Fair-weather Field Research Articles

First measurements of wind-turbine perturbations of fair-weather electric fields

Wind turbines have been shown to develop corona at blade tips due to the presence of the fair-weather electric field, but up to now there have been no published investigations of how the presence of a wind turbine perturbs the fair-weather field as measured on the ground near the turbine. Such data may be useful to evaluate the integrity of turbine lightning protection systems. We present the first such published measurements in this paper. Our model predicts measurable periodic variations, and our experimental measurements show a peak-to-peak perturbation up to about 7 V m−1 in a nominal 100 V m−1 fair-weather field as measured on the ground under the moving turbine's blades. Smaller perturbations are detectable at greater distances.

Thunderstorm and fair-weather quasi-static electric fields over land and ocean

Natural lightning and the associated clouds are known to behave differently over land and ocean, but many questions remain. We expand the related observational datasets by obtaining simultaneous quasi-static electric field observations over coastal land, near-shore water, and deep ocean regions during both fair-weather and thunderstorm periods. Oceanic observations were obtained using two 3-m NOAA buoys that were instrumented with Campbell Scientific electric field mills to measure the quasi-static electric fields. These data were compared to selected electric field records from the existing on-shore electric field mill suite of 31 sensors at Kennedy Space Center (KSC). Lightning occurrence times, locations and peak current estimates for both onshore and ocean were provided by the U.S. National Lightning Detection Network. The buoy instruments were first evaluated on-shore at the Florida coast, and the first system was calibrated for field enhancements and to confirm proper behavior of the system in elevated-field environments. The buoys were then moored 20 mi and 120 mi off the coast of KSC in February (20 mi) and August (120 mi) 2014. Diurnal fair-weather fields at both ocean sites matched will with each other and with those found during the Carnegie cruise, but mean values were 33% smaller, due at least in-part to constraints on the calibration procedure. Diurnal fair-weather fields variations at coastal and inland sites were a poorer match than offshore, likely because the offshore environment is “cleaner” with limited variations in local space charge, lower surface aerosol densities, little surface heating to disturb the surface charge layer during fair weather, and fewer local radioactive sources to modulate the near-surface electrical conductivity. Storm-related static fields were 4-5× larger at both oceanic sites than over land, likely due to decreased screening by near-surface space charge produced by corona current. The time-evolution of the electric field and field changes during storm approach are sufficiently different over land and ocean to warrant further study. This work shows the quality, accuracy, and reliability of these data, and has demonstrated the practicality of off-shore electric field measurements for safety- and launch-related decision making at KSC.

Fair weather electric field meter for atmospheric science platforms

A miniature field meter is described for measuring fair weather electric fields (of magnitude ~100 Vm-1). It is a brushless field mill constructed from machine-cut parts, driven by a computer fan motor. It resolves fair weather fields at ~1 mV per (Vm−1), with a time response of 0.65 s. It implements self-calibration through combining a mechanical shutter with a programmable bipolar calibration electrode. It has a mass of 86 g, dimensions 4 cm × 4 cm x 8 cm and consumes <100 mA at 6 V. This design will facilitate new climate-related measurements using balloons and remotely piloted aircraft.

Fair weather atmospheric electricity

Not long after Franklin's iconic studies, an atmospheric electric field was discovered in "fair weather" regions, well away from thunderstorms. The origin of the fair weather field was sought by Lord Kelvin, through development of electrostatic instrumentation and early data logging techniques, but was ultimately explained through the global circuit model of C.T.R. Wilson. In Wilson's model, charge exchanged by disturbed weather electrifies the ionosphere, and returns via a small vertical current density in fair weather regions. New insights into the relevance of fair weather atmospheric electricity to terrestrial and planetary atmospheres are now emerging. For example, there is a possible role of the global circuit current density in atmospheric processes, such as cloud formation. Beyond natural atmospheric processes, a novel practical application is the use of early atmospheric electrostatic investigations to provide quantitative information on past urban air pollution.

Estimation of global lightning activity and observations of atmospheric electric field

Variations in the global atmospheric electric circuit are investigated using a wide range of globally spaced instruments observing VLF (∼10 kHz) waves, ELF (∼300 Hz) waves, Schumann resonances (4–60 Hz), and the atmospheric fair weather electric field. For the ELF/VLF observations, propagation effects are accounted for in a novel approach using established monthly averages of lightning location provided by the Lightning Image Sensor (LIS) and applying known frequency specific attenuation parameters for daytime/nighttime ELF/VLF propagation. Schumann resonances are analyzed using decomposition into propagating and standing waves in the Earth-ionosphere waveguide. Derived lightning activity is compared to existing global lightning detection networks and fair weather field observations. The results suggest that characteristics of lightning discharges vary by region and may have diverse effects upon the ionospheric potential.

