cloud physics final exam review Flashcards

Terms Definitions
What is LZB?
level of zero buoyancy
When is ΔT negative?
from the surface up to the LFC
What is wmax (maximum vertical velocity) equal to?
=√ (2*CAPE)
What does w stand for?
Vertical velocity of updraft
What does ΔT stand for?
Temperature difference between thermal and surroundings
What does T stand for?
Temperature of surroundings
What does g stand for?
Acceleration of gravity
What does M stand for?
Mass of the thermal
What does D stand for?
Dt
Time rate of change following the thermal
What does z stand for?
Vertical coordinate
What does DM stand for?
Dt
Rate of change of the mass over time (entrainment term)
What is ∑iFi (sum of forces) stand for?
Rate of change of momentum
How is the buoyancy force related to the thermal?
The buoyancy force is negative is positive and directed upwards if the thermal is warmer than the environment and negative and directed downwards if the thermal is colder than the environment.
Why would you want to use Tv instead of just T in this formula?
Because you have to take into account the effects of moisture content on density.
What can D be expanded into?
Dt
A local rate of change ∂
∂t
What does δM mean?
The amount of mass (in kg) entrained from the environment into the cloud over a height interval δz.
What is the entrainment parameter?
μ=1 ∂M
M ∂z
What is the buoyancy term?
G ΔT
T
What is the process of entrainment term?
μW2
When does the cloud dissipate?
When Dw =0
Dt
What is m?
It is the broadening coefficient (about 0.2).
What is z and zo?
z is the height above some reference level zo
What is D stand for?
Diameter of the thermal
What effect does diameter of the cloud have on entrainment?
The larger the diameter of the cloud, the less the effect of entrainment.
What is the water loading/liquid water drag term on a cloud?
g wl
What is wl for stratus clouds?
.5 to 1 gm-3
What is wl for cirrus clouds?
0.1 gm-3
What is wl for cumulus/cumulonimbus clouds?
1-3 gm-3
What type(s) of cloud(s) does drag have a profound effect on?
Drag only has a profound effect on the cumulonimbus clouds, not much effect on stratus and especially not cirrus.
What is potential temperature θ?
The temperature of an air parcel after it has been taken dry adiabatically to 1000 mb.
What is equivalent temperature Te?
The temperature of an air parcel after all its water vapor has been condensed to liquid water.
What is equivalent potential temperature θe?
The temperature of an air parcel after all its water vapor has been condensed to liquid water and the parcel has been taken dry adiabatically to 1000 mb.
What single thermodynamic variable that is a measure of both the water vapor content and the temperature?
θe (equivalent potential temperature)
Which variables are conserved in both dry and moist adiabatic displacements?
θe (equivalent potential temperature) and qT (total water content)
Which variable is only conserved in dry adiabatic displacement?
θ (potential temperature)
What is total water content qT?
The sum of the vapor (q), liquid (qL), and ice (qI)
What is a mixing line?
The line between point A and point B on a conserved variable diagram. This means that if varying proportions of air from levels A and B are mixed, the thermodynamic state of the mixture would lie on the line.
Where is point A at?
It is at a high level in the sounding (low value of qT)
Where is point B at?
It is at a low level in the sounding (high qT)
What does f stand for?
The fraction of unit mass of the final mixture constituted by fluid originally contained in parcel B.
What is the formula for the final mixture of θe?
θe= (1-f)θeA + f θeB
What is the formula for the final mixture of qT?
QT= (1-f)qTA + f qTB
What is the formula for the slope of the line?
(θeB - θeA) / (qTB - qTA)
What is this diagram called?
Paluch diagram after Paluch (1979) who used this method to study entrainment in Colorado cumuli.
Where is entrainment in cumulus clouds dominant?
Through the top of the cloud.
If data points lie to the left of the mixing line, where is the mixing occurring?
The mixing is lateral instead of from cloud base to cloud top.
What are the two classifications of precipitation?
Stratiform and convective
What does stratiform precipitation result from?
