ATMO Ch. 6 Review Questions

Inside a cloud, at which of the following temps. would you expect to see the most supercooled cloud droplet? 35*F, 15*F, or -40*F

15*F. Below freezing but above -40*.

Describe some of the positive consequences of a snowfall.

A blanket of snow is a good insulator (poor heat conductor). It protects sensitive plants and their roots from damaging low temperatures by slowing their loss of heat.

Would the collision and coalescence process work better at producing rain in a warm, thick nimbostratus or a warm, towering cumulus congestus?

A warm, towering cumulus congestus, because rising air currents slow the rate at which droplets fall, allowing them to grow larger in size.

The Palmer Drought Severity Index uses what weather elements to assess drought severity?

Average temp. and precipitation values.

What is the primary difference between a cloud droplet and a raindrop?

Cloud droplets are too small to fall as ran and form on cloud condensation nuclei.

How does the ice crystal (bergeron) process produce precipitation? What is the main premise?

Cold clouds are needed as supercooled water droplets surround each ice crystal. The ice will grow at the expense of the supercooled droplets. The ice crystals also break apart and re-form and then fall as snowflakes which may melt before reaching the ground.

Why do heavy showers usually fall from cumuliform clouds? Why does steady precipitation normally fall from stratiform clouds?

Cumuliform clouds usually mean an unstable atmosphere and cold fronts. Statiform clouds are usually in a stable atmosphere with a possible warm front and calm winds.

How does rain differ from drizzle?

Drizzle droplets are smaller. Most drizzle falls from stratus clouds. Small raindrops may fall through unsaturated air and evaporate a bit so they reach the ground as drizzle.

Why is hail more common in summer than in winter?

Hail requires clouds containing strong convection, which is more likely in summer as the warmer air rises and forms clouds.

How does black ice form?

It forms when light rain, drizzle, or supercooled fog droplets come into contact with surfaces at temps. below freezing.

Describe how icing can be hazardous to aircrafts.

Large supercooled drops hit the wing and break apart to form a film of water which freezes into a sheet of ice. Rime ice may also form on the wing, and they can disrupt the air flow around the wings and the weight.

Why are ice storms often responsible for the loss of power to many people?

Raindrops may freeze on impact and produce freezing rain that disrupts electrical service power lines.

What is the difference between freezing rain and sleet?

Sleet falls into warmer air and then freezes when it falls through cold air. When it hits the ground it will bounce. Freezing rain falls through the cold air only long enough to supercool, and when it reaches a cold object like the ground, it freezes.

How do the atmo conditions that produce sleet differ from those that produce hail?

Sleet forms when there is a layer of above freezing temps. below the cloud base, but the temps. at the surface are below freezing. Hail is produces inside a cumulonimbus cloud by accretion of supercooled water drops onto a large frozen embryo caught in a strong updraft.

Explain how snowflakes in a cloud grow large enough to fall toward the ground.

Snowflakes fall through moist air that forms a thin film of water around the snowflakes and acts like glue when it comes into contact with other flakes.

Why is it never too cold to snow?

The air always contains water vapor that could produce snow.

Describe how a rain shadow forms.

The leeward side has a higher temp. and lower dew point. This causes more evaporation of moisture on the leeward side and a rain shadow forms where there is noticeably less precipitation.

What are some of the negative consequences of an extensive drought?

They can cause crop damage and impact a community's water supply. May lead to a shortage of food.

Explain how mountains influence precipitation.

They promote convection and force air to rise along their windward slopes through orographic uplift. The windward side of the mountain tends to be wet, but as air descends and warms along the leeward side, there is less likelihood of clouds and precipitation.

Explain the main principle behind cloud seeding.

To inject clouds with small particles which act as nuclei so that the cloud particles will grow large enough to fall to the surface as precipitation.

Where are the wettest and driest regions of the world?

Wettest: Khasi Hills in India Driest: Frigid polar region and Arica, Chile.

How are clouds naturally seeded?

When cirriform clouds lie directly above a lower cloud deck, ice crystals may descend from the higher cloud and seed the cloud below it. Supercooled droplets are converted to ice crystals and precipitation is enhanced.

Describe how hail might form in a cumulonimbus cloud.

When graupel (large frozen raindrops) act as embryos that grow by accumulating supercooled liquid droplets.

Describe how the process of collision and coalescence produces precipitation.

When larger cloud droplets (which fall faster than smaller ones) collide and merge with smaller cloud droplets, they become big enough to fall as raindrops.

Explain several ways a flash flood may form.

When thunderstorms stall or move slowly, causing heavy rainfall over a small area. It may also occur when thunderstorms move quickly but keep passing over the area. Also when snow melts along with rainfall.