Ground-based Raman Lidar Research Articles

An iterative algorithm to simultaneously retrieve aerosol extinction and effective radius profiles using CALIOP

Abstract. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite has been widely used in climate and environment studies to obtain the vertical profiles of atmospheric aerosols. To retrieve the vertical profile of aerosol extinction, the CALIOP algorithm assumes column-averaged lidar ratios based on a clustering of aerosol optical properties measured at surface stations. On one hand, these lidar ratio assumptions may not be appropriate or representative at certain locations. One the other hand, the two-wavelength design of CALIOP has the potential to constrain aerosol size information, which has not been considered in the operational algorithm. In this study, we present a modified inversion algorithm to simultaneously retrieve aerosol extinction and effective radius profiles using two-wavelength elastic lidars such as CALIOP. Specifically, a lookup table is built to relate the lidar ratio with the Ångström exponent calculated using aerosol extinction at the two wavelengths, and the lidar ratio is then determined iteratively without a priori assumptions. The retrieved two-wavelength extinction at each layer is then converted to the particle effective radius assuming a lognormal distribution. The algorithm is tested on synthetic data, Raman lidar measurements and then finally the real CALIOP backscatter measurements. Results show improvements over the CALIPSO operational algorithm by comparing with ground-based Raman lidar profiles.

Response of the boundary layer clouds to the surface forcings: A case study of western India

Clouds atop atmospheric boundary layer over an urban location have been studied using a ground-based Raman LIDAR (RL), supported by radiosonde, INSAT-3D & Meteosat-7 geostationary satellite, and ERA5 reanalysis datasets. The low-level clouds over Ahmedabad (23.02°N, 72.57°E) have been formed from the outflow of a large-scale convergence zone extending from the East-West Indian region. The persistence of these clouds throughout the day has been aided by the transport of moisture to cloud heights by turbulent updrafts. The cloud cover broke off with the entrainment of free tropospheric air with the deepening of the boundary layer, disrupting the surface moisture supply. The consecutive two days (10 and 11 June 2016) observations from the RL showed a unique sensitivity of these clouds to the diurnal variation of the atmospheric boundary layer due to the strong coupling between the clouds and the boundary layer. Ground-based LIDARs provide a better platform for studying the low-level boundary layer clouds and their sensitivity to surface forces due to high accuracy and high temporal resolution. Thus, increasing ground-based observations of such boundary layer clouds is essential for a better understanding of climate sensitivity.

Lidar Observations and Data Assimilation of Low-Level Moist Inflows Causing Severe Local Rainfall Associated with a Mesoscale Convective System

Abstract We conducted an observational survey using a ground-based water vapor Raman lidar (RL) during the warm season in Japan to investigate the water vapor structure of low-level inflows that contribute to the formation of a mesoscale convective system (MCS). After the passage of a warm front, low-level moisture convergence contributed to the initiation and development of numerous convective clouds that composed the MCS. The RL observations showed that the vertical profiles of the water vapor mixing ratio (WVMR) associated with low-level inflows into the MCS exceeded 20 g kg−1 below 500 m above sea level, which is comparable to WVMRs in previous reports associated with MCSs in Japan and the United States. We conducted two assimilation experiments using a four-dimensional variational data assimilation system: one is to assimilate operational observational data (CNTL), and the other is to assimilate WVMR vertical profiles and operational observational data (TEST). A comparison between TEST and CNTL showed that data assimilation of the WVMR vertical profiles not only modified the moisture field but also the wind field. It appears that the modifications observed in horizontal wind are related to the modification of the WVMR in the analysis fields. These WVMR and wind modifications improved the reproduction of the frontal surface and forecasting of 6-h precipitation amount slightly. Data assimilation of vertical profiles of the WVMR has positive and negative impacts on the WVMR and horizontal wind, respectively, implying that the vertical profiles of both the horizontal wind and the WVMR might better estimate initial conditions and forecasts. Significance Statement Low-level moisture inflows are one of the key parameters involved in the formation of mesoscale convective systems (MCSs). Therefore, data assimilation of low-level moisture profiles is one of the prospective methods for better forecasting heavy precipitation associated with MCSs. However, few direct observations of the low-level moisture structure associated with MCSs and data assimilation experiments have been undertaken to date. We observed the vertical profiles of moisture associated with an MCS in Japan using a ground-based water vapor Raman lidar and show the existence of a relatively moist low-level inflow into the MCS. The data assimilation of low-level moisture has positive and negative impacts on moisture and horizontal wind, respectively, and improves slightly 6-h precipitation forecasts.

