Defenses for Spring 2026

From Megacities to Wildfire Smoke: Observational Constraints on Atmospheric Ammonia

March 25, 2026

Emily Lill

Urban ammonia (NH3) emissions are an increasingly important component of atmospheric nitrogen cycling and fine particulate matter (PM2.5) formation, yet they remain poorly constrained in both observations and models. While agricultural sources have historically dominated NH3 budgets, emerging evidence suggests that mobile sources and urban activities may play a larger role than currently…

Systematic Relationships Between Overshooting Top Characteristics and Anvil Life Cycle Observed with Geostationary Satellites

March 23, 2026

Rachael Auth

Deep convective storms with strong updrafts generate robust anvils and distinct cloud top structures. These structures, including overshooting tops (OTs) and above-anvil cirrus plumes (AACP), can be routinely identified atop the most powerful storms on the planet, and are often indicative of severe weather, including tornadoes and large hail. The overarching goal of this study is to assess how…

Revisiting the Importance of a Southern Ocean Pattern Effect

February 25, 2026

Killian McSweeney

The spatial pattern of surface warming determines radiative feedbacks (“pattern effect”). The seminal work of Senior & Mitchell (2000) (SM00) argued that Southern Ocean clouds set the evolution of global radiative feedbacks in time and hence, determine climate sensitivity. We revisit their argument in current generation climate models: We quantify the time evolution of local atmospheric…

Contextualizing Past and Future Mean Southwest U.S. Precipitation with Marine Heatwaves

February 04, 2026

Olivia Lee

As the Southwest U.S. (SWUS) grapples with continued drought and increased water scarcity, paleoclimate analyses suggest the SWUS was wetter during past warm climates such as the Pliocene. One hypothesis for a wetter SWUS in the Pliocene is that warmer eastern Pacific sea surface temperature (SST) during the Pliocene enhanced North American Monsoon precipitation. Similarly, warmer California…