Exam 1 Study Flashcards
Saturation
The rate of condensation is equal to the rate of evaporation
Unsaturation
The rate of evaporation is greater than the rate of condensation
Supersaturated
The rate of condensation is greater than the rate of evaporation
Quantities conserved in thermodynamics
Moist static, and equivalent potential temperature
Equivalent potential temperature
The temperature a parcel at a specific pressure level and temperature would have if it were raised to 0mb, condensing all moisture from the parcel and then lowered 1000mb
Why are moist static energy and equivalent potential temperature important quantities
Because they are conserved quantities for moist adiabatic (real) processes
Hydrometeors
Liquid and ice particles in the atmosphere
Excess water mixing ratio
The amount of water available for condensation or deposition
Supersaturation
The amount of excess water vapor available to form hydrometeors
Excess water mixing ratio (re) _______ above ______. Adiabatic re is _______ re typically observed in the atmosphere
Increases, LCL, greater
As hydrometeors ____, water vapor is _______ from the atmosphere, so supersaturation ______.
Grow, removed, decreases
To form cloud droplets
We need condensation to occur
Nucleation
The process by which cloud droplets create and grow
Homogenous nucleation
Never will happen for water molecules. They are too small and can’t overcome the curvature affect
Homogenous nucleation
Never will happen for water molecules. They are too small and can’t overcome the curvature affect
Heterogenous nucleation
Water will always use this
Types of aerosols in the atmosphere
Volcanic ash, pollen, sea salt
Cloud Condensation Nuclei
Aerosols that nucleate
Increased curvature does what
Makes it harder for cloud droplets to form
Increased solute does what
Makes it easier for cloud droplets to form
Kholer curve
Illustrated the equilibrium RH as a function of droplet size, assuming a constant solute mass
Haze
Any condition to the left of the critical radius in the kholer curve which can occur in RH values as low as 70%
Aerosol swelling
Small relatively dry particles with little condensation on them
Only ____ droplets on the ____ side of the Kohler curve are _________
Activated, right, cloud droplets
Critical radius
A droplet radius at the peak of the kohler curve
Critical saturation
Is the supersaturation value at the critical radius
What is the first growth mechanism
Diffusion
Diffusion
Vapor molecules meander through the air, the direction of this is down the humidity gradient toward drier air
Diffusivity
The rate at which a fluid spreads
What does the presence of droplets cause
A supersaturation gradient which allows for growth by diffusion
Kinematic moisture flux
Growth by diffusion
Collision efficiency
- the rate droplets collide
-ranges 0-1
-greatest for two relatively large droplets
Why do we get collisions
Fall rates depend on the size of the droplets
What’s a secondary form of collision
Wake capture
What depends on the size of a droplet
Terminal velocity
Coalescence
Droplets merging to form a larger droplet
Coalescence efficiency
The rate of droplets merging
-ranges 0-1
-greatest when both droplets have R<150 microns
Why don’t larger droplets coalesce
Because of a film of air trapped between them that cannot completely escape before the two droplets bounce off each other
Homogeneous nucleation (ice crystals)
The process of ice crystals forming by the spontaneous freezing of supercooled liquid water droplets at temps near or below -40C
Heterogenous Nucleation (ice crystals)
The process of ice crystals forming in the presence of an impurity
Critical temperature
The temperature at which an ice nucleus must cool in order for the liquid it is in contact with to freeze
Condensation freezing
Middle ground between nucleation an immersion
Nuclei are more attractive as _____ then deposition nuclei, so we get _______ first then ______
CCN, supercooled, freezes
At ____ it takes _____ molecules to form an ice embryo. Number _______ as temp increases making it less likely. The bond forms through ______ and ______ at the right orientation
-40C, 250, increases, random movement, colliding
Contact
Similar process to freezing rain hitting a powerline
Immersion
Larger droplets have more ice nuclei which given them a greater chance of having one that triggers freezing
Ice crystal shape depends on
Temperature and water vapor density excess
Ice crystals also grow in
Diffusion
Since particles come in all different shapes and sizesz the ____ of ice crystal growth by ____ depends on the ____ of the ice crystal
Rate, diffusion, mass
WBF process
Occurs due to the differences in the saturation vapor pressure with respect to liquid water and ice
Precip due to ___ is sensitive to the amount of _____
WBF, ice nuclei
Too few <1 per liter
Few ice crystals form and can take all availiable moisture. They are large, fall to the ground and leave behind small liquid droplets
Just right 1-10 per liter
A number of ice crystals can grow to a considerable to fall as precip
Too many (>10 per liter)
A lot of ice crystals form but they are small and no precip forms
Aggregation
Or “accretion” is a “mixing phase process” over time, this can lead to graupel and even hail
Hail
Forms when water spreads around the ice before freezing, gets caught in updraft and then freezes again
Micro physics parameterizations
-predict the distribution of drop size
-the affects all parts of the model by prescribing mid-tropospheric latent heat release
What do microschemes try to do
-predict all properties of hydrometeors
-predict different shapes
