1.2.4.2.3. Evaporative cooling, virga and downbursts

  • 8 months ago
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  • Author: SW101

[INTRO] 1. What is a Downburst? // [ADVANCED] X. DOWNBURSTS / X.1 What is a Downburst

A downburst is a strong ground-level wind phenomenon often producing severe straight-line winds, up to and sometimes over 150 km/h. A downburst forms as a mass of rain-cooled air rapidly descends from a thunderstorm and impacts the ground, spreading outwards in all directions from the impact point. Downbursts can produce severe damage to buildings, equivalent to EF3 tornado damage. They are also much more common than tornadoes.

Downbursts are produced by rapidly descending air in a thunderstorm, impacting the ground and producing severe straight line winds. There are two types of downbursts, which differ somewhat in how they form and storm environments they are found in: dry and wet downbursts. A typical downburst goes through three stages: Contact, Outburst and Cushion stage. While downbursts differ in their apperance based on their size, cloud base height and the amount of precipitation they contain, they all share these three stages.

  • CONTACT STAGE: is the first stage, before and during contact of the downburst airmass with the ground. In this stage the downburst plummets from the cloud base towards the ground, assuming a shape similar to a water baloon.
  • OUTBURST STAGE: is the mid stage, where the downburst airmass hits the ground and spreads outwards, creating severe straight line winds.
  • CUSHION STAGE: is the final stage of a downburst, as the downburst airmass spreads out further and wind speeds diminish. The cold airmass forms a cold pool on the ground.