Detailed questions about skew-t log-p plot

[the_photon]

Hey all,

Question: I feel like I understand most of the basics of a skew-t log-p plot. Having a background in physics, I am comfortable with logarithmic axes, adiabats and isotherms, and why the grid lines on these plots are funky. However, there are two lines of data that I see on the Storm Prediction Center's radiosonde plots that just don't quite make sense.

The first is the dashed line that is usually just to the right of the observed temperature (which is itself usually in red). From what I have been told, this line shows what temperatures (at various pressures/altitudes) a dry parcel of air would evolve in to if it were released from the surface and lifted adiabatically. Is this correct?

The second line that I am confused about is a line that is usually blue, and usually just to the right of the dew point recordings (which are usually themselves in green). I haven't the vaguest idea what this line is (other than to make guesses -- maybe a saturated parcel of air rising adiabatically?) Can someone explain this blue line? I haven't seen this blue line discussed anywhere in wikipedia, etc.

Last question is that I have noticed on most skew-t log-p diagrams, there is some altitude (usually 800 feet or so above the surface) where the dew point takes a rather rapid drop. Is there a name for this boundary layer? What kinds of conclusions can be drawn from these rapid drops?

thanks all,

the_photon

 

[GPhillips]

http://www.spc.noaa.gov/exper/soundings/help/index.html

should give you help on the SPC skewTs. Click on the various sections for more detailed help about that part of the diagram. They explain the blue line. The dashed red line that kind of parallels the temperature profile is the virtual temperature. See https://en.wikipedia.org/wiki/Virtual_temperature for an explanation of that.

 

[Greg Campbell]

Dashed line (hopefully the one you're thinking of!) is the path a surface parcel will take on its wild ride. The air follows the dry ascending curve until it reaches the condensation level. After that, its lapse rate drops and it follows the moist adiabat. If this path takes it to the right of the temperature line, the parcel becomes unstable and rises. If you sum the area between dashed and ambient, you get a value proportional to instability/cape.

Blue line? Heck if I know!

More at http://convectiveaddiction.com/2010/01/16/skew-t/
Or (shameless plug for Tim V's books!) http://www.weathergraphics.com/

 

[the_photon]

Thanks guys,

It seems as if the blue line is the wet bulb temperature.

the_photon