GC41B-01 INVITED
Patterns of Climate Response to Solar and Anthropogenic Influences in the Recent Past
Whereas general circulation climate models predict negligible response to decadal solar forcing, an array of empirical evidence attests to detectable changes with complex geographical and height patterns approximately in phase with the solar activity cycle. The extensive databases of climate forcings and climate variability measured during the past three decades of the space era permit separation of the solar-driven signal from other influences, by volcanic aerosols, anthropogenic gases, and natural climate variability associated with ENSO, the NAO and the QBO. A multiple regression analysis applied to the University of East Anglia surface temperature dataset and the atmospheric temperature measurements made by the Microwave Sounding Unit shows that the patterns of climate response to solar and other influences persist coherently throughout the troposphere but change abruptly near 20 km in the lower stratosphere. As well, both the solar and volcanic influences produce a distinct meridional asymmetry centered over the low-to-mid latitude Pacific Ocean. We compare the geographical and height patterns determined empirically from the surface and atmospheric temperature observations with simulations made by the GISS Middle Atmosphere General Circulation Model using different spatial resolution, atmospheric layers, ozone parameterizations and ocean couplings. In particular, the 4x5, 53 layer model, has sufficient vertical layers to resolve the stratosphere and includes linearized ozone chemistry.
GC41B-02
Long-term Atmospheric Changes Caused by the Very Large Solar Proton Event in July 2000
Solar cycle 23 was accompanied by eight very large solar proton events (SPEs) between 2000 and 2005, along with numerous smaller events. The very large SPE in July 2000, which was associated with the well-known Bastille Day Solar Storm, caused very substantial changes in the polar mesosphere and stratosphere. Significant downward transport of the SPE-produced NOx from the polar lower mesosphere and upper stratosphere during the Southern Hemisphere winter period resulted in huge enhancements (>100%) in middle stratospheric NOx (NO+NO2) during September 2000 in the polar vortex, which were measured by UARS HALOE (C. E. Randall et al., Geophys. Res. Lett., 28, 2385-2388, 2001). We have used the Whole Atmosphere Community Climate Model (WACCM) to study the longer-term impact of the July 2000 SPE, the third largest SPE period in the past 40 years. This very large SPE provided a wonderful opportunity to study the downward transport of energetic particle precipitation effects in the middle atmosphere. Not surprisingly, the WACCM-simulated polar Northern Hemisphere influences from the July (mid-summer) 2000 SPE were significant for a few months, but the constituent changes were not transported below about 20 hPa. However in the polar Southern Hemisphere (SH) region, the persistent downward transport in the vortex during the months of July-August- September resulted in significant modeled influences for about a year past the SPE. The SH odd nitrogen family, NOy (N, NO, NO2, NO3, N2O5, HNO3, HO2NO2, ClONO2, BrONO2), was greatly enhanced by this SPE and these increases were transported to the lower stratosphere. The SPE-enhanced polar NOy resulted in long-lasting ozone decreases (from catalytic NOy destruction of ozone) and ozone increases (from NOy interference in the chlorine and bromine catalytic ozone destruction cycles). These ozone changes resulted in simulated SH polar stratospheric temperature decreases (1-2K) and increases (1-3K).
GC41B-03
Modeling the Wavelength and Time Dependence of Solar Forcing of Earth~{!/~}s Atmosphere
Solar forcing is the primary external forcing of Earth's climate. Climate response to solar radiative forcing is poorly understood, and previous to SORCE there has been limited information about the spectral character of solar variations. Variations in total solar irradiance (TSI) have contributions from spectral bands ranging from the ultraviolet, through the visible, to the near infrared. These three solar spectral regions, UV, VIS, and NIR, force the stratosphere, troposphere, and ocean mixed layers, respectively. UV is responsible for stratospheric heating, and formation of the ozone layer; VIS heats the Ocean Mixed layer and drives upper oceanic circulation; and NIR directly heats the troposphere by water vapor absorption, as well as through cloud and other feedbacks. In this study, we use a simple 1D radiative convective model (RCM) (Arking, 2005) to study the response of surface and atmospheric temperatures to the spectral forcing of solar radiation as observed by the Spectral Irradiance Monitor (SIM) on SORCE. Preliminary RCM results show significant differences in surface temperature when driven by the SIM spectral solar irradiance (SSI) as compared to responses to SSI variations assumed in previous climate studies (e.g., Kurucz and Bell, 1995). Reference Arking, A., (2005), Effects of Bias in Solar Radiative Transfer Codes on Global Climate Model Simulations, Geophys. Res. Lett., VOL 32, L20717, doi:10.1029/2005GL023644. Kurucz, R. L. and Bell, B., (1995), Cambridge, Smithsonian Astrophys. Obs., CD-rom No. 23.
GC41B-04
On the Connection between Solar Spectral Irradiance and Planetary Wave Drag
An ever-increasing body of evidence shows that changes in solar spectral irradiance (SSI) over the 11-year solar cycle (SC) can produce changes in stratospheric ozone. Changes in stratospheric ozone can in turn produce changes in planetary wave drag (PWD) via wave-induced ozone heating, which was recently expounded upon in a paper by Nathan and Cordero (2007, JGR-Atmospheres). Because SSI-induced changes in PWD may have potentially far-reaching consequences for the global circulation, ranging from changes in the zonal-mean flow to changes in the Brewer-Dobson circulation, it is important to understand the connection between SSI and PWD. In this study we employ a mechanistic model that couples radiation, ozone and dynamics to derive an analytical expression that shows the explicit connection between SSI and PWD. The sensitivity of the stratospheric circulation, particularly stratospheric sudden warmings, to changes in SSI associated with the SC is explored.
