A11E-01 INVITED 08:00h
The Response of the Middle Atmosphere to Solar Variability
The influence of solar variability on the atmosphere and, more generally, on the climate system remains insufficiently understood. We will investigate the response of the chemical composition, thermal structure and circulation of the atmosphere to the 11-year solar cycle and the 27-day solar variability using a General Circulation Model (GCM) with interactive chemistry that extends from the surface to 250 km altitude. This model, called HAMMONIA, is an extension of the ECHAM-5 GCM with the chemical formulation taken from the MOZART-3 Chemical Transport Model.
A11E-02 INVITED 08:20h
The Transfer of the Solar Signal From the Stratosphere to the Troposphere: Northern Winter
The atmospheric response to the solar cycle has been previously investigated with the Freie Universitaet Berlin Climate Middle Atmosphere Model (FUB-CMAM) using prescribed spectral solar UV and ozone changes as well as prescribed equatorial, QBO-like winds. The solar signal is transferred from the upper to the lower stratosphere through a modulation of the polar night jet and the Brewer-Dobson circulation. The interaction between QBO and solar signal are comparable to estimates from observations. These model experiments are further investigated here to show the transfer of the solar signal from the lower stratosphere to the troposphere and down to the surface during northern hemisphere winter. During October and November, the model response is concentrated in the stratosphere. However, during December and January there is a significant response in tropospheric circulation which decays in February. Analysis focuses on the transition from the early winter stratospheric-dominated signal to the mid-winter tropospheric-dominated signal. The results show that the stratosphere has an important effect on tropospheric changes through a stratospheric-tropospheric circulation regime that develops in December and January and disappears in February. The Brewer-Dobson circulation provides the link between low and high latitude changes as well as between upper and lower stratospheric changes. Dynamical heating in the tropical lower stratosphere induces circulation changes (changes in tropopause height, static stability, convection and precipitation) in the tropical troposphere and down to the surface. These effects are identified as indirect effects from the stratosphere mainly because the sea surface temperatures are identical in the solar maximum and minimum experiment. The tropospheric changes confirm results from other simplified model studies as well as results from observations.
A11E-03 INVITED 08:40h
Response of Global Ocean Temperature to the Sun's Quasi-Decadal UV Radiative Forcing of the Stratosphere
Earth's climate system experiences quasi-decadal signals in the tropical global-average temperature in the upper ocean ($<$TO$>$), the troposphere ($<$T5km$>$), and lower stratosphere ($<$TS$>$), with changes of 0.1K, 0.2K, and 1.0K respectively. These temperature signals fluctuated in fixed phase with the quasi-decadal signal in the Sun's irradiance. White et al. (2003a) diagnosed the thermal budget of the quasi-decadal $<$TO$>$ signal in the tropics, finding the anomalous $<$TO$>$ warming tendency driven by downward sensible-plus-latent heat flux ($<$QS + QL$>$) anomalies. Here we find the latter driven by anomalously warm air-sea temperature differences, with $<$T2m$>$ anomalies larger than $<$SST$>$ anomalies and leading by $\sim$1 year. To determine how this happens, we diagnose the thermal budget of the quasi-decadal signal in the tropical atmosphere (20$^{\circ}$S to 20$^{\circ}$N) using the NCEP/DOE reanalysis data set. We find the quasi-decadal signal in the Sun's UV radiative forcing of the lower stratosphere temperature anomalies balanced by anomalous longwave radiation to space and to the troposphere below, and by anomalous thermal convection. The latter produced an anomalous warming tendency in the lower troposphere during anomalous cool lower stratosphere temperature. It has two components; i.e. the anomalous convection of the mean thermal gradient and the mean convection of the anomalous thermal gradient. We find the anomalous warming tendency in the lower troposphere driven principally by the latter component, yielding positive anomalous air-sea temperature differences and downward $<$QS + QL$>$ anomalies that are responsible for the anomalous $<$TO$>$ warming tendency.
A11E-04 09:00h
Composition Changes in the Polar Stratosphere and Mesosphere Induced by the 2003 Solar Proton Events
The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a high-resolution limb sounder on board the European Space Agency ENVISAT satellite, successfully launched on March 1, 2002. MIPAS measures the atmospheric emission in the 4.15-14.6 $\mu$m range with a spectral resolution of 0.05 cm$^{-1}$ (apodised). The instrument scans the limb operationally from 6 km up to 68 km with a near-global latitude coverage both at day and nighttime. From MIPAS spectra many atmospheric constituents are retrieved, including O$_3$, H$_2$O, CH$_4$, CO, and nitrogen oxides (NO and NO$_2$). We show in this paper the significant depletions measured in O$_3$ at high latitudes above 35~km after the solar protons events of 28th October and 4th November 2003 in North and South polar caps. Depletions are also observed in water vapour. The temporal evolution of decreases in O$_3$ of the changes in NO$_x$ (NO+NO$_2$) and NO$_y$ (NO$_x$, HNO$_3$, N$_2$O$_5$, ClONO$_2$) are shown. Increases of lower mesospheric NO$_2$ of near 100 ppbv were measured by MIPAS. The temporal evolution of NO$_2$, O$_3$, and HNO$_3$ along the winter 2003-2004 are also presented. The simultaneous measurements of such a large number of atmospheric species, with global coverage, obtained by MIPAS constitute an unprecedented dataset to study the atmospheric effects caused by large solar proton events.
