<p>Multi-station observations of Schumann resonance (SR) intensity document common behavior in the evolution of continental-scale lightning activity in two super El Niño events, occurring in 1997/98 and 2015/16. The vertical electric field component of SR at Nagycenk, Hungary and the two horizontal magnetic field components in Rhode Island, USA in 1997, and in 2014-2015, the two horizontal magnetic field components at Hornsund, Svalbard and Eskdalemuir, United Kingdom as well as in Boulder Creek, California and Alberta, Canada exhibit considerable increases in SR intensity from some tens of percent up to a few hundred percent in the transition months preceding the two super El Niño events. The UT time distribution of anomalies in SR intensity indicates that in 1997 the lightning activity increased mainly in Southeast Asia, the Maritime Continent and India, i.e. the Asian chimney region. On the other hand, a global response in lightning is indicated by the anomalies in SR intensity in 2014 and 2015. SR-based results are strengthened by comparison to independent lightning observations from the Optical Transient Detector and the World Wide Lightning Location Network, which also exhibit increased lightning activity in the transition months. The increased lightning is attributable to increased instability due to thermodynamic disequilibrium between the surface and the mid-troposphere during the transition. Our main conclusion is that variations in SR intensity may act as a precursor for the occurrence and magnitude of these extreme climate events, and in keeping with earlier findings, as a precursor to maxima in global surface air temperature. As a continuation of our research we plan to set up a webpage dedicated to monitor the actual state of global lightning activity based on SR measurements which may contribute to the early identification of increased instability preceding the next super El Niño event. </p>

W e a t h e r – O c t o b e Daily wind frequencies recorded by John Gadbury in London display a significant bias towards the west–northwest according to Brooks and Hunt (1933) who expected dominant southwest winds. Bias is confirmed by comparisons with contemporary daily records in Rothamstead and London. It is attributed to an over-recorded frequency of west winds, but not inconsistent with the common use of cardinal terms such as ‘westerlies’, as in John Goad’s diary. Over 16 years, Gadbury’s daily westerly winds display consistent and strong periodic patterns, and a mean value just south of west. Significant correlations are discovered with Wittewronge’s record from Rothamstead using monthly and bimonthly wind vectors for 1684–1688. Despite a bias to west winds, the wind structures as a whole are a reliable basis for regional comparisons.

The Earth–ionosphere cavity resonator is occupied primarily by the electromagnetic radiation of lightning below 100 Hz. The phenomenon is known as Schumann resonances (SR). SR intensity is an excellent indicator of lightning activity and its distribution on global scales. However, long-term measurements from high latitude SR stations revealed a pronounced in-phase solar cycle modulation of SR intensity seemingly contradicting optical observations of lightning from satellite, which do not show any significant solar cycle variation in the intensity and spatial distribution of lightning activity on the global scale. The solar cycle-modulated local deformation of the Earth–ionosphere cavity by the ionization of energetic electron precipitation (EEP) has been suggested as a possible phenomenon that may account for the observed long-term modulation of SR intensity. Precipitating electrons in the energy range of 1–300 keV can affect the Earth–ionosphere cavity resonator in the altitude range of about 70–110 km and modify the SR intensities. However, until now there was no direct evidence documented in the literature supporting this suggestion. In this paper we present long-term SR intensity records from eight stations, each equipped with a pair of induction coil magnetometers: five high latitude (|lat| > 60°), two mid-high latitude (50° < |lat| < 60°) and one low latitude (|lat| < 30°). These long-term, ground-based SR intensity records are compared on the annual and interannual timescales with the fluxes of precipitating 30–300 keV medium energy electrons provided by the POES NOAA-15 satellite and on the daily timescale with electron precipitation events identified using a SuperDARN radar in Antarctica. The long-term variation of the Earth–ionosphere waveguide’s effective height, as inferred from its cutoff frequency, is independently analyzed based on spectra recorded by the DEMETER satellite. It is shown that to account for all our observations one needs to consider both the effect of solar X-rays and EEP which modify the quality factor of the cavity and deform it dominantly over low- and high latitudes, respectively. Our results suggest that SR measurements should be considered as an alternative tool for collecting information about and thus monitoring changes in the ionization state of the lower ionosphere associated with EEP.

