A significant decrease of the fundamental Schumann resonance frequency during the solar cycle minimum of 2008-9 as observed at Modra Observatory

Abstract

A significant decrease of the fundamental Schumann resonance frequency during the solar cycle minimum of 2008-9 as observed at Modra ObservatoryThe Schumann resonances (SR) are electromagnetic eigenmodes of the resonator bounded by the Earth's surface and the lower ionosphere. The SR frequency variability has been studied for more than 4 decades. Using data from the period 1988 to 2002,Sátori et al. (2005)showed that the SR fundamental mode frequency decreased on the 11-year time scale by 0.07 - 0.2 Hz, depending on which component of the field was used for estimation and likely also on the location of the observer. A decrease by 0.30 Hz from the latest solar cycle maximum to the minimum of 2009 is found in data from Modra Observatory. This extraordinary fall of the fundamental mode frequency can be attributed to the unprecedented drop in the ionizing radiation in X-ray frequency band. Although the patterns of the daily and seasonal variations remain the same in the solar cycle minimum as in the solar cycle maximum, they are significantly shifted to lower frequencies during the minimum. Analysis of the daily frequency range suggests that the main thunderstorm regions during the north hemisphere summer are smaller in the solar cycle minimum than in the maximum.

Constraining the photon mass via Schumann resonances

“…Let us return to the uncertainties. Monthly averaged daily variations for = 1 are typically ≈ 0.5 Hz [54][55][56], though smaller changes in the range 0.04 − 0.14 Hz were reported during strong solar events [57]. Hence, the frequencies may be determined within δf exp = ±0.25 Hz.…”

Shift of effective lightning areas during pre to post period of solar cycle minimum of 2008-2009 as determined from Schumann resonance studies at Agra, India

“…Pathan, Indian Institute of Geomagnetism, Mumbai, May, 2010). Recently, Ondraskova et al [2009Ondraskova et al [ , 2011 have reported a significant decrease of about 0.30 Hz in the fundamental SR frequency from observations at Modra observatory in Slovak Republic during the latest solar cycle having minimum around 2008-2009. This extraordinary fall of the fundamental mode frequency is attributed to the unprecedented drop in the ionizing radiation in X-ray frequency band, although the patterns of the daily and seasonal variation remain unchanged.…”

“…It is shown that local modulation function depends primarily on source-receiver distance geometry and it can be separated with the technique suggested by Sentman and Fraser [1991]. Ondraskova et al [2009Ondraskova et al [ , 2011 have studied the decrease of SR frequencies and changes in effective lightning areas toward the solar cycle minimum of 2008-2009 using the data from Modra observatory Slovakia. The extraordinary fall in the first mode frequency was interpreted in the light of the suggestion made by Satori et al [2005] that the reduction in X-ray radiation causing decrease in the ionospheric conductivity may be attributed responsible for the observed effect.…”

A prototype data acquisition and processing system for Schumann resonance measurements

“…Authors have made several measurements from sampling 180 up to 230Hz to check possible aliasing effects (Ondrášková, Ševčík & Kostecký, 2009) A commercial DAS with an adjustable sampling rate up to 4 KHz was used as a part of a new observation system to measure magnetic fields in the extremely low frequency band at Moshiri, Hokkaido, Japan. The commercial data acquisition board is placed in a PCI slot of a PC 220m away from the antenna (Ando et al2005).…”