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What is an ordinary cloud droplet’s average diameter?
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A typical cloud droplet is how many times smaller than a typical rain drop?
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Weather Test 3;Sec2
| Question | Answer |
|---|---|
| What is an ordinary cloud droplet’s average diameter? | 20 um or 0.002 cm |
| A typical cloud droplet is how many times smaller than a typical rain drop? | 100 times |
| If a cloud droplet is in equilibrium with its surrounding, the size of the droplet (does/does not) change? | does not |
| If a cloud droplet is in equilibrium with its surrounding, why does the size of the droplets not change? | because the water molecules condensing onto the droplet will be exactly balanced by those evaporating from it |
| If a cloud droplet is not in equilibrium, the cloud droplet size (does/does not) change? | does |
| If a cloud droplet is not in equilibrium, why does the cloud droplet size change? | the droplet size will either increase or decrease, depending on whether condensation or evaporation predominates |
| When a cloud droplet is in equilibrium with its environment, what are the total number of vapor molecules like? | vapor molecules around the droplet remains fairly constant |
| When a cloud droplet is in equilibrium with its environment, the total number of vapor molecules around the droplet remains fairly constant, defining what? | the droplet’s saturation vapor pressure |
| What is another name for the saturation vapor pressure? | equilibrium vapor pressure |
| When a cloud droplet and flat water surface are both in equilibrium, what happens because more vapor molecules surround the droplet? | it has a greater equilibrium vapor pressure |
| When vapor molecules surround a droplet that is in equilibrium, it has greater equilibrium vapor pressure, what is the reason for this? | the water molecules are less strongly attached to a curved (convex) water surface-they evaporate more readily |
| At equilibrium the vapor pressure over a curved droplet of water is (greater/lesser) than that over a flat surface | greater |
| What needs to happen to keep a droplet in equilibrium? | more vapor molecules are needed around it to replace those molecules that are constantly evaporating from its surface |
| Smaller cloud droplets exhibit a (greater/lesser) curvature? | greater |
| Smaller cloud droplets exhibit a greater curvature, which causes what? | a more rapid rate of evaporation |
| Smaller droplets require a (greater/lesser) vapor pressure to keep them from evaporating? | greater |
| When air is saturated with respect to a flat surface, it is unsaturated with respect to what? | a curved droplet of pure water |
| What is it called in cloud physics, as cloud droplets decrease in size, they exhibit a greater surface curvature that causes a more rapid rate of evaporation? | Curvature effect |
| To keep tiny cloud droplets in equilibrium with the surrounding air, what state must the air be in? | supersaturation |
| What is it called when the relative humidity is greater than 100%? | supersaturation |
| The smaller the droplet, the (greater/lesser) its curvature, and the (lower/higher) the supersaturation needed to keep the droplet in equilibrium | greater; higher |
| As droplets become larger, the effect of curvature (greatens/lessens)? | lessens |
| For a droplet whose diameter is greater than 20 um, what is the effect of the curvature effect? | the curvature effect is so small that the droplet behaves as if its surface were flat |
| When the droplet’s size is less than 2um, the relative humidity must be above what % for the droplet to survive? | 100.1 |
| For a given droplet size, what happens when the relative humidity is less than that given by the curve? | the droplet will evaporate and shrink |
| For a given droplet size, what happens when the relative humidity is greater than the value on the curve? | the droplet will grow by condensation |
| A droplet whose diameter is 1 um will grow larger as the relative humidity approaches what %? | 101% |
| Relative humidities (often/rarely) become 101%? | rarely |
| Condensation begins on tiny particles called what? | cloud condensation nuclei |
| What are nuclei that have an affinity for water vapor? | hygroscopic |
| What happens because many of the cloud condensation nuclei are hygroscopic? | condensation may begin on such particles when the relative humidity is well below 100% |
| What happens when condensation begins on hygroscopic salt particles? | they dissolve, forming a solution |
| What happens because salt ions in solution bind closely with water molecules? | it is more difficult for the water molecules to evaporate |
