Livio Belegante

Retrieval of the boundary layer height from active and passive remote sensors. Comparison with a NWP model

In this study, we used boundary layer heights derived from lidar in Romania to validate the Weather Research Forecast (WRF) model improved by ARIA Technologies SA in the framework of ROMAIR LIFE project. Lidar retrievals were also compared to the retrievals from meteorological data, both modeled (Global Data Assimilation System; GDAS) and measured (microwave radiometry). Both the gradient and the wavelet covariance methods were used to compute the boundary layer height (BLH) from the range corrected lidar signal, and their equivalence was shown.The analysis was performed on 102 datasets, spread over all seasons and 3 years (2009–2011). A good agreement was found for the remote sensors (lidar and microwave radiometer) which are co-located and measure simultaneously. The correlation of the measured boundary layer height and the modelled one was 0.66 for the entire dataset, and 0.73 when considering daytime data, i.e., for a well defined boundary layer. A systematic underestimation of the boundary layer height by the WRF during non-convective periods (nocturne, stable atmosphere) was found.

Mix of volcanic ash and Saharan dust over Romania during Eyjafjallajökull eruption

Located at a distance more than 3400Km from Iceland, where the eruption of Eyjafjallajökull volcano occurred, Romania was under the influence of volcanic ash transported by middle altitude air masses across Europe. Apart from two clear episodes on April 18 and April 21, 2010 the mix of volcanic ash with Saharan dust was detected by the multiwavelength Raman lidar in Bucharest. Optical properties of aerosol layers for these particular cases showed an increase of the linear particle depolarization, as well as a decrease of the Angstrom exponent, compared with the pure long-range transported volcanic ash. The case of May 5th, 2010 is analyzed from lidar and ground-level data, accounting for layer dynamics, optical properties and chemical composition. Using high resolution lidar data we could make a clear distinction between ash and dust layers up to their mixing in the PBL. In order to account for similarities and differences, the same analysis was done for May 10th and 11th, when several distinct layers were depicted. The signature of ash (sulfate) was identified by Aerosol Mass Spectrometer at ground-level, on May 5th and May 11th.

Linear approximation of Rayleigh-Brillouin scattering spectra.

Rayleigh-Brillouin scattering is the basis of many remote sensing techniques, including high spectral resolution lidar measurements of aerosols and wind. Rayleigh-Brillouin spectra can be accurately estimated using physics-based models like the so-called Tentis S6 and Pans S7 models. Unfortunately, these are computationally expensive and can be the bottleneck for real-time lidar processing and iterative parameter estimation problems. This short article describes a very efficient linear approximation of the Rayleigh-Brillouin spectra based on Principal Component Analysis (PCA). Using PCA, the outputs of the above models can be approximated with very high accuracy using a single matrix multiplication. The described method can be applied to the output of any detailed scattering model, thus it can be used for a wide range of problems, e.g., for scattering from different gases (Air, N2, O2,…) and for different ranges of temperature and pressure. The precision of the approximation can be adapted to the requirements of the studied problem, and can easily exceed the actual accuracy of the reference models.

Assessment of the total precipitable water from a sun-photometer,microwave radiometer and radiosondes at a continental site insoutheastern Europe

In this study, we discuss the differences in the total precipitable water (TPW), retrieved from a Cimel sunphotometer operating at a continental site in South-East Europe, between the Version 3 (V3) and Version 2 (V2) of the Aerosol Robotic Network (AERONET) algorithms. In addition, we evaluate the performance of the two algorithms comparing their product with the TPW obtained from a collocated microwave radiometer and nearby radiosondes during the period 2007–2017. The TPW from all three instruments was highly correlated, showing the same annual cycle, with lower values during winter and higher 5 during summer. The Sun-photometer and the microwave radiometer depicts the same daily cycle, with some discrepancies during early morning and late afternoon due to the effect of solar zenith angle on the measurements of the photometer. The TPW from the (V3) of the AERONET algorithm has small differences compared with (V2), mostly related to the use of the new laboratory-based temperature coefficients used in V3. The microwave radiometer shows very good performance compared to the radiosondes, especially during nighttime when the differences between the two instruments are almost negligible. The 10 comparison of the sun-photometer data with high-quality independent measurements from radiosondes and radiometer shows that the absolute differences between V3 and the other two datasets are slightly higher compared with V2. However, V3 has a lower dependence from the TPW and the internal sensor temperature, indicating a better performance of the retrieving algorithm. To our knowledge, this is the first in-depth analysis of the V3 TPW and although the findings presented here are for a specific site, we believe that they are representative of other mid-latitude continental stations. 15

Integrated E-System for Pollution and Climate Change Monitoring in the Framework of the Romanian Atmospheric Research 3D Observatory - RADO

The paper presents an overview on the implementation of integrated automated systems for pollution and climate change monitoring in the framework of RADO. RADOs mission is to improve modeling of physical, chemical, and biological processes, to assess the effects of climate change, and to quantify and reduce uncertainties in evaluating the hydrological cycle and its influence on natural resources. For this purpose, the integrated automated e-system, collecting data from different environmental monitoring instruments was developed.

Water analysis from LIDAR investigations on the Romanian Black Sea coast

The aim of the paper is to analyze the fluorescence characteristics of the neritic water on the Romanian Black Sea coast under anthropogenic influences. A fluorescence LIDAR, based on excimer (308 nm) and a dye laser (367, 460 nm) was used in order to map the Dissolved Organic Matter (DOM) and chlorophyll variations in a marine area. Onboard ship campaign was performed during spring time to evidence the algal blooming. Physicochemical parameters of water and chlorophyll concentration were determined also by laboratory measurements of collected samples. The organic compounds and phytoplankton were characterized based on Laser Induced Fluorescence (LIF) and Raman scattering. Highly polluted areas were noted and mapped along the ship trajectory.

Saharan dust event over Bucharest observed by an elastic backscatter lidar

A lidar measurements campaign took in Magurele Platform, southwestern part of Bucharest, during on June 25th, 26th and 28th of 2007 and was intended for aerosol loading characteristics over the urban area. An event of long-range Saharan dust transport to Eastern Europe (Romania) observed during this time is presented in here. We have used an elastic backscattering lidar, based on an Nd:YAG laser, at 1064nm sounding wavelength. It can detect in real time aerosols density profiles up to 10 Km high with a spatial resolution of 12 m. Origin of lidar sampled air masses arriving at various heights over Bucharest have been determined by the analytical back-trajectories from NOAA HYSPLIT model. Saharan dust layers reached the southern part of Romania predominantly by cyclonic circulation due to the strong through observed at all the levels from a cyclonic system located in northwestern part of Africa. Analysis of cloud cover and dust load was estimated by the Dust Regional Atmospheric Modeling (Dream model). The dust event presented highlights how the synergy of Lidar data together with 3-D back trajectories analysis and model calculations can improve our ability to determine accurately the source of high aerosol loading.