A11E-05 09:15h
The Response to Solar Cycle Forcing in he Fully Coupled Chemistry-Climate GISS ModelE
We have incorporated fully interactive chemistry operating seamlessly from the surface through the stratopause into the new state-of-the-art GISS climate model (modelE). The flexible architecture of modelE allows us to easily run the identical atmospheric model with or without chemistry, and coupled to either a fully dynamic ocean, a slab ocean or using prescribed sea surface temperatures (SSTs). We are using this model to examine the atmospheric response to solar cycle variations with both a slab ocean and fixed SSTs, and with and without chemistry. We will present a comparison of the four sets of experiments with observations, including the poleward and downward propagation of zonal wind anomalies, which is substantially improved over our previous simulations. One of the most interesting features of the response is that in addition to displaying the typical ozone increase between solar minimum and maximum centered around 3 hPa, the model is also able to capture the secondary layer of ozone increases in the lowermost tropical stratosphere. We will discuss the relative contribution of chemistry and transport to this feature, and it's impact on dynamics via changing the meridional temperature gradient in the tropopause region.
A11E-06 09:30h
The Solar Cycle Variation of Stratospheric Ozone: An Observational Update and Model Comparisons
The observed solar cycle variation of ozone is a key constraint on climate models that include solar UV / ozone / dynamical coupling as a sun-climate forcing mechanism. Standard multiple regression statistical models have previously been applied to estimate the solar cycle component of stratospheric ozone variability using long-term satellite ozone profile data sets (SBUV(/2) over the 1979 to 1994 time period and SAGE II over the 1984 to 1998 time period). These analyses indicate that (a) the largest percentage ozone increase from solar minimum to maximum is in the upper stratosphere (1-3 hPa); (b) a minimum percentage increase occurs in the tropical middle stratosphere (5-10 hPa); and (c) a larger percentage increase occurs in the tropical and subtropical lower stratosphere, which is mostly responsible for the solar cycle variation of total ozone. This observationally derived altitude dependence in the middle and lower stratosphere differs from the predictions of radiative-photochemical models for the solar UV induced ozone response over a solar cycle; the latter predict a maximum ozone increase in the middle stratosphere (about 5 hPa) and a small or negligible increase in the lower stratosphere. An important unresolved issue is whether interference from decadal changes in the QBO wind field or major volcanic aerosol injections (occurring following solar maxima in 1982 and 1991) may have been partly or entirely responsible for the unexpected altitude dependence derived from observations. Here, we report analysis of the Version 8 SBUV(/2) ozone profile data set extending from 1979 to 2003 (NASA Ozone Processing Team, http://code916.gsfc.nasa.gov/Data\_services/). This time period includes most of solar cycle 23 during which there was no major volcanic eruption. Results continue to show that the ozone solar cycle variation in the low-latitude middle stratosphere (5 to 10 hPa) is very small or negligible. Comparisons are made with model simulations using the NRL CHEM2D model to investigate whether interference from the QBO (which is interactive in the model) can explain this unexpected altitude dependence. Comparisons are made between statistical results for solar cycle 23 and the previous two cycles to evaluate whether interference from volcanic aerosols can explain the altitude dependence.
A11E-07 09:45h
Seasonal linkage of the Arctic Oscillations and its solar cycle modulation
The winter Arctic Oscillation (AO)/Northern Hemisphere annular mode (NAM) and the subsequent summer AO/NAM, which exhibits a different pattern from the winter AO/NAM, have a significant correlation. The correlation coefficient between the DJF-mean winter-NAM and the JJ-mean summer-NAM index for 44 years (1958-2002) is 0.31, which is significant at a 95% confidence level. This winter-to-summer linkage is modulated by the 11-year solar cycle. In solar maximum years (20 years), the correlation is 0.52, which is significant at a 98% level. On the other hand, in solar minimum years (24 years), it is 0.06 and it is not significant. The winter-to-summer linkage may be brought by the persistent snow anomalies in Eurasia, sea ice anomalies in the Barents Sea, and sea surface temperature anomalies in the North Atlantic. These ocean/land surface anomalies caused by anomalies in winter atmospheric circulation tend to persist through spring only in solar maximum years.