Concept Check Questions EXAM II

What are the two criteria by which clouds are classified? Explain how lenticular clouds form.

Form and Height As moist stable air passes over mountainous terrain, a series of standing waves form on the downwind side. As the air ascends the wave crest, it cools adiabatically. If the air reaches its dew point temperature, moisture in the air will condense to form a lenticular cloud

List three forces that combine to direct wind (horizontal airflow). Which of these forces is responsible for generating wind? Briefly describe how the Coriolis force modifies air movement.

Pressure gradient force (generates wind) Coriolis force Friction causes air to be deflected to the right of its path of motion in the Northern Hemisphere and to the left in the Southern Hemisphere.

Are regions that are dry throughout the year dominated by high or low pressure? List two reasons that explain why polar regions experience meager precipitation

High Pressure dominated by high pressure and cold air that holds little moisture

Refer to Figure 4.11 to answer the following questions: When is relative humidity highest during a typical day? When is it lowest? At what time of day would dew most likely form? Define dew-point temperature.

6 am (Highest) 6 pm (Lowest) the temperature at which water vapor begins to condense

How do absolute humidity and mixing ratio differ? What do they have in common? After reviewing Table 4.1, summarize the relationship between air temperature and the amount of water vapor needed to saturate air.

Absolute Humidity is the mass of water vapor in a given volume of air (usually as grams per cubic meter) The mixing ratio is the mass of water vapor in a unit of air compared to the remaining mass of dry air. They are both expressed as the quantity of water vapor contained in a specific amount of air. As temperature increases, the amount of water vapor needed to saturate air increases

What name is given to the processes whereby the temperature of air changes without the addition or subtraction of energy? At what rate does unsaturated air cool when it rises through the atmosphere? Why does the adiabatic rate of cooling change when condensation begins?

Adiabatic Temperature Changes 10 degrees celsius per 1000 m when a parcel of air ascends above the lifting condensation level, the rate at which it cools is reduced. This slower rate of cooling is called the wet adiabatic rate

Name two factors that cause air to subside between 20° and 35° latitude. In the idealized three-cell model of atmospheric circulation, most of the United States is situated in which belt of prevailing winds? Which winds are found between the equator and 30° latitude?

As upper-level flow moves away from the stormy equatorial region, radiation cooling becomes the dominant process. As a result, the air cools, becomes more dense, and sinks. The Coriolis force becomes stronger with increasing distance from the equator, causing the poleward-moving upper air to be deflected into a nearly west-to-east flow by the time it reaches 30° latitude. the ferrel cell, from 30 - 60 latitude Hadley winds

Explain why air pressure decreases with an increase in altitude. Describe how winds blow in relation to areas of high pressure and low pressure. Explain how horizontal convergence aloft affects surface pressure.

As you go up in the atmosphere, there are fewer air molecules, decreasing pressure. Air moves from areas of high pressure to areas of low pressure. Surface air pressure rises when horizontal convergence aloft is greater than horizontal divergence

For surface low pressure to exist for an extended period, what condition must exist aloft? What general weather conditions can we expect when surface pressure is rising? When the pressure tendency is falling?

Condensation must occur at some layer aloft. For example, there must be a way for air aloft to spread out (diverge). If there is high pressure tendencies, fair and clear weather is to be expected. If there is low pressure, stormy and cloudy weather is to be expected.

Describe the direction of cyclonic and anticyclonic flow in both the Northern and Southern Hemispheres. Unlike winds aloft, which blow nearly parallel to the isobars, surface winds generally cross the isobars. Explain what causes this difference.

Cyclonic Flow: same direction of rotation as Earth: counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere Anticyclonic Flow: clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere Friction created by the earth's surface redirects the movement of winds on the surface, while winds aloft are not subject to friction and the Coriolis effect and gradient forces eventually balance each other out—allowing the winds aloft to follow the isobars.

Define monsoon. Explain the cause of the Asian monsoon. Which season (summer or winter) is the rainy season? What areas of North America experience a pronounced monsoon circulation?

Large seasonal changes in Earth's global circulation driven by pressure differences that are generated by unequal heating of Earth's surface. Summer is the rainy season Tucson, Arizona

Water's solid phase, ice, is less dense than liquid water. Why is this unique property of water important? Explain what happens as ice melts to become liquid water. What property of water causes large water bodies to remain warmer than adjacent landmasses in winter but cooler in summer?

Many lakes would freeze solid bottom to top, killing all aquatic life Ice is heated, and melts, which causes hydrogen bonds to break, so the water molecules in as a liquid become more compact. Water has a high heat capacity

Summarize the six processes by which water changes from one state to another. Indicate whether heat is absorbed or released in each case. Why is evaporation called a cooling process? Define latent heat and explain the role that latent heat of condensation plays in the growth of towering clouds.

Melting- solid to liquid - heat absorbed Freezing- liquid to solid - heat released Evaporation- liquid to gas - heat absorbed Condensation- gas to liquid - heat released Sublimation- solid to gas - heat absorbed Deposition- gas to solid - heat released the faster-moving molecules escape the surface. As a result, the average molecular motion (temperature) of the remaining water is lowered the energy used to melt ice does not produce a temperature change. During condensation, water vapor molecules release energy (latent heat of condensation) in an amount equivalent to what was absorbed during evaporation. When condensation occurs in the atmosphere, it results in the formation of fog or clouds (Fig. 4.4A).

