1. MET 61 1 MET 61 Introduction to Meteorology MET 61 Introduction to Meteorology - Lecture 6 Stability Dr. Eugene Cordero San Jose State University W&H: pg 88-93 Stull: Chapter 6: pg 119, 128-131, 135-138 Ahrens: Chapter 5 Class Outline:  Atmospheric stability  Determining stability  Cloud development

2. MET 61 2 MET 61 Introduction to Meteorology Stability  Stable equilibrium-  Unstable equilibrium –

3. MET 61 3 MET 61 Introduction to Meteorology Stability  Stable equilibrium- after disturbance element returns to original state.  Unstable equilibrium – after disturbance, element will move away from original state

4. MET 61 4 MET 61 Introduction to Meteorology

5. MET 61 5 MET 61 Introduction to Meteorology Stable Unstable Neutral Conditionally unstable

6. MET 61 6 MET 61 Introduction to Meteorology Parcel  To explore the behavior of rising and sinking air we use the idea of a parcel.  Parcel is some volume of air, in an imaginary container.  Parcel can expand or contract freely  Parcel is

7. MET 61 7 MET 61 Introduction to Meteorology Parcel  To explore the behavior of rising and sinking air we use the idea of a parcel.  Parcel is some volume of air, in an imaginary container.  Parcel can expand or contract freely  Parcel is about the size of a basketball (?)

8. MET 61 8 MET 61 Introduction to Meteorology

9. MET 61 9 MET 61 Introduction to Meteorology  Environmental lapse rate, . –_____________________  Dry adiabatic lapse rate,  d –_____________________  Moist adiabatic lapse rate,  w –_____________________ Determining Stability

10. MET 61 10 MET 61 Introduction to Meteorology  Environmental lapse rate, . –From radiosonde (sounding)  Dry adiabatic lapse rate,  d –Constant (9.8°/1000m)  Moist adiabatic lapse rate,  s –Varies with temperature/moisture –1°/1000m - 9°/1000m; typical = 6°/1000m Determining Stability

11. MET 61 11 MET 61 Introduction to Meteorology Absolute stability  Absolutely stability – –Difference in temperature between surface and aloft is small.  Conditions: – –Nighttime radiational cooling of surface –Subsidence inversions  Produces flat or stable clouds (stratus)  Fog or haze persists near ground.

12. MET 61 12 MET 61 Introduction to Meteorology Absolute stability  Absolutely stability –Always stable when  <  s –Difference in temperature between surface and aloft is small.  Conditions: –Air aloft warms, surface air cools –Nighttime radiational cooling of surface –Subsidence inversions  Produces flat or stable clouds (stratus)  Fog or haze persists near ground.

13. MET 61 13 MET 61 Introduction to Meteorology

14. MET 61 14 MET 61 Introduction to Meteorology

15. MET 61 15 MET 61 Introduction to Meteorology Absolutely unstable  Always unstable when  >  d  Typically constrained to shallow layers of atmosphere –i.e.____________________________________

16. MET 61 16 MET 61 Introduction to Meteorology Absolutely unstable  Always unstable when  >  d  Typically constrained to shallow layers of atmosphere: –i.e. shallow area near ground on hot sunny days.

17. MET 61 17 MET 61 Introduction to Meteorology

18. MET 61 18 MET 61 Introduction to Meteorology

19. MET 61 19 MET 61 Introduction to Meteorology Conditionally unstable  Conditionally unstable –  >  s AND  <  d –Atmosphere most typically in this state  Rising air parcel is dry _______________  Rising air parcel is saturated _____________

20. MET 61 20 MET 61 Introduction to Meteorology Conditionally unstable  Conditionally unstable –  >  s AND  <  d –Atmosphere most typically in this state  Rising air parcel is dry – stable  Rising air parcel is saturated - unstable

21. MET 61 21 MET 61 Introduction to Meteorology

22. MET 61 22 MET 61 Introduction to Meteorology

23. MET 61 23 MET 61 Introduction to Meteorology

24. MET 61 24 MET 61 Introduction to Meteorology Neutral stability  Condition when –  =  s or  =  d  Atmosphere has no tendency to move more than the initial displacement.

