Solar Cycle Effects Research Articles

F region plasma drifts over Arecibo: Solar cycle, seasonal, and magnetic activity effects

We have used Arecibo incoherent scatter measurements from 1981 to 1990 to determine the characteristics of low‐latitude F region plasma drifts. The measurements show large day‐to‐day variability even during magnetically quiet periods. The average poleward/perpendicular plasma drifts do not change significantly with season and solar cycle except in the midnight‐morning sector. The zonal drifts show clear solar cycle and seasonal effects. The afternoon‐nighttime eastward drifts increase with solar flux; the westward drifts in the early morning‐afternoon sector show a large increase from summer to winter but are independent of solar activity. The two perpendicular velocity components also respond differently to magnetic activity. The average northward/perpendicular drifts decrease with magnetic activity during the day but do not exhibit a systematic response at night. The zonal component shows increased westward drifts occurring predominantly at night. The plasma drifts along the magnetic field lines exhibit large altitudinal and seasonal variations, particularly near solar minimum, and are generally anticorrelated with the perpendicular/north drifts. The drift patterns observed by the Arecibo and the middle and upper atmosphere radars have significantly different seasonal dependence. This can be explained by electrodynamic effects in the corresponding local and conjugate ionospheres. The large longitudinal variation of the quiet time F region plasma drifts results from the displacement between the geographic and dip equators and from magnetic field declination effects. In general, the longitudinal variation should also depend on magnetic activity.

Solar Cycle's Effect on How High Hubble Flies

Solar Cycle's Effect on How High Hubble Flies

An estimate of the local interstellar antiproton spectrum using solar modulation techniques on the data

Strong solar modulation of Galactic cosmic rays occurs in the energy range where balloon flights have measured Galactic antiproton-to-proton ratios. This modulation also varies substantially over the 15 yr period during which these ratios were gathered, due to the effect of the 11 yr solar cycle. This causes large fluctuations in cosmic-ray spectra measured inside the heliosphere. The study detailed in this paper uses both the numerical, one-dimensional model of solar modulation and its force-field approximation to calculate estimates of the antiproton intensity and p-bar/p ratio spectra in local interstellar space, independent of any interstellar production and propagation theory. These spectra include estimates of uncertainties in the modulation calculation. To offset solar-cycle effects, multiple sets of modulation parameters over this period were chosen from careful fits to electron and proton spectra contemporaneous with the p-bar/p ratio measurements. 43 refs.

Solar cycle effects on the structure of the electron density profiles in the dayside ionosphere of Venus

Since 1975, United States and Soviet Venus‐orbiting spacecraft have carried out more than 190 radio occultation measurements of the vertical electron density structure of the dayside ionosphere of Venus: 148 of these have been produced by the Pioneer Venus orbiter between 1979 and 1989; Venera 9 and 10 provided 13 measurements in 1975; and Venera 15 and 16 made 31 measurements in 1983. These measurements were made at various times of the solar cycle, including solar maximum and solar minimum. It has therefore been possible to observe the changes in the electron density structure of the dayside ionosphere of Venus that were brought about by changing solar activity. Some of the resulting observations are as follows: (1) The ionopause height is generally low for values of the solar zenith angle below about 50° regardless of the phase in the solar cycle. (2) At solar maximum, and at times of intermediate solar activity, the ionopause height for solar zenith angles greater than about 50° is highly variable, ranging from a minimum of about 200 km to a maximum of more than 1000 km. (3) At times of solar minimum the great majority of all ionopause heights for all solar zenith angles are uniformly low, lying between 200 and 300 km, with the notable exception of three Venera 9 and 10 measurements. The compressed nature of the Venus ionosphere at solar minimum is most likely produced by permeation of the ionosphere by the solar wind magnetic field, which occurs when the solar wind dynamic pressure exceeds the ionospheric plasma pressure. This happens at times of solar maximum at low solar zenith angles and when the solar wind dynamic pressure is exceptionally high. At solar minimum the Venus ionosphere, like the Martian ionosphere at all phases of the solar cycle, does not appear to have sufficient thermal pressure to balance the incident solar wind pressure.

