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Extreme space weather events can have serious impacts on critical infrastructure, including Global Navigation Satellite Systems (GNSS). The use of GNSS, particularly as sources of accurate timing signals, is becoming more widespread, with one example being the measurement of electricity grid frequency and phase information to aid grid management and stability. Understanding the likelihood of extreme space weather impacts on GNSS timing signals is therefore becoming vital to maintain national electricity grid resilience. This study determines critical intensity thresholds above which the complete failure of a GNSS based timing system may occur. Solar radio bursts are identified as a simple example to investigate in more detail. The probability of occurrence of an extreme space weather event with an intensity equal to or greater than the critical intensity is estimated. Both a power law and extreme value theory were used to evaluate recurrence probabilities based on historical event frequencies. The probability was estimated to be between 3%–12% per decade to cause the complete failure of any GNSS‐based timing system. Plain Language Summary: Society is increasingly reliant on satellite technologies for a wide range of applications. If a huge space weather event were to impact the Earth today, it would likely have catastrophic impacts across many modern technologies including satellites and satellite systems, communications, and electricity grids. Here we assess the probabilities that intense solar events may affect timings derived from Global Navigation Satellite System (of which one commonly used example is the Global Positioning System, or GPS). These timing signals are increasingly used in electricity grid management. Solar radio bursts are used as an example, since they can overwhelm the weak GNSS signal. Statistical methods were employed to assess 46 years of solar radio burst data. Our findings suggest a 3%–12% probability per decade of an event large enough to disrupt the UK electricity grid. Key Points: Extreme space weather can disrupt Global Navigation Satellite Systems (GNSS) timing signals, an increasingly critical aspect of the electricity distribution networkFirst case study illustrating degradation of GNSS timing from solar radio burstsLikelihood of a significantly disruptive event is constrained at 3%–12% per decade [ABSTRACT FROM AUTHOR]

A miniaturized scintillator ("microscintillator"), was flown on a meteorological radiosonde to observe energetic particles in the lower atmosphere. A PiN diode was used to measure the light from the microscintillator to count rates and energies of ionizing radiation from the ground up to the stratosphere (32 km). The flight, over the southern UK on August 27, 2018, occurred during a geomagnetic storm. Low‐energy (50–150 keV) particles in the stratosphere were detected in addition to the usual signal from higher‐energy cosmic rays. Unusually for these miniaturized radiosonde systems, which are designed to be disposable, the payload was retrieved. This allowed for re‐calibration of the microscintillator, which confirmed the low‐energy particle detection. Laboratory tests excluded thermal effects on the microscintillator instrument as the origin of the signal. Data from the NOAA POES spacecraft offer the explanation that the microscintillator detected bremstrahhlung X‐rays from energetic electron precipitation (EEP). EEP events may affect weather and climate through a range of physical mechanisms, and this midlatitude observation, well away from the auroral oval, extends the region over which meteorological effects of EEPs need to be assessed. Our findings underline the value of balloon measurements in providing rapid response to space weather events. The energy‐discriminating and altitude‐sensitive capability of the microscintillator augments spacecraft observations from below. Plain Language Summary: We describe results from flying a miniaturized radiation detector up to 32 km altitude on a weather balloon, in a region of the atmosphere called the stratosphere. The radiation detector was able to measure the energy of the particles it detects in addition to counting them. As well as the counts we expected from high‐energy particles entering the atmosphere from space, we also unexpectedly measured some lower‐energy particles. Normally the weather balloons are not retrieved, but for this flight we were able to retrieve it and test it again in the lab, confirming that the low‐energy particle measurements were real and not due to a problem with the equipment. These low‐energy particles are likely to be X‐rays which can sometimes enter the atmosphere during periods of enhanced space weather activity. The electrons that are known to produce these X rays were present in enhanced concentrations in near‐Earth space, as measured from above by the NOAA POES spacecraft: our measurements are from below. We believe this is the first detection of stratospheric X‐rays well away from the polar regions. X‐rays affect atmospheric chemistry, which, in turn, to a lesser extent, affects the weather. Key Points: Energetic particles in the atmosphere have been observed with a "microscintillator" detector flown on a weather balloonLow‐energy ionizing radiation was unexpectedly observed in the stratosphere. Instrument retrieval and recalibration confirmed the findingsDetection of Bremsstrahlung X rays at unusually low latitudes from a geomagnetic storm is corroborated by spacecraft observations [ABSTRACT FROM AUTHOR]