Compare and contrast rain, drizzle, and mist. Describe sleet and freezing rain. Why does freezing rain result on some occasions and sleet on others? How does hail form? What factors govern the ultimate size of hailstones?

Mist: Droplets large enough to be felt on the face when air is moving 1 meter/second. Associated with stratus clouds Drizzle: Small, uniform droplets that fall from stratus clouds, generally for several hours. Rain: Generally produced by nimbostratus or cumulonimbus clouds. When heavy, size can be highly variable from one place to another. Sleet: Small, spherical to lumpy ice particles that form when raindrops freeze while falling through a layer of subfreezing air. Because the ice particles are small, any damage is generally minor. Sleet can make travel hazardous. Freezing Rain: Produced when supercooled raindrops freeze on contact with solid objects. Freezing rain can form a thick coating of ice that has sufficient weight to seriously damage trees and power lines. Hail: Precipitation in the form of hard, rounded pellets or irregular lumps of ice. Produced in large convective cumulonimbus clouds, where frozen ice particles and supercooled water coexist.

Why does Florida have abundant midafternoon thunderstorms?

On warm days, the airflow is from the ocean to the land along both coasts of Florida. This leads to a pileup of air along the coasts and general convergence over the peninsula. This pattern of convergence and uplift is aided by intense solar heating of the land. As a result, Florida's peninsula experiences the greatest frequency of midafternoon thunderstorms in the United States

How does stable air differ from unstable air? Describe conditional instability.

Stable Air: If the parcel is cooler than the surrounding environment, it will be more dense; and if allowed to do so, it will sink to its original position: resists vertical movement Unstable Air: rising parcel is warmer and hence less dense than the surrounding air, it will continue to rise until it reaches an altitude where its temperature equals that of its surroundings when moist air has an environmental lapse rate between the dry and wet adiabatic rates

What is the primary driving force of surface-ocean currents?

The Coriolis force, which deflects surface currents poleward to form clockwise spirals in the Northern Hemisphere and counterclockwise spirals in the Southern Hemisphere.

In what way are land and sea breezes similar to mountain and valley breezes? Explain how cities create their own local winds.

They both vary by season and they both begin from the same winds this circulation pattern is characterized by a light wind blowing into the city from the surrounding countryside. In cities, massive buildings composed of rocklike materials tend to retain the heat accumulated during the day more than the open landscape of outlying areas. The result is that the warm, less-dense air over cities rises, which in turn initiates the country-to-city flow

What weather condition would lead you to believe that air is unstable? What weather condition would lead you to believe that air is stable?

Unstable air forced aloft: towering clouds are generated that are usually accompanied by heavy precipitation Stable Air forced aloft: Relatively thin widespread clouds typically form, and any precipitation that results is light to moderate

What is supercooled water? Briefly summarize the collision-coalescence process.

Water in the liquid state below 0 degrees celsius involves multiple collisions of tiny cloud droplets that stick together (coalesce) to form raindrops large enough to reach the ground before evaporating.

What advantage does weather radar have over a standard rain gauge?

Weather Radar can track storms before they even occur, which a rain gauge is an "in the moment" collection of data.

Distinguish between clouds and fog. What actually happens when a radiation fog "lifts"? Why is there a relatively high frequency of dense fog along the Pacific coast?

While clouds result when air rises and cools adiabatically, fog results from cooling or when air becomes saturated through the addition of water vapor the Sun warms the ground, the lowest layer of air is heated first, and the fog evaporates from the bottom up. where cold currents prevail

A southwest wind blows from the__________ (direction) toward the__________ (direction). What is the name of the prevailing winds that affect the contiguous United States?

southwest to the north east Westerlies

At what time of year should we expect the fastest polar jet streams? Explain. Why is the polar jet sometimes referred to as the midlatitude jet stream? Describe the expected winter temperatures in the northcentral states when the polar jet stream is located over central Florida.

the fastest upper-air winds are located above regions of the globe having large temperature contrasts across very narrow zones Because this jet stream is often found in the middle latitudes, particularly in the winter the temperature of central florida is cold, but the temperature of northcentral is normal.

What is the intertropical convergence zone (ITCZ)?

the region of low pressure where the trade winds converge

Why is the flow aloft in the midlatitudes predominantly westerly?

the temperature contrast between the poles and equator drives these winds

Describe the process of cloud formation

when air rises and cools to its dew-point temperature by the process of adiabatic cooling. When a parcel of air ascends, it passes through regions of successively lower air pressure causing the parcel to expand and cool adiabatically. At a height called the lifting condensation level, the ascending parcel will have cooled to its dew-point temperature, and saturation is reached.

What is wind, and what generates it? What is average (standard) sea-level pressure, measured in pounds per square inch, millibars, and inches of mercury? Describe atmospheric pressure in your own words.

wind is the result of horizontal differences in atmospheric pressure. Air flows from areas of higher pressure to areas of lower pressure 1013.25 millibars the force per unit area on a surface exerted by the weight of the air above.