Global average ozone change from November 1978 to May 1990

A recent recalibration and reprocessing of the total ozone mapping spectrometer (TOMS) data have made possible a new determination of the global average (69°S to 69°N) total ozone decrease of 3.5% over the 11‐year period, January 1, 1979, to December 31, 1989, with a 2σ error of 1.4%. The revised TOMS ozone trend data are in agreement, within error limits, with the average of 39 ground‐based Dobson stations and with the world standard Dobson spectrometer 83 at Mauna Loa, Hawaii. Superimposed on the 11‐year ozone trend is a possible solar cycle effect, quasi‐biennial oscillation (QBO), annual, and semiannual cycles. Using solar 10.7‐cm flux data and 30‐mbar Singapore wind data (QBO), a time series has been constructed that reproduces the long‐term behavior of the globally averaged ozone. Removal of the apparent solar cycle effect from the global average reduces the net ozone loss to 2.66±1.4% per decade. The precise value of the global average ozone trend depends on the latitude range selected, with ranges greater than ±69° emphasizing the larger variations at high latitudes.

Thermospheric tides at equinox: Simulations with coupled composition and auroral forcings: 2. Semidiurnal component

New simulations of semidiurnal thermospheric winds and perturbation temperatures calculated by the National Center for Atmospheric Research thermospheric general circulation model (TGCM) are presented for equinox conditions. The model now incorporates a self‐consistent calculation of neutral composition and includes high‐latitude energy and momentum sources associated with the aurora. The tidal waves propagating upward from the lower atmosphere are specified by wavelike distributions of the geopotential at the model lower boundary; the boundary geopotential is related to the other model fields through Hough mode tidal functions. The specification of the wave amplitudes and phases is based on lower atmosphere model predictions and thus represents the coupling between the upper and lower atmosphere in a more physically meaningful manner than previous calculations. In these simulations, asymmetric semidiurnal modes are also included. The revised TGCM calculations at geographic longitude 75°W are compared with observational data at low, middle, and high latitudes. In general, the agreement is reasonable, given the limited data available. The predicted solar cycle variation of the semidiurnal tides is consistent with previous works: the temperatures respond more strongly than the winds, and the solar cycle effects are most pronounced in the upper thermosphere. The lower thermosphere is dominated by the upward propagating waves from the lower atmosphere, with little contribution from solar forcing. These upward propagating waves are damped at lower altitudes as solar forcing increases. The effects of coupled composition and auroral forcings on the semidiurnal tidal components are investigated. Both processes alter the simulated solar‐driven tidal fields compared to calculations which neglected these processes: amplitudes may double or triple in restricted altitude and latitude regions, while the times of maxima may shift by a few hours. The TGCM simulations are compared with the Fourier‐decomposed exospheric temperature measured during the September 1984 Equinox Transition Study period. The semidiurnal temperature phase in particular is found to be strongly dependent on the level of geomagnetic activity. Thus the simulation of individual day observations will require careful specification of the auroral forcings which are input into the theoretical models. Simultaneous data obtained at different latitudes are vital to test and confirm the model predictions.

Separation of Solar Effects on Ozone from Anthropogenically Produced Trends

The ozone layer still seems to be the most probable link for a solar-weather relationship, and its association with the solar cycle must therefore be studied and separated from anthropogenically produced trends. The extensive Swiss records of total ozone and vertical distribution from Umkehr and soundings (6, 3 and 2 solar cycles respectively) are used for this purpose and the results compared with those obtained from the corresponding world network data. Total ozone shows a measurable but weakly significant solar cycle signal and a pronounced negative trend since 1970. With the main contribution coming from the ozone maximum layer, the solar cycle effect in mid-latitudes seems to be predominantly produced by variations in the ozone transport. The highest contribution to the negative trend stems, in contradiction to present model results, from a strong ozone depletion in the ozone maximum layer. It is partly compensated for by a pollution produced ozone increase in the troposphere. The variation in the upper stratosphere seems to be damped by the negative temperature feedback.

