April 21, 2017, 1:00 pm - 2:00 pm

April 21, 2017, 1:00 pm - 2:00 pm, Heliophysics Director's Seminar

The Detection of Rossby-like Waves on the Sun

Bob Leamon (672)

Rossby waves are a type of global-scale wave that develops in planetary atmospheres, driven by the planet's rotation. They propagate westward owing to the Coriolis force, and their characterization enables more precise forecasting of weather on Earth. Despite the massive reservoir of rotational energy available in the Sun's interior and decades of observational investigation, their solar analogue has defied unambiguous identification. Here we analyse a combined set of images obtained by the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) spacecraft between 2011 and 2013 in order to follow the evolution of small bright features, called brightpoints, which are tracers of rotationally driven large-scale convection. We report the detection of persistent, global-scale bands of magnetized activity on the Sun that slowly meander westward in longitude and display Rossby-wave-like behaviour. These magnetized Rossby waves allow us to make direct connections between decadal-scale solar activity and that on much shorter timescales. Monitoring the properties of these waves, and the wavenumber of the disturbances that they generate, has the potential to yield a considerable improvement in forecast capability for solar activity and related space weather phenomena.

Spectral Particle Flux Environments of Kuiper Belt Objects in the Outer Heliosphere and the Local Interstellar Medium from Voyager and IBEX

John F. Cooper (672)

The ongoing Voyager 1, Voyager 2, and Interstellar Boundary Explorer (IBEX) missions are providing comprehensive views in-situ (Voyager) and remotely (IBEX) of the outer regions of the heliosphere in transition to the local interstellar medium (LISM). The past measurements by the Pioneer 10, Pioneer 11, and the two Voyager spacecraft have fully explored the supersonic heliosphere and are now being supplemented via the Planetary Data System by solar wind and energetic particle data from the New Horizons spacecraft for measurements enroute to and beyond Pluto. Spectral particle flux distributions from these outposts of the Heliophysics System Observatory can be compiled at eV to GeV and higher energies for applications to problems of pressure balance and other interactions between the inner heliosheath, the outer heliosphere, and the LISM, and to effects of space weathering via surface irradiation on planetary bodies of the outer Kuiper Belt and the inner Oort Cloud. Planet X, if it exists in the suggested orbit inferred from dynamical modeling of known extreme KBOs, would see a mixture of exposures to the outer heliosheath and the LISM. Within the supersonic heliosphere the New Horizons data will provide the new base line for studies of space weathering at Pluto and the main Kuiper Belt. Spectral particle flux knowledge of the outermost and inner heliosphere will be greatly expanded by the planned Interstellar Mapping and Acceleration Probe (IMAP).

Shock Acceleration: An Unexpected Discovery Addresses a ~60 Year Old Question

Lynn Wilson(672)

For over 100 years we have observed ultra high energy cosmic rays bombarding Earth's atmosphere and by the 1970s it was clear that strong astrophysical shock waves must be a major source. However, all theories assumed a pre-existing pool of suprathermal particles that undergo acceleration to ultra-high energies. The source of these suprathermal particles - called the 'injection problem' - remains an outstanding problem even though it is the most crucial part of the energization process. It was recently discovered that relativistic (>500 keV) electrons are being locally produced by small-scale, transient waves and structures upstream of the terrestrial bow shock. No research has ever proposed Earth's relatively low Mach number bow shock, let alone these transient disturbances, as a relativistic electron source. Given the ubiquity of foreshocks in collisionless plasmas, these observations could fundamentally change our understanding of particle acceleration, not just at collisionless shock waves.