Abstract: Long‐term measurements (1972–2015) of the reflectivity of Uranus at 472 and 551 nm display variability that is incompletely explained by seasonal effects. Spectral analysis shows that this nonseasonal variability tracks the 11 year solar cycle. Two mechanisms could cause solar modulation: (a) nucleation onto ions or electrons created by galactic cosmic rays (GCR) or (b) UV‐induced aerosol color changes. Ion‐aerosol theory is used to identify expected relationships between reflectivity fluctuations and GCR flux, tested with multiple regression and compared to the linear response predicted between reflectivity and solar UV flux. The statistics show that 24% of the variance in reflectivity fluctuations at 472 nm is explained by GCR ion‐induced nucleation, compared to 22% for a UV‐only mechanism. Similar GCR‐related variability exists in Neptune's atmosphere; hence, the effects found at Uranus provide the first example of common variability in two planetary atmospheres driven through energetic particle modulation by their host star. [ABSTRACT FROM AUTHOR]

Electrostatic forces from asteroidal photoelectron emission both redistribute regolith and modulate the surface particle size distribution. A 2D particle-in-cell code has been developed to investigate the possibility of direct measurement of the electrical environment near the surface of an asteroid during a sample return mission. The spacecraft is expected to reach equilibrium with the surface photoelectron layer in , which is rapid compared to the descent timescale, permitting the simulation equilibria to be assumed representative of the dynamic spacecraft environment. Typical signals on a set of spacecraft-mounted sampling electrodes during descent are presented. The distorting effect of the spacecraft significantly modifies the potential on any sensing electrodes by introducing an equipotential body; creating a shadow; and photoemitting itself. Optimal locations for mounting the electrodes to measure the asteroid?s surface electric field are suggested, where the potential differences measured are expected to be both readily detectable and representative of the local electrostatic environment. The high electron concentration near the surface is likely to ensure that the spacecraft and surface potential are similar at touchdown, in the absence of other charging effects, such as those introduced by the sampling mechanism. This study was carried out for an asteroid at 3AU, but enhanced photoemission will increase the likelihood of electrostatic regolith disturbance by the spacecraft shadow during descent to an object nearer the Sun. [ABSTRACT FROM AUTHOR]

Lord Kelvin (William Thomson) made important contributions to the study of atmospheric electricity during a brief but productive period from 1859-1861. By 1859 Kelvin had recognised the need for "incessant recording" of atmospheric electrical parameters, and responded by inventing both the water dropper equaliser for measuring the atmospheric potential gradient (PG), and photographic data logging. The water dropper equaliser was widely adopted internationally and is still in use today. Following theoretical considerations of electric field distortion by local topography, Kelvin developed a portable electrometer, using it to investigate the PG on the Scottish island of Arran. During these environmental measurements, Kelvin may have unwittingly detected atmospheric PG changes during solar activity in August/September 1859 associated with the "Carrington event", which is interesting in the context of his later statements that solar magnetic influence on the Earth was impossible. Kelvin's atmospheric electricity work presents an early representative study in quantitative environmental physics, through the application of mathematical principles to an environmental problem, the design and construction of bespoke instrumentation for real world measurements and recognising the limitations of the original theoretical view revealed by experimental work. [ABSTRACT FROM AUTHOR]

Two vertical cosmic ray telescopes for atmospheric cosmic ray ionization event detection are compared. Counter A, designed for low power remote use, was deployed in the Welsh mountains; its event rate increased with altitude as expected from atmospheric cosmic ray absorption. Independently, Counter B's event rate was found to vary with incoming particle acceptance angle. Simultaneous co-located comparison of both telescopes exposed to atmospheric ionization showed a linear relationship between their event rates. [ABSTRACT FROM AUTHOR]

