We outline the development of Mesosphere-Stratosphere-Troposphere (MST) radar research of the middle atmosphere with special emphasis on coupling processes from above and below. The coupling from above is important in high-latitude auroral regions and we therefore include into our descriptions also the Incoherent Scatter (IS) radar observations used to study the lower thermosphere and ionosphere. The possibility of Joule heating of the mesosphere is discussed as well as transport processes and the influence of solar proton events on the mesosphere. A characterization of mesospheric VHF radar echoes is given and their relation to electron density changes discussed. Gravity wave velocity measurements with MST radars in the mesosphere and stratosphere are briefly presented, as well as profiles of the mean horizontal and vertical wind in the troposphere and stratosphere. It is discussed how ST radars could contribute to investigations of the polar stratosphere and the ozone variation. Also the fine structure of VHF ST radar echoes is considered in terms of a similar fine structure in temperature and ozone profiles. ST radars can also be used to study synoptic scale disturbances, troposphere-stratosphere transport by means of observations of tropopause foldings and mean vertical velocity. We finally point out how ST radars could be effectively implemented to study tropical waves and vertical transport between the troposphere and the stratosphere in the tropics during deep convection.

View full abstract

Atmospheric tides are discussed from the perspective of how these waves serve to dynamically couple different regions of the atmosphere from the ground to about 150km. Emphasis is placed on theoretical and modeling efforts which address new mechanisms, with a view towards providing some direction to future theory, modeling, experimental, and data analysis activities. A major area of recent and projected future research concerns the interactions between tides, gravity waves, and the mean tonal flow. Tidal wind oscillations between 70 and 100km modulate the transmissivity of gravity waves to the thermosphere, as well as the deposition of momentum within this height regime due to gravity waves propagating upwards from tropospheric sources. These modulated momentum fluxes in turn feed back to modify the tidal winds as well as the mean zonal flow; in addition, the tidal winds deposit net momentum and heat at the base of the thermosphere as they themselves undergo dissipation. Other promising areas of research include tide/tide and tide-planetary wave interactions, and the responses to transient tidal forcing. In addition, the mutual interactions between tidal dynamics and neutral and ionized constituent densities between 100 and 175km can now be addressed by newly-developed thermosphere-ionosphere general circulation models which include self-consistent interactions between the neutral and ionized species. Future spectral modeling of middle atmosphere tides would also benefit from new calculations of mean monthy thermotidal heating profiles that take into account new empirical prescriptions of seasonal-latitudinal and longitudinal variations of H₂O and O₃ densities derived from measurements by satellite sensors.

View full abstract

Some of the processes which affect the coupling of atmospheric gravity wave energy and momentum through the middle atmosphere are discussed. Changes in gravity-wave generation, propagation, and saturation can all cause variations in wave activity. Amongst the effects considered here are wave saturation, and interactions with the background wind, which act to directionaly filter and to Doppler shift wave energy. It is shown, with reference to observations, that care is required to ensure that propagation and saturation effects do not obscure the identification of wave sources, which must be one of the key goals of STEP.

View full abstract

Neutral atmosphere turbulence exists almost ubiquitously throughout the atmosphere up to heights of about 100km, and then completely disappears above about 120km altitude. It's importance in providing coupling in the lower regions of the atmosphere (troposphere and stratosphere) is well known, but its importance for coupling between the middle atmosphere and ionosphere is not so well understood. In this review, we will concentrate on the role that turbulence plays in the coupling between the middle atmosphere and the low levels of the ionosphere. The discussion will include a review of some of the important principles of turbulence, as well as some of the unique features about middle atmospheric turbulence. A detailed collection of measurements of turbulent eddy diffusion coefficients will be presented, along with some warnings about how these data should be interpreted. The need to understand turbulence at a very fundamental level in order to apply measurements of such “diffusion coefficients” is stressed.

