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The term "cyclone" is best defined as:

any circulation around a low-pressure center

Thunderstorms can be associated with these weather activities:

All of the above

In the mid-latitudes, approximately 1,300 thunderstorms occur on Earth every day. 在中纬度地区，地球上每天大约有1,300次雷暴。

Lightning can temporarily equalize the charges between:

the clouds and the ground 云层和地面

Thunderstorms form when warm, humid air rises in a unstable environment.

当温暖、潮湿的空气在不稳定的环境中上升时，就会形成雷暴。

Thunderstorms and large cumulonimbus clouds are characteristic of:

unstable air. 不稳定的空气。

Generally, there are three stages involved in the development of air mass thunderstorms. They are:

Cumulus stage, mature stage, and dissipating stage. 积云阶段、成熟阶段和消散阶段。

Strong heating of the ground by the Sun is associated with thunderstorms because it:

Leads to greater instability. 导致更大的不稳定。

The intense heating of the ground by the Sun causes the air near the surface to become warm and rise rapidly. As this warm air rises, it cools and condenses, forming cumulonimbus clouds and eventually thunderstorms. This process of warm air rising and cooler air sinking creates an unstable atmosphere, which is conducive to the development of thunderstorms.

Air mass thunderstorms are most likely to occur in the midafternoon because:

The atmosphere is most unstable at that time. 那个时候的气氛是最不稳定的。

During the midafternoon, the ground has been heated by the Sun for several hours, leading to significant warming of the surface air. This creates a large temperature difference between the surface and higher levels of the atmosphere, promoting strong upward vertical motion of air and the formation of thunderstorms. Additionally, the mixing of warm surface air with cooler air aloft enhances atmospheric instability, which is conducive to the development of thunderstorms.

Downdrafts and updrafts found side by side occur during the mature stage in the life cycle of an air mass thunderstorm. 下降气流和上升气流同时出现在气团雷暴生命周期的成熟阶段。

Updrafts dominate the cumulonimbus cloud during the cumulus stage in the life cycle of an air mass thunderstorm. 在气团雷暴生命周期的积云阶段，上升气流主导着积雨云。

Downdrafts totally dominate the dissipating stage of an air mass thunderstorm. 下降气流完全主导气团雷暴的消散阶段。

Some of the most dangerous weather is produced by a type of thunderstorm called a(n):

supercell. 超级细胞。

Squall lines 飑线

Within the same cloud 在同一个云中

False. Drylines are capable of producing thunderstorms not because the dry air mass forces the moist air mass to rise, but rather due to the lifting of moist air over the dryline boundary, creating instability and triggering thunderstorm development.

False. The terms "leader," "flash," and "stroke" are commonly used when describing lightning, not tornadoes. Tornado terminology typically includes terms such as "funnel cloud," "vortex," and "damage path."

True. The total discharge of lightning, composed of several rapid strokes, is indeed known as the flash. Each rapid stroke contributes to the overall flash duration and intensity.

False. In Canada, tornadoes are most frequent during the late spring and summer months, typically from May to September. The peak tornado season varies depending on the region within Canada, but August-September is not generally considered the most frequent period for tornado activity.

False. Tornadoes in the Northern Hemisphere, including those in Canada, most commonly move from southwest to northeast, although they can move in any direction. This pattern is due to the prevailing westerly winds in the mid-latitudes. However, tornadoes can exhibit erratic and unpredictable paths, and they may occasionally move in other directions as well. Therefore, while southwest to northeast movement is most common, it is not exclusive.

False. The Enhanced Fujita scale (EF scale) is not based on the frequency of lightning strikes concurrent with the tornado. Instead, it assesses tornado intensity based on damage caused by the tornado to human-built structures and vegetation. The EF scale ranges from EF0 to EF5, with EF5 being the most intense. The scale was developed by Ted Fujita and Allen Pearson and introduced in 2007 as an update to the original Fujita scale.

