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34 Cards in this Set
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Absolute stability Absolute instability Conditionally unstable |
Absolute stability- ELR is less than both dry/moist adiabatic rate. Absolute unstable- ELR is greater than both dry/moist adiabatic rate. Conditionally Unstable- ELR is between the dry and moist adiabatic rate. |
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How to make the atmosphere more unstable |
Cool air aloft or heat up surface air (greater ELR) - Winds bringing in cold air aoft - daytime heating of surface -influx of warm air by wind (heating surface) |
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How to make the atmosphere more stable |
Warming of air aloft, cooling of surface air (Small diff between air aloft and surface air) -Nihtime cooling of surface, - influx of cold surface air, -air moving over a cod surface -When entire laer of air sinks( subsidies the entire layer will warm by adiabatic compression |
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Triggers for initiating air to produce clouds |
-Surface heating and free convection -uplift along topography -air convergence (air from two directions coming together causes widespead ascent) -uplift along weather fronts. |
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Temp and due point temp change moving over a mountain |
Air parcel ascending a mountain: temps and dew-point temp decrease with dry adiabatic rate. Air Parcel Descending a mountain: warms by compressional heating, will be wamer than the air on windward side. Has lower dew-point and higher temperature, causing rain-shadow desert. |
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How does equilibrium vapor pressure differ over an ice surface and water surface? |
SVP (EVP) is greaer over water than over ice. -Since it is more difficult for molecules to escape from the ice, it requires less water vapor molecules to surround it to produce equilibrium, so the EVP (or SVP saturation vapor pressure) over ice surface is lower than over water surface at the same temperature |
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Curvature Effect |
When air is saturated with respect to a fat water surface, it is unsaturated to a curved water surface--> droplet vaporates -Smaller dropletes requare greater vapor pressure to keep sma droplets requires supersaturated air -inhibits growth |
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Solute Effect |
Hydroscopic salt ions dissolve in water and form solution--> making it difficult for water m. to evap - Equilibrium can be achieved when RH is smalelr than 100% - increase in RH causes droplets to grow. -enhances growth |
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How does terminal velocity change with drop size? What does this mean in real life when you observed rainfall from storm clouds?
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-terminal velocity increases with drop size - Thin clouds produce smaller drops as heir is less time to colect, Cumulus produce alrger raindrops. |
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Size of raindrop in relation to strength of updraft |
Larger the updraft, larger the raindrop |
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Ice-crystal process, Why does it take place? What is supercooled water, and why is supercooled water important in the ice-crystal process? |
Ice crystal process: in the subfreezing air of a cloud, many supercooled liquid droplets surround each ice crystal. There are more vapor molecules above the supercooled liquid because molecules escape the surface of water much easier than ice. This difference in vapor pressure causes water vapor molecules to move (diffuse) towards the ice crystal. (Ice crystals grow bigger at the expense of surrounding water droplets) -Supercooled water is water droplets existing at temperature below freezing. |
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Warm Cloud Cold Cloud *Major Precipitation processes in these clouds |
Cold Cloud= where cloud extend upward into below freezing air temp -Ice crystals and water droplets can coexist. In these 'mixed' clouds, the air is close to being saturated with respect to liquid water, but is supersaturated (an unstable phase) with respect to ice. Consequently, in mixed clouds, ice crystals grow from the vapour phase much more rapidly than do the nearby droplets. This is usually known as the Bergeron - Findeisen process Warm Cloud= clouds that hav above freezing temps at all levels -In 'warm' clouds, precipitation formation depends upon the individual tiny cloud droplets (which of themselves are too small to fall through cloud-environment updraughts) growing by collision / coalescence, such that they eventually become heavy enough to overcome the upward currents and fall from the base of the cloud. |
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What is cloud seeding? How is it related to the ice-crystal process? What are the typical seeding agents? |
Injecting couds with an agent that acts as a nuclei so particales can condensate (produce couds/precip) -Seeding agents= dry ice, silver iodide Cold clouds are ideal because it uses the ice crystal process to cause particle growth |
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What is cloud condensation nuclei? What is ice nuclei? How do they compare in terms of quantities in the atmosphere? |
-Cloud Condensation Nuclei- Small particles (1/100th of cloud droplet) allow water to make transition from vapor to liquid (water needs non-gaseous surface) (soluble) -ice nuclei= particle that acts as the nucleus for the formatin of an ice crystal - IN's are rare when compared to CNN's |
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What are the typical shape of ice crystal habit? Which one is the most common shape? Why? |
The dendrite is the most common shape because it grows more rapidly than other crystal forms. Dendrites exist at the temperature where the difference between saturation vapor pressure in liquid water and ice is the greatest (-12 degrees Celsius) and the ice-crystal process is the most efficient. |
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If most of the precipitation starts as snow in the upper top, how do we get different types of precipitation at the surface? Understand how the atmosphere temp profile affect the surface precip type. |