| What is it called when the dissolving of hygroscopic particles, such as salt, in pure water, thus reducing the relative humidity require for the onset of condensation? | solute effect |
| Due to the solute effect, what happens once an impurity (such as a salt particle) replaces a water molecule in the lattice structure of the droplet? | the equilibrium vapor pressure surrounding the droplet is lowered |
| What happens as a result of the solute effect? | a droplet containing salt can be in equilibrium with its environment when the atmospheric relative humidity is more lower than 100% |
| What happens should the relative humidity of the air increase? | water vapor molecules would attach themselves to the droplet at a faster rate than they would leave, and the droplets would grow larger in size |
| In an unsaturated air full of cloud condensation nuclei of varying sizes, as the air cools the relative humidity (increases/decreases)? | increases |
| When relative humidity reaches a value near 78%, what happens? | the condensation occurs on the majority of nuclei |
| As the air cools further, the relative humidity (increases/ decreases) , with the droplets containing the most salt reaching the (smallest, largest) sizes? | increases; largest |
| Since the (smaller/larger) nuclei are more affected by the curvature effect, only the (smaller/larger) nuclei are able to become cloud droplets? | smaller; larger |
| Over land masses where large concentrations of nuclei exist, there may be many hundreds of droplets per cubic centimeter, all competing for what? | the available supply of water vapor |
| Over the oceans where the concentration of nuclei is (less/more), there are normally (more/fewer), but (larger/smaller) cloud droplets? | less; fewer; larger |
| In a given volume we tend to find more cloud droplets in clouds form over what? | land |
| Larger cloud droplets in clouds usually form over what? | ocean |
| For droplets too small to fall as rain, these minute droplets require what to keep them suspended? | only slight upward air currents |
| What happens to the droplets that fall because there is not enough upward air currents? | these droplets fall descend slowly and evaporate in the drier air beneath the cloud |
| Most clouds (can/cannot) produce precipitation? | cannot |
| Why can most clouds not produce precipitation? | the condensation process by itself is entirely too slow to produce rain |
| How long does the process take to create a raindrop? | several days |
| How long does the process take to produce a cloud? | less than an hour |
| How many cloud droplets does it take to make an average size raindrop? | 1 million |
| What are the two important processes that helps cloud droplets grow larger and heavy enough to fall as precipitation? | 1. The collision-coalescence process 2. The ice-crystal (Bergeron) process |
| In clouds with tops warmer than -15 degrees C, what process can play a significant role in producing precipitation? | collision-coalescence process |
| What must we need to produce the many collisions necessary to form a raindrop? | for some cloud droplets to be larger than others |
| What do larger drops do to form raindrops? | they form on large condensation nuclei, such as salt particles, or they may form through random collisions of droplets |
| Studies suggest that what plays a role in producing larger droplets? | turbulent mixing between the cloud and its drier environment |
| What does air do as cloud droplets fall? | air retards the falling drop |
| The amount of air resistance depends on what? | the size of the drop and on its rate of fall |
| The greater a raindrops speed, the more what? | the more air molecules the drop encounters each second |
| The speed of the falling drop increases until what? | the air resistance equals the pull of gravity |
| What is the constant speed at which a drop continues to fall? | terminal velocity |
| Why do larger drops fall faster before reaching their terminal velocity? | because they have a smaller surface-area-to-weight ratio |
| Larger drops fall (slower/faster) than smaller drops? | faster |
| In calm air, a typical raindrop falls over how many times faster than a typical cloud droplet? | 600 times faster |
| Large droplets overtake and collide with what? | smaller drops in their path |
| What is the merging of cloud droplets by collision called? | coalescence |
| Collision (does/does not) always guarantee coalescence? | does not |
| Why does collision not always guarantee coalescence? | because sometime the droplets actually bounce apart during collision |
| What is the force that holds a tiny droplet together? | surface tension |
| The forces that hold a tiny droplet together are so strong that what would happen if the droplet were to collide with another tiny droplet? | they could not stick together |
