Sciences and Exploration Directorate

Allison Collow


Allison Collow's Contact Card & Information.
Phone: 301.614.6653
Org Code: 610.1
Mail Code 610.1
Greenbelt, MD 20771

Current Projects

Evaluation of Aerosols, Near Surface Temperature, Precipitation, and Radiation in GMAO Products

Earth's Atmosphere

As GEOS continues to evolve, it is important to ensure that the model represents the Earth system in an appropriate manner. Whether due to prescribed boundary conditions, the assimilation of new observations, or physical parameterizations, Dr. Collow works to determine why biases in aerosols, near surface temperature, precipitation, or radiative fluxes may be present in GEOS and reducing these issues in future versions of the model.

Understanding Model Biases to Diagnose the Role of Biomass Burning Aerosol in the Southeast Atlantic


Marine stratocumulus and trade wind cumulus are prominent cloud types over the Atlantic Ocean with regional and global impacts on the energy budget, that can be further complicated by the presence of biomass burning aerosol (BBA). The largest radiative impact due to brown carbon has been shown to occur over the southeast Atlantic Ocean, and BBA has been shown to alter the transition from marine stratocumulus to trade cumulus in large eddy simulations. Despite the importance of the interplay between marine stratocumulus and BBA on the global energy budget, general circulation models (GCMs), including NASA’s Goddard Earth Observing System (GEOS), struggle to accurately simulate properties of both the aerosol and clouds, with considerable variability in the radiative effect of BBA in GCMs. GCMs, including GEOS and MERRA-2, allow for the BBA plume to descend too rapidly as the aerosol is transported across the Atlantic Ocean, a critical factor given that aerosols will interact with radiation differently depending on whether they are located above or within clouds. This has implications on the formation and development of clouds and the transition from marine stratocumulus to trade cumulus, and therefore energy budget within the region. Additionally, GCMs fail to accurately represent low level clouds, such as marine stratocumulus in subsidence regions. Uncertainties remain regarding what physical and dynamical processes are responsible for these model biases. The NASA Earth Venture suborbital mission Observations of Aerosols above Clouds and their interactions (ORACLES) provided a unique opportunity to sample characteristics of clouds, aerosol, and their environment in the southeast Atlantic over the course of three consecutive biomass burning seasons in coordination with a multi-organizational, international effort to address uncertainties associated with aerosols above clouds in the southeast Atlantic. Unlike other field campaigns focused on marine stratocumulus, the troposphere in the southeast Atlantic is not pristine, and instead polluted with smoke and BBA. Through a combination of observations collected as part of the ORACLES field campaign, NASA satellite observations, and modeling using GEOS, research completed through the proposed work will address the science question, “What processes are causing the BBA plume to descend too rapidly over the southeast Atlantic in models such as GEOS?”.

A Reanalysis Synthesis of EOS observations for the National Climate Assessment


Reanalyses such as MERRA-2 contain valuable information that can be used to evaluate the climate across the United States, how it has changed over the past 40 years, and the processes that result in extreme weather events that can be disseminated to the general public and decision makers. As part of this project, Dr. Collow's primary focus is to use the renanalysis products developed by the GMAO to determine the large scale influences that result in regional extreme precipitation events. Dr. Collow also contributes towards ensuring this information is placed in a format that is easily understood by the public by calculating indices to represent characteristics of temperature and precipitation and placing output from MERRA-2 on GMAO's FLUID webpage.


M.S. (2012): Rutgers University
Ph.D. (2015): Rutgers University

Selected Publications


2024. "Benchmarking GOCART-2G in the Goddard Earth Observing System (GEOS)." Geoscientific Model Development 17 (3): 1443-1468 [10.5194/gmd-17-1443-2024] [Journal Article/Letter]

2022. "An evaluation of biomass burning aerosol mass, extinction, and size distribution in GEOS using observations from CAMP2Ex." Atmospheric Chemistry and Physics 22 (24): 16091-16109 [10.5194/acp-22-16091-2022] [Journal Article/Letter]

2022. "An Overview of ARTMIP's Tier 2 Reanalysis Intercomparison: Uncertainty in the Detection of Atmospheric Rivers and Their Associated Precipitation." Journal of Geophysical Research: Atmospheres 127 (8): e2021JD036155 [10.1029/2021jd036155] [Journal Article/Letter]

2022. "Seasonal variability in the mechanisms behind the 2020 Siberian heatwaves." Journal of Climate 35 (10): 3075-3090 [] [Journal Article/Letter]

2020. "Radiative heating rate profiles over the southeast Atlantic Ocean during the 2016 and 2017 biomass burning seasons." Atmospheric Chemistry and Physics 20 (16): 10073-10090 [10.5194/acp-20-10073-2020] [Journal Article/Letter]

2020. "Large-Scale Influences on Atmospheric River Induced Extreme Precipitation Events Along the Coast of Washington State." Journal of Hydrometeorology [10.1175/jhm-d-19-0272.1] [Journal Article/Letter]

2020. "Recent Arctic Ocean Surface Air Temperatures in Atmospheric Reanalyses and Numerical Simulations." Journal of Climate 33 (10): 4347–4367 [10.1175/jcli-d-19-0703.1] [Journal Article/Letter]

2016. "Large Scale Influences on Summertime Extreme Precipitation in the Northeastern United States." Journal of Hydrometeorology JHM-D-16-0091.1 [10.1175/jhm-d-16-0091.1] [Journal Article/Letter]

2016. "The Seasonal Cycle of the Radiation Budget and Cloud Radiative Effect in the Amazon Rainforest of Brazil." J. Climate JCLI-D-16-0089.1 [10.1175/jcli-d-16-0089.1] [Journal Article/Letter]

2016. "Cloudiness over the Amazon Rainforest: Meteorology and Thermodynamics." J. Geophys. Res. Atmos. [10.1002/2016jd024848] [Journal Article/Letter]

2015. "A one-year study of the diurnal cycle of meteorology, clouds and radiation in the West African Sahel region." Quarterly Journal of the Royal Meteorological Society 142 (694): 16-29 [10.1002/qj.2623] [Journal Article/Letter]


2017. "An Evaluation of Teleconnections Over the United States in an Ensemble of AMIP Simulations with the MERRA-2 Configuration of the GEOS Atmospheric Model." NASA Technical Report Series on Global Modeling and Data Assimilation, NASA/TM-2016-104606 47 68 [Report]