Vertical Structure of Dust Aerosols Observed by a Ground-Based Raman Lidar with Polarization Capabilities in the Center of the Taklimakan Desert

The vertical structure of dust properties in desert sources is crucial for evaluating their long-range transportation and radiative forcing. To investigate vertical profiles of dust optical properties in the Taklimakan Desert, we conducted ground-based polarization Raman lidar measurements in Tazhong (83.39°E, 38.58°N, 1103 m above sea level), located at the center of the Taklimakan Desert in the summer of 2019. The lidar system developed by Lanzhou University for continuous network observation is capable of measuring polarization at 532 and 355 nm and detecting Raman signals at 387, 407, and 607 nm. The results indicate that dust aerosols in the central Taklimakan Desert were regularly lifted over 6 km during the summer with a mass concentration of 400–1000 µg m−3, while the majority of the dust remained restricted within 2 km. Moreover, the height of the boundary layer can reach 5–6 km in the afternoon under the strong convention. Above 3 km, dust is composed of finer particles with an effective radius (Reff.) less than 3 μm and a Ångström exponent (AE) related to the extinction coefficient (AEE)532,355 greater than 4; below 3 km, however, dust is dominated by coarser particles. In addition, the particle depolarization ratios (PDR) of Taklimakan dust are 0.32 ± 0.06 at 532 nm and 0.27 ± 0.04 at 355 nm, while the lidar ratios (LRs) are 49 ± 19 sr at 532 nm and 43 ± 12 sr at 355 nm. This study firstly provides information on dust vertical structure and its optical properties in the center of the desert, which may aid in further evaluating their associated impacts on the climate and ecosystem.

Experimental investigation of the stable water isotope distribution in an Alpine lake environment (L-WAIVE)

Abstract. In order to gain understanding on the vertical structure of atmospheric water vapour above mountain lakes and to assess its link with the isotopic composition of the lake water and with small-scale dynamics (i.e. valley winds, thermal convection above complex terrain), the L-WAIVE (Lacustrine-Water vApor Isotope inVentory Experiment) field campaign was conducted in the Annecy valley in the French Alps during 10 d in June 2019. This field campaign was based on an original experimental synergy between a suite of ground-based, boat-borne, and two ultra-light aircraft (ULA) measuring platforms implemented to characterize the thermodynamic and isotopic composition above and in the lake. A cavity ring-down spectrometer and an in-cloud liquid water collector were deployed aboard one of the ULA to characterize the vertical distribution of the main stable water isotopes (H216O, H218O and H2H16O) both in the air and in shallow cumulus clouds. The temporal evolution of the meteorological structures of the low troposphere was derived from an airborne Rayleigh–Mie lidar (embarked on a second ULA), a ground-based Raman lidar, and a wind lidar. ULA flight patterns were repeated several times per day to capture the diurnal evolution as well as the variability associated with the different weather events encountered during the field campaign, which influenced the humidity field, cloud conditions, and slope wind regimes in the valley. In parallel, throughout the campaign, liquid water samples of rain, at the air–lake water interface, and at 2 m depth in the lake were taken. A significant variability of the isotopic composition was observed along time, depending on weather conditions, linked to the transition from the valley boundary layer towards the free troposphere, the valley wind intensity, and the vertical thermal stability. Thus, significant gradients of isotopic content have been revealed at the transition to the free troposphere, at altitudes between 2.5 and 3.5 km. The influence of the lake on the atmosphere isotopic composition is difficult to isolate from other contributions, especially in the presence of thermal instabilities and valley winds. Nevertheless, such an effect appears to be detectable in a layer of about 300 m thickness above the lake in light wind conditions. We also noted similar isotopic compositions in cloud drops and rainwater.