| How does coalescence appear to be enhanced? | if colliding droplets have opposite (attractive) electrical charges |
| Scientists feel that the difference in electrical charge that exists between cloud droplets results from what? | the bouncing collisions between them |
| The weak separation of charge and the weak electrical fields in developing, relatively warm clouds (are/are not) significant in initiating precipitation? | are not |
| What is often enhanced in thunderstorms where strongly charged droplets exist in a strong electrical field | coalescence |
| What is an important factor influencing cloud droplet growth by the collision process? | the amount of time the droplets spend in the cloud |
| A very large cloud droplet of 200 um falling in still air takes how many minutes to travel through a cloud 500 m tick and over how many minutes if the cloud thickness is 2500 m? | 12; 60 minutes |
| Rising air currents in a forming cloud do what? | slow the rate at which droplets fall toward the ground |
| A thick cloud with strong updrafts maximizes what? | the time cloud droplets spend in the cloud and, hence, the size to which they can grow |
| A warm stratus cloud is typically less than –m thick and has (fast/slow) (upward/downward movement) ? | 500 m; slow; upward |
| When a warm stratus cloud has a slow upward air movement, a large droplet would be in the cloud for a relatively (long/short) amount of time and grow by coalescence? | short |
| If the air beneath the cloud is moist, the droplets may reach the ground as what? | drizzle |
| What is the lightest form of rain? | drizzle |
| If the stratus cloud base is fairly high above the ground, what will happen to the cloud droplets? | the drops will evaporate before reaching the surface, even when the relative humidity is 90% |
| What are clouds that have above-freezing temperatures at all levels? | warm clouds |
| In warm clouds, how does precipitation form? | by the collision and coalescence process |
| In tropical regions, droplets rise, capturing smaller droplets, and the updraft in cloud is able to balance gravity on the drop, where it remains suspended, and once the fall velocity of the drop is greater than the updraft velocity, what happens? | the drop slowly descends, capturing more droplets |
| Raindrops that reach the earth’s surface are rarely larger than what? | 5 mm |
| The collisions between raindrops tend to break them up into what? | many smaller droplets |
| A large drop colliding with another large drop may result in what? | oscillations within the combined drop |
| What happens as the drop grows after large droplets collide with other large droplets? | these oscillations may tear the drop apart into many fragments, all smaller than the original drop |
| What is rain that falls from warm clouds? | warm rain |
| What is the most important factor in the production of raindrops? | the cloud’s liquid water content |
| In a cloud with sufficient water, other significant factors are? | 1. The range of droplet sizes 2. The cloud thickness 3. The updrafts of the cloud 4. The electric charge of the droplets and the electric field in the cloud |
| Thin stratus clouds with slow, upward air currents are only able to produce what? | drizzle |
| Towering cumulus clouds associated with rapidly rising air can cause what? | heavy showers |
| What is a type of rain formation that is extremely important in the middle and high latitudes, where the clouds extend upward into regions where the air temperature is well below freezing? | ice crystal process |
| What is another name for ice crystal process? | Bergeron |
| What are clouds in the ice-crystal process called? | cold clouds |
| In the cold air just above the 0 degree C isotherm, is the water liquid or ice? | liquid |
| What are water droplets existing at temperature below freezing? | supercooled |
| Is the distribution of ice crystals random or uniform? | random, as the downdrafts contain more ice than the updrafts |
| At what elevation & degree do we see ice crystals? | 7600 m; -40 degrees C |
| What is the region of a cloud where only ice particles exist? | glaciated |
| Why are there so few ice crystals in the middle of the cloud, even though temperatures are well below freezing? | the smaller the amount of pure water, the lower the temperature at which water freezes; since cloud droplets are extremely small, it takes very low temperatures to turn them into ice |
| Just as liquid cloud droplets form on condensation nuclei, ice crystals form in subfreezing air on particles called what? | ice nuclei |
| The number of ice-forming nuclei available in the atmosphere is (large/small), especially at temperatures above -10 Degrees C? | small |
