Characterization of Cirrus Clouds over Cabo Verde by means of Polarization Lidar Measurements
Date of announcement: 09.01.2024
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
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
Dry marine aerosol layers in the atmosphere
Date of announcement: 01.09.2024
Marine environments are often characterized by high humidity, so sea salt
aerosol occurs as droplets. Dry air can be mixed in at the upper part of the
humid marine aerosol layer, which leads to a strong decrease in relative
humidity, causing the sea salt to crystallize and occur in a cube-like form
2 (relative humidity < 48%). This phase transition leads to altered optical
properties, in particular the depolarization ratio, and can therefore be detected
with a polarization lidar. But how often do these dry marine layers
occur? And what is the effect on the radiation budget if the marine aerosol
can no longer be assumed to be spherical? These questions will be investigated as part of a Master's thesis. The TROPOS lidar observations from the Polarstern cruises on the Atlantic Ocean (Bremerhaven to Cape Town or Punta Arenas), as well as the coastal lidar sites in Punta Arenas (Chile), Mindelo (Cape Verde) and
Haifa (Israel) are suitable for this purpose.
Contact: Dr. Moritz Haarig, haarig[at]tropos.de
Spatiotemporal evolution of Cloud Top Height (CTH) for selected ACTRIS stations
Date of announcement: 02.09.2024
Clouds contribute significantly to the Earth’s radiative budget and our limited knowledge on their interactions with other atmospheric components induce large uncertainties to radiative transfer calculations and in general circulation models. With respect to that, Cloud Top Height (CTH) is a key-parameter that provides valuable information on the vertical distribution of liquid water, cloud thermodynamic phase, cloud classification, etc.
In this thesis, the student will use the CTH product from the recently-launched EarthCARE satellite. The CTH product will be examined for overpasses co-located with ACTRIS ground-based stations (e.g., in Mindelo, Cabo Verde, in Leipzig, Germany, in Limassol, Cyprus etc.) and a study over the spatiotemporal evolution of the CTH over that specific station will be performed. EarthCARE’s CTH will also be validated with radar-derived CTH from Cloudnet.
Kontakt: Dr. Athena A. Floutsi, floutsi@tropos.de
Aufbau eines neuen Aerosoleinschubs für die Messung von Aerosolpartikeln mit einer hubschraubergetragenen Platform
Ausschreibungsdatum: 16.05.2024
Die Wechselwirkungen zwischen Aerosolpartikeln und Wolken stellen immer noch eine der größten Unsicherheiten der heutigen Wetter- und Klimavorhersage dar. Das liegt unter anderem am Mangel an direkten Messungen, d.h., dass die Prozesse direkt und vor Ort betrachtet werden.
Zur Untersuchung dieser Prozesse direkt an und in der Wolke wurde am Leibniz-Institut für Troposphärenforschung (TROPOS) das hubschraubergetragene Messsystem ACTOS (Abbildung 1) entwickelt.
Aktuell wird die Plattform komplett überarbeitet und neben einer Reihe bekannter Sensoren werden auch neue Geräte integriert. Ein Segment, der aus einem 19inch-Einschub besteht, ist dabei für Aerosolmessgeräte reserviert. Dabei werden die Größenverteilungen von etwa 6 nm bis 10 m gemessen sowie der Absorptionskoeffizient bestimmt. Die Geräte dazu sind bereits vorhanden.
Die Konzeptionierung, der Aufbau und Test dieses Einschubs könnten im Rahmen eines Praktikums, einer Masterarbeit (FH oder Uni) oder eine Hiwi-Jobs erfolgen.
Kontakt: Dr. Birgit Wehner, birgit@tropos.de, 0341/27177309
Ausschreibung
Sensitivity of Tropical Cyclones to Cloud Microphysics
Date of announcement: 05.01.2024
Tropical cyclones potentially intensity in future as the climate warms, however, significant uncertainties remain. In the proposed work, the development of tropical cyclones is investigated using convection-permitting simulations with the ICON model combined together with satellite observations. The choice of the cloud microphysics scheme plays an important role for the simulation of tropical cyclones because it controls the phase partitioning within the cloud bands and thus the pathways for precipitation formation. Some indications exist that more sophisticated cloud microphysical descriptions can also lead to better topical cyclone forecasts.
Contact: Dr. Fabian Senf, TROPOS, senf@tropos.de, phone: 0341 2717 7170