Illuminating the vertical dimension of cloud systems

One of the science teams at the WCRP Global km-Scale Hackathon 2025 that emerged from the WarmWorld modules is the hk25-Curtains team, which focuses on an exciting intersection between modeling and satellite observations. It is closely linked to the cross-cutting hackathon science team hk25-EarthCARE. The latter focuses on analyzing data from the ESA-JAXA’s EarthCARE satellite — launched in May 2024 — which uses a unique combination of four active and passive instruments for observing clouds, aerosols, and radiation. The participants joining the hk25-EarthCARE team compare satellite observations with high-resolution climate model outputs along EarthCARE’s orbital swaths. Initial efforts center on tropical deep convection observed during the ORCESTRA campaign over the Tropical Atlantic, with plans to expand to other systems like tropical cyclones and stratocumulus clouds.

Leveraging output from the km-scale ICON model, the hk25-Curtains team extracts “virtual curtains” from the simulations along the EarthCARE satellite tracks. Here, the term “curtains" refers to the shape of the dataset - a vertical veil unfolding under the satellite, while “virtual" refers to projection of these 2025 orbit tracks onto the simulated year 2020, available in the simulations used during the hackathon. These are then compared with curtain observations from ESA’s EarthCARE satellite, which provides lidar and radar measurements to reveal cloud and aerosol structures with unprecedented clarity.

One of the main tools used by hk25-Curtains is the satellite product emulator PAMTRA (Passive and Active Microwave radiative TRAnsfer tool), which emulates satellite observations—such as radar reflectivity—from model output. Participants also have access to and collaboratively create tailored Jupyter Notebooks and work with simulated curtain tracks intersecting key features — tropical storms, frontal systems, and clear-air regions.

The goal is to identify where models perform well, where discrepancies arise, and how these insights can support ongoing model development. This work closely aligns with WarmWorld’s Better and Easier modules, leveraging ICON–PAMTRA integration to develop new methodologies for joint analysis of model output and observations—ultimately enriching comparative exploration and uncertainty communication.

Come back to have a look at some of the curtains plotted this week!..