Raman scattering in the Earth’s atmosphere is caused predominantly by its most abundant molecular components, N2 and O2. After the computation of the optical properties that govern the spectral and ...angular redistribution of light due to various inelastic scattering events, viz. rotational Raman scattering (RRS), vibrational Raman scattering (VRS), and rovibrational Raman scattering (RVRS), covered in Part I of this series, the next challenge in the simulation of inelastic scattering in the Earth’s atmosphere is to carry out radiative transfer (RT) computations across several wavelengths simultaneously.
In this part of our work, we provide the RT formulation for fully polarized simulations of inelastic scattering using the matrix-operator-method-based RT model vSmartMOM. The formalism is optimized for easy use with GPUs, allowing an unprecedented speedup of accurate multi-wavelength RT computations of inelastic scattering using the full Stokes-vector, thus allowing its operational use without coarse spectral binning (Rozanov and Vountas, 2014), or single scattering approximations (Sioris and Evans, 1999) at longer wavelengths.
After comparing our model against the current state-of-the-art, we demonstrate the use of vSmartMOM to simulate Raman lidar measurements, the Ring effect, the ghosting of Fraunhofer lines due to vibrational Raman scattering and spectral corrections due to inelastic scattering in the O2 A-band in the Earth’s atmosphere. We use our model (1.) to validate the convention of neglecting the contribution of VRS and RVRS, and (2.) to quantify the speed and accuracy of the single scattering approximation in the O2 A-band.
•First exact polarized simulations of rotational, vibrational and rovibrational Raman scattering.•GPU acceleration achieves unprecedented speed-ups, allowing operational use.•Applications include Raman Lidar, Ring effect, ghosting of Fraunhofer lines, and the infilling of telluric lines of absorption lke the O2 A-band.•Exciting implications for trace gas retrievals in the UV/Vis, greenhouse gas retrievals, and fluorescence studies.
We present the new Atmospheric Raman Temperature and Humidity Sounder (ARTHUS). We demonstrate that ARTHUS measurements resolve (1) the strength of the inversion layer at the planetary boundary layer ...top, (2) elevated lids in the free troposphere during daytime and nighttime, and (3) turbulent fluctuations in water vapor and temperature, simultaneously, also during daytime. Very stable and reliable performance was demonstrably achieved during more than 2,500 hr of operations time experiencing a huge variety of weather conditions. ARTHUS provides temperature profiles with resolutions of 10–60 s and 7.5–100 m vertically in the lower free troposphere. During daytime, the statistical uncertainty of the water vapor mixing ratio is <2 % in the lower troposphere for resolutions of 5 min and 100 m. Temperature statistical uncertainty is <0.5 K even up to the middle troposphere. ARTHUS fulfills the stringent WMO breakthrough requirements on nowcasting and very short range forecasting.
Plain Language Summary
The observation of atmospheric moisture and temperature profiles is essential for the understanding and prediction of earth system processes. These are fundamental components of the global and regional energy and water cycles; they determine the radiative transfer through the atmosphere and are critical for the cloud formation and precipitation. Also, it is expected that the assimilation of high‐quality, lower tropospheric WV and T profiles will result in a considerable improvement of the skill of weather forecast models particularly with respect to extreme events. Here we present the Atmospheric Raman Temperature and Humidity Sounder, an exceptional tool for observations in the atmospheric boundary layer during daytime and nighttime with a very short latency. This performance serves very well the next generation of very fast rapid‐update‐cycle data assimilation systems for nowcasting and short‐range weather forecasting. Ground‐based stations and networks can be set up or extended for climate monitoring, verification of weather, climate and earth system models, and data assimilation for improving weather forecasts.