The Effect of Solar Flux Variations and Trace Gas Emissions on Recent Trends in Stratospheric Ozone and Temperature

Trend analyses of satellite and ground-based observations clearly indicate that temperatures and ozone concentrations in the upper stratosphere are undergoing long-term changes. Variations in solar ultraviolet radiation during the 11-year solar cycle are influencing stratospheric temperatures and photochemistry from above. Forcings from below result from the increasing atmospheric concentrations of long-lived trace constituents, such as carbon dioxide, methane, nitrous oxide, several chlorofluorocarbons and other halocarbons. Using the LLNL two-dimensional chemical-radiative-transport model of the global atmosphere, we evaluate the influences of these external forcings on the middle atmosphere. Our calculations include recent estimates of the variations in solar ultraviolet radiation since 1974. Model results for the solar cycle effects on total ozone, upper stratospheric ozone and temperature are within the uncertainty (in some cases, large) range of observational data analyses. The model calculations including both solar variability and the effects of changing trace gas emissions can explain much of the observed trends in upper stratospheric ozone and temperature from 1979 to 1986.

Electron density structures in the polar F region

Arctic campaigns conducted over the last decade, using digital ionospheric sounders and all-sky imaging photometers have allowed an ordering of the typically very irregular behavior of the polar cap ionosphere, and a preliminary definition of the solar cycle effects. Under quiet magnetic conditions the polar cap is populated with sun-aligned F layer arcs. Under magnetically active conditions (Bz < 0) large patches of enhanced plasma densities move rapidly from the cusp region across the polar cap. Both arcs and patches are highly structured. NmF2 enhancements up to a factor of ten above the background are observed in patches, while density enhancements in arcs are a factor of two to three. Summer and winter ionospheric soundings in the central polar cap (Qaanaaq, Greenland, 87° CG Latitude) under various solar cycle conditions, establish the observed pattern as a start for the systematic modeling of this most turbulent region. The general occurrence of patches is controlled by the sign for the IMF Bz component; patches occur typically when Bz < 0. The sub-cusp solar produced ionosphere had previously been identified as the potential source region of the patch plasma. At solar minimum IONCAP foF2 model results for 73° CGL on the magnetic noon meridian (postulated source region) provide an envelope for the observed maximum patch densities. For solar maximum conditions, the source region is likely at times at lower latitudes (< 65° CGL). 1982 through 1989 observations show a direct dependence of the patch maximum foF2 values on sunspot number.

Solar cycle effects on the near‐Earth space environment

Forecasts of the magnitude of solar activity in the 1990s (solar cycle 22) imply that the expected levels of activity might be some of the most extreme ever recorded, and almost certainly the levels of activity will be the highest experienced during the space age. Even as early as 1 year before the expected maximum of solar cycle 22 in 1990, unprecedented levels of solar activity (for example, the solar flares and solar particle events of August–October 1989) and geomagnetic activity (for example, the auroral events and geomagnetic storms of March 1989) have been observed. These solar and geophysical events have stirred scientific interest both in the long‐term behavior of solar activity and in the physics which couples the energy of solar events to the near‐Earth environment. Furthermore, the operational community (including those involved in satellite operations, telephone and radio communication, electric power distribution, aviation, and others) have experienced many adverse effects of these solar and geophysical events. Many more episodes of activity are expected throughout the upcoming 4–5 years. The purpose of this paper is to review the direct and indirect influences of solar activity on the near‐Earth environment and to describe some of the implications of the high levels of solar activity which are expected to occur in the 1990–1994 time period.

