As the abyssal oceans warm, stratification is also expected to change in response. This change may impact mixing and vertical transport by altering the buoyancy flux, internal wave generation, and turbulent dissipation. In this study, repeated surveys of three hydrographic sections in the Southwest Pacific Basin between the 1990s and 2010s are used to estimate the change in buoyancy frequency
According to recent field studies, almost half of the New Particle Formation (NPF) events occur aloft, in a residual layer, near the top of the boundary layer. Therefore, measurements of the meteorological parameters, precursor gas concentrations, and aerosol loadings conducted at the ground level are often not representative of the conditions where the NPFs take place. This paper presents new measurements obtained during the Turbulent Flux Measurements of the Residual Layer Nucleation Particles, conducted at the Southern Great Plains research site. Vertical turbulent fluxes of 3–10 nm‐sized particles were measured using a sonic anemometer and two condensation particle counters with nominal cutoff diameters of
- PAR ID:
- 10372215
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 127
- Issue:
- 17
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract . We find that below the °C isotherm, is on average reduced by a scaling factor of , a 12% reduction, per decade that intensifies with depth. At °C, we observe the biggest change: , or a 29% reduction per decade. Within the same period, the magnitude of vertical diffusive heat flux is also reduced by about , although this estimate is sensitive to the choice of estimated diffusivity. Finally, implications of these results for the heat budget and global ocean circulation are qualitatively discussed. -
Abstract Temperature and salinity measurements of a warm‐core eddy at the northern flank of the Ross Gyre are analyzed for dominant mixing mechanisms. The eddy is centered at the depths of the Circumpolar Deep Water and carries heat towards the gyre. Vertical and horizontal heat fluxes out of the eddy associated with internal wave turbulent mixing and thermohaline intrusions are estimated. Upward internal wave turbulent heat flux is
W , whereas, the lateral intrusive heat flux is of the order of W . The horizontal flux due to intrusions is suggested to be the dominant mechanism for eddy decay and yields an eddy lifetime of about 6 months. The thermohaline intrusion‐eddy suppression mechanism is proposed and shown to be effective in suppressing the eddy field at the northern flank of the Ross Gyre. This effect has important implications for setting the basin‐wide heat budget and regulating sea‐ice cover. -
Abstract In this study, we report on turbulent mixing observed during the annual stratification cycle in the hypolimnetic waters of Lake Michigan (USA), highlighting stratified, convective, and transitional mixing periods. Measurements were collected using a combination of moored instruments and microstructure profiles. Observations during the stratified summer showed a shallow, wind‐driven surface mixed layer (SML) with locally elevated dissipation rates in the thermocline (
) potentially associated with internal wave shear. Below the thermocline, turbulence was weak ( ) and buoyancy‐suppressed ( < 8.5), with low hypolimnetic mixing rates ( ) limiting benthic particle delivery. During the convective winter period, a diurnal cycle of radiative convection was observed over each day of measurement, where temperature overturns were directly correlated with elevated turbulence levels throughout the water column ( ; ). A transitional mixing period was observed for spring conditions when surface temperatures were near the temperature of maximum density ( T MD3.98 ) and the water column began to stably stratify. While small temperature gradients allowed strong mixing over the transitional period ( ), hypolimnetic velocity shear was overwhelmed by weakly stable stratification ( ; ), limiting the development of the SML. These results highlight the importance of radiative convection for breaking down weak hypolimnetic stratification and driving energetic, full water column mixing during a substantial portion of the year (>100 days at our sample site). Ongoing surface water warming in the Laurentian Great Lakes is significantly reducing the annual impact of convective mixing, with important consequences for nutrient cycling, primary production, and benthic‐pelagic coupling. -
Abstract Experimental evidence shows that temperature‐humidity (
) similarity in the atmospheric surface layer (ASL) is reduced as Bowen ratio ( ) increases over land. However, underlying physical mechanisms remain not well understood. With large‐eddy simulations, dissimilarity is investigated in the steady‐state, convective boundary layer (CBL) over homogeneous landscape with varying . As increases from 0.4 to 2.0, the entrainment ratio for slightly decreases but that for q largely increases. As a result, local production of humidity variance is substantially enhanced in the upper CBL and transported to the lower CBL by vigorous large eddies, contributing significantly to nonlocal fraction. However, the increased temperature variance in the ASL associated with strong heat flux is larger than that transported from the upper CBL. Such asymmetry in vertical diffusion induced by varying partitioning of surface fluxes strongly regulatesdissimilarity even under perfect conditions valid for Monin‐Obukhov similarity theory. -
Abstract The physical circulation of the Southern Ocean sets the surface concentration and thus air‐sea exchange of
. However, we have a limited understanding of the three‐dimensional circulation that brings deep carbon‐rich waters to the surface. Here, we introduce and analyze a novel high‐resolution ocean model simulation with active biogeochemistry and online Lagrangian particle tracking. We focus our attention on a subset of particles with high dissolved inorganic carbon (DIC) that originate below 1,000 m and eventually upwell into the near‐surface layer (upper 200 m). We find that 71% of the DIC‐enriched water upwelling across 1,000 m is concentrated near topographic features, which occupy just 33% of the Antarctic Circumpolar Current. Once particles upwell to the near‐surface layer, they exhibit relatively uniform levels and DIC decorrelation timescales, regardless of their origin. Our results show that Southern Ocean bathymetry plays a key role in delivering carbon‐rich waters to the surface.