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130 Cards in this Set
- Front
- Back
Hydrologic Cycle
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The continuous movement of water from the earth's surface to the atmosphere and back to the surface, then to the atmosphere.
Basic Process: Evaporation and Transpiration |
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Transpiration
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the water absorbed by vegetaion and then released to the atmosphere.
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Evaportranspiration
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The combined amount of water lost by evaporation and transpiration
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States of water (Matter)
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Solid
Liquid Gas |
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Melting
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Solid to liquid
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Evaporation
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Liquid to a Vapor
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Condensation
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Vapor to a Liquid
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Sublimation
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Solid to Gas
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Deposition
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Gas to a Solid
Releases energy |
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Humidity
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the amount of water vapor in the air
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Specific Humidity
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Grams of water vapor per kilogram of air
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Absolute Humidity
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Grams of water vapor per cubic meter of air
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Relative Humidity
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Ratio of a parcel of air's actual amount of water vapor to the parcel's water vapor capacity, expressed as a percentage.
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Partial Pressure
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Each component of the atmosphere makes up a part of the total air pressure.
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Water Vapor Pressure
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That portion of the air pressure which is made up of water vapor
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Saturation
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When the air is holding all the water vapor it can
The capacity of water vapor the air can hold is a function of temperature. |
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Warmer air can hold more water vapor
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Saturation vapor pressure increases with increasing temperature
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Specific Humidity
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The mass of water vapor per unit mass of air
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Relative Humidity (RH)
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Actual water vapor content/water vapor capacity X 100
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RH = 100%
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The air is saturated
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Dew Point
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The temperature at which saturation will occur, given sufficient cooling.
It is an indication of the moisture level in the air Controlled by Vapor pressure, not by air T |
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What controls Relative Humidity?
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This is controlled by the water vapor content and the air's capacity, which is controlled by T
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Dew Point
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The Temperature at which saturation will occu, given sufficient cooling.
It is an indication of the moisture level in the air. |
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How to change the RH?
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by adding or subtracting water vapor
lowering or raising the T |
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When the R.H. varies during the day it's because of a change in air temperature or a change in the amount of moisture (water vapor) in the air
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Examples of how to bring air to the point of saturation:
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By adding water vapor to air (Temperature is held constant)
By cooling the air ( vapor content constant) |
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Adiabatic
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The term for processes in which no heat is added or removed.
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Adiabatic Temperature Change
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Expanding Air = Temperature Decreases
Compressing Air = Temperature Increases |
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Adiabatic Temperature Change
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The temperature changes without heat being added or taken away.
This is caused by changes in pressure of a gas. |
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Adiabatic Heating
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When a parcel of air decends, the pressure of the parcel increases. Due to this increase in pressure, the parcel's volume decreases and its temperature increases, thus increasing the internal energy.
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Adiabatic Cooling
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When the pressure applied on a parcel of air decreases, the air in the parcel is allowed to explan as the volume increases, the temperature falls and internal energy decreases.
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Rising Air
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In the atmosphere rising air expands and cools
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Sinking Air
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In the atmosphere sinking air is compressed and warmed.
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Rate of Adiabatic Change
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The Rate at which the temperature changes as it rises or falss through the atmosphere.
This varies based on the humidity of the air Dry = unsaturated Wet = Saturated |
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Gas Law
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At the surface as temperature decreases, density and pressure increases as temperature increases, air density and pressure decreases.
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Dry Adiabatic Rate (DAR)
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When air is unsaturated air temperature is greater than the dew point temperature.
Rising Air = Cools at 1C/100m Fallin Air = Warms at 1C/100m |
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Wet or Saturated Adiabatic Rate (SAR or SALR)
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When the air is saturated
Air Temperature = Dew Point Temperature; RH = 100%. Not at a constant rate, 5-9 degrees celsius per 1000 meters. It is dependent on the moisture content of the air. The more water vapor condensing to liquid there is in the air, the slower the rate of decline. |
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SAR Con't
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So as air rises by convection it cools and the air temperature may reach the dew point temperature (saturation) and thus condesation may begin. If there is enough water vapor in the air parcel, then a cloud may form. The level of the atmosphere where this occurs is known as the condesation level.
