An Etymological Dictionary of Astronomy and Astrophysics
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Random fluctuations of the atmosphere caused by the constant injection of energy into the atmosphere from solar and local sources, changing the temperature and pressure of the air where it is absorbed and leading to fluid instabilities. The development over time of the instabilities gives rise to fluctuations in the density of air, and therefore the → refractive index of the atmosphere. → turbulence; → seeing.

→ atmospheric; → turbulence.

A regime of → turbulence characterized by a high → Reynolds number, showing many general aspects that are common to different flows (statistical symmetries, persistent dissipation, energy cascade, → intermittency). Despite those universal features, the understanding of developed turbulence remains as one of the greatest unsolved conceptual problems, on the borderline between mathematics and physics, with numerous ramifications from astrophysics through meteorology to engineering.

Developed, p.p. of → develop; → turbulence.

The interplay between supersonic turbulence and self-gravity in star forming gas.

Gravo-, from grav-, from → gravity + epenthetic vowel -o- + → turbulence.

→ Turbulence in which spatial derivatives of all mean turbulent quantities are negligible.

→ homogeneous, → turbulence.

The broadening of a star's → spectral lines due to → Doppler shifts from motions of different parts of the star's atmosphere.

→ macro; → turbulence.

The → turbulence phenomenon involving relatively smaller physical volumes compared to → macroturbulence. In stellar atmospheres, it is a bulk gas motion with a characteristic size less than the local photon → mean free path. Microturbulence is one of the most significant mechanisms that can cause → line broadening in the stellar spectrum. The presence of microturbulence de-saturates strong lines and increases their → equivalent widths. Microturbulence in → hot stars brings about gas motions with velocities 0-20 km s^-1. A physical connection may exist between microturbulence in hot star atmospheres and a subsurface → iron convection zone. Microturbulence may also be at the origin of → wind clumping in hot stars.

→ micro-; → turbulence.

A → turbulence that is not continuous in space, but is separated by regions of stability and → laminar flow.

Patchy adj. of → patch; → turbulence.

A type of → turbulence with motions more vigorous in the horizontal than in the vertical direction occurring in internal radiation zone of → rotating stars. Same as → shear turbulence.

→ rotation; → induced; → turbulence.

A type of → instability occurring within a → fluid as a result of the → shear caused by → differential rotation. The condition for shear instability is expressed by the → Richardson criterion. Shear turbulence is likely the most efficient → mixing process in stellar → radiative zones.

→ shear; → turbulence.

A state of hydrodynamic → flow in which the velocity at each point fluctuates rapidly and randomly so that only statistical properties can be recognized and subjected to analysis. Turbulence is the most striking manifestation of the non-linear nature of the laws of hydrodynamics, with the irregularity of flows increasing with the → Reynolds number measuring the strength of non-linear effects. The regime of intermediate Reynolds numbers corresponds to a highly non-universal regime of the onset of turbulence, whereas high Reynolds numbers, common in practical situations, characterize the regime of → developed turbulence. → laminar flow; → chaos.

From L. turbulentia, from turbulentus "full of commotion, restless," from turba "turmoil, crowd;" maybe related to Pers. târ "dark, obscure, cloudy," Laki tur "balk, refractory, restive."

šubnâki, from âšub "turmoil, disturbance," âšoftan "to agitate, disturb;" Mid.Pers. âšôb "confusion, turmoil," âšoftan "to destroy, disturb;" Av. xšuf- "to tremble;" cf. Skt. ksobh- "to stagger, begin to swing, tremble;" Pol. chybac "to rock, move to and fro;" Lith. skubus "hasty, fast;" Goth. afskiuban "to shove;" O.E. scufan "to shove;" PIE base *k^(w)seub^h-, + -nâk state suffix, -i noun suffix.

The process whereby turbulence evolves by exchanging energy, leading to → dissipation.

→ turbulence; → decay.