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Forschungsprojekte


Arctic Amplification Clouds and Radiation Cloud Phase Remote Sensing
Polar O
C
E
A
N
E
T
VERDI, RACEPAC
ACLOUD, AFLUX
PASCAL
PAMARCMiP
ANT-Land
HALO-(AC)³, Cirrus-HL
Mid-Latitudes Azores
NAWDEX, ML-Cirrus
Tropics ACRIDICON-CHUVA, ATTO
NARVAL I & II, EUREC4A


a) Role of clouds and surface properties for Arctic Amplification Arctic Amplification
b) Interactions of radiative energy fluxes and cloud evolution Arctic Amplification
c) Identification and effects of phase transitions in clouds Arctic Amplification
d) Improvement of passive remote sensing – spectral and directional Arctic Amplification




a) Role of clouds and surface properties for Arctic Amplification


Within the Transregional Collaborative Research Centre TR 172 on "Arctic Amplification: Climate relevant atmospheric and surface processes, and feedback mechanisms" (AC)³, our group is coordinating five sub-projects investigating the role of cloud and surface properties for the Arctic Amplification. Clouds are known to significantly influence the surface energy budget depending on their macro- and microphysical properties. Therefore, our group characterized the surface radiative budget and cloud properties by solar and terrestrial radiation measurements, ground-based, airborne and on a tethered ballon. The energy gain due to clouds will be estimated from these measurements in combination with radiative transfer simulations that are used to quantify the impact of single cloud properties. Similarly, the absorption of solar radiation by snow and sea ice is investigated. Airborne and ground-based measurements of spectral and broadband albedo estimate the spatial and temporal variability of snow and sea ice properties. In particular, the impact of sea ice heterogeneity in cloudy and clear sky scenarios and the impact of black carbon deposition in the snow layer on the surface energy budget will be investigated.

ACLOUD
PASCAL
AFLUX
PAMARCMiP
HALO-(AC)³
Cirrus-HL
VERDI
RACEPAC


b) Interactions of radiative energy fluxes and cloud evolution


Clouds strongly influence the radiative budget. In particular, the solar and terrestrial radiative energy flux below and above the cloud change in dependence of the cloud properties, the cloud live cycle. E.g., clouds with increasing optical thickness reduce the downward solar radiation at the surface, while the terrestrial radiation at the surface only changes for thin clouds and is mostly defined by the cloud layer temperature. These and other parameters such as (cloud phase, particle size, shape, and solar position) and their impact on the cloud radiative forcing will be investigated within a series of project aiming for different types of clouds. Therefore, broadband and spectral radiation will be measured with different platforms in addition to complementary measurements of cloud macro- and microphysical properties. With help of radiative transfer simulations these measurements will be put into a general context. Based on these simulations, sensitivity studies changing individual cloud properties will be performed. On the other hand, changes of the radiative profile especially in a small altitude range at cloud top may also influence the cloud evolution. Divergences in the radiative fluxes, in terms of heating or cooling rates, induce vertical motion either large scale leading to a general change in cloud properties or small scale leading to cloud top entrainment. In our group we will investigate these processes by spatially resolved measurements of the radiation profiles and mapping of the cloud top temperatures which can be used as a measure of the cloud top cooling. The broadband and spectral radiation measurements will also be compared to products of numerical weather forecast models with the aim to identify potential biases due to an incorrect representation of clouds and their macro- and microphysical properties in the models.

ACLOUD
PASCAL
AFLUX
PAMARCMiP
HALO-(AC)³
Cirrus-HL
Azores
NARVAL I & II
ML-Cirrus
NAWDEX
EUREC4A


c) Identification and effects of phase transitions in clouds


Cloud radiative properties strongly depend on the cloud phase. Therefore our group developed techniques to identify the cloud phase by solar radiation measurements. Differences of the ice and liquid water spectral absorption are used to define different ice indices and estimate the amount of ice and liquid water in the cloud. Different observation geometries, either airborne or ground-based are employed depending on the type of cloud to be investigated. Spectral imaging is used to extend the view on the cloud into two-dimensional space. Airborne spectral imaging aims to map the cloud thermodynamic phase down to scales of 10 m. This will help to estimate the importance of small scale cloud inhomogeneities of stratiform clouds but also to follow the cloud phase change in large scale weather systems. Using ground based measurements with a scanning imaging device, sides of deep convective clouds will be analyses. Identifying the altitude of phase transition from liquid to ice particles in such clouds in combination with temperature profiling, allows to analyze the freezing level. In combination with a characterization of the aerosol state, statistical analysis of the cloud freezing level will help to estimate the impact of aerosol particles on the cloud phase and consequently on the cloud live cycle.

ACLOUD
AFLUX
VERDI
RACEPAC
HALO-(AC)³
Cirrus-HL
ACRIDICON-CHUVA
ATTO
NARVAL I & II
ML-Cirrus
NAWDEX
EUREC4A


d) Improvement of passive remote sensing – spectral and directional


Our group extensively applies passive solar remote sensing techniques for the retrieval of cloud and snow retrieval. We apply airborne measurements which compared to satellite measurements have I) a higher spatial, II) a higher spectral resolution, and III) can be obtained close to the cloud or surface. The higher number of spectral channels, typically 1024 pixel in the range of 300-1000 nm and about 256 pixel in the range between 1000-2500 nm, allows detailed analysis of the spectral imprint of clouds, the atmosphere, and different surfaces. Separating these spectral signatures provides the opportunity to develop algorithms which are able to retrieve a multitude of cloud, atmosphere and surface properties. Another information included in remote sensing measurements is the directional dependence of the reflected radiation. By used of imaging measurements such as a 180° fish-eye camera the reflected radiation field can be analyzed in high spatial resolution. Quantities such as the bi-directional reflection distribution function BRDF can be derived from the measurements. Our group employs such measurements mainly for snow surfaces and cloud layers. Snow BRDF is analyzed in dependence of surface roughness and solar zenith angles. These measurements are used to validate models of snow reflectivity and improve the retrieval of snow grain size.

ACLOUD
AFLUX
VERDI
RACEPAC
PAMARCMiP
ANT-Land
HALO-(AC)³
Cirrus-HL
ACRIDICON-CHUVA
ATTO
NARVAL I & II
ML-Cirrus
NAWDEX
EUREC4A


Letzte Aktualisierung am 31. 10. 2016 von André Ehrlich