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NASA NTRS1979

Solar-terrestrial influences on weather and climate; Proceedings of the Symposium, Ohio State University, Columbus, Ohio, August 24-28, 1978

The book contains most of the invited papers and contributions presented at the symposium/workshop on solar-terrestrial influences on weather and climate. Four main issues dominate the activities of the symposium: whether solar variability relationships to weather and climate is a fundamental scientific question to which answers may have important implications for long-term weather and climate prediction; the sun-weather relationships; other potential solar influences on weather including the 11-year sunspot cycle, the 27-day solar rotation, and special solar events such as flares and coronal holes; and the development of practical use of solar variability as a tool for weather and climatic forecasting, other than through empirical approaches. Attention is given to correlation topics; solar influences on global circulation and climate models; lower and upper atmospheric coupling, including electricity; planetary motions and other indirect factors; experimental approaches to sun-weather relationships; and the role of minor atmospheric constituents.

Mccormac, B. M.↗
NASA NTRS1980

A review of observational evidence for short and long term ultraviolet flux variability of the Sun

Observation of the Sun in the 160 to 400 nm wavelength region reveals no significant broadband variation with solar flares, variability associated with the rotation of active regions, and a possible long term change which may be related to the 11 year sunspot cycle or longer. A continuing ultraviolet solar flux variability below 200 nm was observed from 1969 through the present from satellites, which is modulated at solar rotation rates. Recent observations from Nimbus-7 show the solar flux is varying by significant amounts also in the regions from 200 nm up to the Calcium 2 H-line at 396.8 nm. Typically the flux may vary over a solar rotation from about 10 percent at 160 nm to slightly less than 1 percent at the Ca2 K-line. Results of an evaluation of observations from rockets, satellites, and the ground measurements are discussed.

Heath, D. F.↗
NASA NTRS1980

A physical model of Titan's clouds

A physical model of the formation and growth of aerosols in the atmosphere of Titan has been constructed in light of the observed correlation between variations in Titan's albedo and the sunspot cycle. The model was developed to fit spectral observations of deep methane bands, pressures, temperature distributions, and cloud structure, and is based on a one-dimensional physical-chemical model developed to simulate the earth's stratospheric aerosol layer. Sensitivity tests reveal the model parameters to be relatively insensitive to particle shape but sensitive to particle density, with high particle densities requiring larger aerosol mass production rates to produce compatible clouds. Solution of the aerosol continuity equations for particles of sizes 13 A to about 3 microns indicates the importance of a warm upper atmosphere and a high-altitude mass injection layer, and the production of aerosols at very low aerosol optical depths. Limits are obtained for the chemical production of aerosol mass and the eddy diffusion coefficient, and it is found that an increase in mass input causes a decrease in mean particle size.

Toon, O. B.↗
NASA NTRS1981

Coronal holes, solar wind streams, and geomagnetic disturbances during 1978 and 1979

It was found that, during 1978 and 1979, coronal holes reflected the influence of differential rotation, and were present within a slowly evolving large-scale pattern in spite of the relatively high level of sunspot activity. The long-lived 28.5-day pattern is not produced by a rigidly rotating quasi-stationary structure on the sun, but appears to be produced by a nonstationary migratory process associated with solar differential rotation. The association between coronal holes and solar wind speed enhancements at earth continues to depend on the latitude of the holes (relative to the heliographic latitude of earth), but even the best associations since 1976 have speeds of only 500-600 km/s rather than the values of 600-700 km/s that usually occurred during the declining phase of sunspot cycle 20.

Sheeley, N. R., Jr.↗
NASA NTRS1981

Representations of solar EUV fluxes for aeronomical applications

Pilot studies performed on Atmosphere Explorer-E satellite data on solar EUV fluxes for the rising part of the sunspot cycle 21 have demonstrated the feasibility of expressing the variability of solar EUV fluxes in aeronomically attractive terms involving a relatively small total number of date-dependent variables supported by the relatively large number of wavelength-peculiar parameters. Attention is given to the distribution of solar EUV sources and their variability, observations of solar cycle variations, and a model representation of EUV variability.

Hinteregger, H. E.↗
NASA NTRS1981

Predominant periods in the time series of drought area index for the Western High Plains AD 1700 to 1962

The detection of the combined presence of the Hale magnetic sunspot cycle (22.28 years) and the lunar nodal tidal cycle (18.61 years) in both the Eastern North American January air temperatures and the Western U.S. High Plains drought series led to an extended analysis of the Drought Area Index time series. This analysis indicated that the mean dominant period of the drought series should be 20.0 to 20.5 years and that the principal period should be resolvable into two components of about 22.28 and 18.61 years. This note details the successful accomplishment of this task.