A case study on the vertical distribution and characteristics of aerosols using ground-based raman lidar, satellite and model over Western India

ABSTRACT Ahmedabad is an urban site in western region of India. Dust loading and its variability are very high over this semi-arid location. A state-of-the-art ground-based Raman lidar has been used for the study of day-to-day variability in vertical distribution of aerosol loading over Ahmedabad (23.02° N, 72.57° E) from 8 to 11 May 2018. We have done a comprehensive study about vertical profiles of aerosols across two wavelengths recorded simultaneously, namely, 355 nm and 532 nm, over this location. An interesting hump feature has been noted on 9 May at around 18 h (Local Time), with an additional peak at 19 h on 10 May. The loading over this region has more fine-mode aerosols than coarse-mode particles. Further, findings from ground-based lidar have been compared with MACC-II model simulations and Cloud-Aerosol Lidar with Orthogonal Polarization on-board Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observational. Back-trajectory analysis showed majority of the influx came from middle-east, carrying mineral dust and traces of marine aerosols from Arabian Sea, except for 11 May, where low-level dust carrying trajectories and also coarser dust particles were not seen. This type of manifestation has also been observed while classifying aerosols over Ahmedabad using Lidar Depolarization Ratio and Lidar Ratio obtained from Raman Lidar. Fine mode aerosols have been characterized as industrial, vehicular and marine, while coarser as mineral dust and biomass burning. This study focuses on local variation and classification of aerosols based on size and type, which will further help in better estimation of radiative budget and other impacts of aerosols.

Environmental impacts of fireworks on aerosol characteristics and radiative properties over a mega city, India

The study focusses to investigate the variations in aerosol characteristics, concentrations and radiative properties due to the burning of firecrackers during Diwali festival event followed with New year festival celebrations over a representative urban environment. A six day's long intensive in situ measurements of Black Carbon, Particulate Matter and Aerosol Optical Depth were collected to capture pre to post-Diwali and New Year festival celebrations marked with massive fireworks. We observed an increase of 286%, 89.5%, and 60.5%, in BC, PM10, and PM2.5 concentrations, respectively on festival night as compared to pre-event days. An increase in in situ measured AOD is comparable with concurrent satellite derived AOD. Angstrom exponent, α > 1.0 along with high turbidity coefficient; β estimated for the festival period clearly implies the abundance of fine-mode particles, probably the smoke aerosols loading from fireworks. The Mie-scattered return signals received by the ground based Raman LiDAR at 532 nm showed an increased concentration of ‘anthropogenic aerosols’, attributed to the increased crackers activity. Space based CALIPSO LiDAR observations also validate the presence of ‘polluted dust’ and ‘smoke’ types aerosols at the near surface to 5 km altitude over the study area. A sharp increase in gaseous air pollutants like SO2 and NOx concentrations exceeding the National Ambient Air Quality Standards is also observed. The COART model run simulations in SWIR region showed an increased ‘cooling’ at the surface (−125 Wm−2 to −185 Wm−2) as compared to ‘warming’ in the atmosphere during the event period. A maximum heating rate (1.9 Kday−1) due to total aerosol radiative forcing is also estimated. These investigations provide useful insights into the impact of burning firecrackers on urban air quality besides radiative impacts at a regional scale. Such celebration induced air pollution events may lead to severe health impacts; particularly respiratory and cardiovascular ailments in the resident population.

Water vapor mixing ratio and temperature inter-comparison results in the framework of the Hydrological Cycle in the Mediterranean Experiment\u2014Special Observation Period 1

