Hydrodynamic attractors in heavy ion collisions: a review

A review of the recent progress of relativistic hydrodynamic attractors is presented, with a focus on applications in heavy ion collisions and the quark gluon plasma. Pedagogical introductions to the effective descriptions relevant for attractors in high energy physics, namely hydrodynamics, holography and kinetic theory, are followed by highlights of some recent advances.Comment: 46 pages, 8 figures. Invited review article for EPJ C special issue "Frontiers in Holographic Duality." v2: added a discussion on non-conformal systems and an appendix of useful abbreviations, references updated, typos corrected. Version accepted for publicatio

On the Vertical Structure of the Thin Surface Layer of the Ocean During a Weak Wind

The regularities of the near-surface quasihomogeneous layer (NQL) formation during the daytime have been studied. The experiments were carried out on the 18th cruise of the R/V Akademik Vernadskiy (JASIN-78 international program) with an upward-floating sonde. According to the experimental data, the thickness of the NQL in the midday hours under stable meteorological and radiation conditions practically does not change compared with the morning and evening. The possibility of describing the NQL by means of an integral model taking into account the volume absorption of solar radiation was considered. A comparison of the experimental and theoretical values of the mixed layer depth has been carried out according to the data of measurements in four different regions of the Atlantic Ocean

Dissipation of Turbulent Energy in the Wind-Generated Wave Layer of the Ocean

The vertical distribution of the turbulent energy dissipation rate in the wind-generated wave layer of the ocean is investigated. The experiments were carried out on the 36th cruise of the R/V Akademik Kurchatov near the surface of the Atlantic Ocean using an ascending turbulimeter probe. The free ascent speed of the probe was 2.2 m/sec. Spectral analysis of the velocity fluctuation recordings showed the presence of a region corresponding to the spectrum for local-isotropic turbulence. The vertical distribution of the turbulent energy dissipation rate calculated from experimental data exhibited a sharp increase in the upper two-meter layer of the ocean. It is shown that it is possible to describe the vertical distribution of the turbulent energy dissipation rate in the wind-generated wave layer of the ocean using the model of A. Yu. Benilov

Sharp Frontal Interfaces in the Near-Surface Layer of the Ocean in the Western Equatorial Pacific Warm Pool

During the TOGA COARE rich horizontal temperature and salinity variability of the near-surface layer of the ocean in the western Pacific warm pool was observed. High-resolution measurements were made by probes mounted on the bow of the vessel in an undisturbed region at ~1.7-m depth during four COARE cruises of the R/V Moana Wave. The authors observed several tens of cases of periodic sharp frontal interfaces of width 1– 100 m and separation 0.2–60 km. The sharp frontal interfaces were often found in frontal regions and on the periphery of freshwater puddles. Maneuvers of the ship were conducted to determine the spatial orientation of a sharp frontal interface. The interfaces revealed anisotropy with respect to the wind direction. They were most sharp when the wind stress had a component along the buoyant spreading of the front. A possible origin of the sharp frontal interfaces is discussed. These interfaces may develop by nonlinear evolution of long-wave disturbances on the near-surface pycnocline that is often observed in the warm pool area. A shallow-water model may describe some features of the observations. A dimensionless number of the Reynolds type is a criterion of transition from wave train solution to dissipative shock-wave structure. The model predicts spatial anisotropy depending on the relative angle between the wind stress and horizontal density gradient

Time evolution of a toy semiholographic glasma

We extend our previous study of a toy model for coupling classical Yang-Mills equations for describing overoccupied gluons at the saturation scale with a strongly coupled infrared sector modeled by AdS/CFT. Including propagating modes in the bulk we find that the Yang-Mills sector loses its initial energy to a growing black hole in the gravity dual such that there is a conserved energy-momentum tensor for the total system while entropy grows monotonically. This involves a numerical AdS simulation with a backreacted boundary source far from equilibrium.Comment: 17 pages, 7 figures, v2: minor changes in section 3 and acknowledgement

Observation of Wave-Enhanced Turbulence in the Near-Surface Layer of the Ocean During TOGA COARE

Dissipation rate statistics in the near-surface layer of the ocean were obtained during the month-long COARE Enhanced Monitoring cruise with a microstructure sensor system mounted on the bow of the research vessel. The vibration contamination was cancelled with the Wiener filter. The experimental technique provides an effective separation between surface waves and turbulence, using the difference in spatial scales of the energy-containing surface waves and small-scale turbulence. The data are interpreted in the coordinate system fixed to the ocean surface. Under moderate and high wind-speed conditions, we observed the average dissipation rate of the turbulent kinetic energy in the upper few meters of the ocean to be 3–20 times larger than the logarithmic layer prediction. The Craig and Banner (J. Phys. Oceanogr. 24 (1994) 2546) model of wave-enhanced turbulence with the surface roughness length from the water side z0 parameterized according to the Terray et al. (J. Phys. Oceanogr. 26 (1996) 792) formula z0=cHs provides a reasonable fit to the experimental dissipation profile, where z is the depth (defined here as the distance to the ocean surface), c≈0.6, and Hs is the significant wave height. In the wave-stirred layer, however, the average dissipation profile deviates from the model (supposedly because of extensive removing of the bubble-disturbed areas close to the ocean surface). Though the scatter of individual experimental dissipation rates (10-min averages) is significant, their statistics are consistent with the Kolmogorov\u27s concept of intermittent turbulence and with previous studies of turbulence in the upper ocean mixed layer

Observation of Large Diurnal Warming Events in the Near-Surface Layer of the Western Equatorial Pacific Warm Pool

Because of the relatively calm winds which prevail over the western Pacific warm pool, the diurnal cycle of temperature in the near-surface layer of the ocean is often quite pronounced. During the TOGA Coupled Ocean-Atmosphere Response Experiment (COARE), very high resolution measurements of near-surface thermohaline and turbulence structures were made using bowmounted probes and a free-rising profiler. Experimental data demonstrate a strong dependence of near-surface thermal structure on weather conditions, In calm weather, SST was observed to exceed 33.25°C; this was associated with a diurnal warming of more than 3°C in the top I m of the ocean. A 1-D model of transilient type reproduces the diurnal cycle at low wind speeds and the evening deepening of the diurnal thermocline. Precipitation influenced the diurnal cycle by trapping heat in the near-surface region. During daytime evaporation, surface salinity increased slightly, but deep convection was inhibited by the strong vertical temperature gradient. Contour plots calculated using observations from bow sensors “scanning” the upper meters of the ocean due to ship\u27s pitching in some cases revealed strong horizontal variability of the shallow diurnal thermocline with amplitude ∼ 2°C on scales of 0.2–6 km