Multiple records of global temperature contain periods of decadal length with flat or declining temperature trend, often termed a ‘hiatus’. Towards assessing the physical reality of two such periods (1940–1972 and 1998–2014), lightning data are examined. Lightning activity is of particular interest because on many different time scales it has been shown to be non-linearly dependent on temperature. During the earlier hiatus, declining trends in regional thunder days have been documented. During the more recent hiatus, lightning observations from the Lightning Imaging Sensor in space show no trend in flash rate. Surface-based, radiosonde-based and satellite-based estimates of global temperature have all been examined to support the veracity of the hiatus in global warming over the time interval of the satellite-based lightning record. Future measurements are needed to capture the total global lightning activity on a continuous basis.

Every lightning flash contributes energy to the TEM mode of the natural global waveguide that contains the Earth’s Schumann resonances. The modest attenuation at ELF (0.1 dB/Mm) allows for the continuous monitoring of the global lightning with a small number of receiving stations worldwide. In this study, nine ELF receiving sites (in Antarctica (3 sites), Hungary, India, Japan, Poland, Spitsbergen and USA) are used to provide power spectra at 12-minute intervals in two absolutely calibrated magnetic fields and occasionally, one electric field, with up to five resonance modes each. The observables are the extracted modal parameters (peak intensity, peak frequency and Q-factor) for each spectrum. The unknown quantities are the geographical locations of three continental lightning ‘chimneys’ and their lightning source strengths in absolute units (C2 km2/sec). The unknowns are calculated from the observables by the iterative inversion of an evolving ‘sensitivity matrix’ whose elements are the partial derivatives of each observable for all receiving sites with respect to each unknown quantity. The propagation model includes the important day-night asymmetry of the natural waveguide. To overcome the problem of multiple minima (common in inversion problems of this kind), location information from the World Wide Lightning Location Network has been used to make initial guess solutions based on centroids of stroke locations in each chimney. Results for five consecutive days in 2009 (Jan 7-11) show UT variations with the African chimney dominating on four of five days, and America dominating on the fifth day. The amplitude variations in absolute source strength exceed that of the ‘Carnegie curve’ of the DC global circuit by roughly twofold. Day-to-day variations in chimney source strength are of the order of tens of percent. Examination of forward calculations performed with the global inversion solution often show good agreement with the observed diurnal variations at individual receiving sites, lending confidence to the 3-chimney model for global lightning.

A variety of putative influences upon Schumann resonance (SR) signals have been eval- uated for the case of a 20 year record of measurements of two magnetic-field detectors and one electric-field detector located at West Greenwich Rhode Island, U.S.A. (71.6 W, 41.6 N). The detector-specific SR sig- nals considered are the values of the parameters of the first six modes of an eight-mode, three-parameter, Lorentzian-line-shape model. The three parameters of the model are peak-center frequency, peak-quality factor, and peak intensity. This model was used to fit the daily-average Fourier-transform intensity spectra spanning the frequency range 3 Hz - 56 Hz. This results in 54 SR signals: 3 channels 6 modes / channel 3 parameters / mode. We also computed an expected climatological-daily-average intensity spectra for each day and detector and fit these spectra to the above mentioned Lorentzian model. A linear regression of the observed pa- rameters to the expected parameters finds that on average the climatological-daily-average data account for 35% of the variance (R 2 = 0.35) of the original SR series, with the best fits obtained for the Lorentzian-fit parameter peak-intensity where 70% of the variance of the original series was explained. Averaging across channels and parameters, the second and third modes were best modeled by the climatological-average data, explaining 50% of the total variance; all above results are significant at thep 0:001 level. We then subtracted the observed SR signals from the expected SR signals to generate residual SR signals. The residual SR time series display a systematic variation following the 11-year sunspot cycle. A linear regression of a nominal sunspot cycle with the residual time series averaged across all modes and channels, finds R 2 values for peak-center frequency = 0.59, peak-quality factor = 0.31, and peak intensity = 0.0. Averaging the residual time series across all modes and fit parameters, the sunspot cycle is found in each channel; the R 2 value for the E/W channel = 0.30, the R 2 for the N/S channel = 0.37, and the R 2 value for the Ez channel = 0.24 The sunspot-cycle pattern is strongest the mode 1 data (R 2 = 0.48) and decreases with increasing mode number; theR 2 for mode 6 = 0.15; all significant at thep 0:001 level. We then examined various putative influences upon these residual SR signals using a variety of tech- niques. The results indicate that direct measures of solar activity (e.g. sunspot number and area) most strongly influence peak-center frequency and peak-quality factor (median R 2 = 0.50) and less so the peak- intensity (medianR 2 = 0.02). Terrestrial temperature signals (e.g. Ocean temperature anomalies) influence peak-intensity (median R 2 = 0.15) but not peak-center frequency nor peak-quality factor (median R 2 = 0.01). We also examined the spectral characteristics of the residual SR signals. Both the peak-center frequency and peak-quality factor parameters, averaged over all of the modes and channels, display strong peaks at 11 years, 365 days, 180 days; in contrast, the peak-intensity parameter displays no similar features. This indicates that the values of the peak intensity parameter are well predicted by the global total lightning and the uniform-cavity model, while the peak-center frequency and peak-quality factor parameters are not. The values of these two parameters have a significant variation over the sunspot cycle unaccounted for by the global total lightning and the uniform-cavity model.

