The impact of human activities on the global climate may lead to large disruptions of the economic, social and political status quo in the middle and long term. Understanding the dynamics of the Earth's climate is thus of paramount importance and one of the major scientific challenges of our time. The estimation of the relative contribution of the many components (interacting each other) of the Earth's climate system requires observation and continuous monitoring of various atmospheric physical and chemical parameters. Temperature, water vapor and greenhouse gases concentration, aerosol and clouds loads, and atmospheric dynamics are parameters of particular importance in this respect. The quantification of the anthropogenic influence on the dynamics of these above-mentioned parameters is of crucial importance nowadays but still affected by significant uncertainties. In the present context of these huge uncertainties in our understanding of how these different atmospheric compounds contribute to the radiative forcing, the research presented in this report is related to the following topics: Development of lidar-based remote sensing techniques for monitoring atmospheric compounds and processes Aerosols – cirrus – contrails optical properties up to the tropopause Water vapor mixing ratio and relative humidity estimation in the upper troposphere Temperature profiling in the upper troposphere-lower stratosphere Characterization of the long-range transported mineral aerosols (i.e. Saharan dust outbreaks) Planetary boundary layer-upper troposphere exchanges (i.e. August 2003 heatwave effect) In the above research frames, the development and application of measurement techniques for the monitoring of climate-change parameters, this work refers to the implementation of a multi-wavelength LIDAR1 system (JFJ - LIDAR)2 at the International Scientific Station of Jungfraujoch (ISSJ, 46°33' N, 7°59' E, at 3580 m ASL- above sea level). The JFJ3 station is situated above the planetary boundary layer (PBL) almost all year long and is located in a mountain pass linking the Swiss plateau to the North with the Rhone Valley to the South through the Aletsch glacier corridor. Measurements with the JFF-LIDAR system provide regular vertical and horizontal remote sensing of water vapor, temperature, and optical properties (backscatter and extinction coefficients) of aerosols, cirrus clouds and contrails in the upper troposphere (UT)4. The lidar system is based on the laser emission at 355, 532 and 1064 nm and on subsequent detection of both elastic (Mie) and inelastic (Raman) atmospheric backscatter light. The backscattering collected radiation is precisely: the elastic at 355, 532 and 1064 nm; the rotational-vibrational Raman radiation from nitrogen at ~ 387 nm, and from water vapor at ~ 407 nm as well as the pure rotational nitrogen/oxygen Raman excited at ~ 532 nm. The depolarization of the initially linearly polarized radiation was also detected at 532 nm and it was use to distinguish between water and ice contents in cirrus clouds, but also it may reveal long-range transported mineral aerosols such as Saharan dust. Profiles of backscatter and extinction coefficients of aerosols-cirrus-contrails, needed for estimation of the radiative balance of the atmosphere, are derived from elastic and Raman light scattering processes, or through a combination of both, using devoted algorithms and software developed within this research. Data gathered from routine measurements are statistically analyzed and interpreted in comparison with similar measurements obtained from colocated techniques. Optical and microphysical properties of a typical contrail were studied. The UT water vapor mixing ratio profiles are estimated from the ratio of ~ 407 nm and ~387 nm Raman radiation excited by 355 nm. Upon appropriate calibration, real time water vapor mixing ratio profiles derived from LIDAR measurements are found in good agreement with the closest radiosounding techniques, and co-located measurements such as the GPS5 and sun photometer based measurements. The water vapor profiles, combined with simultaneous temperature profiles taken from atmospheric models, radiosounding or, more realistically, based on the pure rotational Raman technique, were used for the estimation of relative humidity profiles which allow the identification of UT super-saturation regions. Air temperature profiles were obtained up to the lower stratosphere using the backscatter of pure rotational Raman radiation excited by 532 nm. These first results compare well to simultaneous regional radiosounding measurements, and follow standard atmospheric models. The pure rotational Raman backscatter was also used for determining absolute extinction and the lidar ratio for cirrus clouds. Based on the JFJ-LIDAR measurements, supported by co-located and regional measurements, the research presents also in detail two case studies related to climate problematic: The first concerns the tracking of a Saharan dust outbreak (SDO) and the derivation of its optical properties. The second study refers to the analysis of the evolution and consequences of the high altitudes planetary boundary layer (PBL)6 convection during the August 2003 heat - wave episode. The results presented within this research provide a promising basis for extending these JFJ-LIDAR observations from the upper troposphere into the stratosphere by using the existent astronomic telescope (~15 times increased sensitivity) and a new (~ 3 times more powerful) laser source. Consequently DIAL7 technique for measuring the stratospheric ozone will be developed and implemented in the near future at JFJ. Future challenges include also JFJ-LIDAR remote control operation and the ability of real time obtained atmospheric calibrated profiles (i.e. optical properties of aerosols-cirruscontrails, water vapor, temperature and ozone). --------------------1 LIDAR – LIght Detection And Ranging 2 JFJ-LIDAR is the acronym used here for Jungfraujoch multi-wavelength LIDAR system 3 JFJ is the abbreviation for Jungfraujoch 4 UT will be used as abbreviation for upper troposphere (from ~ 3600 m ASL to the tropopause atmospheric region) 5 GPS is the acronym for Global Positioning System 6 PBL - planetary boundary layer – its top is usually situated under the altitude of the JFJ station (i.e. 3600m ASL) 7 DIAL - is the acronym coming from DIfferential Absorption Lidar