The cloudy side of the Arctic Weather Satellite

There is a continued need to extend the global observations of our atmosphere to improve weather and climate forecasts. At the same time, there is a demand for decreasing costs and faster introduction of new technologies. The concept of "new space" has been introduced as a response. The Arctic Weather Satellite (AWS) is an operational mission developed according to this principle.

AWS  is part of ESA´s Earth Watch programme, while its origin and present construction are found mainly inside Sweden.There is a single instrument on the AWS platform, a cross-track microwave scanner with 19 channels.

Most AWS channels have a counterpart on existing microwave sounders, but AWS will also have four channels around 325 GHz, matching a wavelength of about 0.9 mm. According to current launch plans, AWS will be the first operational missing entering the sub-mm domain.

The team behind this proposal has a leading role in the preparations for the Ice Cloud Imager (ICI), a later mission focusing on sub-mm observations.

This proposal aims to ensure that the AWS project fully benefits from the developments around ICI.Further, the proposal is designed to complement the ongoing studies around AWS. These studies are done from a perspective of weather forecasting, emphasizing "heritage channels".

In contrast, this project focuses on the 325 GHz channels and developing an AWS climate product.The main activity is to develop and produce an ice cloud product parallel to the one planned for ICI. The retrieval target is ice water path, complemented with mean mass height and particle diameter. We will also attempt to retrieve profiles of ice water content (IWC).

The retrievals are based on data and tools developed for the operational ICI processing combined with a machine learning approach of Bayesian character. These AWS retrievals will complement two similar IWP products in development (based on geostationary IR and GMI).

Among these, the AWS product is expected to have the best accuracy, while the other two are better for studying, for example,  diurnal variations. The retrieval algorithm will be shared with SMHI, which will apply it to generate AWS-based nowcasting data. After the launch of the satellite, we will also perform an in-depth analysis of AWS 325 GHz radiances.

This effort is motivated by these observations being the first of their kind.

While existing bias correction procedures used at the weather centre can assess the quality of the other AWS channels, the new 325 GHz channels require special attention as limitations in the forward operator must be considered. This activity will be performed in collaboration with ECMWF.

The project would also allow Patrick Eriksson to provide extended support to the centre in their preparations towards AWS, this inside his role as present ECMWF fellow.In summary, this proposal covers efforts towards using the upcoming AWS mission entirely.

In this way, the project should contribute to reaching phase two of the mission, which is to launch a constellation of satellites (EPS-Sterna).