330 AOS Analyzing soundings
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Objectives Materials Needed
Skew-T diagram
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Procedure
1. Plot the temperature and dewpoint from the two soundings provided at the end of this handout. Plot the wind barbs on two separate vertical lines on the right hand side of your chart. 2. Write your answers to the following questions or tasks on a sheet of paper that you will hand in along with your Skew-T chart. Except where noted, all tasks should be done for both soundings. 3. Taking an average of the potential temperature and mixing ratio in the lowest 50 mb of the sounding, draw a parcel line from the middle of that layer (i.e., 25 mb above the surface) up to the top of your chart. 4. Determine whether there is a level of free convection (LFC). If there is, record it along with the associated equilibrium level (EL). 5. Mark areas of positive and negative buoyancy with a '+' or '-', as appropriate. 6. On your Skew-T, shade a parallelogram bounded by the temperatures -70 and -80 degrees C and by the pressures 200 and 250 mb. This area graphically represents an energy of Rd (T2 - T1 ) ln(p2 /p1 ), which works out to approximately 640 joules per kg. Using this area as a visual reference, estimate both CAPE and CIN, if present, for the two soundings (if there is no CAPE, there is also no CIN). 7. Find the Lifted Index (LI) as well as the Showalter Index (SI), following the definitions in the book. Interpret the values you obtain in terms of the threat of convective activity. Reminder: the SI is based on a parcel lifted from the 850 mb level, not the surface, so you'll have to sketch a new parcel line. Also, the Albuquerque sounding starts at 840 mb, so you can't compute SI for that sounding. 8. Find the convective temperature Tc and the convective condensation level (CCL) for a parcel originating at the surface. 9. Determine whether the lapse rate at the CCL is stable or conditionally unstable. If it is the latter, find and record the associated equilibrium level Both (EL).
10. soundings were taking shortly after dawn. The forecast high temperature for Albuquerque on that day was 32 . Based on this information, and assuming Td at the surface does not change, estimate how much CIN (if any) is expected to remain during the hottest part of the day and how much CAPE (if any) will be present. Compare your values with those you found earlier. 11. For each sounding, visually identify (using the top and bottom pressure levels) ALL major contiguous layers that are (a) conditionally unstable, and (b) absolutely unstable, based on the lapse rate criteria for local stability.
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GRB (Greenbay), 12Z p(mb) 988.0 981.0 925.0 892.0 850.0 786.0 769.0 732.0 700.0 660.0 652.0 644.0 581.0 555.0 500.0 400.0 364.0 283.0 250.0 230.0 200.0 115.0 100.0 z(m) 214. 272. 745. 1035. 1417. 2031. 2202. 2587. 2934. 3385. 3478. 3572. 4351. 4696. 5470. 7060. 7705. 9370. 10170. 10705. 11600. 15108. 15990. T 2.2 2.0 -0.3 -1.3 -3.7 -7.7 -6.7 -7.1 -9.9 -13.5 -13.5 -12.9 -16.1 -16.3 -23.1 -36.7 -41.9 -52.1 -53.3 -55.5 -54.7 -58.3 -57.3
08 Nov. 2007 Td -2.8 -6.0 -6.3 -8.3 -8.0 -8.8 -7.5 -8.2 -10.8 -15.0 -36.5 -43.9 -49.1 -48.3 -47.1 -45.7 -50.9 -62.1 -63.3 -65.5 -64.7 -70.3 -69.3 dd 140 149 220 252 275 221 242 272 280 283 284 284 301 303 305 300 300 310 310 310 305 310 305 ff (kts) 4 7 17 14 5 13 18 27 30 33 34 34 44 49 47 48 51 74 73 72 65 45 44
ABQ
(Albuquerque), z(m) 1618. 1796. 3181. 3624. 4152. 4917. 5910. 6689. 7389. 7610. 8570. 8757. 9690. 11681. 14554. 15662. 16352. 16640. T 21.6 22.8 13.4 10.8 6.8 -0.1 -7.5 -11.5 -17.3 -18.3 -26.5 -26.7 -33.1 -48.7 -66.9 -71.5 -72.3 -71.1
12Z Td 11.6 12.8 7.4 1.8 -2.2 -2.8 -13.5 -28.5 -26.3 -28.3 -35.5 -35.7 -35.7 -54.7 -73.9 -78.5 -79.3 -78.1
26 Aug. 2007 dd 160 177 230 230 169 120 140 182 199 205 291 309 270 288 309 330 347 5 ff (kts) 6 12 4 4 4 6 13 14 9 8 4 3 14 32 23 23 21 17
p(mb) 840.0 823.0 700.0 664.0 623.0 567.0 500.0 452.0 412.0 400.0 351.0 342.0 300.0 224.0 142.0 118.0 105.0 100.0
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