Thunderstorm Processes Research Articles

A laboratory study of the influence of water vapour and mixing on the charge transfer process during collisions between ice crystals and graupel

Laboratory experiments, in which vapour grown ice crystals interact with riming graupel targets, simulate charging processes in thunderstorms. The introduction of cooled, moist, laboratory air into a supercooled droplet and ice crystal cloud enhances charge transfer and, when the air-stream is directed at the riming target, can reverse its charge sign. The suggestion is that the extra water vapour introduced increases the supersaturation and influences particle diffusional growth. The results have been considered in terms of the Relative Growth Rate Hypothesis, which states that the interacting ice surface growing fastest by vapour diffusion charges positively. A corollary to this was noted, when dry air is introduced into a cloud of ice crystals so that both the crystals and target surface sublimate, the ice surface that sublimates fastest charges negatively. The experiments are relevant to considerations of the reasons why earlier sets of charge transfer results give different liquid water and temperature boundaries between positive and negative graupel charge sign. The differences appear to be connected to the techniques used, in particular, to the mixing of separate droplet and ice crystal clouds before riming, which can lead to positive rimer charging in conditions of low-rime accretion rate, as observed in the present study. Further work is needed to resolve questions concerning the most naturally representative manner of performing these laboratory simulations.

Intensive X-ray emission bursts during thunderstorms

The intensive X-ray emission during thunderstorms was studied at a height of 3340 m above sea level. For the first time, short-time (1–5 min) bursts of X-ray emission were observed. The bursts are highly correlated over a wide space region (about 0.5 km). The main component of X-ray emission in bursts has energies between 50–80 keV. The observed bursts could be attributed to the bremsstrahlung determined by the runaway breakdown (RB) effect in the thundercloud's electric field. Ground-based observations of RB open a wide range of opportunities for the studies of fundamental processes in thunderstorms.

Stochastic Considerations in Thunderstorm Modeling

A mesoscale stochastic model of thunderstorm activity is developed to simulate the hourly development of both air mass and squall-line storms. This modeling technique is based on Poisson occuring thunderstorms, Markov cloud formation and movement, and rainfall-producing convective cells, and is intended to provide a more complete theoretical understanding of the thunderstorm process. The rain cells form according to a prescribed probabilistic model within clouds on an hourly basis, with a relatively high likelihood of generation of a new cell in the vicinity of a previous cell. The cells are described by a center magnitude with a Gumbel distribution and an exponential or power law decay formula. The stochastic model is programmed for simulation in a fairly general program that allows many different variables in the thunderstorm process to be either prescribed, or simulated from appropriate probability distributions.

On the influence of the electric field upon the processes in thunderstorms

During the last decade the interest has been grown greatly concerning the question of the electric field influence upon elementary and electric processes in clouds, and in the first place in cumulo-nimbus ones having the largest electric fields. We can point out the works carried out in this direction by SARTOR (1954) , MAGONO and KOENUMA (1958) , LEVIN (1961) , MAGARVEY and BLANKFORD (1962), BARTLETT, HEWAL and MASON (1963) and MATTHEWS and MASON (1964). A good many of investigations in this direction has been carried out by Muchnik and Rudko at the Ukrainian Hydrometeorological Research Institute. A short description of these investigations is given below. DOI: 10.1111/j.2153-3490.1965.tb00215.x

On the influence of the electric field upon the processes in thunderstorms

During the last decade the interest has been grown greatly concerning the question of the electric field influence upon elementary and electric processes in clouds, and in the first place in cumulo-nimbus ones having the largest electric fields. We can point out the works carried out in this direction by SARTOR (1954) , MAGONO and KOENUMA (1958) , LEVIN (1961) , MAGARVEY and BLANKFORD (1962), BARTLETT, HEWAL and MASON (1963) and MATTHEWS and MASON (1964). A good many of investigations in this direction has been carried out by Muchnik and Rudko at the Ukrainian Hydrometeorological Research Institute. A short description of these investigations is given below.