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Condesation Level
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Height at which condesation occurs, where cloud formation begins (Usually seen as the bottom of a cloud mass).
RH=100%, Air Temperature = Dew Point Temperature |
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The rate of Temperature change is slower for saturated air than for unsaturated air.
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Stability
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Refers to the tendecy of an air parcel with its water vapor either to remain in place or to change vertical position by ascending or descending
Stable Air resists displacement Unstable Air continues to rise until it reaches air with density and a temperature similar to its own |
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Rules of Stability
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1) When an air parcel is warmer than the surrounding air, the parcel will rise
2) When an air parcel is colder than the surrounding air, it will tend to stay at the same level or sink 3) The Envrionmental Lapse Rate (ELR) is the temperature profile of the atmosphere (surrounding air). The ELR determines air stability. The acutal temperature lapse rate in the lower atmosphere at any particular time under local weather conditions is the ELR |
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Unstable Air
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When an air parcel is warmer than the surrounding air, the parcel will rise
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Stable Air
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When an air parcel is colder than the surrounding air, it will tend to stay at the same level or sink
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Envrionmental Lapse Rate (ELR)
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is the temperature profile of the atmosphere (surrounding air). The ELR determines air stability.
The actual temperature lapse rate in the lower atmosphere at any particualr time under local weather conditions is the ELR. |
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Types of Stability
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Absoulte Stability
Absolute Instability Conditional Instability |
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Absolute Stability
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The condition of air when the ELR < DAR
Usually results in no uplift of air, but subsidence or sinking air. Often associated with high pressure cells. Clear Skies, maybe a few stratus clouds. |
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Temperature Inversion
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More severe example of absolute stability.
When the air temperature is increasing with increasing altitude in the troposphere. |
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Absolute Instability
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The Condition of air when ELR>DAR
Often occurs during the warmest months and on clear days; often leads to cloud formation, cumulus clouds and precipitation. Often associated with low pressure cells. |
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Conditional Instability
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The condition of the air when the ELR is between the DAR and the SAR
SAR<ELR<DAR Air can vary between stable and unstable Usually if air is saturated the upper portion is unstable If the air is unsaturated then the lower portion is stable |
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Importance of Stability
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For daily weather patterns
Controls whether clouds form or not and the type partially controls precipitation type and amounts |
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Lifting Mechanisms
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Convective Lifting
Orographic Lifting Frontal Wedging Convergence |
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Convective Lifting
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The process by which a parcel of air at the suface by convection, then the whole parcel rising into the atmospher since it is warmer than the surrounding air
The heating helps produce unstable conditions Common in summertime as afternoon thundershowers Part of the process that occurs in low pressure cells in conjunction with convergence |
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Orographic Lifting
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The process by which air is forced to rise over a mountain range or other elevated land barrier and thus cool adiabatically
Little or no precipitation occurs on the leeward side, it occurs on the windward side. |
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Rain Shadow Desert
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Orographic lifting creates this on the leeward side
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Frontal Wedging
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The process by which cold, dense air acts similarly to a mountain barrier forcing warmer, less dense air to rise over it.
The leading edge of a mass of cold air is know as a cold front and similarly the leading edge of a mass of warm air is known as a warm front. So this mechanism is associated with warm and cold fronts and mid latitude wave cyclones (frontal systems) Usually produces clouds and precipitation; often severe storms or thunderstorms. |
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Convergence
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The process by which winds come together from opposite direction and are forced to rise due to compression or squeezing
Part of the process that occurs in low pressure cells Both convection and convergence are at work to form the ITCZ |
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Clouds, Fog, and Dew all have 2 propertices in common:
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Must form from Saturated Air (RH=100%, dew pint temperature=air temperature)
Must have a surface on which the water capr can condense |
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Condensation Nuclei
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Microsopic particles of dust, salt, smoke, etc
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Hygroscopic Nuclei
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Are very water absorbent condesation nuclei usually of sulfate and nitrate crystals.
