Microinstabilities and models of the solar wind

The collision-dominated two-fluid plasma models of the solar wind are shown to become collisionless and subject to microinstabilities at a few solar radii. Assuming that once the plasma is unstable it stays close to marginal stability models of the solar wind are constructed including waves and proton heating. The resulting models have higher velocities and proton temperatures than the collision dominated two fluid models.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Chemical response of the middle atmosphere to solar variations

The possible variation of the trace species concentration in the middle atmosphere related to long term solar irradiance variability is estimated by means of a one-dimensional numerical model.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.Aspirant au Fonds National de la Recherche Scientifique.     

Short-period intensity fluctuations of integral sunlight

An attempt has been made to detect short-period solar luminosity fluctuations in the vicinity of 5 min, analogous to the observed velocity oscillation. Using silicon photodiodes to monitor integral sunlight, an upper limit for the amplitude of the intensity fluctuations of 3 x 10^-5 rms was found.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Solar irradiance between 120 and 400nm and its variations

The solar ultraviolet irradiance measurements in the 120–400 nm wavelength range are reviewed and compared showing still important discrepancies between the irradiance values deduced from the most recent observations.The possible variations of the solar ultraviolet irradiances with the 27-day rotation period of the Sun and with the 11-year activity cycle are presented and discussed on the basis of the available irradiation fluxes obtained during the rising phase of solar cycle 21.The spectral features of both kinds of variation are clearly related to the solar atmospheric layer from which the corresponding radiation is emitted.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

A 1600 year long record of solar change derived from atmospheric 14C levels

Tree-ring ¹⁴C measurements indicate the long-term solar variations, as modulations of the cosmic ray flux, shown in Figure 1.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

A two-dimensional solar spectrometer

A precise two-dimensional positioning device has been developed for use in conjunction with a resonant scattering spectrometer to study the spatial distribution of solar velocity fields. The principle of operation and constructional details are discussed and the experimental performance is evaluated. As an illustration of its use preliminary data obtained from a meridional scan are presented.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Solar pulsations observed from the geographic South Pole: Initial results

Initial results of round-the-clock observations of solar oscillations at the South Pole are briefly summarized by describing the Figures 1 to 4.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The response of ozone to solar activity variations: A review

Observational evidence and theoretical predictions of the response of ozone to solar variations are reviewed. Short-term solar proton effects, possible effects of galactic cosmic rays modulated by the Sun, and the effects of 27-day solar rotation and 11-year solar cycle variations are discussed. Solar proton effects on HO _x chemistry in the mesosphere and NO _x chemistry in the stratosphere with resulting catalytic destruction of O₃ help validate present day photochemical models. If there is an 11-year solar cycle variation in global ozone, the large dynamical effects at individual locations and the lack of good global coverage of ground based and in situ measurements can disguise it. Recently, with the global coverage of satellites, it has become possible to accurately determine global mean ozone. It has been found that variations in global mean ozone filtered for seasonal variations are highly correlated with variations of the 10.7 cm solar activity index and that global mean ozone responds rapidly to solar activity index variations. Photochemical models indicate that the observed 3% variations in global mean ozone over the solar cycle can be accounted for by solar UV variations which are not inconsistent with recent solar measurements.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The observation of the solar irradiance and its variations,challenging space metrology

The problems associated with the accurate determination of the total and spectral irradiances of the Sun are discussed. It is estimated that an ultimate accuracy of the order of 2 to 5 × 10^–4 should be aimed at and be feasible for total solar irradiance measurements made with second generation objectively characterised absolute radiometers.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

A high precision Solar Ultraviolet Spectral Irradiance Monitor for the wavelength region 120–400 nm

There exists a growing need to improve the accuracy of measurement of the absolute solar flux within the wavelength range 120–400 nm. Although full-disk solar fluxes and variations thereof in the 120–400 nm region are required to model the solar atmosphere, current increased interest in the measurements arises from their importance in modeling the terrestrial atmosphere. We describe the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) experiment under development at the Naval Research Laboratory (NRL) for flight aboard the Space Shuttle and the Upper Atmospheric Research Satellite (UARS). SUSIM will monitor the solar flux in the 120–400 nm region with high precision, using an in-flight calibration system to reduce absolute error to < 10%, and error relative to the 400 nm continuum to < 1%.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

On the nature of the apparent response of the vorticity area index to the solar magnetic field

The apparent response of the vorticity area index to the solar magnetic field is confined to tropospheric regions of intense circulation. Discussions and calculations that include larger volumes of the troposphere would not be expected to show a significant Sun-weather effect. Analysis of the effect in time intervals outside the original 1963–73 is also discussed. An assessment of this Sun-weather effect at the present time is given.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Reflections on solar variability

The Sun is a variable star in many respects: there are secular varitions related to the general solar evolution, and - as discovered in recent years - there are many short period variations of which the 5 min and 160 min pulsations are the most important ones. Magnetic fields in the outer convective mantle play a dominant role in the 22-years cycle. The origin of solar magnetic variability is a key problem in astrophysics. The relation between solar variability and changes in the Earth's climate is a crucial element in climatology.Introductory talk to the 14th ESLAB Symposium: Physics of Solar Variations, 16–19 September, 1980, Scheveningen, The Netherlands.     

