Lightning is a powerful natural display of atmospheric electricity, a sudden discharge that equalizes electrical charges between regions. These regions can be within a single cloud, between different clouds, or between a cloud and the ground. Cloud-to-ground lightning is particularly impactful due to its direct interaction with the Earth’s surface. Among these events, positive lightning stands out as a less common, yet remarkably potent, type of electrical discharge.
The Formation of Positive Lightning
Lightning generation in thunderstorms begins with charge separation, where different parts of a cloud accumulate opposing electrical charges. Within a towering cumulonimbus cloud, strong updrafts carry supercooled water droplets and small ice crystals upward. Larger, denser ice particles like graupel fall or remain suspended lower in the storm. Collisions between rising ice crystals and descending graupel cause ice crystals to acquire a positive charge and graupel to become negatively charged.
This process typically leads to the upper regions of the thunderstorm cloud, including the anvil, becoming positively charged. Conversely, the middle and lower sections of the cloud accumulate negative charges. Most cloud-to-ground lightning transfers negative charge from the cloud’s base to the ground. However, positive lightning originates from the positively charged upper parts or anvil of the storm.
For positive lightning to occur, a pathway for this upper positive charge must develop downward towards the ground. This often happens when strong upper-level winds tilt the storm or when the anvil cloud extends horizontally, removing the shielding effect of negative charges in the main storm body. If the electrical potential difference between this elevated positive charge and the ground becomes sufficiently large, a positively charged leader can descend, initiating the powerful discharge. This unique formation mechanism means positive lightning can occur in areas far from the main rain shaft or even the core of the thunderstorm.
Unique Characteristics of Positive Lightning
Positive lightning possesses distinct physical properties that differentiate it from negative lightning. It involves a net transfer of positive charge from the upper, positively charged regions of a thunderstorm. This requires the electrical discharge to travel a greater distance through the atmosphere.
Positive lightning flashes exhibit significantly higher electrical charge, voltage, and current compared to negative counterparts. An average negative lightning bolt carries about 30,000 amperes and 300 million volts. Large positive lightning strikes can reach up to 400,000 amperes and one billion volts, making them up to ten times more powerful. Positive lightning typically has a longer flash duration.
Positive lightning often strikes far from the storm’s core, occurring 10 to 25 miles away. These strikes can appear to come from a clear sky where thunder is not audible, a phenomenon known as a “bolt from the blue.” Unlike negative lightning, which often consists of multiple strokes, positive lightning is usually a single, powerful stroke.
Why Positive Lightning is More Dangerous
The characteristics of positive lightning contribute to its increased danger. Its significantly higher electrical charge and current, which can be many times greater than negative strikes, translate into a much higher destructive potential. This immense energy can cause more severe damage to structures. Its extended flash duration also increases the likelihood of igniting fires.
Positive lightning’s ability to strike many miles away from the thunderstorm’s main body, often under clear skies, creates a substantial hazard. This “bolt from the blue” phenomenon means people can be struck without prior indication of a nearby storm. This lack of warning makes it particularly hazardous for outdoor activities.
Its greater power and unexpected nature pose a significant threat to living beings, contributing to a higher fatality rate among lightning strike victims. It can also cause extensive damage to power lines, leading to widespread outages. Its intense energy and unpredictable reach make positive lightning a formidable atmospheric phenomenon.