Search Results
Abstract
During a hydrographic survey within the Iberian Basin and the Gulf of Cadiz, a combined CTD-ADCP profiling system is used to resolve the mesoscale mass distribution and flow fields of the Mediterranean Water tongue. Generally, the geostrophic flow pattern and the shear field of the ADCP velocities are in good agreement, except in near-coastal regions where strong ageostrophic velocity components can be expected. The error of the absolute velocity strongly depends on the uncertainty of the global positioning system and the duration of a CTD-ADCP cast, whereas the accuracy of the shear velocities does not exceed the inherent instrumental error of 1 cm s−1. Similar estimates of the geostrophic currents yield a strong dependence on the geographical latitude and the distance between two CTD locations used for the application of the dynamic method. Effects of internal tide phenomena on geostrophy are considered by vertical displacements of isopycnals.
Abstract
During a hydrographic survey within the Iberian Basin and the Gulf of Cadiz, a combined CTD-ADCP profiling system is used to resolve the mesoscale mass distribution and flow fields of the Mediterranean Water tongue. Generally, the geostrophic flow pattern and the shear field of the ADCP velocities are in good agreement, except in near-coastal regions where strong ageostrophic velocity components can be expected. The error of the absolute velocity strongly depends on the uncertainty of the global positioning system and the duration of a CTD-ADCP cast, whereas the accuracy of the shear velocities does not exceed the inherent instrumental error of 1 cm s−1. Similar estimates of the geostrophic currents yield a strong dependence on the geographical latitude and the distance between two CTD locations used for the application of the dynamic method. Effects of internal tide phenomena on geostrophy are considered by vertical displacements of isopycnals.
Abstract
The use of a hot-wire anemometer for high-resolution turbulence measurements in a two-phase flow (e.g., atmospheric clouds) is discussed. Experiments in a small wind tunnel (diameter of 0.2 and 2 m in length) with a mean flow velocity in the range between 5 and 16 m s−1 are performed. In the wind tunnel a spray with a liquid water content of 0.5 and 2.5 g m−3 is generated. After applying a simple despiking algorithm, power spectral analysis shows the same results as spectra observed without spray under similar flow conditions. The flattening of the spectrum at higher frequencies due to impacting droplets could be reduced significantly. The time of the signal response of the hot wire to impacting droplets is theoretically estimated and compared with observations. Estimating the fraction of time during which the velocity signal is influenced by droplet spikes, it turns out that the product of liquid water content and mean flow velocity should be minimized. This implies that for turbulence measurements in atmospheric clouds, a slowly flying platform such as a balloon or helicopter is the appropriate instrumental carrier. Examples of hot-wire anemometer measurements with the helicopter-borne Airborne Cloud Turbulence Observation System (ACTOS) are presented.
Abstract
The use of a hot-wire anemometer for high-resolution turbulence measurements in a two-phase flow (e.g., atmospheric clouds) is discussed. Experiments in a small wind tunnel (diameter of 0.2 and 2 m in length) with a mean flow velocity in the range between 5 and 16 m s−1 are performed. In the wind tunnel a spray with a liquid water content of 0.5 and 2.5 g m−3 is generated. After applying a simple despiking algorithm, power spectral analysis shows the same results as spectra observed without spray under similar flow conditions. The flattening of the spectrum at higher frequencies due to impacting droplets could be reduced significantly. The time of the signal response of the hot wire to impacting droplets is theoretically estimated and compared with observations. Estimating the fraction of time during which the velocity signal is influenced by droplet spikes, it turns out that the product of liquid water content and mean flow velocity should be minimized. This implies that for turbulence measurements in atmospheric clouds, a slowly flying platform such as a balloon or helicopter is the appropriate instrumental carrier. Examples of hot-wire anemometer measurements with the helicopter-borne Airborne Cloud Turbulence Observation System (ACTOS) are presented.
