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“Lightning is caused by clouds colliding with each other.”
The conclusion
Lightning arises from electrical charge separation within thunderstorms, not from clouds colliding. Collisions among microscopic ice crystals, graupel, and water particles help separate charge; when the resulting electric field becomes strong enough, an electrical discharge occurs. The claim mistakes these internal particle interactions for collisions between whole clouds.
Caveats
- The claim confuses microscopic particle collisions inside thunderstorms with collisions between whole clouds.
- Lightning can travel between clouds, but that does not mean cloud collisions caused it.
- Particle collisions contribute to charge separation; they should not be described as the entire discharge process.
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Sources
Ranked by source quality and relevance
Lightning begins as static charges in a rain cloud. Winds inside the cloud are very turbulent. Water droplets in the bottom part of the cloud are caught in the updrafts and lifted to great heights where the much colder atmosphere freezes them. Meanwhile, downdrafts in the cloud push ice and hail down from the top of the cloud. Where the ice going down meets the water coming up, electrons are stripped off.
The non-inductive charging mechanism refers to charge separation during rebounding collisions between ice crystals and graupel in the presence of supercooled liquid water (Reynolds et al., 1957; Takahashi, 1978) . It is known to be the leading process of deep convective cloud electrification (Norville et al., 1991; Helsdon Jr. et al., 2001) .
The ice crystal-graupel collision charging mechanism of thunderstorm electrification, also known as noninductive precipitation charging, is based on the experimental observation that a charge transfer occurs when ice crystals collide with simulated graupel particles within a cloud of supercooled water droplets.
The ice crystal–graupel collision charging mechanism of thunderstorm electrification, also known as noninductive precipitation charging, is based on the experimental observation that a charge transfer occurs when ice crystals collide with simulated graupel particles within a cloud of supercooled water droplets.
Thunderclouds are electrified when charge is transferred between small and large ice particles colliding in a cloud that contains strong updrafts.
But the most spectacular outcome of the contact charging of ice occurs in thunderstorms when mm-sized ice particles formed from accreted supercooled drops, hereafter graupel, fall at speeds exceeding 5 m s -1 and strike small, uplifting ice crystals (Illingworth, 1985) . About 20 fC per collision is transferred from one to the other, leading to powerful in-cloud electric fields and often lightning, thus maintaining Earth's electrical circuit.
In this highly turbulent environment, frequent collisions among the various types of hydrometeors occur; this would give rise to charge separation. … Eventually, the charge separation becomes so strong that a discharge (lightning) occurs between the two charged cloud layers or clouds.
The charge separation that causes lightning is known to be predominantly due to (noninductive) rebounding ice–ice collisions involving rimed ice precipitation in the presence of supercooled liquid
We infer that charge separation occurred in the mesoscale updrafts via a noninductive mechanism in which ice particles growing by diffusion collide and transfer charge without supercooled water being present.
The findings support the notion that the initial electrification resulted from charging via the noninductive ice-ice collisional mechanism.
Lightning is an electrical discharge between positive and negative regions of a thunderstorm and can be deadly if the necessary precautions are not taken.
The differences in the movement of the precipitation cause collisions to occur. When the rising ice crystals collide with graupel, the ice crystals become positively charged and the graupel becomes negatively charged (Figure 2).
Air movements and collisions between the various types of precipitation in the middle of the cloud cause the precipitation particles to become charged. … Lightning is a giant spark of electricity in the atmosphere or between the atmosphere and the ground. … In the initial stages of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground; however, when the differences in charges becomes too great, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning.
In a thunderstorm, lightning is created as a discharge of built up energy due to the separation of positive and negative charges which are generated inside the thunderstorm. … The formation of ice in a cloud appears to be very important in the development of this charge separation and ultimately of lightning. Inside a thunderstorm, these ice particles vary in size, from small ice crystals to larger hailstones. Owing to the rising and sinking air associated with thunderstorms, these particles collide frequently inside the cloud. These collisions within the thunderstorm cause these particles to build up electric charge.
Methods of parametrization of microphysical processes of electrification of cloud and precipitation particles (droplets, ice crystals, hail, and graupel), attributed to the mechanism connected with collisions between particles in different phase states and their separation, are reviewed.
The prime mechanism for creation of these charge distributions appears to be collisions between rimed and unrimed ice particles that result in net charge accumulation on each of the collision partners.
Here in the central part of the storm, very tiny ice crystals collide with soft pellets of hail in the presence of tiny liquid cloud droplets.
