Isabel McCoy

2012 Research Experience for Undergrads

Examining stratocumulus properties over the Southeast Pacific

It was an honor to be accepted into the JISAO internship program this summer. As a physics student attending the New Mexico Institute of Mining and Technology, I had experienced atmospheric science in a limited way. This REU, I thought, would be the perfect opportunity to broaden my knowledge of the subject. I worked with Dr. Andreas Muhlbauer of JISAO and Dr. Robert Wood of the University of Washington Atmospheric Sciences Department on identifying characteristics of stratocumulus clouds. To do this, I learned a new set of techniques in MATLAB (from reading in NetCDF files to statistically analyzing satellite data) and acquired various atmospheric concepts from scientific articles and from in depth discussions with my mentors. Dr. Muhlbauer and Dr. Wood excelled at mentorship, taking every opportunity to teach me about clouds, satellite data, and any other atmospheric particulars that were applicable. They, even more than the project, have inspired me to pursue my interest in atmospheric science and possibly continue on to graduate school in that subject. JISAO itself cemented this feeling, as it was a marvelous place to experience research for the first time.

In this research project we were interested in learning more about the micro- and macro-physical properties of Stratocumulus (Sc) clouds. Sc, one of the most prevalent low clouds, has a significant impact on the energy budget of our planet, acting as an important cooling source in the atmosphere. One of the heightened areas of occurrence for this type of cloud is over the Southeast Pacific, a region that was sampled over October and November in the year of 2008 by the VOCALS Regional Experiment (REx) and where we focused our efforts. Having the aircraft data from this experiment was a boon to our endeavor, providing an accurate source of data to eventually compare our results to. Another vital contribution was the set of stratocumulus cloud occurrence points provided by Dr. Wood. In 2006 Wood et al.* developed a neural network algorithm categorizing MODIS data (from the Aqua Satellite on NASA’s A-Train) into four stratocumulus cloud cases based on their morphologies: homogeneous stratiform, inhomogeneous disorganized MCC (Mesoscale Cellular Convection, the formation type), closed MCC, and open MCC. I used the resulting data, a set of occurrence locations and times for each of the four cases, as the basis for our novel method of analyzing stratocumulus clouds. First, I filtered the occurrence data (to coincide with the VOCALS REx experiment) and examined the accuracy of the identifications (by over-plotting the points on GOES 10 imagery from the geostationary satellite in the area). I only considered the occurrences closest to the CloudSat overpass (a satellite also on NASA’s A-Train, bearing a Cloud Profiling Radar, CPR), extracting those points with an algorithm of my design. Finally, I segmented out sections of the CloudSat data based on the cloud type occurrence nearest to the data collection site. In this fashion, I could obtain segments of CPR data about each type of stratocumulus cloud, which was subsequently used to develop various cloud statistics.

From the beginning, we had always been more interested in Closed and Open MCC and how they contrasted. Beyond the obvious cloud coverage dissimilarity, we were curious how the precipitation and structure of the clouds differed. To appraise them, I created several plots: Cloud Fraction Altitude Diagrams (describing the frequency of hydrometeors occurring at a certain cloud height), Probability Distribution Functions (a measure of drizzle rates), and Cumulative Distribution Functions (an integrated version of the PDF’s previously discussed). This last was compared to the VOCALS REx aircraft data with satisfactory results. Along with deriving a novel method for analyzing Stratocumulus clouds, we found that in the Southeast Pacific region over the VOCALS period, open MCC cells precipitate more and have a larger range of drizzle rates than closed, while closed MCC cells tend to be slightly taller than open MCC cells (although they appear quite similar). These insights may be important to future climate models, improving the ability to predict changes in planetary albedo due to changes in stratocumulus cloud.

I feel privileged to have been a part of this research, from the data accumulation to the analysis, and am grateful for the guidance of Dr. Muhlbauer and Dr. Wood. Being part of this internship and experiencing the support of my mentors, of Dr. Thomas Ackerman, and of my fellow interns, will be a treasured memory. It goes without saying that having the opportunity to explore Seattle in the summer was exceptional. I would highly recommend this REU, both to students already fixed on an atmospheric/oceanic future and those who are still undecided.

*Wood, R., and Hartmann, D. L., 2006: Spatial variability of liquid water path in marine low cloud: The importance of mesoscale cellular convection. J. Climate, 19, 1748-1764

Video

Poster

Isabel's research poster

Click on poster for full-size image [PDF]