Validation of the Aeolus Level-2B wind product over Northern Canada and the Arctic

Abstract

Abstract. In August 2018, the European Space Agency (ESA) launched the Aeolus satellite, whose Atmospheric LAser Doppler INstrument (ALADIN) is the first space-borne Doppler wind lidar to regularly measure vertical profiles of horizontal line-of-sight (HLOS) winds with global sampling. This mission is intended to assess improvement to numerical weather prediction provided by wind observations in regions poorly constrained by atmospheric mass, such as the tropics, but also, potentially, in polar regions such as the Arctic where direct wind observations are especially sparse. There remain gaps in the evaluation of the Aeolus products over the Arctic region, which is the focus of this contribution. Here, an assessment of the Aeolus Level-2B (L2B) wind product is carried out, progressing from specific locations in the Canadian North to the pan-Arctic. In particular, Aeolus data are compared to a limited sample of coincident ground-based Ka-band radar measurements at Iqaluit, Nunavut, to a larger set of coincident radiosonde measurements over the Canadian North, to Environment and Climate Change Canada (ECCC)'s short-range forecast, and to the reanalysis product, ERA5, from the European Centre for Medium-Range Weather Forecasts (ECMWF). Periods covered include the early phase of the first laser flight model (flight model A – FM-A; September to October 2018), the early phase of the second laser flight model (flight model B – FM-B; August to September 2019), and the middle phase of FM-B (December 2019 to January 2020). The adjusted r-squared between Aeolus and other local datasets is around 0.9 except for lower values for the comparison to the Ka-band radar, reflecting limited sampling opportunities with the radar data. This consistency is degraded by about 10 % for the Rayleigh winds in the summer due to solar background noise and other possible errors. Over the pan-Arctic, consistency, with correlation greater than 0.8, is found in the Mie channel from the planetary boundary layer to the lower stratosphere (near surface to 16 km a.g.l.) and in the Rayleigh channel from the troposphere to the stratosphere (2 to 25 km a.g.l.). In all three periods, Aeolus standard deviations are found to be 5 % to 40 % greater than those from ECCC-B and ERA5. We found that the L2B estimated error product for Aeolus is coherent with the differences between Aeolus and the other datasets and can be used as a guide for expected consistency. Our work shows that the high quality of the Aeolus dataset that has been demonstrated globally applies to the sparsely sampled Arctic region. It also demonstrates the lack of available independent wind measurements in the Canadian North, lending urgency to the need to augment the observing capacity in this region to ensure suitable calibration and validation of future space-borne Doppler wind lidar (DWL) missions.

Impact of the Aeolus Level‐2B horizontal line‐of‐sight winds in the Environment and Climate Change Canada global forecast system

“…This study is part of the Aeolus Cal/Val project ‘National Participation of Environment and Climate Change Canada in Cal/Val Aeolus’, which also includes the validation of Aeolus products over the Arctic regions (Chou et al ., 2022). It includes preliminary data (not fully calibrated/validated and not yet publicly released) of the Aeolus mission that is part of the ESA Earth Explorer Programme.…”

Validation of the Aeolus L2B wind product with airborne wind lidar measurements in the polar North Atlantic region and in the tropics

“…For the use of Aeolus observations in NWP models, a detailed characterization of the data quality as well as the minimization of systematic errors are crucial. Thus, several scientific and technical studies have been performed and published in the meantime, addressing the performance of ALADIN (Atmospheric LAser Doppler INstrument) on board Aeolus and the quality of the wind data products (e.g., Bedka et al, 2021;Martin et al, 2021;Baars et al, 2020;Guo et al, 2021;Zuo et al, 2022;Wu et al, 2022;Chou et al, 2022;Belova et al, 2021).…”

Scale‐dependent impact of Aeolus winds on a global forecast system

“…We first carry out an analysis of the impact of Aeolus and operational winds on forecast skill in different regions (the Northern Hemisphere (NH) and SH extratropics, the Tropics, and the Arctic), and at different vertical levels (the troposphere and stratosphere). The separate focus on the Arctic is motivated by our ongoing research on the impact of Aeolus winds on Arctic forecasting, which began with an assessment of Aeolus quality in the Arctic region (Chou et al, 2022) and previous literature examining impacts of different observing systems on the Arctic region (Naakka et al, 2019;Randriamampianina et al, 2021;Yamazaki et al, 2015).…”