L. L. Hood

SOLAR INFLUENCES ON CLIMATE

The development of this review article has evolved from work carried out by an international team of the International Space Science Institute (ISSI), Bern, Switzerland, and from work carried out under the auspices of Scientific Committee on Solar Terrestrial Physics (SCOSTEP) Climate and Weather of the Sun‐Earth System (CAWSES‐1). The support of ISSI in providing workshop and meeting facilities is acknowledged, especially support from Y. Calisesi and V. Manno. SCOSTEP is acknowledged for kindly providing financial assistance to allow the paper to be published under an open access policy. L.J.G. was supported by the UK Natural Environment Research Council (NERC) through their National Centre for Atmospheric Research (NCAS) Climate program. K.M. was supported by a Marie Curie International Outgoing Fellowship within the 6th European Community Framework Programme. J.L. acknowledges support by the EU/FP7 program Assessing Climate Impacts on the Quantity and Quality of Water (ACQWA, 212250) and from the DFG Project Precipitation in the Past Millennium in Europe (PRIME) within the Priority Program INTERDYNAMIK. L.H. acknowledges support from the U.S. NASA Living With a Star program. G.M. acknowledges support from the Office of Science (BER), U.S. Department of Energy, Cooperative Agreement DE‐FC02‐97ER62402, and the National Science Foundation. We also wish to thank Karin Labitzke and Markus Kunze for supplying an updated Figure 13, Andrew Heaps for technical support, and Paul Dickinson for editorial support. Part of the research was carried out under the SPP CAWSES funded by GFG. J.B. was financially supported by NCCR Climate–Swiss Climate Research.

Initial mapping and interpretation of lunar crustal magnetic anomalies using Lunar Prospector magnetometer data

Maps of relatively strong crustal magnetic field anomalies detected at low altitudes with the magnetometer instrument on Lunar Prospector are presented. On the lunar nearside, relatively strong anomalies are mapped over the Reiner Gamma Formation on western Oceanus Procellarum and over the Rima Sirsalis rille on the southwestern border of Oceanus Procellarum. The main Rima Sirsalis anomaly does not correlate well with the rille itself but is centered over an Imbrian-aged smooth plains unit interpreted as primary or secondary basin ejecta. The stronger Reiner Gamma anomalies correlate with the locations of both the main Reiner Gamma albedo marking and its northeastward extension. Both the Rima Sirsalis and the Reiner Gamma anomalies are extended in directions approximately radial to the center of the Imbrium basin. This alignment suggests that Imbrium basin ejecta materials (lying in many cases beneath the visible mare surface) are the sources of the nearside anomalies. If so, then the albedo markings associated with the stronger Refiner Gamma anomalies may be consistent with a model involving magnetic shielding of freshly exposed mare materials from the solar wind ion bombardment. Two regions of extensive magnetic anomalies are mapped in regions centered on the Ingenii basin on the south central farside and near the crater Gerasimovic on the southeastern farside. These regions are approximately antipodal to the Imbrium and Crisium basins, respectively. The Imbrium antipode anomaly group is the most areally extensive on the Moon, while the largest anomaly in the Crisium antipode group is the strongest detected by the Lunar Prospector magnetometer. A consideration of the expected antipodal effects of basin-forming impacts as well as a combination of sample data and orbital measurements on the nearside leads to the conclusion that the most probable sources of magnetic anomalies in these two regions are ejecta materials from the respective impacts. In both regions the strongest individual anomalies correlate with swirl-like albedo markings of the Reiner Gamma class visible on available orbital photography.

Solar cycle variation of stratospheric ozone: Multiple regression analysis of long-term satellite data sets and comparisons with models

This material is based on work supported by the National Science Foundation Climate Dynamics program under grant ATM-0424840. Additional support from NASA under a grant from the Living With a Star research program is also gratefully acknowledged.

