foF2 hysteresis variations and the semi-annual geomagnetic wave

Seasonal and solar cycle variations of the foF2 hysteresis magnitude are investigated. Data for the noon foF2 monthly medians for Slough (51.48°N, 0.57°W), the monthly means for the sunspot numbers, and for the geomagnetic activity index aa(N) for the northern hemisphere for the period 1933–1986, covering solar cycle from 17 to 21, are used. It is found that: (1) the greatest negative amplitudes of the foF2 hysteresis variation are near the equinoxes, and (2) the solar cycle average noon foF2 hysteresis magnitude is linearly correlated with the solar cycle average semi-annual geomagnetic amplitude of the aa-index. These results support the hypothesis that the foF2 hysteresis is due to the geomagnetic activity variation during the sunspot cycle.     

A search for a solar cycle-temperature relationship in the middle atmosphere over Volgograd

The variation of temperature in the middle atmosphere (15–80 km) at Volgograd (49°N, 44°E) during an 11-year solar cycle (1971–1982) has been studied. The temperature of the stratosphere did not show any significant influence of the sunspot cycle, but the temperatures of the mesosphere showed a strong in-phase relationship with the solar cycle. Computed correlation and regression coefficients were positive and highly significant in this region. At 60 and 70km the temperature variations were almost linearly related to the sunspot number. Seasonal studies indicated that solar activity has a much stronger influence on temperature during the winter than during the summer.     

Solar cycle variation of the total electron content around equatorial anomaly crest region in east asia

The monthly mean hourly values of total electron content data obtained at Lunping Observatory (geographic coordinates 25.00°N, 121.17°E; geomagnetic coordinates 14.3°N, 191.3°E) by using the ETS2 satellite beacon signal during the period from March 1977 to December 1990 have been used to analyze the solar cycle variations of total electron content (TEC) around equatorial anomaly crest region in East Asia. Positive, correlations were found between the 12 month running average of monthly mean TECs and sunspot numbers. By using the linear regression analysis method, the contour charts for real diurnal and seasonal variations of TEC at certain sunspot numbers were constructed and described. The diurnal variation of TEC was represented by the sum of its diurnal mean and first three harmonic components. The solar cycle variations of these components have also been discussed.     

Variability of the solar cycle length during the past five centuries and the apparent association with terrestrial climate

Solar data have been used as parameters in a great number of studies concerning variations of the physical conditions in the Earth's upper atmosphere. The varying solar activity is distinctly represented by the 11-yr cycle in the number of sunspots. The length of this sunspot period is not fixed. Actually, it varies with a period of 80–90 yr. Recently, this variation has been found to be strongly correlated with long-term variations in the global temperature. Information about northernhemisphere temperature based on proxy data is available back to the second half of the sixteenth century. Systematic monitoring of solar data did not take place prior to 1750. Therefore, a critical assessment of existing and proxy solar data prior to 1750 is reported and tables of epochs of sunspot minima as well as sunspot cycle lengths covering the interval 1500–1990 are presented. The tabulated cycle lengths are compared with reconstructed and instrumental temperature series through four centuries. The correlation between solar activity and northern hemisphere land surface temperature is confirmed.     

Observations of random and quasi-periodic scintillations at southern mid-latitudes over a solar cycle

An extended period (1973–1985) of recording of random and Fresnel type quasi-periodic (QP) scintillations in southern mid-latitudes, using satellite beacon transmissions at a frequency of 150 MHz, has provided some new information on the morphology of scintillation-producing irregularities.It has become evident that a pronounced daytime increase of the random type of scintillations in the southern winter (at 1200–1600 LT) occurs throughout the solar cycle and becomes a distinct daytime maximum during the years of sunspot minimum. Scintillations are most intense in the pre-midnight period in the southern summer (2000–2400 LT). There is a gradual decline in scintillation activity by about 40% from the period of sunspot maximum to the period of sunspot minimum. It appears that a specific type of sporadic-E, so-called constant height Es (Esc), is responsible for daytime scintillation activity in winter. Night-time scintillations are strongly correlated with the presence of the range-spread type of spread-F, but not so with the frequency-spread type.There are two peaks in the occurrence of QP scintillations, predominantly in the southern summer: in the late morning (0800–1000 LT) and in the pre-midnight period (2000–2200 LT). The daytime QP scintillations occur mainly polewards of the station, whereas the night-time scintillations are recorded predominantly equatorwards. There is a distinct increase in the occurrence number of QP scintillations with a decrease in the sunspot number.     

