Water, Precipitation, and Humidity Flashcards
True or False: earth is a closed system in terms of water
True
What is the Hydrological Cycle?
All water is recycled in what is called the hydrological cycle
___________ is crucial to the idea of humidity and water cycles.
Latent heat
What are the five Atmospheric Humidity Indices?
-Vapor pressure (mb or kPa)
-Mixing ratio (grams per kilogram of dry air)
- Specific humidity (grams per kilogram of air (water in the air+air))
-Relative humidity (%)
-Dew-point temperature (°C)
_____________; The atmospheric pressure (in millibars; mb) associated with the gaseous water in the air. How much pressure is that gaseous water exerting.
Vapor Pressure
Is vapour pressure affected by temperature changes?
No
True or False: If you change the air parcel’s temperature, the vapour pressure doesn’t change (as long as you don’t add or remove water)
True
True or False: Saturation Vapour Pressure remains constant, no matter the change in temperature.
False, it changes with temperature changes.
________________: Maximum amount of vapor pressure that the air can hold at a given temperature, impacted by temperature.
Saturation Vapour Pressure
Does hot air hold less or more moisture?
more
**True or False: Air hovering over a liquid water surface can hold more moisture than air hovering over a frozen water surface. **
True.
What does Unsaturated Air over liquid water mean?
If the air over this water is unsaturated, it means that more water molecules are evaporating from the surface than are condensing onto the surface.
What does Saturated air over liquid water mean?
If the air over this water is saturated, it means that there are equal numbers of water molecules evaporating and condensing.
For a given temperature, what does it mean when we have reached equilibrium?
We have reached the maximum vapor pressure for that temperature: the saturation vapor pressure.
What happens when the saturation temperature has been reached?
We cannot hold any more moisture. And we get condensation out of the air if more moisture is added.
What does Saturated air over frozen water mean?
Saturation over ice occurs with fewer water molecules in the air than over liquid water at the same temperature, because the ice particles aren’t as likely to escape as water vapor.
Saturation over ice occurs with ______________ in the air than over liquid water at the same temperature, because the ice particles aren’t as likely to escape as water vapour.
fewer water molecules
True or False: Saturation is reached sooner with air over frozen water.
True
The saturation vapour pressure over ice is _______ than the saturation vapour pressure over water.
lower
What is it called when water that is still liquid at temperatures below 0°C?
Super Cooled Water
Define Mixing Ratios:
The number of grams of water vapor for every kilogram of dry air (not including the water vapor).
True or False: Mixing Ratios are affected by temperature changes.
False, it is not affected by temperature changes.
If you change the air parcels temperature, the mixing ratio ______ change (as long as you don’t add or remove water).
does not
Define Saturation Mixing Ratio:
Saturation mixing ratio (g/kg) is the maximum number of g/kg (this increases as temperature increases).
Will Saturation Mixing Ratio change with temperature changes?
Yes, it will.
________________: The number of grams of water vapor for every kilogram of air (including the water vapor).
Specific Humidity
Is Specific Humidity affected by temperature changes?
No, it is not.
What is Saturation Specific Humidity?
Saturation specific humidity (g/kg) is the maximum number of g/kg (this increases as temperature increases).
What is Humidity?
How much water is in the air
What units is humidity measured in? (3)
-Vapor Pressure (mb)
-Mixing Ratio (g/kg): -g of water vapor per kg of dry air
-Specific Humidity (g/kg):g of water vapor per kg of air
What is relative humidity?
The ratio of the amount of water vapor present to the amount that could be present (at the same temperature).
In short, what is relative humidity?
How much water is in the air vs. How much it could handle at that temperature.
Is relative humidity affected by temperature change?
Yes
What form of humidity is most affected by temperature change?
Relative humidity
How is relative humidity expressed?
In percentages.
True or False: If you change the air parcels temperature, the relative humidity will change.
True
How is relative humidity calculated?
Relative humidity= (Actual water vapor in the air)/ (Maximum water vapor possible in the air at that temperature) x100
When do we often have low relative humidity?
We often have low relative humidity around noon, when we reach the highest temperatures of the day.
Why is it that we have low relative humidity around noon?
The air is warm and can handle a lot more moisture, therefore, relative humidity decreases regardless of whether we have added water or not.
Why does relative humidity increase in the evening?
Overnight temperatures decrease, relative humidity increases because it is less able to retain moisture.