-represent different scales
What do microschemes try to do
-predict all properties of hydrometeors
-predict different shapes
-represent different scales
Bin
Microphysics as accurately and generally as possible. No predetermined distribution drop size distrubutions
Bulk
Divide microphysics into predetermined discrete bins and compute the evolution of those. Assume a Marshall-Palmer distribution and fit parameters
Bulk Advantages
-fewer number of prognostic variables=computationally cheap
-easy to integrate
-tweakable parameters
Bulk limitations
-cannot represent more than one distribution at a time
-“frozen” distributions for single-moment schemes
Bin advantages
-more realistic
-process that depends on size distribution
-terminal velocity-> aggregation better represented
-represent specific parameterizations and particle interactions
-Allows for bio dial (+) distributions-and for them to vary
Bin limitations
-computationally expensive
-difficult to validate
-knowledge of ice phase physics is lacking
Single moment
Predicts mixing ratios of hydrometeors (Prediction of mass)
Double moment
Prediction of the number of hydrometeors
Triple moment
Double moment + refelctivity
Class 5
Predicts 5 types of particles (Ice, snow, liquid, graupel, vapor snow)
Class 6
Predicts 6 types of particles (ice, snow, liquid, graupel, vapor snow, cloud water)
Single moment advantages
Computationally efficient
Single moment limitations
Inherent uncertainty due to fixed parameters
Double moment advantages
Mass and number are independent: can represent different environment
Double moment limitations
Difficult to validate
Mass and number are independent: very sensible to use with bin scheme
Black box syndrome
Ignorance of assumptions, processes, implementations, within the parameterizations
Radar
Radio detection ranging
-active remote sensing technique
-a transmitter sends out pulse of EM radiation, measuring the amount of power reflected (scattered) back
Z-R relationship
How reflectivity influences rain fall
Doppler Radar
Account for Doppler shift: can interpret whether particles are moving towards or away from it
Dual Polarization Radar
Transmits and recieve pulses in both a horizontal and vertical orientation, helps forecasters with better estimates of the size, shape, and variety of particles
Benefits of dual polarization radar
-improved accuracy of precip estimates: better flash flood detection
-Ability to discern between heavy rain, hail, snow, and sleet
-improved detection of non-meteorological echoes
-detect of aircraft icing conditions
-identification of the melting layer
Differential Reflectivity (ZDR)
Tells you about the shape of particles. Use it to tell if droplets are big or small
Correlation Coefficient (CC)
Tells you how similar things are. Low values are notorious for tornadoes since non-meteorological object can be put in the sky
Low cc (<0.8)
Non Meteorological (Birds, insects)
Moderate cc values (0.80-0.97)
Metr (Non Uniform) hail, melting snow
High cc (>0.97)
Metr (Unifor) rain, snow
Specific Differnetial Phase KDP
Tells us how much liquid water is present based on change in speed of horizontal and vertical waves
KDP Values: hail, snow, rain
Near 0 (expect 3 for melting), between -1 and 0.5, between 0 and 5
Spectrum Width
A measurement in velocity dispersion: good indicator for turbulence
Radar attenuation
The absorption or reflection of radar signals as radar pulse penetrates an area of precip
L Bands
Use mostly for clear air turbulence studies
S Bands
NWS uses this
-not easily attenuated: makes it useful for near and far weather observations
-requires large antenna dish and a large motor to power it
C Bands
-more easily attenuated
-best for short range weather observations
-does not require large dish
-best for TV stations
X Bands
Use for studies on cloud development because they can detect tiny water particles and also used to detect light precip like snow
-attenuate easy -> short range
-portable-> Doppler on wheels
-major airplanes equipped with this
K bands
Split down the middle due to strong absorption line in water vapor
W Band
Measure ocean sea spray but not in rain
Parabolic Dish Vs. Phased Array
Approx. 6-10 min for a parabolic dish radar to get complete volume scan of the atmosphere. Phased Array takes seconds
AirBourne Phases Array Radar (APAR)
Consist of 4 array antennas: 2 mounted on the fuselage behind the rear doors, 1 on the tail, and one on the nose
Clausius Claperyon Equation
-Illustrates how saturation vapor pressure of water increases with temperature
-Helps explain why warmer air can hold moisture
What does the difference between the Clausius Clpaeryon Equation and the Emphrirical Equation tells is
Accounts for the change in droplet shape as its falling
Warm Cloud Formation
-LCL 100% humidity with excess water mixing ration
-then condenses into CCN
-Cloud droplets form, collisions do not occur bc they are not big enough and do not have enough inertia
-don’t have enough mass to move through the air
-Growth by condensation is a slow process up until 20 micron meters, this process is not negligible bc collisions and other mechanisms occur
-growth occur until they fall caused by terminal velocity is larger than updraft velocity or they move outside updraft
Cold cloud formation
A droplet goes up but does not freeze right away. Need ice nuclei. Too few, and only freezes, too much and they all freeze but they are too small to grow. Sweet spot 1-10
The smaller the droplet
The larger the gradient: why there is a steep slope
Stokes Law accounts for
A spherical droplet but once they are larger