Rome rainfall and sunspot numbers

The accumulated departure from mean (ADM) of the 208 yr Rome rainfall strongly inversely resembles the ADM of sunspot numbers. The ADM for the Bay of Biscay sea surface temperature also strongly resembles sunspot numbers and Rome rainfall. These data suggest that long-term increasing solar radiation warms parts of the North Atlantic Ocean, which in turn affects the fall and winter storm paths resulting in lower rainfall in Rome and conversely, decreasing solar radiation produces the opposite effect. The accumulated departure from mean (ADM) plotting method is used to compare different records of the same length.     

Learning in Single Hidden-Layer Feedforward Network Models: Backpropagation in a Spatial Interaction Modeling Context

Learning in neural networks has attracted considerable interest in recent years. Our focus is on learning in single hidden-layer feedforward networks which is posed as a search in the network parameter space for a network that minimizes an additive error function of statistically independent examples. We review first the class of single hidden-layer feedforward networks and characterize the learning process in such networks from a statistical point of view. Then we describe the backpropagation procedure, the leading case of gradient descent learning algorithms for the class of networks considered here, as well as an efficient heuristic modification. Finally, we analyze the applicability of these learning methods to the problem of predicting interregional telecommunication flows. Particular emphasis is laid on the engineering judgment, first, in choosing appropriate values for the tunable parameters, second, on the decision whether to train the network by epoch or by pattern (random approximation), and, third, on the overfitting problem. In addition, the analysis shows that the neural network model whether using either epoch-based or pattern-based stochastic approximation outperforms the classical regression approach to modeling telecommunication flows.     

Solar origin of geomagnetic storms and predictions

Changes of the large-scale solar magnetic fields are described and related to the occurrence of solar coronal phenomena which are associated with geomagnetic storms. Only for the very largest geomagnetic storms is there agreement on the coronal origin. However, when and where coronal mass ejections occur are still very difficult questions to answer. Artificial neural networks have been used to forecast geomagnetic storms either from daily solar input data or from hourly solar wind data. With solar data as input, predictions one-three days or even a month in advance are possible, while using solar wind data as input predictions about an hour in advance are possible. The latter predictions have been very successful. Finally, the effects of geomagnetic storms on power and satellite systems are reviewed.     

Solar activity effects on equatorial plasma bubble zonal velocity and its latitude gradient as measured by airglow scanning photometers

Using a new mode of scanning 630-nm photometer operation the zonal velocities of ionospheric plasma depletions were measured over Cachoeira Paulista in Brasil in two east-west planes tilted 30°N and 30° S with respect to zenith. The measurements cover a time period of approximately 2 years, from January 1988 to January 1990, a period marked by significant increase in solar activity of the ongoing cycle. The results have permitted a rather detailed evaluation of the local time and latitude variations in the zonal plasma bubble velocity as a function of solar activity. Although the mean trend in the velocity local time variation is a decrease from early evening to post-midnight hours, a strong tendency for velocity peaks is observed near 21 LT and midnight. The velocities as well as their height (latitude) gradients show perceivable increases with solar activity represented as sunspot numbers. The present results are compared with the ambient plasma velocities measured using the Jicamarca radar by Fejer el al. (1985), J. Geophys. Res. 90, 12249, with that measured on board the DE 2 satellite on the equatorial latitudes by Coley and Heelis (1989), J. geophys. Res. 94, 6751, and with various theoretical calculations, in an attempt to bring out the salient features of the plasma dynamics of the equatorial ionosphere.     

spread-F ionospheric irregularities and their relationship to stable auroral red arcs at magnetic mid-latitudes

The signature of the stable auroral red arc (SAR arc) as it appears on ionograms is described. The key features are a very significant increase in the amount of spread-F and a reduction in the maximum plasma density compared with regions just equatorward and poleward of the SAR arc Identification of the SAR arc signature is made by using complementary data from the global auroral imaging instrument on board the Dynamics Explorer-1 satellite.At sunspot minimum there is a positive correlation between the occurrence of spread-F on ionograms from Argentine Islands, Antarctica (65°S, 64°W; L = 2.3) and magnetic activity. In contrast, at sunspot maximum there is a weak negative correlation when the K magnetic index is less than 6. but a significant increase in spread-F occurrence at K ⩾ 6. Detailed study of ionograms shows that there are two distinct regions where considerable spread-F is observed. These are the region where SAR arcs occur and the poleward edge of the mid-latitude ionospheric trough. They are separated by a region associated with the trough minimum, where comparatively little spread-F is seen. It is suggested that the movement of these features to lower latitudes with increasing magnetic and solar activity can explain the lack of correspondence between variations of spread-F occurrence as a function of magnetic activity at sunspot maximum compared with that at sunspot minimum at Argentine Islands.     

