Variability in the angular momentum of the atmosphere, related to wind and mass, mirror climate and weather fluctuations. Important signals derive from the strength of the subtropical upper-level jets. Notable variability occurs on diurnal, subseasonal, annual, semiannual, interannual, and decadal/interdecadal scales, including from the quasi-biennial oscillation and the El Niño Southern Oscillation. Torques against the surface transfer angular momentum by pressure against mountains or by frictional action, related to changes in Earth's rotation, namely length of the day changes pole motion. Observations and models provide evidence for secular increases in angular momentum in both the recent and upcoming centuries.
Coastal wetlands are vegetated landforms that offer a multitude of ecosystem services to society. The vulnerability of these ecosystems to relative sea-level rise (RSLR) is connected to the amount of suspended sediment available in the adjacent water bodies. Sediment is transported by numerous processes onto the wetland surface, where it can contribute to vertical accretion and counteract RSLR. Here, we used maps of total suspended solids (TSS) concentration from the NASA Airborne Visible InfraRed Imaging Spectrometer Next Generation (AVIRIS-NG), numerical modeling, aerial imagery, and field observations to infer the mechanisms controlling wetland dynamics within western Terrebonne Bay, a sinking lagoon in the Mississippi River Deltaic Plain. Specifically, we aimed to understand how wetlands respond when land sinks, using western Terrebonne Bay as a test case. This study revealed that subsidence can augment suspended sediment in the water column by increasing tidal prism and triggering channel erosion. Sediment resuspension can support accretion in the remaining wetland platforms, ultimately affecting their elevation. Understanding these feedback mechanisms has direct implications for forecasting and managing the impacts of RSLR on wetlands in lagoons and river deltas.
Disruptions in the stratospheric polar vortex (SPV) are often associated with extreme winter weather. Assessing the state of the vortex is typically achieved using a combination of zonal winds at 10 hPa averaged around the 60° N latitude circle, geopotential height anomalies (GPHAs) at various pressure levels, and/or stratospheric temperatures. Stratospheric height anomalies at a particular level are caused by temperature variations in the entire atmospheric column below it, meaning observed SPV patterns may, in fact, be dominated by tropospheric rather than stratospheric variability. Here we propose and demonstrate an additional metric that largely excludes tropospheric influences to help assess SPV behavior. We analyze anomalies in fields of 50–10 hPa layer thickness rather than geopotential heights and employ objective pattern clustering to identify representative anomaly configurations and disruptions, assess changes in pattern frequency, identify “stretched vortex” configurations, and relate patterns to other atmospheric variables. We find an increasing frequency of anomalously low-thickness (cold) SPV patterns, which is consistent with increasing greenhouse gas concentrations but inconsistent with results based on GPHAs. According to our metric, stretched SPV configurations exist on 39
The sea level seasonal cycle provides a useful benchmark for evaluating ocean general circulation models (OGCMs). We leverage this observational signal to assess OGCM errors in sea surface height (SSH) variability across the global ocean. Specifically, we analyze two OGCM simulations at 1° (∼100km) and 0.1° (∼10km) resolution, and compare them with observational estimates from two gridded satellite products over 1993-2018. Both simulations exhibit systematic errors, including an underestimation of seasonal variability in the tropics and misrepresentation of variability in eddy-rich regions and along continental shelves. Increasing horizontal resolution improves agreement with observations in many coastal and marginal sea regions by better resolving bathymetry, coastline geometry, and regional dynamics. However, substantial misfits persist at low latitudes, where seasonal SSH variability is primarily wind driven. Our results indicate that two main factors contribute to the spatial structure of errors in the seasonal cycle of SSH in OGCMs: small-scale, highly resolution-dependent processes in coastal and shelf regions, and large-scale wind-stress biases in the tropics. Improving OGCM fidelity across scales therefore requires concurrent advances in both ocean model resolution and wind-stress accuracy.
