measurements at the southernmost tip of South America. Two case studies are presented to demonstrate the potential of the new lidar technique. Successful aerosol–cloud-interaction (ACI) studies based on measurements with the upgraded aerosol–cloud lidar in combination with a Doppler lidar of the vertical wind component could be carried out with 1 min temporal resolution at these pristine conditions. In a stratocumulus layer at the top of the convective boundary layer, we found values of Nd and NCCN (for 0.2 % water supersaturation) ranging from 15–100 and 75–200 cm−3, respectively, during updraft periods. The studies of the aerosol impact on cloud properties yielded ACI values close to 1. The impact of aerosol water uptake on the ACI studies was analyzed with the result that the highest ACI values were obtained when considering aerosol proxies (light-extinction coefficient αpar or NCCN) measured at heights about 500 m below the cloud base (and thus for dry aerosol conditions).