Since the Industrial Revolution, human-caused (anthropogenic) emissions of greenhouse gases and pollutants, including sulfur, have changed the composition of the Arctic atmosphere. Greenhouse gas emissions and climate feedbacks have resulted in an Arctic amplification, the phenomenon of rapidly warming Arctic temperatures and of sea-ice extent declining at a rate of 7.2% per decade since the 1980s. Other anthropogenic emissions, such as sulfur aerosols, can reflect sunlight and increase cloud cover, temporarily decreasing temperatures. Since the 1980s, clean air policies have reduced the emissions of sulfur aerosols, which have contributed to Arctic amplification. The majority of Arctic sulfate aerosols come from anthropogenic emissions, but natural sources include sea salt, volcanoes, or biological activity. Sea-ice algae produce dimethylsulfide (DMS), which converts to sulfate aerosols through oxidation in the atmosphere. With the decline in sea-ice extent, the habitats of Arctic biota such as algae are diminishing, and it is unclear how declining sea ice will affect biogenic sulfate aerosols and DMS emissions in the future. Here we investigate the relationship between sea-ice extent decline and DMS emissions thorough analysis of an ice core collected in Summit, Greenland to understand the relative contribution of biological activity to Arctic aerosol abundance. To analyze the biogenic sulfate in the ice core, we concentrate ice core meltwater samples, precipitate sulfate in the concentrated sample solution, measure the sulfur isotopes on a stable isotope mass spectrometer, and run GEOS-Chem model simulations to interpret the observed trends. The isotopes of sulfur in sulfate indicate what portion of the atmospheric sulfate aerosols result from biological activity. We hypothesize that biogenic sulfate has decreased with declining sea-ice extent due to the reduction of sea-ice habitats for sea-ice algae. The response of Arctic sulfate aerosol abundance to the decline of sea ice holds implications for the future of Arctic amplification.

 With lightning serving as a threat to life and property, understanding the factors that contribute to its frequency are important. Lightning forms when ice particles within clouds separate into lighter and heavier pieces, which creates charge separation in the cloud. If the updraft (a region of vertically moving air) within the cloud causes the distance between the positively- and negatively-charged regions of cloud to be large enough, an electric current flows to cancel this difference in charge. Convection associated with cold air outbreaks over the Northeast Pacific Ocean can occasionally produce lightning. These cold air outbreaks are extensions of larger synoptic scale systems (i.e. extratropical cyclones) that are powered by strong horizontal temperature gradients, the gradients themselves are defined by fronts. It is in the areas of colder air aloft, behind the cold front, where convection can occur. Unfortunately, limited observations in this region make it difficult for forecast models to accurately predict these electrically-active storms. Lightning data from the World Wide Lightning Location Network (WWLLN) is used during the wintertime months of November–March from 2015–2018 to relate the density of cloud-to-ground lightning strikes to the cold air outbreak events classified by anomalies of height from the climatological mean using the European Center for Medium-Range Weather Forecast (ECMWF) Re-Analysis (ERA5) dataset. This dataset is also used to calculate atmospheric instability in order to quantify the ability of the atmosphere to support convection. Finally, satellite measurements of cloud top height are used to evaluate whether a relationship exists between cloud depth and lightning frequency. Preliminary results suggest an increase in lightning activity as post-frontal convection associated with these cold air outbreaks makes landfall onto the West Coast. The findings from this study will benefit forecasting post-frontal convection over oceanic regions and their effects as the storms move over land.

The Intertropical Convergence Zone (ITCZ) is a low-pressure band near the equator where the Northern and Southern hemisphere trade winds converge, characterized by heavy rainfall. The ITCZ typically moves seasonally, migrating north during the Northern hemisphere summer, and south during the Southern hemisphere summer, but there has also been a clear overall southward shift of the ITCZ since 1850. This project uses data from the latest Coupled Model Intercomparison Project (CMIP6) historical simulations to investigate this southward shift, made clear by changing precipitation patterns across the hemispheres. This shift could be caused by aerosols, which preferentially cooled the Northern hemisphere. It is known that the ITCZ is drawn toward the hemisphere with more heating, so this project explores and breaks down the global energy budget over the historical period simulated in the models (1850-2014) to further understand the causes of this shift.

Clouds, in general, are difficult to account for in climate and numerical weather prediction models. They represent a complex mix of radiative forcings that currently aren’t fully understood or quantifiable. Especially difficult are “mixed-phase” clouds: clouds that exist below the freezing temperature of water but are composed of both ice crystals (water in the solid phase) and supercooled liquid droplets (water in the liquid phase). Hence the name “mixed-phase”. While common, the formation of ice in these clouds remains poorly understood – further observations are vital for obtaining insight into this process. Fortunately, we have new measurements that can provide much-needed insight into their behavior. So far, I have been using measurements from the Department of Energy’s Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) atmospheric observatory on Graciosa Island in the Azores archipelago which is in the northeastern Atlantic Ocean west of Portugal. The observatory is an ideal site for analyzing these clouds for several reasons, but chief among them is its Raman lidar. By measuring a phenomenon called Raman scattering and utilizing algorithms developed by a previous UW graduate student Tyler Thorsen, this instrument can detect different cloud types and aerosol sizes with high confidence up to twenty kilometers into the atmosphere. I’ve been exploring this data using the programming language Python, looking for patterns in these clouds utilizing the ground-based ENA data and verifying my findings with the lidar on the NASA satellite Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The poster will explore how the phase of clouds over the Azores varies with season and with temperature.

Marine heatwaves are the phenomena of abnormally warm ocean surface temperatures that last for an extended period of time. The most severe marine heatwave of recent times occurred from 2013 to 2016 in the Northeastern Pacific. This event, nicknamed ‘The Blob’, was scientifically fascinating because the ocean-atmosphere system maintained itself for so long in an anomalous state. In mid-2019, a marine heatwave with a likeness to ‘The Blob’ began forming. This research project focuses on analyzing the anomalous patterns in sea surface temperature, clouds, radiative fluxes, and turbulent fluxes that arise during the formation and duration of this event. We set out to understand if the more recent 2019 marine heatwave evolves in a similar way to that of ‘The Blob,’ and how it differs. This project uses NOAA Climate Forecast System Reanalysis (CFSR) data, which assimilates measurements using complex models to create the best estimates of atmospheric and oceanic variables with complete global spatial coverage. With this project, we aim to understand the atmospheric response to marine heatwaves using geospatial plots of mean temperature, fluxes, and cloud cover. We expect to see differences in the atmosphere response with regards to the net flux that caused the quick dissipation of the recent marine heatwave.