1f. Determining Stability from Thermodynamic DiagramsThe static
stability of air can be determined numerically by comparing the
environmental lapse rate to the saturated and dry adiabatic lapse rates.
Thermodynamic diagrams can also be very useful in this regard. Figure
6–1–1 provides a simple schematic showing how this comparison is done.
The figure compares three hypothetical temperature profiles against the
SALR and the DALR on a portion of a simplified thermodynamic diagram.
The lines labeled as moist adiabat and dry adiabat plot the change in
temperature a saturated or unsaturated parcel of air would experience if
it were lifted or lowered. The three hypothetical temperature profiles
illustrate examples in which the air is absolutely unstable (profile
1—the temperature decreases more rapidly than the DALR), conditionally
unstable (profile 2—ELR is between the DALR and SALR), and absolutely
stable (profile 3—ELR is less than the SALR).Reading a Thermodynamic
DiagramIn the real world, the ELR varies from the surface upward. For
example, at one level the air might be absolutely stable, whereas at
another level it might be conditionally or absolutely unstable.
Thermodynamic diagrams allow the forecaster to observe the resultant
changes in stability at different levels visually, rather than by having
to compute the ELR repeatedly for comparison to the adiabatic lapse
rates. Figure 6-1-2 shows a temperature (heavy line on right) and dew
point (heavy line on left) sounding plotted on a Stuve diagram (see
Chapter 3) that includes dry and moist adiabats. The dry adiabats are
shown in green and slope steeply to the left as they extend upward. The
dashed blue lines are the moist adiabats. From the surface to 850 mb,
the temperature profile is parallel to that of the adjacent dry
adiabats, indicating the layer has neutral stability. Above that is a
shallow layer, which is statically stable. From 800 mb to about 650 mb,
the air is conditionally unstable. And just above that, there is a very
shallow inversion layer with temperature increasing with height.Use of
Thermodynamic Diagrams in ForecastingThe changes in stability at
different levels may appear to make the use of the thermodynamic diagram
a daunting task for the forecaster, but the situation has several
remedies. Professional meteorologists have a number of numerical indexes
calculated for every sounding. The indexes are based on temperature-dew
point combinations at varying levels and are computed automatically
when the soundings are plotted. Forecasters refer to these values for
initial guidance in their interpretations of how stability conditions
will influence the likelihood of cloud cover, precipitation, or violent
weather....FIGURE 6-1-1 Temperature Profiles. Stability can be
determined by comparing temperature profiles with the slope of the dry
and wet adiabats. Profile 1 is absolutely unstable, profile 2
conditionally unstable, and profile 3 absolutely stable....FIGURE 6-1-2
Thermodynamic Diagram. Thermodynamic diagram plotting temperature (heavy
line on right) and dew point (left) profiles for Detroit, Michigan, on
June 27, 2002. The dry adiabats (showing how a parcel of unsaturated air
would change if lowered or lifted) are shown in green and slope steeply
to the left as they extend upward. The dashed blue lines are the moist
adiabats, showing how the temperature of saturated parcels would change
if displaced vertically. The slightly arcing, red dashed lines show
mixing ratio values. The profile in heavy black on the right represents
the temperature profile. At any pressure level you can see what the
saturation specific humidity is by interpolating between the red dashed
lines. The profile on the left depicts the dew point. That line can be
used to interpolate the actual specific humidity at any pressure
level.How can comparisons between temperature soundings and dry adiabats
be used to provide stability information? Get solution
2f. Determining Stability from Thermodynamic DiagramsThe static stability of air can be determined numerically by comparing the environmental lapse rate to the saturated and dry adiabatic lapse rates. Thermodynamic diagrams can also be very useful in this regard. Figure 6–1–1 provides a simple schematic showing how this comparison is done. The figure compares three hypothetical temperature profiles against the SALR and the DALR on a portion of a simplified thermodynamic diagram. The lines labeled as moist adiabat and dry adiabat plot the change in temperature a saturated or unsaturated parcel of air would experience if it were lifted or lowered. The three hypothetical temperature profiles illustrate examples in which the air is absolutely unstable (profile 1—the temperature decreases more rapidly than the DALR), conditionally unstable (profile 2—ELR is between the DALR and SALR), and absolutely stable (profile 3—ELR is less than the SALR).Reading a Thermodynamic DiagramIn the real world, the ELR varies from the surface upward. For example, at one level the air might be absolutely stable, whereas at another level it might be conditionally or absolutely unstable. Thermodynamic diagrams allow the forecaster to observe the resultant changes in stability at different levels visually, rather than by having to compute the ELR repeatedly for comparison to the adiabatic lapse rates. Figure 6-1-2 shows a temperature (heavy line on right) and dew point (heavy line on left) sounding plotted on a Stuve diagram (see Chapter 3) that includes dry and moist adiabats. The dry adiabats are shown in green and slope steeply to the left as they extend upward. The dashed blue lines are the moist adiabats. From the surface to 850 mb, the temperature profile is parallel to that of the adjacent dry adiabats, indicating the layer has neutral stability. Above that is a shallow layer, which is statically stable. From 800 mb to about 650 mb, the air is conditionally unstable. And just above that, there is a very shallow inversion layer