Monteverdi Metr 201 Quiz #4 100 pts.

Transcription

1 DEPARTMENT OF GEOSCIENCES Name San Francisco State University April 27, 2012 Monteverdi Metr 201 Quiz #4 100 pts. A. Definitions. (5 points each for a total of 25 points in this section). (a) Convective Condensation Level --The elevation at which a lofted surface parcel heated to its Convective Temperature will be saturated and above which will be warmer than the surrounding air at the same elevation. (b) Convective Temperature --The surface temperature that must be met or exceeded in order to convert an absolutely stable sounding to an absolutely unstable sounding (because of elimination, usually, of the elevated inversion characteristic of the Loaded Gun Sounding). (c) Lifted Index -- the difference in temperature (in C or K) between the surrounding air and the parcel ascent curve at 500 mb. (d) wave cyclone -- a cyclone in which a frontal system is centered in a wave-like configuration, normally with a cold front on the west and a warm front on the east. (f) conditionally unstable sounding (conceptual definition) a sounding for which the parcel ascent curve shows an LFC not at the ground, implying that the sounding is unstable only on the condition that a surface parcel is force lofted to the LFC. B. Units. (3 pts each for a total of 15 pts) Provide the units used conventionally for the following: Θ K o * T d C o or F o ( PGA) z m s -2 ** w cm s -1

2 a x m s -2 *Θ = Theta **PGA = Pressure Gradient Acceleration C. Sounding (4 pts each for a total of 28 points in this section). Examine the sounding given below. Note the locations given at A, B, C, D, E and F. Two copies of are provided. One of the copies has only the standard parcel ascent curve for this case. The other copy has colored areas (red and blue) added to which letters F and E, respectively, refer.

3 1. This sounding is (choose the correct answer by circling your choice) (a) Absolutely stable (b) Absolutely unstable (c) Conditionally unstable (d) None of the above 2. The line (solid red) indicated by the letter A is the (a) Parcel Ascent Curve (b) Dew Point Temperature Lapse Rate (c) Environmental Lapse Rate (d) Condensation Lapse Rate (e) Dry Adiabatic Lapse Rate 3. The line (dashed red) indicated by the letter B is the (a) Parcel Ascent Curve (b) Dew Point Temperature Lapse Rate (c) Environmental Lapse Rate (d) Condensation Lapse Rate (e) Dry Adiabatic Lapse Rate

4 4. The level indicated by the letter C is the (a) Equilibrium Level (b) Lifting Condensation Level (c) Level of Free Convection (d) Equilibrium Level (e) Convective Temperature 5. The level indicated by the letter D is the (a) Equilibrium Level (b) Lifting Condensation Level (c) Level of Free Convection (d) Equilibrium Level (e) Convective Temperature 6. The area colored blue indicated by the letter E is (a) the layer in which the lofted parcel is warmer than the surrounding air at the same elevation (b) the layer in which the lofted parcel is colder than the surrounding air at the same elevation (c) proportional to the Convective Available Potential Energy (CAPE) (d) the layer through which the air parcel will be freely buoyant (will loft without any forcing) (e) Choices (a), (c) and (d) are correct. 7. The area colored red indicated by the letter F is (a) the layer in which the lofted parcel is warmer than the surrounding air at the same elevation (b) the layer in which the lofted parcel is colder than the surrounding air at the same elevation (c) proportional to the Convective Available Potential Energy (CAPE) (d) the layer through which the air parcel will be freely buoyant (will loft without any forcing) (e) Choices (a), (c) and (d) are correct.

5 D. Short Answer. (Answer below or on back in complete sentences, with subject, verb and object in each sentence, please) (16 pts each for a total of 32 points in this section) 1. The philosophical underpinning of sounding analysis is something called parcel theory. In a few sentences, briefly describe what is meant by parcel theory. One way of helping meteorologists assess the risk for buoyant updrafts is to use so-called parcel theory, in which one air parcel at the surface is assumed to have the same temperature and dewpoint of the environment at the surface, and is lifted relative to the environmental air. Parcel theory has its limitations, since it is difficult to define how large or small a parcel really is and what mechanisms exist that selectively lift the small parcel and not the entire atmospheric layer. In addition, parcel theory fails to accomodate the fact that considerable entrainment of surrounding air occurs as buoyant plumes develop. However, parcel theory has been shown to be successful in explaining thunderstorm development. Hence, we will use it in this presentation. 2. Severe weather meteorologists in the Great Plains often examine maps of surface dew points as part of the suite of products they use in their forecast decision tree. Give and briefly describe TWO reasons for this. Dew point temperature analyses can be used to infer the position of the dry line in the Great Plains. Severe thunderstorms often form east of the dry line. Dew point temperatures at a given level are directly proportional to the mixing ratio at the level. Thus, dew point temperatures can be used to infer plumes of water vapor available for cumulonimbus development. Dew point temperatures at the surface are, in the absence of other effects, directly proportional to the amount of potential CAPE in the sounding. Hence, dew point temperatures at the surface can be used to estimate regions in which the atmosphere has potential for afternoon thunderstorm development.