View full abstract

Both energetic protons and electrons can produce odd nitrogen compounds, NO_y (N, NO, NO₂, NO₃, N₂O₅, HNO₃, HNO₄, ClONO₂), through interactions with the background atmosphere. The long lifetime of the NO_y family (up to several months in the middle atmosphere) as well as the NO_y species' significant influence on stratospheric ozone abundance make the charged particle increases of NO_y important. Galactic cosmic rays produce NO_y in the lower stratosphere, solar protons produce NO_y in the middle and upper stratosphere as well as the mesosphere, and relativistic electrons produce NO_y in the upper stratosphere and mesosphere, each affecting the NO_y middle atmosphere budget directly. Production of NO_y constituents by solar protons has been associated with an observed polar ozone depletion during and after the August 1972 solar proton event and a polar NO increase after the July 1982 solar proton event. Auroral electron and photoelectron production of NO_x (N, NO, NO₂) in the thermosphere and its subsequent transport downwards to the polar mesosphere and upper stratosphere is an important component of the NO_y budget in the middle atmosphere in the wintertime at high latitudes, e.g., the NO₂ enhancements measured by the limb infrared monitor of the stratosphere (LIMS) in the polar lower mesosphere and upper stratosphere during the winter of 1978-79 are thought to be caused by downward transport of NO_x.

View full abstract

Results from Rayleigh lidar during the last solar cycle indicate a highly significant correlation with the solar flux both on the scale of the 11-year and 27-day cycles. The height profile of the response to solar variability for both cycles presents a succession of positive and negative correlations which are difficult to explain on the basis of a purely radiative and photochemical forcing. The similarity between the response as a function of height seen from lidar data and as a function of latitude seen from radiosondes and satellites data for both cycles provides a strong support to the hypothesis of dynamical forcing proposed by several authors. It leads to the conclusion that such an effect can only be simulated by three dimensional fully coupled models.

View full abstract

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.

View full abstract

The middle atmosphere holds a rich variety of particulate matter, ranging from meteoritic debris to sulfate aerosols to polar stratospheric ice clouds. Volcanic eruptions strongly perturb the stratospheric sulfate (JUNGE) layer. High-altitude “noctilucent” ice clouds condense at the cold menopause. The properties of these particles—including composition, size and geographical distribution—are discussed, and their global effects—including chemical, radiative and climatic roles—are surveyed. Polar stratospheric clouds (PSCs) catalyze reactions of chlorine compounds that “activate” otherwise inert chlorine reservoirs, leading to severe ozone depletions in the southern polar stratosphere during austral spring. PSCs also modify the composition of the polar stratosphere through complex physicochemical processes, including dehydration and denitrification. The sulfate aerosol layer can reflect solar radiation and increase the planetary albedo, thereby cooling the surface and altering the climate. Major volcanic eruptions, which enhance the stratospheric sulfate aerosol burden by a factor of 100 or more, may cause significant global climatic anomalies. Sulfate aerosols also appear capable of activating stratospheric chlorine reservoirs on a global scale. Accordingly, if atmospheric concentrations of chlorine (associated with anthropogenic use of chlorocarbons) increase by a factor of two or more in future decades, significant worldwide ozone depletions could occur.

View full abstract

An approach to using three-dimensional (3D) models to simulate realistic ozone variability is described. The technique represents planetary and tropospheric cyclonic scales accurately. Therefore, it is possible to define the origins of the dynamical variability of ozone. Then smaller effects, such as solar variability, can be evaluated against this realistic dynamical background.

View full abstract

Out of the various radiative, chemical-photochemical and dynamical processes, the global scale dynamical motions are distinctly different in the equatorial middle atmosphere compared to those at other latitudes. The quasi-biennial oscillation (QBO) and the semiannual oscillation (SAO) of the zonal wind are two dominant components of wind field in the equatorial middle atmosphere. Both are dynamically driven through momentum deposition by dissipating planetary waves originating in the troposphere and propagating into the middle atmosphere. These oscillations constitute outstanding examples of the forcing from “below” and of the coupling between the tropical-extratropical latitudes.
In spite of good theoretical models and hypotheses, our quantitative knowledge of the wave amplitudes, their height and spatial distributions, and their variabilities in the equatorial middle atmosphere is very meagre. Such knowledge is vital for a definitive understanding of several basic processes such as the interactions between the tropical and extratropical latitudes, the waves driving the QBO and SAO, the dynamical effects on the radiatively driven annual oscillation (AO), the mechanism(s) underlying the QBO phase-dependent solar cycle variation of the high latitude winter temperatures and the generation of “turbulence” through breaking. The extreme paucity of data on the dynamics of the equatorial mesosphere and lower thermosphere is a major constraint which will hopefully overcome in the near future with the help of MST/MF radars.

