Cumulonimbus clouds

Thunderstorms (cumulonimbus clouds) come in many sizes and shapes, ranging from small air-mass thunderstorms to large supcrcells. Thunderstorms are influenced by the surrounding atmosphere and nearby convective activity. Sometimes a thunderstorm is composed of a single, isolated cumulonimbus cloud. At other times, cumulonimbus clouds are so numerous that they form a continuous sheet, losing any separate identity. 

The final stage in the life of a cumulonimbus cloud IS marked by dissipation. The lower regions of the cloud break up, while the upper anvil spreads out. 

When a tornado forms, large thunderclouds can be seen in the sky. They are either cumulonimbus clouds or a super cell. The cloud becomes hard and dense. Masses of clouds at the bottom begin to twist and turn, and a tornado is formed. 

The troposphere extends to a height of about 15 km. Cumulonimbus clouds, or thun-derheads, produce thunder, lightning, and rain. 

Cloud types often are classified based on altitude. High clouds have their bases above 7 km (23,000 ft) and include the wispy mare s tail clouds known as cirrus the cirrocumulus, known as mackerel sky and the layers of cirro-stratus. Middle clouds have altitudes between 2 and 7 km (6500 to 23,000 ft), and are either the rounded altocumulus or the layered altostratus. Low clouds have bases from near Earth s surface to about 2 km (6500 ft), and include stratocumulus, stratus, and nimbostratus. Nimbostratus clouds usually bring rain or snow. Clouds with vertical development extend from about 2 to 7 km or more, and include cumulonimbus (thunderhead clouds) and cumulus. 

Atmospheric measurements in a variety of circumstances show that the RHS of (21.13) generally has a magnitude of order 10 cm s 1 in the midtroposphere. (Updraft rates in cumulonimbus clouds can, however, reach values of 5ms. )... 

Figure 15.31 shows a zonally averaged climatology based on six cloud types high clouds (Ci, Cs), middle clouds (As, Ac), low clouds (St, Sc), cumulus, cumulonimbus, and nimbostratus. The altitude, thickness, and cloud cover are shown with a 10° resolution. Note that the cirrus base heights vary with latitude but their thickness is fixed at 1.7 km due to limitations of the observations. 

A severe storm with swirling winds that may reach speeds of hundreds of km per hour is called a tornado. Such a storm is also referred to as a twister . The sky is covered by large cumulo-nimbus clouds and violent thunderstorms a funnel-shaped swirling cloud may extend downward from a cumulonimbus cloud and reach the ground. Tornadoes are narrow storms that leave a narrow path of destruction on the ground. 

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