The solar cycle variation of total ozone: Dynamical forcing in the lower stratosphere

Multiple regression methods are applied to estimate the solar cycle variation of (1) zonal mean ozone as a function of altitude and latitude using a combination of Nimbus 7 solar backscattered ultraviolet (SBUV) and National Oceanic and Atmospheric Administration (NOAA) 11 SBUV/2 ozone profile data for a 15-year period; (2) total ozone as a function of latitude, longitude, and season using Nimbus 7 total ozone mapping spectrometer (TOMS) data for a 13.3-year period; (3) lower stratospheric temperature as a function of latitude, longitude, and season using microwave sounding unit (MSU) Channel 4 data for a 16-year period; and (4) lower stratospheric geopotential height as a function of latitude, longitude, and season in the northern hemisphere using Berlin height data for a 30-year period. According to the SBUV-SBUV/2 data, most (about 85%) of the 1.5–2% solar cycle variation of global mean total column ozone occurs in the lower stratosphere (altitudes < 28 km). Evidence is obtained for a related solar cycle variation of lower stratospheric temperature (50–150 mbar) and geopotential height (30, 50, and 100 mbar) with geographic dependences similar to that of the solar cycle variation of total ozone. Specifically, total ozone, lower stratospheric temperature, and lower stratospheric geopotential height have annual mean solar regression coefficients in the northern hemisphere that reach a maximum near 30°N latitude within a longitude sector extending from approximately 160°E to 250°E. Maximum variations from solar minimum to maximum in this sector are approximately 11 Dobson units, 0.8 K near 100 mbar, and 60 m at 50 mbar, respectively. Seasonal solar regression coefficients tend to be statistically significant over larger areas in summer but have larger amplitudes within limited regions in winter. These geographic similarities between total ozone, lower stratospheric temperature, and geopotential height solar coefficients suggest that changes in lower stratospheric dynamics between solar minimum and maximum may play an important role in driving the observed total ozone solar cycle variation. To test this hypothesis, a simplified perturbation ozone transport model is applied to calculate the expected total ozone variation owing to dynamical forcing for the calculated geopotential height solar coefficients, climatological ozone mixing ratios, and zonal winds. For the summer season during which the solar regression coefficients are significant over the largest area, both the amplitude and latitude dependence of the observed solar cycle ozone variation are approximately consistent with the model estimates.

Mapping of crustal magnetic anomalies on the lunar near side by the Lunar Prospector electron reflectometer

Lunar Prospector (LP) electron reflectometer measurements show that surface fields are generally weak in the large mare basalt filled impact basins on the near side but are stronger over highland terranes, especially those lying antipodal to young large impact basins. Between the Imbrium and Nectaris basins, many anomalies correlate with the Cayley and Descartes Formations. Statistical analyses show that the most strongly magnetic nearside terranes are Cayley-type light plains, terra materials, and pre-Imbrian craters. Light plains and terrae include basin impact ejecta as a major component, suggesting that magnetization effects from basin-forming impacts were involved in their formation. The magnetization of pre-Imbrian craters, however, may be evidence of early thermal remanence. Relatively strong, small-scale magnetic anomalies are present over the Reiner Gamma feature on western Oceanus Procellarum and over the Rima Sirsalis rille on the southwestern border of Procellarum. Both Apollo subsatellite and LP data show that the latter anomaly is nearly aligned with the rille, though LP magnetometer and reflectometer data show that the anomaly peak is actually centered over a light plains unit. This anomaly and the Reiner Gamma anomaly are approximately radially aligned with the center of Imbrium, suggesting an association with ejecta from this basin.

Quasi-Decadal Variability of the Stratosphere: Influence of Long-Term Solar Ultraviolet Variations

Abstract A multiple regression statistical model is applied to investigate the existence of upper-stratospheric ozone, temperature, and zonal wind responses to long-term (solar cycle) changes in solar ultraviolet radiation using 11.5 years of reprocessed Nimbus-7 Solar Backscattered Ultraviolet (SBUV) data and 12.4 years of National Meteorological Center (NMC) data. A positive solar cycle variation of independently measured ozone and temperature occurs with maximum amplitude near the low-latitude stratopause. The seasonal solar regression coefficients near 1 mb for both ozone and temperature occur at low latitudes supporting a role for photochemical and radiative forcing in their origin. Zonal wind perturbations that correlate with long-term solar ultraviolet variations are a strong function of season and pressure level. Above ∼2 mbar, the largest solar-correlated zonal wind enhancements occur at middle winter latitudes near the time of winter solstice in both hemispheres. The Northern Hemisphere December...