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Clouds
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A form of condesation best descrived as a dense, visible aggreagation of minute droplets of water and tiny crystals of ice
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How do clouds form?
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A parcel of moist air reaches the point of saturation where the water vapor is changed to liquid water droplets. Either by coolin the air temperature to the dew point temperature or by adding more water vapor.
Cooling the air temperature is the most common method |
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Cloud Classification
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Two Criteria for Classifying Clouds:
1) Height of cloud base above the surface. 2) Degree of vertical development. |
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Height of Cloud Base
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3 Categories
< 2000m =Strato Clouds 2000m-6000m alto < 6000m = cirro |
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Degree of Vertical development
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is an indication of the degree of stability/instability
2 Main Categories: Startus = Layer, horizontal development Cumulus= heap or cotton balls, vertical development Cirrus=curl of hair, clouds found the highest up in the atmosphere, composed of ice crystals Nimbus= Violent rain, cumluonibus and nimbostratus |
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Fog
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Basically a cloud on ground level
Condensation can occur in some instances where the RH is as low as 75% - 80% As water droplets get bigger they become visible, this decreases visibility (being able to look through the droplets) If visibility is reduced to 1km, the haze or cloud is categorized as FOG. |
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4 Main Categories of Fog
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1) Radiation Fog (Ground Fog)
2) Advection Fog 3)Upslope Fog 4) Evaporation Fog |
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Radiation Fog (Ground Fog)
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Produced over land when radiational cooling decreased air temperature to the dew point temperature
Valley Fog is of this type, it forms in low lying areas from cold, heavy air draining down hill and collecting in the valley bottom. forms best on calm clear nights in late fall and winter. |
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Advection Fog
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Occurs when warm moist air moves over a cold surface and the air cools to below its dew point.
Advection= Horizontal movement of air This type of fog is usually associated with winds of 10-30 kph and is often 300-600m thick. |
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Upslpoe Fog
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Created when warm moist air flows up along an elevated plane, hill, or mountain.
Air temperature reached dew point temperature by adiabatic cooling as it rises. |
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Evaporation Fog
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When air reaches saturation by adding water vapor not lowering temperature
Water evaporates into the parcel of air |
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2 Main types of Evaporation Fog
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1)Steam Fog
2)Frontal Fog |
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Steam Fog
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Forms when cold air moves over warm water; the warmer water evaporates into the unsaturated cold air causing saturation, condesation, and fog formation.
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Frontal Fog
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Forms as warm raindrops evaporate in cool air mass as they fall
This is the type of fog associated with systems and dreary, drizzly days. |
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Dew
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Water that has condensed onto objects near the ground when their temperatures have fallen below the dew point temperature of the surface air.
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Frozen Dew
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Dew which has formed (liquid) and then frozen (solid)
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Frost or Hoarfrost
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Covering of ice produced by deposition when the dew point temperature is below freezing.
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1 Raindrop =
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1 million cloud droplets
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Bergeron Process or Ice-Crystal Process
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Discovered by Tor Bergeron
Primary process for forming rain in the middle and high latitudes Requires untilizing 2 properties of water: 1) pure water in the air doesn't freeze until -40C. 2) Saturation vapor pressure over ice crystals is much lower that over supercooled liquid water. Water < 0C is called supercooled Need temperatures below -10C; at temperatures b/w -10C & -20C will have both liquid drops and ice crystals. Difference in vapor pressure allows for supersaturation to exist Under supersaturated conditions, ice crystals collect more water vapor than they lose and thus grow. As they grow, may break up and these pieces act as freezing nuclei to make more crystals. |
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Collision-Coalescence Process
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Primary process in tropics for raindrop formation.
