Artificial neural networks (ANNs) constitute a class of flexible nonlinear models designed to mimic biological neural systems. In this entry, we introduce ANN using familiar econometric terminology and provide an overview of ANN modeling approach and its implementation methods. † Correspondence: Chung-Ming Kuan, Institute of Economics, Academia Sinica, 128 Academia Road, Sec. 2, Taipei 115, Taiwan; ckuan@econ.sinica.edu.tw. †† I would like to express my sincere gratitude to the editor, Professor Steven Durlauf, for his patience and constructive comments on early drafts of this entry. I also thank Shih-Hsun Hsu and Yu-Lieh Huang for very helpful suggestions. The remaining errors are all mine.

Artificial neural networks

A comparison of methods to avoid overfitting in neural networks training in the case of catchment runoff modelling

A statistical point-process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences. The parameters are estimated ty the maximum likelihood method. Using the estimated model, the “residual point process” of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity. For instance, seismic quiescences can be measured quantitatively by using the residual process. Some examples are provided to illustrate such analyses. Furthermore, a time series of the magnitudes on the residual point process is considered, to investigate its dependence either on the time or on the history of the seismicity. By assuming the exponential distribution at each time and modelling of the b- value , we can examine such dependences and estimate them. Two practical examples are shown.

Statistical model for standard seismicity and detection of anomalies by residual analysis

Optimizing neural networks for river flow forecasting – Evolutionary Computation methods versus the Levenberg–Marquardt approach

Lightning produces electromagnetic fields and waves in all frequency ranges. In the extremely low frequency (ELF) range below 100 Hz, the global Schumann Resonances (SR) are excited at frequencies of 8 Hz, 14 Hz, 20 Hz, etc. This review is aimed at the reader generally unfamiliar with the Schumann Resonances. First some historical context to SR research is given, followed by some theoretical background and examples of the extensive use of Schumann resonances in a variety of lightning-related studies in recent years, ranging from estimates of the spatial and temporal variations in global lighting activity, connections to global climate change, transient luminous events and extraterrestrial lightning. Both theoretical and experimental results of the global resonance phenomenon are presented. It is our hope that this review will increase the interest in SR among researchers previously unfamiliar with this phenomenon.

https://www.mdpi.com/2073-4433/7/9/116/pdf

ELF Electromagnetic Waves from Lightning: The Schumann Resonances

Enhanced tropical convection is associated with increased upper-tropospheric relative humidity. The positive co-relationship between deep convection and upper-tropospheric humidity is observed for both regional and temporal variations over a wide range of space and time scales. The regions of increased upper-tropospheric moisture are found to be strongly correlated with an enhanced greenhouse trapping, although the effects of lower-tropospheric moisture and temperature lapse rate are also observed to be important. The greenhouse effect of water vapour increases sharply when temperature increases, leading to a positive feed back for climate change. Upper-tropospheric water-vapour (UTWV) variability and global lightning activity are closely linked suggesting that upper-tropospheric water-vapour changes can be inferred from the records of global lightning activity. The continental deep-convective thunderstorms could transport large amount of water vapour into the upper troposphere, which would dominate the variations of global UTWV while producing most of the lightning on Earth. Global lightning produces Schumann resonance modes, which are trapped in the Earth-ionospheric waveguide. As there are approximately 50–100 lightning flashes per second around the globe, the variability of the intensity of the Schumann resonances represents a continuous measure of the variability of global lightning activity which is dependent on UTWV. Thus monitoring of SR would provide a tool for time-tracking UTWV changes which will contribute to a better understanding of the processes affecting climate change. The correlation between troposheric water content and Schumann Resonance field can be explored using data of several years, which is still lacking to the world researchers. From the observed nature of correlation of time series data, a model will be built which will be made useful to forecast the water vapour content from the observed value of Schumann Resonance data. Climatic condition would be forecasted using SR data with the sequence below: SR data ⇒ Water vapour content ⇒ climate forecasting

/pdf/schumann-resonance-a-latest-wonder-for-climate-forecast-uet01d1hh1.pdf

Schumann resonance: A latest wonder for climate forecast!

Some experiments on June 8, 2004, the day of transit of Venus across the Sun, were undertaken at Kolkata (latitude:
22°34lN) to observe the effect, if any, of transit of Venus on FWF, ELF and VLF amplitudes. The result
shows a good correlation between their temporal variations during the transit. The observation was unbelievable
as the Venus subtends only 1/32th of the cone subtended by Sun on Earth. This anomaly may be explained on
the assumption that the height of Venusian atmosphere with high content of CO2, and nitrogen which absorbs
electromagnetic and corpuscular radiations from Sun, depleting the solar radiation reaching the Earth to a considerable
extent. As a result, relevant parameters of Earths atmosphere are modulated and here we show how
these changes are reflected in identical behaviour of fair weather field and ELF and VLF spectra.

/pdf/the-effect-of-recent-venus-transit-on-earths-atmosphere-qokuowx8qh.pdf

The effect of recent Venus transit on Earths atmosphere

The effect of solar eclipse of July 22, 2009, obscuring up to 91 %, upon the value of point discharge current (PDC) has been reported in this paper. The observation had been taken from Kolkata (Lat. 22.56°N, Long. 88.5°E). During the eclipse period, significant variations in the magnitude of PDC were observed than their average value for the same period in other days. The average value of the PDC for the successive ±10 days adjacent to the solar eclipse day was about 2.253 A.U. (Arbitrary Unit), while the minimum value showed about 2.242 A.U. at the time of greatest phase at 06:26.4 IST (Indian Standard Time). The results are mainly interpreted in terms of changes of the conductivity of the medium during the solar eclipse.

Point Discharge Current During a Solar Eclipse

On May 25, 2009, remarkable effects on the recording on VLF sferics over Kolkata (latitude: 22.56° N, longitude: 88.5° E) at 3 kHz and 9 kHz are observed due to severe cyclonic storm, AILA, followed by severe thundershowers and lightning. The results and analyses of the recorded data along with other characteristics will be presented in this paper.

http://ieeexplore.ieee.org/iel5/5398767/5407062/05407108.pdf

AILA-2009 and its Effects on VLF sferics

Field solutions for a dipole in an anisotropic plasma medium are obtained in the presence of an infinitesimally small electric current source and time-varying irregularities through the use of inverse Fourier-transform technique. The derived solutions can be utilized for the evaluation of the field at an arbitrary distance and are also useful to lossy medium.

Syam Sundar De

Papers

Schumann resonance: A latest wonder for climate forecast!

The effect of recent Venus transit on Earths atmosphere

Point Discharge Current During a Solar Eclipse

AILA-2009 and its Effects on VLF sferics

Field solution for a dipole in an anisotropic medium containing time-varying irregularities