Why is relative humidity very affected by temperature?
Air temperature very much impacts relative humidity because it impacts the ability of air to hold on to moisture
Define Dew Point Temperature:
The temperature to which the air must be lowered to make it saturated (e.g., RH = 100%)
In short, what is Dew Point Temperature?
How much must we cool down water to reach saturation.
Is Dew Point Temperature affected by temperature changes?
No
Why is Dew Point Temperature not affected by changes in temperature?
Based only on how much moisture is in the air and temperature to reach that point.
Regarding Dew Point Temperature, If the temperature is below freezing, it is sometimes called the _____________________.
frost-point temperature
True or False: At saturation, evaporation rate is equal to condensation rate (equilibrium).
True
What is another way to define Dew Point Temperature?
The dew-point temperature is the temperature at which a given mass of air becomes saturated and net condensation begins to form water droplets.
Give an example, step by step, of Saturation due to Decreasing Air Temperature.
It is why we have water on the side of a cold glass, ice cold water cooler down the surface, the cold glass chills the surrounding air layer (pulling energy from the air). It cools down the air around the glass to saturation. We know as the air cools; the air is no longer able to hold on to that much moisture. That excess moisture beyond saturation in that, thin layer or air around the glass it reaches. It reaches dew point, and we get condensation on the glass.
What are two humidity instruments?
Hair Hygrometer and Sling Psychrometer
How does the Hair Hygrometer work?
Principle: Human hair changes in length (up to 4%) with respect to changes in relative humidity (0 – 100%).
How does the Sling Psychrometer work?
Principal: more evaporation when there is less humidity in the air (the air is more capable of accepting additional moisture). Evaporation dominates in this balance between evaporation and condensation. The question is by how much. One thermometer has a sock on it, another bulb is exposed to the air, wet the cloth and spin psychrometer above your head, getting evaporation off the cloth. The evaporation dictates how much moisture in the air, latent heat dictates the result.
Regarding the Sling Psychrometer, what is relative humidity dictated by?
Relative humidity depends on the difference in temperature between the dry bulb and the wet bulb to dictates how much evaporation we had and how much latent heat of evaporation occurred.
-AKA, Relative humidity depends on the difference between Td and Tw.
How do we measure relative humidity regarding a sling psychrometer?
We can find out by measuring the latent heat of evaporation.
Define an air parcel:
An air parcel is a body of air that has a specific temperature and humidity.
True or False: If an item is less dense than its surrounding air, it will be buoyant.
True
Give an example of buoyant force vs. gravitational force
oil and water, oil floats to the top because it is less dense.
When does saturation occur?
Saturation occurs when the dewpoint temperature and the air temperature become the same.
What types of conditions inhibit cloud formation?
-Rising, but not saturated.
-Not moving; stable
-Sinking.
True or False:In general, where you see clouds, air is RISING. Rising air expands.
Expanding air loses energy and cools.
True.
Does sinking air rise or compress?
compresses
When is saturation inhibited?
Saturation is inhibited when the difference between the air temperature and dewpoint increases
Rising parcels of air expand due to a decrease in __________.
pressure
What happens when a sinking particle of air is compressed?
Some of the work that was keeping the parcel expanded, is converted back to kinetic energy.
Consequently, the average kinetic energy of the air molecules in the parcel is raised…. this we record as an increase in the temperature.
______________: A process that changes the temperature of an air parcel without actually adding or removing any heat from the parcel
Adiabatic Process
What does the Adiabatic Process assume?
Assumes that the parcel of air is a ‘closed system’, getting no energy from the environment around it and giving no energy to the environment around it. Simply warming and cooling.
True or False:-RISING parcels of air COOL (adiabatically) SINKING parcels of air WARM (adiabatically).
true
What depicts the rate of temperature change?
Whether the water is changing phases.
What does DAR stand for?
Dry Adiabatic Lapse Rate (DAR)
When is the DAR applied?
The Dry Adiabatic Lapse Rate (DAR) applies when water is not changing phase (have not yet reached condensation or saturation).
RISING parcels of air COOL adiabatically at the rate of ___°C per kilometer.
10
SINKING parcels of air WARM adiabatically at the rate of ___°C per kilometer.
10
________________: the rate at which “dry” air cools by expansion (if ascending) or heats by compression (if descending).
Dry Adiabatic Rate (DAR)
What does the ‘dry’ in DAR refer to?
