First insight into thermodynamic profiles, IWV and LWP from ground-based microwave radiometers during MOSAiC

The Arctic is currently experiencing a more rapid warming compared to the rest of the
world. This phenomenon, known as Arctic Amplification, is the result of several processes.
Within the Collaborative Research Centre on Arctic Amplification: Climate Relevant Atmospheric
and Surface Processes and Feedback Mechanisms (AC)3, our research focuses
on the influence of water vapour, the strongest greenhouse gas. The collection of data
about water vapour is essential to understand its impact on Arctic Amplification. Over
the past decades, a positive trend in integrated water vapour in the Arctic has been
identified using radiosondes and reanalyses for certain regions and seasons. However, inconsistent
magnitudes of the moistening trend in the reanalyses cause the need of a more
thorough investigation. While radiosondes offer precise measurements of thermodynamic
(temperature and humidity) profiles, they fail to capture the variability of water vapour
because of the low sampling rate (two to four sondes per day) and spatial coverage. To
obtain a more complete picture of water vapour variability, remote sensing instruments
(satellite- and ground-based) are used. Microwave radiometers (MWRs) onboard polar
orbiting satellites allow the coverage of the entire Arctic but suffer from uncertainties
related to surface emission. Observations at the surface gathered during the Multidisciplinary
drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign can
serve as reference measurements in the central Arctic for the assessment of water vapour
products from reanalyses, models and satellite retrievals.

In this study, we give a first insight into the variability of integrated water vapour (IWV),
liquid water path (LWP) and thermodynamic profiles retrieved from two ground-based
MWRs onboard the research vessel Polarstern throughout the MOSAiC campaign. The
first radiometer is a standard low frequency HATPRO system and the other one is the
high-frequency MiRAC-P, which is particularly suited for low water vapour contents. The
retrieved quantities are compared with radiosonde measurements. A first analysis reveals
that the IWV is very well captured by the MWR measurements. Over the observation
period (October 2019 - October 2020), a large variety of meteorological conditions occurred.
Besides the considerable seasonal cycle, which is especially interesting because of
the contrast between polar night and polar day, several synoptic events contribute to the
variety of conditions, which will be highlighted as well.

We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research
Foundation) — Project 268020496 — TRR 172, within the Transregional Collaborative Research Center
"Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms
(AC)3". Data used in this manuscript was produced as part of the international Multidisciplinary drifting
Observatory for the Study of the Arctic Climate (MOSAiC) with the tag MOSAiC20192020 and the
Polarstern expedition AWI_PS122_00.