| As the temperatures decrease, how do particles change? | they become active and promote freezing |
| What are other examples of excellent ice nuclei? | some types of bacteria in decaying plant leaf material and ice crystals themselves |
| When do particles serve as excellent ice-forming nuclei? | if their geometry resembles that of an ice crystal |
| Why is it difficult to find substances in nature that have a lattice structure similar to ice? | since there are so many possible lattice structures |
| In the atmosphere, it is (easy/hard) to find hygroscopic (water-seeking) particles? | easy |
| Ice –forming nuclei are (common/rare) compared to cloud condensation nuclei? | rare |
| In a cold cloud, theres (one/several) types of ice-forming nuclei present? | several |
| What are certain ice nuclei that allow water vapor to deposit at ice directly into their surfaces in cold, saturated air? | deposition nuclei |
| Why does deposition nuclei have its name? | because, in this situation, water vapor changes directly into ice without going through the liquid phase |
| What are ice nuclei that promote the freezing of supercooled liquid droplets? | freezing nuclei |
| What are the 3 kinds of things that freezing nuclei do? | cause freezing after they are immersed in a liquid drop; promote condensation, then freezing; cause supercooled droplets to freeze if they collide with them |
| What is it called when supercooled droplets freeze if they collide with them? | Contact freezing |
| What are the particles involved in contact freezing called? | contact nuclei |
| Studies suggest what about contact nuclei? | that they can be just about any substance |
| How does contact freezing play a part in the production of ice crystals in some clouds? | it is the dominant force in this production |
| Why are there so few ice crystals in the cold mixed region of some clouds? | cloud droplets may freeze spontaneously, but only at the very low temperatures usually found at high altitudes |
| Ice nuclei initiates the growth of what? | ice crystals |
| Because there are many more cloud condensation nuclei than ice nuclei, we are left with what? | a cold cloud that contains many more liquid droplets than ice particles, even at temperatures as low as -10 degrees C |
| Is the tiny liquid or the solid particles large enough to fall as precipitation? | neither |
| In the subfreezing air of a cloud, what surrounds each ice crystal? | many supercooled liquid droplets |
| What happens when both the liquid droplets and the ice crystals are in equilibrium? | the number of molecules leaving the surface of both the droplet and the ice crystal must equal the number of molecules returning |
| Why are there more vapor molecules above the liquid? | the molecules escape the surface of water much easier than they escape the surface of air |
| Whap happens because molecules escape the surface of water much easier than they escape the surface of ice? | more molecules escape the water surface at a given temperature, requiring more in the vapor phase to maintain saturation |
| The saturation vapor pressure just above a water surface is (lesser/greater) than the saturation vapor pressure above an ice surface? | greater |
| What does the difference in vapor pressure cause? | water vapor molecules to move (diffuse) from the water droplet toward the ice crystal |
| The removal of vapor molecules reuces what? | vapor pressure above the water droplets |
| What happens when the droplet is now out of equilibrium with its surroundings? | it evaporates to replenish the diminished supply of water vapor above it |
| What happens during the ice-crystal process? | ice crystals grow larger at the expense of the surrounding water droplets |
| The constant supply of moisture to ice crystals causes what? | allows it to enlarge rapidly |
| What happens when ice crystals become heavy enough to overcome updraft in the clouds? | they begin to fall |
| What is the process of ice crystals growing larger as they collide with supercooled cloud droplets? | accretion |
| What is the icy matter than forms in accretion? | graupel |
| What is another name for graupel? | snow pellets |
| What happens as graupel falls? | it may fracture or splinter into tiny ice particles when it collides with cloud droplets; these splinters may grow to become new graupel, which may produce more splinters |
| What is the process of ice crystals colliding then sticking together? | aggregation |
| What is the end product of aggregation of clumping together of ice crystals? | snowflake |
| If the snowflake melts before reaching the ground, it continues to fall as what? – | raindrop |
| What is generally the ratio of ice crystals to water droplets? | 1:100,000 to 1:1,000,000 |
