# Stability

The following questions are drawn from pp.239-267, 275-278 :

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1. In general (not just in meteorology), what do we mean by a *stable* or *unstable* system? How do you tell the difference? In particular, what is the characteristic response to a small perturbation in each case? What is a *metastable* system?

2. What do we mean by each of the following three terms?

a) Local stability

b) Potential instability

c) Parcel (or non-local) stability

3. What are the key assumptions of the *parcel method*? When are these assumptions unrealistic, and what are the consequences?

4. Given the local lapse rate of temperature or potential temperature, be able to tell whether that lapse rate is stable or unstable with respect to unsaturated adiabatic motions.

5. What is a layer called in which the lapse rate is greater than the dry adiabatic lapse rate, and why are such layers comparatively uncommon, especially at any significant distance above the surface?

6. Without any math, explain what the Brunt-Vaisaila frequency refers to and how, in general, it changes with increasing stability.

7. Explain what conditional instability is and how we determine whether it exists in a temperature profile. When does *conditional* instability become *actual* instability?

8. Explain what *potential instability* is. Be able to determine on a Skew-T diagram whether a layer bounded by specified temperatures and dewpoints exhibits potential instability. Also be able to determine this from a profile of \(\theta_e\).

9. Given a complete sounding AND the starting pressure, temperature, and dewpoint of an arbitrary parcel, be able to determine the parcel’s LCL, CCL, convective temperature Tc, and, if present, its LFC(s), EL(s), and areas of CAPE and CIN.

10. Given a complete sounding, be able to evaluate the likely occurrence and depth or strength of convective clouds as a result of either the lifting or heating of parcels drawn from a particular level or layer (e.g., the lowest 50 hPa).

11. Given a numerical value for CIN and/or CAPE in J/kg, determine the theoretical minimum starting updraft speed to overcome the CIN and/or the maximum theoretical updraft speed generated from the CAPE. By what approximate factor should the latter value be adjusted to account for real-world conditions? What are those real world conditions that reduce the actual updraft speed relative to the theoretical value?