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STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 The effect of nonmigrating tides on the upper thermospheric zonal wind observed by CHAMP Haeusler Kathrin 1 , Luehr Hermann 1 , Oberheide Jens 2 1 2 GFZ German Research Centre for Geosciences, Department of Physics and Astronomy, Clemson University Measurements performed by the accelerometer onboard the CHAMP satellite have revealed unexpected results about thermospheric dynamics. Concerning the equatorial zonal wind at 400 km altitude, a discovered four-peaked longitudinal structure was related to the eastward propagating diurnal tide with zonal wavenumber 3 (DE3). It was demonstrated that DE3, excited by latent heat release in tropical deep convective clouds, propagates directly from the troposphere into the upper thermosphere. The eastward propagating diurnal tide with zonal wavenumber 2 (DE2), the westward propagating diurnal tide with zonal wavenumber 2 (DW2), and the standing diurnal tide (D0) are further strong nonmigrating tides present in the CHAMP zonal wind. While DE3 and DE2 amplitudes are increasing with decreasing solar flux, DW2 and DO amplitudes are decreasing. For our study an extended data set of wind readings is now available starting from June 2001 to December 2007 as compared to the previous four years of measurements from 2002 – 2005. We show tidal spectra for this time period and compare it to the results of a physics-based empirical fit model based on Hough Mode Extension fits to TIMED tides. The observed solar cycle dependencies of the various tides are discussed.
STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 Solar influences on climate through stratosphere-troposphere coupling Haigh Joanna Imperial College London This presentation will consider two different aspects to how solar activity may influence the climate of the lower atmosphere. The first aspect concerns the dynamical coupling processes whereby changes in tropospheric circulation and temperature are produced in response to solar heating of the stratosphere. A simplified general circulation model has been used to investigate the chain of causality. Spinup ensemble experiments have been performed to examine the evolution of the tropospheric circulation in response to heating perturbations. The study focuses on a perturbation which is largest in the tropical lower stratosphere, as found previously to be the solar 11-year cycle signal in observational data, but the mechanisms discussed have wider relevance for the impact of stratospheric perturbations on the troposphere. The results demonstrate the importance of changing eddy momentum fluxes in driving the tropospheric response; it is apparent that feedback between the tropospheric eddy fluxes and tropospheric circulation changes is required to produce the full model response. The latitudinal distribution of the stratospheric heating determines the direction of displacement of the tropospheric jets and storm tracks: heating of lower latitudes produces poleward shifts, as observed in analyses of the response of zonal winds to solar cycle variability. The second aspect concerns solar radiative forcing of climate and its dependence on the spectrum of solar irradiance variability. A 2D (latitude-height) radiative-photochemicaltransport model is used to investigate the response of the atmosphere to changes in solar spectral irradiance between 2004 and 2007. The results obtained using spectra measured by SORCE/SIM are compared with those obtained using data from an established multiparameter model of spectral irradiance. The latter produces a broad structure of increased ozone (2004 relative to 2007) with maximum values of around 0.8% near 40km altitude while the SIM data produce a peak increase of over 2% in low latitudes around 35km along with significant decreases above 45km. This unanticipated structure is also detected in the profile of ozone change in contemporaneous measurements of ozone from the MLS instrument on EOS-Aura. The decreases are due to enhanced destruction by the HOx which results from increased O( 1 D) from O2 photolysis. Taking into account the stratospheric effects it is found that with the SIM data solar radiative forcing at the tropopause is out of phase with solar activity. If this type of spectral variability has occurred over previous solar cycles, or on longer timescales, an entire revision would be necessary of the attribution of causes to observed variations in temperature throughout the atmosphere.
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scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

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