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DEPARTMENT of GEOSCIENCES Name______San Francisco State University May 7, 2013 Spring 2009 DEPARTMENT OF GEOSCIENCES Name_____________ San Francisco State University May 7, 2013 Spring 2009 Monteverdi Metr 201 Quiz #4 100 pts. A. Definitions. (3 points each for a total of 15 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. (e) 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. (2 pts each for a total of 8 pts) Provide the units used conventionally for the following: θ ____ Ko * o o Td ______C ___or F ___________ PGA -2 ( )z ______m s _______________** w ____ m s-1_____________*** *θ = Theta = Potential Temperature **PGA = Pressure Gradient Acceleration *** At Equilibrium Level of Severe Thunderstorms € 1 C. Sounding (3 pts each for a total of 27 points in this section). Examine the sounding (two copies) given below. Note the locations given at A, B, C, D, E, F, G and H. 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. 2 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. 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 3 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. 8. The line (thin black) indicated by the letter G 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 9. The level indicated by the letter H is the (a) Equilibrium Level (b) Lifting Condensation Level (c) Level of Free Convection (d) Equilibrium Level (e) Convective Temperature D. Short Answer. (Answer below or on back in complete sentences, with subject, verb and object in each sentence, please) (50 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.” (17 pts) 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 4 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. 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. (17 pts) 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. 3. Severe weather meteorologists in the Great Plains know that wave cyclones play an important role in setting the environment for severe convection. Briefly discuss ONE factor associated with a wave cyclone located over Oklahoma that might encourage severe thunderstorms over Texas. (16 pts) As wave cyclones emerge into the Great Plains, air with high dew point temperature (and mixing ratio) is drawn northward across Texas. This air tends to have high values of surface based CAPE associated with it. Thus, the wave cyclone is creating a situation in which one of the ingredients for thunderstorms is brought over Texas. As wave cyclones emerge into the Great Plains, a boundary between warm moist and warm dry air, called the Dry Line, forms. Severe thunderstorms tend to form just east of the Dry Line in some circumstances. With a wave cyclone over Oklahoma, the Dry Line would probably extend southward across Texas. 5 6 .
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