Helicity

{
  "id": "MLC-T-MET-001274",
  "term": "Helicity",
  "field": "Meteorology and atmospheric science",
  "definitions": [
    "A measure of the correlation between the velocity and vorticity vectors in a fluid flow, representing the amount of 'twist' or 'linkage' in the flow. In meteorology, storm-relative helicity quantifies the potential for a thunderstorm to produce rotating updrafts, which are characteristic of supercells. It is often calculated from wind profiles obtained by sounding data.",
    "A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve. Helicity is proportional to the strength of the flow, the amount of vertical wind shear, and the amount of turning in the flow (i.e. vorticity).\n\nAtmospheric helicity is computed from the vertical wind profile in the lower part of the atmosphere (usually from the surface up to 3 km), and is measured relative to storm motion. Higher values of helicity (generally, around 150 m^2/s^2 or more) favor the development of mid-level rotation (i.e. mesocyclones). Extreme values can exceed 600 m^2/s^2."
  ],
  "see_also": [
    "storm-relative environmental helicity",
    "streamwise vorticity"
  ],
  "references": [
    "NWS Glossary"
  ],
  "url": "https://mlchart.com/terminology/meteorology/helicity/"
}