need larger cloud droplets from large condesation nuclei or hygroscopic nuclei Small droplets don't coalesce and collide by themselves cery well Max size of a raindrop is 5mm if it gets bigger, then it gets pulled apart bu friction and drag The collison-coalescence process is the idea behind cloud seeding. |
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Precipitation Types
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1) Rain
2) Snow 3) Sleet 4) Freezing Rain 5) Hail |
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Rain
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At least .5mm to 5mm in size
From nimbostratus and cumulonimbus clouds Can start frozen or liquid --> liquid (before ground) |
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Snow
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1-2mm in size
Water vapor deposited as ice crystals that stay frozen Frozen (cloud) --> frozen (as it hits the ground) Ration of snow to rain is 10in = 1in |
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Sleet
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.5-5mm in size
freezes as it falls and is a frozen raindrop which freezes on contact with solid objects/surfaces Frozen (cloud) --> Liquid (in atmosphere as it falls) --> liquid/frozen (liquid as it hits ground then freezes) |
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Hail
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5mm-10cm+
Hard, rounded pellets or lumps of ice; only produced in large cumulonimbus clouds/thunderstorms Needs a series/networks of updrafts and down drafts largest reported hailstone =1.67lbs and over 5.5" in diameter |
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Pressure Systems
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The areas of uplift (ITCZ) and subsidence (STH) affect precipitation patterns
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Winds
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Don't blow in nice straight paths and where they meet, like the polar front, are turbulent
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Seasonality
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These pressure belts and winds shift from season to season
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Landmasses and Oceans
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Mountains get in the way of winds and moisture differential heating
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STH
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Don't have the same characteritics on both the east and west side
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Eastside of STH
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Subsidence, temperature inversion, and upwellin of cold ocean currents = stable dry conditions
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Westside of STH
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little subsidence, more uplifting, convergence, and warm ocean currents = greater instability and wet conditions.
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Rainshadow Deserts
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Due to mountain barriers and ornographic effect leeward side often much drier than windward side.
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Monsoon
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A wind system that exhibts a pronounced seasonal reversal in direction.
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Air Mass
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An immense body of air, some 1600+ km acroos and 1-3km thick, with relatively homogeneous physical properties (density, temperature, and moistiure) at a give altitude
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Classification Scheme for Air Masses
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2-Letter abbreviations are used to indicate source region, characteristics, and types of Air Masses
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Source Regions
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Area in which air mass orginates
Source region determines inital characteristics of the air mass 2 Criteria: 1) Large and physically uniform area 2) characterized by a general stagnation of atmospheric circulation |
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Types of Air Masses
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Continental Arctic (cA)
Continental Polar (cP) Continental Tropical (ct) Maritime Polar (mP) Maritime Tropical (mT) |
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Continental Arctic (cA)
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Arctic Basin and Greenland
Bittery cold and very dry Stable |
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Continental Polar (cP)
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Interior Canada and Alaska
Very Cold to cool and dry, stable |
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Continental Tropical (cT)
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Northern interior Mexico and SW U.S. ( Summer only)
Hot and dry Unstable |
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Maritime Polar (mP)
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1) North Pacific; cool and humid; unstable in winter and stable in summer
2) NW Atlantic; cold (winter) to cool (summer) and humid; unstable in winter, stable in summer |
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Maritime Tropical (mT)
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1) Gulf of Mexico, Caribbean and Western Atlantic; warm and humid and unstable on the western side of the STH
2) Subtropical, eastern Pacific; warm and humid but stable on the eastern side of a STH |
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Fronts
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A boundary separating air masses of different densities
One air mass is usually warmer and more moist Size varies from 15 to 200km wide |
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Polar Front
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Wave Cyclones; develop in conjunction or along the polar front
Low pressure cells and front are the primary structure of mid-latitude wave cyclones |
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Types of Fronts
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1) Cold
2) Warm 3) Stationary 4) Occluded |
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Cold Front
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Boundary at the forward edge of an advancing cold air mass that is displacing warm air
Moves at approx 35kpm and has a slope of 1:100 Cumulus and cumulonimbus clouds associated with cold fronts Symbolized on weather maps as a line with triangles on it. |
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Warm Front
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Boundary at the forward edge of an advancing warm air mass that is displacing cooler air
Moves at approz 25 kph with a slope of 1:200 May see evidence of the approaching front up to 1000km ahead of it Usually stratus clouds associated with warm fronts Symbolized on weather maps as a line with semi circles on it |
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Stationary Front
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When air movement is almost parallel to the boundary (front) and the surface position of the front moves at less that 5mph foward speed
Symbolized by oppostie facing circles and triangles |
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Occluded Front
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A front formed when a cold front takes over and replaces a warm front at the surface (semi circles and triangles on the same side of the line.
