Long-term measurements of the high-frequency magnetic field (0.1-100 Hz) have been made at Eskdalemuir Observatory in the United Kingdom since September 2012. We analyze five years of dynamic spectrograms to examine the occurrence and behavior of the Schumann and ionospheric Alfvén resonances (IAR) and Pc1 pulsations. The resonances, observed as diffuse bands, arise from reflections of energy both within the Earth-ionosphere cavity and from the nonlinear conductivity gradient of the ionosphere. Schumann Resonances (SR) occur continuously but IAR are observed to arise at local nighttime in ∼50% of days in the data set. Typically, IAR are found at frequencies of 1-8 Hz, but we find them extending out to 30 Hz and strongly superimposing over the first three Schumann resonances around 9% of the time. These phenomena include constructive and destructive interference, nonlinear frequency changes over the span of several hours, and polarity enhancements. In addition, the magnitude of the IAR does not decline rapidly with frequency as often proposed. We find that the IAR and their superposition with SR are strongly controlled by season and geomagnetic activity. We compare 6 days with the most unusual IAR behavior in the data set to ionosonde measurements of f 0 F 2 , a proxy for ionospheric conductivity but find little correlation. We suggest that, as current theoretical modeling does not account for these observations, further work is needed to understand how they arise. Plain Language Summary Measurements of the very rapid changes of the Earth's magnetic field(changes at a rate of between 1 and 50 times per second) show very weak repeating patterns. They are caused by magnetic fields from lightning strikes in thunderstorms near the equator. The lightning strikes are strong enough to "echo" around the globe repeatedly for a few seconds before fading, similar to the sound from a resonating bell. These patterns repeat at fixed periods of around 8, 14, and 21 times per second and are called the Schumann resonances. At night time, other patterns appear in the measurements caused by magnetic waves temporarily trapped in the upper atmosphere (called the ionosphere) between heights of 100 and 1,000 km. These patterns are labeled the ionospheric Alfvén resonances are a relatively unstudied feature of the Earth's magnetic field. We looked at these patterns in magnetic field data collected from Eskdalemuir Observatory in the United Kingdom over the past 5 years. We checked how often these types of patterns occurred and found a link to the seasons and how active, in general, the magnetic field is. We also found unusual and currently unexplained patterns including interference between the Schumann and ionospheric Alfvén resonances.

The Schumann resonances are an electromagnetic phenomenon detectable in the Extremely Low Frequency waveband using a search coil magnetometer. They are created by the continuous discharge of lightning globally. The variation of the intensity and frequency of the resonances can generally be related to (a) the diurnal changes in location and intensity of the global lightning centres, (b) the conductivity properties of the ionosphere and (c) general changes in global temperatures. We have collected and analysed seven years of data (from 2012 to 2019) using two horizontal highfrequency magnetometers installed at Eskdalemuir Geomagnetic Observatory in the UK. The site is magnetically quiet and offers an excellent location to monitor the variation of the Schumann resonances in the 1-50 Hz frequency band. We analyse the variation of the first three Schumann resonances to illustrate the quality of the data and confirm many of the previously observed seasonal variations at other sites globally. We see a long-term decline in the frequencies of each resonance, and evidence for a similar change in the intensity over the seven-year period.

Expert | Impartial | Innovative Ÿ It has been proposed that its signature is detectable within the intensity variations of the Schumann Resonances (SR) due to changes in the location and magnitude of the major lightning centres.Ÿ We extract the frequency and intensity values from each resonance every 10 min, averaged to a daily value and compare them to the Realtime Multivariate MJO (RMM) index.Ÿ We use Empirical Mode Decomposition (EMD) to determine if modes correlate between the SR and RMM.Ÿ The relationship is not wholly consistent, implying that robust and reliable detection of the MJO in SR data remains challenging.The Madden-Julian Oscillation (MJO) is a quasi-periodic (~30-90 days) eastward-moving atmospheric mode which primarily modifies rainfall patterns in the equatorial regions from Africa to the Pacific Ocean.Ÿ Using six years of induction coil data recorded at the Eskdalemuir Observatory in the UK, we investigate whether the MJO is detectable in the first Schumann Resonance. Equatorial Rainfall and the MJO The Real-Time Multivariate MJO Index Empirical Model DecompositionChannel