with temperature increasing with height.Use of Thermodynamic Diagrams in ForecastingThe changes in stability at different levels may appear to make the use of the thermodynamic diagram a daunting task for the forecaster, but the situation has several remedies. Professional meteorologists have a number of numerical indexes calculated for every sounding. The indexes are based on temperature-dew point combinations at varying levels and are computed automatically when the soundings are plotted. Forecasters refer to these values for initial guidance in their interpretations of how stability conditions will influence the likelihood of cloud cover, precipitation, or violent weather....FIGURE 6-1-1 Temperature Profiles. Stability can be determined by comparing temperature profiles with the slope of the dry and wet adiabats. Profile 1 is absolutely unstable, profile 2 conditionally unstable, and profile 3 absolutely stable....FIGURE 6-1-2 Thermodynamic Diagram. Thermodynamic diagram plotting temperature (heavy line on right) and dew point (left) profiles for Detroit, Michigan, on June 27, 2002. The dry adiabats (showing how a parcel of unsaturated air would change if lowered or lifted) are shown in green and slope steeply to the left as they extend upward. The dashed blue lines are the moist adiabats, showing how the temperature of saturated parcels would change if displaced vertically. The slightly arcing, red dashed lines show mixing ratio values. The profile in heavy black on the right represents the temperature profile. At any pressure level you can see what the saturation specific humidity is by interpolating between the red dashed lines. The profile on the left depicts the dew point. That line can be used to interpolate the actual specific humidity at any pressure level.How do forecasters deal with the fact that stability conditions change with altitude when trying to predict the formation of clouds, precipitation, or violent weather? Get solution
2f. Determining Stability from Thermodynamic DiagramsThe static stability of air can be determined numerically by comparing the environmental lapse rate to the saturated and dry adiabatic lapse rates. Thermodynamic diagrams can also be very useful in this regard. Figure 6–1–1 provides a simple schematic showing how this comparison is done. The figure compares three hypothetical temperature profiles against the SALR and the DALR on a portion of a simplified thermodynamic diagram. The lines labeled as moist adiabat and dry adiabat plot the change in temperature a saturated or unsaturated parcel of air would experience if it were lifted or lowered. The three hypothetical temperature profiles illustrate examples in which the air is absolutely unstable (profile 1—the temperature decreases more rapidly than the DALR), conditionally unstable (profile 2—ELR is between the DALR and SALR), and absolutely stable (profile 3—ELR is less than the SALR).Reading a Thermodynamic DiagramIn the real world, the ELR varies from the surface upward. For example, at one level the air might be absolutely stable, whereas at another level it might be conditionally or absolutely unstable. Thermodynamic diagrams allow the forecaster to observe the resultant changes in stability at different levels visually, rather than by having to compute the ELR repeatedly for comparison to the adiabatic lapse rates. Figure 6-1-2 shows a temperature (heavy line on right) and dew point (heavy line on left) sounding plotted on a Stuve diagram (see Chapter 3) that includes dry and moist adiabats. The dry adiabats are shown in green and slope steeply to the left as they extend upward. The dashed blue lines are the moist adiabats. From the surface to 850 mb, the temperature profile is parallel to that of the adjacent dry adiabats, indicating the layer has neutral stability. Above that is a shallow layer, which is statically stable. From 800 mb to about 650 mb, the air is conditionally unstable. And just above that, there is a very shallow inversion layer with temperature increasing with height.Use of Thermodynamic Diagrams in ForecastingThe changes in stability at different levels may appear to make the use of the thermodynamic diagram a daunting task for the forecaster, but the situation has several remedies. Professional meteorologists have a number of numerical indexes calculated for every sounding. The indexes are based on temperature-dew point combinations at varying levels and are computed automatically when the soundings are plotted. Forecasters refer to these values for initial guidance in their interpretations of how stability conditions will influence the likelihood of cloud cover, precipitation, or violent weather....FIGURE 6-1-1 Temperature Profiles. Stability can be determined by comparing temperature profiles with the slope of the dry and wet adiabats. Profile 1 is absolutely unstable, profile 2 conditionally unstable, and profile 3 absolutely stable....FIGURE 6-1-2 Thermodynamic Diagram. Thermodynamic diagram plotting temperature (heavy line on right) and dew point (left) profiles for Detroit, Michigan, on June 27, 2002. The dry adiabats (showing how a parcel of unsaturated air would change if lowered or lifted) are shown in green and slope steeply to the left as they extend upward. The dashed blue lines are the moist adiabats, showing how the temperature of saturated parcels would change if displaced vertically. The slightly arcing, red dashed lines show mixing ratio values. The profile in heavy black on the right represents the temperature profile. At any pressure level you can see what the saturation specific humidity is by interpolating between the red dashed lines. The profile on the left depicts the dew point. That line can be used to interpolate the actual specific humidity at any pressure level.How do forecasters deal with the fact that stability conditions change with altitude when trying to predict the formation of clouds, precipitation, or violent weather? Get solution
