Quantification of the Radiative Effect of Arctic Cirrus by Airborne Radiation Measurements - A Case Study

Observations of cloud related processes in the Arctic are needed to evaluate the representation of clouds in weather and climate models and to improve our understanding of processes of Arctic amplification and Arcitc-midlatitude linkages. One remaining uncertainty of the Arctic climate system are cirrus clouds and their influence on the radiative budget. Arctic cirrus is known to warm the climate system on annual average, especially when present over the sea ice covered central Arctic. 
The HALO-(AC)³ airborne campaign in spring 2022 investigated changes within air masses on their way in and out of the central Arctic with the High Altitude LOng Range research aircraft (HALO), which was equipped with a suite of remote sensing instrumentation. Two flights were used to explicitly investigate the cloud radiative effect of single layer isolated cirrus between 81 and 90 degrees North.
Flight legs above and below the cirrus with measurements of spectral solar irradiance from the Spectral Modular Airborne Radiation measuremenT system (SMART) make a direct estimation of the cloud radiative effect possible. The cirrus was sufficiently thick to reduce the transmission of solar radiation by around 25%. However, significant inhomogeneities in the cirrus were observed.
We present a case study of the radiative effect of Arctic cirrus and compare airborne irradiance measurements to simulations from an offline run of the ecRad radiation scheme which is operationally used in the ECMWF's Integrated Forecasting System.