Manifestations of global disturbances of the geomagnetic field in dynamics of thunderstorms

Используя метод диагностики электрического состояния грозовой атмосферы по вариациям вторичных частиц космических лучей, регистрируемых установкой «Ковёр» БНО ИЯИ РАН, обнаружено явление взаимного влияния магнитосферной бури и грозовой активности. Установлено, что во время магнитосферных суббурь малой мощности, на предварительной стадии и в начале фазы развития, возможно проникновение магнитосферно — ионосферных возмущений на средние широты (∼40° с.ш.) над грозовыми очагами. Этот эффект проявляется в виде диффузного свечения типа «полярное сияние» яркостью ∼3 ·10-4 кд·м-² и локальных возмущений электрического поля с характерной разностью потенциалов в тропосфере ±100 МВ. Зарегистрировано локальное магнитное возмущение (∼1 нТл), соответствующее возникновению локального вертикального тока в атмосфере, максимум которого совпал с началом взрывной фазы зарождения суббури. Using the method of diagnosing the electrical state of a thunderstorm atmosphere by variations of the secondary particles of cosmic rays recorded by the Carpet air shower array of the Baksan Neutrino Observatory (North Caucasus), the phenomenon of the mutual influence of a magnetic storm and thunderstorm activity was discovered. It has been established that during magnetic substorms of low power, at the preliminary stage and at the beginning of the development phase, penetration of magnetospheric–ionospheric disturbances at mid latitudes (∼400 N) above lightning centers is possible. This effect manifests itself in the form of a diffuse glow of the aurora type with a brightness of ∼3 ·10-4 cd·m-² and local disturbances of the electric field with a characteristic potential difference in the troposphere of order of ±100 MV. A local magnetic disturbance (∼ 1 nT) was recorded, corresponding to the appearance of a local vertical current in the atmosphere, whose maximum coincided with the beginning of the expansion phase of substorm nucleation.

Elongation and branching of stem channels produced by positive streamers in long air gaps

The elongation and branching of long positive spark discharges in the laboratory and in lightning have been attributed to the formation of thermalized channels inside a diffuse, glow-like streamer section at the leader head. It is experimentally shown here that the structured morphology of streamers produce low-density stem channels that elongate and branch well before a new leader channel section is formed. These non-thermalized stems are also shown to develop ahead of a developing leader channel. These findings are based on high-speed photography and Schlieren imaging used to visualize both the morphology of streamer filaments and stem channels. Numerical analysis is also performed to estimate the axial temperature and density of the stem channels. A stem-driven mechanism for the propagation and branching of positive long air gap discharges is proposed and discussed based on the presence of not-yet thermalized, low density channels formed by streamer ensembles at the leader head.

Optical discrimination of sprite and lightning by use of green light from ~495-505 nm

<p>Sprites are transient illuminations of the middle atmosphere above thunderclouds which often occur after intense lightning discharges. Here we report optical recordings of sprites and lightning taken with a video camera and photometers in northern Colombia during October 2019.</p><p>Optical observations of sprites are often superimposed on the scattered light produced by the parent lightning discharge. This superposition of two optical sources can result in a misinterpretation of the photometer recordings, for example the determination of the rise time of an optical waveform.</p><p>Here we propose to use the green light emissions from ~495-505 nm to discriminate between sprite and lightning. This experimental discrimination has become possible because recent modeling studies suggest that lightning emits green light whilst sprite do not emit green light (Gordillo Vazquez et al., 2011; Xue et al., 2015).</p><p>The optical signals are detected by a white light video camera and a photometer which is fitted with a ~495-505 nm band pass filter to detect green light. The observed lightning discharges are characterized by significant green emissions in the ~495-505 nm wavelength band. These green emissions are part of the diffuse glow detected by the video camera which is caused by the scattered light from the lightning discharge. This light is scattered during its propagation through the atmosphere which is most likely caused by aerosols, for example related to the ambient humidity and dust. The majority of sprite observations are contaminated by such a diffuse glow with significant ~495-505 nm emissions. The observation of one particular sprite does not exhibit any significant ~495-505 nm emissions and it is therefore attributed to a ‘pure sprite’. The rise time of these optical emissions and the characteristics of other wavelengths recorded by several photometers will be reported for this particularly pure sprite event.</p><p>The knowledge gained from these ground-based observations may assist the interpretation of measurements with photometers onboard the ASIM payload on the International Space Station and the forthcoming TARANIS satellite.   </p><p> </p><p> </p><p>Gordillo-Vazquez, F.J., Luque, A. and Simek, M.(2011). Spectrum of sprite halos. Journal of Geophysical research, <strong>116</strong>, A09319. doi: 10.1029/2011JA016652.</p><p>Xue, S., Yuan, P., Cen, J., Li, Y. and Wang, X.(2015). Spectral observations of a natural bipolar cloud-to-ground lightning. Geophysical Research Letters, <strong>120</strong>, 1972–1979. doi:10.1002/2014JD022598</p>

Nonequilibrium discharges in air and nitrogen plasmas at atmospheric pressure

Diffuse glow discharges were produced in low temperature (<2000 K) atmospheric pressure air and nitrogen plasmas with electron number densities in excess of 1012 cm­3, more than six orders of magnitude higher than in thermally heated air at 2000 K. The measured discharge characteristics compare well with the predictions of a two-temperature kinetic model. Experimental and modeling results show that the steady-state electron number density exhibits an S-shaped dependence on the electron temperature, a behavior resulting from competition between ionization and charge-transfer reactions. Non-Maxwellian effects are shown to be unimportant for the prediction of steady-state electron number densities. The power requirements of DC discharges at atmospheric pressure can be reduced by several orders of magnitude using short repetitive high-voltage pulses. Between consecutive pulses, the plasma is sustained by the finite rate of electron recombination. Repetitive discharges with a 100-kHz, 12-kV, 10-ns pulse generator were demonstrated to produce over 1012 electrons/cm3 with an average power of 12 W/cm3, 250 times smaller than a DC discharge at 1012 cm­3.