JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 17, No. 7-8, July – August 2015, p. 911 - 917 Study of planetary boundary layer height from LIDAR measurements and ALARO model A. TIMOFTE a,b , L. BELEGANTE c* , M. M. CAZACU a,d , B. ALBINA a , C. TALIANU c , S. GURLUI a a Faculty of Physics, Alexandru Ioan Cuza University of Iasi, Bulevardul Carol I, nr. 11, 700506 Iasi, Romania, Atmosphere Optics, Spectroscopy and Lasers Laboratory (LOA-SL Iasi) b National Meteorological Administration, Regional Forecast Center Bacau, 3 Timpului Str., Bacau, Romania c National Institute of R&D for Optoelectronics, 409 Atomistilor Street, Magurele, IlfovPO Box MG-5, RO-77125 Romania d Physics Department, Gheorghe Asachi Technical University of Iasi, 59A Mangeron Blvd., 700050 Iasi, Romania The time evolution of the Planetary Boundary Layer (PBL) height has a significant impact on weather events and air quality since it is one of the parameters affecting the atmospheric state. This paper presents results concerning the PBL height retrieval using several techniques and assessment methods. The studies are focused on remote sensing methods, radiosoundings and numerical models. The PBL height behaviour has been studied in two sites by means of vertical humidity, temperature profiles and range corrected lidar signal. A good correlation between lidar, microwave radiometry and radio sounding profiles has been evidenced for the analyzed period. PBL height estimation performed by ALARO has a permanent offset with respect to the other methods during the cold season. (Received May 29, 2015; accepted June 24, 2015) Keywords: PBL height, Lidar, ALARO, Radio-soundings, Microwave radiometer 1. Introduction The Planetary Boundary Layer (PBL) height is an important weather parameter affecting the concentration of pollutants near the ground surface. It determines the atmospheric volume in which the pollutants are emitted [1]. The PBL height is a diagnostic variable in forecasting models, for the dispersion and transport of pollutants through the atmosphere. The correct assessment of the PBL height in air quality dispersion models and weather forecast models can drastically increase the accuracy of the output [2, 3]. For local scale dispersion models designed to estimate the environmental impact of urban pollution accidents, the interaction between the mesoscale circulation and the PBL must be taken into account. The diurnal variation of the PBL height has important implications for energy transfer at the surface – atmosphere interface [4] and its representation can be useful for many applications including radiative transfer studies. By understanding the processes that take place in the PBL, the weather and climate modeling community can better integrate these phenomena in numerical models: e.g. the PBL should be properly described in weather forecasting models to correctly predict the diurnal cycle, low-level winds and the convergence [5]. Moreover, the PBL is directly influenced by surface conditions and it differs from the free troposphere in many thermodynamic properties, content and movement [6]. The phenomena occurring in the PBL are also important in aviation: fog and wind shears. Also, ground frost, hoarfrost, dew and evapo-transpiration processes are taking place in this layer and are of particular interest for the agriculture community [7]. The PBL height ranges from a few hundred meters to several kilometers according to the season and topography. Also the diurnal variation, strongly dependent on surface temperature has a strong influence on the PBL height. Above large areas of water, the PBL height varies relatively slowly in time and space because of the caloric capacity of water [5, 8]. The PBL height is an important parameter for assessing the degree of turbulence and dispersion of pollutants in the atmosphere [9]. Seibert et al. (2000) described multiple PBL height estimation methods and consequently evidenced that the meteorological condition are closely related to the applicability of its definition [10]. Different definition can determine appreciable differences in the estimated height [3]. The study was focused on seven different methods to determine the PBL height from a single data set - radiosonde profiles [11]. The results highlighted that the estimated PBL height differs by several hundred meters according to the assessment method. The seasonal variation could also be dependent on the different methods for assessing the PBL height. Seibert et al. (2000) emphases that a good approach would be to use the same method to compare different PBL height estimates determined from different sources (e.g. radio sounding, passive and active remote sensing). Meanwhile Seidel et al. (2012) recommended a definition based on bulk Richardson number for the PBL height. The importance of meteorological conditions was