2: Violent Weather Flashcards
Saturation, Pressure, Humidity
What is fog
water in gas form
Hydrological Cycle
Water cycle
Condensation –> precipitation –> surface and snowmelt runoff –> evaporation –> transpiration (cyclic)
image 9
What is humidity and how can it be quantified or measured
atmosphere is a mixture of dry air and water vapor. Measured by:
* vapor pressure (e)
* mixing ratio
What is vapor pressure and mixing ratio
- vapour pressure (e): partial pressure exerted by water vapour alone
- Mixing ratio: mass of water vapour divided by mass of dry air
What is saturation
evaporation = condensation
* air has reached its saturation vapor pressure es (subscript) so vapor pressure cannot exceed this (besides supersaturation)
* vapor pressure = saturation vapor pressure
* any additional water vapor added to the air will immedietly be condensed out into liquid water (dew, fog, cloud) because air cannot hold any more water vapor
image 10
What does saturation vapor pressure depend on and relationship when increasing
- depends only on temperature
- increases exponentially with temperature
What does graph of es(T) look like and what is it. Explain relationship between e and es.
- exponential graph of vapor pressure vs temperature called the saturation curve
- along the curve, the air is saturated: e=es
- to the right of the curve the air is not saturated: e<es
- to the left of the curve the air is supersaturated: e>es
image 11
water vapor, saturation, and temperature relationship
- if you decreasw T then you need little water vapor to reach saturation because cld air is compressed
- if you increase the temperature then you need lots of water vapor to reach saturation
image 11
Pa, kPA, hPa, mb relationships
1000 Pa = 1kPa
100 Pa = 1hPa
1hPa = 1mb (millibar)
Ways to reach saturation
- Saturation by mixing
- Saturation by addition of water vapor
- Saturation by isothermal compression
- Saturation by lifting
- Saturation by isobaric cooling
MAILI
What is an isobar
equal pressure
What is saturation by isobaric cooling? Which image?
- Image 12
- Lower the temperature to Td (dewpoint temperature) to reach the saturation vapour pressure
- This is how ground fog forms at night: the surface cools isobarically through longwave radiation and the air above the ground cools to saturation
relationship between T and Td on a saturation curve
if the distance between T and Td is large then the air is very dry, if the distance is small then the air is humid
What is dewpoint temperature
- Td
- The temperature to which an air parcel must be isobarically cooled to reach saturation vapor pressure
Saturation by addition of water vapor and which image?
- Image 13
- Increase water vapor, which isothermally increases the vapor pressure, to reach saturation vapor pressure
- temperature remains constant
Saturation by isothermal compression and which image
- Compression of air parcel decreases the volume and increases the density –> vapor pressure increase which reaches saturation vapor pressure
- image 13
Saturation by lifting and what image?
- image 14
- combo of temperature and pressure changes can result in an air parcel becoming saturated
Saturation by mixing and what image
- if two unsaturated air masses, one warm and one very cold, are mixed together, the resulting mixture can be supersaturated so will condense into a mixing fog
- image 15
Saturation below freezing and what picture
- the saturation vapor pressure of air over water is higher than over ice
- the difference arises because it takes less energy to evaporate than it does to sublimate (solid to gas)
- image 16
- tiny water droplets in the atmosphere can remain in liquid form to temperature and are said to be supercooled
What is mixing ratio and specific humidity
Mixing Ratio (w): the ratio of the mass of water vapour to the mass of dry air in a given volume of air
- Formula: w = mv/md
- The unit of mixing ratio is g/kg but is mostly dimensionless
Specific humidity (q): ratio of mass of water vapour to the total mass of air
- usually use relative humidity instead
- q = mv/(mv+md)
Saturation Mixing Ratio
- when humidity is 100%
- mixing ratio for the saturated air
- w = mvs (saturated water vapor)/md
- could also be 0.622*(saturation vapour pressure/total atmospheric pressure)
What is relative humidity
- ratio of mixing ratio (w) divided by saturation mixing ratio (ws) times 100%
- more commonly: vapour pressure/saturation vapour pressure times 100–> RH= (VP/SVP)*100
- cannot exceed 100%, if it does then that means the air parcel is saturated with fog in the atmosphere
Relationships between temperature, vapour pressure, saturation vapour pressure, and relative humidity and which image
- image 17
- If cooling, VP→, T↓, SVP↓, RH↑
- If warming, VP→, T↑, SVP↑, RH↓
What is dewpoint
- denoted by Td
- the temperature at which air must be cooled at a constant pressure to reach the saturation
- saturation vapour pressure evaluated at the dew point temperature is equal to the vapour pressure at that temperature of the air
- RH = (SVP (Td)/SVP (T), Td is basically VP
What is precipitable water
- the total content of a vertical column of air from the surface to the top of the atmosphere
- moisture in the atmosphere
- condensation of all water vapour in the atmosphere would produce a uniform global wading pool
Weight of cold and warm air, and what is stable and unstable
Warm air: light
Cold air: heavy
Stable: light air over heavy air
Unstable: heavy air over light air
What is a capping lid
allows heavy layer to be on top of lighter layer, if broken it causes convection —> overturning of heavy layer to be bottom and light on top
Ways to break capping lid
- Vigorous convection
- Mountain and topography
- Near surface convergence: different air masses converge
What is Adiabatic lifting
a parcel of air is contained in a balloon skin that allows transfer of pressure but no mixing with ambient air. During lifting/ascent, the pressure of the air drops and the air expands —> adiabatic expansion results in cooling ( inc height, dec pressure, dec temperature). For dry mass:
- each 100m ascent is 1C temperature cooling
- each 100m descent is 1C temperature warming
On a clear calm day, when does RH fall and why
between sunrise and early afternoon due to the increase of temperature due to increase in saturation vapour pressure
What affects saturation vapour mixing ratio
only temperature and it is proportional. If T inc then so does saturation vapour mixing ratio
what happens to air density as you ascend in the atmosphere
air density decreases as you go up bc pressure decreases
Ex: a parcel at height z = 0m has temperature T = 15C. What is T at z = 2500m after adiabatic lifting?
