Thermodynamics Study Set Flashcards
What does density do with height in the molecular boundary layer?
Density increases with height
What does Rho stand for?
Density
What does Theta represent?
Real Heat
What does Theta E represent?
Total Heat
What is important to note regarding total heat?
The amount of total heat never changes dry or wet
What weather process is responsible for making real heat?
Condensation
What is another abbreviation for the Planetary Boundary Layer?
CBL
What does the word eccentric represent?
Dry adiabatic
What is important to note regarding the Planetary Boundary Layer?
The Planetary Boundary Layer is where eddies are located
What are the two different types of eddies?
Mechanically Induced and Thermally Induced
What is responsible for mechanically induced eddies in the atmosphere?
The wind
When do thermally induced eddies occur?
During the day
What is important to note regarding Mechanically Induced eddies?
You can still get mechanically induced eddies even on a cloudy day
What are the important of eddies in the atmosphere?
They’re responsible for mixing the water vapor and the heat within the Planetary Boundary Layer
In the Planetary Boundary Layer, what two things remain constant with height?
The temperature and the mixing ratio
What is the Dewpoint Lapse Rate regarding the Dry Adiabatic?
2 degrees Celsius per kilometer
The measure of the energy required by the atmosphere, at a given time and place, to inhibit the ability of an air parcel to rise is what meteorological quantity?
Lifted condensation level
When convective inhibition values are high, the risk of thunderstorm development is what?
Low
In which of the following ways can convective inhibition values be determined?
Skew-T plotting and mathematical calculations
What is the wet-bulb temperature?
The lowest temperature that can be reached by evaporating water into the air
What is the importance of the skew-T/log-P thermodynamic diagram?
The skew-T/log-P thermodynamic diagram is used to plot vertical profiles of atmospheric temperature, moisture, and wind
Data for the vertical atmospheric profiles, also known as sounding plots, come from numerous sources such as what?
Radiosondes, dropsondes, pibals, aircraft, NWP model output, and satellite sounders
Most weather soundings are generated in what way?
Electronically
How does pressure decrease regarding the atmosphere?
Pressure decreases logarithmically with increasing height in the atmosphere
What are the horizontal lines on the skew-T/log-P thermodynamic diagram referred to as?
Isobars
What are Isobars?
Lines of equal pressure
How are the Isobars spaced on a skew-T/log-P thermodynamic diagram?
Logarithmically from about 1050 hPa at the bottom to 100 hPa at the top
Isobar lines are plotted every what on a skew-T/log-P thermodynamic diagram?
Every 50 hPa
What are Isotherms?
Lines of constant temperature
When talking about Isotherms on a skew-T/log-P thermodynamic diagram, how are they plotted?
On the skew-T diagram, isotherms are straight, solid lines, sloping from the lower left to upper right
What do Dry Adiabats represent?
Lines of constant potential temperature
When talking about Dry Adiabats on a skew-T/log-P thermodynamic diagram, how are they plotted?
On the skew-T diagram, dry adiabats are the slightly-curved, solid lines sloping from the lower right to upper left
What is the importance of the Dry Adiabat lines on a skew-T/log-P thermodynamic diagram?
They indicate the rate of temperature change in a parcel of dry air rising or descending adiabatically, i.e., with no loss or gain of heat by the parcel
The dry adiabat for each multiple of 10°C shares a label with the what on a skew-T/log-P thermodynamic diagram?
Isotherms
What do Saturation Adiabats lines represent?
Lines of constant equivalent potential temperature
What are other names for Saturation Adiabats?
Moist adiabats or saturation pseudo-adiabats
When talking about Saturation Adiabats on a skew-T/log-P thermodynamic diagram, how are they plotted?
On the skew-T diagram, saturation adiabats are the slightly curved lines
What should someone note regarding Saturation Adiabats on a skew-T/log-P thermodynamic diagram?
The slope and spacing of the lines varies significantly with height and temperature, particularly at lower levels
What is the importance of Saturation Adiabats?
Saturation adiabats represent the rate of temperature change in a rising parcel of saturated air (assuming that all the condensed water vapor is liquid and falls out immediately as the parcel rises—the pseudo-adiabatic assumption)
When do the saturation adiabats become parallel to the dry adiabats when talking about a skew-T/log-P thermodynamic diagram?
At low values of moisture, temperature, and pressure
What are Saturation Mixing Ratio lines also known as?
Humidity mixing ratio lines
What do Saturation Mixing Ratio lines represent?
Constant values of water vapor capacity—specifically, the number of grams of water required to saturate one kilogram of dry air at a particular temperature and pressure
When talking about Saturation Mixing Ratio lines on a skew-T/log-P thermodynamic diagram, how are they plotted?
On the skew-T diagram, the saturation mixing ratio (ws lines are the slightly-curved, dashed lines sloping from the lower left to upper right
What should someone note regarding Saturation Mixing Ratio lines?
Since the vapor capacity of air varies non-linearly with temperature, the labeling interval for Ws lines is not uniform
In order for someone to create temperature and dewpoint curves on a skew-T diagram, what must they do first?
