AGU 2006 Highlights Le Kuai Dec. 19, 2006 Le Kuai Dec. 19, 2006

Effects of Planetary Wave-induced Ozone Heating on “Downward Control”: Implications of Climate Variability Terry Nathan and Eugene Cordero Planetary wave Planetary wave Stratospheric ozone heating Planetary wave drag (PWD) (the residual circulation) Induce affect “downward control” troposphere Climate system

Effect of solar cycle on the troposphere-stratosphere coupling in the Southern Hemisphere winter Yuhji Kuroda G Both the observation and simulation analysis indicate that the strength of the troposphere-stratosphere coupling tends to be stronger with the strength of the ultra violet (UV) radiation. G Analysis indicates the coupling of the stratospheric Southern Annular Mode (S-SAM) in late winter with the upward planetary waves, ozone, and temperature variability is more prominent in the high solar year. G Both the observation and simulation analysis indicate that the strength of the troposphere-stratosphere coupling tends to be stronger with the strength of the ultra violet (UV) radiation. G Analysis indicates the coupling of the stratospheric Southern Annular Mode (S-SAM) in late winter with the upward planetary waves, ozone, and temperature variability is more prominent in the high solar year. Stronger troposphere- Stratosphere Coupling in HS years Stronger UV Higher ozone Dynamical interaction

Arctic Ozone Loss and Climate Markus Rex, Ross J. Salawitch, Timothy Canty, Peter von der Gathen, Sabine Kleppek G Interannual variability of chemical ozone loss in the Arctic is mainly driven by the winter average of air cold enough to allow for the existance of Polar Stratospheric Clouds (Vpsc). G Maximum values of Vpsc reached during the cold Arctic winters increased by more than a factor of three. This change in the Arctic stratosphere contributed to the large ozone losses observed since the mid-1990s in the Arctic. G Dynamical feedback mechanism: 1) Rising GHG concentrations increase the meridional temperature gradient. This leads to changes in wave propagation properties and further cooling of the Arctic stratosphere. 2) Overall increasing momentum fluxes may make this situation less frequent, but once it occurs, colder conditions can develop. G Interannual variability of chemical ozone loss in the Arctic is mainly driven by the winter average of air cold enough to allow for the existance of Polar Stratospheric Clouds (Vpsc). G Maximum values of Vpsc reached during the cold Arctic winters increased by more than a factor of three. This change in the Arctic stratosphere contributed to the large ozone losses observed since the mid-1990s in the Arctic. G Dynamical feedback mechanism: 1) Rising GHG concentrations increase the meridional temperature gradient. This leads to changes in wave propagation properties and further cooling of the Arctic stratosphere. 2) Overall increasing momentum fluxes may make this situation less frequent, but once it occurs, colder conditions can develop.

QBO Effects in a Chemistry Climate Model of the Entire Atmosphere Hauke Schmidt, Marco A. Giorgetta, and Guy P. Brasseur G This study focus on possible effects of the QBO on chemistry and dynamics above the stratosphere. G The Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA) is a chemistry climate model that extends from the surface to the thermosphere. G This study focus on possible effects of the QBO on chemistry and dynamics above the stratosphere. G The Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA) is a chemistry climate model that extends from the surface to the thermosphere.

Fig. 3 shows the annual mean ozone response to solar cycle UV variations as simulated by HAMMONIA from the surface to the lower thermosphere. The increase of ozone in the stratosphere and around the mesopause is caused by increased photodissociation of O2, the decrease in the upper mesosphere is due to increased OH caused by Lyman-αdissociation of water vapor. Mesospheric and stratospheric responses are in the range suggested by observations. However, the uncertainty of existing observational analyses is large. Fig. 4 shows the annual mean temperature response to the solar cycle as simulated by HAMMONIA. However, relatively stable features of different observations are the upper stratospheric temperature increase and a secondary local response maximum in the equatorial lower stratosphere. This latter maximum is simulated to be strongest in northern hemisphere winter. Kodera and Kuroda (JGR, 2002) suggest a mechanism starting with increased heating in the summer upper stratosphere that leads to a slowing of the Brewer-Dobson circulation via wave-mean flow interactions, and finally to this lower stratospheric temperature increase. Fig. 3 shows the annual mean ozone response to solar cycle UV variations as simulated by HAMMONIA from the surface to the lower thermosphere. The increase of ozone in the stratosphere and around the mesopause is caused by increased photodissociation of O2, the decrease in the upper mesosphere is due to increased OH caused by Lyman-αdissociation of water vapor. Mesospheric and stratospheric responses are in the range suggested by observations. However, the uncertainty of existing observational analyses is large. Fig. 4 shows the annual mean temperature response to the solar cycle as simulated by HAMMONIA. However, relatively stable features of different observations are the upper stratospheric temperature increase and a secondary local response maximum in the equatorial lower stratosphere. This latter maximum is simulated to be strongest in northern hemisphere winter. Kodera and Kuroda (JGR, 2002) suggest a mechanism starting with increased heating in the summer upper stratosphere that leads to a slowing of the Brewer-Dobson circulation via wave-mean flow interactions, and finally to this lower stratospheric temperature increase.

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