Geomagnetic Spectra Research Articles

Solar and Geomagnetic Activity Effects on Global Surface Temperatures

It is a clear fact that the Earth's climate has been changing since the pre-industrial era, especially during the last three decades. This change is generally attributed to two main factors: greenhouse gases (GHGs) and solar activ ity changes. However, these factors are not all-independent. Furthermore, contributions of the above-mentioned factors are still d isputed. The aim of th is paper is relation in the longer t ime (1880-2011), between changer of g lobal surface temperature (GST), and solar geomagnetic activ ist represented by sunspot number (Rz) and geomagnetic indices (aa , Kp ), and to what degree they are connected. The geomagnetics aa are more effect ive on global surface temperature than solar activity. Furthermore, the global surface temperature are strongly sensitive to the 21.3-yr, 10.6-yr, and 5.3-yr variations that observed in the considered geomagnetic and sunspot spectra. The present changes in aa geo magnetics may reflect part ially some future changes in the global surface temperatures.

Spectral Analysis of Solar Variability and their Possible Role on the Global Warming

Our understanding of the indirect effect of changes in solar output and feedbacks in the climate system is minimal. There is much need to refine our understanding of key natural forcing mechanisms of the climate, including solar irra-diance changes, in order to reduce uncertainty in our projections of future climate change. Through the recent years, the conflict between researchers about whether global warming is a human-generated phenomenon or a result of solar variability has raised many question marks. The aim of this work is to try to answer some of these questions by studying the possible role of some solar variability parameters such as the geomagnetic index (aa) and the sunspot number (Rz) in global temperature changes. Here, we present a correlative study of the possible contributions for the two components that may be closely associated with the climate, throughout the last 130 years (1880-2008). We compared the correlation analysis and the power spectral density (PSD) of the Rz and aa with that of the continuous records of the GT in order to get a closer look at a possible connection between them. Our results displayed that the correlations between both (aa & GST) and (Rz & GST) are +0.66 and +0.38, respectively when both parameters Rz and aa precedes by 2-3 yrs. The correlation of GST-aa is two times higher than that of GST-Rz. The GST spectrum reflected significant periods at 21.3-yr, 10.7-11.6 yr variations that observed in the considered geomagnetic and sunspot spectra.

Induction in a transatlantic cable at periods between 20 minutes and one day

Power spectral anaylses are presented of the voltage fluctuations in a transatlantic cable on two days of moderate geomagnetic activity and four days of magnetic quiet. The voltage fluctuations with periods from about twenty minutes to a day are predominantly of geomagnetically‐induced origin, with similar peaks often found in the geomagnetic and voltage spectra. The voltage spectral power Sv at a given frequency f can be expressed in terms of the horizontal field spectral power SH as βSHfγ.

The power spectrum of the solar wind speed for periods greater than 10 days

The Los Alamos Scientific Laboratory experiments on the Vela 2‐6 and Imp 6‐8 satellites have provided more than 11 years of solar wind speed data. The length of this data set provides sufficient frequency resolution to study in detail the power spectrum of speed variations in the range near the solar rotational frequency. Year‐by‐year power spectra show such large differences that the solar wind time series is probably nonstationary. The spectrum of the entire 11‐year time series shows broad bands of power near periods of 27 days (corresponding to the rotational period of the sun), 13.5 days, and higher harmonics. The band of power near 27 days extends from about 25 to about 31.5 days and contains a number of sharply defined peaks. Similar groups of peaks near a period of 27 days in a highly correlated time series, the geomagnetic index aa, have been explained as a solar latitude effect caused by differential rotation. However, recent observations indicate that the source regions of the solar wind during this last solar cycle did not participate in differential rotation; that is, there was a preferred range of longitudes for the sources. We suggest that the individual peaks in both the solar wind and the geomagnetic spectra are probably not due to differential rotation, although the band of power near 27 days almost certainly reflects solar rotation. Rather, the multipeak nature of the power spectra can be explained by a wave packet concept in which recurring high‐speed streams are described as a series of pulses (separated by a constant period) that last for a varying number of solar rotations. Subsequent wave packets have the same period but are shifted in phase to mimic the range of possible longitudes for sources of solar wind streams. Power spectra obtained for such idealized wave packets closely resemble the measured spectra of the solar wind speed and geomagnetic activity. We do not find the frequencies predicted by a theory concerning the nonradial oscillation of the sun.

High resolution geomagnetic spectra in Indian region: Lunar tides

A search for major and minor lunar geomagnetic tides in the Indian region is made from high resolution power spectra, obtained by the Maximum Entropy Method (MEM), at two low latitude stations. The results indicate, on the basis of frequency comparison, that only near the dip equator is there clear evidence for the lunar tidal mechanism being the dominant factor over the amplitude modulation mechanism. Amplitudes of the lunar terms near 1 and 2 c day −1 show equatorial enhancement with greater enhancement for the semidiurnal terms. The lunar semidiurnal term, M 2, shows the largest enhancement.

Interactive computing and graphics in the interpretation of geomagnetic spectra

Transformations of spectral estimates of sampled geomagnetic data have been developed to facilitate the analyses of digitally recorded signals. Exploratory data analysis is performed by visual inspection of multi-dimensional displays created on graphic recording devices and the storage tube of a graphics terminal. Programs allow the on-line user of a large computer both to process and to view graphs of selected data after various transformations. Simple keyboard commands executed by interactive programs expedite the selection and examination of transformed data. Systematic patterns, discerned on the CRT display, are permanently recorded by an attached hard-copy graphic unit on a photographic print. Useful graphic techniques developed include 3-D isometric plots, histograms and multiple function displays. To utilize fully the interactive graphical analysis capabilities, a number of signal selection and transformation programs have been implemented. These include a post-whitening transform applied to geomagnetic spectra spanning the ⋍0.3–⋍63-mHz band and a number of smoothing and non-linear amplitude normalization transforms for facilitating visual comparisons of the morphology of signal estimators viewed as functions of time and frequency. The main results are programs implementing computer techniques for organizing, processing and transforming geomagnetic spectra.

ULF geomagnetic power nearL=4, 4. Relationship to the FredericksburgKindex

The total power and slope of 2-hour nonoverlapping H component geomagnetic power spectra obtained during a 12-day period in January 1972 are statistically related at corresponding times to the K indices determined at the longitude of the stations and the global Dst indices. Although the power level increases and the spectral slope steepens with more positive K and more negative Dst values, there is no one-to-one relationship between the spectral parameters (power and best-fit slope) and the geomagnetic indices. Thus it is not readily possible to accurately predict the latitudinal distribution of geomagnetic power from a given value of the K index. It is proposed that the introduction of geophysical indices based upon geomagnetic power levels should eventually provide more physical insight into geomagnetic disturbance phenomena.

The relationship between geomagnetic variations and the circulation at 100 mb

Statistical methods are used to study the relationship, over a five-year period, between geomagnetic storms and the height gradients of the 100-mb surface over the United States. In the case of the superposed epoch analysis, the parameters studied were variations from population values of the mean height gradients and the standard deviation of the height gradients for the period 5 days before to 15 days following the geomagnetic storm. No pattern was found in the tested statistical significance at the 5 per cent and 1 per cent levels. The geomagnetic and height gradient spectra were constructed from the two time series and the coherency between the two series was computed. The coherency was found to be very small for all periods from 4 to 60 days. The conclusion is drawn that there is no obvious relationship between the two sets of data.