Secular trend of geomagnetic elements in the Indian region

Abstract

In the present study, secular trends and jerks in the geomagnetic elements D, H and Z are investigated at the six Indian magnetic observatories using annual and monthly mean values for all days, quiet days and night base (night time mean). The residuals of all-day annual and monthly means are computed by removing a polynomial fit from their best fitting curves. The residuals of D, H and Z curves do not show any parallelism with the 11-year sunspot cycle. At Alibag, the D residual shows a periodicity of 2 solar cycles, whereas the H and Z residuals indicate a quasi-periodicity of 3 solar cycles for the period 1921-2009. At the Indian stations, an in-phase solar cycle component is observed for 2 of the solar cycles in the D and Z residuals, while the H residual shows outof-phase variations with the sunspot cycle for the period 1958-2009. Two geomagnetic jerks, 1970 and 1991, are well reflected in the monthly and annual mean values in the Indian region, as observed globally.

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

“…Therefore, under the condition of a constant neutral wind velocity, it can be thought that a decrease of the magnetic field intensity due to the secular variation of the Earth's magnetic field [e.g., Bloxham and Gubbins 1985;Hongre et al 1998;Korte and Constable 2011;Nahayo and Kotze 2012;Bhardwaj and Subba Rao 2013] causes a reduction of the Sq amplitude associated with the weakening of the dynamo field. However, because the height-integrated ionospheric conductivity is also affected by the intensity of the magnetic field, the dependence of the Sq amplitude on the magnetic field is more complicated.…”

Colaba–Alibag magnetic observatory and Nanabhoy Moos: the influence of one over the other

“…The annual inequality of I , and Z, was influenced by 11-year periodicity and the secular march of Z was fairly parallel to that of I (Moos, 1910b). Bhardwaj and Rao (2013) found two-solar-cycle periodicity in D, and quasi-periodicity of three solar cycles in H residuals for the period 1958 to 2009 at Alibag. Furthermore, Alibag data from 1927 to 1997 were analyzed by Bhardwaj (2009), who found a quasi-biennial oscillation-like signal with a periodicity of ∼ 24 months and peak-to-peak variation in H with sunspot numbers.…”

Secular Behavior in the Geomagnetic Data at Permanentobservatories in Argentina

“…Actualmente han sido identificados una serie de impulsos para los años 1901,1913,1925,1932,1938,1949,1958,1969,1978,1986,1991,1999,2003,2006, 2014 y 2017 (ver Bhardwaj y Subba-Rao [13] , Torta et al [14]).…”

“…Es importante remarcar que tanto en los trabajos anteriormente mencionados como en Bhardwaj y Subba-Rao [13] , existen antecedentes del ajuste de la serie de los promedios anuales mediante polinomios de alto grado.…”