Plot the temperature and dewpoint at each individual pressure level in the sounding. All mandatory and significant level sounding data should be plotted
In order for someone to create temperature and dewpoint curves on a skew-T diagram, what is the second step they must do?
Connect the temperature points with straight lines between successive pressure levels, often using red. Similarly, connect the dewpoints with straight lines, often using green or blue
Define Dewpoint
The temperature to which a parcel of air at a constant pressure becomes saturated without any addition of water vapor
What is the Saturation Mixing Ratio?
The saturation mixing ratio (ws) is the ratio of the mass of water vapor (Mv) to the mass of dry air (Md) in a parcel of air at saturation. In other words, Ws is the maximum amount of water vapor that a parcel can hold without condensation
The Saturation Mixing Ratio is expressed in parts per what?
Parts per thousand. Usually grams of water vapor per kilogram of dry air
How can someone find the Saturation Mixing Ratio when using a skew-T diagram?
To find the saturation mixing ratio for a given temperature and pressure on a plotted sounding, read the value, either directly or by interpolation, of the saturation mixing-ratio line that crosses the T curve at that pressure
In a sample of moist air, what is the mixing ratio?
The ratio of the mass of water vapor to the mass of dry air
What is the mixing ratio expressed in?
Parts per thousand, usually grams of water vapor per kilogram of dry air
How is the mixing ratio different from the saturation mixing ratio?
It measures the actual amount of water vapor present while the saturation mixing ratio measures the amount of water vapor that would be present at saturation
How can someone find the mixing ratio on a Skew-T diagram?
Read the value, either directly or by interpolation, of the saturation mixing ratio line that crosses the dewpoint temperature curve at that certain pressure
What should someone always remember regarding the mixing ratio?
The mixing ratio at a particular pressure is the saturation mixing ratio of the dewpoint. Not the temperature
What is Relative Humidity?
The ratio (expressed as a percent) of the amount of water vapor in a given volume of air to the amount that volume would hold if the air were saturated
What can the Relative Humidity be computed by?
The mixing ratio and the saturation mixing ratio
What is a Dewpoint Depression?
The difference between the temperature and the dewpoint temperature at a particular pressure level
The moisture output from rawinsonde observations is typically reported in terms of what?
The dewpoint depression
Saturated conditions have a dewpoint depression of what?
Zero
Dry conditions have a dewpoint depression of what?
More than 30 degrees Celsius
Rapid drying conditions above the fog support what?
Radiative and evaporative cooling at the fog top. This cooling helps to maintain the fog
What is Saturation Vapor Pressure?
The part of the total atmospheric pressure attributable to water vapor if the air were saturated
How can someone find the Saturation Vapor Pressure while using a Skew-T diagram?
From the temperature curve at the given pressure on the sounding, always follow the isotherm to the 622 hPa isobar
What is Vapor Pressure?
The part of the total atmospheric pressure attributable to water vapor
What is the difference between finding the Vapor Pressure and the Saturation Vapor Pressure on the Skew-T diagram?
One starts with the dewpoint to find the vapor pressure while one starts with the temperature to find the saturation vapor pressure
How can someone find the Vapor Pressure while using a Skew-T diagram?
From the dewpoint temperature curve at the given pressure on the sounding, always follow the isotherm to the 622 hPa isobar
Define Virtual Temperature
The temperature at which dry air would have the same density as the moist air at a given pressure
Two air samples with the same virtual temperature have the same what?
Density, regardless of their actual temperature or relative humidity
How does water vapor compare to dry air?
Water vapor is less dense than dry air
How does warm air compare to cool air?
Warm air is less dense than cool air
Since water vapor is less dense than dry air and warm air is less dense than cool air, the virtual temperature is always what to the actual temperature?
Always greater than or equal to
Since the saturation mixing ratio increases exponentially with temperature, the virtual temperature correction becomes what?
Increasingly important for higher dewpoints
How can someone figure out the Virtual Temperature while using a Skew-T diagram?
- Determine the mixing ratio, which is the value of the saturation mixing ratio line passing through the dewpoint at a given pressure
- The virtual temperature is then computed as follows:
Tv minus T plus (w/6)
What is Potential Temperature (Theta)?
The temperature that a sample of air would have if it were brought dry-adiabatically to a pressure of 1000 hPa
Potential Temperature is commonly expressed in what unit?
Kelvin
How can someone figure out the Potential Temperature while using a Skew-T diagram?
From the temperature curve at the given pressure, follow the dry adiabat to the 1000 hPa isobar
How does a dry adiabat relate to potential temperature?
The dry adiabat is an isotherm of constant potential temperature
What is the Lifting Condensation Level?
The height at which a parcel of air becomes saturated when it is lifted dry-adiabatically
How can someone figure out the Lifting Condensation Level while using a Skew-T diagram?
The LCL is located on a sounding at the intersection of the saturation mixing ratio line that passes through the surface dewpoint temperature with the dry adiabat that passes through the surface temperature
When the moisture content in the near-surface layers varies significantly, an average moisture value of the lower layer may be used in place of the surface-parcel moisture value to compute the what?