Bell, P. R.↗
NASA NTRS1981

Multi-spacecraft observations of heliographic latitude-longitude structure in the solar wind

The heliographic latitude-longitude structure of high speed solar winds observed prior to the maximum of sunspot cycle 20 is investigated by multi-spacecraft comparisons. It is shown that differences in solar wind structures are due to two different kinds of spatial structures. One structure is found to be consistent with the simultaneous existence of a single, broad stream at latitudes above 7 deg N and a series of narrow streams at lower latitudes, while the other is consistent with the existence of a latitudinally sloping stream boundary near the solar equator. For latitude separations less than 3.5 deg, cross-correlations of Explorer-Mariner velocities show only previously reported systematic increases in velocity with latitude, and for latitude separations from 3.5 to 6.2 deg, differences in high speed streams shift in longitude and/or amplitude are also identified on a timescale of one solar rotation.

Rhodes, E. J., Jr.↗
NASA NTRS1981

Observational, reference and model data on solar EUV, from measurements on AE-E

Information on solar irradiance at wavelengths below 185 nm, observed by the EUVS experiment on the AE-E satellite over the entire development of the present sunspot cycle 21, is important to a variety of investigations of planetary thermospheres and ionospheres. Since strictly observational information is generally lacking in both the completeness and the spectral detail required by the more advanced programs, it has been necessary to develop computer models in connection with fully detailed compilations of an appropriate reference spectrum. The period of July 13-18, 1976, is selected as an observationally reliable AE-E data reference period reflecting solar conditions of minimum activity for solar cycle 21. It is pointed out that the assignments of absolute irradiance-reference values have been drawn for all available sources of information other than that provided by AE-E.

Hinteregger, H. E.↗
NASA NTRS1983

Comparison of heliospheric current sheet structure obtained from potential magnetic field computations and from observed polarization coronal brightness

A comparison is conducted of the structure of the heliospheric current sheet early in sunspot cycle 21 as computed from the observed photospheric magnetic field with a potential field approximation and as inferred from synoptic maps of the observed coronal polarization brightness. On most of the solar rotations compared, the two methods give essentially the same results; the basic shape of the warped current sheet and the amplitude (in solar latitude) of the displacements of the sheet from the solar equator are similar. On one rotation the current sheet computed with the potential field approximation appears to be distorted by a large photospheric region of unbalanced magnetic flux.

Wilcox, J. M.↗
NASA NTRS1983

Baseline ozone results from 1923 to 1955

Baseline total atmospheric ozone values from the year 1923 to 1955 are reported which have been derived from observations of the solar constant made by Smithsonian Institution sites in both the Northern and Southern Hemispheres. Ozone was determined from absorption by the broad, weak Chappuis band near 0.6 microns as measured on 1194 days at Mt. Montezuma, Chile and 970 days at Table Mountain, California. Results show systematic changes on the order of 25 percent in the ozone level at Montezuma with a time scale of 10-20 years, although the previously reported 30 percent decrease between 1920-1930 and 1940-1950 is found to have been erroneous. Comparisons of ozone data with geomagnetic indices and sunspot number show a suggestive correlation of ozone with sunspot number, although the relation is not borne out by comparison of ozone and sunspot cycles, or by Fourier analysis. Comparison of ozone data in the Chappuis band obtained by a modern filter-wheel radiometer with that obtained from a Dobson spectrometer at Mauna Loa Observatory shows Chappuis band measurements to be 14 percent lower.

Angione, R. J.↗
NASA NTRS1983

Climatic response to a time varying solar constant

Recent measurements of the solar constant, theoretical arguments, and climatic measurements combined with signal processing suggest the possibility that the solar constant varies significantly on time scales ranging from billions of years to 11-yr (sunspot) cycles, and even to scales of a few weeks. Simple climate models with a time varying solar constant are examined here, with emphasis on the heat balance models (North et al., 1981). Linear heat balance model results are presented for high (10 cycles/yr) and low (0.1 cycle/yr) frequencies, providing a useful guide in estimating the direct heat response to solar variability.

North, G. R.↗
NASA NTRS1983

The structure of the heliospheric current sheet - 1978-1982

Continuing the study near solar minimum in 1976-1977 (Hoeksema et al., 1982), the configuration of the heliospheric magnetic field for the period 1976-1982 is calculated using a potential field model. Particular attention is given to the structure during the rising phase, maximum, and early decline of sunspot cycle 21, from 1978 to 1982. Four warps in the current sheet (the boundary between interplanetary magnetic field toward and away from the sun) are seen early in this interval; these give rise to a four-sector structure in the interplanetary magnetic field observed at earth. It is noted that the location of the current sheet changes slowly and extends to a heliographic latitude of approximately 50 deg. The strength of the polar field correction throughout this period is determined and included in the model calculations. The lower latitude magnetic fields become much stronger as the polar fields weaken and reverse polarity near maximum, decreasing the effect of the polar field correction.

