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Answer to #1
TRUE
Answer to #2
ANSWER: Large raindrops fall faster and reach the ground before smaller ones, which is why they typically occur at the beginning of a rain shower. These large drops originate in warm, convective cumulus clouds. Clouds that have above-freezing temperatures at all levels are called warm clouds. In such clouds, precipitation forms by the collision and coalescence process. For example, in tropical regions, where warm cumulus clouds build to great heights, convective updrafts of at least 1 m/sec (and some exceeding many tens of meters per second) occur. Suppose a cloud droplet of 100 m is caught in an updraft whose velocity is 6.5 m/sec (about 15 mi/hr). As the droplet rises, it collides with and captures smaller drops in its path and grows until it reaches a size of about 1000 m. At this point, the updraft in the cloud is just able to balance the pull of gravity on the drop. Here, the drop remains suspended until it grows just a little bigger. Once the fall velocity of the drop is greater than the updraft velocity in the cloud, the drop slowly descends. As the drop falls, larger cloud droplets are captured by the falling drop, which then grows larger. By the time this drop reaches the bottom of the cloud, it will be a large raindrop with a diameter of over 5000 m (5 mm).
Answer to #3
ANSWER: A standard rain gauge consists of a funnel-shaped collector attached to a long measuring tube. The cross-sectional area of the collector is 10 times that of the tube. Hence, rain falling into the collector is amplified tenfold in the tube, permitting measurements of great precision. A wooden scale, calibrated to allow for the vertical exaggeration, is inserted into the tube and withdrawn. The wet portion of the scale indicates the depth of water. So, 10 inches of water in the tube would be measured as 1 inch of rainfall. Because of this amplification, rainfall measurements can be made when the amount is as small as one-hundredth (0.01) of an inch. An amount of rainfall less than one-hundredth of an inch is called a trace. The measuring tube can only collect 2 inches of rain. Rainfall of more than this amount causes an overflow into an outer cylinder. Here, the excess rainfall is stored and protected from appreciable evaporation. When the gauge is emptied, the overflow is carefully poured into the tube and measured.
The tipping bucket rain gauge. This gauge has a receiving funnel leading to two small metal collectors (buckets) attached to each other and mounted on a pivot. The bucket beneath the funnel collects the rain water. When it accumulates the equivalent of one-hundredth of an inch of rain, the weight of the water causes it to tip and empty itself. As the first bucket turns on the pivot, the second bucket immediately moves under the funnel to catch the water. When it fills, it also tips and empties itself, moving the other direction on the pivot, and the original bucket moves back beneath the funnel. Each time a bucket tips, an electric contact is made, causing a pen to register a mark on a remote recording chart. Adding up the total number of marks gives the rainfall for a certain time period. A problem with the tipping bucket rain gauge is that during each tip it loses some rainfall and, therefore, undermeasures rainfall amounts, especially during heavy downpours. The tipping bucket is the rain gauge used in the automated (ASOS) weather stations.
Remote recording of precipitation can also be made with a weighing-type rain gauge. With this gauge, precipitation is caught in a cylinder and accumulates in a bucket. The bucket sits on a sensitive weighing platform. Special gears translate the accumulated weight of rain or snow into millimeters or inches of precipitation. The precipitation totals are recorded by a pen on chart paper, which covers a clock-driven drum. By using special electronic equipment, this information can be transmitted from rain gauges in remote areas to satellites or land-based stations, thus providing precipitation totals from previously inaccessible regions.
Answer to #4
ANSWER: Hail is produced in a cumulonimbus cloud when graupel, large frozen raindrops, or just about any particles (even insects) act as embryos that grow by accumulating supercooled liquid droplets. Violent, upsurging air currents within the cloud carry small embryos high above the freezing level. As the embryos pass through regions of varying liquid water content, a coating of ice forms around them and they grow larger and larger. When the ice particles are appreciable size, they become too large and heavy to be supported by the rising air, and they then begin to fall as hail. As they slowly descend, the hailstones may get caught in a violent updraft only to be carried upward once again to repeat the cycle.
