Hydrostatic equilibrium

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

Effects of deviations from hydrostatic equilibrium on atmospheric corrections to satellite and lunar laser range measurements

Abstract: The accuracy of the atmospheric correction to laser range measurements is one of the main limiting factors for distance measurements to retroreflectors on artificial satellites and on the Moon. The main part of this correction is currently obtained by using the local atmospheric pressure and zenith angle to determine the integrated atmospheric density along the observing path. One of the factors affecting this method of correction is possible deviations of the atmosphere from hydrostatic equilibrium for observation sites in mountainous areas. This article examines the integrated equations of motion for the atmosphere and estimates the effect of such deviations on the overall range error. It is found that the expected error is less than 1 cm most of the time, even for elevation angles as low as 20°.

Hydrostatic and non-hydrostatic simulations of dense waters cascading off a shelf: The East Greenland case

Abstract: The cascade of dense waters of the Southeast Greenland shelf during summer 2003 is investigated with two very high-resolution (0.5-km) simulations. The first simulation is non-hydrostatic. The second simulation is hydrostatic and about 3.75 times less expensive. Both simulations are compared to a 2-km hydrostatic run, about 31 times less expensive than the 0.5 km non-hydrostatic case. Time-averaged volume transport values for deep waters are insensitive to the changes in horizontal resolution and vertical momentum dynamics. By this metric, both lateral stirring and vertical shear instabilities associated with the cascading process are accurately parameterized by the turbulent schemes used at 2-km horizontal resolution. All runs compare well with observations and confirm that the cascade is mainly driven by cyclones which are linked to dense overflow boluses at depth. The passage of the cyclones is also associated with the generation of internal gravity waves (IGWs) near the shelf. Surface fields and kinetic energy spectra do not differ significantly between the runs for horizontal scales L > 30 km . Complex structures emerge and the spectra flatten at scales L 30 km in the 0.5-km runs. In the non-hydrostatic case, additional energy is found in the vertical kinetic energy spectra at depth in the 2 km L 10 km range and with frequencies around 7 times the inertial frequency. This enhancement is missing in both hydrostatic runs and is here argued to be due to the different IGW evolution and propagation offshore. The different IGW behavior in the non-hydrostatic case has strong implications for the energetics: compared to the 2-km case, the baroclinic conversion term and vertical kinetic energy are about 1.4 and at least 34 times larger, respectively. This indicates that the energy transfer from the geostrophic eddy field to IGWs and their propagation away from the continental slope is not properly represented in the hydrostatic runs.

A thrust bearing and method for equalizing load

Abstract: A multi-pad (24), fluid film thrust bearing (8) has the pads suspended from the carrier ring on hydrostatic oil pressure regions. The oil is pressurized hydrodynamically by relative rotation between a load surface and the bearing surface of each pad; and the oil is passed through each pad to a rear cavity where the hydrostatic pressure region is established. A manifold interconnects all of the hydrostatic pressure regions for the individual pads in order to average the hydrostatic pressures and provide for static and dynamic load equalization.

The temperature-density structure of coronal loops in hydrostatic equilibrium

Abstract: The temperature and density structure are computed for a comprehensive set of coronal loops that are in hydrostatic and thermal equilibrium. The effect of gravity is to produce significant deviations from the usual uniform-pressure scaling law (T∼(pL) 1/3) when the loops are taller than a scale height. For thermally isolated loops it lowers the pressure throughout the loop, which in turn lowers the density significantly and also the temperature slightly; this modifies the above scaling law considerably. For more general loops, where the base conductive flux does not vanish, gravity lowers the summit pressure and so makes the radiation decrease by more than the heating. This in turn raises the temperature above its uniform pressure value for loops of moderate length but lowers it for longer loops. A divergence in loop cross-section increases the summit temperature by typically a factor of 2, and decreases the density, while an increase in loop height (for constant loop length) changes the temperature very little but can halve the density. One feature of the results is a lack of equilibrium when the loop pressure becomes too large. This may explain the presence of cool cores in loops which originally had temperatures below 2 × 106 K. Loops hotter than 2 × 106 K are not expected to develop cool cores because the pressure necessary to produce non-equilibrium is larger than observed.