Solar Modal Structure of the Engineering Environment The Sun has more than ten million normal modes and they affect engineered systems as they operate on Earth, in the oceans and in space.

Thispaperdescribessomeunanticipatedeffectsof the normal modes of the sun on engineering and scientific systems. We begin with historical, scientific, and statistical background, then present evidence for the effects of solar modes on various systems. Engineering evidence for these modes was first noticed in an investigation of communications satellite failures and second in a study of excessive dropped calls in cellular phone systems. The paper also includes several sections on multitaper estimates of spectra, canonical coher- ences, robust, and cyclostationary variants of multitapering, and related statistical techniques used to separate the various components of this complex system. In our attempt to understand this unexpected source of problems, we have found that solar modes are detectable in the interplanetary magnetic fields and energetic particles at the Ulysses spacecraft, five astronomical units from the Earth. These modes couple into the magnetosphere, the ionosphere, the geomagnetic field, and atmospheric pressure. Estimates of the power spectrum of data from solar radio telescopes and induced voltages on ocean cables show what appear to be solar modes at both lower and higher frequencies than the optically measured solar p-modes. Most surprisingly, these modes are easily detected in seismic data, where they literally shake the Earth.