| What happens when there are too few ice crystals in the cloud? | each crystal grows large and falls out of the cloud, leaving the majority of the cloud behind (unaffected) |
| If there are very few ice crystals, there is little of what? | precipitation |
| Who was the first person to propose theory of ice cystals due to differences in vapor pressure between ice and supercooled water? | Alfred Wegener |
| Who made additions to Wegeners theory ? | Tor Bergeron |
| What German meterorologist made additional contributions to Bergeron’s theory? | Walter Findeisen |
| What is the ice-crystal theory of rain formation? | Wegener-Bergeron-Findeisen process (Bergeron process) |
| In cold, strongly convective clouds, how long does precipitation take? | precipitation may begin only minutes after the cloud form and may be initiated by either the collision-coalescence or the ice-crystal (Bergeron) process |
| Any falling drop of liquid water? | rain |
| What must a rain drop have a diameter equal to? | 0.5 mm |
| What is a drop of water whose diameter is smaller than 0.5 mm? | drizzle |
| Most drizzle falls from what? | a stratus cloud; however, may partially evaporate |
| Occasionally, the rain falling from a cloud never reaches the surface, why? | because the low humidity causes rapid evaporation |
| As the drops of rain become smaller, their rate of fall (increases/decreases), and they appear to hang in the air as what? | decreases; rain streamers |
| What are evaporating streaks of precipitation called? | virga |
| When do raindrops fall from a cloud and not reach the ground? | if they encounter rapidly rising air |
| Largeraindrops have a terminal velocity of what? | 9m/sec (20m/hr) |
| What happens if raindrops encounter rising air whose speed is greater than 9m/sec? | they will not reach the surface |
| What happens if the updraft in the air weakens or changes direction and becomes a downfdraft? | the suspended drops will fall to the ground as a sudden rain shower |
| What are the showers falling from cumuliform clouds like, as the cloud moves overhead and then drifts on by? | usually brief and sporadic |
| What is itcalled if the shower is excessively heavy? | cloudburst |
| What is possible beneath a cumulonimbus cloud, when large convection currents of rising and descending air? | it is entirely possible that the one side of a street may be dry (updraft side) while a heavy shower is occurring across the street (downdraft side) |
| Continuous rain, usually falls from what? | a layered cloud that covers a large area and has smaller vertical air currents |
| Rain streamers are usually caused by what? | by ice changing to water |
| Most evaporation occurs (above/below) the virga line? | below |
| Raindrops that reach the earth’s surface are seldom larger than what? | 6 mm (0.2 in) |
| What is the reason that raindrops that reach the earth’s surface are rarely larger than 6 mm? | the collisions (whether glancing or head-on between raindrops tend to break them up into many smaller drops |
| What happens when raindrops grow too large? | they become unstable and break apart |
| After a rainstorm, why does visibility usually improve? | because precipitation removes (scavenges( many of the suspended particles |
| What happens when rain combines with gaseous pollutants, such as oxides of sulfur and nitrogen? | it becomes acidic |
| What is an adverse effect on plants and water resources, and is becoming a major problem in many industrialized regions of the world? | acid rain |
| Why is it important to know the interval of time over which rain falls? | did it fall over severaldays, gradually soaking into the soil? Or did it come all at once in a cloudburst, rapidly eroding the land, clogging city gutters, and causing floods? |
| What is the amount that falls in a given period? | intensity of rain |
| Intensity of rain is always based on what? | the accumulation during a certain interval of time |
| What is light rainfall rate? | 0.01-0.10 |
| What is moderate rainfall rate? | 0.11-0.30 |
| What is heavy rainfall rate? | >0.30 |
| In summer, the freezing level is usually above what? | 3600m |
| Snowflakes can generally fall about how many meters below the freezing level before completely melting? | 300 m |
| What is it called when ice crystals and snowflakes fall from high cirrus clouds? | fall streaks |
| Fallstreaks behave in much the same way as what? | virga |
| What happens as the ice particles fall into drier air? | they usually sublimate (change from ice into vapor) |
| What happens because the winds at higher levels move the cloud and ice particles horizontally more quickly than do the slower winds at lower levels? | fallstreaks appear as dangling white streamers |
