Allison Collow

Understanding extreme events that have societal impacts

Extreme events like heat waves, flooding, and poor air quality can have profound impacts on society. It is important to understand why these events occur and evaluate their representation in models. This illuminates focus areas for what should be improved in numerical predication models to enable more accurate forecasts for better prepardness.

Atmospheric Rivers

Atmospheric rivers, or the transport of narrow filaments of enhanced water vapor, have been connected to some of the most extreme precipitation events in regions like the west coast of the United States. While precipitation can be difficult to forecast, atmospheric rivers can be more robust in long term forecasts and be indicative that there is potential for an extreme precipitation event. In large data sets, tracking methods can be used to detect the presence of an atmospheric river however results can differ depending on the tracking method used. It is therefore important to understand what type of tracking method should be used depending on the application and how the results may be impacted. Studies can then be conducted with the appropriate methodology to determine why atmospheric rivers result in extreme events.

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

Aerosols

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?”.

Applications and Impacts of Extreme Events Using NASA GMAO Products

Weather

Reanalyses such as MERRA-2 contain valuable information that can be used to evaluate and understand 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.