Investigation of Arctic Mixed-Phase Clouds during ACLOUD By Airborne Active and Passive Microwave Remote Sensing (MiRAC) and Forward Simulations

In May/June 2017 the aircraft field campaign ACLOUD (Arctic CLoud Observations Using airborne measurements during polar Day) has successfully been completed. Two identical but complimentary equipped research aircraft, Polar 5 & 6 by the Alfred Wegener Institute for Polar and Marine Research, Germany, were operated from Longyearbyen at Spitzbergen to investigate Arctic boundary layer mixed-phase clouds by in situ and remote sensing measurements. Flight pattern were coordinated with satellite overpasses and ground-based measurements at the research station in Ny-Ålesund and the research vessel Polarstern which performed comprehensive measurements with an ice floe camp at 80(?) deg north.

A key component of the remote sensing instrumentation on Polar 5 is the novel Microwave Radar/radiometer for Arctic Clouds (MiRAC). It consists of a 94 GHz frequency modulated continuous wave (FMCW) radar and passive radiometer with frequencies in the sub-millimeter range between 183 and 340 GHz similar to future satellite missions aiming at ice clouds and moisture profiling. Together with the other remote sensing measurements, i.e. lidar, spectral solar, and in situ measurements, the radar reflectivity and other radar moments can be used to derive properties of arctic mixed-phase clouds. A key tool in this process are radiative transfer forward simulations with the passive and active mircowave transfer model (PAMTRA).

Within this presentation we will introduce the concept of MiRAC, including the process of correcting for aircraft motion, and first results of the measurements taken during ACLOUD including validation with ground-based radar. Furthermore, we will introduce PAMTRA and present its capabilities as a tool for cloud and precipitation studies involving measurements with active and passive microwave instruments. This involves forward simulating the measurements based on atmospheric models, sensitivity studies investigating various scattering assumptions, and comparison between models, satellites and airborne measurements. Finally, first results of retrieval approaches for arctic-mixed phase clouds are presented.