A balloon measurement of the isotopic composition of galactic cosmic ray boron, carbon, and nitrogen

The isotopic compositions of galactic cosmic ray boron, carbon, and nitrogen have been measured at energies near 300 MeV amu^-1, using a balloon-borne instrument at an atmospheric depth of ~5 g cm^-2. The calibrations of the detectors comprising the instrument are described. The saturation properties of the cesium iodide scintilla tors used for measurement of particle energy are studied in the context of analyzing the data for mass. The achieved rms mass resolution varies from ~ 0.3 amu at boron to ~ 0.5 amu at nitrogen, consistent with a theoretical analysis of the contributing factors. Corrected for detector interactions and the effects of the residual atmosphere, the results are ^(10)B/B = 0.33^(+0.17)_(-0.11), ^(13)C/C = 0.06^(+0.13)_(-0.01), and ^(15)N/N = 0.42 (+0.19)_(-0.17). A model of galactic propagation and solar modulation is described. Assuming a cosmic ray source composition of solar-like isotopic abundances, the model predicts abundances near earth consistent with the measurements.

Theoretical and experimental analysis of pneumatic balloon microactuators

This paper presents a theoretical and experimental analysis of a biologically inspired balloon-type pneumatic microactuator. The operation principle of pneumatic balloon actuators (PBA's) is based on an asymmetric deflection of two PDMS layers with different thicknesses or different Young's moduli that are bonded together. A new analytical 2D model that describes the complex behavior of these actuators is presented and validated using both 3D FEM models and measurements. The actuators have dimensions ranging from 11 mm × 2 mm × 0.24 mm to 4 mm × 1 mm × 0.12 mm. Their fabrication is based on micromolding of PDMS, and can therefore easily be fabricated in high throughput. Measurements showed that the analytical model provides a qualitative description of the actuator behavior, and showed that the larger actuators are capable of delivering a 7 mm stroke at a supply pressure of 70 kPa and a force of max 22 mN at a supply pressure of 105 kPa. © 2011 Elsevier B.V. All rights reserved.

Vibration of a high-altitude tethered balloon with application to climate engineering

A balloon tethered at an altitude of 20 km could deliver a particulate cloud leading to global cooling. Tethering a balloon at this altitude poses significant problems with respect to vibration and stability, especially in regions of high wind. No-one has ever proposed, yet alone launched, a balloon at an altitude of 20 km tethered to the ground. Owing to wind, the tether needs to be 23 km in length and is to be fixed to a ship at sea or on land in equatorial regions. Whilst the balloon at 20 km is subject to relatively modest wind conditions, at jet stream altitudes (10km) the tether will experience much higher wind loadings, not only because of the high wind speeds of up to 300 km / hr but also because of the high air density. A tether of circular cross section in these high winds will be subject to horizontal and downward drag forces that would bring the aerostat down. For this reason it is advantageous to consider a self-aligning tether of an aerodynamic cross section whereby it is possible to reduce the drag substantially. One disadvantage of a non-circular tether is the possibility of flutter and galloping instabilities. It is reasonably straightforward to model these phenomena for short lengths of aerofoil, but the situation becomes more complex for a 20 km tensioned tether with large deflection and curvature, variable wind speed, variable air density and variable tension. Analysis using models of infinite length are used to establish the stability at a local scale where the tension, aerodynamic and geometric properties are considered constant. Dispersion curve analysis is useful here. But for dynamics on a long-wavelength scale (several km) then a full non-linear analysis is required. This non-linear model can be used to establish the local values of tension appropriate for the dispersion analysis. This keynote presentation will give some insight into these issues.

The modes of a tethered, spherical balloon

Observations of a tethered meteorological balloon show that a strong vibration coupling exists between axial forcing of the tether and ovalling deformations of the balloon. Such coupling may lead to system instabilities and fatigue failure in a tethered-balloon system. This is particularly relevant in the case of a balloon launched from a moving vessel, as is proposed as part of the SPICE geoengineering project. This paper investigates the vibration characteristics of a tethered, spherical balloon using a simple analytical model: a tensioned, spherical membrane attached to a spring. The analytical solution for the natural frequencies and modeshapes of this system is compared to transfer functions obtained by laser vibrometry. These results are then used to determine the most suitable method of modelling the dynamic response of a tethered balloon.