Key Points
Fulfills World Meteorological Organization breakthrough requirements for nowcasting/very short range forecasting in the lower troposphere
Resolves strength of the inversion layer at the planetary boundary layer top and elevated lids above during daytime and nighttime
Provides statistics on turbulent fluctuations in water vapor and temperature simultaneously in the lower troposphere
Aerosol vertical distribution plays a crucial role in cloud development and thus precipitation since both aerosol indirect and semi-direct effects significantly depend on the relative position of ...aerosol layer in reference to cloud, but its precise influence on cloud remains unclear. In this study, we integrated multi-year Raman Lidar measurements of aerosol vertical profiles from the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) facility with available Value-Added Products of cloud features to characterize aerosol vertical distributions and their impacts on warm clouds over the continental and marine ARM atmospheric observatories, i.e., Southern Great Plains (SGP) and Eastern North Atlantic (ENA). A unimodal seasonal distribution of aerosol optical depths (AODs) with a peak in summer is found at upper boundary layer over SGP, while a bimodal distribution is observed at ENA for the AODs at lower levels with a major winter-spring maximum. The diurnal mean of upper-level AOD at SGP shows a maximum in the early evening. According to the relative positions of aerosol layers to clouds we further identify three primary types of aerosol vertical distribution, including Random, Decreasing, and Bottom. It is found that the impacts of aerosols on cloud may or may not vary with aerosol vertical distribution depending on environmental conditions, as reflected by the wide variations of the relations between AOD and cloud properties. For example, as AOD increases, the liquid water paths (LWPs) tend to be reduced at SGP but enhanced at ENA. The relations of cloud droplet effective radius with AOD largely depend on aerosol vertical distributions, particularly showing positive values in the Random type under low-LWP condition (<50 g m−2). The distinct features of aerosol-cloud interactions in relation to aerosol vertical distribution are likely attributed to the continental-marine contrast in thermodynamic environments and aerosol conditions between SGP and ENA.
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•Upper-level AOD at SGP peaks in summer and early evening.•A bimodal seasonal distribution is observed at ENA for lower-level AOD.•Random, Decreasing, and Bottom are the primary vertical distributions at both sites.•Aerosols tend to suppress cloud water production at SGP but invigorate it at ENA.•AOD-droplet effective radius relations vary with aerosol vertical distributions.
During the Intensive Observing Period 15b of the first Special Observation Period of the Hydrological Cycle in the Mediterranean Experiment (HyMeX), a variety of mesoscale convective systems (MCSs) ...impacted the Cevennes‐Vivarais (CV) target area leading to over 100 mm of 24 h accumulated rainfall on 20 and 21 October 2012. The CV area was first impacted by a V‐shaped MCS developing over the Cevennes mountains, then by a MCS initiated on the eastern foothills of the Pyrenees and finally by three MCSs initiating over the sea. The MCSs initiated and propagated along a well‐defined storm track ahead of an approaching upper‐level trough, as observed with the 15 min resolution Spinning Enhanced Visible and Infrared Imager. The storm track was characterized by strong southeasterly winds over the Mediterranean and high integrated water vapour content (IWVC), as derived from observations from the Moderate‐resolution Imaging Spectroradiometer (MODIS) and the Atmospheric Infrared Sounder (AIRS). The ground‐based Water‐vapour Raman Lidar, located in the Balearic Islands, captured the increasing moistening of the free troposphere, up to 5 km, associated with the eastward propagation of the surface low from Gibraltar to a location west of the Balearic Islands. MODIS and AIRS observations, together with Weather Research and Forecasting (WRF) model simulations, revealed the tropical origin of the high moisture content characterizing the storm track, with IWVC values on the order of 35 kg m−2, and enhanced moisture being observed below 500 hPa. The WRF simulations also showed that the MCS initiation offshore was very likely caused by low‐level wind convergence and conditionally unstable air along the storm track, between North Africa and southern France. Low‐level convergence resulted from the interaction between a strong southwesterly swirling flow around the low‐pressure centre and an easterly low‐level jet present along the southern France coastline.
