Weather Wonders Answered

Red sprites are upper-atmospheric Transient Luminous Events (TLEs) occurring 50 to 90 km above Earth's surface in the mesosphere—far above commercial aviation and storm tops. When an exceptionally energetic positive cloud-to-ground (+CG) lightning stroke drains tens of coulombs of charge from a wide stratiform anvil, the sudden quasi-electrostatic field excites low-pressure nitrogen molecules into glowing crimson tendrils for 5 to 20 milliseconds. Low-light mirrorless cameras aimed 150–400 km away over clear foreground horizons record them far more readily than the dark-adapted human eye.

Its true name is a circumhorizontal arc. Rainbows form in spherical liquid raindrops opposite the sun; circumhorizontal arcs appear 46 degrees below the sun in high-altitude ice-crystal cirrus clouds only when the sun stands higher than 57.8 degrees above the horizon. Because of that geometric cutoff, observers north of 55°N (such as Northern Scotland or Scandinavia) can never see one from sea level, regardless of cloud cover.

No. Radar and wind-tunnel research confirms that giant hailstones generally take a single curved, horizontal-to-arcing ride across a wide supercell updraft. Alternating clear and milky layers simply record transitions between high liquid-water regions (wet growth, clear ice) and colder/lower-water regions (dry rime growth, air-bubble-rich opaque ice).

Scale, lifetime, and cloud coupling. Fire whirls are surface boundary-layer vortices spun up by buoyant shear flames without deep cloud attachment. Fire-generated tornadoes (such as the 2018 Carr Fire EF3-equivalent vortex) are anchored continuously from the surface into a rotating pyrocumulonimbus cloud base kilometers overhead.

Known as Alexander's dark band (described by Alexander of Aphrodisias around 200 CE), this 8-degree band between the 42-degree primary bow and 51-degree secondary bow appears dark because raindrops scatter once-reflected rays strictly inside 42 degrees (brightening the interior of the primary bow) and twice-reflected rays outside 51 degrees, starving the zone in between of internally reflected sunlight.

Viral clips claiming rainbow clouds predict earthquakes almost invariably show ordinary cloud iridescence or circumhorizontal arcs in lenticular or cirrocumulus clouds that occur somewhere every day. Because cirrus ice optics happen frequently over mountain belts that are also seismically active, hindsight bias links routine sky optics to subsequent tremors without any causal physical mechanism.

Polar mesospheric clouds form around 80 to 85 km altitude—the coldest layer of Earth's atmosphere in summer (−120 °C), where trace water vapor freezes onto meteoric smoke nanoparticles. Because they sit five times higher than tropospheric weather clouds, sunlight continues grazing them from below the horizon an hour or two after ground-level sunset.

A shelf cloud (arcus) traces cool, sinking rain-cooled air spreading outward away from a storm, whereas a tornado requires concentrated, persistent vertical rotation under an updraft base (often a localized wall cloud). While severe straight-line winds or brief gustnadoes occur along shelf clouds, the entire multi-kilometer shelf does not drop as a giant tornado.

Keep the uncropped original RAW/JPEG file with EXIF timestamp (and UTC offset), approximate compass bearing, lens focal length (e.g., 24mm vs. 200mm), exposure duration, and a second frame taken 30–60 seconds later. Two frames separated by half a minute instantly distinguish stationary standing wave clouds or scud tags from rotating vortices.