1 The Thermodynamic Diagram Adapted by K. Droegemeier for METR 1004 from Lectures Developed by Dr. Frank Gallagher III OU School of Meteorology

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The Thermodynamic Diagram

Adapted by K. Droegemeier for METR 1004 from Lectures

Developed by Dr. Frank Gallagher III

OU School of Meteorology

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What is it?

The thermodynamic diagram, of which there exist many types, is a chart that allows meteorologists to easily assess, via quantitative graphical analysis, the stability and other properties of the atmosphere given a vertical profile of temperature and moisture (i.e., a sounding).

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Stve Diagram

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Stve Diagramto be used in

this class

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Skew-T Log-p

Diagram

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What Can it Be Used to Estimate?

Cloud base and cloud top height Expected intensity of updrafts, downdrafts, and outflow

winds Likelihood of hail Storm and cloud type (supercell, multicell, squall line) Storm motion Likelihood of turbulence Likelihood of storm updraft rotation 3D location of clouds Precipitation amount High temperature Destabilization via advection, subsidence And many others….

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The Stuve DiagramThe Stuve Diagram

Construction:

+300 C

Altitude in Km or1,000’s of feet

Pressure levelsin mb.

How high is the500 mb level?

-400 CTemperature

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this class

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Thermodynamic DiagramThermodynamic Diagram Saturation mixing ratio line (yellow):

T

p It provides the saturation mixingratio associated with the dry bulbtemperature, or the mixing ratioassociated with the dew point.The same line provides both

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this class

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Thermodynamic DiagramThermodynamic Diagram Saturation mixing ratio line (yellow):

It provides the saturation mixingratio associated with the dry bulbtemperature, or the mixing ratioassociated with the dew point.The same line provides both

What is ws at p=1000 mb and T=-100 C?

What is the RH at 1000 mb when T=240 C and Td=130 C?

If T=200 C and RH = 70%, what is Td at 1000 mb?

T

p

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Thermodynamic DiagramThermodynamic Diagram

Dry adiabats (green):

Unsaturated air that rises or sinksdoes so parallel to the dry adiabats.This line simply shows the rate oftemperature decrease with height foran unsaturated parcel.

T

p

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this class

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Thermodynamic DiagramThermodynamic Diagram

Dry adiabats (green):

What is the temperature of an unsaturated air parcel at 1000 mb and T=200C if lifted to 900 mb? to 600 mb?

What will be the temperature of an unsaturated air parcel at 600 mb and T= -200C if it sinks to 1000 mb?

T

pUnsaturated air that rises or sinksdoes so parallel to the dry adiabats.This line simply shows the rate oftemperature decrease with height foran unsaturated parcel.

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Temperature of a parcel at 1000 mbTparcel = 20C

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Parcel is unsaturated, so if liftedto 600 mb, it follows parallel toa dry adiabat (green line) – notethat the parcel goes parallel tothe NEAREST green line.

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Temperature of a parcellifted dry adiabatically to600 mb. Tparcel = -20C

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Thermodynamic DiagramThermodynamic Diagram Moist (pseudo) adiabats (red):

T

p Saturated air that rises or sinksdoes so parallel to the moist adiabats.This line simply shows the rate oftemperature decrease with height fora saturated parcel.

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this class

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Thermodynamic DiagramThermodynamic Diagram Moist (pseudo) adiabats (red):

Problem: (a) Moist air rising from the surface (T=12oC) will have a temperature of _________ at 1 km. (b) If dry, the temperature will be? Why?

(a) T = 12oC + (-6oC km-1) x (1 km) = 6oC(b) T = 12oC + (-10oC km-1) x (1 km) = 2oC

T

p Saturated air that rises or sinksdoes so parallel to the moist adiabats.This line simply shows the rate oftemperature decrease with height fora saturated parcel.

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Using the Thermodynamic DiagramUsing the Thermodynamic Diagramto Assess to Assess

Atmospheric StabilityAtmospheric Stability

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The Thermodynamic Diagram

We’ll use two types of thermodynamic We’ll use two types of thermodynamic diagrams in this class.diagrams in this class.– The simpler of the two is the StThe simpler of the two is the Stve ve

diagram, and we’ll use this to familiarize diagram, and we’ll use this to familiarize you with the use of such diagramsyou with the use of such diagrams

– The more popular (in the U.S.) and more The more popular (in the U.S.) and more useful is the Skew-T Log-p diagram, which useful is the Skew-T Log-p diagram, which we’ll apply later.we’ll apply later.

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Stve diagram

GreenDry Adiabats

RedMoist Adiabats

YellowSaturation

MixingRatio

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Thermodynamic DiagramThermodynamic Diagram Stability: To determine the stability you

must plot a sounding. A sounding is the temperature at various heights as measured by a balloon-borne radiosonde.

The sounding is alsocalled the environmental lapse rate (ELR).

WARMCOLD

T

p

Note: We also plot dew point on the chart -- we’ll get to that later.

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Types of Stability

Unsat Sat

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Stability May Vary With Height

Stable

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Example: Dry Neutral

Neutral to Dry ProcessesUnstable to Moist Processes

ELR

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Example: Moist Neutral

Stable to Dry ProcessesNeutral to Moist Processes

ELR

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Example: Absolutely Unstable

Unstable to Dry ProcessesUnstable to Moist Processes

ELR

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Example: Conditionally Unstable

Stable to Dry ProcessesUnstable to Moist Processes

ELR

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Example: Absolutely Stable

Stable to Dry ProcessesStable to Moist Processes

ELR

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Norman Sounding

3 February 1999

TemperatureSounding

Dew PointSounding

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Definitions

Lifting Condensation Level (LCL)– The level to which a parcel must be raised dry The level to which a parcel must be raised dry

adiabatically, and at constant mixing ratio, in adiabatically, and at constant mixing ratio, in order to achieve saturationorder to achieve saturation

– It is determined by lifting the surface dew point It is determined by lifting the surface dew point upward along a mixing ratio line, and the upward along a mixing ratio line, and the surface temperature upward along a dry surface temperature upward along a dry adiabat, until they intersect.adiabat, until they intersect.