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Mid-Latitude Wave Cyclone
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A low pressure cell that forms and moves along a front.
Counter-Clockwise circulation (NH) around the cyclone tends to produce the wavelike deformation of the front. Last 3 to 5 days |
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Stages of the Wave Cyclone Life Cycle:
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Stage 1: 2 air masses, a cold and a warm are set up alon a front and are moving parallel to it.
Stage 2: A wave forms and warm air starts to move poleward while cold air moves equatorward Stage 3: Cyclonic (counter-clockwise) circulation develops, with general convergence at the surface and uplifting; warm air overrides the cold air (frontal wedging) Cold Front and warm front clearly established Stage 4: Cold front moving faster than the warm front and begins to overtake it; occulsion begin, beginning formation of an occulded front Stage 5: Full development of an occluded front and maximum intensity of the wave cyclone; steep pressure gradient and strong winds. Stage 6: Sloping discontinuity (front) begins to disappear, pressure gradient weakends, energy exhausted and system dissipates. |
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Winds of a Wave Cyclone
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Warm Sector: Primarily Southwesterly to southerly
Cool Sector: Southeasterly to easterly and then northeasterly Cold Sector: Northerly, to northwesterly to westerly |
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Moisture, Sky, and Weather Conditions
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Warm Sector: Humid to very humid; clear skies to scattered cumulus clouds; warm temperatures
Cool Sector: Humid, large area of stratus clouds with light to moderate precipitation ahead of the warm front; clouds thinner further from the front (cirrus type clouds) cool temperature . Cold Sector: dry, clear air back from the cold front; intense precipitation along and just behind the cold front; cold temperatures |
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Cyclogenesis
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The process that creates or develops a new wave cyclone, or strengthens an existing wave cyclone.
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Criteria for a wave cyclone to form:
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Cyclonic flow must be established.
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Vorticity
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rotation of the air
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Relative Vorticity
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The Vorticity (spin) relative to Earth's Surface
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Earth Vorticity
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Which is due to Earth's daily rotation about it axis
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If the flows are both in the same direction (counterclockwise in NH) then they complement each other increasing absoulte vorticity
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Low pressure cells in the NH basically show positive vorticity, while high pressure cells in the NH basically show negative vorticity.
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Rossby Waves and Vorticity
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The Vorticity changes as you move along a wave which is caused by convergence (coming together) of air in one portion and divergence (pullin apart) in another.
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On the down slope of a trough there is more convergence and thus increased vorticity or spin, while on the upslope there is divergence and decreased vorticity.
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Upper-Level Divergence
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Helps draw air upward from the surface and acting as a lifting mechanism above the surface low pressure cell.
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Speed Divergence
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In a Rossby Wave speed divergence occurs basically on the downslope of a trough
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Speed Convergence
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In a Rossby Wave occurs on the upslope of a trough.
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Difflunence
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Moving air is being spread apart on the trough upslope
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Confluence
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Moving ait is being forced closer together on the trough on the downslope.
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The role of geostrophic winds (Rossby WAves and the Jet Stream) is not only the development of a mid-latitude cyclone system, but also to move the wave cyclone along
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