Department of Geosciences Name San Francisco State University Spring 2013 Metr 201 Monteverdi Quiz #5 Key 150 pts. 1. Definitions. (5 points each for a total of 20 points in this section). (a) Coriolis Acceleration -- -- an accleration experienced by frictionless objects moving relative to a rotating surface. On earth, Coriolis acceleration deflects all frictionless moving objects to the right of their path in the Northern Hemisphere, and its magnitude ranges from zero at the Equator to a maximum value at the North Pole. (b) Geostrophic Wind -- the theoretical wind that would result from an exact balance between the Coriolis acceleration and the pressure gradient acceleration so that, in the Northern Hemisphere, air would flow parallel to the isobars (height contours) clockwise around highs and counterclockwise around lows, and faster in regions in which the pressure (height) gradients are the largest. (c) CIN --In a conditionally unstable state, the air parcel must be force lifted through a layer in which the air parcel is relatively cold compared to its surroundings to its LFC. If the equation used to calculate CAPE yields a negative number, then the acceleration due to buoyancy is negative (directed downward). The resulting calculation yields negative CAPE or Convective Inhibition Energy (CIN) (d) EL -- In a conditionally or absolutely unstable state, the elevation at which buoyant air parcel s ascent curve crosses over the Environmental Lapse Rate. This is normally near the tropopause or higher. 2. Longer Answer Questions (105 points). Answer neatly in complete sentences in the spaces provided or on the back of the exam sheets. Show all steps for calculations. (a) Physicists often prefer the term Coriolis Effect to Coriolis Acceleration. Explain why. (30 pts) Newton s Second Law of Motion says that in the absence of other effects an object in motion will remain in motion, at a constant speed and direction unless acted upon by an outside force or acceleration. In reality, frictionless objects moving over the face of the earth, for example, are moving in a straight line and at a constant speed when viewed from space. 1
Even though this motion appears to describe a spiral relative to the earth, relative to space the object is in straight line motion (and with no change in speed). Hence, there are no outside real accelerations acting on the object. (b) You are provided with the paired (a) CAPE/CIN charts; and (b) Visible Satellite Images for 1700 UTC and 2200 UTC on 29 April 2010. Note the locations labeled A and B. (Note: no radar images given...so even though the question was misworded, you should recognize that you are looking at a satellite image and not a radar image). Explain the differences in the satellite presentation at locations A and B given the evolution of the CAPE/CIN field you see on the top chart. [Note: this is an essay question. It does not need to be long. However, it needs to be written in proper English, NEATLY, with sentences that have a subject, verb and object] (30 points) The morning CAPE and CIN field suggests that all of the soundings in the area are potentially unstable, but that large values of CIN need to disappear from these soundings before the soundings become nearly absolutely unstable. The values of CAPE at the two locations are roughly similar, but it is clear that by the afternoon while the CIN disappeared at location A, there was still significant values of it at B. Thus, the convective temperature was probably attained at A, and thunderstorm initiation should be observed at location A, but not at B. The radar reflectivity and visible satellite plots substantiate this, with both showing heavy precipitation associated with a cumulonimbus cloud at A, but clear skies and no precipitation at B. 2
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(c) The chart on the next page is the 500 mb chart for the eastern Atlantic for 12 UTC 10 May 2013. Note the station reporting a 40 knot (20.7 m/s) wind highlighted in red. The orange lines show the natural coordinate system centered on the observation in question. Locations 2 and 1 are 500 km apart. i. Label the two axes for the coordinate system. (10 pts) This is a natural coordinate system. The s-axis is tangent to the wind with the positive end on the downstream side. The n-axis is at right angles to the wind, with the positive direction to the left. See diagram. ii. The geostrophic wind relation is V g = g f Δz Compute the value of Δz. Show all steps. (35 pts) Δz = z z 2 1 = 500 km = 500000 m The 500 mb heights at the two locations can be read right off of the chart. Z 2 = 576 dm = 5760 m Z 1 = 585 dm = 5850 m Substituting these values into the expression gives: Δz = 5760 5850 ( )m 500000 m = -2.0 X 10-4 = -0.0002 4
3. Sounding Interpretation. You are provided with the sounding for Brownsville TX (KBRO) for 12 UTC 9 May 2013. (25 points) 5
Your task is to transform the sounding to one that estimates conditions for afternoon heating. On this skew-t log p diagram, the saturation mixing ratio lines are dark grey and slope from left (at the bottom) to right (at the top) and are labeled at the bottom in g/kg. a. Find the Convective Condensation Level, and the Convective Temperature (indicate on the diagram) (10 pts) b. Draw the parcel ascent curve that would occur if the afternoon temperature achieves the Convective Temperature. (5 pts) c. Shade in the CAPE for the ascent curve that results. (5 pts) d. This sounding is an example of the type of sounding that has great potential for explosive convection in the afternoon, even though the morning sounding has a strong inversion. What is the popular name that severe weather forecasters give this type of sounding? Loaded Gun Sounding (5 pts) 6