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ATSC 3032 Tephigrams, and static stability

ATSC 3032 Tephigrams, and static stability. sources: handout text online module called “ Skew T mastery ”. 1. Aerological diagrams. Radiosonde (or rawinsonde ) data Maps Vertical profiles. Instrument contains: Hygristor, thermistor, aneroid barometer, and radio transmittor

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ATSC 3032 Tephigrams, and static stability

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  1. ATSC 3032Tephigrams, and static stability sources: handout text online module called “Skew T mastery”

  2. 1. Aerological diagrams • Radiosonde (or rawinsonde) data • Maps • Vertical profiles Instrument contains: Hygristor, thermistor, aneroid barometer, and radio transmittor At the ground, a highly directional radio direction finding antenna is used to obtain the wind speed and direction at various levels in the atmosphere by tracking the radiosonde and determining the azimuth and elevation angles.

  3. Aerological diagrams • Hydrostatic balance • Ideal gas law • Hypsometric equation

  4. Aerological diagrams: different types emagram

  5. Stuve pressure temperature

  6. Stuve

  7. Skew T log p

  8. Fig 1d. Elements of a tephigram. First, the 5 lines are shown separately, and then they are combined in the lower-right image.

  9. 2. using a tephigram

  10. tephi

  11. LCL (lifting condensation level) • Applications • Determine the height of the base of cumulus clouds, given surface observations of T and Td : • Determine the cloud base temperature: HLCL ground

  12. wet-bulb potential temperature potential temperature

  13. equivalent potential temperature saturated equivalent potential temperature

  14. wet bulb temperature: energy balance on the damp sock: LE = H LE = 6 u [esat(Tw)-e] H = 4 u [T-Tw] (Regnault balance)

  15. Applications 1. Layer thickness (between po and p) Dz Dz = 100 DT

  16. 2. Precipitable water

  17. 3. Chinook (Föhn) effect

  18. east west Cascade Mountains

  19. 4. subsidence

  20. 5. Turbulent mixing, mixed layer (stratus), MCL

  21. Oakland

  22. Conserved or not conserved?

  23. Conserved or not conserved?

  24. 3. stability

  25. stability

  26. Local vs non-local stability

  27. qe* d < 0 dz Conditional vs absolute stability Case II:

  28. Absolutely stable Conditionally unstable Absolutely unstable

  29. equilibrium level severe benign LFC no convection convective inhibition

  30. Typical wet-season tropical sounding qe* d Conditional instability: < 0 dz

  31. Potential instability or Potential instability:

  32. Lifting a potentially unstable layer

  33. Latent instability WLR: wet-bulb lapse rate deep convection source layer

  34. Stability indices

  35. Significant level indices e.g. UW sounding site • WB0: Wet bulb zero, Tw = 0°C ideally 7-9,000ft MSL, yet well below the FL • PWAT: Precipitable water (mm) the higher the better • LCL: Lifting condensation level (mb, from surface data) the lower the better • TOTL: Total totals index =T 850 +Td 850 - 2T 500 (°C) the higher the better, thunderstorms probable when TOTL>50 • KINX: K index =T 850 + Td 850 -T 500 -(T-Td)700 (°C) the higher the better • SWET: Sweat index or severe weather threat - the higher the better, for severe storms, SW>300 SWET= 12*Td850 +20*(TOTL-49) + 2*U850 +U500 +125*(0.2+sinf) where f= [wind direction 500 - wind direction 850 ] U is expressed in kts and TOTL-49 is set to 0 if TOTL<49 • MLTH and MLMR: mean mixed layer (lowest 500 m) potential temp and mixing ratio

  36. PARCEL indices Lifted index uses: Actual sfc temp or Estimated max sfc temp or Mean mixed-layer temp (note: always use virtual temp!)

  37. Showalter index SI=T500-Tp,850

  38. PARCEL indices • LIFT: Lifted index (°C) must be negative LI = T500 – T parcel,near-sfc [a 50 mb deep mixed layer is often used] • LFTV: lifted index, but Tv is used. • SHOW: Showalter index (°C, as LI but starts from 850mb) must be negativeSHOW = T500 – T parcel,850 • CAPE: Convective available potential energy - should be over 500J/kg • CAPV: CAPE using Tv • CINS: Convective inhibition (external energy) - ideally 100-300 J/kg • CINV: CIN using Tv • CAP: Cap strength (C) Tenv –Tparcel @LCL - should be <5°C • LFC: Level free convection (LFCT and LFCT) (mb) - should be close to the LCL • EQL: Equilibrium level or level of neutral buoyancy (EQLT and EQLV)(mb) - should be high • MPL: Maximum parcel buoyancy level (mb) - level where buoyancy (Tp-Tenv) is maximum

  39. Wind parameters • STM: Estimated storm motion (knts) from 0-20,000ft AGL layer, spd 75% of mean, dir 30 deg veer (to the right) from mean wind. • HEL: Storm relative helicity 0-10,000ft AG (total value) • SHR+: Positive shear magnitude 0-3000m AG (sum of veering shear values) • SRDS: Storm relative directional shear 0-3000m AG (directional difference of storm relative winds) • EHI: Energy helicity index (prop to positive helicity * CAPE) • BRN: Bulk Richardson number 500-6000m AG (BRN = CAPE/.5BSHR2) • BSHR: Bulk shear value (magnitude of shear over layer), shear calculated between 1000-500 mb or 500 m –6000 m AGL

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