True. Doppler radars are capable of detecting the motion of precipitation particles. By analyzing the Doppler shift in the radar signals, which occurs due to the motion of the precipitation particles toward or away from the radar, meteorologists can determine the speed and direction of the precipitation. This information is valuable for monitoring weather patterns, including the presence and intensity of storms, as well as for tracking the movement of severe weather phenomena such as thunderstorms and tornadoes.

False. One of the most prominent features of middle-latitudes weather is its instability and variability rather than stability and monotony. Middle-latitudes experience frequent changes in weather patterns due to the interaction of air masses, frontal systems, and other atmospheric disturbances. This results in a wide range of weather conditions, including fluctuations in temperature, precipitation, and wind patterns. Therefore, middle-latitudes weather is characterized by its dynamic and often unpredictable nature, rather than stability and monotony.

True. Fronts are indeed boundaries between two different air masses of different densities. These air masses often have different temperature, humidity, and pressure characteristics, leading to contrasting weather conditions along the front. There are several types of fronts, including cold fronts, warm fronts, stationary fronts, and occluded fronts, each associated with specific weather phenomena and patterns of movement.

True. Roll clouds are often associated with squall lines. Squall lines are long lines of thunderstorms that form along or ahead of a cold front. Roll clouds can develop along the leading edge of a squall line, especially in the presence of strong winds and atmospheric instability. These roll clouds, also known as arcus clouds, are typically low, horizontal, and tube-shaped, appearing to roll as they move across the sky. They are a distinctive feature of squall lines and are often observed in association with severe weather events such as thunderstorms and heavy rain.

False. Warm fronts can indeed produce cumulonimbus clouds under certain conditions. Cumulonimbus clouds are associated with strong vertical development and can form in a variety of weather systems, including warm fronts. When a warm front advances, warm, moist air rises over cooler air, leading to the development of towering cumulus clouds, which can evolve into cumulonimbus clouds if the atmospheric conditions support their growth. Cumulonimbus clouds associated with warm fronts can bring heavy rain, thunderstorms, and other severe weather phenomena. Therefore, warm fronts can produce cumulonimbus clouds under the right atmospheric conditions.

False. MCC stands for "Mesoscale Convective Complex," which is a type of organized cluster of thunderstorms that can persist for many hours, often lasting through the night. MCCs are characterized by their large size, typically covering hundreds of kilometers, and they often exhibit a complex internal structure with multiple storm cells. While MCCs can produce fast-moving storms within the complex, the entire complex itself may not necessarily move quickly. In fact, MCCs can sometimes move relatively slowly or remain nearly stationary for extended periods, producing prolonged periods of heavy rain, lightning, and severe weather. Therefore, MCCs are not typically described as fast-moving storms.

True. Cold fronts moving over large bodies of water, such as the Great Lakes, can indeed produce lake-effect snow. When cold air passes over the relatively warmer waters of a lake, the lower atmosphere becomes unstable, leading to the formation of convective clouds and snow showers downwind of the lake. The moisture picked up from the lake enhances snowfall rates, resulting in localized bands of intense snowfall known as lake-effect snow bands. These bands can produce significant accumulations of snow over relatively small areas, impacting nearby coastal regions. Therefore, cold fronts passing over large bodies of water in winter can generate lake-effect snow.

True. The most violent and destructive tornadoes typically originate from supercell thunderstorms. Supercells are highly organized and long-lived thunderstorms characterized by a persistent rotating updraft called a mesocyclone. These rotating updrafts provide the necessary conditions for the formation of strong and long-lived tornadoes, including violent tornadoes with EF4 or EF5 intensity ratings on the Enhanced Fujita scale. Supercell thunderstorms are responsible for the majority of significant tornado outbreaks and the most catastrophic tornado events, making them the primary source of the most violent tornadoes. Therefore, it is true that the most violent tornadoes come from supercell thunderstorms.