Figure 7. Charge-separation characteristics in a sheared environment depend on temperature and cloud liquid-water content, as shown in these schematics developed from laboratory observations (data from Saunders and Peck 1998). The vertical vectors show up- or downdraft velocity. Graupel grows only in the region where liquid water exists, and charge separation occurs only where graupel and ice are growing. Secondary ice-crystal production takes place under the appropriate conditions in the -5-degree scenario, and the crystals may be carried to higher levels by the updraft. Thus in both the coldest and warmest conditions, little negative charge develops.