CO₂ Surface Variability, from the Stratosphere or Not?

Fluctuations in atmospheric CO2 can be measured with great precision and are used to identify human-driven sources as well as natural cycles of ocean and land carbon. One source of variability is the stratosphere, where the influx of aged CO2-depleted air can produce fluctuations at the surface. This process has been speculated a potential source of interannual variability (IAV) in CO2 that might obscure the quantification of other sources of IAV. Given the recent success in demonstrating that the stratospheric influx of N2O- and chlorofluorocarbon-depleted air is a dominant source of their surface IAV in the southern hemisphere, we here apply the same model and measurement analysis to CO2. Using chemistry-transport modeling or scaling of the observed N2O variability, we find that the stratosphere-driven surface variability in CO2 is at most 10 % of the observed IAV and is not an important source. The southern hemisphere stations with multi-decadal CO2 records can provide clues to sources through the phase shifts of the IAV relative to the northern hemisphere.

From the middle stratosphere to the surface, using nitrous oxide to constrain the stratosphere-troposphere exchange of ozone

Stratosphere-troposphere exchange (STE) is an important source of tropospheric ozone, affecting all of atmospheric chemistry, climate, and air quality. Observations and the theory of tracer correlations provide only coarse (±20 %) global-mean constraints. For fluxes resolved by latitude and month we rely on global chemistry-transport models (CTMs), and unfortunately, these results diverge greatly. Overall, we lack guidance from model-measurement metrics that inform us about processes and patterns related to the STE flux of ozone. In this work, we use modeled tracers (N2O, CFCl3) whose distributions and budgets can be constrained by satellite and surface observations, allowing us to follow stratospheric signals across the tropopause. The satellite derived photochemical loss of N2O on annual and quasi-biennial cycles can be matched by the models. The STE flux of N2O-depleted air in our CTM drives surface variability that closely matches observed fluctuations on both annual and quasi-biennial cycles, confirming the modeled flux. The observed tracer correlations between N2O and O3 in the lowermost stratosphere provide a seasonal, hemispheric scaling of the N2O flux to that of O3. For N2O and CFCl3, we model greater southern hemispheric STE fluxes, a result supported by some metrics, but counter to prevailing theory of wave-driven stratospheric circulation. The STE flux of O3, however, is predominantly northern hemispheric, but observational constraints show that this is only caused by the Antarctic ozone hole. Here we show that metrics founded on observations can better constrain the STE O3 flux which will help guide future model assessments.

Basin-Scale and Near-Surface Circulation in the Gulf of Mexico

In the aftermath of the Deepwater Horizon event, GoMRI-funded research consortia carried out several field campaigns in the northern Gulf of Mexico with the objectives of understanding physical processes that influence transport of oil in the ocean and evaluating the accuracy of current-generation ocean models. A variety of new instruments were created to achieve unprecedented levels of dense and overlapping datasets that span five orders of magnitude of spatial and temporal scales. The observational programs: GLAD (DeSoto Canyon, Summer 2012), SCOPE (Destin inner shelf, Winter 2013 14), LASER (DeSoto Canyon, Winter 2016) and SPLASH (Louisiana shelf, Spring 2017) were designed to capture transport by ocean currents that are not presently well resolved by operational models. The overarching objective of these experiments was to collect data from a variety of sensors (drifting, aerial and ship-board) to document the circulation and near-surface variability of fronts, where much of the surface oil tends to be concentrated. Two state-of-the-art models were also run in real-time during all the experiments; a multiply-nested Navy Coastal Ocean Model with horizontal resolutions ranging from 1 km in the outer nest down to 100 m, as well as a fully coupled atmosphere-wave-ocean model. The purpose of this submission is to summarize the advances made in both understanding and modeling the near-surface transport in the Gulf of Mexico.

Lagrangian dynamics in the Gulf of Trieste from high resolution HF-Radar

<p>The Gulf of Trieste (GoT) is shared by Italy, Slovenia and Croatia, with most of its coasts belonging to Italy and Slovenia, along with the two main harbours; the Harbour of Trieste (Italy) and Koper (Slovenia). Both are subject to heavy marine traffic and exposed to different threats including oil spills, maritime accidents and SAR operations. The GOT High frequency radar network provides near-real time data of sea surface currents and waves since 2016. In this work we provide a statistical description of surface variability in terms of Lagrangian descriptors in order to elucidate the transport and retention in the GoT as well as to provide the seasonal evolution of the residence time. Among the most widely used Lagrangian techniques, we focus the study on Lagrangian Coherent Structures and Path-integrated topological variables like Lagrangian divergence and Lagrangian vorticity. </p>