Ice nucleating particles strongly influence cirrus cloud properties but remain difficult to measure at cirrus temperatures. By combining EMAC (ECHAM/MESSy Atmospheric Chemistry) model simulations with in situ observations from the CIRRUS-HL (Cirrus in High-Latitudes) campaign, we investigate aerosol-cirrus interactions across latitudes. While the model generally agrees with observations, it overestimates ice crystal number concentrations detrained from convection, which we correct applying a new radius-temperature parametrization from the observations.