Stuve diagram exercise

Weather and Climate
PHYS 189
Stuve diagrams
We are going to use Stuve diagrams to understand some of the concepts we learned in previous classes.
Also–perhaps more interesting–we’ll find levels where we are most likely to have clouds (or determine that
clouds are particularly unlikely in some area).
1. Starting with the Stuve diagram for your location, label the environmental temperature profile
and the dew point temperature profile. [HINT: which one is always less than the other?] Label
somewhere near the top so you have room for the other exercises.
2. In the troposphere, temperature generally decreases with altitude at the environmental lapse rate:
ELR = −
The ELR is different from the dry adiabatic lapse rate (DALR) and the saturated adiabatic lapse
rate (SALR) The DALR and SALR describe the cooling of a parcel, while the ELR gives the actual
information of what the environment is doing. Find a region on your Stuve diagram that has a relatively
constant ELR and calculate it. Be sure to identify the upper and lower altitudes used for ∆z.
3. A temperature inversion is where the temperature actually increases with height (the ELR is
negative). Are there any inversions on your diagram? If so, label them. NOTE: inversions only
exist on temperature profiles, not on dew point profiles.
4. Locate 900 mb line on your diagram. What is the environmental temperature at this level? What is
the saturation mixing ratio? [HINT: saturation mixing ratio is the value where the temperature at a
given pressure intersects the lines that slope gradually to the upper left corner. ]
5. What is the dew point at 900 mb? What is the actual mixing ratio? [HINT: Use the same procedure
for finding the saturated mixing ratio, except use the dew point profile instead of temperature.]
6. What is the relative humidity at 900 mb?
7. Find the pressure level for the ground (probably between 850-950 mb). Suppose you have an air parcel
that is lifted from the ground. If the air parcel has a temperature close to the surface temperature,
will it rise at the DALR or the SALR? This depends on whether the air is saturated near the surface.
8. Suppose it rises at the DALR. Then it follows the more steeply sloped lines (these are dry adiabats)
until it becomes saturated. What level does it become saturated? Here’s how to find out:
(a) First, what is the parcel’s actual mixing ratio near the surface?
(b) Allow the parcel to rise, following a path that is parallel to the dry adiabats. When it crosses a
saturated mixing ratio line with the same value as the initial mixing ratio, the parcel is saturated.
(c) Find the pressure (or altitude) where this occurs.
This level is called the lifting condensation level (LCL). Draw the parcel trajectory from the
surface to the LCL, making sure it follows the DALR.
9. Now the parcel is saturated so it rises at the saturated adiabatic lapse rate (it follows the saturated
adiabats). Draw the parcel trajectory as it follows the SALR.
10. Now compare the trajectory you drew–the temperature of an air parcel that was lifted from the ground–
to the temperature of the environment. If your line is on the left of the temperature line, your parcel
is cooler than the environment and it will only rise by forced conditions (winds, for example). The
atmosphere is stable under these conditions.
If your parcel’s trajectory is to the right of the temperature profile, then it is warmer than the environment and it will rise with no further assistance. The atmosphere is unstable in these conditions and
you are more likely to have thunderstorms.
Does your sounding have generally stable or unstable conditions?
11. The pressure level (or altitude) at which your parcel becomes warmer than the environment is the
level of free convection (LFC). If your sounding is unstable, where is the LFC?
12. If your atmosphere is unstable, a parcel will rise until it reaches the level of neutral buoyancy
(LNB). This is where the parcel cools back to the temperature of the environment. If you have an
unstable environment, what is the LNB?
13. Based on your analysis, do you think your location was clear or cloudy on the date of your sounding?