Recent Northern Winter Climate Trends due to Ozone Changes and Increased Greenhouse Gas Forcing ?

• Main Authors: Graf, H., Perlwitz, J., Kirchner, I., Schulte, I.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1995
• Subjects: North Atlantic; Siberia
• Online Access: http://hdl.handle.net/21.11116/0000-0002-7689-F; http://hdl.handle.net/21.11116/0000-0002-768B-D; http://hdl.handle.net/21.11116/0000-0005-A2C1-9

Recently considerable trends in ozone concentration with positive values mainly in the upper troposphere, and decreasing concentrations in the lower stratosphere of the Northern Hemisphere middle and high latitudes were shown (WMO. 1992). The data basis consists approximately of 15 to 20 years of observations at various locations. These changes are discussed on the background of observed variations of tempera- ture and circulation during the last decades. The observed increased lower stratospheric high latitude westerlies are part of a natural coupled mode of lower stratospheric and tro- pospheric circulation. This coupled mode has its strongest tropospheric effects over the North Atlantic with increased westerlies. and positive air temperature anomalies over Scandinavia and Siberia. The intensity of the part of this natural coupled mode which is associated with enhanced polar stratospheric westerlies has increased during the last decades. A primary contribution to this intensification due to the low latitude greenhouse- gas effects is suggested. The observed ozone trends when introduced into a General Cir- culation Model do not produce substantial changes in circulation supporting the initial greenhouse gas effects. Concluding. a comprehensive climate model including atmospheric chemistry in combination with a good representation of the whole stratosphere is needed to study future climate scenarios. Most possibly greenhouse-gas effects and ozone concentration are not independent.