The large scale ascent of stably stratified saturated air.
What is precipitation at a grid point?
It is the sum of the condensation produced in parcels lifted from all the model's vertical layers.
How does this effect stratiform precipitation?
Since the area of stratiform precipitation extends across many of the model's grid points, such precipitation is grid-scale and therefore well-resolved by the model.
How does this effect convective precipitation?
Convective precipitation from deep cumulonimbus clouds occurs on a scale smaller than a grid box. Thus it is sub-grid and cannot be explicitly resolved by the model. It must therefore be parameterized in terms of other quantities that are forecast by the model.
What does P stand for?
Precipitation
What does -drs stand for?
dt
Condensation rate
Why is there a negative sign in front of the condensation rate?
Because when a saturated parcel is lifted, its temperature (and therefore its saturation mixing ratio, rs) decreases.
What is undiluted ascent?
When there is no air being entrained to the air parcel. A point at the very top would go straight to the 4 km level.
What does rs stand for?
Saturation mixing ratio
Why does the stratiform precipitation equation lead to an over estimate of precipitation?
Because the evaporation of the condensed water is not taken into account.
What are four reasons of why we need to map the global distribution of rainfall?
Initialization of NWP models, initialization and testing of climate models, flash flood forecasting, and monitoring of global climate change.
Why is it difficult to get a precise measurement of rainfall?
Rain gauges only measure at one spot, which means it doesn't represent an entire area because of the high spatial variability of rainfall.
What device does a better job of estimating the rainfall over the entire United States but still has numerous sources of error?
Radar
What must we use to figure out an estimate of how much rain falls over the oceans?
Geostationary satellite data
What two things do the algorithms (equations) relate in order to estimate the rainfall amount?
The rain rate and the radiative characteristics of the cloud tops
How are the algorithms developed?
By calibrating the satellite radiance measurements with the land-based rain gauge and radar data
What is the rule of thumb for precipitating clouds which doesn't always turn out to be true?
The lower the cloud top temperature, the greater the precipitation rate.
Why is the rule above not always true?
Comparison of cloud and coincident radar echoes shows that not all clouds with high cloud tops produce rainfall at the surface.
What method must be included when using satellite data to derive rain?
A method to discriminate between precipitating and non-precipitating clouds.
What is the auto-estimator?
It is based on cloud top temperature (IR BB temp) calibrated with radar-derived surface estimates with some corrections applied.
What are the dimensions of the pixels for the Auto-Estimator?
4 km * 4 km
How often do we get a new satellite image?
Every 15 minutes
What blackbody temperatures are associated with higher rain rates?
Lower blackbody temperatures
What is the formula for this relationship?
R=1.1183*1011e(-3.6382*10^-2)*T^1.2
What does R stand for?
Rainfall rate in mm h-1
What does T stand for?
Cloud top brightness temperature in K
What information does the auto-estimator provide?
Average hourly rainfall totals, and 3,6, 24 hour accumulations
What corrections must be applied to obtain a better estimate for the auto-estimator?
Moisture correction factor, cloud growth rate correction factor, parallax correction, and orographic correction.
Where is rainfall overestimated?
Dry environments
Where is rainfall underestimated?
Moist environments
What is the correction factor that you should apply based on?
It is based on model derived precipitable water and relative humidity distributions.
What is parallax?
When the satellite shows the rain falling in a different pixel(s) than it really is.
What formula do we use to fix this parallax problem?
Tan θ=x/h, where θ is the angle, x is the pixel number you have to correct, and h is the height of the cloud top.
What directions do you make the adjustment in?
The north, south and east, west direction.
What is the formula for vertical velocity?
W=V~h*▼h
What is V~h?
Topographic heights
What is h?
Elevation of topography
What is the seeder-feeder effect?
When a higher cloud precipitates onto a low or middle cloud, making the lower cloud precipitate a lot.
Why does an orographic correction need to be made concerning mountainous areas?
This is because windward slopes the rainfall is heavier and on leeward slopes there is a rainshadow, the area is drier.
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