ST L2: Thunderstorm Cells and Supercells / Latent Heat and the Sun, the Source of Atmospheric Heat Flashcards
Life cycle of one thunderstorm cell?
5-15 mins
Briefly state stages of thunderstorms.
1: cumulus phase
2: mature stage
3: dissipating stage
4. storm propagation
Describe the cumulus phase.
Thunderstorms starts as a cumulus phase, having all updraft, no precipitation (i.e., rain, snow, sleet, hail, etc), and no anvil
Describe the mature stage.
having both up and downdrafts (both of which could be violent), having precipitation (which could be heavy) and the start of an anvil with a sharp or crisp outline
Describe the dissipating stage of thunderstorms.
with only downdrafts, weaker precipitation, and a large anvil with a diffuse outline
However, even after the original (mother) storm has dissipated, the gust front that it earlier created might encounter some more warm boundary layer air before it dies.
Describe the process of storm propagation.
When the gust front encounters some more warm boundary layer air before dying, the cold gust-front air plows under the warmer, humid boundary layer air, triggering an updraft that can spawn a new (daughter) thunderstorm.
Describe some organization of thunderstorms.
orographic thunderstorms, multicell storms, squall-line thunderstorms, air mass thunderstorms, supercell storms
Describe orographic thunderstorms.
Mountain-related storms. They sometimes stay over mountains because of the wind shear that fuels the storm from the boundary layer. These unmoving storms can cause flash floods
Describe multi-cell storms
Thunderstorm with many cells. Most common type of thunderstorm. In some multi-cell storms, there is a flanking line of clouds sticking out from main updraft. In the flanking line, there are often new cells in the cumulus stage. As they grow, the winds blow cells into main updraft. By then, cells are often in the mature stage.
Describe squall-line thunderstorms.
Thunderstorms that form in lines called squall lines, where heaviest rain cells merge into a long narrow line. (special type of multi-cell storm). These lines of storms can move toward the east or southeast, even though individual thunderstorms within them are moving northeast. These storms can be triggered along strong cold front or strong air-mass boundaries.
Describe air mass thunderstorms.
garden-variety storms that pop up in scattered locations within a large air mass due to strong heating of the ground by the Sun. These don’t need to form along fronts or boundaries. They are often short lived.
Describe supercell storms
Often severe, long lasting, often rotating, having violent wind gusts, and can cause tornadoes and hail. Supercell thunderstorms are often the most dangerous variety, and often consist of just ONE rotating cell.
Types of the cell:
- low precipitation (LP) supercell: produce lots of hail;
- classic supercell: have rainy downdrafts and rain-free updrafts; and
- high precipitation (HP) supercell: have updrafts that are mostly surrounded by rain.
Supercells can last for 30 minutes and longer, due to favorable wind shear in the environment. There is often low altitude flow from the southeast, mid-altitude flow from the southwest, and fast upper-level flow is from the west. It is this mid-level wind (at roughly 5 km above ground) that steers thunderstorms toward the northeast, allowing the supercell storm to continuously draw in new humid boundary-layer air as fuel.
What is wind shear?
when the wind speed or direction changes with altitude
What is a mesocyclone?
When the whole supercell thunderstorm is rotating. Barrel-shaped look of the storm. Sometimes there are cloud striation that spiral around main updraft clouds. Mesocyclone rotation can be observed by Doppler radar.
What is the Doppler Radar?
Detects motions inside the storm.
From what are the strongest tornadoes formed?
Mesocyclone rotations
Where do thunderstorm cells and supercells get their fuel/energy from?
Warm humid air near the ground.
What is a remote sensor?
an instrument that is remote from (outside of) the storm, but can measure the storm.
What is dBZ?
Disaster intensity scale for rainfall. Quantifies rain rate over specific area. Measure of the reflectivity of a radar signal reflected off water vapour.
