Dynamical response of the Southern Hemisphere to the 11-Year solar cycle.

Kern, Jessica (2019) Dynamical response of the Southern Hemisphere to the 11-Year solar cycle. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, VIII, 101 pp.

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Abstract

Understanding the dynamical influence of the 11-year solar cycle on Earth’s climate andits tropospheric effects is important in order to improve decadal climate prediction. Moststudies which investigate the downward transfer of the solar cycle signal focus on theNorthern Hemisphere (NH). In contrast, the dynamical influence of the 11-year solarcycle on the Southern Hemisphere (SH) is analyzed in this thesis with an exceptionallylong (999 years) high-top model simulation of CESM1(WACCM)under pre-industrialconditions but time-varying solar cycle forcing. The constructed solar forcing only includessolar variabilities on timescales up to the 11-year solar cycle and hence neglects long-termsecular changes of the solar irradiance such as the Gleissberg cycle.The strong relative increase in UV radiation during solar maximum (SolMax) induces awarming at the tropical upper stratosphere which leads to a strengthening of the merid-ional temperature gradient in the upper stratosphere from July to September in the SH.As a result of the thermal wind balance, a westerly wind anomaly appears in the mid-latitudinal upper stratosphere during SolMax which propagates downward and polewardfrom July to October. The interactions of planetary waves with the zonal mean flow leadto a dynamical solar response indicated by the onset of the Eliassen–Palm flux (E–Pflux) divergence difference in July which coincides with the beginning of the downwardpropagation.The zonal mean westerly wind anomaly is expected to strengthen the polar vortex whichwould result in a positive annular mode pattern as seen in theNH. However, the horizontalstructure of geopotential height anomalies exhibits a polar vortex shift towards the Pacificfrom August to October in the SH during SolMax instead of a strengthening. Althoughthese geopotential height differences are found by other studies, these studies only examinethe downward transfer in zonal mean analysis. However, in this study the regional sectoranalyses reveal that the strongest westerly wind anomaly inthe Indian ocean occurs inJuly whereas in the Atlantic sector the strongest anomaly is found in August. Both regionsshow the typical poleward propagation of the westerly wind anomaly which is missing inthe Pacific region. The Pacific ocean sector is the only sectorwhich reveals statisticallysignificant tropospheric impacts on the zonal wind from August to October which areconnected to the stratosphere by a downward transfer. This highlights the importance toinvestigate regional differences and suggests that the zonal mean approach is insufficientto examine the top-down mechanism in the SH.

Document Type: Thesis (Master thesis)
Thesis Advisor: Matthes, Katja and Kruschke, Tim
Additional Information: Jessica Danker nach Heirat
Subjects: Course of study: MSc Climate Physics
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
OceanRep > Leibniz-Institut für Meereswissenschaften
Date Deposited: 07 Oct 2020 09:35
Last Modified: 09 Oct 2020 12:10
URI: https://oceanrep.geomar.de/id/eprint/50639

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