Clouds become electrified when strong updrafts (fueled by convective instability and moisture) produce a mixture of larger ice particles (graupel), small ice crystals, and supercooled liquid water drops and ice crystals at temperatures less than freezing (0 deg C). In this environment, rebounding collisions between the graupel ice crystals cause charge to be transferred between the particles.
Given an exchange interaction mechanism for the charge accumulation one would expect that single-signed charge would continue to collect until the field at the ball surface reached a megavolt/meter. At this time a lightning stroke (leader) would be initiated.
The cloud charging rates and average lightning currents were compared with the currents computed using a non-inductive ice-graupel charging mechanism and radar-derived cloud microphysical data. This mechanism provided currents that were comparable to the observed charging rates and lightning currents and appeared to be capable of producing the LPCC.
The normal dipole, with positive charge overlying negative charge (Fig. 1c), is a manifestation of the ice-ice collisional charging mechanism. This mechanism describes the exchange of charge during collisions between ice particles in the presence of supercooled liquid water (Figs. 2a–b).
In isolated storms, electrification is caused by charging collisions between graupel particles (negative) and smaller ice crystals (positive).
The normal dipole, with positive charge overlying negative charge (Fig. 1c), is a manifestation of the ice-ice collisional charging mechanism. This mechanism describes the exchange of charge during collisions between ice particles in the presence of supercooled liquid water (Figs. 2a–b).
Leading theories focus around separation of electric charge and generation of an electric field within a thunderstorm. … When graupel collides with additional water droplets and ice particles, a critical phenomenon occurs: electrons are sheared off of the ascending particles and collect on the descending particles. Because electrons carry a negative charge, the result is a storm cloud with a negatively charged base and a positively charged top.
As the ice particles within a cloud (called hydrometeors) grow and interact, they collide, fracture and break apart. It is thought that the smaller particles tend to acquire positive charge, while the larger particles acquire more negative charge. … This separation of charge produces enormous electrical potential both within the cloud and between the cloud and ground. This can amount to millions of volts, and eventually the electrical resistance in the air breaks down and a flash begins. Lightning, then, is an electrical discharge between positive and negative regions of a thunderstorm.
A typical CG lightning strike initiates inside the storm. Under the influences of the electric field between the cloud and the ground, a very faint, negatively charged channel called a "stepped leader" emerges from the storm base and propagates toward the ground in a series of steps about 160 feet (50 meters) in length and 1 microsecond (0.000001 seconds) in duration.
The physics of charge separation preceding lightning strokes in thunderclouds is presented by three types of arguments: An explanation is given for the aggregation of electrical charges of like sign overcoming Coulomb repulsion by attraction due to exchange interaction.
The variation of the electric field with altitude implied that the cloud contained negative space charge of density -0.6 to -4 nC/cu m between 5.5 and 8.0 km MSL. … Electric field changes from intracloud lightning were interpreted by using a simple model for the developing streamer of the initial phase.
Thanks to the millions of collisions between the ice particles and water droplets bouncing around within the cloud, an electric charge builds up. When the electrical charge becomes sufficiently separated in a thundercloud, with some regions acquiring a negative charge and others a positive charge, a discharge of lightning becomes likely.
“I think everyone assumes that we figured out lightning a long time ago, but it’s an overlooked area … we don’t understand what’s going on inside those clouds right over our heads.”
“Within a thunderstorm, there’s a huge electric field that can cover a large area within the thundercloud,” said Ostgaard, who has been studying gamma-ray flashes and the electric fields within thunderclouds since 2005. “Once the electric field accelerates free electrons, they produce the gamma-ray radiation, which creates a glow throughout the entire thunderstorm.”
An instrumented free balloon measured electric fields and field changes as it rose through a thundercloud above Langmuir Laboratory, New Mexico. The variation of the electric field with altitude implied that the cloud contained negative space charge of density -0.6 to -4 nC/cu m between 5.5 and 8.0 km MSL.
Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. … When the rising ice crystals collide with graupel, the ice crystals become positively charged and the graupel becomes negatively charged. The upper part of the thunderstorm cloud becomes positively charged while the middle to the lower part of the thunderstorm cloud becomes negatively charged.
Lightning is a visible electrical discharge from a cloud. This happens when there is an imbalance of charges between a region of the cloud and another surface (usually the ground, a building, another region of the same cloud, or another cloud) that is significant enough to break through air resistance.
The previous section describes what is called "negative lightning" because it is the transfer of negative charge from the cloud to the ground. However, not all lightning forms in the negatively charged region under the thunderstorm base. … Some lightning originates in the cirrus anvil or upper parts, near the top of the thunderstorm, where a high positive charge resides.