During a 4-week run in October-November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H2SO4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm-3 s-1, and growth rates between 2 and 37 nm h-1. The corresponding H2SO4 concentrations were typically around 106 cm-3 or less. The experimentally-measured formation rates and H2SO4 concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1 °C). [ABSTRACT FROM AUTHOR]

During a 4-week run in October-November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the CLOUD experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H2SO4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm-3s-1, and growth rates between 2 and 37 nm h-1. The corresponding H2SO4 concentrations were typically around 106 cm-3 or less. The experimentally-measured formation rates and H2SO4 concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1°C). [ABSTRACT FROM AUTHOR]

A silicon field emitter neutralizer is under development at the Rutherford Appleton Laboratory for the LISA Pathfinder mission [B.J. Kent et al., Class Quantum Grav. 22, S483 (2005)]. A summary of this project from the fabrication point of view is presented in this article. An investigation of the effect of fabrication uniformity on emission characteristics showed that the geometrical nonuniformity, including tip height and gate diameter, across a 4-in. wafer is below 15%. This variation had only a small effect (∼10%) on the field-emission characteristics. In order to improve the reliability of the silicon field emitters for the space environment operation, a thin aluminum nitride (AlN) film is coated on the silicon emitters, and the chromium gate electrode is oxidized in furnace. The effects of adding the layer of AlN and thermal oxidation of the chromium gate electrode on field emission and lifetime were investigated in this article. A fabrication yield analysis estimated that 50% of arrays on the original wafer functioned correctly in the final device, but that this can be substantially improved by a more rigorous device handling control. [ABSTRACT FROM AUTHOR]

Development of reliable field emission devices requires detailed characterization of variability over the device lifetime. Silicon tip manufacturing processes and test equipment limitations are theoretically predicted to cause ∼5% variability in field emission currents. Long-duration emission current measurements at both constant voltage and constant current, controlled with a software feedback loop, were made. Power spectra from the two operational modes were significantly different. The software feedback loop response was determined; it is expected to contribute ∼1% of the standard deviation in emission current when used to control emission by modulating the gate voltage. Convolution of constant voltage time series with the software feedback loop response reproduced the spectral characteristics of constant current time series, indicating that many of the differences between the two operating modes were caused by the operating mode itself rather than the field emitters tested. This has implications for the operating mode of the application for which the device is intended. [ABSTRACT FROM AUTHOR]

Measurements of ions in atmospheric air are used to investigate atmospheric electricity and particulate pollution. Commonly studied ion parameters are (1) air conductivity, related to the total ion number concentration, and (2) the ion mobility spectrum, which varies with atmospheric composition. The physical principles of air ion instrumentation are long established. A recent development is the computerized aspirated capacitor, which measures ions from (a) the current of charged particles at a sensing electrode, and (b) the rate of charge exchange with an electrode at a known initial potential, relaxing to a lower potential. As the voltage decays, only ions of higher and higher mobility are collected by the central electrode and contribute to the further decay of the voltage. This enables extension of the classical theory to calculate ion mobility spectra by inverting voltage decay time series. In indoor air, ion mobility spectra determined from both the voltage decay inversion, and an established voltage switching technique, were compared and shown to be of similar shape. Air conductivities calculated by integration were: 5.3±2.5 and 2.7±1.1 fSm-1, respectively, with conductivity determined to be 3 fSm-1 by direct measurement at a constant voltage. Applications of the relaxation potential inversion method include air ion mobility spectrum retrieval from historical data, and computation of ion mobility spectra in planetary atmospheres. [ABSTRACT FROM AUTHOR]

