Intercomparison of Stratospheric Wind Observations from the Aeolus Satellite and the Loon Balloon Network

Abstract:

The representation of stratospheric winds in numerical weather prediction systems have significant uncertainties. Due to the very limited number of global stratospheric wind observations, it is difficult to validate these numerical model predictions. ESA’s Doppler Wind Lidar mission Aeolus, launched on 22 August 2018, provides accurate measurements of the horizontal line-of-sight (HLOS) wind speed from the surface up to 30 km. The Aeolus wind product is being operationally assimilated by ECMWF, Météo-France and the German Weather Service (DWD). Independent measurements are very valuable for the assessment of the data quality of the Aeolus wind product. Observations from the Loon balloon network provide a unique opportunity to validate Aeolus observations in the lower stratosphere, a region where only very few in situ wind observations are available. Loon is continuously launching super-pressure balloons in the stratosphere for providing internet connection to remote areas in the world. Additional to the communication instrumentation, the balloons carry sensors to measure GPS location, altitude and atmospheric variables.

This study aims at the validation of Aeolus observations in the tropical lower stratosphere with balloon observations provided by Loon. While Aeolus measures instantaneous vertical profiles of the HLOS wind speed, Loon yields temporally highly resolved and very accurate wind vectors in a specific altitude range along the balloon trajectories. Hence, Loon observations can be used to complement Aeolus wind profiles in order to characterize the horizontal sub-grid scale wind variability and to investigate typical wind length scales in the lower stratosphere.

In this paper, collocated Aeolus and Loon observations are analyzed for the months of August and September, 2019. Wind vectors from the ECMWF short-range forecasts are also considered for the comparison. The quality control decisions and collocation criteria will be discussed. Special emphasis is given to the Central Andes region in Latin America, where most of the Loon observations are concentrated for the considered period. This region is characterized by strong vertical wind shear and orographic effects, which lead to significant challenges in the comparison. These effects will be discussed on the basis of case studies.