Dry refers to air that is less than saturated (relative humidity is less than 100%)
_____________; Temperature cools as pressure falls and altitude increases. The temperature change depends on the relative humidity of the parcel.
Adiabatic Cooling at the DAR
Is the Adiabatic Cooling at the DAR rising, sinking or changing phase?
rising
_______________: Temperature warms as pressure increases and altitude decreases. Sinking air that is ‘dry’ warms at the dry adiabatic rate.
Adiabatic Heating at the DAR
Is the Adiabatic Heating at the DAR rising, sinking or changing phase?
Sinking
________________; Applies when water is changing phase. It is also called the moist or saturated adiabatic lapse rate. (MAR or WAR)
Moist Adiabatic Lapse Rate
What does the Moist Adiabatic Lapse Rate depend on ?
The rate depends on how much water is changing phase (how much condensation we actually have).
At what temperature do rising parcels of air cool in the Moist Adiabatic Lapse rate? (water condensing)
6°C/km
What is happening in a parcel of unsaturated air?
-the air temperature is dropping -we are getting closer to the dewpoint
-expansion and adiabatic cooling
What happens if the parcel has rised far enough?
-the dewpoint will be reached —the air will become saturated(100% relative h)
What happens if the parcel rises beyond this point?
-water vapor will condense or freeze -we will see cloud droplets (or ice)
True or False: further cooling of the air (beyond dewpoint) will cause the relative humidity to be greater than 100% (super-saturation). Therefore, some of the water vapor must condense (or freeze) to keep the relative humidity at max 100%.
true
Define Atmospheric Stability:
Stability refers to the tendency of an air parcel either to remain in place or to change vertical position by ascending or descending. Striking a balance between buoyancy and gravity.
What does the degree of stability depend on?
The degree of stability depends on the temperature difference between inside an air parcel and the air surrounding the parcel.
How is the degree of stability determined?
-The rate at which the rising air parcel cools (dry or wet adiabatic rate?) as it moves up through the atmosphere. If it cools at the dry adiabatic rate, it is cooler quicker.
-The temperature profile of the air through which the air parcel is rising (the environmental lapse rate). We can use graphs to make these assessments.
What is the Environmental Lapse Rate?
is the actual lapse rate at a particular time and place. It can vary by several degrees per kilometer.
What is the Normal Lapse Rate?
average decrease in temperature with increasing altitude, a value of 6.5°C/km.
What is the ratio of the dry adiabatic lapse rate?
10°C/km
What is the moist adiabatic lapse rate?
6°C/km
When will we have unstable air?
we will have unstable air if the environmental lapse rate is greater than the DAR.
When will we have conditionally unstable air?
Conditionally unstable if it is found between the MAR and the DAR
When will we have stable air?
It will be stable if the environmental lapse rate is less than the MAR.
What is the cloud formation process?
Adiabatic cooling by vertical lift.
-Air parcel cools to the dew-point temperature.
-Air parcels become saturated.
-Condensation occurs.
Define a cloud:
A cloud is a collection of liquid water droplets and/or ice crystals.
How does a liquid cloud droplet start?
Each liquid cloud droplet starts with a piece of ‘dirt’. A droplet will only form if water vapor has something to condense on to a condensation nucleus,
What is a Cloud condensation nucleus (CCN)
A droplet will only form if water vapor has something to condense on to a condensation nucleus
What are CCN’s made up of?
meteoric dust, windblown clay and silt, volcanic material, smoke from forest fires, and sea salt
Are cloud droplets or raindroplets bigger?
rain droplets
What is an Ice Crystal?
Liquid water droplets in a cloud will only freeze if they have something to freeze on to; an ice nucleus
What would happen if we didn’t have Cloud Condensation Nuclei?
Without these nuclei, liquid water will stay liquid (super-cooled) all the way down to ~-36°C. -Ex) clay, black carbon, bacteria, organics, etc., AKA once living things.
True or False: At temperatures above 0°C, a cloud is all liquid water droplets
True
True or False: Below -36°C, a cloud will be all ice.
True
True or False:For precipitation to fall from clouds, cloud droplets must grow to form raindrops.
True
What two processes allow cloud droplets to grow?
-Water vapor condenses on to existing droplets.
-Collision- Coalescence Process; Existing water droplets collide and merge.
What is the Collision Coalescence Process?
Existing water droplets collide and merge.
