Ryan M. Holmes
Stanford University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Ryan M. Holmes.
Journal of Physical Oceanography | 2014
Ryan M. Holmes; Leif N. Thomas; LuAnne Thompson; David Darr
AbstractTropical instability vortices (TIVs) in the equatorial Pacific exhibit energetic horizontal and vertical circulation characterized by regions of high Rossby number and low Richardson number. Their strong anticyclonic vorticity and vertical shear can influence the broader-scale circulation by driving lateral mixing and vertical exchange between the ocean surface and interior. The authors use a set of nested high-resolution simulations of the equatorial Pacific, with a finest grid size of 3 km, to examine the vortex dynamics associated with TIV core water formation. TIV cores are characterized by low values of the Ertel potential vorticity (PV) as the relative vorticity is anticyclonic with magnitude comparable to the local Coriolis parameter. A study of the variation of PV and other scalars along Lagrangian fluid parcel tracks entering the TIVs shows that the low-PV water in their cores is a mix of Equatorial Undercurrent (EUC) water and North Equatorial Counter Current (NECC) water. The EUC water ...
Nature | 2017
C. de Lavergne; Gurvan Madec; Fabien Roquet; Ryan M. Holmes; Trevor J. McDougall
The abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less-dense waters above them. Understanding what controls the strength and structure of these interhemispheric flows—referred to as the abyssal overturning circulation—is key to quantifying the ocean’s ability to store carbon and heat on timescales exceeding a century. Here we show that, north of 32° S, the depth distribution of the seafloor compels dense southern-origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2.5 kilometres. Unless ventilated from the north, the overlying mid-depths (1 to 2.5 kilometres deep) host comparatively weak mean meridional flow. Backed by analysis of historical radiocarbon measurements, the findings imply that the geometry of the Pacific, Indian and Atlantic basins places a major external constraint on the overturning structure.
Journal of Physical Oceanography | 2015
Ryan M. Holmes; Leif N. Thomas
AbstractSmall-scale turbulent mixing in the upper Equatorial Undercurrent (EUC) of the eastern Pacific cold tongue is a critical component of the SST budget that drives variations in SST on a range of time scales. Recent observations have shown that turbulent mixing within the EUC is modulated by tropical instability waves (TIWs). A regional ocean model is used to investigate the mechanisms through which large-scale TIW circulation modulates the small-scale shear, stratification, and shear-driven turbulence in the EUC. Eulerian analyses of time series taken from both the model and the Tropical Atmosphere Ocean (TAO) array suggest that increases in the zonal shear of the EUC drive increased mixing on the leading edge of the TIW warm phase. A Lagrangian vorticity analysis attributes this increased zonal shear to horizontal vortex stretching driven by the strain in the TIW horizontal velocity field acting on the existing EUC shear. To investigate the impact of horizontal vortex stretching on the turbulent he...
Geophysical Research Letters | 2016
Ryan M. Holmes; James N. Moum; Leif N. Thomas
Little is known about mixing in the abyssal equatorial oceans in spite of its inferred importance for upwelling dense water. Here we present full-depth microstructure turbulence profiles obtained in the equatorial Pacific that show evidence for intense wind-generated abyssal mixing. Mixing was intensified over the bottom 700xa0m where the diffusivity reached 10−3xa0m2xa0s−1, of similar intensity to mixing driven by tidal flow over rough topography. However, here the mixing was found over smooth topography. We suggest that the intense mixing could have been driven by surface-generated equatorial waves through two possible mechanisms: (1) near-bottom wave trapping as a result of the horizontal component of the Earths rotation and (2) inertial instability. The generation of lee waves over smooth topography at low latitudes and their subsequent breaking is another viable mechanism for the mixing.
Journal of Physical Oceanography | 2016
Ryan M. Holmes; Leif N. Thomas
AbstractTropical instability waves (TIWs) and equatorial Kelvin waves are dominant sources of intraseasonal variability in the equatorial Pacific Ocean, and both play important roles in the heat and momentum budgets of the large-scale flow. While individually they have been well studied, little is known about how these two features interact, although satellite observations suggest that TIW propagation speed and amplitude are modulated by Kelvin waves. Here, the influence of Kelvin waves on TIW kinetic energy (TIWKE) is examined using an ensemble set of 1/4° ocean model simulations of the equatorial Pacific Ocean. The results suggest that TIWKE can be significantly modified by 60-day Kelvin waves. To leading order, TIWs derive kinetic energy from the meridional shear and available potential energy of the background zonal currents, while losing TIWKE to friction and the radiation of waves. The passage of Kelvin waves disrupts this balance. Downwelling (upwelling) Kelvin waves induce decay (growth) in TIWKE ...
Journal of Physical Oceanography | 2018
Sally J. Warner; Ryan M. Holmes; Elizabeth H. McHugh Hawkins; Martı́n S. Hoecker-Martı́nez; Anna C. Savage; James N. Moum
AbstractTwo extremely sharp fronts with changes in sea surface temperature >0.4°C over lateral distances of ~1 m were observed in the equatorial Pacific at 0°, 140°W and at 0.75°N, 110°W. In both c...
Climate Dynamics | 2018
Ryan M. Holmes; Shayne McGregor; Agus Santoso; Matthew H. England
Tropical instability waves (TIWs) are a major source of internally-generated oceanic variability in the equatorial Pacific Ocean. These non-linear phenomena play an important role in the sea surface temperature (SST) budget in a region critical for low-frequency modes of variability such as the El Niño–Southern Oscillation (ENSO). However, the direct contribution of TIW-driven stochastic variability to ENSO has received little attention. Here, we investigate the influence of TIWs on ENSO using a
EPL | 2011
Ryan M. Holmes; David M. Williams
Nature Climate Change | 2017
Paul Spence; Ryan M. Holmes; Andrew McC. Hogg; Stephen M. Griffies; Kial D. Stewart; Matthew H. England
1/4^circ
Macromolecules | 2011
Ryan M. Holmes; David M. Williams