Chapter 5
Download
1 / 44

Chapter 5 - PowerPoint PPT Presentation


  • 175 Views
  • Updated On :

Chapter 5. Soundings. There are four basic types of sounding observations. (1) Radiosondes An instrument package lifted by a balloon with sensors for pressure, temperature, humidity. (2) Pibals (Pilot balloons)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Chapter 5' - tamar


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Chapter 5 l.jpg

Chapter 5

Soundings


Slide2 l.jpg


Slide3 l.jpg

  • (2) Pibals (Pilot balloons)

    • Carry no instruments. Are usually tracked with theodolite. The balloon is assumed to rise at a constant rate once the correct amount of gas is placed in the balloon.

    • By knowing the time of flight and the elevation and azimuth angle to the balloon, the position of the balloon, thus the wind speed and direction at various heights can be obtained.


Slide4 l.jpg

  • (3) Rawinsondes

    Combines radiosonde (instrument package) and method of tracking:

    Tracked by either a radio direction finder antenna, a radar, or by GPS


Slide5 l.jpg

  • (4) Dropsondes

    - dropped from an aircraft or from a constant pressure balloon


2 upper air maps l.jpg
(2) Upper-air Maps

  • Remember the format for plotting data on an upper-air map.

  • Error on pg. 5

  • The height tendency is plotted to the lower-right of the station circle.

  • This is not the position of the pressure tendency on surface maps.

    • That goes to the right of the station circle.

Radiosonde/rawinsonde - a circle.

Aircraft observation - a square.

Satellite derived wind - a star.


3 sounding diagrams l.jpg
(3) Sounding Diagrams

  • Sounding diagrams are used to represent the character of the air by profiles of temperature, moisture, wind as measured vertically through the atmosphere above a location.

  • Common ones used are:

    • Stuve diagram

    • Emagram

    • Tephigram

    • Skew-T log-P diagram


Slide8 l.jpg

A Log-pressure diagram

A linear pressure diagram


Slide9 l.jpg

A Stuve diagram logrithmic vertical scale.

A Skew-T log-P diagram


Slide10 l.jpg

plotted on the diagram has a different meaning depending on which set of lines you are considering.

  • There are several sets of lines on these diagrams and a point


Slide11 l.jpg


Slide12 l.jpg

  • Other lines on the Skew-T diagram which set of lines you are considering.

    • Potential Temperature (also called dry adiabats).

      • Potential temperature is the temperature a parcel of air would have if it descended to a particular pressure level (no exchange of heat with the environment).

      • The standard reference pressure is 1000 mb.

      • Can by calculated by Poisson’s Equation.

Po = reference pressure

Rd=gas constant for dry air 287J/kg

cp=specific heat of dry air at constant pressure, 1004J/kg


Slide15 l.jpg

  • Saturation Mixing Ratio lines which set of lines you are considering.: the value of the mixing ratio of saturated air at the given temperature and pressure with respect to a flat water surface.

  • Determined using the Clausius-Clapeyron Equation:

ro = 0.611kPa

To=273.15oK

Rv=461J/kg oK

Lv=2.5 x 106 J/oK

Ld=2.83 x 106 J/oK

I am using “r” to represent mixing ratio. Sometimes “e” is used.


Slide17 l.jpg

  • Saturation Equivalent Potential Temperature which set of lines you are considering.: (Sometimes just called equivalent temperature.) The temperature a parcel of air at a given temperature and pressure would have if it were saturated, and if all that water were condensed and removed and the parcel brought down to some reference level, usually 1000 mb.


Slide18 l.jpg


5 vertical derivatives and the hydrostatic equation l.jpg
(5) Vertical Derivatives and the Hydrostatic Equation which is then absorbed by the gas molecules of the air, so the air temperature increases. So, an air temperature’s saturated equivalent potential temperature is always warmer than its potential temperature.

  • Consider the vertical derivative of temperature with respect to pressure. This is simply the instantaneous change of temperature with pressure at some level; or

  • One could also determine


Slide21 l.jpg

  • Procedure: which is then absorbed by the gas molecules of the air, so the air temperature increases. So, an air temperature’s saturated equivalent potential temperature is always warmer than its potential temperature.

    • Pick the level (pressure) at which you wish to compute the derivative.

    • Draw a line tangent to the temperature profile at that level.

    • Going from higher pressure to lower pressure, pick a point about 50mb lower along the tangent line and determine the pressure and temperature.

    • Pick a point about 50mb above along the tangent line and determine the pressure and temperature.

    • Determine (P1-P2) and (T1-T2) from these values, making certain that P1 and T1 are the values lower in the atmosphere.


Slide23 l.jpg


Slide24 l.jpg

  • The Hydrostatic Equation results from considering the vertical forces acting on an air parcel which is not moving.

    • These are gravity (directed down) and

    • the vertical pressure gradient force (directed up) which results from pressure being higher near the Earth’s surface and less as height increases.


Slide25 l.jpg


Slide26 l.jpg

  • or or forces are the same.

  • The Hydrostatic equation.

  • However, this has density in it which is difficult to measure and most thermodynamic diagrams don’t have scales for density.