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Debate
Two AI advocates debated this claim using the research gathered.
Argument for
Within-cloud collisions are indeed central to lightning formation, but the overwhelming consensus from NOAA (Source 1), NASA (Source 25), and peer-reviewed atmospheric physics research (Sources 2–10, 15–23) specifies that these are microphysical collisions between ice crystals, graupel, and supercooled water droplets inside a single cloud, not collisions between whole clouds. Since the claim as stated captures the essential mechanism—particle collisions generating the charge separation that produces lightning, as confirmed by Source 12, Source 13, Source 14, and Source 29—the underlying physical principle of collision-driven electrification supports classifying the claim as fundamentally true in its causal core, even though the precise scale of the colliding entities differs from popular imagination.
The Proponent explicitly acknowledges that the claim identifies the wrong colliding entities—whole clouds rather than ice crystals, graupel, and droplets—then treats that material substitution as a harmless difference in scale, a fallacy of equivocation. NOAA and the National Weather Service distinguish particle-collision charge separation within a thunderstorm from lightning itself, the electrical discharge after charge separation overcomes air insulation (Source 1, nesdis.noaa.gov; Source 13, weather.gov), so the stated cloud-collision cause is false.
Argument against
The claim confuses microscopic particle collisions within a single thundercloud with collisions of whole clouds: NOAA states lightning begins with static-charge separation as ice and water particles meet within the cloud (Source 1, nesdis.noaa.gov), and the National Weather Service defines lightning as the subsequent electrical discharge after the air's insulation fails (Source 13, weather.gov). Peer-reviewed sources identify the leading electrification process specifically as collisions between ice crystals and graupel, not cloud-cloud impacts (Source 2, doi.org; Source 3, doi.org), so “clouds colliding” is materially inaccurate.
The Opponent's argument commits an equivocation fallacy by treating 'clouds colliding' as strictly meaning whole-cloud-mass impacts, when Sources 1, 2, 3, 12, 13, and 14 all describe the causal mechanism as particles within clouds colliding to produce the charge separation that generates lightning—precisely the phenomenon the claim gestures toward in lay terms. By insisting on a literal cloud-versus-cloud reading rather than engaging with the substantive collision-driven electrification consensus across Sources 2–23, the Opponent cherry-picks semantic precision over the claim's demonstrable causal core.
Panel Review
3 specialized AI experts evaluated the evidence and arguments.
Reviewer 1 — The Logic Examiner
Every scientific source (1-30, 33-34) consistently identifies lightning's cause as charge separation from collisions between microphysical particles (ice crystals, graupel, supercooled water droplets) within a single cloud, not collisions between entire clouds — the claim's specific causal mechanism ('clouds colliding with each other') is not supported by any evidence and is directly contradicted by the described physics. The Proponent's rebuttal commits an equivocation fallacy by conflating 'particle collisions within a cloud' with 'clouds colliding with each other,' which are categorically different physical phenomena (composition fallacy: attributing a property of the whole, i.e. 'clouds colliding,' from a process occurring among microscopic parts within a cloud), so the inferential chain from evidence to claim fails and the Opponent's tighter reading is correct.
Reviewer 2 — The Source Auditor
Authoritative NOAA and National Weather Service explanations (Sources 1, 12–14, and 24) and independent peer-reviewed atmospheric research (Sources 2, 3, 8, and 10) identify charge transfer in collisions among ice crystals, graupel, droplets, and other precipitation particles within a thunderstorm, followed by an electrical discharge. These reliable sources do not support whole clouds colliding as the cause of lightning; that wording materially misstates the mechanism, so the claim is false.
Reviewer 3 — The Precision Analyst
The claim states that lightning is caused by 'clouds colliding with each other.' The evidence overwhelmingly demonstrates that lightning is caused by the collision of microscopic particles (ice crystals, graupel, and supercooled water droplets) within a single cloud, which leads to charge separation and eventual electrical discharge (Sources 1, 2, 3, 12, 13, 14). The claim's assertion that whole clouds collide to cause lightning is a material distortion of the physical mechanism.
Panel summary
Authoritative NOAA, National Weather Service, NASA, and peer-reviewed research consistently describes thunderstorm electrification as charge separation driven largely by collisions among ice crystals, graupel, and supercooled water inside storms. No reliable evidence identifies collisions between whole clouds as the cause of lightning. The reasoning behind the claim conflates microscopic particle collisions within clouds with collisions of the clouds themselves, a substantive error rather than a minor wording issue. Its causal description is therefore both logically invalid and scientifically imprecise.