View full abstract

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.

View full abstract

The available data allow a description of the decadal oscillation for at most four periods. It is well correlated with the 11-year solar cycle. In the lower stratosphere the correlation pattern is the same through the year: Positive correlations in middle and low latitudes with the larger values over the oceanic, western half of the hemisphere. In winter this pattern is weak. When the winter data are divided according to the phase of the Quasi-Biennial Oscillation in the equatorial stratosphere, the correlation pattern in the east years is similar to that found during the rest of the year. It is, however, of the opposite sign in the west years, which is due to the tendency for major midwinter warmings of the polar vortex in west years to occur at maxima in the 11-year solar cycle.
Because of the marked decadal oscillation in the lower stratosphere one needs several decades to ascertain if long term trends exist in the regions where the oscillation dominates the interannual variability.

View full abstract

The statistical testing of a relationship between the 11-year solar cycle and the climate over extensive areas of the globe requires allowances for (1) the mutually corresponding temporal autocorrelations of the two variables (i. e., the solar flux has a strong autocorrelation associated with its 11-year cycle, and any variable that is well correlated the flux probably does also), and (2) the spatial correlation among neighboring grid points of the field variables. Both factors reduce the degrees of freedom in the time-space system and increase the likelihood of chance occurrences of high amplitude correlation patterns. One effective testing approach is the Monte Carlo technique, where a no-effect background distribution of the correlation field is generated by randomly shuffling an appropriate parameter.
When this procedure is applied to the field of correlation between the solar flux and the Northern Hemisphere 700mb height over the 1951-90 period, significant results are found for the January-February period if the years are stratified by the phase of the stratospheric QBO. The east QBO phase currently yields stronger results.

View full abstract

Detailed studies of a wave-2 stratospheric warming simulated by a general circulation model of the middle atmosphere are presented. The December-January warming is preceded by increases in both wave-1 and wave-2 amplitudes several days prior to the warming. The warming peaks with a maximum in wave-2 amplitude, wave propagation towards the pole as shown by E-P flux vectors and increased E-P flux convergence.
Forcing the tropical winds to correspond to the QBO patterns significantly alter the warming event. The warming is strengthened during the easterly phase of the QBO and weakened during the westerly phase. For the upper stratospheric warming of this study, the important factor seems to be the presence of easterlies near the equator around 40km altitude, but the mechanism by which the equatorial winds influence the stratospheric warming is not clear.

View full abstract

The dynamical response of the middle atmosphere to weak perturbations induced at stratopause heights is studied. Simulation experiments have been carried out using a global 3-d numerical model of the middle atmosphere. The goal of the study is a better understanding of the physical mechanisms leading to significant correlations between oscillations in the lower and middle stratosphere and solar variability associated with the sun's rotation. Beside the definition of the initial conditions and of the structure of the forcing function there is evidence that stationary and transient planetary waves play an essential role for the development of the response signal.

View full abstract

For the radiosonde station De But, The Netherlands, it is found that after solar proton events temperatures increase in the troposphere and decrease in the lower stratosphere, being indicative of an anticyclonic tendency. This tendency turns out to be strongest for events occurring during the East phase of the QBO.
This result is consistent with the association between the 11-year solar cycle, the QBO and the lower atmosphere over Europe, as recently published by Labitzke and VAN LOON. It is likely therefore that the long-term association consists of the cumulative effect of a number of individual solar events, which are more frequent during the maximum of the 11-year cycle. This may help to find the physical mechanism (s) at work in the solar-climate relationship. The possibility of solar induced thermal effects at tropopause level is suggested in the paper.