The effect of recent Venus transit on Earth’s atmosphere

Some experiments on June 8, 2004, the day of transit of Venus across the Sun, were undertaken at Kolkata (latitude: 22°34lN) to observe the effect, if any, of transit of Venus on FWF, ELF and VLF amplitudes. The result shows a good correlation between their temporal variations during the transit. The observation was unbelievable as the Venus subtends only 1/32th of the cone subtended by Sun on Earth. This anomaly may be explained on the assumption that the height of Venusian atmosphere with high content of CO2, and nitrogen which absorbs electromagnetic and corpuscular radiations from Sun, depleting the solar radiation reaching the Earth to a considerable extent. As a result, relevant parameters of Earth’s atmosphere are modulated and here we show how these changes are reflected in identical behaviour of fair weather field and ELF and VLF spectra.

The Effects of Solar Eclipse of August 1, 2008 on Earth’s Atmospheric Parameters

Several experiments were undertaken at Kolkata (latitude: 22°34′N, longitude: 88°30′E) on the solar eclipse day of August 1, 2008 to observe the effects of the solar eclipse on Fair Weather Field (FWF) and VLF amplitude and phase. The experimental results presented here show significant deviations of the observed parameters from their normal values, as they are determined by the average of the records obtained on 5 days adjacent to the day of the solar eclipse.

Retrieving Storm Electric Fields from Aircraft Field Mill Data. Part II: Applications

Abstract The Lagrange multiplier theory developed in Part I of this study is applied to complete a relative calibration of a Citation aircraft that is instrumented with six field mill sensors. When side constraints related to average fields are used, the Lagrange multiplier method performs well in computer simulations. For mill measurement errors of 1 V m−1 and a 5 V m−1 error in the mean fair-weather field function, the 3D storm electric field is retrieved to within an error of about 12%. A side constraint that involves estimating the detailed structure of the fair-weather field was also tested using computer simulations. For mill measurement errors of 1 V m−1, the method retrieves the 3D storm field to within an error of about 8% if the fair-weather field estimate is typically within 1 V m−1 of the true fair-weather field. Using this type of side constraint and data from fair-weather field maneuvers taken on 29 June 2001, the Citation aircraft was calibrated. Absolute calibration was completed using the “pitch down method” developed in Part I, and conventional analyses. The resulting calibration matrices were then used to retrieve storm electric fields during a Citation flight on 2 June 2001. The storm field results are encouraging and agree favorably in many respects with results derived from earlier (iterative) techniques of calibration.

A laboratory test of the electrification phenomenon in wind-blown sand flux

The measured data in the wind-tunnel tests show that the wind-blown sand particles acquired a negative charge when their diameters are smaller than 250 μm and positive charge when their diameters are larger than 500 μm, which confirms Latham’s assumption that the large particles in wind-blown sand flux acquired positive charge while negative charge developed on small ones. In the meanwhile, the measured data also show that the average charge-to-mass ratio for wind-blown sand particles decreases with the increase of the particle diameter and the wind velocity, and increases with the rise of height. The electric field in wind-blown sand flux is mainly formed by the moving charged sand particles. Its direction is vertical to the Earth’s surface and upward, which is opposite to that of the fair-weather field. The electric field increases with wind velocity and height increasing. These experimental results will lay the foundation for developing the theoretical analysis of the electrification phenomenon in wind-blown sand flux.

Space charge generated by wind tunnel fires

Plume clouds resulting from wildland fires (pyrocumulus) sometimes produce lightning discharges to ground. These discharges were found to carry positive charge to ground exclusively in several cases. Emission of space charge was observed from woody materials burned in the presence of an external electric field. Measurements done in a large wind tunnel for this study confirm and extend measurements made in open air. The net charge given up by the fire in the wind tunnel has sign appropriate to reduce an applied electric field (negative for the earth's fair weather field), and magnitude directly proportional to the magnitude of the applied electric field and the fuel consumption: Q=0.034+0.0015 E, where Q is the net charge liberated in nC g −1, and E is the applied electric field in V m −1 (positive upward). There is a weak dependence of the net charge on wind speed, probably due to wind tunnel airflow characteristics. The net charge in the smoke is a small difference between large amounts of charged ions of both signs liberated by the fire. For fires burning under fair-weather electric fields, the amount and sign of charge released by the mechanism studied cannot be the direct cause of anomalous lightning from pyrocumulus.

The Global Electric Circuit

On a clear day, there is a downward electric field of 100 to 300 volts/meter at Earth's surface, although this field is not noticeable in daily life. That is, one does not encounter a 1 kV potential difference when getting into a car on an upper floor in a parking garage, and electrocution is not the major hazard associated with jumping out of trees. The major reason why we don't notice the fair-weather field is that virtually everything is a good conductor compared to air. Objects such as tree trunks and our bodies are excellent ionic conductors that short out the field and keep us from noticing it. But the field is there.

