SA51B-01
Characterization of Convective Systems in Africa in Terms of their Vertical Structure, Electrification and Dynamics
Mesoscale Convective Systems (MCS) are cloud systems that occur from an ensemble of thunder storms and result in a precipitation that covers a huge contiguous area. They are long-lived storm system having dimensions much larger than an individual storm. Storm systems associated with MCSs over the Africa are tracked for the period July to December 2004 and their properties at different stages of their life are investigated in terms of the vertical reflectivity profile, electrification and dynamics of clouds. The research is facilitated by remote sensing data, which include instantaneous vertical reflectivity fields derived from the TRMM precipitation radar (PR), coincident 1/2-hourly observations of long-range lightning accumulation and Global IR fields. Results show a strong indication of the magnitude and intensity of electrification of a thunderstorm with the stage of its life. More vigorous dynamic conditions with intense electrification are observed during the growing stage of the storm and more or less stable situation uniform distribution of electrification has been distributed to most of the pixels in the storm during its maturity stage and less rainfall and electrification during its decaying stage was a general observation during the period. The vertical reflectivity has been found to be strongly related to the electrification and the stage of the convective life cycle in such away that the reflectivity decrease as the storm matures and decays. A good correlation is observed between the strength of vertical profile of reflectivity, which is a proxy for the ice concentration, and lightning activity.
SA51B-02
Electric Storm Effects on the Soft and Hard Cosmic Rays Components Observed in Mexico City
The effects of electric thunderstorms on the electromagnetic and muon components of the cosmic ray secondary flux were studied during severe storms in 2004 and part of 2005 analyzing the variations of the counting rates shown in the upper and lower scintillators of the muon telescope installed in Mexico City. Results show that for positive configurations of the electric field soft component particles show an increase of flux that can be interpreted as particle acceleration. For the hard component the inverse effect is observed, that is a decrease in the counting rates for positive electric field storms. These results are in agreement with those obtained by Khaerdinov et al (1 and 2). (1) Khaerdinov N.S., Lidvansky A.S., Petkov V.B., and Surovetsky Yu P. 2003, Effect of Disturbed Electric Field of the Atmosphere on Cosmic Rays: 1. Soft Component, Proc. 28th ICRC, pp. 4169-4172. (2) Khaerdinov N.S., Lidvansky A.S., Petkov V.B. 2003, Effect of Disturbed Electric Field of the Atmosphere on Cosmic Rays: 2. Hard Component, Proc. 28th ICRC, pp. 4173-4176.
SA51B-03
Polarization Catastrophe Contributing to Rotation and Tornadic Motion in Cumulo-Nimbus Clouds
When the concentration of sub-micron ice particles in a cloud exceeds 2.5E21 per cubic cm, divided by the squared average number of water molecules per crystallite, the polarization catastrophe occurs. Then all ice crystallites nucleated on aerosol dust particles align their dipole moments in the same direction, and a large polarization vector field is generated in the cloud. Often this vector field has a radial component directed away from the vertical axis of the cloud. It is induced by the pre-existing electric field caused by the charged screening layers at the cloud surface, the screening shell of the cloud. The presence of a vertical component of the magnetic field of the earth creates a density of linear momentum G=DxB in the azimuthal direction, where D=eE+P is the electric displacement vector and e is the vacuum permittivity. This linear momentum density yields an angular momentum density vector directed upward in the nordic hemisphere, if the polarization vector points away from the vertical axis of the cloud. When the cloud becomes colloidally unstable, the crystallites grow beyond the size limit at which they still could carry a large ferroelectric saturation dipole moment, and the polarization vector quickly disappears. Then the cloud begins to rotate with an angular momentum that has the same direction. Due to the large average number of water molecules in a crystallite, the polarization catastrophe (PC) is present in practically all clouds, and is compensated by masking charges. In cumulo-nimbus (thunder-) clouds the collapse of the PC is rapid, and the masking charges lead to lightning, and in the upper atmosphere also to sprites, elves, and blue jets. In stratus clouds, however, the collapse is slow, and only leads to reverse polarity in dissipating clouds (minus on the bottom), as compared with growing clouds (plus on the bottom, because of the excess polarization charge). References: P.H. Handel: "Polarization Catastrophe Theory of Cloud Electricity", J. Geophysical Research 90, 5857-5863 (1985). P.H. Handel and P.B. James: "Polarization Catastrophe Model of Static Electrification and Spokes in the B-Ring of Saturn", Geophys. Res. Lett. 10, 1-4 (1983).
SA51B-04
Laboratory Simulation of Field Ion Emission From Dust Grains
Field ion emission is one of the most interesting processes in dusty plasma science. This process limits the maximum positive charge and electric field intensity at the dust grain surface. In our laboratory, we carry out experimental simulations of dust charging processes. Our setup is based on electrodynamic quadrupole trap where we are able to hold a single dust particle for a long time (typically tens of hours). The grain bombardment by the ion beam results in its charging to a high positive potential. The charge is then released by field ion emission. We have studied many discharging characteristics from conductive dust grains charged by ions of several gasses with energies up to 10 keV. We have found that the field ion emission depends on many factors (i.e., ion beam energy, ion mass, total dose of ion bombarding, and history of dust grain charging). In the contribution, we discuss aforementioned effects and their importance for the processes in the interplanetary space.