Characterization of Cirrus Clouds over Cabo Verde by means of Polarization Lidar Measurements
Date of announcement: 25.08.2025
Cirrus clouds consist of ice crystals, which can be formed homogeneously (from solution droplets) or heterogeneously (on an aerosol particle). The special shape of the ice crystals causes them to depolarize light. This property is exploited with a polarization lidar to detect cirrus clouds.
Since June 2021, TROPOS has been operating such a lidar device in Mindelo on Cape Verde (see picture), which measures the depolarization ratio at 3 wavelengths. The aim of the master's thesis is to exploit the polarization measurements to obtain more information about the shape, vertical structure and formation mechanism of tropical cirrus clouds.
Contact: Moritz Haarig, haarig[at]tropos.de
Ice Multiplication - What processes in clouds can potentially contribute to the secondary increase in ice crystal number?
Date of Announcement: 21.05.2024
In mixed-phase clouds (consisting of ice crystals and supercooled liquid droplets), more ice crystals may be present than would be expected from the primary freezing of liquid droplets. In recent years, several processes have been proposed to explain the phenomenon. These processes together are called ice multiplication or secondary ice production. Possible mechanisms are for example collisions between two ice crystals or the breaking of freezing drops, where smaller ice splinters are produced and thus more ice particles are present than before.
The aim of the offered thesis is to assess the significance of ice multiplication on cloud properties. First, a brief overview of the ice multiplication processes proposed in the literature needs to be provided. Based on this, these processes will then be applied to existing simulated cloud properties (cloud droplet and ice crystal size distributions) of a cloud microphysics model. Own simulations with an idealized version of this model can (Bachelor thesis) or will (Master thesis) be be added. The work provides an introduction to microphysical processes in clouds and their description for e.g. weather models. Knowledge of Python, R, etc. is necessary for data analysis.
Contact:
Dr. Roland Schrödner, Tel.: +49 (0)341 2717 7388, eMail: roland.schroedner[at]tropos.de
How Clouds and Aerosols Modulate the Radiation Balance over Cape Verde
Date of announcement: 07 October 2025
What influences the radiation balance in Mindelo (e.g. Island effects, desert dust, cloud regime)? This question will be addressed by analyzing broadband and spectral aerosol and cloud radiative effects with a focus on radiation closure
studies at Mindelo (Cape Verde) ACTRIS station, using new geostationary satellite (MTG) and reference surface observations.
The study includes:
• Cloud and aerosol cases selected from the novel Flexible Combined Imager (FCI) onboard MTG.
• Use of radiation transfer forward model for spectral and broadband simulations with input from surface observations (e.g., Cloudnet including cloud radar, lidar and microwave radiometer)
• Radiative closure with model simulation, and satellite and surface observations for validation.
• First comparisons with new EarthCARE radiation products.
Contact: Prof. Dr. Andreas Macke, macke[at]tropos.de or Jonas Witthuhn (witthuhn@tropos.de), Sebastian Bley (bley@tropos.de), Anja Hünerbein (anjah@tropos.de)
Investigating the optical properties of marine aerosol using the
EarthCARE satellite
Date of announcement: 07 October 2025
With the recently
launched EarthCARE satellite mission, having a high-spectralresolution lidar on board, the optical properties of marine aerosol can be studies for the first time based on backscatter, extinction,
and depolarization measurements even in very remote locations, like for example the Southern oceans.
In this work, the regional and seasonal patterns of the optical properties of marine aerosol will be investigated using data from the EarthCARE satellite. The analysis can cover several predefined regions, e.g., representing all seas and oceans, which can be defined further during the course of the ongoing work.
Contact: Dr. Athena A. Floutsi, floutsi[at]tropos.de or Dr. Holger Baars, baars@tropos.de
EarthCARE observations of wildfire smoke
Date of announcement: 25 August 2025
The new satellite EarthCARE launched in May 2024 carries an advanced atmospheric lidar (ATLID) which is perfectly suited to study the elevated smoke plumes on a global scale. It provides layer heights and optical properties of the smoke plumes. We have observed that large parts of the Arctic are filled with smoke since June 2025.
