Life under solar UV radiation in aquatic organisms.

Aquatic photosynthetic organisms are exposed to solar ultraviolet (UV) radiation while they harvest longer wavelength radiation for energetic reasons. Solar UV-B radiation (280-315 nm) affects motility and orientation in motile organisms and impairs photosynthesis in cyanobacteria, phytoplankton and macroalgae as measured by monitoring oxygen production or pulse amplitude modulated fluorescence analysis. Upon moderate UV stress most organisms respond by photoinhibition which is an active downregulation of the photosynthetic electron transport in photosystem II by degradation of UV-damaged D1 protein. Photoinhibition is readily reversible during recovery in shaded conditions. Excessive UV stress causes photodamage which is not easily reversible. Another major target is the DNA where UV-B mainly induces thymine dimers. Cyanobacteria, phytoplankton and macroalgae produce scytonemin, mycosporine-like amino acids and other UV-absorbing substances to protect themselves from short wavelength solar radiation.     

Model simulations of the impact of the 27-day solar rotation period on stratospheric ozone and temperature

Results are presented from two-year simulations of the effects of short-term solar ultraviolet (UV) variability using the Met. Office coupled chemistry-climate model. The model extends from the ground to 0.1 mbar and contains a complete range of chemical reactions allowing representation of all the main ozone formation and destruction processes in the stratosphere. The simulations were achieved by incorporating a 27-day oscillation in the pre-calculated model photolysis rates. Amplitudes for this signal were determined using solar spectral UV observations from the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) instrument. Two experiments were carried out, one in which the UV variability was included in both the photolysis and radiation schemes and one in which only the photolysis scheme was modified.

The model reproduced several main features of observed correlations between short-term solar UV variability and both ozone and temperature in the tropical upper stratosphere, including the downward propagation of the phase lag and sensitivities of ozone and temperature to solar UV which are similar in magnitude to those observed. In the lower stratosphere, the ozone response to solar UV variability has not been well characterised from observations. Both model runs show a reversal of the propagation of phase lag below 10mb. The model response was found to be different between the two runs indicating that radiatively induced dynamical effects may play a significant role in the ozone response to solar UV variability.     

A high-altitude barium radial injection experiment

On 16 March 1980 a rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The purpose of the experiment, named “King Crab,” was to advance knowledge of the instabilities, waves, and optical and magnetic effects produced. The TV images of the injection are spectacular, revealing three major regimes of expanding material which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km “black hole” surrounding the injection point. Preliminary computer simulations show a similar rayed structure development due to an electrostatic instability.     

Advanced pointing systems for space astronomy

Requirements on image stability are increasing, often at the same time that instrument external disturbances are increasing. Pointing large diameter optics from the shuttle bay is the prime current example of this situation. In order to achieve cost-effective advanced pointing systems in the face of these problems, a system approach must be taken that encompasses a realistic assessment of requirements, the best possible detector technology, and a broad look at space vehicles and pointing systems that are available. As an example, a rocket instrument for making measurements of the interstellar gas uses a standard pointing system to achieve a spectral resolution of 2 × 10⁵.     

Software architecture for building

Test system developers can benefit greatly from a software architecture that allows for easy interchangeability of instruments in those systems. Using open industry standard software architectures such as Virtual Instrument Software Architecture (VISA), and Interchangeable Virtual Instruments (IVI), developers are able to create systems with interchangeable test instrumentation. This paper describes the VISA and IVI software standards and demonstrates how their use within a broader software architecture, which includes standard development environments and flexible test executive software, facilitates the creation of interchangeable test systems     

Direct observation of charge state abundances of energetic He,C, O,and Fe emitted in solar flares

The ionic charge states of helium, carbon, oxygen, and iron have been determined for three solar particle enhancements by an electrostatic deflection analyzer, which is combined with a thin window proportional counter dE/dX vs. E system. The observations are obtained during the periods September 23 to 29, 1978, June 6 to 8, 1979, and September 15 to 26, 1979, with an instrument onboard the ISEE-3 spacecraft. The mean ionic charge states for He, C, and oxygen exhibit a high degree of ionization with values of Q = 2, 6, and 7.2, respectively. The charge state of iron is near 13 charge units. Variations from flare to flare and within the September 23, 1978 flare are small. The most surprising feature of the charge state measurement is the observation of a small (～10%) but finite contribution of singly ionized helium.     

Estimation of wave vector characteristics

In the realistic case of multiple electromagnetic plasma wave sources and multiple propagation paths, auto-correlation and cross-correlation products of the six wave components can be utilized to fit model parameters for the wave normal vector and Poynting vector distribution functions. With the complete wave vector characteristics, the wave mode can be identified, the index of refraction derived and the wave ray traced back towards the wave source region. Plasma wave instrumentation suitable for estimating some wave vector characteristics has been carried on satellites starting with FR-1 in 1964 and has evolved in various configurations on OGO-5, Injun-5, GEOS, Voyager, ISEE, Dynamics Explorer and the proposed OPEN spacecraft. Plasma wave research needs to advance along two parallel lines: (a) developing more sophisticated computer techniques for extracting the wave vector information from extensive data sets and (b) utilizing microprocessor technology in flight instruments to recognize specified phenomena and to capture the appropriate wave data for further on-board or ground processing.