View full abstract

Among possible external forcing agents for tropospheric response to solar variability, the variation of MeV-GeV particle fluxes, resulting in changes in stratosphere-troposphere ionization and electric fields, is a plausible candidate. The MeV-GeV particle hypothesis fits reported correlations of geopotential heights, temperatures and vorticity area index (VAT) on the one hand with solar proton events, high-speed solar wind plasma streams, magnetic storms and Forbush decreases of galactic cosmic rays on the other hand. Both solar wind magnetic structures and changes in the terrestrial magnetosphere modulate the incoming particle fluxes. The day-to-day correlations are strongest in winter.
Mechanisms linking MeV-GeV flux changes with tropospheric changes are speculative. Among a number of processes to be investigated, one not previously considered involves the electrofreezing of supercooled water droplets in high clouds of cyclones; their growth by the Wegener-Bergeron instability; sedimentation to lower level supercooled clouds where they enhance freezing and latent heat release; the intensification of convection; and in warm core winter cyclones the extraction of energy from the baroclinic instability to further intensify the cyclone; leading to changes in the general circulation. On a longer time scale changes in water/ice ratio in cirrus may lead to changes in cloud radiative forcing and also to changes in the general circulation.

View full abstract

The effect of variable solar activity (on the 11-year solar cycle time scale) on surface temperature at Toronto has been evaluated for three recent decades. For this data segment, it is highly probable that variable solar activity did influence climate and that the effects for the three decades were often significantly different. These inter-decade differences in solar effects were not random, but were organized in a coherent pattern in time. This pattern was substantially independent of season, climate parameter or statistical test, although there were major seasonal variations in the relative magnitude of modulated solar effects compared to unmodulated solar effects. The inter-decade variability had a maximum in spring and a minimum in autumn; on the other hand, the net effects of solar variability (ignoring interdecade variations) were weakest in spring and strongest in autumn.

View full abstract

Long-term (decades to centuries) variations in the surface temperature of the earth may have been caused, at least in part, by variations in the sun's total irradiance (the solar “constant”). The observed similarity between the envelope of the 11-year solar-activity cycle and a time series of globally averaged sea-surface temperatures over the past 130 years lends some credibility to this possibility, and suggests that long-term variations in irradiance may accompany the long-term variations in solar activity. This connection has been explored with the aid of a one-dimensional model of the thermal response of the global ocean to variations in surface heating, and the inferred relationship has been extended backward in time to deduce a total irradiance at the time of the Maunder Minimum of solar activity about 1% less than the present value. The underlying cause for a connection between solar activity and luminosity on long time scales is unknown, and presents a major challenge for solar physics.

View full abstract

The inventory of atmospheric radiocarbon exhibits quasi-periodic variations over its entire 9000 year record with major periods at Λ_m-=200 and Λ_c-2300 years. Both periods are inconstant and subject to random variability (For the 200 year period the large standard deviation, σ_m^1/2-129 years, relative to the mean suggests a significant noise contribution to this period). This -200 year period marks maxima in the radiocarbon inventory and suggests a correspondence with an extension of the Maunder minimum throughout the Holocene and suggests resolution of the long-standing issue of Maunder cyclicity. The radiocarbon maxima are amplitude modulated by the -2300 year period and thus vary significantly in peak value. Detection of a Maunder-like sequence of minima in tree ring growth of Bristlecone pine and its correlation with the Maunder-like cyclicity in the radiocarbon record supports the inference that solar forcing of the radiocarbon record is accompanied by a corresponding forcing of growth of timberline Bristlecone pine. Because of the quasi-random character of the Maunder period, prediction of climate if tied to the Maunder cycle, other than probabilistically, is significantly hindered. The probability appears to be about 67% that a given climatic maximum lies anywhere between 80 and 338 years.

View full abstract

Previous measurements of the heights of radio meteors using VHF radars have distributions peaking at around 95km with few meteors detected above 105km. Using HF radars (frequencies 2 and 6MHz) near Adelaide, South Australia, we have now shown that there are many more meteors than previously believed ablating at above 100km, with the peak being at 110-120km, and meteors being detected to at least 140km. The gross difference from VHF measurements, as typified by our own observations at 54MHz, is because the higher frequencies are severely biased by the so-called “echo ceiling” effect. The HF height distributions have been confirmed by co-workers using the Jindalee over-the-horizon radar in central Australia, which operates at frequencies of 6-30MHz. These results have implications for a number of different areas of atmospheric research; for example the existence of metallic ions at altitudes of 140km and above, since ablation is apparently occurring much higher than was previously thought to be the case.