The topic of the master thesis is use EarthCARE to study the occurrence, lofting and removal processes of the smoke plumes. Furthermore, the interaction of the smoke layers with cirrus clouds is of great interest.
Contact: Moritz Haarig, haarig[at]tropos.de
Characterization of the atmosphere above Antarctica by means of ground-based remote sensing
Date of announcement: 25.02.25
The Antarctic continent and its surrounding Southern Ocean are key components of the global climate system. In the framework of the field experiment, continuous Observations of Aerosol-Cloud-Interaction in Antarctica (COALA), novel observations of aerosol and clouds by means of ground-based remote sensing have been performed by TROPOS in Antarctica at the German Neumayer Station III (70.67°S, 8.27°W) from January to December 2023. The deployment of the OCEANET-Atmosphere remote-sensing observatory covers the full ACTRIS aerosol and cloud profiling capabilities additionally to meteorological, radiation, and air chemistry in-situ observations at the Antarctic station.
The master thesis shall focus on microphysical properties of (shallow) mixed-phase clouds retrieved from lidar and radar synergy. Depending on the student’s interest, the topic can be developed towards, e.g., characterizing the aerosol properties relevant for cloud formation or intercomparison with reanalysis datasets among other possibilities including sensor synergy.
Contact: Dr. Martin Radenz, TROPOS (radenz@tropos.de), Dr. Holger Baars, TROPOS (baars@tropos.de)
Assessing humidity growth effects of different aerosol types using
ground-based Raman lidar observations
Date of announcement: 01.09.2024
Hygroscopic growth and shrinkage processes change the size, refractive
index, and partly also the shape of aerosol particles and thus also their
optical, radiative and nucleating properties (e.g., Haarig et al., 2017).
PollyXT Raman lidars (Engelmann et al., 2016) have the capability to
measure water vapor mixing ratio (e.g., Dai et al., 2018). Simultaneous
profiling of water vapor mixing ratio and particle optical properties
allow to study aerosol hygroscopicity (e.g., Althausen et al., 2020;
Navas-Guzmán et al., 2019). For calibration and calculation of relative
humidity, the use of radiosonde, model, and microwave radiometer data
can be intercompared. Data from PollyNET (Baars et al., 2016), a
network of PollyXT lidars, from contrasting stations with different
aerosol and humidity conditions like Germany, Cabo Verde, Cyprus, and
Tajikistan shall be used.
Contact: Julian Hofer, hofer[at]tropos.de
Profile intercomparison of CCN datasets retrieved from ground-based
lidars, aerosol model reanalysis and spaceborne lidar
Date of announcement: 01.09.2024
Vertical profiles of microphysical and cloud-relevant aerosol properties
such as cloud condensation nuclei (CCN) concentration can be estimated
using polarization lidar techniques (e.g., Mamouri and Ansmann, 2016).
Global CCN datasets retrieved from the spaceborne lidar CALIPSOCALIOP
(Choudhury and Tesche, 2022; 2023) and the aerosol model
reanalysis CAMS (Block et al., 2024), which became available recently
and are already used for comparison studies (e.g., Choudhury et al.,
2024), can be intercompared with retrievals from PollyNET (Baars et al.,
2016), a network of ground-based PollyXT polarization Raman lidars
(Engelmann et al., 2016), at multiple, contrasting stations like Germany,
Cabo Verde, Cyprus, and Tajikistan. Identifying similarities and
differences between the ground-based and spaceborne-lidar-derived
CCN datasets may improve the underlying retrieval methods and
ultimately the understanding and quantification of aerosol-cloudinteraction.
Contact: Julian Hofer, hofer[at]tropos.de