Stability and the SKEWT

1
Stability and the SKEWT
2
Level of Free Convection (LFC)

• The Level of Free Convection (LFC) is the first
  level at which the temperature of the parcel is
  greater than the temperature of the environment.
• The LFC is the first level at which the parcel
  will become buoyant and rise without being lifted.

3
LFC (Cont.)

• The first place where the curve representing the
  temperature of an air parcel is to the right (i.e
  the parcel is warmer) of the curve representing
  the temperature of the environment represents the
  LFC on a SKEWT diagram.

4
Tparcel
Tenvironment
LFC
LCL
5
Equilibrium Level (EL)

• The Equilibrium Level (EL) is the first level
  above the Level of Free Convection where the
  temperature of the air parcel is equal to the
  temperature of the environment.
• The EL represents the first level where the
  parcel is no longer buoyant and it is no longer
  being accelerated upward.

6
EL (Cont.)

• The first place above the LFC where the curve
  representing the temperature of an air parcel
  crosses the curve representing the temperature of
  the environment indicates the Equilibrium Level
  on a SKEWT diagram.

7
Tparcel
Tenvironment
EL
LFC
LCL
8
Convective Inhibition (CIN)

• The Convective Inhibition (CIN) is the energy per
  unit mass that must be supplied to an air parcel
  in order to lift it from the Earths surface to
  the Level of Free Convection.

9
CIN on the SKEWT

• On a SKEWT diagram area is proportional to work
  and energy.
• The CIN is depicted as the area between the curve
  representing the temperature of the parcel and
  the curve representing the temperature of the
  environment between the Earths surface and the
  Level of Free Convection.

10
CIN on the SKEWT (Cont.)

• Some meteorologist refer to the CIN as the
  negative area on the SKEWT diagram.
• A larger CIN indicates that more energy must be
  supplied to the parcel by some outside source in
  order for it to reach the Level of Free
  Convection and become buoyant.

11
Tparcel
Tenvironment
EL
LFC
LCL
CIN
12
Convective Available Potential Energy (CAPE)

• The Convective Available Potential Energy (CAPE)
  is the energy per unit mass, beyond that needed
  to do the work of expansion, that is available to
  accelerate an air parcel vertically between the
  Level of Free Convection and the Equilibrium
  Level.

13
CAPE on a SKEWT

• The CAPE is depicted as the area between the
  curve representing the temperature of an air
  parcel and the curve representing the temperature
  of the environment between the Level of Free
  Convection and the Equilibrium Level.

14
CAPE on the SKEWT (Cont.)

• Some meteorologists refer to CAPE as the positive
  area on the SKEWT diagram.
• A larger CAPE indicates that there is potentially
  more energy available to accelerate an air parcel
  upwards after it reaches the Level of Free
  Convection and produce stronger updrafts.

15
Tparcel
Tenvironment
EL
CAPE
LFC
LCL
CIN
16
Sample Sounding

• pressure (mb) T (C) Td(C)
• 1000 26 20
• 950 23 19
• 900 20 17
• 850 14 11
• 800 11 8
• 750 7 4
• 700 5 1
• 650 3 0
• 600 0 -6
• 550 -4 -10
• 500 -8 -15
• 450 -10 -18
• 400 -14 -22

17
(No Transcript)
18
Convective Temperature

• The Convective Temperature (CT) is the
  temperature that an air parcel at the surface
  must reach in order for it to become unstable and
  start to rise.

19
Convective Temperature (Cont.)

• On a sunny day the absorption of solar radiation
  may cause the temperature at the surface to
  increase to the Convective Temperature.
• After air parcels reach the Convective
  Temperature, they rise and will form cumuliform
  clouds if they reach saturation.

20
Convective Condensation Level

• The Convective Condensation Level (CCL) is the
  level at which saturation would occur if an air
  parcel reaches the Convective Temperature and
  starts to rise.

21
Finding the CCL on the SKEWT

• Plot the radiosonde sounding of temperatures for
  the environment.

22
Tenvironment
23
Finding the CCL on the SKEWT (Cont.)

• Plot a point at the surface dew point temperature
  and pressure.

24
Tenvironment
25
Finding the CCL on the SKEWT (Cont.)

• Plot a line parallel to the mixing ratio lines
  from the point at the surface dew point
  temperature and pressure.

26
Tenvironment
27
Finding the CCL on the SKEWT (Cont.)

• The CCL is the point where the line parallel to
  the mixing ratios crosses the temperature
  soundings for the environment.

28
Tenvironment
CCL
29
Finding the Convective Temperature on the SKEWT

• Draw a line parallel to the adiabats from the
  point at the CCL back to the surface.

30
Tenvironment
CCL
31
Finding the Convective Temperature on the SKEWT
(Cont.)

• The temperature where the adiabat crosses the
  surface pressure is the Convective Temperature.

32
Tenvironment
CCL
CT
33
Sample Sounding

• pressure (mb) T (C) Td(C)
• 1000 26 20
• 950 23 19
• 900 20 17
• 850 14 11
• 800 11 8
• 750 7 4
• 700 5 1
• 650 3 0
• 600 0 -6
• 550 -4 -10
• 500 -8 -15
• 450 -10 -18
• 400 -14 -22

34
(No Transcript)
35
Tparcel
Tenvironment
EL
LFC
CCL
LCL
36
Why is the CCL higher than the LCL?
37
Why is the CCL higher than the LCL?

• The Convective Condensation Level (CCL) is higher
  than the Lifting Condensation Level (LCL) because
  the temperature increases to the Convective
  Temperature before the air starts to rise.
• Therefore the air parcel must rise farther in
  order to cool until it reaches saturation.

38
Tparcel
Tenvironment
EL
LFC
CCL
LCL
CT
T