  • We can get rid of density using the Ideal Gas Law equation.


Slide27 l.jpg

  • Considering the Ideal Gas Law equation: forces are the same.

    • V = volume

    • n = number of molecules (moles) of the gas.

    • R* = universal gas constant = 8.3169 J/moleoK

  • If we divide both sides by V, volume and, if we multiply both sides by:

  • Where md is the molecular mass of dry air/mole, we get:

  • But, (n × md) is simply the mass, so we can replace

  • with density, ρ.


Slide28 l.jpg

  • And, is simply the gas constant for dry air, R forces are the same.d which equals 287 J/kgoK. (note error, pg. 17).

  • This results in:

  • Then, we can combine the hydrostatic and ideal gas law equation.

  • Writing the Ideal Gas Law equation for an expression for density gives:

  • and substituting into the Hydrostatic Equation gives:


Slide29 l.jpg

  • Consider this equation for dry air, we can write it as: forces are the same.

  • Which is:

  • We can see that pressure decreases in a natural logarithmic manner from the equation showing the derivative of pressure with height.

  • And, that change of pressure with height is dependent on temperature.

  • If a layer of the atmosphere is isothermal, changes in height of pressure surfaces are directly proportional to the logarithm of pressure.


Slide30 l.jpg


6 lapse rate l.jpg
(6) Lapse Rate are from the standard atmosphere, and would not be correct for the actual atmosphere. However, we can make a height scale on the sounding diagram which fits the actual atmosphere.

  • Lapse rate is the rate at which temperature decreases with height.

  • If all we have is temperature and pressure data, then using the Hydrostatic equation we can get an expression for the change of temperature with height related to the change of temperature with pressure.


Slide32 l.jpg

  • The Hydrostatic equation can be written as: are from the standard atmosphere, and would not be correct for the actual atmosphere. However, we can make a height scale on the sounding diagram which fits the actual atmosphere.

  • Then we can write the lapse rate

    as:

    Also, remember that

    So you could substitute in for density.


7 the buoyancy equation l.jpg
(7) The Buoyancy Equation are from the standard atmosphere, and would not be correct for the actual atmosphere. However, we can make a height scale on the sounding diagram which fits the actual atmosphere.

  • Suppose the atmosphere is not “in balance” as expressed by the Hydrostatic equation. Then, there is vertical motion.

  • The Vertical Momentum Equation expresses this situation.

  • This is the acceleration produced because of a difference between the gravitational force/unit mass and the pressure gradient force/unit mass.

  • “D” is called the total derivative - the rate of change of the value of a quantity associated with a particular air parcel.


Slide34 l.jpg


Slide35 l.jpg

  • The air around the parcel - assuming it is not moving vertically - is expressed by the hydrostatic equation which, if we move all terms to the right of the equal sign, can be written as:

  • Where o is the density of the environmental air.

  • The density of the parcel can be written as a perturbation of the environmental air density; or: o + ’


Slide36 l.jpg

  • The vertical momentum equation then becomes: vertically - is expressed by the hydrostatic equation which, if we move all terms to the right of the equal sign, can be written as:

  • Subtracting the environmental hydrostatic equation from this one (change sign and add) gives:

  • Combining terms and rearranging gives:

  • From the second term above, we can see that:

  • So we can substitute - g for

  • And get:


Slide37 l.jpg

  • So, if vertically - is expressed by the hydrostatic equation which, if we move all terms to the right of the equal sign, can be written as:’ is negative, (density is less than the environment - which occurs when the temperature of the parcel is warmer than the environment) then the right side of the equation is positive and the parcel accelerates upward.


Slide38 l.jpg


Slide39 l.jpg

  • The air molecules drag against the parcel creating a drag force. This is usually small enough that for most purposes it can be ignored. vertical momentum equation can also be written using potential temperature.

  • The right side does not have a negative sign, because a warm parcel would have a higher potential temperature, just as it would have a lower density. (The density term is not in the equation.)


8 the thermodynamic equation l.jpg
(8) The Thermodynamic Equation air molecules drag against the parcel creating a drag force. This is usually small enough that for most purposes it can be ignored.

  • This equation expresses how the potential temperature of an air parcel changes over time due to various processes (primarily adding or removing heat energy by phase changes or with the environment).

  • If there is no phase change occurring, and assuming no exchange of heat with the environment, the right side is zero and there is no change of potential temperature.

  • On a thermodynamic diagram, you are following parallel to the dry adiabats.


Stability l.jpg
Stability air molecules drag against the parcel creating a drag force. This is usually small enough that for most purposes it can be ignored.

Remember:

Is Absolutely Unstable Air.

Is Absolutely Stable Air.

Is Conditionally Unstable Air.


Slide42 l.jpg


9 latent heat release l.jpg
(9) Latent Heat Release saturated), we follow parallel to the dry adibats (potential temperature lines).

  • What happens if the air becomes saturated and continues to rise.

  • Remember: It becomes saturated at the Lifting Condensation Level.


Questions l.jpg
Questions saturated), we follow parallel to the dry adibats (potential temperature lines).

  • Do: 2, 4, 5, 6, 7.