Hydrostatic equilibrium

About: Hydrostatic equilibrium is a research topic. Over the lifetime, 2451 publications have been published within this topic receiving 62172 citations.

Hydrostatic and Non-hydrostatic Simulations of the 6 August 1993 Kagoshima Torrential Rain

Abstract: Comparative experiments with real data using hydrostatic and non-hydrostatic models are performed for the torrential rain which occurred on 6 August 1993 in Kagoshima, the southern Kyushu, Japan. A modified version of the three-dimensional anelastic model (Saito, 1994; Kato and Saito 1995) is used, which is nested with the operational hydrostatic model (the Japan Spectral Model) of the Japan Meteorological Agency. An explicit warm rain process predicting cloud water and rainwater and the moist convective adjustment are individually or conjunctionally employed in the model. The non-hydrostatic simulations of 5 and 10 km horizontal-resolution with a warn rain scheme reproduce continuously heavy rain which corresponds well with the observation. As Kato and Saito (1995) pointed out in a previous comparative experiment of ideal moist convection, the hydrostatic simulation tends to overestimate and overexpand precipitation in comparison with the non-hydrostati(: counterpart, and the drag effect of hydrostatic water loading is more significant for convective development than the non-hydrostatic effect. Furtermore, in the 5 km simulations, the hydrostatic approximation greatly overestimates the total precipitation, more than in the simultation of ideal moist convection (Kato and Saito, 1995). From these results, a non-hydrostatic model with hydrostatic water loading is recommended for a high-resolution numerical prediction model.

Diagnostic potential of the Ca II 8542A line for solar filaments

Abstract: In this study we explore the diagnostic potential of the chromospheric Ca II line at 8542A for studying the magnetic and dynamic properties of solar filaments. We have acquired high spatial resolution spectropolarimetric observations in the Ca II 8542A line using the CRISP instrument at the Swedish 1-m Solar Telescope. We use the NICOLE inversion code to infer physical properties from observations of a solar filament. We discuss the validity of the results due to the assumption of hydrostatic equilibrium. We have used observations from other telescopes such as CHROTEL and SDO, in order to study large scale dynamics and the long term evolution of the filament. We show that the Ca II 8542A line encodes information of the temperature, line-of-sight velocity and magnetic field vector from the region where the filament is located. The current noise level only allow us to estimate an upper limit of 260G for the total magnetic field of the filament. Our study also reveals that if we only consider information from the aforementioned spectral line, the geometric height, the temperature and the density can be degenerated parameters outside the hydrostatic equilibrium approach.

Heat Transfer from Thin Wires to Superfluid Helium under Reduced Gravity

Abstract: The heat transfer from thin wires to He II has been investigated at low hydrostatic pressures on ground and at milligravity on board of the NASA KC-135 aircraft. The peak heat flux density at low gravity is found to be less than 10% lower than the lowest laboratory values, the recovery heat flux density, however, about 50%. For the recovery heat flux density a large scatter was observed, indicating a significant drop of this quantity in the milligravity region.

Gravitational viscoelastodynamics for a hydrostatic planet

Abstract: The response of planetary bodies to perturbations with periods of less than several days is conventionally studied assuming elastic constitutive behaviour. The defining feature of elastic solids is the proportionality between stress and strain. The phenomena governed by the associated field theory of elastodynamics can be classified into the propagation of seismic waves, free oscillations, and short-period body and load tides. For the latter two classes, it is necessary to account also for gravity and the presence of initial stress in planetary interiors. This is accomplished by the field theory of gravitational elastodynamics (GED).

Rotation of a rigid satellite with a fluid component: a new light onto Titan’s obliquity

Abstract: We revisit the rotation dynamics of a rigid satellite with either a liquid core or a global subsurface ocean. In both problems, the flow of the fluid component is assumed inviscid. The study of a hollow satellite with a liquid core is based on the Poincare–Hough model which provides exact equations of motion. We introduce an approximation when the ellipticity of the cavity is low. This simplification allows to model both types of satellite in the same manner. The analysis of their rotation is done in a non-canonical Hamiltonian formalism closely related to Poincare’s “forme nouvelle des equations de la mecanique”. In the case of a satellite with a global ocean, we obtain a seven-degree-of-freedom system. Six of them account for the motion of the two rigid components, and the last one is associated with the fluid layer. We apply our model to Titan for which the origin of the obliquity is still a debated question. We show that the observed value is compatible with Titan slightly departing from the hydrostatic equilibrium and being in a Cassini equilibrium state.