Quantification of the benefits of a streamlined tether for a high-altitude-tethered balloon

A high-altitude tethered balloon (HATB) reaching a height of 20 km has numerous applications including communications, meteorological monitoring, surveillance and, for the current paper, geoengineering. The HATB configuration consists of a 20 km tether rising up from the ground through the troposphere, where the wind-regime can be turbulent and include high-wind velocities due to the jet-stream, up into the more stable stratosphere where the tether would be attached to a spherical balloon. This paper evaluates wind-excited vibration of a HATB and will investigate the advantages of using a streamlined instead of a circular tether profile. Streamlining the tether reduces drag but introduces stability problems and complicates the numerical modelling. Consequently, prior to a thorough investigation of the stability issues due to fluid-structure interaction, a 3D nonlinear lumped-mass HATB model is used to quantify the benefit of a streamlined tether. The benefit is quantified by comparing the system specifications - such as balloon size and the tension in the tether - required to meet certain design requirements driven by the Stratospheric Particle Injection for Climate Engineering (SPICE) project. The SPICE project is investigating the feasibility of climate engineering using a HATB.

The balloon.

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A three-dimensional magnetometer for motion sensing of a balloon-carried atmospheric measurement package

An instrument is described which carries three orthogonal geomagnetic field sensors on a standard meteorological balloon package, to sense rapid motion and position changes during ascent through the atmosphere. Because of the finite data bandwidth available over the UHF radio link, a burst sampling strategy is adopted. Bursts of 9s of measurements at 3.6Hz are interleaved with periods of slow data telemetry lasting 25s. Calculation of the variability in each channel is used to determine position changes, a method robust to periods of poor radio signals. During three balloon ascents, variability was found repeatedly at similar altitudes, simultaneously in each of three orthogonal sensors carried. This variability is attributed to atmospheric motions. It is found that the vertical sensor is least prone to stray motions, and that the use of two horizontal sensors provides no additional information over a single horizontal sensor

A double-Gerdien instrument for simultaneous bipolar air conductivity measurements on balloon platforms

A bipolar air conductivity instrument is described for use with a standard disposable meteorological radiosonde package. It is intended to provide electrical measurements at cloud boundaries, where the ratio of the bipolar air conductivities is affected by the presence of charged particles. The sensors are two identical Gerdien-type electrodes, which, through a voltage decay method, measure positive and negative air conductivities simultaneously. Voltage decay provides a thermally stable approach and a novel low current leakage electrometer switch is described which initiates the decay sequence. The radiosonde supplies power and telemetry, as well as measuring simultaneous meteorological data. A test flight using a tethered balloon determined positive (σ+) and negative (σ−) conductivities of σ+ = 2.77±0.2 fS m−1 and σ− = 2.82±0.2 fS m−1, respectively, at 400 m aloft, with σ+/σ− = 0.98±0.04.

A lightweight balloon-carried cloud charge sensor

Despite the importance of microphysical cloud processes on the climate system, some topics are under-explored. For example, few measurements of droplet charges in nonthunderstorm clouds exist. Balloon carried charge sensors can be used to provide new measurements. A charge sensor is described for use with meteorological balloons, which has been tested over a range of atmospheric temperatures from -60 to 20 degrees C, in cloudy and clear air. The rapid time response of the sensor (to >10 V s(-1)) permits charge densities from 100 fC m(-3) to 1 nC m(-3) to be determined, which is sufficient for it to act as a cloud edge charge detector at weakly charged horizontal cloud boundaries.

Comparison of balloon-carried atmospheric motion sensors with Doppler lidar turbulence measurements

Magnetic sensors have been added to a standard weather balloon radiosonde package to detect motion in turbulent air. These measure the terrestrial magnetic field and return data over the standard uhf radio telemetry. Variability in the magnetic sensor data is caused by motion of the instrument package. A series of radiosonde ascents carrying these sensors has been made near a Doppler lidar measuring atmospheric properties. Lidar-retrieved quantities include vertical velocity (w) profile and its standard deviation (w). w determined over 1 h is compared with the radiosonde motion variability at the same heights. Vertical motion in the radiosonde is found to be robustly increased when w>0.75 m s−1 and is linearly proportional to w. ©2009 American Institute of Physics