This paper reports results from an inter-comparison effort involving water vapor and temperature sensors, which took place in the North-Western Mediterranean in the period September–November 2012 in the framework of the first Special Observing Period of the Hydrological cycle in the Mediterranean Experiment. The involved sensors are the ground-based Raman lidars BASIL and WALI, the airborne water vapor differential absorption lidar LEANDRE 2, flying onboard the ATR42 aircraft, as well as additional water vapor and temperature sensors (radiosondes, aircraft in situ sensors, and a microwave radiometer). The main objective of the inter-comparison is the determination of the measurement uncertainty affecting these sensors. The effort benefitted from dedicated ATR42 flights in the framework of the EUropean Facility for Airborne Research (EUFAR) Project “WaLiTemp.” Comparisons between BASIL and LEANDRE 2 in terms of water vapor mixing ratio indicate a vertically averaged mean bias, overline{mathrm{bias}} , and mean absolute bias, left|overline{mathrm{bias}}right| , between the two sensors of − 0.08 g kg−1 (or − 2.50%) and 0.67 g kg−1 (or 2.77%), respectively. For all sensors’ pairs including LEANDRE 2, the inter-comparison range is 0.5–3 km, while for all other sensors’ pairs, the inter-comparison range is 0.5–6 km. Comparisons between BASIL and the microwave radiometer indicate overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values between the two sensors of − 0.02 g kg−1 (or − 1.11%) and 0.22 g kg−1 (or 7.31%), respectively, for water vapor mixing ratio measurements, and a value for both overline{mathrm{bias}} and left|overline{mathrm{bias}}right| of 0.62 K for temperature measurements. Comparisons of BASIL with the radiosondes indicate overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values of 0.28 g kg−1 (or 1.56%) and 0.51 g kg−1 (or 6.66%), respectively, for water vapor mixing ratio measurements, and − 0.43 K and 0.77 K, respectively, for temperature measurements, while comparisons of BASIL with aircraft in situ sensors indicate overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values of 0.22 g kg−1 (or 1.17%) and 0.43 g kg−1 (or 4.62%), respectively, for water vapor mixing ratio measurements, and 0.15 K and 0.47 K, respectively, for temperature measurements. Comparisons of LEANDRE 2 with the radiosondes result in overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values of 0.21 g kg−1 (or 0.76%) and 1.10 g kg−1 (or 11.05%), respectively, while comparisons of LEANDRE 2 with the aircraft in situ sensors indicate a value of both overline{mathrm{bias}} and left|overline{mathrm{bias}}right| of 0.76 g kg−1 (or 8.9%). Comparisons of in situ sensors with the radiosondes reveal overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values of 0.36 g kg−1 (or 2.26%) and 0.36 g kg−1 (or 4.72%), respectively, for water vapor mixing ratio measurements, and 0.61 K and 0.62 K, respectively, for temperature measurements, while comparisons of in situ sensors with the microwave radiometer indicate overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values of − 0.37 g kg−1 (or − 2.01%) and 0.58 g kg−1 (or 12.59%), respectively, for water vapor mixing ratio measurements, and a value of both overline{mathrm{bias}} and left|overline{mathrm{bias}}right| of 0.75 K for temperature measurements. Comparisons of the microwave radiometer with the radiosondes indicate overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values of 0.13 g kg−1 (or 0.83%) and 0.20 g kg−1 (or 17.75%), respectively, for water vapor mixing ratio, and a value of both overline{mathrm{bias}} and left|overline{mathrm{bias}}right| of 0.74 K for temperature measurements. Our attention was also focused on the water vapor inter-comparison between BASIL and the transportable ground-based Raman lidar WALI, which took place in Candillargues on 30 October 2012, with results indicating overline{mathrm{bias}} and left|overline{mathrm{bias}}right| values between the two sensors of − 0.005 g kg−1 (or − 1.31%) and 0.24 g kg−1 (or 4.32%), respectively. Based on the available dataset and benefiting from the circumstance that BASIL could be compared with all other sensors, the overall bias of all sensors was also estimated. For water vapor mixing ratio measurements, the overall bias is 0.0079 g kg−1, 0.159 g kg−1, 0.084 g kg−1, − 0.201 g kg−1, 0.099 g kg−1, and − 0.141 g kg−1 for BASIL, LEANDRE 2, WALI, the radiosondes, the microwave radiometer, and the aircraft in situ sensor, respectively, being within ± 0.02 g kg−1 for all water vapor sensors. For temperature measurements, the overall bias is 0.11 K, 0.54 K, − 0.04 K, and − 0.51 K for BASIL, the radiosondes, the microwave radiometer, and the aircraft in situ sensor, respectively.