What happens in the Ice Crystal Process (AKA the Bergeron-Findeisen Process)?
Water that evaporates from the liquid droplets will tend to be preferentially deposited on the nearby ice crystals. If we have both supercooled and water droplets, then our droplets can get smaller and get evaporation off of them.
What happens when a liquid droplet and an ice crystal are at the same temperature?
If the air over the ice is saturated…. the air over the liquid will not be saturated.
-The droplet shrinks by evaporation. The water vapor it loses gets deposited on the ice crystals because the air over it can’t hold any more water vapor (already at saturation).
-The ice crystal grows
Define Precipitation:
When the droplets or crystals get big enough, they can fall towards the surface, as precipitation (hydrometeors)
What is another word for precipitation?
Hydrometeors
________: is precipitation that doesn’t make it to the ground.
Virga
What are the 7 types of precipitation?
Rain
Drizzle
Snow
Snow Grains
Ice Pellets
Snow Pellets
Hail
What are snow grains?
very small opaque white particles, diameter <1mm
-solid equivalent of drizzle, do not bounce when they hit the surface.
What are Ice Pellets?
transparent ice particles, diameter <5mm
-raindrops that have frozen or snow that melted and froze again, this bounce when they hit the surface.
What are snow pellets?
white, opaque ice particles; up to 5mm diameter (AKA graupel)
-brittle and hard, bounce when they hit a hard surface. Fairly low density due to air gaps between frozen droplets, like hail.
How does Hail Growth occur?
Strong updrafts (upward moving wind, keeping the ice in suspension) pushes water droplets above a level in the cumulonimbus cloud cold enough to encourage freezing. It grows on the way up as additional droplets (likely supercooled) accumulate onto the surface.
How are clouds identified?
Altitude and Form
What are the three classifications of cloud formation?
-Stratiform; flat and layered
-Cumuliform; puffy, globular, vertically developed
-Cirriform; wispy, high level
What are the four classifications of cloud by altitude?
-Low Clouds; up to 2000m
-Middle Clouds; 2000-6000m
-High Clouds; 6000-13,000m
-Vertical Clouds; Near surface to 13,000m (across layers)
What are the 10 common clouds?
cirrus,
stratus,
cumulus, and
nimbus clouds,
there are cirrostratus,
cirrocumulus,
altostratus,
altocumulus,
stratocumulus,
nimbostratus, and
cumulonimbus
Tell me about a cumulonimbus cloud?
Cumulonimbus (nimbo or nimbus meaning there is precipitation), high levels of vertical development, ‘anvil head’ forms where it hits stable conditions at the level of the stratosphere. Extreme storms.
Explain a Lenticular cloud:
Species associated with cumulus forms (strato, alto, cirro) .Results from orographic lifting (pushed over a mountain).
Explain a Mammatus Cloud:
occurring most often with cumulonimbus clouds, mammatus is borrowed from Latin, meaning breast or utter.
Explain an Asperities Cloud:
Occurring most often with strato and altocumulus clouds.
What is happening during fog?
the air temperature and the dewpoint temperature at ground level are nearly identical. (We get saturation at ground level)
What are the five basic fog types?
Radiation Fog, Rime Fog, Ice-Crystal Fog, Advection Fog, Evaporation Fog
_____________: radiative cooling near the surface chills the air to saturation. Occurs on clear nights over moist land. Valley fog is a type of radiation fog that occurs in low lying areas.
Radiative Fog
____________: Supercooled fog that deposits rime on cold mornings. It occurs most frequently on clear nights, over moist land (this time under subzero temperatures). Opaque and rough ice deposit. Problem for aircraft, requires deicing before takeoff.
Rime Fog
What is the difference between Rime fog and Hore Frost?
Deposition of water vapor on to frozen surfaces in the absence of fog (skips the liquid stage) Produces delicate spikey crystals.
______________: with very cold temperatures; ice crystal may form in the air by sublimation from atmospheric moisture. Requires very cold air (below -30°C). Fairly common in Winnipeg.
Ice Crystal Fog
______________: When air moves (advects) into an area where saturation is initiated. Moist air is then chilled by contact with colder surfaces. This is the most common type of fog in the prairies, when warm moist air from the south moves over top of a cold prairie surface.
Advection Fog
What is Advection?
advection is the horizontal movement of air.
___________: Occurs where there is cold air over warmer water AKA Sea Smoke or Steam Fog
Evaporation fog