Heliocentric distance and temporal dependence of the interplanetary density‐magnetic field magnitude correlation

The Helios, IMP 8, ISEE 3, and Voyager 2 spacecraft are used to examine the solar cycle and heliocentric distance dependence of the correlation between density n and magnetic field magnitude B in the solar wind. Previous work had suggested that this correlation becomes progressively more negative with heliocentric distance out to 9.5 AU. Here we show that this evolution is not a solar cycle effect, and that the correlations become even more strongly negative at heliocentric distances larger than 9.5 AU. There is considerable variability in the distributions of the correlations at a given heliocentric distance, but this is not simply related to the solar cycle. Examination of the evolution of correlations between density and speed suggests that most of the structures responsible for evolution in the anticorrelation between n and B are not slow‐mode waves, but rather pressure balance structures. The latter consist of both coherent structures such as tangential discontinuities and the more generally pervasive “pseudosound” which may include the coherent structures as a subset.

Solar cycle effects on the upper atmosphere - Implications for satellite drag

High thermospheric temperatures are maintained against thermal diffusion primarily by the absorption of extreme ultraviolet (EUV) radiation by atmospheric constituents (mainly, atomic oxygen). Because the solar flux of EUV varies strongly over the 11-yr solar cycle, thermospheric temperatures likewise vary strongly over the solar cycle. In an average solar cycle, solar EUV and thermospheric temperature increase by about a factor of two. from solar cycle minimum to solar cycle maximum. Because density is mainly an integrated effect of temperature, the change in density over the solar cycle is amplified with respect to the temperature change. Changes in temperature cause changes in composition and these changes act to mitigate the direct thermal effects. The net effect of temperature and composition is to give order-of-magnitude changes in density over the solar cycle. The atmospheric drag on satellites is proportional to atmospheric density. The effects on satellite lifetimes are profound. A fairly typical satellite initially at 500 km would have a lifetime of about 30 years under typical solar cycle minimum conditions and only about 3 years under solar maximum conditions. Large increases in the rate of change of orbital period from solar minimum to solar maximum are possible. The fractional increase in the highly reactive species atomic oxygen can exceed two orders of magnitude.

Solar cycle effects on trapped energetic particles

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Solar cycle effects on near-earth plasmas and space systems

Abstract : Solar physicists have predicted that the upcoming maximum of solar activity, scheduled to occur near 1990, might be the most extreme ever recorded. Based on the observed rate of increase in solar activity starting with the most recent minimum in 1986 the upcoming solar maximum will be the most severe of those which have occurred during the space age. Correlations between solar activity and disturbances in the near-earth magnetospheric and ionospheric plasmas which adversely affect communications and space systems are well documented. The implementation of larger, more complex (and perhaps more susceptible) space systems over the last decade, has led to concern and speculation about the expected performance and survivability of these space systems over the next decade. Unfortunately, because of the complex and sometimes indirect interactions between the sun and the plasma environment in near-earth space, very few firm quantitative predictions can be made regarding the expected effects of an extreme solar maximum on the near-earth environment or on the complex systems operating in that environment. A number of qualitative predictions can be made with high confidence. Satellite communications links in the VHF/UHF range will suffer signal fades more often and with greater severity. Short wave and airline communications will be sporadically disrupted. Satellites will experience electrical charging of their surface and internal dielectric components, resulting in disruptive electrostatic discharges and micro- electronic devices on satellites will experience upsets more often.

