Engineering topics

Droege, W.

Publications and source records attributed to Droege, W..

3 records

NASA NTRS1997

Spatial evolution of 26-day recurrent galactic cosmic ray decreases: Correlated Ulysses COSPIN/KET and SOHO COSTEP observations

A Lomb (spectral) analysis was performed on the galactic comsic ray flux from February 1996 to June 1996. The most probable frequency is approximately 28 days and not 26 or 27 days, corresponding to one solar rotation. The amplitude of the recurrent cosmic ray decreases (RCRDs) is approximately 2.3 percent on both spacecraft. The variation in the solar wind speed shows the same periodicites and is anticorrelated to the variation in the cosmic ray flux. In contrast to the RCRDs, the amplitude found in the solar wind speed is four times larger at WIND (120 km/s) than at Ulysses (32 km/s). The solar wind proton density and magnetic field strength yielded no significant periodicities, neither at Ulysses nor at WIND. Comparing the RCRDs with coronal hole structures observed in the FE XIV line, it was found that a single coronal hole close to the heliographic equator can account for the RCRDs observed 'simultaneously' at Ulysses and SOHO. The coronal hole boundaries changed towards lower Carrington longitudes and vanished slowly. The changes of the boundaries during the investigated period could explain a 28-day periodicity.

Heber, B.↗

NASA NTRS1995

Ulysses high energy particle observation of the effects of recurrent high speed streams

Since June 1992 The Kiel Electron Telescope on board Ulysses measures variations of more than 10% in the fluxes of high energy H and He showing a periodicity of about 27 days, which are coincident with the passage of corotating interaction refios (CIR). At low energies MeV protons are accelerared at the shocks of the CIRs. These effects were observed up to high southern latitudes, where the signature of time of the conference Ulysses will have passed the solar equator and climbed up to 70 deg N at solar distance of 1.7 AU. In this paper we study the intensity variations with latitude as a function of magnetic rigidity.

Droege, W.↗

NASA NTRS1985

Stochastic particle acceleration in solar flares

It is proposed that particles during the second phase of solar flares are accelerated by stochastic resonant scattering off hydromagnetic waves and first order Fermi acceleration in shock waves generated in the impulsive phase of the flare. Solutions allow arbitrary power law momentum dependences of the momentum diffusion coefficient as well as the momentum diffusion coefficient as well as the momentum loss time. The acceleration time scale to a characteristic energy approximately 100 keV for protons can be as short as 5s. The resulting electron spectra show a characteristic double power law with a transition around 200 keV and are correlated to the proton spectra evaluated under equal boundary conditions, indicating that electrons and protons are accelerated by the same mechanism. The correlation between the different spectral indices in the electron double power law and between electron and proton spectra are governed by the ratio of first to second order acceleration and therefore allow a determination of the Alfven Mach number of the shock wave.

Droege, W.↗