| Fallstreaks descending into lower, supercoolds clouds may do what? | may actually seed them |
| What do snowflakes that fall through moist air that is slightly above freezing do? | slowly melt as they descend |
| How are giant snowflakes formed? | a thin film of water forms on the edge of the flakes, which acts like glue, snowflakes come in contact with it and create giant snowflake |
| What are large, soggy snowflakes associated with? | moist air and temperatures near freezing |
| What happens when snowflakes fall through extremely cold air with a low moisture content? | small, powdery flakes of “dry” snow accumulate on the ground |
| (Snow/rain) scatters sunlight better? | snow |
| Because snow scatters sunlight more effectively than rain, what happens when you look toward the sun? | the region of falling precipitation looks darker above the melting level than below it |
| A fernlike branching star shape? | dendrite |
| The type of crystal that forms, as well as its growth rate, depends on what? | the air temperature and relative humidity (the degree of supersaturation between water and ice) |
| Dendrites are common at temperatures between what? | -12 degree C and -16 degrees C |
| The maximum growth rate of ice crystals depends on what? | the difference iin saturation vapor pressure between water and ice |
| When does the difference in saturation vapor pressure reach a maximum in temperature range? | where dendrite crystals are most likely to grow |
| As ice crystals fall through a cloud, they are constantly exposed to what? | to changing temperature and moisture conditions |
| Why is it that snow crystals may assume many complex patterns? | because ice crystals can join together to form a much larger snowflake |
| What is snow falling from developing cumulus clouds? | flurries |
| What are light showers that fall intermittently for short durations and produce only light accumulations? | flurries |
| What is a more intense snow shower that is brief but heavy falls of snow are comparable to summer rain showers, usually fall from cumuliform clouds? | snow squall |
| The intensity of snow is based on what? | its reduction of horizontal visibility at the time of observation |
| Drifting snow is usually accompanies by what? | blowing snow |
| What is snow lifted from the surface by the wind and blown about in such quantities that horizontal visibility is greatly restricted? | blowing snow |
| What is the combination of drifting and blowing snow, after falling snow has ended? | ground blizzard |
| What is a weather condition characterized by low temperatures and strong winds (greater than 30 knots) bearing large amounts of fine, dry, powdery particles of snow, which can reduce visibility to only a few meters? | blizzard |
| How is a blanket of snow a valuable resource of nature? | it is a good insulator (poor heat conductor); protects sensitive plants and their root systems from damaging low temperature by retarding the loss of ground heat |
| In cold climates that receive little snow, by is it often difficult to grow certain crops? | because the frozen soil makes spring cultivation almost impossible; frozen ground prevents early spring rains from percolating downward into the soil |
| What happens if subsequent rains do not fall? | the solid could even become moisture-deficient |
| What does the accumulation of snow in mountains provide for? | winter recreation, and the melting snow in spring and summer is of great economic value in that is supplies streams and reservoirs with much needed water |
| In what ways can a winter snow be hazardful? | avalances, collapseing roods, clog streets |
| What is light snowfall intensity? | greater than ½ mile |
| What is moderate snowfall intensity? | greater than ¼ mole, less than or equal to ½ mile |
| What is heavy snowfall intensity? | less than or equal to ¼ mile |
| What is a tiny ice pellet that is a type of precipitation consisting of transparent pellets of ice 55mm or less in diameter | sleet |
| What is rain or drizzle that falls in liquid form and the freezes upon striking a cold object or ground | Freezing rain/drizzle |
| A coating of ice produced by freezing rain and freezing drizzle? | glaze |
| What is a white or milky granular deposit of ice formed by the rapid freezing of supercooled water drops as they come in contact with an object in below-freezing air | rime |
| In the winter temperature profile where the air temperature is below freezing, what is the type of precipitation associated with it? | snowflakes that reach the surface |
| In the winter temperature profile where a zone of above freezing, what is the type of precipitation associated with it? | snowflakes partially melt; then, it the deep, subfreezing aira t the surface, the liquid freezes into sleet |