This study revisits the sprite polarity paradox, first manifest by observations that exceptional cloud‐to‐ground flashes with negative polarity generally did not produce detectable sprites. The paradox is here resolved by the Transient Luminous Event (TLE) known as the halo, which on account of its inferior brightness (0.3 MR versus 1.5 MR) and substantially shorter duration (1 ms versus 10–100 ms) in comparison with the sprite, is not readily detectable in ground‐based video cameras with standard field duration (16.7–20 ms). Observations with improved temporal resolution (ISUAL (Imager of Sprites and Upper Atmospheric Lightnings) from space and PIPER (Photometric Imager of Precipitated Electron Radiation) observations from the ground) provide evidence that flashes with negative polarity dominate the global halo population, and that the halo numbers are more than sufficient to account for the previously missing TLEs. The evidence for lightning polarity‐dependent TLEs (sprites, positive and halos, negative) is attributable to the well established but incompletely understood contrast in the behavior of negative and positive lightning flashes to ground.

Sprites have been detected in video camera observations from Niger over mesoscale convective systems in Nigeria during the 2006 AMMA (African Monsoon Multidisciplinary Analysis) campaign. The parent lightning flashes have been detected by multiple Extremely Low Frequency (ELF) receiving stations worldwide. The recorded charge moments of the parent lightning flashes are often in excellent agreement between different receiving sites, and are furthermore consistent with conventional dielectric breakdown in the mesosphere as the origin of the sprites. Analysis of the polarization of the horizontal magnetic field at the distant receivers provides evidence that the departure from linear magnetic polarization at ELF is caused primarily by the day–night asymmetry of the Earth–ionosphere cavity. Copyright © 2009 Royal Meteorological Society

No abstract is available.

The Geostationary Lightning Mapper (GLM) is a single channel, near-IR imager/optical transient event detector, used to detect, locate and measure total lightning activity over the full-disk. The next generation NOAA Geostationary Operational Environmental Satellite (GOES-R) series will carry a GLM that will provide continuous day and night observations of lightning. The mission objectives for the GLM are to: (1) Provide continuous, full-disk lightning measurements for storm warning and nowcasting, (2) Provide early warning of tornadic activity, and (2) Accumulate a long-term database to track decadal changes of lightning. The GLM owes its heritage to the NASA Lightning Imaging Sensor (1997- present) and the Optical Transient Detector (1995-2000), which were developed for the Earth Observing System and have produced a combined 13 year data record of global lightning activity. GOES-R Risk Reduction Team and Algorithm Working Group Lightning Applications Team have begun to develop the Level 2 algorithms and applications. The science data will consist of lightning events, groups, and flashes. The algorithm is being designed to be an efficient user of the computational resources. This may include parallelization of the code and the concept of sub-dividing the GLM FOV into regions to be processed in parallel. Proxy total lightning data from the NASA Lightning Imaging Sensor on the Tropical Rainfall Measuring Mission (TRMM) satellite and regional test beds (e.g., Lightning Mapping Arrays in North Alabama, Oklahoma, Central Florida, and the Washington DC Metropolitan area) are being used to develop the prelaunch algorithms and applications, and also improve our knowledge of thunderstorm initiation and evolution.