Searching for l = 1 modes of solar oscillations

An instrument to measure the non-full-disk low-order solar oscillations that uses a magneto-optical filter in Na-D lines is described. It has the advantage, over the resonant cells used by other observers, that it gives an image of the Sun and a higher photonic flux.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Solutions of the two-fluid solar wind equations: Adiabatic and conduction dominated solutions

The equations governing the two-fluid spherically symmetric models of the solar wind have been solved numerically for a wide range of base conditions. As predicted from an asymptotic analysis we find a whole domain of solutions which are asymptotically adiabatic with the proton and electron temperatures tending to equality and varying like r ^{- 4/3}. In these 4/3 solutions the electron and proton heat conduction is asymptotically negligible and if it is neglected the resulting equations can be integrated analytically and shown to have the 4/3, 4/3 behaviour.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Tropospheric effects of variable solar activity

Within 12 hr after strong solar flares at middle to high latitudes a cooling at tropopause level is observed along with changes in temperature and height of isobaric levels in the troposphere. Delayed tropospheric effects are reported to occur at 2–4 days after a flare. It is suggested that the early effect through changing the baroclinic instability conditions of the troposphere is responsible for the occurrence of the late effects. Computations show that the observed early effect may amplify the growth rate of the most unstable wave by at least 20% and perhaps by a factor of 1.5 to 2.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The sun's rotation and perturbations of geopotential height and temperature fields in the stratosphere

The morphology of a solar activity effect apparently connected with the Sun's rotation and showing up in 25-day and 13.6-day oscillations of stratospheric geopotential and temperature fields is analysed in this study. The used data cover the height range between roughly 20 and 30 km and a timespan from July 1965 to October 1971. Most prominent responses are found for zonal harmonic wave number 1 at the oscillation period of 25 days (solar rotation period modulated by seasonal changes) and for the zonally averaged meteorological quantities at the oscillation period of 13.6 days. Additional statistically significant effects show up in the zonal harmonics with wave number 1 and 3 at half the solar rotation period and in the zonal means with periodicities near 25–27 days. The results point towards a modulation of the quasistationary stratospheric planetary wave with a positive geopotential anomaly around roughly 180° longitude by solar activity changes. The direct physical mechanisms of this Sun-climate relationship are not yet clear, but it can be concluded that atmospheric dynamics is an important factor for its morphology and that downward propagation of such effects seems possible and should be investigated in future studies.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

A catalogue of high-speed plasma streams in the solar wind

A catalogue of 346 well defined high-speed plasma streams detected in solar wind observations 1964–75 is presented. The data base for the study is the compilation of interplanetary plasma/magnetic field data prepared by J. King. It is believed that the catalogue may be found useful for studies of various solar-interplanetary and solar-terrestrial phenomena.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Structure of the 5-minute solar oscillations 1976–1980

The discrete structure in the 5 min velocity oscillations of the solar surface has been confirmed by a re-analysis of data obtained between 1976 and 1979, and in addition a preliminary analysis of 1980 data show excellent consistency of the determined frequencies over the five year period. It is further shown that atmospheric transparency, as measured by the power in the solar intensity fluctuations, shows no correlation with the measured amplitude of the velocity fluctuations, over 2 orders of magnitude.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The age dependence of photospheric tracer rotation

From the analysis of the motions of sunspot groups recorded at Catania Astrophysical Observatory over a 7-years period from 1972 to 1978 the mean angular velocity as a function of latitude and age is calculated. The results suggest that the age of photospheric tracer (sunspot groups) affects the rotation curve slope. The implications of this result are discussed.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Solar radiation and its variation in time

In order to assess the variability of the solar radiation, the record of determinations of the total and spectral solar irradiance of the last 15 years is analysed. Although the datapoints for the period before 1969 suggest a slight decrease, the uncertainties of these determinations are too large to render this statement significant. Together with the results of the following period (1969–1980) which show that within the uncertainty no change is detectable, it can be concluded, that the solar constant has not changed during the last 15 years. The same result is found from the spectral distribution record, though not as conclusive as for the solar constant, due to the much larger uncertainties of the spectral data.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.