Abstract
Abstract. We used 3 years of water vapour and ozone measurements to study the dynamics in the Arctic middle atmosphere. We investigated the descent of water vapour within the polar vortex, major and minor sudden stratospheric warmings and periodicities at Ny-Ålesund. The measurements were performed with the two ground-based microwave radiometers MIAWARA-C and GROMOS-C, which have been co-located at the AWIPEV research base at Ny-Ålesund, Svalbard (79∘ N, 12∘ E), since September 2015. Both instruments belong to the Network for the Detection of Atmospheric Composition Change (NDACC). The almost continuous datasets of water vapour and ozone are characterized by a high time resolution of the order of hours. A thorough intercomparison of these datasets with models and measurements from satellite, ground-based and in situ instruments was performed. In the upper stratosphere and lower mesosphere the MIAWARA-C water vapour profiles agree within 5 % with SD-WACCM simulations and ACE-FTS measurements on average, whereas AuraMLS measurements show an average offset of 10 %–15 % depending on altitude but constant in time. Stratospheric GROMOS-C ozone profiles are on average within 6 % of the SD-WACCM model, the AuraMLS and ACE-FTS satellite instruments and the OZORAM ground-based microwave radiometer which is also located at Ny-Ålesund. During these first 3 years of the measurement campaign typical phenomena of the Arctic middle atmosphere took place, and we analysed their signatures in the water vapour and ozone measurements. Two major sudden stratospheric warmings (SSWs) took place in March 2016 and February 2018 and three minor warmings were observed in early 2017. Ozone-rich air was brought to the pole and during the major warmings ozone enhancements of up to 4 ppm were observed. The reversals of the zonal wind accompanying a major SSW were captured in the GROMOS-C wind profiles which are retrieved from the ozone spectra. After the SSW in February 2018 the polar vortex re-established and the water vapour descent rate in the mesosphere was 355 m d−1. Inside of the polar vortex in autumn we found the descent rate of mesospheric water vapour from MIAWARA-C to be 435 m d−1 on average. We find that the water vapour descent rate from SD-WACCM and the vertical velocity w‾* of the residual mean meridional circulation from SD-WACCM are substantially higher than the descent rates of MIAWARA-C. w‾* and the zonal mean water vapour descent rate from SD-WACCM agree within 10 % after the SSW, whereas in autumn w‾* is up to 40 % higher. We further present an overview of the periodicities in the water vapour and ozone measurements and analysed seasonal and interannual differences.
Highlights
In the Arctic middle atmosphere the solar irradiation conditions change dramatically throughout the year
We find that the water vapour descent rate from SD-WACCM and the vertical velocity w∗ of the residual mean meridional circulation from SD-WACCM are substantially higher than the descent rates of MIAWARA-C. w∗ and the zonal mean water vapour descent rate from SDWACCM agree within 10 % after the stratospheric warmings (SSWs), whereas in autumn w∗ is up to 40 % higher
The ozone time series was intercompared with balloon-borne ozone measurements where there was a reasonable overlap in altitude and measurements from the OZORAM ground-based microwave radiometer
Summary
In the Arctic middle atmosphere the solar irradiation conditions change dramatically throughout the year. In this article we focus on the analysis of dynamical events in the polar middle atmosphere as seen from Ny-Ålesund using water vapour and ozone data from ground-based microwave radiometers. Air masses descend within the polar vortex and in the absence of solar irradiation the water vapour maximum descends with it This leads to a negative gradient across the vortex edge in the mesosphere and a positive gradient in the lower and middle stratosphere (Lossow et al, 2009; Maturilli et al, 2006). In the Arctic MIAWARA-C is the only ground-based instrument continuously measuring middle-atmospheric water vapour profiles except for the Vespa radiometer (Mevi et al, 2018) located at Thule, Greenland. 6. we report on typical phenomena of the Arctic middle atmosphere as observed in the water vapour, ozone and wind time series from Ny-Ålesund: the descent of air in the polar vortex during its formation
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