It was for a long time believed that lidar systems based on the use of high-repetition micro-pulse lasers could be effectively used to only stimulate atmospheric elastic backscatter echoes, and thus ...were only exploited in elastic backscatter lidar systems. Their application to stimulate rotational and roto-vibrational Raman echoes, and consequently, their exploitation in atmospheric thermodynamic profiling, was considered not feasible based on the technical specifications possessed by these laser sources until a few years ago. However, recent technological advances in the design and development of micro-pulse lasers, presently achieving high UV average powers (1–5 W) and small divergences (0.3–0.5 mrad), in combination with the use of large aperture telescopes (0.3–0.4 m diameter primary mirrors), allow one to presently develop micro-pulse laser-based Raman lidars capable of measuring the vertical profiles of atmospheric thermodynamic parameters, namely water vapor and temperature, both in the daytime and night-time. This paper is aimed at demonstrating the feasibility of these measurements and at illustrating and discussing the high achievable performance level, with a specific focus on water vapor profile measurements. The technical solutions identified in the design of the lidar system and their technological implementation within the experimental setup of the lidar prototype are also carefully illustrated and discussed.
The planetary boundary layer (PBL) height is a key variable in climate modeling and has an enormous influence on air pollution. A method based on the wavelet covariance transform (WCT) applied to ...lidar data is tested in this paper as an automated and non‐supervised method to obtain the PBL height. The parcel and the Richardson number methods applied to radiosounding data and the parcel method applied to microwave radiometer temperature profiles are used as independent measurements of the PBL height in order to optimize the parameters required for its detection using the WCT method under different atmospheric conditions. This optimization allows for a one‐year statistical analysis of the PBL height at midday over Granada (southeastern Spain) from lidar data. The PBL height showed a seasonal cycle, with higher values in summer and spring while lower values were found in winter and autumn. The annual mean was 1.7 ± 0.5 km a.s.l. during the study period. The relationship of the PBL height with aerosol properties is also analyzed for the one‐year period.
Key Points
This study uses the WCT to determine automatically mixing height from lidar data
The method was optimized comparing with radiosoundings and microwave radiometer
One year analysis of the PBL height is done, correlating with aerosol properties
In the framework of regular European Aerosol Research Lidar Network (EARLINET) observations, aerosol layers have been monitored with a multiwavelength aerosol Raman lidar in the upper troposphere and ...lower stratosphere over Leipzig (51.4°N, 12.4°E), Germany, since the summer of 2008. The origins of these layers are eruptions of different volcanoes on the Aleutian Islands, Kamchatka, Alaska, and on the Kuril Islands. FLEXPART transport simulations show that the volcanic aerosol is advected from Alaska to central Europe within about 7 days. The aerosol layers typically occurred in the upper troposphere above 5 km height and in the lower stratosphere below 25 km height. The optical depths of the volcanic aerosol layers are mostly between 0.004 and 0.025 at 532 nm. The wavelength dependence of the backscatter coefficients and extinction coefficients indicate Ångström exponents from 1.0–2.0. Lidar ratios in the stratosphere are found in the range from 30–60 sr (355 nm) and 30–45 sr (532 nm). The estimation of the effective radius, surface‐area, and mass concentrations of a volcanic aerosol layer, observed well within the stratosphere at end of August 2009, reveals values of 0.1–0.2 μm, 5–10 μm2 cm−3, and 0.3–0.5 μg m−3, respectively.
Asian mineral dust is one of the main aerosol sources in the Earth-atmosphere system, which generates significant effect on air quality, human health, and climate change. Meanwhile, knowledge of ...vertical optical properties of dust aerosol is crucially needed for identification of the dust source and improved understanding of radiative effect in climate model. In the study, triple-wavelength polarization Raman lidar observation combined with photometer, radiosonde and simultaneous model data was performed at Kashi in the northwestern of Tarim Basin. Taklimakan desert, located in the center of Tarim Basin, is the largest desert of Asia. Base on the measurement and model, two typical dust sources in different altitude were identified in the study, namely Taklimakan desert (East Road), Central Asia desert and Middle East desert (West Road). Particle size distribution of photometer shows that these cases were all coarse-mode-dominated with effective radius larger than 1.7 μm. The lidar observations revealed particle linear depolarization ratios (PLDR) of the Taklimakan dust ranged from 0.28 to 0.34 at 355 nm, 0.33 to 0.35 at 532 nm and 0.29-0.35 at 1064 nm, while lidar ratios (LR) ranged from 47 to 54 sr at 355 nm and from 42 to 51 sr at 532 nm wavelength. Spectral variation of LR and PLDR for Asian dust and Saharan dust was analyzed. All observed Asian dust present the consistent spectral variation that lidar ratio at 355 nm is higher than that of 532 nm, which however is not the case for Saharan dust. Both Saharan and Asian dust measurement PLDR at 532 nm is larger than that of 355 nm and 1064 nm. The measured dust properties provide particularly valuable information for dust simulation and dust climate model for different dust source.
