Download Observation and Photography of a Kevin-Helmholtz Instability Cloud and more Study Guides, Projects, Research Mechanical Engineering in PDF only on Docsity! Clouds 2: Kevin-Helmholtz Instability MCEN 4228: Flow Visualization November 29, 2007 Sean Hulings Figure 1: Kevin-Helmholtz Instability Cloud As an extension of the first cloud assignment, I continued to explore the skies for interesting and new cloud formations. Throughout the semester I was very intent on photographing a cloud that displayed the phenomena associated with the theory known as Kevin- Helmholtz instability. I was doubtful at first considering their rarity; however I happened to be in the right place at the right time and captured the image as seen in Figure 1. I have classified this cloud as Cirrus Kelvin-Helmholtz Colombia. My image was taken mid-afternoon on the 21st of October in southeast Boulder, Colorado. I tried to take most of my pictures either during the early morning or early evening so that the atmospheric conditions present would most closely match that of the sounding data collected at the Denver weather-balloon site. I captured the photograph from a stair landing at my apartment complex. The clouds were located high in the south-western portion of the sky just past the southernmost flatiron. I estimate that the elevation of the clouds between 5000 and 6000 meters. The weather on this day was particularly windy. This was especially true for the early morning which had mild to extreme gusts. As the day progressed, the winds slowly tapered down. According to the skewT plot seen in Figure 2, the atmosphere was stable from ground level to 5650 meters. From 5650 meters to roughly 9000 meters the atmosphere changes to an unstable condition. As we continue in elevation from this point the conditions demonstrate generally stable conditions. The skewT experimental data appears to be consistent with the formation of Kelvin- Helmholtz instability clouds. Kevin-Helmholtz instabilities occur when velocity shear is present within a continuous fluid or when there is sufficient velocity difference across the interface between two fluids. I believe that what we are observing in my photograph is the result of a significant velocity difference across the clouds interface. With reference to the skewT plot, there is a substantial velocity difference between roughly 4800 and 5650 meters. This is a good indication that this is the location of the cloud formation and the driving force behind the repeating wave-like structure. Kevin-Helmholtz instabilities also tend to form in stable atmosphere conditions. As stated earlier, the elevation that I assume this cloud to be at is under stable conditions. In addition to cloud shapes in the sky, the Kelvin-Helmholtz instability can be observed in sand dunes, rising cigarette smoke, and water waves.