View full abstract

Electrical currents and fields in fair weather near the surface of the earth are part of a global circuit. Thunderstorms are the main source generators. The classical model of a global circuit assumes an equipotential layer at high altitude to act as the connecting link between thunderstorms and fair weather areas. Recently, evidence is mounting that extraterrestrial sources of currents and ionization do modulate the global circuit to a measurable degree. Electric fields at the surface and at balloon altitude correlate at times with geomagnetic activity or solar flares. Problems associated with detecting such modulations are inadequate measurement techniques, local space charge noise, and the need to maintain widely spaced observation stations with good time synchronization. Newer modeling efforts have included non-isotropic current flows along magnetic field lines and thus opened the global circuit to the study of influences from extraterrestrial sources. An international project on Global Atmospheric Electricity Measurements (GAEM) has been defined. Measurements will focus on synchronized measurements of electric field and Maxwell current densities in the time domain of seconds to hours and their correlation to solar variability.

View full abstract

Solar EUV irradiance plays a fundamental role in shaping the structure of the thermosphere and the ionosphere. Radiometric observations in this spectral domain are lacking since 1980. New models have been developed based upon the Solar Mesosphere Explorer (SME) Lyman alpha measurements during the declining phase of cycle 21 and the rising phase of the current cycle. This paper will review the recent results obtained in EUV irradiance studies, including solar EUV modeling, for wavelengths from the FUV H Lyman-alpha line at 121.6nm down to the X-rays.

View full abstract

Recent measurements of the relative temporal variations of solar UV radiation are reviewed. The long-term increase in solar UV irradiance during the rise of solar cycle 22 through April 1990 is comparable to the decrease from the solar cycle 21 peak in late 1981 to the 1986 minimum. Although several marked differences occur in the short-term or solar-rotational variations of the UV and Ottawa 10.7cm radio flux (F10), the shape of the long-term solar-cycle increase of F10 is quite similar to that of UV enhancements.

View full abstract

Synoptic, long-term observational programmes provide a wide diversity of information on the solar-terrestrial environment. Such data sets are particularly valuable in certain locations, on the ground, or in space. Further, such data sets are necessary for identifying the baseline from which anthropogenic changes may occur, for characterising transient events, for placing the results of short-term experiments in context, and also for carrying out statistical analyses. Results for all of these four examples can be interpreted according to present understanding of the physics of solar-terrestrial phenomena. Inadequacies are identified and understanding is thereby improved. New hypotheses are put forward and tested; new modelling schemes and new observational techniques are devised.
Some examples are presented, dealing with different physical parameters of solar, interplanetary, magnetospheric, ionospheric, thermospheric and geomagnetic phenomena. Considerations of mass, momentum and energy transfer across the magnetopause, and of energy dissipation in the polar, auroral and midlatitude upper atmosphere are emphasised, on time scales ranging from a few minutes to a century. Such studies are essential for the success of the Solar Terrestrial Energy Programme, STEP, the research aspects of which are underpinned by synoptic programmes. They will open the door to more successful predictions of the solar-terrestrial environment, an ever-developing requirement for mankind at the end of the twentieth century.

View full abstract

The cosmic radiation that reaches the earth is inversely correlated with solar activity as represented by the sunspot number. Thus one of the longest solar-terrestrial data records (solar data) has been combined with one of the shortest data records (cosmic radiation) to learn more about the cosmic radiation that reaches the earth's environment. A brief summary of solar and cosmic radiation data records and several interesting scientific results that have been found with these data are presented.

View full abstract

Near-Earth and deep space sources of in situ solar wind magnetic field and plasma data are reviewed, as well as the public accessibility of such data. Then the 1963-1989 multi-source hourly resolution compilation of near-Earth field and plasma parameters (the “?OMNItape”) is discussed. Finally, the variations in selected solar wind parameters over 2.5 solar cycles are presented and discussed. Variabilities among solar cycles are stressed. North-south asymmetries in the apparent rotation rate of the source of the solar wind and divergence of the solar wind flow away from the heliospheric current sheet are highlighted.