Hoeksema, J. T.↗
NASA NTRS1984

A second chance for Solar Max

Using NASA's Tracking and Data Relay Satellite as a communications link, astronomers are able to receive scans from the Solar Maximum Mission (SMM) satellite immediately and regularly at the Goddard Space Flight Center. This major operational improvement permits the examination of SMM imagery and spectra as they arrive, as well as the formulation of future observational sequences on the basis of the solar activity in progress. Attention is given to aspects of the sun that change in the course of the 11-year sunspot cycle's movement from maximum to minimum. Proof has been obtained by means of SMM for the near-simultaneity of X-ray and UV bursts at flare onset.

Maran, S. P.↗
NASA NTRS1985

Detectability of extrasolar planetary transits

Precise stellar photometry can be used to detect other planetary systems. However, the intrinsic variability of stellar luminosity imposes a fundamental limit on the sensitivity of this method. Based on recent precise solar observations made from the Solar Maximum Mission satellite, it appears that the detection of earth-sized planets will be marginal during periods of high stellar activity. However, with a suitable photometer larger planets should be readily detectable even in the presence of stellar activity equal to that of the sun at the peak of its sunspot cycle. The high precision, multiple-star photometric system required to detect planets in other stellar systems could be used to monitor flares, starspots, and global oscillations.

Borucki, W. J.↗
NASA NTRS1986

Mesospheric ozone changes associated with 27-day solar ultraviolet flux variations

Solar ultraviolet flux changes associated with the 27-day solar rotational period cause corresponding variations in mesospheric ozone near the maximum of the 11-year sunspot cycle. This statement is based on a correlation and spectral analysis of ozone mixing ratios, deduced from Solar Mesospheric explorer satellite-based measurements of 1.27-micron O2 airglow emission and solar flux observations made from the same spacecraft in 1982. With the Lyman-alpha flux taken as an indicator of solar ultraviolet variability, spectral analysis shows a primary period of 27.1 days with a secondary period of 13.5 days. The 27.1-day period is observed in the ozone mixing ratio data together with other periods, including 13.5 days. Both a classical statistical analysis and a time series treatment show that, for 244 days, there is a correlation between ozone and solar flux near 50 km and between 65 and 70 km. Calculations predict a positive correlation over the entire mesosphere if there is no change in temperature accompanying the solar flux. Lack of correlation is temperature induced.

Aikin, A. C.↗
NASA NTRS1986

Prediction of geomagnetic activity on time scales of one to ten years

The long-term prediction of geomagnetic indices that characterize the state of the magnetosphere is discussed. While a prediction of the yearly average sunspot number is simultaneously a prediction of the yearly number of sudden-commencement storms, it is not a prediction of the number of disturbed or quiet half days. Knowledge of the sunspot cycle phase leads to a good estimate of the correlation expected between activity during one 27-day solar rotation period and the next.

Feynman, J.↗
NASA NTRS1988

Model of Jovian F region ionosphere

To date, seven electron density profiles of the Jovian ionosphere have been furnished by the radio occultation experiments aboard the Pioneer and Voyager space probes. The data correspond to various localities (latitudes and longitudes) and times (dawn and dusk) and phases of sunspot cycle (high and low). This renders comparative studies difficult. Nevertheless, the possibility of existence of diurnal variation, equatorial anomaly, and auroral particle precipitation in the Jovian ionosphere have been put forth. The grand magnitude and depth of the equatorial anomaly, in particular, is a matter of great interest and speculation. Correct interpretations of the data and the physical processes in the complex Jovian atmospheric environment will remain a major task for the Aeronomer for decades to come. Model studies of a Jovian ionosphere created by solar EUV radiation and subjected to model ExB drifts showed that equatorial anomaly similar to that in the terrestrial ionosphere can indeed be produced in the Jovian ionosphere. However, owing to the difference in size and rotation period of the two planets and the ionic compositions, much larger drift velocities are required to produce a comparable anomaly in the Jovian atmosphere.

Tan, A.↗
NASA NTRS1987

Is solar neutrino capture rate correlated with sunspot number?

The statistical significance of the apparent correlation between sunspots and the observed neutrino rate is quantified. It is shown that the correlation depends almost entirely upon four low neutrino capture rates near the beginning of 1980. A calculation based on standard electroweak theory and neutrino production processes demonstrates that a correlation, if real, would be extremely puzzling on energetic grounds alone. It is concluded that measurements with the Cl-37 detector during the next sunspot cycle will be needed to show that there is a physical correlation, since the existing data are not statistically significant at a definitive level.

Bahcall, J. N.↗