Chapter 10: Thunderstorms Flashcards
A thunderstorm should be thought of as
a process which takes heat and moisture near the Earth’s surface and transports it to the upper levels of the atmosphere.
A thunderstorm should be thought of as a process which takes heat and moisture near the Earth’s surface and transports it to the upper levels of the atmosphere. The by-products of this process are
the clouds, precipitation, and wind that we associate with the thunderstorm
All thunderstorms, whether or not they become severe, must have three conditions present in order to form.
moisture
instability
lift
The first necessary condition is moisture in
the lower to mid-levels of the atmosphere.
The first necessary condition is moisture in the lower to mid-levels of the atmosphere. As air rises in a thunderstorm updraft, moisture
condenses into small water drops which form clouds (and eventually precipitation).
The first necessary condition is moisture in the lower to mid-levels of the atmosphere. As air rises in a thunderstorm updraft, moisture condenses into small water drops which form clouds (and eventually precipitation). When the moisture condenses
heat is released into the air, making it warmer and less dense than its surroundings. The added heat allows the air in the updraft to continue rising.
The second necessary condition is instability. If the air-mass is unstable
air which is pushed upward by some force will continue upward
The second necessary condition is instability. If the air-mass is unstable, air which is pushed upward by some force will continue upward. An unstable airmass usually contains
relatively warm (usually moist) air near the earth’s surface and relatively cold (usually dry) air in the mid and upper levels of the atmosphere.
. An unstable airmass usually contains relatively warm (usually moist) air near the earth’s surface and relatively cold (usually dry) air in the mid and upper levels of the atmosphere. The low-level air will
rise in an updraft because it is less dense than the surrounding air.
An unstable airmass usually contains relatively warm (usually moist) air near the earth’s surface and relatively cold (usually dry) air in the mid and upper levels of the atmosphere. The low-level air will rise in an updraft because it is less dense than the surrounding air. The air will
continue to move upward until it becomes colder and more dense than its surroundings.
The third necessary condition is a source of lift. Lift is a mechanism for
starting an updraft in a moist, unstable airmass
The third necessary condition is a source of lift. Lift is a mechanism for starting an updraft in a moist, unstable airmass. The lifting source can take on several forms. The most common source is called
differential heating (convection).
differential heating (convection)
). As the sun heats the earth’s surface, portions of the surface (and the air just above the surface) will warm more readily than nearby areas. These “warm pockets” (bubbles) are less dense than the surrounding air and will rise. If the air has sufficient moisture and is unstable, a thunderstorm may form
The source of lift can also be
mechanical in nature
……………………………. also act as triggers by lifting moist, low-level air to the point where the low-level air is warmer and less dense than its environment at which time thunderstorms can form.
Orographic lifting,
advancing cold fronts,
outflow boundaries,
drylines, and
sea breeze fronts
The Thunderstorm Life Cycle
cumulus stage
mature stage
dissipating (decaying) stage
Cumulus Stage
Warm, moist air rises in a series of convective updrafts. As this occurs the air begins to condense into a cumulus cloud. The condensation releases heat into the cloud, warming the air. This, in turn, causes it to rise adiabatically
Cumulus Stage
Warm, moist air rises in a series of convective updrafts. As this occurs the air begins to condense into a cumulus cloud. The condensation releases heat into the cloud, warming the air. This, in turn, causes it to rise adiabatically. The cloud edges during this stage are
sharp and distinct, indicating that the cloud is composed primarily of water droplets
Cumulus Stage
Warm, moist air rises in a series of convective updrafts. As this occurs the air begins to condense into a cumulus cloud. The condensation releases heat into the cloud, warming the air. This, in turn, causes it to rise adiabatically. The cloud edges during this stage are sharp and distinct, indicating that the cloud is composed primarily of water droplets. The process continues and works to form a
towering cumulus cloud
Cumulus Stage
Warm, moist air rises in a series of convective updrafts. As this occurs the air begins to condense into a cumulus cloud. The condensation releases heat into the cloud, warming the air. This, in turn, causes it to rise adiabatically. The cloud edges during this stage are sharp and distinct, indicating that the cloud is composed primarily of water droplets. The process continues and works to form a towering cumulus cloud. The convective cloud continues to
grow upward, eventually growing above the freezing level where supercooled water droplets and ice crystals coexist.
……………………………………………….. start the initiation of cool downdrafts, which leads to the second stage
The beginning of falling precipitation and cool air entrainment from the environment
Mature Stage
This stage is characterized by
the presence of both updrafts and downdrafts within the cloud.
This stage is characterized by the presence of both updrafts and downdrafts within the cloud. The downdrafts are initiated by
by the downward drag of falling precipitation
Mature Stage
This stage is characterized by the presence of both updrafts and downdrafts within the cloud. The downdrafts are initiated by the downward drag of falling precipitation. The downdraft is strengthened by
evaporative cooling, as the rain falling with the downdraft enters drier air below the cloud base and evaporates