Laboratory 3, Part IV: Complete the following (100 points)

Answer on separate sheets with answers that are made up of complete, coherent sentences. Do NOT jam answers onto a photocopy of this page. (5 points)

1. Examine this infrared satellite loop. A frame from this loop is given as Figure 1 (click on image to get higher resolution version of it). Answer the following questions:
(a) The imagery you will be using for this exercise was obtained from the US Navy. This particular infrared imagery uses a standard enhancement curve to portray temperatures. What is the name of the enhancement curve used here and state the reason why? (10 points)

This is the ZA enhancement curve. This is a grey scale color table that is designed to highlight the coldest cloud tops associated with enhanced convection with shades of light grey to white.


(b) Note the locations A, B and C on Fig. 1. Refer back to the satellite loop. Now, using the handout on kinematics, state whether the clouds at each location are dominantly showing evolution consistent with translation (advection), divergence or vorticity (rotation). Please state the evidence why for each case in near, coherent sentences. (15 points)

A is located with a zonal cloud band (which also has some cloud fingers attached to it). This cloud band is an example of cloud elements embedded in a mostly translational field characterized by advection.

B is located within a broad cloud shield in which lateral spreading is evident in the satellite loop. Thus, the clouds at location B are showing evolution consistent with divergence.

C is located with a center of counterclockwise rotation. This cyclone is imposing rotation to the cloud field.

Figure 1: GOES 10 Image, 9 March 2006 1830 UTC

2. Examine the following satellite loop showing a splitting supercell in South Dakota (the south or right-moving member of which was associated with tornadoes).

South Dakota Tornadic Supercell

Now examine Fig. 2, which provides one frame from this loop. Note locations A and B on Fig. 2. Refer back to the satellite loop. Now, using the handout on kinematics, state whether the clouds at each location are dominantly showing evolution consistent with translation (advection), divergence or vorticity (rotation). Please state the evidence why for each case in near, coherent sentences. (20 points)

At A, convective clouds appear to develop on the Black Hills, and then translate in a more or less linear manner consistent with advection. One can also note that these clouds appear to dissipate some distance downstream from the Black Hills.

The clouds at B appear to evolve in two ways. Clearly, cloud top divergence is associated with massive expansion of the anvil of this cumulonimbus cloud. But, the cloud system also appears to be translating as it is growing. Thus, the cloud at B is undergoing evolution from divergence and advection (translation).

Figure 1: GOES 11 Image, 24 July 2000, 0100 UTC

2. Examine Fig. 3a, 3b and 3c, GOES satellite imagery of Katrina at its most intense stage.

Figure 3a, b and c: GOES Imagery of Katrina at 1235 UTC 28 August 2005

State the type of image and the enhancement curve used (if applicable) for each image, and provide the reasons why. (30 points)

Figure 3a is a Visible image of Katrina, without enhancement. Figure 3b is an infrared image of Katrina, with a grey scale enhancement curve designed to emphasize the coldest tops in the whites. Thus, this enhancement is the ZA. Finally, Figure 3c is a color enhancement. It is most comparable to the MB enhancement curve in the ranges of temperatures in which color shifts occur.

3. Examine this webpage on the Gulf of Mexico Loop Current.

Now examine the three images below, corresponding to the SST pattern, Current Velocities and Sea-surface altimetry for July 25, 2005, in the Gulf of Mexico, about a month before Katrina moved into the region and intensified so dramatically. (30 points)

SST Currents Altimetry

(a) Discuss the evidence that you see that the Loop Current was present.

One can discern evidence that the Loop Current was present in each of the images. In the first image, one can see warmer temperatures in a meander that extends from southeast to northwest from the tip of Cuba. Some of that warmer water then swirls towards the west along the coast of Texas and towards the east along the coast of Florida.

In the second image, the current vectors clearly show the same meander, and the fact that the vectors show greater length along a preferred path corroborate the fact that this is a current.

The third image shows the altimetry. The Loop Current should be in a region of high altimetry gradiend with a high or ridge in the altimetry field to the right of the current, and that is exactly what is apparent.

(b) Discuss the evidence that you see that the SST pattern on the left hand diagram is consistent with the current information provided in the middle panel.

Clearly warmer water is being taken northward into the Gulf of Mexico by the current. Some of that warmer water then swirls towards the west along the coast of Texas and towards the east along the coast of Florida.

(c) Discuss the evidence that you see on the right two panels that the current information was consistent with what you would expect from the sea surface altimetry and the principle of geostrophic flow in the ocean.

This altimetry is consistent with a meander in which the currents are in geostrophic balance. One can see that the current vectors are parallel to the altimetry contours, with higher values to the right of the current vectors.