Measurement of the stochasticity of low-latitude geomagnetic temporal variations

Abstract

Abstract. Ground magnetometer measurements of total magnetic field strength from 6 stations at low latitudes were analyzed using power spectrum and Hurst range scaling techniques. The Hurst exponents for most of these time-series were near 0.5, which indicates stochasticity, with the highest latitude stations exhibiting some persistence with Hurst exponents greater than 0.6. Although no definite correlations are evident, the relative increase of the Hurst exponent with latitude suggests the possibility that the underlying dynamics of the magnetosphere change with latitude. This result may help quantify the dynamics of the inner magnetosphere itself without the direct presence of the solar wind driver.

Complexity signatures in the geomagnetic <i>H</i> component recorded by the Tromsø magnetometer (70° N, 19° E) over the last quarter of a century

“…Hamid et al (2009) similarly examine data from specific sites. The nature of the data used in this study is somewhat different to that of the data used by Wanliss and Reynolds (2003) and Hamid et al (2009), however. The geomagnetic field is usually (but not exclusively) defined by three components: declination, D ( • ); horizontal, H (nT); and vertical, Z (nT).…”

“…The results weighted towards longer timescale fluctuations, however, exhibit small enough uncertainties that, taken collectively, one can conclude that α is slightly less than 1.5, the significance of which will be discussed forthwith. Other studies of complexity in geomagnetic, or geomagnetically related, time series have either used isolated periods of, for example, months (Wanliss and Reynolds, 2003;Hamid et al, 2009), albeit with a time resolution comparable to that used here, or much longer derived data sets of, for example, the AE index with a different time resolution. Rypdal and Rypdal (2010) studied the AE index on timescales similar to those addressed here.…”

“…One can see, therefore, that calculating D by, for example, the method of Grassberger and Procaccia (1983) can potentially yield H but not unambiguously provide the same information as α. Following the sequence used by Hall (2014), rather than blindly launching into a determination of α which will almost inevitably yield some result, the data are examined first for indications of non-linearity by inspections of the probability density function (PDF) and quantile-quantile (Q-Q) analyses (Wilk and Gnanadesikan, 1968). A PDF can indicate qualitatively whether the distribution is non-Gaussian.…”

“…This study uses values of H with 10 s time resolution in the interval 1988-2013 inclusive. In contrast to the studies by Wanliss and Reynolds (2003) and Hamid et al (2009), here entire years are analysed. Another important difference is the geographical location: at high latitude, most geomagnetic disturbances occur in the evening sector, and the fluctuations in H reflect the rotation of the Earth underneath the auroral oval's typically zonally aligned current systems, which move meridionally backwards and forwards in a sporadic fashion over the magnetometer site.…”

“…Davis and Sugiura, 1966). Wanliss and Reynolds (2003) have determined β for a number of low-latitude records although references therein accentuate the preceding focus on global indices. Hamid et al (2009) similarly examine data from specific sites.…”