The Leipzig Aerosol and Cloud Remote Observations System LACROS &#160;&#8211; a mobile infrastructure for aerosol-cloud-interaction observations at hot spots of atmospheric research&#160;
Authors: Seifert Patric , Bühl Johannes , Radenz Martin , Engelmann Ronny , Baars Holger , Jimenez Cristofer , Witthuhn Jonas , Ohneiser Kevin , Teisseire Audrey , Hajipour Majid , Floutsi Athina , Skupin Annett , Heese Birgit , Klamt Andi , Ansmann Albert , Wandinger Ulla , Deneke Hartwig , Macke Andreas 
Published: December 2021

&lt;p&gt;The large number of unsolved questions concerning the interaction between aerosol particles and clouds and corresponding indirect effects on precipitation and radiative transfer demand new measurement strategies and systems to resolve the atmospheric processes involved. Obtaining synergistic information about cloud and aerosol properties from multi&amp;#8211;instrument and hence multi&amp;#8211;sensor observations is a key approach to overcome the current lack of knowledge. Motivated by these needs, the mobile multi&amp;#8211;instrument platform Leipzig Aerosol and Cloud Remote Observations System LACROS was set-up in 2011 by Leibniz Institute for Tropospheric Research (TROPOS). LACROS nowadays is the central component of a sophisticated framework of synergistic state-of-the-art measurement techniques and methodologies, embedded into an environment of comprehensive data management.&lt;/p&gt;
&lt;p&gt;The current setup of LACROS comprises a set of state-of-the-art remote-sensing instruments such as a 35-GHz scanning polarimetric cloud radar, multi-wavelength polarization Raman lidars, Doppler lidar, micro rain radar, microwave radiometer, laser disdrometer, as well as sensors for direct and diffuse downwelling solar and terrestrial radiation. All instruments are installed within customized sea-freight containers. This ensures a highest-possible mobility of the whole set of instruments. LACROS is a central mobile exploratory platform of the European Union Aerosol, Clouds, and Trace Gases Research Infrastructure (ACTRIS, http://www.actris.net). A variety of ways for physical, remote, and virtual access to the LACROS capabilities are provided via the European Union project ATMO-ACCESS (https://www.atmo-access.eu).&lt;/p&gt;
&lt;p&gt;LACROS measurements focus on three main tasks: (1) Investigation of mixed-phase cloud processes by exploiting co&amp;#8208;located remote-sensing observations of microphysical properties and radiative effects of aerosols and clouds and their interactions. (2) Instrument validation and development of algorithms and new measurement techniques for cloud and aerosol microphysics retrievals such as, i.e., dual&amp;#8208;field&amp;#8208;of&amp;#8208;view lidar to derive cloud droplet size information, or retrievals of aerosol microphysical properties from combined lidar and Sun photometer measurements. (3) Field deployments in key regions of atmospheric research, where the processes under investigation are already naturally constrained and observations can ideally be combined with in-situ observations or model simulations.&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;This contribution will present the current setup of LACROS and its recent deployments in Leipzig, the Netherlands, Cyprus and southern Chile, results of aerosol-cloud-interaction studies by means of both, case studies and multi-site long-term statistics, as well as an overview on the current and future involvement of LACROS in cal/val activities of new methods and satellite missions.&amp;#160;&lt;/p&gt;