Atmospheric convection
This process is driven by parcel-environment instability, meaning that a "parcel" of air is warmer and less dense than the surrounding environment at the same altitude.
This expansion contributes to increased winds, cumulus cloud development, and decreased surface dew points (the temperature below which condensation occurs).
Convection plays a crucial role in weather patterns, influencing cloud formation, wind, and the development of thunderstorms, which can be associated with severe weather phenomena like hail, downbursts, and tornadoes.There are a few general archetypes of atmospheric instability that are used to explain convection (or lack thereof);[according to whom?]
[citation needed] Most atmospheric deep convection occurs in the tropics as the rising branch of the Hadley circulation and represents a strong local coupling between the surface and the upper troposphere which is largely absent in winter midlatitudes.
[4][5] The mass of lighter air rises, and as it does, it cools due to its expansion at lower high-altitude pressures.
If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form, which supports lightning and thunder.
Generally, thunderstorms require three conditions to form: moisture, an unstable airmass, and a lifting force (heat).
Single-cell thunderstorms form in environments of low vertical wind shear and last only 20–30 minutes.
Thundersnow is one situation where forcing mechanisms provide support for very steep environmental lapse rates, which as mentioned before is an archetype for favored convection.
The small amount of latent heat released from air rising and condensing moisture in a thundersnow also serves to increase this convective potential, although minimally.
Despite the fact that there might be a layer in the atmosphere that has positive values of CAPE, if the parcel does not reach or begin rising to that level, the most significant convection that occurs in the FCL will not be realized.
Such forcing mechanisms encourage upward vertical velocity, characterized by a speed that is relatively low to what one finds in a thunderstorm updraft.
Jet streak dynamics through the imbalance of Coriolis and pressure gradient forces, causing subgeostrophic and supergeostrophic flows, can also create upward vertical velocities.
Former theory suggested that hailstones were subjected to multiple descents and ascents, falling into a zone of humidity and refreezing as they were uplifted.
The storm's updraft, with upwardly directed wind speeds as high as 180 kilometres per hour (110 mph),[14] blow the forming hailstones up the cloud.
As the hailstone ascends it passes into areas of the cloud where the concentration of humidity and supercooled water droplets varies.
When the hailstone moves into an area with a high concentration of water droplets, it captures the latter and acquires a translucent layer.
This may take at least 30 minutes based on the force of the updrafts in the hail-producing thunderstorm, whose top is usually greater than 10 kilometres (6.2 mi) high.
It will later begin to melt as it passes into the air above freezing temperature[17] Thus, a unique trajectory in the thunderstorm is sufficient to explain the layer-like structure of the hailstone.
Tornadoes come in many sizes but typically form a visible condensation funnel whose narrowest end reaches the earth and is surrounded by a cloud of debris and dust.
A few examples on the smaller scale would include: Convection mixing the planetary boundary layer (PBL) and allowing drier air aloft to the surface thereby decreasing dew points, creating cumulus-type clouds that can limit a small amount of sunshine, increasing surface winds, making outflow boundaries/and other smaller boundaries more diffuse, and the eastward propagation of the dryline during the day.
On a larger scale, the rising of the air can lead to warm core surface lows, often found in the desert southwest.