- In the summer, the freezing level is usually above 3600m, and the snowflakes falling from the cloud melt before reaching the ground. However, in the winter the freezing layer is much lower and falling snowflakes generally have a better chance of survival. -Sleet: starts as ice in the below freezing atmosphere layer, falls into above freezing layer and begins to melt and then falls through a deep subfreezing surface layer where it partially starts to turn back to ice -Freezing rain: rain falls through a cold layer but does not freeze, the drops reach the surface as supercooled water and upon hitting an object freeze Snow: entire atmosphere is below freezingRain: entire bottom layer of atmosphere is above freezing Hail: Falling Ice Crystals freeze Supercooled droplets on contact (accretion) |
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How do we measure rainfall? |
Rain gauge: weighing, tipping bucket, Doppler radar and space satellites. 10in snow = 1in rain |
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What us gas law? How are temp, pressure and density related? |
Gas Law= Presure= density X temp X constant examples - Shorter column of cold, more dense air exerts same surface pressure as a taller column of less dense air. -warm air aloft is associated with high atmospheric pressure and cold air aloft is associated with low atmospheric pressure |
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How does atmospheric pressure change with height? How about in cold air columns vs. warm columns |
-Atmosheric pressure always decreases with increasing height -However, atmospheric pressure decreases more rapidly in cold air as compared to warm air. This is because you pass through the molecules in cold air more quickly as it takes a shorter column of cold, more-dense air to exert the same surface pressure as a column of warm air. So, decreases more quickly in cold air. |
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How do we calculate the sea level pressure from station pressure? |
-Station Pressure = Sea Level Pressure x e^( -elevation / (temperature x 29.263))
- Station pressure observations are adjusted to a mean sea level (representing average surface of ocean) is reading is caled SLP (10mb per 10meters) |
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Constant height chart and constant pressure chart |
CHC: A synoptic chart for any surface of constant geometric altitude above mean sea level (a constant- height surface), usually containing plotted data and analyses of the distribution of such variables as pressure, wind, temperature, and humidity at that altitude.
CHC: A synoptic chart for any surface of constant geometric altitude above mean sea level (a constant- height surface), usually containing plotted data and analyses of the distribution of such variables as pressure, wind, temperature, and humidity at that altitude. 850mb: The temperature field shows where warm and cold air are located. 500mb : often referred to as the steering level as most weather systems and precipitation follow the winds at this level. 200: wind speed |
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What is a ridge What is a trough |
Ridge= elongatde highs on isobaric map where the air is warm Trough= elongated lows on isobaric map were air is cold causing a linear depression The wavelike patterns of an isobaric surface reflect the changes in air temperature. An elongated region of warm air aloft shows up on an isobaric map as higher heights (ridge); the colder air shows as lower heights (trough). |
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In the mid latitude (NH), how do surface wind blow around High and Low pressure center? How do wind blow in the upper troposphere? What is causing the difference? |
High pressure center= blow clockwise and outward Low Pressure center= counterclockwise and inward -Surface winds cross isobars. -Winds in the upper troposphere flow parallel to isobars and with high pressure on the right and low to left |
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What causes the wind to blow? What is pressure gradient force? How is the direction and magnitude of PGF related to isobars? How is wind speed related to isobars? |
Horizontal differences in atmospheric pressure causes wind to blow - PGF= net force directed from higher toward lower pressure - directed from higher toward lower pressure at right anges to the isobars. Mag directly related to net PGF force - Step pressure gradiants (close togeher) equate to stonger winds |
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Major forces that affect the wind? |
Coriolis force, friction, PGF |
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Coriolis Effect and charateristics |
Apparent force due to reotatin of earth- causes wind to deflect to the RIGHT in NH and left of path in SH Stronger wind= greater deflection No coriolis at equator greeatest at poles Only influence direction, not speed Has significant impact over long distances, minimal over short |
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Geostrophic Wnd? How is produced? |
Geo wind is the fow of air that turns from Coriolis Effect - produced by balance between PGF and CF |
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Can you use wind (or cloud movement) to determine the upper level pressure situation? How about surface pressure situation?
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By standing with backs to direction where clouds are moving, Lower pressure will always be on left and higher pressure to right. |
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What is hydrostatic balance? How is wind (divergence and convergence) related to vertical motion? |
When PGF and gravity force are exactly balanced. No net VERTICAL force acting on it, no net vert acceleration |
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What are the scales of atmospheric motion? |
Microscale(2m)- smoke in chimney Mesoscale(20km) thunderstorms tornadoes etc Synoptic scale (2000km)- state/weather map |
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What is a wind rose? Represents what? |
Windrose represent prevailling winds. Indicates percentage of time the wind bows from a direction. |
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How is wind direction defined? |
Wind direction is defined by the direction it is blowing from. For example a 180 degree wind is blow directly from the south.
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Why is surface wind generally stronger/gustier in afternoon? |
atmosphere is less stable in afternoon- surface winds are mre likely to occue when atmosphere is unstable |
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Sea and Land breeze? Causes |
Sea breeze is a tpe of thema circulation. Uneven heating rates of land and water cause these coastal winds Day: land hot, water cold = sea breeze Night: water hot, land cold = land breeze |