Solar cycle variation of ƒoF2

For solar cycle 19 (1954–1964), the 12 monthly mean values of noon-time ƒoF2 at Ahmedabad (23°N, 73°E) show a large hysteresis effect when plotted against sunspot number or against geomagnetic Ap. However, a multiple regression analysis for the dependence of ƒoF2 on solar 2800 MHz flux and geomagnetic Ap, simultaneously, shows a better matching. Thus, long-term predictions need to take into account not just sunspot number but some solar index and geomagnetic index as two key parameters, simultaneously.     

Types of ionospheric scintillations in southern mid-latitudes during the last sunspot maximum

A 5-yr study (1987–1992) has been undertaken at a southern mid-latitude station, Brisbane (35.6°S invariant latitude) on scintillation occurrences in radio-satellite transmission (at a frequency of 150 MHz) from polar orbit Transit satellites, within a sub-ionospheric invariant latitude range 20–55°S. Over 7000 recorded passes were used to define the spatial and temporal occurrence pattern of different types of scintillation events. Two predominant scintillation types were found: so-called type P (associated with a scintillation patch close to the magnetic zenith) and type S (characteristic of the equatorward edge of auroral scintillation oval). Type S was by far the most frequent during sunspot maximum (1988–1992), with sharp occurrence peaks in the summer-autumn period. Its seasonal occurrence showed a high degree of correlation (correlation coefficient r = 0.8) with the seasonally averaged 10.7 cm solar radio flux. This type occurred mainly at night-time except in austral summer where 40% of scintillations were detected in daytime, coinciding with the well-known summer peak of sporadic-E occurrence. Type P was more predominant during a year (1987) of ascending sunspot activity but decreased to a much lower level during the sunspot maximum.     

Morphology of the D-region in northern Scandinavia during the campaigns MAC/SINE and MAC/EPSILON in 1987

The morphology of the lower ionosphere was examined by the riometer and ionosonde networks in Scandinavia during the campaigns MAC/SINE and MAC/EPSILON. The campaigns were carried out during 1987 when the solar activity was low. The minimum sunspol number 14 was observed in 1986. The sunspot number was already increasing during the year 1987, while the Ap-value and riometer absorption were still decreasing. During the campaign MAC/SINE the rockets were launched during quiet periods, and during the campaign MAC/EPSILON during more disturbed periods. The variations in ionospheric parameters, ionospheric absorption and foF2 are presented for the campaign periods. Some interesting events are pointed out.     

Three‐Dimensional Neurointerpolation of Annual Mean Precipitation and Temperature Surfaces for China

Climatic variables such as annual mean precipitation and temperature display complex and nonlinear variation with latitude, longitude, and elevation. Neural networks are universal approximators and very good at detecting and representing nonlinear relationships between dependent and independent variables. In this paper we use resilient backpropagation (Rprop) neural networks to interpolate annual mean precipitation and temperature surfaces for China. Climate surfaces are interpolated from a total of 288 long‐term climate station data points using latitude, longitude, and elevation derived from a 5‐kilometer resolution digital elevation model. Initial trials of Rprop suggested very fast learning, insensitivity to selection of learning parameters, and a tendency not to overtrain. Cross‐validation was used to determine the best network structure and assess the error inherent in climate interpolation. With the error explicit, the final neurointerpolations of annual mean precipitation and temperature were constructed using all 288 climate station data points. Maps of residuals are also presented. The neurointerpolation of temperature was very successful and captures most of the regional trends found in established climate maps of China as well as significant topographically defined detail. For annual mean temperature the Rprop neural network was found to be an accurate and robust global spatial interpolator. However, the precipitation surface captures only the major latitudinally and continentally defined trends and misses many subregional rainfall features probably because of the influence of other nonparameterized atmospheric and topographic factors.     

Day-to-day ionospheric variations in a period of high solar activity

In November and December 1979 the solar 10.7 cm radio flux density, sunspot number, X-ray flux and EUV flux were high and very variable. The day-to-day variations of noon F2-layer height and Elayer electron density at three ionosonde stations (Slough, Port Stanley and Huancayo) are found to be well correlated with the day-to-day variations of solar activity. The short-term E- and F-layer variations are consistent with those derived from longer-term studies.     