View full abstract

The magnetic fields of the Earth, the planets and the sun, provide a basis for the basic structure of our solar system. The geomagnetic field has been explored and measured for centuries, and it is known that it experiences major changes on time scales ranging from seconds to millions of years. These changes are associated with the internal source of the geomagnetic field, which is not completely understood. Measurements conducted by spacecraft during the last few decades, have explored the geomagnetic field and revealed details about both internal and external sources. The external sources are associated with the complex system of currents that flows in the “comet-like” configuration of the distant geomagnetic field called the magnetosphere, which is produced by the solar wind. The magnetic fields due to the external sources can vary with time scales from a few seconds to several years, related to solar cycle activity. The study of these phenomena span scientific disciplines extending from the geophysics of the Earth's core to solar and space plasma physics. A crucial element of this study is the continuous and accurate monitoring of the geomagnetic field and the appropriate means to archive this important data set.

View full abstract

The balloon measurements of the ionizing radiation have been performed at several locations of the USSR and in the Antarctic every day for more than 30 years. A number of latitude surveys were also accomplished. The methods and data presentation are described.

View full abstract

A short chronicle of data collection in the ionosphere, thermosphere and atmosphere is given, highlighting the different measurement techniques and their effect on the overall data volume. Several data sources and their uses are discussed in greater detail, including the data obtained by the worldwide ionosonde network, by the incoherent scatter radars, by the Alouette and ISIS topside sounders, and by the Atmosphere Explorer satellite. The need for continuous monitoring from ground and space is stressed, as well as the need for preservation of older data records and their full scientific exploitation.

View full abstract

Solar-Terrestrial Physics (STP) programs involving global data acquisition have characterized international science in the 20th Century and made necessary the creation of a system of national and international data centers. Under aegis of the International Council of Scientific Unions, the World Data Center (WDC) system was established in 1957 to provide a voluntary mechanism for the collection, copying, exchange, and dissemination of geophysical and solar data taken by International Geophysical Year projects. At first, WDCs collected mainly analog data recorded by monitoring arrays of IGY instruments. In the three decades since IGY, techniques shifted from mainly analog recording to digital, and data centers shifted from mainly servicing analog images on film and publishing summary tables to providing numerical data on digital media for computer analysis.
In the 1960s, WDCs began to provide collection and dissemination of information and derived data products as well as original data. During the late 1970s, merged multi-component data sets were created on central host computers to support joint analysis projects by groups of scientists and individuals. A major trend in the late 1980's is acquisition and merger of large digital data sets from ground-based and satellite sensors. The data are made available on high density computer media (particularly CD-ROM optical discs) together with summary analog images and access software for browsing or moving data from the storage media to other computers. Tables and images are still published in the 1990s and are especially needed in places with limited access to personal computers and lacking easy connections to on-line central data collections.
The cumulative amount of STP data held by WDC-A has grown substantially since 1957. However, each year since the early 1960s has shown a decline in the global coverage of key types of data as monitoring networks diminished. The rise in cost to process large digital databases produced by modern instruments and the high cost of labor-intensive analog data reduction has contributed to the annual decline of some types of data deposited with the WDCs. Finally, there is a situation that is difficult to quantify; namely, some key geophysical observing sites are located in countries that seldom use their output. During periods of economic stress these facilities receive low priority for continued operation. Under current world conditions, it is difficult for some nations to justify the continued expense to continue operating basic monitoring sites, e.g., magnetic observatories, ionosondes, and other instruments that produce essential records needed as input for general models, planetary indices, or other often-used, basic global data products.

View full abstract

The World Data Centre system was created at the time of the International Geophysical Year (1957-8) to collect, archive and distribute many kinds of geophysical and solar data. Since then, the World Data Centre system has served many international programmes and has broadened into new areas. Today there are about forty World Data Centres to serve the science of the 1990s, notably the Solar-Terrestrial Energy Programme and the International Geosphere-Biosphere Programme. This paper describes the WDC system, primarily from the viewpoint of solar-terrestrial physics.

View full abstract