| In the winter temperature profile in the shallow subfreezing surface air, what is the type of precipitation associated with it? | the melted snowflakes, now supercooled liquid drops, freeze on contact, producing freezing rain |
| In the winter temperature profile where the air temperature is above freezing in a sufficiently deep layer, what is the type of precipitation associated with it? | precipitation reaches the surface as rain |
| What are small, opaque grains of ice, the solid equivalent of drizzle? | snow grains |
| What is the physical appearance and diameter of a snow grain? | fairly flat or elongated, with diamters generally less than 1mm (0.04 in) |
| Snow grains fall from what; and never do what? | they fall in small quantities from stratus clouds, and never in the form of a shower; upon striking a hard surface, they neither bounce nor shatter |
| What are white, opaque grains of ice, with diameters less than 5mm (0.2 in)? | snow pellets |
| How are snow grains unlike snow pellets? | they are brittle, crunchy, and bounce (or break apart) upon hitting a hard surface |
| Where do snow pellets usually fall as/from? | usually fall as showers, especially from cumulus congestus clouds |
| When ice crystals collide with the supercooled water droplets, they immediately freeze the droplets, producing a spherical accumulation of icy matter (rime) containing many tiny air spaces, what 2 effects do these bubbles have on growing ice particles? | 1. They keep its density low 2. They scatter light, making the particle opaque |
| What is it called when ice particles accumulate a heavy coating of rime? | graupel |
| What is it called when the freezing level is at a low elevation and the graupel reaches the surface as light, round clump of snowlike ice? | snow pellet |
| On the surface, the accumulation of snow pellets sometimes give the appearance of what? | topica pudding-therefore referred to as tapioca snow |
| What is it called, in a thunderstorm, when the freezing level is well above the surface, graupel that reaches the ground? | soft ahir |
| What are pieces of ice, either transparent or partially opaque, ranching in size from that of small peas to that of gold balls or larger? | hailstones |
| When and where is hail produced? | cumulonimbus clouds-usually an intense thunderstorm-when graupel, or large frozen raindrops, or just any particles act as embryos that grow by accumulating supercooled liquid droplets |
| What is it called when embryos grow by accumulating supercooled liquid droplets? | accretion |
| Hailstones begin as what? | embryos that remain suspendedin the cloud by violent updrafts |
| What happens when updrafts of hailstone embryos are tilted? | the ice particles are swept horizontally through the cloud producing the optimal trajectory for hailstone growth |
| Along the path of producing hailstones, what happens when ice particles collide with supercooled liquid droplets? | freeze on contact; the ice particles eventually grow large enough and heavy enough to fall toward the ground as hailstones |
| growing hailstone enters a region inside the storm where the liquid water content is relatively low, called what? | dry growth regime |
| What happens when the growing hailstone enters the dry growth regime? | supercooled droplets will freeze immediately on the stone, producing a coating of white or opaque rime ice containing many air bubbles |
| What happens as supercooled water droplets freeze onto the hailstone’s surface? | the liquid-to-ice transformation releases latent heat, which keeps the hailstone’s surface temperature watermer than that of its environment |
| What happens as long as the hailstone’s surface temperature remains below freezing? | liquid supercooled droplets freeze on contact, producing a coating of rime |
| What is the region called where the liquid-water contact is higher? | wet growth regime |
| What happens should the hailstone get swept into the wet growth regime? | the supercooled water droplets will collect so rapidly on the stone that, due to the release of latent heat, the stone’s surface temperature will remain at 0 degree C |
| What happens when the supercooled droplets no longer freeze on impact? | instead, they spread a coating of water around the hailstone, filling in the poroud regions |
| As the water coating the hailstone slowly freezes, what happens? | air bubbles are able to escape, leaving a layer of clear ice around the stone; therefore, as a hailstone passes through a thunderstorm of changing liquid content alternating layers of opaque and clear ice form |
| As a thunderstorm moves along, it may deposit its hail in a long narrow band called what? | hailstreak |
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arcall