Passage VI

Lightning occurs when separate regions of positive and negative electrical charge develop in a cloud. Three experiments examined how these charges develop.

Experiment 1

Figure 1 shows the electrical charge (+ or -), altitude, and temperature, in degrees Celsius (°C), measured by several weather balloons as they rose through a thundercloud.

Experiment 2

Opposite charges may develop when H₂O ice crystals and graupel (large ice and water particles) collide in a thundercloud. A chamber was filled with air at a known temperature (°C) and water content, in grams per cubic meter (g/m³). The charge, in coulombs (C), that formed on graupel falling through suspended H₂O ice crystals and water droplets in the chamber was measured. The procedure was repeated for other temperatures and water contents. The results are shown in Figure 2.

Experiment 3

When water droplets containing dissolved ions freeze, opposite charges may develop between the newly formed ice crystals and the still unfrozen droplets. As the ice crystals and droplets separate in a cloud, charged regions form.

Solutions of four sodium (Na) salts, containing fluoride (F^-) , chloride (Cl^-), bromide (Br^-), or iodide (I^-) ions, were each made at six different concentrations, in moles per liter (moles/L). The solutions were slowly cooled until freezing began. The electrical potential (whether the droplets had a positive or negative charge with respect to the ice crystals) was measured in volts. The results are shown in Figure 3.