[1] Understanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar-terrestrial interactions, and the mechanisms determining the response of the Earth's climate system. We provide a summary of our current understanding in each of these three areas. Observations and mechanisms for the Sun's variability are described, including solar irradiance variations on both decadal and centennial time scales and their relation to galactic cosmic rays. Corresponding observations of variations of the Earth's climate on associated time scales are described, including variations in ozone, temperatures, winds, clouds, precipitation, and regional modes of variability such as the monsoons and the North Atlantic Oscillation. A discussion of the available solar and climate proxies is provided. Mechanisms proposed to explain these climate observations are described, including the effects of variations in solar irradiance and of charged particles. Finally, the contributions of solar variations to recent observations of global climate change are discussed.

[1] Previous multiple regression analyses of the solar cycle variation of stratospheric ozone are improved by (1) analyzing three independent satellite ozone data sets with lengths extending up to 25 years and (2) comparing column ozone measurements with ozone profile data during the 1992-2003 period when no major volcanic eruptions occurred. Results show that the vertical structure of the tropical ozone solar cycle response has been consistently characterized by statistically significant positive responses in the upper and lower stratosphere and by statistically insignificant responses in the middle stratosphere ($28-38 km altitude). This vertical structure differs from that predicted by most models. The similar vertical structure in the tropics obtained for separate time intervals (with minimum response invariably near 10 hPa) is difficult to explain by random interference from the QBO and volcanic eruptions in the statistical analysis. The observed increase in tropical total column ozone approaching the cycle 23 maximum during the late 1990s occurred primarily in the lower stratosphere below the 30 hPa level. A mainly dynamical origin for the solar cycle total ozone variation at low latitudes is therefore likely. The amplitude of the solar cycle ozone variation in the tropical upper stratosphere derived here is somewhat reduced in comparison to earlier results. Additional data are needed to determine whether this upper stratospheric response is or is not larger than model estimates.Citation: Soukharev, B. E., and L. L. Hood (2006), Solar cycle variation of stratospheric ozone: Multiple regression analysis of longterm satellite data sets and comparisons with models,

The magnetometer and electron reflectometer experiment on the Lunar Prospector spacecraft has obtained maps of lunar crustal magnetic fields and observed the interaction between the solar wind and regions of strong crustal magnetic fields at high selenographic latitude (30°S to 80°S) and low (∼100 kilometers) altitude. Electron reflection maps of the regions antipodal to the Imbrium and Serenitatis impact basins, extending to 80°S latitude, show that crustal magnetic fields fill most of the antipodal zones of those basins. This finding provides further evidence for the hypothesis that basin-forming impacts result in magnetization of the lunar crust at their antipodes. The crustal magnetic fields of the Imbrium antipode region are strong enough to deflect the solar wind and form a miniature (100 to several hundred kilometers across) magnetosphere, magnetosheath, and bow shock system.

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An improved gravity model from Doppler tracking of the Lunar Prospector (LP) spacecraft reveals three new large mass concentrations (mascons) on the nearside of the moon beneath the impact basins Mare Humboltianum, Mendel-Ryberg, and Schiller-Zucchius, where the latter basin has no visible mare fill. Although there is no direct measurement of the lunar farside gravity, LP partially resolves four mascons in the large farside basins of Hertzsprung, Coulomb-Sarton, Freundlich-Sharonov, and Mare Moscoviense. The center of each of these basins contains a gravity maximum relative to the surrounding basin. The improved normalized polar moment of inertia (0.3932 ± 0.0002) is consistent with an iron core with a radius of 220 to 450 kilometers.

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The nature of stratospheric ozone and temperature responses to changes in solar ultraviolet flux occurring at low latitudes on the time scale of the solar rotation period is investigated using 22 months of Nimbus 7 solar backscattered ultraviolet (SBUV) ozone and stratosphere and mesophere sounder (SAMS) temperature data. After filtering to remove periods ≳35 days, average cross‐correlation functions for low‐latitude residual ozone versus SBUV measurements of the solar irradiance at 205 nm are largest (R = 0.3–0.6) at phase lags ranging from −3.6 ± 0.6 days at 0.7 mbar to 3.2 ± 0.5 days at 10 mbar. Maximum correlation coefficients for residual temperature variations (R = 0.2–0.35) are obtained versus the 205‐nm flux at lags ranging from 3.6 ± 0.9 days at 0.3 mbar to 13.0 ± 0.7 days at 10 mbar. In both cases, correlations generally increase when the 205‐nm flux is used as the solar ultraviolet variable rather than proxy indicators such as the 10.7‐cm flux. The consistency between response estimates calculated for separate latitude bands and the tendency for correlation coefficients to be larger during time periods of relatively strong 27‐day solar ultraviolet flux variations supports a causal relationship. Linear regression analyses are therefore performed to determine mean ozone and temperature response amplitudes for given changes in the 205‐nm flux at low latitudes as a function of pressure level in the upper stratosphere. Peak‐to‐peak variations in the 205‐nm flux were as large as 6% on the solar rotation time scale during the study period, yielding maximum ozone responses of 3% (∼0.37 μg g−1) near 3 mbar and maximum temperature responses of 0.36% (∼1 K) near the stratopause. The observed ozone and temperature responses and their phase lags are interpreted, using a model that accounts to first order for the coupled behavior of solar‐induced ozone and temperature perturbations in the upper stratosphere and lower mesosphere. The model appears capable of accounting for gross features of the observed ozone and temperature responses, including the negative ozone phase lags relative to the 205‐nm flux found above 3 mbar. Using the measured response amplitudes and phase lags, the model is applied to estimate the change in O2 photolysis rate in the upper stratosphere produced by a given change in the 205‐nm flux on the considered time scale. The mean temperature dependence of perturbation‐order ozone concentration changes is also constrained by the data.

The 11 year solar-cycle component of climate variability is assessed in historical simulations of models taken from the Coupled Model Intercomparison Project, phase 5 (CMIP-5).Multiple linear regression is applied to estimate the zonal temperature, wind and annular mode responses to a typical solar cycle, with a focus on both the stratosphere and the stratospheric influence on the surface over the period ∼1850-2005. The analysis is performed on all CMIP-5 models but focuses on the 13 CMIP-5 models that resolve the stratosphere (high-top models) and compares the simulated solar cycle signature with reanalysis data. The 11 year solar cycle component of climate variability is found to be weaker in terms of magnitude and latitudinal gradient around the stratopause in the models than in the reanalysis. The peak in temperature in the lower equatorial stratosphere (∼70 hPa) reported in some studies is found in the models to depend on the length of the analysis period, with the last 30 years yielding the strongest response.A modification of the Polar Jet Oscillation (PJO) in response to the 11 year solar cycle is not robust across all models, but is more apparent in models with high spectral resolution in the short-wave region. The PJO evolution is slower in these models, leading to a stronger response during February, whereas observations indicate it to be weaker. In early winter, the magnitude of the modelled response is more consistent with observations when only data from 1979-2005 are considered. The observed North Pacific high-pressure surface response during the solar maximum is only simulated in some models, for which there are no distinguishing model characteristics. The lagged North Atlantic surface response is reproduced in both high-and low-top models, but is more prevalent in the former. In both cases, the magnitude of the response is generally lower than in observations.