A Closer Look at the Effect of the 11-Year Solar Cycle and the Quasi-biennial Oscillation on Northern Hemisphere 700 mb Height and Extratropical North American Surface Temperature

Abstract A recently discovered association between the 11-year solar cycle and the Northern Hemispheric low-frequency atmospheric circulation structure, which is most easily delectable when the two phases of the Quasi-biennial Oscillation (QBO) are considered individually, is described and subjected to global statistical significance tests. Highly significant relationships are found during the January–February period. This is especially true for the west QBO phase, in which the solar flux is positively correlated with 700 mb heights and surface temperatures over central and northern Canada, and negatively correlated with heights in the western Atlantic along 30°N and with temperature in the southern and much of the eastern portions of the United States. The pattern of the flux-height correlation field resembles primarily the Tropical/Northern Hemisphere (TNH) long-wave circulation pattern and secondarily the North Atlantic Oscillation (NAO) pattern. For east QBO phase years a different structure is found,...

A parametric study of space radiation exposures to critical body organs for low earth orbit missions

The geomagnetically-trapped and galactic cosmic radiation environments are two of the major sources of naturally-occurring space radiation exposure to astronauts in low earth orbit. The exposure is dependent primarily on altitude, spacecraft shielding, crew stay-times, and solar cycle effects for a 28.5 deg orbital inclination. Based on Space Shuttle experience, the calculated results of a parametric study are presented for several mission scenarios using a computerized anatomical man model and are compared with the NASA crew exposure limits for several critical body organs.

Empirical global model of upper thermosphere winds based on Atmosphere and Dynamics Explorer satellite data

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been used to generate an empirical wind model for the upper thermosphere, analogous to the MSIS model for temperature and density, using a limited set of vector spherical harmonics. The model is limited to above approximately 220 km where the data coverage is best and wind variations with height are reduced by viscosity. The data base is not adequate to detect solar cycle (F10.7) effects at this time but does include magnetic activity effects. Mid‐ and low‐latitude data are reproduced quite well by the model and compare favorably with published ground‐based results. The polar vortices are present, but not to full detail.

Solar cycle effects in intervals of pulsations of diminishing periods pulsation activity

We report that intervals of pulsations of diminishing periods (IPDP) type plasma wave events which are associated with magnetospheric substorms are less frequent in the years of high solar activity than in years of low activity. This new result is based on two independent continuous data sets from 1974 to 1985. We show also that IPDP events occur throughout the recurrent magnetic storms in 1976, whereas they appear more sporadically in 1980, i.e., during high solar activity. It is concluded that several factors such as changes in plasmapause position, attenuation of horizontal ionospheric wave propagation, and heavy ion densities in the magnetosphere can contribute to the observed long‐term variability.

Solar cycle and seasonal variations of the low latitude OI 630 nm nightglow

Regular zenith measurements of the OI 630 nm nightglow emission have been carried out at Cachoeira Paulista (22.7°S, 45.0°W; geomag. 11.9°S), Brazil, since 1975. The long series of observations during the period 1975–1982, including the ascending phase of the last solar cycle, permitted studies of solar cycle effects and seasonal variations. A large intensity increase, about seven times, from low solar activity to high solar activity has been observed. Also, the seasonal-nocturnal intensity variations show large changes between years of low and high solar activity. The characteristics of the variations observed are closely related to the equatorial electric field variations, since the observation site is under the southern equatorial ionospheric anomaly crest.

Geomagnetic parameters derived from an analytic description of the earth's magnetic field.

A recent geomagnetic model containing 720 trend and trigonometric coefficients represents each spherical harmonic coefficient as a continuous function of time which exactly duplicates the IGRF coefficients at the nine IGRF epochs (1945 to 1985 at five year intervals) and allows a reasonable prediction five years beyond the last epoch. Use of this model permits time derivatives of magnetic elements and other derived quantities to be taken so that a detailed look at several geomagnetic parameters vs time can be obtained. It is shown that from 1945 to 1985 the quadrupole field contributed 2.6 times more power to the secular variation field on the surface of the Earth than the dipole field. It is also shown that the root-mean-squared surface field shows a strong periodicity which may be related to the solar cycle. This apparent solar-cycle effect diminishes with time as more satellite data are used indicating that an appreciable part of it may be caused by noisy data and a poor distribution of data for a couple of decades following World War II.