Comment on “Solar wind mechanism suggested for weather and climate change”] Weather and climate changes arising from solar wind effects on thunderstorm electrification

In “Solar Wind Mechanism Suggested for Weather and Climate Change” [Eos, August 9,1994], Brian A. Tinsley suggests that solar activity is modulating weather and climate through the effects it produces on the Earth's fair‐weather electric field. This may well be true. It is questionable, however, whether the fair‐weather electric field is strong enough to cause ice crystal formation in clouds by electrofreezing, as he has assumed.From Pruppacher [1973], it is evident that demonstrations of electrofreezing involve electric fields about a thousand times more intense and a million‐fold more energetic than the electric field Tinsley believes is causing the formation of ice crystals in clouds. Acceptance of the idea that the fair weather field plays a significant role in the glaciation of clouds must await demonstrations that electrofreezing can be produced by electric fields of less than 100 Vm−1.

Elements of fair weather electricity

The electric fair weather field and conduction current in the lower atmosphere are primarily controlled by ions. Ions in turn are subject to parameters such as mobility, lifetime, and generation rate that vary with altitude. A physical model is described which permits theoretical prediction of the above ionic parameters as well as the electric field at altitudes from 0 to 35 km. The model obeys Ohm's law.

Sign discriminating field mill

The construction and analysis of a symmetric rotating field mill is described. Theoretical modelling of the mill's operation successfully predicts the experimentally observed features of the mill output. A pick-up phase signal generated by the mill rotor blades cutting field lines of a permanent magnet was used as a sampling pulse in a sample-and-hold electronic arrangement to determine both magnitude and direction of an impressed electric field. The mill's output voltage regressed on the electric field gave a correlation coefficient of 0.998. The sensitivity of the mill could be set arbitrarily and field changes of 0.5 V/m could be measured routinely. The time constant of 0.3 s makes the mill ideal for studies of the fair-weather field as well as of other phenomena with relatively long time constants. Special steps were incorporated in the mill construction to reduce effectively the damaging effects of water condensation on the performance of the mill.

Observations of unusual structures of high‐latitude stratospheric electric fields

We report the observation, by means of balloon‐borne sensors, of three cases of unusual stratospheric electric field structures at high latitudes. In all three cases a region of downward directed electric field is flanked by regions with upward field. In two out of the three cases, the central downward field is much stronger than the average fair weather field. The vertical current densities involved are &lt;5×10−11 A/m2. These field structures are observed only about 0.5% of the time.

Thunderstorm Electrification—Inductive or Non-Inductive?

Abstract Most of the precipitation related theories on charge generation in thunderstorms fall into one of two categories: the inductive or polarization mechanism initiated by the ambient fair-weather field, and the non-inductive mechanism connected with certain electrochemical or thermoelectric particle characteristics. Our numerical study addresses the question of which mechanism gives more realistic results with regard to charge distribution and hold strength and what effect a combination of the two processes produces. The investigation is a first attempt using a simplified model. In this model the microphysical processes of particle growth and simultaneous electrification are embedded in a steady state two-dimensional vortex circulation with and without vertical wind shear. The net space charge and potential are obtained everywhere in the cloud and the resulting electric fields are calculated. Computations are made for the collisions of growing solid precipitation (graupel) particles with either super...

Aurorae and the fair weather field

Variations in the fair weather electric field may be associated with auroral events, as well as with solar cosmic rays and variations in the magnetospheric and ionospheric fields. There is a large vertical electric field in the mesosphere, corresponding to a total potential of around 100 kV.

Electrification experiments on Elk Mountain

During the winter of 1976, along with the continuing studies of ice crystals in the cap cloud on Elk Mountain, measurements were made of ice crystal charges and the atmospheric electric field strength. The electric field was, in general, found to be of the same sign as the fair weather field. The net particle charges were predominantly positive with mean values of the order of ±10−14 C with fairly symmetrical distributions of positive and negative charges. The ‘mirror image’ effect was seldom observed perhaps because of the small extent and short lifetime of the cap cloud. The absence of large negative charges suggests that the particles and particle charges do not originate from blowing snow. A mechanism of charging which may explain the symmetrical charge distributions is inductive charge transfer between particles which contact and then separate in random directions relative to the electric field.

Spherical capacitor hypothesis of the earth's electric field

Stemming from the suggestion that the earth-ionospheric fair weather field arises from the lowest order resonant excitation of the earth-ionosphere cavity by lightning, it is shown that the same field is generated through electrostatic induction by equivalent charge dipoles from thunderclouds in the earth's atmosphere. An electrostatic induction model was used to derive from known worldwide thunderstorm data the magnitude of the expected earth-ionosphere fair weather potential. A value of only approximately one third of the observed potential was obtained. Possible sources of the discrepancy are suggested.

The Role of Particle Interactions in the Distribution of Electricity in Thunderstorms

Abstract The growth of electric fields in clouds resulting from charge rearrangement due to particle interaction and translation is calculated under the assumption that the initial electrification is provided by the fair weather charge distribution of the atmosphere or by some other basic charge separating process. The results demonstrate that particle interaction must be taken into account in the electrification process during the precipitation formation period. In fact, they show that, starting with the normal fair weather field, it is possible to explain qualitatively and quantitatively many of the presently known observations of the electrical growth and field recovery behavior of thunderstorms.