GC41B-05
Modeling quasi-decadal variability in the QBO and its impact on stratospheric ozone and climate
Simulations of the 11-year solar cycle's effects on stratospheric photochemistry and dynamics are performed with the zonally averaged CHEM2D model. These simulations indicate that the duration of the westerly QBO phase at solar maximum is 3 months shorter than at solar minimum, as a result of solar-induced heating anomalies interacting with the tropical component of the mean meridional circulation. The modeled solar cycle ozone response, determined via multiple linear regression, is compared with observational estimates from the combined Solar Backscattered Ultraviolet (SBUV/2) data set for the period 1979--2003. We find that a model simulation including the effects of this solar-QBO interaction plus an imposed 11-year variation in planetary wave forcing produces a lower stratospheric ozone response that is in good agreement with the SBUV-derived ozone response. Recent observational studies have questioned the connection between solar UV forcing and the quasi- decadal variation in the QBO, particularly after the mid-1990's. We examine other possible mechanisms that may introduce quasi-decadal variability in the QBO, including anomalous wintertime extratropical planetary wave activity and changes in convective latent heating associated with tropical sea-surface temperature fluctuations.
GC41B-06
Effect of QBO and ENSO on the solar cycle modulation of winter North Atlantic Oscillation
Effect of the Quasi-Biennial Oscillation (QBO) and the El Niņo Southern Oscillation (ENSO) on the 11-year solar cycle modulation of the winter-mean North Atlantic Oscillation (NAO) is examined through analysis of observational data from 1958 to 2000. It is found that the solar cycle modulation of the NAO is more strongly enhanced in the westerly phase of the 50-hPa QBO wind and the cold phase of ENSO, although separation of these effects is statistically difficult. On these phases, signal of the winter-mean NAO extends more to the upper stratosphere and summer-AO reappears more strongly in high solar years, whereas the signal is weaker throughout in low solar years.
GC41B-07
Impact of Solar Variability on the Earth's Annular Modes
We investigate the effect of solar variability on the Annular Modes in the Earth's atmosphere. The Northern Annular Mode (NAM), and Southern Annular Mode (SAM) have two basic states corresponding to higher pressure at high latitudes with a band of lower pressure at lower latitudes and the other way round (Thompson and Wallace, 1998). Two states arise due to the dynamical interaction of planetary waves and zonal mean wind (Limpasuvan and Hartmann, 2001; Ruzmaikin et al., 2006). Solar variability influences the modes via the change of the UV flux in upper atmosphere. The influence depends on the phase of the Quasi Biennial Oscillation and time in the winter season (Ruzmaikin and Feynman, 2002). We investigate the effects on the Annular Modes caused by the Maunder Minimum, the 11-year cycle, and the 27-day solar variabilities using the NCEP Reanalysis, the solar UV flux from SORCE mission and ozone and temperature data from the MLS instrument on Aura spacecraft. We discuss a possible mechanism by which solar variability can affect the Annular Modes and the climate patterns in general involving the Rossby-Palmer conjecture (Palmer, 1999). In contrast to the standard linear evaluation of climate sensitivity to an external forcing we outline a non-linear approach to the forcing problem (Ruzmaikin, 2007). In particular, we evaluate the distributions of residence times spent in each state of the pattern and show how these distributions depend on solar variability. References: Thompson, D. W. J. and J. M. Wallace, Geophys. Res. Lett., 25, 1297, 1998; Limpasuvan, V., and D. Hartmann, J. Climate, 13, 4414, 2001; Ruzmaikin, A., J, Feynman, J. Geophys. Res., 107, D14, 10.1029/2001JD001239, 2002; Ruzmaikin, A., J. K. Lawrence and A. C. Cadavid, J. Atmos. Space Phys., 68, 1311, 2006; Palmer, T. N., Bull. Amer. Meteor. Soc., 79, 1412 1998: Ruzmaikin, A., Advances in Space Res., doi:10.1016/j.asr.2007.01.076 2007.
GC41B-08
Solar-Cycle Warming at the Earth's Surface
Using the NCEP/NCAR Reanalysis and the ERA-40 datasets, we analyze the global response of the Earth's surface temperature to oscillations in the total solar irradiance associated with the 11-year solar cycle. Three analysis methods are considered, with increasing levels of sophistication: global-mean averaging, composite- mean-difference projection and linear discriminant analysis (LDA). Within each dataset, the analysis results are consistent with each other (i.e., each within the other's error bars), with the method of LDA yielding the smallest error bar, and the unfiltered global-mean data yielding the largest error bar in the temperature amplitude. All three methods are able to demonstrate that there exists an 11-year oscillatory signal in the temperature data which is statistically significant and attributable (i.e., related) to the solar cycle. Using the LDA method, we deduce the spatial surface pattern over the globe which best distinguishes the solar maximum years from the solar minimum years. The resulting warming pattern shows a polar amplification of warming and a preferential warming over continents than over oceans. We propose that if positive feedback processes such as ice-albedo, water-vapor/lapse rate and cloud feedbacks (similar to some of those studied for the greenhouse warming problem) are incorporated, then the magnitude of the surface warming is consistent with direct solar radiative forcing.