Observing water vapor from satellites: a multi-parameter retrieval in the Arctic compared to MOSAiC in-situ measurements

Water vapor is a significant component of the hydrological cycle as well the Earth‘s atmosphere, being a crucial greenhouse gas. It contributes to the rapid warming of the Arctic, called Arctic amplification, by the water vapor feedback. However, obtaining a long-term dataset to monitor trends and variability of water vapor in the Arctic - which is important to understand its role in Arctic amplification - is hampered by the sparseness of in-situ measurements and the challenges for satellite remote sensing retrievals. Monthly mean values of integrated water vapor (IWV) strongly differ (up to 30%) between different satellite products in the central Arctic (Crewell et al. (2021)). In the microwave domain, space-borne radiometers allow water vapor retrieval over the open ocean but over sea ice the retrievals have higher uncertainties and are more challenging due to high and variable sea-ice emissivity.

Here we present a comparison of a satellite-based integrated water vapor retrieval to in-situ measurements, especially radiosondes, taken during the MOSAiC campaign (mosaic-expedition.org). The one-year MOSAiC ice drift expedition provides a full year of IWV reference measurements in the central Arctic. The satellite retrieval is based on microwave radiometer measurements from the AMSR-E/2 sensors at 6 different frequencies. Utilizing an optimal estimation method allows to simultaneously retrieve integrated water vapor and six other geophysical parameters, including sea ice concentration and ice type (Scarlat et al., 2017, 2020). Overall the satellite retrieval can reproduce the temporal water vapor variability. We show how warm and moist air intrusions are captured by the method. However, significant biases are observed, which we try to tackle by taking variable snow surface emissions into account.

We aim for an improved Arctic-wide and longterm water vapor dataset that will help to quantify how the water vapor feedback contributes to Arctic amplification.

Crewell et al. (2021). A systematic assessment of water vapor products in the Arctic: from instantaneous measurements to monthly means, Atmos. Meas. Tech., 14, 4829–4856, https://doi.org/10.5194/amt-14-4829-2021. 

Scarlat et al. (2017). Experiences With an Optimal Estimation Algorithm for Surface and Atmospheric Parameter Retrieval From Passive Microwave Data in the Arctic. IEEE J-STARS, 10, 3934–3947.  https://doi.org/10.1109/jstars.2017.2739858

Scarlat et al. (2020). Sea Ice and Atmospheric Parameter Retrieval From Satellite Microwave Radiometers: Synergy of AMSR2 and SMOS Compared With the CIMR Candidate Mission. J. Geophys. Res. Oceans, 125(3). https://doi.org/10.1029/2019JC015749