REPORT

Clouds First: Boulder Cumulonimbus

Jamie Frankel

Flow Visualization

Photo Taken 9/11/2019 at 6:12PM

The purpose of this image was to capture my favorite texture of cloud: fluffy. Before embarking into the secret world of clouds “fluffy” was the only method I had of describing clouds that interested me. After learning more about clouds I can now define this cloud as a cumulonimbus cloud. This picture however neither shows the exact top or bottom of the cloud as it was meant to focus on the texture.

I shot this image from the front of my house in Boulder Colorado half a mile East of the campus. I stood on the sidewalk and pointed my camera at a 45° angle into the sky facing almost due East at 6:12 PM when I arrived home after school. This was the first “fluffy cloud” that I had seen in days and I was intent on capturing it. Around this time came light rain and there were winds from the North East (Company, 2019).

The clouds seemed to be moving very fast that day as if in a rush to disappear and bring about exciting weather. By 6:30PM there was 68% cloud coverage in the sky (Inc., n.d.). There was a high of 77° and a low of 55° that day (AccuWeather, 2019). The convective available potential energy or CAPE, which is the amount of instability potentially available to a thunderstorm assuming all other conditions are favorable, of the Skew-T diagram provided below in Figure 1 shows a reading of 2,037 J/kg. CAPE of 1,500 J/kg is large and values above 2,500J/kg imply an extremely large instability. This very unstable atmosphere is supported by a large lifted index of -5.53, values less than -7 represent an extreme instability which allows for high accelerations within updrafts (Haby). From the information in Figure 1 I would estimate that the cloud’s height begins around 2280 meters as that is the closest point between the temperature and dewpoint curve.  Between the ground and the bottom of the cloud the air cools at the dry adiabatic lapse rate, then the air condenses and cools at the saturated adiabatic lapse rate throughout the height of the cloud, at altitudes higher than the top of the cloud the air cools again at the dry adiabatic lapse rate. I believe this Skew-T also shows a subsidence inversion between 750 millibars and 700 millibars. A subsidence inversion is where the air actually warms as it rises before cooling off and can be seen where the temperature line jogs right (Gunnlaugsson, 2019).

Figure 1: Skew-T diagram of September 11th in Denver.

I chose to shoot the image as I did because I wanted to focus on the most textured part of the cloud. I shot at the angle I did to rid the image of the surrounding houses and telephone wires. I shot this image using a Cannon Rebel T6. The shutter speed was 1/320 seconds, the fstop was f/13, the ISO was 100 and the focal length was 43mm. The original picture Figure 2 was augmented in Gimp along the curve shown in Figure 3 to create the final image of Figure 4. The final image brought out the darkness in the middle of the cloud ultimately giving more contrast to the shape. As a result of this editing the sky also changed color. The field of view is slightly balanced as in the bottom of the picture you can see the tops of trees. This is meant to indicate the angle at which the picture was shot and help give the picture some perspective. The image is 5184 pixels wide and 3456 pixels tall.

Figure 2: Original Image.

Figure 3: Adjustment curve used to edit original image.

Figure 4:  Final image.

I really like the enhanced color in the picture, I believe it brings out a royalty to the image. I additionally really enjoy how the enhanced texture came out. I wish however that I had not shot the image so that the bottom and top of the cloud were not in the frame. I do believe I fulfilled my intent. I would like to get more detail in the shape of the cloud next time.  I think the Skew-T definitively supports that this is a cumulonimbus cloud very well.

Bibliography

AccuWeather. (2019). AccuWeather. Retrieved from https://www.accuweather.com/en/us/boulder/80302/september-weather/327347?year=2019

Company, T. W. (2019). Retrieved from Weather Underground : https://www.wunderground.com/history/daily/us/co/boulder/KFNL/date/2019-9-11

Gunnlaugsson, T. (2019, 5 19). How to Read a Skew-T Chart -for Soaring Pilots.

Haby, J. (n.d.). Instability . Retrieved from The Weather Prediction: http://www.theweatherprediction.com/severe/ingredients/instability/

Inc., C. L. (n.d.). Average Weather on September 11 in Boulder Colorado . Retrieved from WeatherSpark: https://weatherspark.com/d/3561/9/11/Average-Weather-on-September-11-in-Boulder-Colorado-United-States#Sections-Temperature

Julie. (2018, 4 26). Introductio to the Skew-T Log P Diagram. (N. W.-B. Office, Compiler) Billings, United States. Retrieved from https://www.youtube.com/watch?v=zz60yFkwCrc