Characterization of atmospheric aerosol optical properties based on the combined use of a ground-based Raman lidar and an airborne optical particle counter in the framework of the Hydrological Cycle in the Mediterranean Experiment – Special Observation Period 1

Abstract. Vertical profiles of the particle backscattering coefficient at 355, 532 and 1064 nm measured by the University of Basilicata Raman lidar system (BASIL) have been compared with simulated particle backscatter profiles obtained through a Mie scattering code based on the use of simultaneous and almost co-located profiles provided by an airborne optical particle counter. Measurements were carried out during dedicated flights of the French research aircraft ATR42 in the framework of the European Facility for Airborne Research (EUFAR) project “WaLiTemp”, as part of the Hydrological Cycle in the Mediterranean Experiment – Special Observation Period 1 (HyMeX-SOP1). Results from two selected case studies are reported and discussed in the paper, and a dedicated analysis approach is illustrated and applied to the dataset. Results reveal a good agreement between measured and simulated multi-wavelength particle backscattering profiles. Specifically, simulated and measured particle backscattering profiles at 355 and 532 nm for the second case study are found to deviate less than 15 % (mean value =5.9 %) and 50 % (mean value =25.9 %), respectively, when considering the presence of a continental–urban aerosol component, while slightly larger deviation values are found for the first study. The reported good agreement between measured and simulated multi-wavelength particle backscatter profiles testifies to the ability of multi-wavelength Raman lidar systems to infer aerosol types at different altitudes.

Retrieval of aerosol profiles by Raman lidar with dynamic determination of the lidar equation reference height

A reference height that often needs to be assumed in aerosol retrieval from Raman lidar tends to cause high uncertainty in retrieving the vertical distribution of aerosol optical properties. Here, a novel method is proposed to determine the height-revolved reference height, which is then used to retrieve aerosols from Raman lidar. This method can automatically avoid the atmospheric layers with the presence of aerosols, clouds and low signal to noise ratio (SNR). Based on elastic (at 355 nm) and inelastic (at 387 nm) signals collected during the period from 5 December 2016 to 5 March 2017 by a ground-based Raman lidar in Beijing, China, the aerosol optical properties, such as extinction coefficient, backscattering coefficient and lidar ratio have been successfully retrieved. Results show that the averaged nighttime aerosol optic depth (AOD) from Raman lidar is in good agreement with early morning AOD retrieved from a collocated sunphotometer. The AOD exhibits a strong diurnal variation with a peak at 1500 Beijing time. On average, the nighttime AOD at 355 nm is 0.32, whereas the daytime AOD is 0.72 over Beijing during the study period. The column averaged lidar ratio is 44 sr at 355 nm, roughly consistent with previous studies. Our findings shed light on the pathways towards improving the retrieval of vertical distribution of aerosols optical properties during nighttime.

An Investigation of Optically Very Thin Ice Clouds from Ground-Based ARM Raman Lidars

Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Pacific (TWP) are analyzed. The optically very thin ice clouds, with ice cloud column optical depths below 0.01, are about 23% of the transparent ice-cloudy profiles from the RL, compared to 4–7% from CALIPSO. The majority (66–76%) of optically very thin ice clouds from the RLs are found to be adjacent to ice clouds with ice cloud column optical depths greater than 0.01. The temporal structure of RL-observed optically very thin ice clouds indicates a clear sky–cloud continuum. Global cloudiness estimates from CALIPSO observations leveraged with high-sensitivity RL observations suggest that CALIPSO may underestimate the global cloud fraction when considering optically very thin ice clouds.

Springtime aerosol load as observed from ground-based and airborne lidars over northern Norway

Abstract. To investigate the origin of springtime aerosols in the Arctic region we performed ground-based and airborne 355 nm Raman lidar observations in the north of Norway (Hammerfest). Two lidars were embedded (i) on an ultralight aircraft for vertical (nadir) or horizontal line-of-sight measurements and (ii) in an air-conditioned van on the ground for vertical (zenith) measurements. This field experiment was designed as part of the Pollution in the ARCtic System (PARCS) project of the French Arctic Initiative and took place from 13 to 26 May 2016. The consistency among lidar measurements is verified by comparing nadir, horizontal line of sight, and ground-based Raman lidar profiles. Dispersion of the order of 0.01 km−1 is obtained among lidar-derived aerosol extinction coefficients at 355 nm. The aerosol load measured in the first 3 km of the troposphere remains low throughout the campaign, with aerosol optical thickness (AOT) of 0.1 at 355 nm (∼0.05 at 550 nm). The main contributors to the evolution of the aerosol load at low altitude prove to be one of the flares of the nearby Melkøya gas processing facility, the oceanic source, and the transport of aerosols from industrial sites in Russia. Moreover, ground-based lidar measurements allowed us to identify three cases of long-range aerosol transport (between 3 and 8 km above the mean sea level). Using back trajectories computed with the Lagrangian model FLEXPART-WRF, these aerosol plumes are shown to be the result of the strong forest fires that occurred in the area of Fort McMurray, in Canada. They can at most double the AOT value over the Arctic area, with an anomaly of 0.1 on the AOT at 355 nm.