Simulation of ionospheric currents and geomagnetic field variations of Sq for different solar activity

Variations of ionospheric Sq electric currents and fields caused by changes in electric conductivity due to changes in solar activity are studied using the International Reference Ionosphere (IRI) model. Calculations are made for R (sunspot number) = 35 and 200 on the assumption of constant (1, −2)mode tidal winds. It is shown that electric fields grow when solar activity is high, because the ratio of the conductivity in the F-region to that in the E-region increases. Currents in the F-region become stronger than those in the E-region, and nocturnal currents are not negligible when solar activity becomes high. F-region currents also play an important role in the westward currents on the high latitude side of the current vortex. The calculated geomagneticH component at the equator has a depression around 1600 LT for R = 35, while it decreases smoothly from 1100 LT to 1900 LT for R = 200. This difference is consistent with the observed geomagnetic field variation. The ratio of total Sq currents obtained by our simulation is about 3.5, which is a little larger than is found in the observed results.     

Lunar and solar daily variations of the geomagnetic field at Italian stations

Mean hourly values of magnetic declination D, horizontal intensity H and vertical intensity Z observed at Italian stations have been analyzed to determine solar and luni-solar diurnal components, together with the corresponding terms O₁ and N₂ of the lunar tidal potential.The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. Differences between the dependence of S and L on season and sunspot number are considered and tentative explanations offered. The oceanic tidal effect has been determined and it is apparent that this is more likely to show the influence of the Atlantic Ocean rather than the Mediterranean Sea.     

Faraday polarization fluctuations associated with amplitude scintillations at Lunping

The diurnal, seasonal and solar cycle variations of Faraday polarization fluctuations (FPF) associated with amplitude scintillations observed at Lunping, Taiwan (25.0°N, 121.2°E : geographic) during the period 1978–1981 are presented. The occurrence of polarization fluctuations is maximum in the premidnight hours. FPFs occur either simultaneously or with a time lag after the onset of amplitude scintillations. There is an increase in FPF activity with an increase in sunspot activity. Occurrence of FPF peaks in the equinoxes. There had been a moderate activity in summer while the winter occurrence is a minimum. The seasonal occurrence pattern compared with reports from other locations indicates a longitudinal control on FPF activity. The maximum probable duration of FPF ranges from 15 to 30 min. It was found that the association of FPF with range spread-F is much better than that with frequency spread-F. Large ambient ionization densities corresponding to plasma frequencies greater than 15 MHz appear to create a favourable environment for the occurrence of FPF.     

Do beats affect sun-weather correlations?

Kinget al. (1977) have presented evidence to suggest that variations in the height of the 500 mbar level may be solar induced. Using a superposed epoch analysis they show a high correlation between the 27.5 day variation (frequency 0.0364 day⁻¹) in the sunspot number and the tropospheric pressure using a ten year run of data. It is suggested here that using such an analysis, side bands in the isobaric height variations spaced equally either side of the 0.0364 day⁻¹ component may add to enhance the variation at 0.0364 day⁻¹. That such a situation may occur is confirmed by an analysis of isobaric height data at three Australian locations for the winter of 1973 which shows that the isobaric surfaces do not respond to the solar component, but that frequency components spaced equally either side of the solar components do occur.     

Exploratory Analysis of Similarities in Solar Cycle Magnetic Phases with Southern Oscillation Index Fluctuations in Eastern Australia

There is growing interest in the role that the Sun's magnetic field has on weather and climatic parameters, particularly the ~11 year sunspot (Schwab) cycle, the ~22 yr magnetic field (Hale) cycle and the ~88 yr (Gleissberg) cycle. These cycles and the derivative harmonics are part of the peculiar periodic behaviour of the solar magnetic field. Using data from 1876 to the present, the exploratory analysis suggests that when the Sun's South Pole is positive in the Hale Cycle, the likelihood of strongly positive and negative Southern Oscillation Index (SOI) values increase after certain phases in the cyclic ~22 yr solar magnetic field. The SOI is also shown to track the pairing of sunspot cycles in ~88 yr periods. This coupling of odd cycles, 23–15, 21–13 and 19–11, produces an apparently close charting in positive and negative SOI fluctuations for each grouping. This Gleissberg effect is also apparent for the southern hemisphere rainfall anomaly. Over the last decade, the SOI and rainfall fluctuations have been tracking similar values to that recorded in Cycle 15 (1914–1924). This discovery has important implications for future drought predictions in Australia and in countries in the northern and southern hemispheres which have been shown to be influenced by the sunspot cycle. Further, it provides a benchmark for long‐term SOI behaviour.