-10C
Ex: Air with t = -2C descends from 2800m to 800. What is the final T
18C
Ex: A air parcel has a temperature of 25C and RH of 20%. What is the RH after the air has
cooled to 10C? What is the RH if the cooling continues to 0C. Look at image 18
51.6% (at 10C( and 103.66% (at 0C). Page 19
Ex: Air of T = 20C has a vapour pressure = 15 mb. What is the relative humidity? Look at image 18
64%. Page 18
Ex: What is the relative humidity of a air mass of temperature 20C and dew point
temperature of 15C?. Look at image 18
73%. Page 23
Ex: What is the temperature of a air mass of relative humidity 20% and dew point
temperature of 5C? Image 18
around 31C
The temperature of air outside is -20C and dew point temperature of -25C. What is the
relative humidity of the air? If this air gets heated to get a comfortable 20C temperature,
estimate the new dew point temperature and new relative humidity? Look at image 18
Outside: 64%
Inside after heating: 3%
What is Lapse Rate
the temperature decrease with height
What is DALR and ELR
- DALR: Dry Adiabatic Lapse Rate. Any parcel of air with RH less than 100%, termed unsaturated, will cool as it rises at a constant rate = 1C/100m
- ELR: Environmental Lapse Rate. The observed lapse of temperature of the environment with respect to height. Aka actual air temperature
Displacements of unsaturated air and which picture
- image 19
- Stable air layer: displaced parcel is forced to return to its original altitude. Stable air inhibits vertical motion (left)
- Unstable air layer: displace parcel accelerates away from its original altitude. Unstable air enhances vertical motion (right)
Relationship of ELR and DALR with Unsaturated air
Stable: ELR < DALR if ELR «_space;10C/km
Neutral: ELR = DALR
Unstable: ELR > DALR (ELR cools faster than DALR) if ELR»_space; 10C/km
When do unstable conditions in unsaturated air occur
- Strong winds from different directions, making different temperatures at different heights. This leads to Clear Air Turbulence (CAT) about 10km above ground. Aviation hazard
- on a clear summer day, heating of the dry ground can result in short live adiabatic lapse rate in the lowest 20m above ground —> results in mirage, rising thermals, and rotating dustdevils
4 indications of stable atmospheric conditions
- temperature inversion
- isothermal condition
- no change in temperature with altitude (isothermal condition)
- increase in temperature with altitude (temperature inversion)
stability in saturated, cloudy air
condensation of water vapour into liquid cloud releases heat of about 2500J/g. This release of latent heat changes the temperature and therefore the lapse rate of a rising parcel
what is MALR
- moist adiabatic lapse rate
- when a parcel of saturated/cloudy air ascends, the cooling due to adiabatic expansion is partly reduced by the release of latent heat during condensation. Varies but average is 5-6C/1000m.
What is conditional instability
air layer is unstable for saturated air parcels and stable for unsaturated air parcels
- lapse rate is greater than 6C but less than 10C
Is RH of saturated parcels affected
no because its already at 100% humidity
relationship between ELR, DALR, and MALR in regards to stability
ELR > DALR is absolutely unstable
MALR < ELR < DALR is conditionally unstable
ELR < MALR is absolutely stable
How is the stability of a sounding determined
by comparing the ELR with the MALR and DALR
What happens to the saturation mixing ratio when a saturated cloudy air flows up the windward slopes of a mountain range
saturation mixing ratio (water vapour/dry air) decreases due to decrease in temperature bc of decrease in pressure