Lifting Condensation Level
What is Equivalent Temperature?
The temperature a sample of air at a pressure level would have if all its moisture were condensed out by a pseudo-adiabatic process
What is another name for Equivalent Temperature?
Adiabatic Equivalent Temperature
How can someone figure out the Equivalent Temperature while using a Skew-T diagram?
- From the dewpoint at the given pressure, draw a line upward parallel to the saturation mixing-ratio lines. Also, from the temperature curve at the given pressure, draw a line upward along a dry adiabat until it intersects the line drawn from the dewpoint. Recall that this level is the LCL
- From the LCL, follow a saturation adiabat upward to a pressure where the saturation adiabat parallels the dry adiabat. This is the pressure level where all the moisture has been condensed out of the sample
- From this pressure, follow a dry adiabat back to the original pressure. The isotherm value at this point is equal to the equivalent temperature (Te)
What is the Equivalent Potential Temperature (theta-e)?
The temperature a sample of air would have if all its moisture were condensed out by a pseudo-adiabatic process and the sample then brought dry-adiabatically back to 1000 hPa
The Equivalent Potential Temperature is identical to what?
The equivalent temperature
How is the Equivalent Potential Temperature different from the Equivalent Temperature?
The sample is brought dry-adiabatically from the equivalent temperature at the initial level to the equivalent potential temperature at the 1000 hPa level
Equivalent Potential Temperature is commonly expressed in what unit?
Kelvin
How can someone figure out the Equivalent Potential Temperature while using a Skew-T diagram?
- From the dewpoint at the given pressure, draw a line upward along a saturation mixing-ratio line. Also, from the T curve at the given pressure, draw a line upward along a dry adiabat until it intersects the line drawn from the dewpoint at the LCL
- From this intersection, follow a saturation adiabat upward to a pressure where the saturation adiabat parallels the dry adiabat. This is the pressure level where all the moisture has been condensed out of the sample
- From this pressure, follow the dry adiabat down to the 1000 hPa isobar. The temperature where the dry adiabat crosses the 1000 hPa isobar is the equivalent potential temperature (theta-e)
What is the Wet Bulb Temperature?
The temperature to which a parcel of air at a constant pressure cools through the evaporation of water into it
When is the Wet Bulb Temperature reached?
When the air parcel achieves saturation
The Wet Bulb Temperature will always fall between what two things?
The dewpoint and the temperature unless the air is saturated
At saturation, what three things are equal?
The temperature, dewpoint, and the wet bulb temperature
In the real atmosphere, the wet bulb temperature often provides what?
A good estimate of what the surface temperature will become after the onset of precipitation and once conditions become saturated
How can someone figure out the Wet Bulb Temperature while using the Skew-T diagram?
- From the temperature, proceed up along a dry adiabat
- From the dewpoint, proceed up along a mixing ratio line
- From where the two lines intersect, proceed down the saturation adiabat to the original level
What is the Wet Bulb Potential Temperature?
The Wet Bulb Temperature a sample of air would have if it were brought along a saturation adiabat to a pressure of 1000 hPa
What is the Wet Bulb Potential Temperature equivalent to?
The Wet Bulb Temperature
The Wet Bulb Potential Temperature is typically expressed in what unit?
Kelvin
How can someone find the Wet Bulb Potential Temperature while using the Skew-T diagram?
- Find the wet-bulb temperature
- From the wet-bulb temperature, follow the saturation adiabat to the 1000 hPa isobar
- The isotherm value at this intersection equals the wet-bulb potential temperature at the given pressure
What is the Convective Condensation Level?
The height to which a parcel of air, if heated sufficiently from below, will rise adiabatically until it is just saturated
How can someone figure out the Convective Condensation Level while using a Skew-T diagram?
To determine the CCL on a sounding, start at the surface dewpoint, process upward along the saturation mixing ratio line until this line intersects the temperature profile on the sounding
When the moisture content in the near-surface layers varies significantly, an average moisture value of the lower layer may be used in place of the surface-parcel moisture value in computing what?
The CCL
What is the Convective Temperature?
The surface temperature that must be reached to start the formation of convective clouds caused by solar heating of the near-surface layer
How can someone figure out the Convective Temperature while using a Skew-T diagram?
From the Convective Condensation Level on the temperature profile, proceed downward along a dry adiabat to the pressure level at the surface
What is the Wet-Bulb Zero Level?
The lowest level in a sounding at which the wet-bulb temperature is zero degrees Celsius
During the onset of a cool season precipitation event, the higher the initial wet-bulb zero level, the what?
The less chance of the precipitation changing to freezing/frozen precipitation at the surface
During the convective season, lower wet-bulb zero levels can indicate a higher probability of what?
Hail occurrence
What is the Level of Free Convection?
The height at which a parcel of air, when lifted, becomes warmer than its surroundings and thus convectively buoyant
How can someone figure out the Level of Free Convection while using a Skew-T diagram?
From the Lifting Condensation Level, proceed upward along a saturation adiabat until you intersect the sounding temperature curve
What is the Tropopause?
The boundary between the troposphere and the stratosphere