On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/16

• Main Authors: Matthias, Vivien, Ern, Manfred
• Format: Article in Journal/Newspaper
• Language: English
• Published: EGU 2017
• Subjects: info:eu-repo/classification/ddc/550; polar night
• Online Access: https://juser.fz-juelich.de/record/842039; https://juser.fz-juelich.de/search?p=id:%22FZJ-2018-00323%22

The mid winter 2015/16 was characterized by an unusually strong polar night jet (PNJ) and by extraordinarily large stationary planetary wave (SPW) amplitudes in the subtropical mesosphere. The aim of this study is to find the origin of these mesospheric SPWs in mid winter 2015/16. The time period studied here is split into two time periods. The first period runs from late December 2015 until early January 2016 and the second period from early January until mid January 2016. While the SPW 1 dominates in the subtropical mesosphere in Period I, it is the SPW 2 that dominates in Period II. There are three possibilities how SPWs can occur in the mesosphere: 1) they propagate upward from the stratosphere, 2) they are in situ generated by longitudinally variable gravity wave (GW) drag, or 3) they are in situ generated by barotropic and/or baroclinic instabilities. Using global satellite observations from the Microwave Limb Sounder (MLS) and from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) the origin of the mesospheric SPWs is investigated for both time periods. We found that due to the strong PNJ the SPWs were not able to propagate upward into the mesosphere northward of 50°N but were deflected upward and equatorward into the subtropical mesosphere. We show that the SPWs observed in the subtropical mesosphere are the same SPWs as in the mid-latitudinal stratosphere. At the same time we found evidence that the mesospheric SPWs in polar latitudes were in situ generated by longitudinally variable GW drag and that there is a mixture of in situ generation by longitudinally variable GW drag and by instabilities in mid latitudes. Our results based on observations show that every three mechanisms, upward propagating SPW and in situ generated SPWs by longitudinally variable GW drag and instabilities can act at the same time which confirms earlier model studies. Additionally, a possible contribution or impact of the unusually strong SPWs in the subtropical mesosphere to the disruption of the QBO in ...