Measurements of atmospheric electricity aloft

Measurements of the electrical characteristics of the atmosphere above the surface have been made for over 200 years, from a variety of different platforms, including kites, balloons, rockets and aircraft. From these measurements, a great deal of information about the electrical characteristics of the atmosphere has been gained, assisting our understanding of the global atmospheric electric circuit, thunderstorm electrification and lightning generation mechanisms, discovery of transient luminous events above thunderstorms, and many other electrical phenomena. This paper surveys the history of atmospheric electrical measurements aloft, from the earliest manned balloon ascents to current day observations with free balloons and aircraft. Measurements of atmospheric electrical parameters in a range of meteorological conditions are described, including clear air conditions, polluted conditions, non-thunderstorm clouds, and thunderstorm clouds, spanning a range of atmospheric conditions, from fair weather, to the most electrically active

Influence of ion attachment on the vertical distribution of the electric field and charge density below a thunderstorm

A numerical model called PICASSO [Production d'Ions Corona Au Sol Sous Orage (French) and Production of Corona Ions at the Ground Beneath Thundercloud (English)], previously designed, is used to describe the evolution of the principal electrical parameters below a thunderstorm, taking into account the major part played by corona ions. In order to improve the model restitution of a real situation, various improvements are performed: an initial vertical distribution of aerosol particles is introduced instead of the previously used uniform concentration; time and space calculation steps are adjusted according to the electric field variation rate; the upper boundary condition is improved; and the coefficients of ion attachment are reconsidered with an exhaustive bibliographic study. The influence of the ion attachment on aerosol particles, on the electric field and charge density aloft, is studied by using three different initial aerosol particle concentrations at ground level and two types of initial vertical distributions: uniform and non-uniform. The comparison between field data and model results leads to adjust the initial aerosol particle concentration over the experimental site at the value of 5000 cm-3 which appears to be highly realistic. The evolutions of the electric field and of the charge density at altitude are greatly influenced by the aerosol concentration. On the contrary, the surface intrinsic field, defined as the electric field that would exist underneath a thundercloud if there were no local charges, is weakly affected when the model is forced by the surface field. A good correlation appears between the success in the triggered lightning attempts and this intrinsic field evaluation. Therefore, when only the surface field is available, the model can be used in a triggered lightning experiment

precipitation and lightning activity in thunderstorms,

5-13 juin 200

Influence of water conductivity on microdischarges from raindrops in strong electric fields.

(9-13 juin 2003)

A New Videosonde with a Particle Charge Measurement Device for In Situ Observation of Precipitation Particles

A new videosonde designed for microphysical soundings inside thunderclouds is described. This sensor makes use of a charge-coupled device (CCD) camera and can provide the phase (liquid or ice), the shape, the size, and the electric charge of each precipitating particle detected singly, the size of which ranges from 0.5 mm to 2 cm and the electric charge from ±1 to ±400 pC. The performances of the videosonde are analyzed and evaluated. It is found that the accuracy on the size measurement varies between about 13% for the smaller sizes and less than 2.6% for the larger sizes; meanwhile the average accuracy on the charge measurement is 3.2%. The determination of several large-scale parameters deduced from the videosonde data and comparable with radar observations and electrical soundings is presented. An intercomparison experiment with a disdrometer at the ground shows that the size distribution is perfectly restituted for large drops, even though the video permits filming at a maximum rate of only 50 images per second. The discrepancies that appear for smaller sizes are probably due to windy conditions to which small particles are much more sensitive, but it does not affect the rainfall-rate determination

Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers.

Electric field measurements above ground have shown that the space charge layer created by corona at ground level shields the background electric field produced by the thundercloud. Therefore it is expected that this space charge layer can also influence the conditions required to initiate upward lightning from tall objects. For this reason, a numerical model that describes the evolution of the main electrical parameters below a thunderstorm is used to compute the space charge layer development. The time variation of the electric field measured at 600 m above ground during the 1989 rocket triggered lightning experiment at the Kennedy Space Center (Florida) is used to drive the model. The obtained space charge density profiles are used to compute the conditions required to initiate stable upward lightning positive leaders from tall towers. Corona at the tip of the tower is neglected. It is found that the space charge layer significantly affects the critical thundercloud electric fields required to initiate upward lightning leaders from tall objects. The neutral aerosol particle concentration is observed to have a significant influence on the space charge density profiles and the critical thundercloud electric fields, whereas the corona current density does not considerably affect the results for the cases considered in the analysis. It is found that a lower thundercloud electric field is required to trigger a lightning flash from a tall tower or other tall slender grounded structure in the case of sites with a high neutral aerosol particle concentration, like polluted areas or coastal regions

A New Videosonde with a Particle Charge Measurement Device for In Situ Observation of Precipitation Particles

A new videosonde designed for microphysical soundings inside thunderclouds is described. This sensor makes use of a charge-coupled device (CCD) camera and can provide the phase (liquid or ice), the shape, the size, and the electric charge of each precipitating particle detected singly, the size of which ranges from 0.5 mm to 2 cm and the electric charge from ±1 to ±400 pC. The performances of the videosonde are analyzed and evaluated. It is found that the accuracy on the size measurement varies between about 13% for the smaller sizes and less than 2.6% for the larger sizes; meanwhile the average accuracy on the charge measurement is 3.2%. The determination of several large-scale parameters deduced from the videosonde data and comparable with radar observations and electrical soundings is presented. An intercomparison experiment with a disdrometer at the ground shows that the size distribution is perfectly restituted for large drops, even though the video permits filming at a maximum rate of only 50 images per second. The discrepancies that appear for smaller sizes are probably due to windy conditions to which small particles are much more sensitive, but it does not affect the rainfall-rate determination

A new videosonde for in situ observation of precipitation particles.

9-13 juin 200

Surface precipitation electric current produced by convective rains during MAP

This paper presents data from measurements of electric field, precipitation current density, and rainfall parameters performed during the Mesoscale Alpine Program experiment in northern Italy during autumn 1999. Several days of the period provided substantially charged rainfall of both polarities. The average proportions of each polarity are close, but the negative one is slightly larger (54%). Three Doppler radars provided a description of the cells' development and dynamics. A case of a deeply convective cell occurred on 17 September 1999. In this case, the precipitation current density is first positive, reaches more than 100 nA m−2, and changes its polarity when the rainfall is maximum with a value close to 200 mm h−1. We also consider several shallow convective cells passing over the experimental site on 3 October. Two cells among a set of eight did not produce electrical parameter variations although they displayed development and radar reflectivity structure similar to that of the others. The dynamical study shows that the vertical velocity (averaged over 1 km × 1 km mesh) was weaker within these two cells with a value of only 0.5 m s−1 while it reached 1.5 m s−1 within the other cells. Both charge polarities were observed on the rain produced by electrified cells, first the negative one and then the positive one. A very tight correlation between surface electric field and precipitation current is observed out at the surface, displaying the mirror image effect. The ground electric field is due to the cloud charge, in contrast with that carried down to the ground by the rainfall. In order to reproduce the field evolution created by the cell passage, we test different models of charge distribution. A model including a horizontal distribution is found to provide a field evolution in best agreement with the observations. According to this model the net charge of the cloud above the site is chronologically positive and negative, which can be the result of the evacuation of an opposite charge by the rain