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What causes Clouds?

Cumulus. Stratus. What causes Clouds?. What are their Names?. Cumulonimbus. Cirrus. Adiabatic lapse rate = Δ T / ∆Alt. Adiabatic means TE insulated air parcel (imaginary box of air). P Vol TE stays the same T. DALR ~ 10 0 C/km.

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What causes Clouds?

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  1. Cumulus Stratus What causes Clouds? What are their Names? Cumulonimbus Cirrus

  2. Adiabatic lapse rate = ΔT / ∆Alt. • Adiabatic means TE insulated air parcel (imaginary box of air) P Vol TE stays the same T DALR ~ 100C/km How does the temperature change in the troposphere? ELR ~ 6.50/km Altitude (km) ΔDew Pt. ~ 20/km Air Parcel T(0C) • DALR = Dry adiabatic lapse rate = cooling rate for air parcel <dew pt. • Moist ALR = cooling rate for a.p. > dew pt. (latent heat release) • ELR = Environmental lapse rate = surrounding atm. lapse rate • ΔDew pt. = change due to P change • Lifting Condensation Level = (DALR-Δdew pt)-1x (TG-dew pt) • If ELR<DALR, then air is stable • If ELR>DALR, then air is unstable, rising air will gain buoyancy

  3. Problem: Cumulus clouds are observed on a sunny afternoon. The temperature is 250C and the dew point is 70C. How high are the flat bottoms of the cumulus clouds? Answer: 2.25 km or 7380 ft.

  4. Match the cloud type with the probable lift mechanism(s). Cloud TypesLift Mechanism 1. Cumulus: A. Convection B. Cold fronts 2. Stratus: C. Warm fronts D. Stationary fronts 3. Cumulonimbus: E. Convergence F. Orographic lift 4. Cirrus: A C D E F A B B C D E

  5. Name 2 ways that the moisture in an air sample can begin to condense? 1. Lower its temperature! 2. Add moisture!

  6. Let’s recall a few terms and add one or two… Moisture Evaporation Condensation Dew Point Undersaturation Saturation Supersaturation Lapse rate Adiabatic DALR ELR Dew Pt. LR AH RH MALR = Moist ALR, the lower LR caused by latent heat release during condensation

  7. What is relative humidity (RH)? Relative humidity is a percentage measure of the amount of moisture in the air compared to the total amount present at saturation for a given air temperature. RH = Dv / SDv x 100% Or RH = Partial Pv / SPv x 100% Partial Pv is P of only water molecules attaching to microdroplet SPv is P of water molecules attaching at dew point

  8. Solve these problems about air samples? 1. T = 800F, Pv = 35 mb, RH? RH = 100% 2. T = 700F, Pv = 10.2 mb, RH? RH = 41% 3. TD = 280C, Pv = 4.6 mb, RH? RH = 12% 4. RH = 50%, Pv = 14.8 mb, T? T = 750F 5. T = 900F, RH = 30%, TD? TD = 540F 6. Air just above the ground has a saturated vapor pressure of 4.0 mb. What phase of water will occur if the ground cools the air to the dew point? Frost

  9. Consider 2 parcels of air… Parcel 1: T=310F, Td=280F Parcel 2: T=890F, Td=480F 1. Which parcel has the absolute humidity? Parcel 2 2. Which one has the highest RH? Parcel 1 3. Which one will reach its dew point first at equal cooling rates? Parcel 1 4. If both parcels reach saturation, which one has the highest potential precipitation? Parcel 2

  10. Unstable atm Stable atm ELR -60C/km MALR: Latent heat released -5 to -60C/km Altitude Td Td DALR -100/km SPv Temperature What happens to rising air? tropopause W. Jetstream

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