25. MET 61 25 MET 61 Introduction to Meteorology Neutral stability  Condition when –  =  s or  =  d  Atmosphere has no tendency to move more than the initial displacement.

26. MET 61 26 MET 61 Introduction to Meteorology

27. MET 61 27 MET 61 Introduction to Meteorology Example Radiosonde observations show temperature at the following heights: Surface12C 1000m 4C 2000m-2C 3000m-6C 1.If a parcel of dry air is forced up to 1000m, is the parcel neutral, stable or unstable? 2.If a parcel of saturated air is forced up to 1000m, is the parcel neutral, stable or unstable? 3.Repeat the above (1 and 2) for a parcel forced up to 3000m

28. MET 61 28 MET 61 Introduction to Meteorology Causes of instability  Cooling: –  Warming –Daytime solar heating –  _______________________________

29. MET 61 29 MET 61 Introduction to Meteorology Causes of instability  Cooling: –Winds bring in colder air (cold advection) –Radiational cooling (clouds or atm)  Warming –Daytime solar heating –Warm advection –Air moving over a warm surface  Cooling aloft or warming surface – more unstable conditions

30. MET 61 30 MET 61 Introduction to Meteorology Mixing and lifting  Mixing can either enhance or reduce the stability – –Mixing can produce more unstable conditions –Winds bring in colder air (cold advection) –Radiational cooling (clouds or atm)  Lifting – –Convective instability

31. MET 61 31 MET 61 Introduction to Meteorology Mixing and lifting  Mixing can either enhance or reduce the stability –Wind mixing can stir up inversion layer –Mixing can produce more unstable conditions –Winds bring in colder air (cold advection) –Radiational cooling (clouds or atm)  Lifting –Subsidence produces more stable conditions –Air rising can produce more unstable conditions –Convective instability

32. MET 61 32 MET 61 Introduction to Meteorology

33. MET 61 33 MET 61 Introduction to Meteorology

34. MET 61 34 MET 61 Introduction to Meteorology

35. MET 61 35 MET 61 Introduction to Meteorology

36. MET 61 36 MET 61 Introduction to Meteorology

37. MET 61 37 MET 61 Introduction to Meteorology

38. MET 61 38 MET 61 Introduction to Meteorology

39. MET 61 39 MET 61 Introduction to Meteorology

40. MET 61 40 MET 61 Introduction to Meteorology

41. MET 61 41 MET 61 Introduction to Meteorology

42. MET 61 42 MET 61 Introduction to Meteorology

43. MET 61 43 MET 61 Introduction to Meteorology

44. MET 61 44 MET 61 Introduction to Meteorology

45. MET 61 45 MET 61 Introduction to Meteorology H=125m(T-T d ) H=222ft(T-T d )

46. MET 61 46 MET 61 Introduction to Meteorology Activity 5: Due Wednesday Feb 26 Consider the following situation: You are meeting some friends for a hike at Rancho San Antonio. The plan is to hike to the top of Black Mountain. After arriving at the park, you casually glance at your weather geek watch and notice that the surface temperature is 34°C and that the elevation is 350m. (your recent tour of Europe convinced you to keep your watch in metric.). One of your friends asks if they should bring a sweater, since it may be cold on top. You, the aspiring meteorologist, speak authoritatively, and explain how the lapse rate might be used to estimate the temperature at the top of Black Mountain, which is approximately 3,552ft. Question 1: How cold will it be on the top of Black Mountain. Be sure to state any assumptions. Question 2: You now notice that Black Mountain is engulfed in a big cloud, with the cloud base roughly 1000 ft above you. Now revise your estimate of the temperature at the top of Black Mountain? Question 3: If you were told that the environmental lapse rate is 10°C per 1000m, determine if the atmosphere is stable or unstable at the summit of Black Mountain. If air is forced upward over Black Mountain, what type of clouds would you expect to form (stratus or cumulus)?

47. MET 61 47 MET 61 Introduction to Meteorology