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CLOUD PARTICLES DISTRIBUTION IN A THUNDERSCLOUD
I.M. GUBENKO1, K.G. RUBINSTEIN1 and M.M. KURBATOVA1
1
Hydrometeorological Research Center of the Russian Federation, 11-13, B. Predtechensky lane,
Moscow, Russia
Keywords: THUNDERSTORMS, NUMERICAL SIMULATION, CLOUD PARTICLES,
ATMOSHERIC ELECTRICITY.
INTRODUCTION
Well-known that there is a close relationship between electrical and microphysical processes between
cloud particles: electric field formation and charge separation interconnect to dynamics of air flow,
moisture distribution and phase composition of the cloud. It is especially important for the thunderclouds
since lightning discharges are the greatest threat to human, technical devices and engineering structures.
For this moment the atmospheric electric field is insufficiently studied due to the lack of in-situ
measurements in cumulus clouds at the mature stage. However, there are possibilities to use output data of
numerical weather prediction models for explicit algorithms of thunderstorm forecast and analysis of
spatio-temporal microphysical and electrical characteristics. Such techniques are based on computation of
the electric field.
The aim of presented work is the explicit electrification and lightning forecast using Cumulonimbus (Cb)
electrification model implemented within the WRF-ARW (Weather Research and Forecast) model. WRFARW model has an option of many cloud microphysics parametrizations. In current research Thompson,
Purdue Lin and WDM6 schemes including vapor and 5 classes of hydrometeors (ice and snow crystals,
graupels, rain and cloud droplets) are studied (Lim, 2010; Lin et al, 1983; Thompson et al, 2004). So the
objectives of this study are:
1.Physical and mathematical description of the Cb electrification model.
2.Analysis of spatio-temporal microphysical and electrical characteristics of solid particles in a
simulated thunderstorm cloud for observed supercell storm in Moscow region, 13-14 of July, 2016.
3.Sensitivity test results of thresholds of the electrical characteristics of solid particles in Cb for the
lightning activity occurrence to the type of used WRF-ARW microphysics parameterization schemes.
METHODS
The possibility of using the electrification model for the thunderstorm forecast is studied in this research.
Cb electrification model uses ouput obtained from hydrodynamic mesoscale model WRF-ARW: profiles
of hydrometeors’ fractions (snow, ice particles and graupels), cloud water content, air temperature and
vertical wind component in the layer of 1020-300 hPa.
Cb electrification model is a set of equations describing the processes of charge generation and separation
in convective clouds, constants and profiles of meteorological data. Charge generation process is
described by equations taking into account the diameters of interacting hydrometeors (snow, ice particles,
graupels, cloud droplets), their concentration, the fraction of particles between which there was a collision
/merger, the resulting charge from a collision/merger, gravitational speed of particles’ sedimentation and
air temperature (Gardiner et al, 1985; MacGorman et a., 2001; Mansel et al, 2005; Ziegler et al., 1991).
The model includes the equations describing non-inductive, inductive mechanisms and its combination the integrated schemes of charge generation.
Non-inductive mechanism of the charge generation implies the interaction of solid hydrometeors (ice
crystals+graupels, particles of snow+graupels). Inductive charging equation implies the interaction of
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graupels and cloud droplets (Zeigler et al, 1991). Pairwise interaction between other hydrometeors is
neglected because of the small charge generated as a result of the collision/merger between particles
(Latham and Mason, 1962; Gaskel, 1989; Mansel et al, 2005).
Charge separation unit of the elecrization model includes equations of the total volume charge, potential
and electric field intensity.
CONCLUSIONS
Maximum concentration and terminal speeds of solid hydrometeors and their total space densities strongly
depend on used WRF-ARW microphysics parameterization scheme. So there are no any common
thresholds for the lightning prediction. Model spatio-temporal microphysical and electrical characteristics
do not contradict the results obtained experimentally in studies of electricity in thunderclouds and radar
maps of observed convective cells (Mansell, 2005).
ACKNOWLEDGEMENTS
This work was supported by the Russian Foundation for Basic Research under grants А 14-08-01105, А
15-05-02395 and A 16-05-00822.
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