Improved identification of the solution space of aerosol microphysical properties derived from the inversion of profiles of lidar optical data, part 3: case studies.

We conclude our series of publications on the development of the gradient correlation method (GCM), which can be used for an improved stabilization of the solution space of particle microphysical parameters derived from measurements with multiwavelength Raman and high-spectral-resolution lidar (3 backscatter +2 extinction coefficients). We show results of three cases studies. The data were taken with a ground-based multiwavelength Raman lidar during the Saharan Mineral Dust Experiment in the Cape Verde Islands (North Atlantic). These cases describe mixtures of dust with smoke. For our data analysis we separated the contribution of smoke to the total signal and only used these optical profiles for the test of GCM. The results show a significant stabilization of the solution space of the particle microphysical parameter retrieval on the particle radius domain from 0.03 to 10 μm, the real part of the complex refractive index domain from 1.3 to 1.8, and the imaginary part from 0 to 0.1. This new method will be included in the Tikhonov Advanced Regularization Algorithm, which is a fully automated, unsupervised algorithm that is used for the analysis of data collected with the worldwide first airborne 3 backscatter +2 extinction high-spectral-resolution lidar developed by NASA Langley Research Center.

Feasibility study to measure HDO/H2O atmospheric profiles through a raman lidar

The Raman lidar technique as currently applied for the retrieval of WV mixing ratio profiles allows, in theory, to estimate HDO/H2O atmospheric profiles. The objective of this study is to develop a lidar simulator and to study the feasibility of the groundbased Raman lidar HDO measurement. Thus, the characteristics of a realistic lidar system for the estimation of HDO/H2O atmospheric profiles are investigated through a set of numerical simulations.

Water vapour inter-comparison effort in the framework of the hydrological cycle in the mediterranean experiment – special observation period (hymex-sop1)

Accurate measurements of the vertical profiles of water vapour are of paramount importance for most key areas of atmospheric sciences. A comprehensive inter-comparison between different remote sensing and in-situ sensors has been carried out in the frame work of the first Special Observing Period of the Hydrological cycle in the Mediterranean Experiment for the purpose of obtaining accurate error estimates for these sensors. The inter-comparison involves a ground-based Raman lidar (BASIL), an airborne DIAL (LEANDRE2), a microwave radiometer, radiosondes and aircraft in-situ sensors.

Study of Droplet Activation in Thin Clouds Using Ground-Based Raman Lidar and Ancillary Remote Sensors

A methodology for the study of cloud droplet activation based on the measurements performed with ground-based multi-wavelength Raman lidars and ancillary remote sensors collected at CNR-IMAA observatory, Potenza, South Italy, is presented. The study is focused on the observation of thin warm clouds. Thin clouds are often also optically thin: this allows the cloud top detection and the full profiling of cloud layers using ground-based Raman lidar. Moreover, broken clouds are inspected to take advantage of their discontinuous structure in order to study the variability of optical properties and water vapor content in the transition from cloudy regions to cloudless regions close to the cloud boundaries. A statistical study of this variability leads to identify threshold values for the optical properties, enabling the discrimination between clouds and cloudless regions. These values can be used to evaluate and improve parameterizations of droplet activation within numerical models. A statistical study of the co-located Doppler radar moments allows to retrieve droplet size and vertical velocities close to the cloud base. First evidences of a correlation between droplet vertical velocities measured at the cloud base and the aerosol effective radius observed in the cloud-free regions of the broken clouds are found.

