How can we understand the solar cycle signal on the Earth's surface?.

Kodera, Kunihiko, Thieblemont, Remi, Yukimoto, Seiji and Matthes, Katja (2016) How can we understand the solar cycle signal on the Earth's surface?. Open Access Atmospheric Chemistry and Physics, 16 . pp. 12925-12944. DOI 10.5194/acp-16-12925-2016.

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To understand solar cycle signals on the Earth's surface and identify the physical mechanisms responsible, surface temperature variations from observations as well as climate model data are analyzed to characterize their spatial structure. The solar signal in the annual mean surface temperature is characterized by (i) mid-latitude warming and (ii) no warming in the tropics. The mid-latitude warming during solar maxima in both hemispheres is associated with a downward penetration of zonal mean zonal wind anomalies from the upper stratosphere during late winter. During Northern Hemisphere winter this is manifested in a modulation of the polar-night jet whereas in the Southern Hemisphere the subtropical jet plays the major role. Warming signals are particularly apparent over the Eurasian continent and ocean frontal zones, including a previously reported lagged response over the North Atlantic. In the tropics, local warming occurs over the Indian and central Pacific oceans during high solar activity. However, this warming is counter balanced by cooling over the cold tongue sectors in the southeastern Pacific and the South Atlantic, and results in a very weak zonally averaged tropical mean signal. The cooling in the ocean basins is associated with stronger cross-equatorial winds resulting from a northward shift of the ascending branch of the Hadley circulation during solar maxima. To understand the complex processes involved in the solar signal transfer, results of an idealized middle atmosphere–ocean coupled model experiment on the impact of stratospheric zonal wind changes are compared with solar signals in observations. The model results suggest that both tropical and extra-tropical solar surface signals can result from circulation changes in the upper stratosphere through (i) a downward migration of wave–zonal mean flow interactions and (ii) changes in the stratospheric mean meridional circulation. These experiments support earlier evidence of an indirect solar influence from the stratosphere.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
Kiel University
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/acp-16-12925-2016
ISSN: 1680-7316
Date Deposited: 01 Mar 2016 10:57
Last Modified: 01 Feb 2019 15:16

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