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 Stull: Chapter 6: pg 119, , Ahrens: Chapter 5 Class Outline:  Atmospheric stability  Determining stability  Cloud development

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

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

MET 61 4 MET 61 Introduction to Meteorology

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

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

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 (?)

MET 61 8 MET 61 Introduction to Meteorology

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

MET 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

MET 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.

MET 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.

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

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

MET 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.

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET 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 _____________

MET 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

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

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

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

MET MET 61 Introduction to Meteorology

MET 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

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

MET 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

MET 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

MET 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

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

MET MET 61 Introduction to Meteorology

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

MET 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)?

MET MET 61 Introduction to Meteorology