Lidar Observations of Low-level Wind Reversals over the Gulf of Lion and Characterization of Their Impact on the Water Vapour Variability

Water vapour measurements from a ground-based Raman lidar and an airborne differential absorption lidar, complemented by high resolution numerical simulations from two mesoscale models (Arome-WMED and MESO-NH), are considered to investigate transition events from Mistral/Tramontane to southerly marine flow taking place over the Gulf of Lion in Southern France in the time frame September-October 2012, during the Hydrological Cycle in the Mediterranean Experiment (HyMeX) Special Observation Period 1 (SOP1). Low-level wind reversals associated with these transitions are found to have a strong impact on water vapour transport, leading to a large variability of the water vapour vertical and horizontal distribution. The high spatial and temporal resolution of the lidar data allow to monitor the time evolution of the three-dimensional water vapour field during these transitions from predominantly northerly Mistral/Tramontane flow to a predominantly southerly flow, allowing to identify the quite sharp separation between these flows, which is also quite well captured by the mesoscale models.

Measurement of the Linear Depolarization Ratio of Aged Dust at Three Wavelengths (355, 532 and 1064 nm) Simultaneously over Barbados

A ground-based polarization Raman lidar is presented, that is able to measure the depolarization ratio at three wavelengths (355, 532 and 1064 nm) simultaneously. This new feature is implemented for the first time in a Raman lidar. It provides a full dataset of 3 backscatter coefficients, two extinction coefficients and 3 depolarization ratios (3+2+3 lidar system). To ensure the data quality, it has been compared to the well characterized two wavelength polarization lidar POLIS. Measurements of long-range transported dust have been performed in the framework of the Saharan Aerosol Long-Range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) in the Caribbean.

Aircraft Evaluation of Ground-Based Raman Lidar Water Vapor Turbulence Profiles in Convective Mixed Layers

AbstractHigh temporal and vertical resolution water vapor measurements by Raman and differential absorption lidar systems have been used to characterize the turbulent fluctuations in the water vapor mixing ratio field in convective mixed layers. Since daytime Raman lidar measurements are inherently noisy (due to solar background and weak signal strengths), the analysis approach needs to quantify and remove the contribution of the instrument noise in order to derive the desired atmospheric water vapor mixing ratio variance and skewness profiles. This is done using the approach outlined by Lenschow et al.; however, an intercomparison with in situ observations was not performed.Water vapor measurements were made by a diode laser hygrometer flown on a Twin Otter aircraft during the Routine Atmospheric Radiation Measurement (ARM) Program Aerial Facility Clouds with Low Optical Water Depths Optical Radiative Observations (RACORO) field campaign over the ARM Southern Great Plains (SGP) site in 2009. Two days with Twin Otter flights were identified where the convective mixed layer was quasi stationary, and hence the 10-s, 75-m data from the SGP Raman lidar could be analyzed to provide profiles of water vapor mixing ratio variance and skewness. Airborne water vapor observations measured during level flight legs were compared to the Raman lidar data, demonstrating good agreement in both variance and skewness. The results also illustrate the challenges of comparing a point sensor making measurements over time to a moving platform making similar measurements horizontally.

Balloon-borne and Raman lidar observations of Asian dust and cirrus cloud properties over Tsukuba, Japan

The vertical distributions of the microphysical and optical properties of tropospheric aerosols and cirrus cloud were measured using an instrumented balloon and a ground-based Raman lidar over Tsukuba, Japan (36°N, 140°E), during the Asian dust events on 9 and 21 May 2007 to investigate the influence of Asian mineral dust on ice cloud formation in the upper troposphere. The instrumented balloon measured the particle size distribution, ice crystal images, dew/frost point, relative humidity, and temperature. The Raman lidar measured the particle backscattering and extinction coefficients and the depolarization ratio at a wavelength of 532 nm. The results of the balloon measurements showed that supermicrometer (0.7 to 2.8 µm in optical-equivalent radius) dust particles and ice crystals (10 to 400 µm in maximum dimension) were present in the upper troposphere (8 to 12 km in altitude), with number concentrations varying from 5 × 10−3 to 0.6 cm−3 for dust and from 5 × 10−3 to 0.15 cm−3 for ice crystals. The Raman lidar measurement indicated that the particle depolarization ratios were 15 to 35% in the altitude range of 6 to 12 km, indicating the predominance of nonspherical particles in the region. The temperature ranged from −33 to −63°C, and the relative humidity with respect to ice (RHi), estimated from the total (vapor plus condensate) water content obtained with the Snow White hygrometer in the cloud, was 130% at maximum on 9 May, which was close to the activation point of Asian mineral dust as ice nuclei to form ice crystals.