Entrance region

{
  "id": "MLC-T-MET-000872",
  "term": "Entrance region",
  "field": "Meteorology and atmospheric science",
  "definitions": [
    "A specific area within a jet stream where air parcels accelerate as they enter the core of the jet. This acceleration leads to divergence aloft and convergence at lower levels, influencing vertical motion in the atmosphere. The entrance region is characterized by a distinct pattern of ageostrophic flow.",
    "The region upstream from a wind speed maximum in a jet stream (jet max), in which air is approaching (entering) the region of maximum winds, and therefore is accelerating. This acceleration results in a vertical circulation that creates divergence in the upper-level winds in the right half of the entrance region (as would be viewed looking along the direction of flow).\n\nThis divergence results in upward motion of air in the right rear quadrant (or right entrance region) of the jet max. Severe weather potential sometimes increases in this area as a result. See also exit region, left exit region."
  ],
  "see_also": [
    "Exit Region",
    "Left Exit Region"
  ],
  "references": [
    "NWS Glossary"
  ],
  "url": "https://mlchart.com/terminology/meteorology/entrance-region/"
}