Apparent solar cycle variations of upper stratospheric ozone and temperature: Latitude and seasonal dependences

Although only 15 years of continuous global satellite data are available, existing measurements are consistent with a significant, in-phase solar cycle variation of upper stratospheric ozone and temperature. Here we investigate the latitude and seasonal dependences of this variation using 15 years (1979–1993) of combined solar backscattered ultraviolet (SBUV) and SBUV/2 ozone profile measurements and 14 years (1980–1995) of National Meteorological Center (NMC) temperature analyses. These dependences are estimated by applying a multiple regression statistical model to monthly zonal mean time series extending from 60°S to 60°N latitude and approximately 25- to 50-km altitude. Solar variability is represented in the statistical model by the Mg II index, a close proxy for solar UV variations at wavelengths that affect the photochemical production of ozone. In agreement with earlier studies, although an apparent solar cycle variation of both ozone and temperature is present in the upper stratosphere, no detectable solar cycle variation is present in the middle stratosphere (30- to 35-km altitude). Ozone increases of 4 – 6% from solar minimum to solar maximum are found near 2 mbar at middle latitudes, with comparable amplitudes in both summer and winter hemispheres. While the presence of a large positive ozone response in the northern hemisphere during winter appears to be qualitatively consistent with theoretical predictions, the amplitude of the observed ozone variation is nearly twice as large as estimates based on current two-dimensional models of the middle atmosphere. Temperature increases of 2.5 K are found near 1 mbar at low latitudes throughout the year, in addition to a seasonally varying temperature response of 2.5 – 3 K near 5 mbar at middle and high latitudes in the summer hemisphere. A one-dimensional radiative model is used to calculate the expected change in equilibrium temperature associated with the observed solar cycle variability in the ozone profile under the assumption of fixed dynamical heating (FDH). Near the equatorial stratopause, the temperature response calculated with the FDH model is within 0.5 K of the observed response. At higher latitudes near 4 mbar, the FDH model cannot account for the large amplitudes and strong latitude dependences of the NMC-derived temperature variation. This would suggest that changes in stratospheric dynamics over the 11-year solar cycle may also be important for understanding the observed temperature and ozone variations.

Lunar magnetic anomalies and surface optical properties

For typical solar wind conditions, lunar magnetic anomalies with dipole moments m >> 5 x 1013 gauss-cubic centimeters will strongly deflect the solar wind, producing local plasma voids at the lunar surface. The correlation of the largest observed anomalies (m ∼ 1016 gauss-cubic centimeters) with unusual, relatively high albedo surface features may therefore imply that solar wind ion bombardment is an important determinant of the optical properties of the lunar surface.

Initial measurements of the lunar induced magnetic dipole moment using Lunar Prospector Magnetometer data

Twenty-one orbits of Lunar Prospector magnetometer data obtained during an extended passage of the Moon through a lobe of the geomagnetic tail in April 1998 are applied to estimate the residual lunar induced magnetic dipole moment. Editing and averaging of individual orbit segments yields a negative induced moment with amplitude −2.4 ±1.6 × 1022 Gauss-cm³ per Gauss of applied field. Assuming that the induced field is caused entirely by electrical currents near the surface of a highly electrically conducting metallic core, the preferred core radius is 340±90 km. For an iron-rich composition, such a core would represent 1 to 3% of the lunar mass.

Effects of Solar UV Variability on the Stratosphere

Previously thought to produce only relatively minor changes in ozone concentration, radiative heating, and zonal circulation in the upper stratosphere, solar ultraviolet (UV) variations at wavelengths near 200 nm are increasingly recognized as a significant source of decadal variability throughout the stratosphere. On the time scale of the 27-day solar rotation period, UV variations produce a stratospheric ozone response at low latitudes that agrees approximately with current photochemical model predictions. In addition, statistical studies suggest an unmodeled dynamical component of the 27-day response that extends to the low and middle stratosphere. On the time scale of the 11-year solar cycle, the ozone response derived from available data is characterized by a strong maximum in the upper stratosphere, a negligible response in the middle stratosphere, and a second strong maximum in the tropical lower stratosphere. The 11-year temperature response derived from NCEP/CPC data is characterized by a similar altitude dependence. However, in the middle and upper stratosphere, disagreements exist between analyses of alternate temperature data sets and further work is needed to establish more accurately the 11-year temperature response. In the lower stratosphere, in contrast to most model predictions, relatively large-amplitude, apparent solar cycle variations of geopotential height, ozone, and temperature are observed primarily at tropical and subtropical latitudes. As shown by the original work of Labitzke and van Loon [1988], additional large responses can be detected in the polar winter lower stratosphere if the data are separated according to the phase of the equatorial quasi-biennial wind oscillation. A possible explanation for the unexpectedly large lower stratospheric responses indicated by observational studies is that solar UV forcing in the upper stratosphere may influence the selection of preferred internal circulation modes in the winter stratosphere.