Johannes Bühl

Dual‐FOV Raman and Doppler lidar studies of aerosol‐cloud interactions: Simultaneous profiling of aerosols, warm‐cloud properties, and vertical wind

Date of Acceptance: 24/04/2014 This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made

LACROS: the Leipzig Aerosol and Cloud Remote Observations System

The study of interactions between aerosol particles, atmospheric dynamics and clouds and their resulting corresponding indirect effects on precipitation and radiative transfer demand new measurement strategies combining the strength of lidar, radar, and in-situ instrumentation. To match this challenge the Leipzig Aerosol and Cloud Remote Observations System (LACROS) has been set up at TROPOS, combining the strengths of a unique set of active and passive remote sensing and in-situ measurement systems.

Seasonal variability of heterogeneous ice formation in stratiform clouds over the Amazon Basin

Based on 11 months of polarization lidar observations in the Amazon Basin near Manaus, Brazil (2.3∘S, 60∘W), the relationship between temperature and heterogeneous ice formation efficiency in stratiform clouds was evaluated in the cloud top temperature range between −40 and 0∘C. Between −30 and 0∘C, ice-containing clouds are a factor of 1.5 to 2 more frequent during the dry season. Free-tropospheric aerosol backscatter profiles revealed a twofold to tenfold increase in aerosol load during the dry season and a Monitoring Atmospheric Composition and Climate—Interim Implementation reanalysis data set implies that the aerosol composition during the dry season is strongly influenced by biomass burning aerosol, whereas other components such as mineral dust do not vary strongly between the seasons. The injection of smoke accompanied by the likely dispersion of biological material, soil dust, or ash particles was identified as a possible source for the increased ice formation efficiency during the dry season.

Persistence of orographic mixed‐phase clouds

Mixed-phase clouds (MPCs) consist of ice crystals and supercooled water droplets at temperatures between 0 and approximately −38°C. They are thermodynamically unstable because the saturation vapor pressure over ice is lower than that over supercooled liquid water. Nevertheless, long-lived MPCs are ubiquitous in the Arctic. Here we show that persistent MPCs are also frequently found in orographic terrain, especially in the Swiss Alps, when the updraft velocities are high enough to exceed saturation with respect to liquid water allowing simultaneous growth of supercooled liquid droplets and ice crystals. Their existence is characterized by holographic measurements of cloud particles obtained at the high-altitude research station Jungfraujoch during spring 2012 and winter 2013 and simulations with the regional climate model COSMO (Consortium of Small-Scale Modeling).

Removing the Laser-Chirp Influence from Coherent Doppler Lidar Datasets by Two-Dimensional Deconvolution

AbstractA chirped laser pulse can introduce artifacts into datasets of coherent Doppler wind lidars. At close vicinity of strong signal peaks undesired artificial velocities can be measured and continuous signals can be shifted by a constant factor. It is shown how to remove these artifacts and how to retrieve accurate velocity estimations from both clouds and the planetary boundary layer. Therefore, a two-dimensional deconvolution technique is applied to the wind lidar datasets in order to correct the chirp effect in the range and frequency space. The chirp correction for a 1-h measurement of vertical velocities in the atmosphere is presented. The method is applied to the averaged Doppler spectra. Therefore, no access to the raw heterodyne signal is necessary. The complexity of the data acquisition software and the amount of data to be stored is hereby significantly reduced. Simulations suggest that the remaining velocity error resulting from the laser pulse chirp is smaller than 0.02 m s−1 and chirp-ind...

Combining cloud radar and radar wind profiler for a value added estimate of vertical air motion and particle terminal velocity within clouds

Vertical-stare observations from a 482MHz radar wind profiler and a 35GHz cloud radar are combined on the level of individual Doppler spectra to measure vertical air motions in clear air, clouds and precipitation. For this purpose, a separation algorithm is proposed to remove the influence of falling particles from the wind profiler Doppler spectra and to calculate the terminal fall velocity of hydrometeors. The remaining error of both vertical air motion and terminal fall velocity is estimated to be better than 0.1ms−1 using numerical simulations. This combination of instruments allows direct measurements of in-cloud vertical air velocity and particle terminal fall velocity by means of ground-based remote sensing. The possibility of providing a profile every 10s with a height resolution of < 100m allows further insight into the process scale of in-cloud dynamics. The results of the separation algorithm are illustrated by two case studies, the first covering a deep frontal cloud and the second featuring a shallow mixed-phase cloud.

Strategic positioning of the ERATOSTHENES Research Centre for atmospheric remote sensing research in the Eastern Mediterranean and Middle East region

The aim of this article is to present the importance of a permanent state-of-the-art atmospheric remote sensing ground based station in the region of the Eastern Mediterranean and Middle East (EMME). The ERATOSTHENES Research Centre (ERC) with the vision to become a Centre of Excellence for Earth Surveillance and Space-Based Monitoring of the Environment (EXCELSIOR H2020: Teaming project) already operates (within Phase 1) a fully established EARLINETt-Cloudnet supersite at Limassol, Cyprus, for a period of 2 years, in close collaboration with the German Leibniz Institute for Tropospheric Research (TROPOS), The scientific aspects of this prototype-like field campaign CyCARE (Cyprus Cloud Aerosol and Rain Experiment) - a common initiative between the Cyprus University of Technology (CUT), Limassol and TROPOS- are presented in this paper. Cy-CARE has been designed by TROPOS and CUT to fill a gap in the understanding of aerosol-cloud interaction in one of the key regions of climate change and how precipitation formation is influenced by varying aerosol/pollution and meteorological conditions The guiding questions are: How may rain patterns change in future and what may be the consequences of climate change in arid regions such as EMME. EXCELSIOR is a team effort between CUT (acting as the coordinator), the German Aerospace Centre (DLR), the Institute for Astronomy and Astrophysics Space Applications and Remote Sensing of the National Observatory of Athens (NOA), TROPOS and the Cyprus Department of Electronic Communications of the Ministry of Transport, Communications and Works (DEC-MTCW) who will work together to improve the network structures significantly, resulting in Cyprus being regarded as a cornerstone of a European Network of active remote sensing of the atmosphere.