Research

Our research focus can be divided into the following topics: (1) to investigate detailed microstructure of atmospheric ice crystals and (2) the link to ice crystal optical properties and (3) to understand the role of ice clouds in our climate system.

1. Detailed Ice Crystal Microphysics

Ice crystals imaged by the PHIPS probe over the US eastern cost during the IMPACTS campaign.

"No ice crystal is the same."

Increasing amount of laboratory and field observations are starting to reveal that deviations from the ideal hexagonal crystal shape are more a rule than an exeption.

We investigate the morphological complexity of laboratory generated and real atmospheric ice crystals. Our methods include high-resolution optical microscopy for studying microscale structures and analysing high-resolution light scattering patters for mesoscale feautures of individual ice crystals.

2. Ice Crystal Optical Properties

Angular scattering functions of plate-like crystals (b) and columnar crystals (c). Similar angular scattering behaviour is measured for both cases although the underlying habit is different.

Our main focus lies on characterisation of ice crystal optical properties in the short-wave region. Our aim is to improve the representation of ice cloud short-wave asymmetry parameter in global climate models. For this, we perform field measurements with a polar nephelometer developed at KIT and use the data to develop new measurement-based parameterisations for cloud asymmetry parameter. So far we have been able to show that the short-wave asymmetry parameter is largely determined by the structural complexity of ice crystals. We frequently observe a stable angular scattering function with increased sidewards scattering that is associated with complex crystals.

3. Radiative Properties of Ice Clouds

Change in the top-of-the-atmosphere short-wave cloud radiative effect due to crystal complexity. From Järvinen et al., 2018, ACP.

There exists still a large uncertainty related to the radiative effect of cirrus clouds. Climate and weather forcast models usually assume simplified ice crystals shapes, whose optical properties do not necessary match those of natural cirrus ice crystals. This can cause significant bias in the model. Our studies have shown that cirrus clouds are actually more reflecting than previously though. This can be explained by the increased side- and backscattering from complex crystals compared to their pristine counterparts. We want to improve the short-wave optical parameterisation of cirrus clouds by introducing new optical ice crystal model that is validated using in-situ measurements.