Water vapor mixing ratio and relative humidity profiles were derived from the multi-wavelength Raman PollyXT lidar at the EARLINET site in Warsaw, using the Rayleigh molecular extinction calculation ...based on atmospheric temperature and pressure from three different sources: i) the standard atmosphere US 62, ii) the Global Data Assimilation System (GDAS) model output, and iii) the WMO 12374 radiosoundings launched at Legionowo. With each method, 136 midnight relative humidity profiles were obtained for lidar observations from July 2013 to August 2015. Comparisons of these profiles showed in favor of the latter method (iii), but it also indicated that the other two data sources could replace it, if necessary. Such use was demonstrated for an automated retrieval of water vapor mixing ratio from dusk until dawn on 19/20 March 2015; a case study related to an advection of biomass burning aerosol from forest fires over Ukraine. Additionally, an algorithm that applies thresholds to the radiosounding relative humidity profiles to estimate macro-physical cloud vertical structure was used for the first time on the Raman lidar relative humidity profiles. The results, based on a subset of 66 profiles, indicate that below 6km cloud bases/tops can be successfully obtained in 53% and 76% cases from lidar and radiosounding profiles, respectively. Finally, a contribution of the lidar derived mean relative humidity to cloudy conditions within the range of 0.8 to 6.2km, in comparison to clear-sky conditions, was estimated.
•Automated retrieval of water vapor mixing ratio from Raman lidar•Cloud vertical structure estimation from relative humidity profiles (Raman lidar versus radiosonde)•Contribution of Raman lidar derived relative humidity to total water for different level clouds
•Parameterized equations of PM mass concentration and extinction coefficient were established at different levels of relative humidity.•The sample datasets contain a large number of and long-term ...different seasonal and weather pollution conditions.•Derivation of PM mass concentration profiles by using single-wavelength Raman lidar and the parameterized equations.•Vertical distribution characteristics of PM1, PM2.5 and PM10 mass concentrations in Xi'an were obtained.
Considering the importance of the aerosol optical parameters detection for environmental monitoring, a method of converting single-wavelength Raman lidar backscattered echoes to aerosol mass concentrations is proposed to obtain a high-resolution vertical distribution of particulate matter (PM) mass concentrations. PMx (x = 1, 2.5, 10) mass concentrations and extinction coefficients at 355 nm and 532 nm were obtained using a combination of a colocated visibility meter and wide-range particle spectrometer (WRAS), and parameterized equations between the aerosol extinction coefficient and mass concentration at different levels of relative humidity (RH) were established (the sample datasets included different seasonal and weather pollution conditions in Xi'an, China, for 2018 and 2019). The results demonstrate that parametric analysis of sample datasets at three levels of RH (RH < 60%, 60% ≤ RH < 75%, and RH ≥ 75%) can better reflect the long-term variation characteristics of aerosols: the aerosol extinction coefficients show an exponential relationship with PM1 and PM2.5 mass concentrations, and the correlation coefficients are both above 0.965 even at different levels of RH, while the correlation with PM10 is 0.808. The extinction coefficient and RH profiles can be retrieved using single-wavelength Raman lidar, and then the aerosol mass concentration distribution can be calculated by combining parameterized equations. The deviation of mass concentration profiles between 355 and 532 nm Raman lidar was analyzed, and it is a constraint that the calculation of the PM mass concentration profile is made in the planetary boundary layer (PBL). The derivation uncertainty of PMx and the limitations of the method are also discussed. Finally, cases of vertical distribution and variations in PMx on pollution-free and hazy days are presented.
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