Motivated by the detection of infrared absorption bands from atmospheric cluster ions in laboratory experiments, a narrowband filter radiometer has been constructed for ion detection in the atmosphere. It uses a filter centered at 9.15 μm wavelength with 5% bandwidth, protected by a diamond-like-carbon coated germanium auxiliary filter, and fitted to a standard pyrradiometer. A sensitivity of (29.3±0.1) μV/(W m-2) has been determined in a laboratory calibration using a blackbody source. Atmospheric experiments show that the filter radiometer, when used with a stable, low-noise amplifier, can respond to cluster-ion fluctuations. The filter radiometer’s sensitivity to atmospheric ion changes is (0.47±0.05) (mW m-2)/(ions cm-3). [ABSTRACT FROM AUTHOR]

A letter to the editor is presented related to an article thunderstorm by John Turnpenny that was published in the previous issue of the periodical.

Karen Aplin and Giles Harrison examine the 1859 Carrington flare and consider what the data mean for our understanding of space weather today.Karen Aplin and Giles Harrison examine international records of the 1859 Carrington flare and consider what they mean for our understanding of space weather today. [ABSTRACT FROM AUTHOR]

The authors' comments on B.E. Sauer and his colleagues' research paper "A Robust Floating Nanoammeter" published in the online version of the journal on May 7, 2009. They say it is surprising the paper authors do not focus more on the novel aspects of nanoammeter. According to them, the paper also does not offer any information on the time response of the nanoammeter. This information could have been used by other scientists and engineers to determine the applicability of the device.

Neutralizers are required to prevent spacecraft charging from satellite ion propulsion. This paper discusses the development of a gated silicon tip field emitter (FE) neutralizer, specified to deliver 6 mA, with each tip emitting a mean current of 7 nA. It is important to investigate factors affecting the lifetime of field emitter arrays for a space application, as longevity and reliability are both critical requirements. Semi-automated procedures to prepare 400 arrays, each consisting of 765 FEs, for life tests are described with failure conditions strictly defined by mission constraints. Results of 25 life tests on 72 arrays driven to failure at constant emission current are summarized, and a case study of one test is presented. Two of the three failure mechanisms identified are consistent with thermal failure and damage by ion bombardment. Reduced field enhancement from tip erosion caused by ion bombardment is a common explanation for FE failure. However, scanning electron microscope examination of tip apex diameters showed no significant relationship between array failure and apex geometry. The third failure mechanism was associated with short-lived arrays and may be caused by manufacturing defects. Substantial intrinsic variability was observed in the arrays tested, even with the rigorous production standards required for space applications. Arrays without manufacturing defects had lifetimes of thousands of hours. [ABSTRACT FROM AUTHOR]

Ion measurements in atmospheric air allow atmospheric ion-aerosol charge exchange to be investigated, which is thought to be important in cloud processes. Classical aspiration ion measurement techniques have been significantly improved by the use of electronic switching systems to permit the selection of different mobilities, with adjacent instruments using the combination of Voltage Decay and ion current techniques used for calibration. An integrated programable ion mobility spectrometer using the same collection electrodes in both modes is described here, with which high-resolution measurements (1 s sampling) of ion concentration fluctuations have been made. Mobility spectrum information has also been extracted by varying the bias voltage under full computer control. The integrated system can determine small ion concentrations to ±1%, to a minimum mobility μ∼0.1 cm2 V-1 s-1 (corresponding to a particle radius of ∼2 nm). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Accurate measurements of atmospheric ions are desirable in order to investigate atmospheric aerosol processes. A cylindrical capacitor ion counter is described which has a flexible computerized control system, to allow selection of ion mobility by changing the bias voltage across the capacitor. Ion measurements obtained correlate well with the ionization rate measured with an adjacent Geiger counter in clean air. Measurements of air ions using the device in current and voltage decay modes show consistent results. The collecting electrode is exposed directly in the air stream to be sampled, eliminating diffusive losses in intake tubes. The system can measure ion concentrations from 20 ions cm[sup -3] (including typical atmospheric concentrations) and can sample ions rapidly. These characteristics enable comprehensive air conductivity measurements to be made. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]