NASA Center for Climate Simulation

As part of NASA’s Women’s History Month celebration, this spotlight shines on NASA Center for Climate Simulation (NCCS) user Allison Collow. We follow Collow’s career from her college and graduate school years at Rutgers University to her recent work researching aerosols and atmospheric rivers with NASA Goddard Space Flight Center’s Global Modeling and Assimilation Office (GMAO) and the University of Maryland, Baltimore County (UMBC).

Allison Collow

Hometown: Marlboro, New Jersey

Career Path: I attended Rutgers University, where I earned a bachelor’s degree in meteorology and a Ph.D. in atmospheric science. My dissertation focused on cloud radiative effect in the Sahel and Amazon using field campaign observations. Following grad school, I started a postdoc with Mike Bosilovich in the GMAO through the Goddard Earth Sciences Technology and Research (GESTAR) cooperative agreement. I have been with the GMAO since.

Current Role: My core role within the GMAO is to evaluate aerosols and their properties in the Goddard Earth Observing System (GEOS) model so that they can be better represented in future versions of GEOS. I also assist with the imagery that is available for the MERRA-2 reanalysis on FLUID [a GMAO visualization and analysis system hosted on the NCCS DataPortal] and the computation of climate extremes statistics in MERRA-2.

[Editor’s note: The initial 40 years (1980–2019) of MERRA-2, run on the NCCS Discover supercomputer, took 21,915 computing hours across four streams using 184 processor cores each and yielded just over 2 petabytes of data. MERRA-2 continues assimilating data daily.]

NCCS support of research: Aside from having the entire MERRA-2 and M2AMIP [MERRA-2 Atmospheric Model Intercomparison Project] datasets at my fingertips, the NCCS has provided the computational resources required for me to run AMIP-style experiments and study the influence of sea ice and land surface forcing on near-surface temperature and on the large-scale atmospheric circulation. The storage and computing time required for an ensemble of 40-year simulations is substantial.

Studying atmospheric rivers: I began studying atmospheric rivers because of their impact on the hydrologic cycle on the West Coast of the United States. The American Meteorological Society defines an atmospheric river as “a long, narrow, and transient corridor of strong horizontal water vapor transport that is typically associated with a low-level jet stream ahead of the cold front of an extratropical cyclone.” I am particularly interested in the contribution of atmospheric rivers to extreme precipitation events. Precipitation is difficult to forecast, however, models can accurately predict atmospheric rivers at longer lead times because they are a large-scale feature of the atmosphere.

More recently, I have been working on the uncertainty in atmospheric rivers based on the usage of various reanalysis products and detection tools through the Atmospheric River Tracking Method Intercomparison Project (ARTMIP). I used an interactive Discover computing node to calculate integrated water vapor transport from hourly MERRA-2 data — all accessible on online disk — then analyzed statistics of detected atmospheric rivers from 12 detection tools and studied the associated precipitation on a GMAO computer.

Due to differences in water vapor climatology, ARTMIP results show that MERRA-2 has a larger annual frequency for the detection of atmospheric rivers than the ERA5 [from the European Centre for Medium-Range Weather Forecasts] and JRA-55 [from the Japan Meteorological Agency] reanalyses, but this is especially true for the most intense atmospheric rivers. By comparison, ERA5 tends towards thinner atmospheric rivers and JRA-55 towards more moderate-strength atmospheric rivers.

Working with the Scientific Visualization Studio (SVS): Working with the SVS was an incredible experience. The whole team is tremendously talented, and Greg Shirah did a fantastic job with the animation. In a Journal of Hydrometeorology paper, I looked at the top 5% extreme precipitation events in coastal Washington State, all of which were related to atmospheric rivers, using MERRA-2. One of the most intense events occurred on December 12, 2010, and this was the case study selected for the animation. The event resulted in widespread flooding and mudslides in western Washington State.

The visualization (see above) shows the lifecycle of this atmospheric river from its formation near Hawaii though its depletion of moisture after reaching the mountainous terrain in the Pacific Northwest United States. The large-scale dynamics of the atmosphere that form the atmospheric river are demonstrated by the winds (arrows) and sea level pressure (whether high [H] or low [L]), while the impact of the atmospheric river is shown by liquid (pink to yellow shading) and frozen (white shading) precipitation and changes in soil moisture (tan to green shading) and snow depth (gray to blue shading).

The scientific visualization team was eager to use new software to create a three-dimensional view. One of my favorite parts of the resulting video is the 360-degree spin around the atmospheric river, where you can see that most of the water vapor (blue shading) is close to the surface and that there is a gradient in the height as the low pressure to the north assists with lifting the moisture and causing precipitation (pink to yellow shading). While this is theoretically known, I have never seen it visualized in this manner before and found it helpful to conceptualize an atmospheric river in the eastern Pacific Ocean.

Current research focus: My current research focuses on biomass burning aerosols, how they are represented in the GEOS model, and the role that these aerosols play in the energy budget, both directly and indirectly, through their influence on clouds.

The southeast Atlantic is home to a prominent deck of marine stratocumulus clouds as well as plumes of biomass burning aerosols from southern Africa. The GEOS model struggles to accurately represent the smoke with respect to the height of the smoke plume within the atmosphere and the optical properties for how smoke interacts with radiation. My goal is to improve both aspects within the model so that we can gain a better understanding of the three-way interaction between smoke, clouds, and radiation.

Inspiration: I am highly self-motivated and am inspired by all the amazing work being done by the GMAO and the rest of the Earth Sciences Division!

Challenges: The recent pandemic has been a challenge as a researcher and the mom of a toddler. It was tough to balance my work to stay competitive in the field while caring for her during long stretches of daycare closures.

Jarrett Cohen, NASA Goddard Space Flight Center
March 23, 2022