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INTERPRETING A SKEW-T LOG-P AEROLOGICAL DIAGRAM

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Presentation on theme: "INTERPRETING A SKEW-T LOG-P AEROLOGICAL DIAGRAM"— Presentation transcript:

1 INTERPRETING A SKEW-T LOG-P AEROLOGICAL DIAGRAM

2 Locate pressure level (and matching ICAO Height)
400 m ASL 970 hPa

3 Read off T and Tdp from that level
T = 32°C Tdp = 7°C

4 Follow Tdp upwards along line of constant mixing ratio.
Mixing ratio = 6.5 g/kg

5 Follow T upwards along dry adiabat.
Potential temperature = 307 K = 34°C

6 Lines cross at Lifting Condensation Level = cloud base.
LCL = 670 hPa LCL = m (ICAO)

7 Dry adiabat is cooler than Environmental Lapse Rate (right-hand red line) at all levels.
Air is stable

8 Between the surface and 900hPa the reversed ELR shows the mixing layer.
As the day heats up this will move to the right, to the grey line.

9 Now… Let’s add heat to the surface air with a fire (no additional moisture).
T = 50°C

10 Potential temperature = 323 K
LCL = 540 hPa LCL = m (ICAO) LCL = -2°C

11 Dry adiabat is warmer than ELR – air is unstable.
Above LCL air rises along Saturated Adiabat.

12 Dynamic inversion when saturated adiabat and ELR cross.
P = 250 hPa Height = m (ICAO) T = -42°C

13 Winds at surface 35 kts (60 km/hr) from N

14 Winds at LCL 30 kts (50 km/hr) from NW

15 Winds at dynamic (plume) inversion.
55 kts (100 km/hr) from W

16 So under these conditions a hot backburn would move to the south, but its plume, rising to 10km height, would increasingly rotate to the left as it rose.

17 Additionally, pyro-cumulus clouds would form within the plume at 5000m.
We have no information on fuels, and so cannot assess how much cloud.

18 CALCULATING HAINES INDEX
T850=27°C T700=12°C DP850=-1°C Stability term = 3 (range of 15°) Moisture term = 3 (range of 28°) Index = 3+3 = 6

19

20 CALCULATING CONTINUOUS HAINES INDEX (CH)
CA = (T850-T700)/2-2 CA = 5.5 CB = (T850-DP850)/3-1 If(CB > 9) then CB = 9 If(CB > 5) then CB = 5+(CB-5)/2 CH=CA+CB CB=6.7 CH=12.2 95% HI = 8.5

21 CALCULATING FUEL MOISTURE CONTENT
FMI = 21-(2*T-Tdp)/4 FMI=7% FMC=7*FMI/DF If DF = 10, FMC = 5%


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