Assessing the quality of novel Aeolus winds for NWP applications at NCMRWF

This study illustrates the validation of Aeolus Horizontal Line-Of-Sight (HLOS) winds, both Rayleigh-clear and Mie-cloudy, using in situ satellite wind (Atmospheric Motion Vectors, AMVs) observations, and NWP equivalents for three months, June-August 2020, covering the Indian summer monsoon season. Estimated errors in the Mie-cloudy (Rayleigh-clear) winds are clustered around 0.5-4 m center dot s(-1) (3-8 m center dot s(-1)), and the differences between Aeolus Mie-cloudy (Rayleigh-clear) and sonde winds are within +/- 5 m center dot s(-1) (+/- 8 m center dot s(-1)), but the systematic error is close to zero over the Northern Hemisphere where there are more sonde reports. Validation shows the quality of Mie-cloudy winds is better than Rayleigh-clear winds. Though the comparison against the observations like sonde (radiosonde and pilot balloons together) and aircraft indicate the quality of the Aeolus winds, their sparse spatial and temporal coverage limits the validation. Validation of Aeolus winds against AMVs provides similar results but with a better and nearly complete picture of the quality and quantity, with more information over the data-sparse and remote regions. Statistical scores suggest the characteristics of the Aeolus winds at different vertical levels and geographical regions remain the same irrespective of the validation reference datasets. The Indian summer monsoon features like Low-Level Jet (LLJ) and Tropical Easterly Jet (TEJ) are well represented in the Aeolus winds. This study also investigated the impact of the Aeolus HLOS winds over the Indian region through the collocated radiosonde and ALADIN wind profile assimilation experiments. Observing System Experiments (OSEs) suggest assimilation of Aeolus winds produced marginal improvement in the simulation of north Indian Ocean cyclones.