Answer to #5
ANSWER: Advantages: A blanket of snow is a good insulator. A light, fluffy covering of snow protects sensitive plants and their root systems from damaging low temperatures by retarding the loss of ground heat. Snow can prevent the ground from freezing downward to great depths. The accumulation of snow in mountains provides for winter recreation, and the melting snow in spring and summer is of great economic value in that it supplies streams and reservoirs with much-needed water. Disadvantages: Rapid melting of the snowpack may flood low-lying areas. Too much snow on the side of a steep hill or mountain may become an avalanche as the spring thaw approaches. The added weight of snow on the roof of a building may cause it to collapse, leading to costly repairs and even loss of life. Each winter, heavy snows clog streets and disrupt transportation.
Answer to #6
ANSWER: Under certain conditions, clouds may be seeded naturally. For example, when cirriform clouds lie directly above a lower cloud deck, ice crystals may descend from the higher cloud and seed the cloud below. As the ice crystals mix into the lower cloud, supercooled droplets are converted to ice crystals, and the precipitation process is enhanced. Sometimes the ice crystals in the lower cloud may settle out, leaving a clear area or hole in the cloud. When the cirrus clouds form waves downwind from a mountain chain, bands of precipitation often formproducing heavy precipitation in some areas and practically no precipitation in others.
Answer to #7
ANSWER: Snowflakes that fall through moist air that is slightly above freezing slowly melt as they descend. A thin film of water forms on the edge of the flakes, which acts like glue when other snowflakes come in contact with it. In this way, several flakes join to produce giant snowflakes often measuring several inches or more in diameter. These large, soggy snowflakes are associated with moist air and temperatures near freezing. However, when snowflakes fall through extremely cold air with a low moisture content, small, powdery flakes of dry snow accumulate on the ground.
Answer to #8
ANSWER: The main premise is that the saturation vapor pressure just above a water surface is greater than the saturation vapor pressure above an ice surface. This difference in vapor pressure causes water vapor molecules to move (diffuse) from the droplet toward the ice crystal. The removal of vapor molecules reduces the vapor pressure above the droplet. Since the droplet is now out of equilibrium with its surroundings, it evaporates to replenish the diminished supply of water vapor above it. This process provides a continuous source of moisture for the ice crystal, which absorbs the water vapor and grows rapidly. Hence, during the ice-crystal (Bergeron) process, ice crystals grow larger at the expense of the surrounding water droplets.
Answer to #9
ANSWER: Spontaneous or homogeneous freezing is the freezing of pure water (without the benefit of some nucleus). For this type of freezing to occur, enough molecules within the water droplet must join together in a rigid pattern to form a tiny ice structure, or ice embryo. When the ice embryo grows to a critical size, it acts as a nucleus. Other molecules in the droplet then attach themselves to the nucleus of ice and the water droplet freezes. Tiny ice embryos form in water at temperatures just below freezing, but at these temperatures thermal agitations are large enough to weaken their structure. The ice embryos simply form and then break apart. At lower temperatures, thermal motion is reduced, making it easier for bigger ice embryos to form. Hence, freezing is more likely. The chances of an ice embryo growing large enough to freeze water before the embryo is broken up by thermal agitation increases with larger volumes of water. Consequently, only larger cloud droplets will freeze by homogeneous freezing at air temperatures higher than -40 degrees Celsius. In air colder than -40 degrees Celsius, however, it is almost certain that an ice embryo will grow to critical size in even the smallest cloud droplet. Thus, any cloud that forms in extremely cold air (below -40 degrees Celsius), such as cirrus clouds, will almost certainly be composed of ice, since any cloud droplets that form will freeze spontaneously.
Contact freezing is the process in which contact nuclei cause supercooled droplets to freeze if they collide with them. Contact freezing may be the dominant force in the production of ice crystals in some clouds.
Accretion is the process of ice crystals growing larger as they collide with supercooled cloud droplets. Upon contact, the liquid droplets freeze into ice and stick together. It occurs in especially those clouds with relatively warm tops.
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