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Example: LCL

Surface DataT = 10oCTd = 3oC

Mixing Ratio = 5 g kg-1

TTd

LCL = 900 mb

Data at LCLTLCL = 2oC


Notes:

Dry adiabaticascent from

surface

Constantmixing ratio

RH increasesas parcel

ascends (T andTd approachone another;

RH is100% at LCL

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Definitions

Lifting Condensation Level (LCL)– The LCL is CLOUD BASE HEIGHT for a The LCL is CLOUD BASE HEIGHT for a

parcel lifted mechanically, e.g., by a front. parcel lifted mechanically, e.g., by a front. Remember, it is the LIFTED OR LIFTING Remember, it is the LIFTED OR LIFTING condensation level.condensation level.

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Example: LCL



TTd

LCL = 900 mb

Notes:

Dry adiabaticascent from

surface

Constantmixing ratio

RH increasesas parcel

ascends (T andTd approachone another;

RH is100% at LCL

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Definitions

Level of Free Convection (LFC)– The level to which a parcel must be lifted in The level to which a parcel must be lifted in

order for its temperature to become equal to order for its temperature to become equal to that of the environment. that of the environment.

– It is found by lifting a parcel vertically until it It is found by lifting a parcel vertically until it becomes saturated, and then lifting it further becomes saturated, and then lifting it further until the temperature of the parcel crosses the until the temperature of the parcel crosses the ELRELR

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Example: LFC


Mixing Ratio = 5 g kg-1 TTd

LCL = 900 mbLFC = 840 mb

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Definitions

Level of Free Convection (LFC)– Any subsequent lifting will result in the parcel Any subsequent lifting will result in the parcel

being warmer than the environment, i.e., being warmer than the environment, i.e., instability.instability.

– This is what “free convection” means – the This is what “free convection” means – the parcel will convect freely after reaching the parcel will convect freely after reaching the LFCLFC

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Example: LFC




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Definitions

Equilibrium Level– A level higher than the LFC above which A level higher than the LFC above which

the temperature of a rising parcel the temperature of a rising parcel becomes equal to that of the becomes equal to that of the environment, i.,e. the parcel has zero environment, i.,e. the parcel has zero buoyancy or is in equilibrium with the buoyancy or is in equilibrium with the environmentenvironment

– It is found by lifting a parcel until its It is found by lifting a parcel until its temperature becomes equal to the ELRtemperature becomes equal to the ELR

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Example: LFC and EL




EL = 580 mb

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Definitions

Equilibrium Level– Any subsequent lifting above the EL Any subsequent lifting above the EL

leads to stabilityleads to stability– The EL marks the “top” of The EL marks the “top” of

thunderstorms, though in reality the thunderstorms, though in reality the upward momentum of updraft air makes upward momentum of updraft air makes thunderstorms overshoot the EL thunderstorms overshoot the EL (overshooting top)(overshooting top)

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Example: LFC and EL




EL = 580 mb

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Definitions

Convective Condensation Level– The level at which convective clouds will form due to The level at which convective clouds will form due to

surface heating alone.surface heating alone.

– It is found by taking the surface dew point upward It is found by taking the surface dew point upward along a mixing ratio line until it intersects the ELR.along a mixing ratio line until it intersects the ELR.

Convective Temperature (Tc)

– The temperature required at the ground for convective The temperature required at the ground for convective clouds to form.clouds to form.

– It is found by taking a parcel at the CCL downward It is found by taking a parcel at the CCL downward along a dry adiabat to the surface. along a dry adiabat to the surface.

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Example: LCL, CCL, and Tc



LCL = 900 mb

CCL = 750 mb

Tc = 23oC

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Example: Positive and Negative Areas



LCL = 900 mb

LFC = 800 mb

EL = 510 mb

Positive Area

NegativeArea

Need to pushparcel up!!!!

Parcel warmerthan environment!

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CAPE

Convective Available Potential Energy– The “positive area” on a thermodynamic The “positive area” on a thermodynamic

diagram, or the area between the MALR and diagram, or the area between the MALR and ELR curves in the layer where the parcel is ELR curves in the layer where the parcel is warmer than the environment, is proportional to warmer than the environment, is proportional to the energy available in the atmosphere to do the the energy available in the atmosphere to do the work of lifting/accelerating a parcel vertically. work of lifting/accelerating a parcel vertically.

– The theoretical maximum updraft of a The theoretical maximum updraft of a thunderstorm is equal to the square root of thunderstorm is equal to the square root of 2xCAPE 2xCAPE

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How Can CAPE Increase?

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How Can CAPE Increase?

Hotter surface temperature More low-level moisture Cool the mid-levels

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TdT

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W(surface) = 11 g/kg

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What Changes with Height as a Parcel Rises?

TTd

Below LCL (cloud base)

T Tdwws RH

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TTd

Below LCL (cloud base)

T decreasesTd decreasesw is constantws decreasesRH increases

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TTd

At LCL

Tw RH

LCL = 900 mb

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TTd

At LCL

T = Tdw = ws RH = 100%

LCL = 900 mb

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TTd

Above LCL

TTdwws RH

LCL = 900 mb

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TTd

Above LCL

T decreasesTd decreasesw decreasesws decreasesRH = 100%

LCL = 900 mb

Documents

1 The Thermodynamic Diagram Adapted by K. Droegemeier for METR 1004 from Lectures Developed by Dr. Frank Gallagher III OU School of Meteorology