PUNCH

Current PredictionPrediction in TimeEvolution Over Time

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Given that this year’s prediction model captures both the corona and inner heliosphere in near-real-time, it is possible to synthesize data for NASA’s recently launched Heliophysics Small Explorer mission: the Polarimeter to UNify the Corona and Heliosphere, PUNCH. One of many unique and exciting aspects of the PUNCH mission is the large field of view that continuously images the outer corona and inner heliosphere in visible light. This is made possible by the fact that PUNCH is actually a constellation of four satellites orbiting Earth that seamlessly combine their individual perspectives to create a single wide-angle observation that covers roughly 1.6$^\circ$ to 45$^\circ$ in the sky (approximately 6 to 180 solar radii).

In the images above, we show the primary observables of the PUNCH mission, both for the time of totality on August 12th and for the evolving view of Earth during the period simulated. The first image on the left is the K-coronal total brightness, $tB$. This is a measure of the visible photospheric light that is scattered by coronal and heliospheric electrons toward the observer. The efficiency of scattering depends on the geometry between the Sun, the scattering parcel of plasma, and the observer, but it is proportional to the mass density of plasma integrated along the line of sight. This means that brighter and dynamic features, such as streamers and coronal mass ejections (CMEs), are visible as brightness enhancements. The relative speed of each structure is also a measure of its local outflow velocity (i.e., the solar wind).

The middle panel shows a related product, the polarized brightness, $pB$. This includes only the polarized component of the scattered K-corona light, which is always a smaller fraction of light than the total brightness (which is both polarized and unpolarized). In many ways the two images or movies look similar, but the relative contribution of the two components actually encodes information on the three-dimensional location of the scattering plasma in space. This is shown in the final plot on the right, which shows the polarization ratio, defined as $pB/tB$. As one can see by comparing to the $tB$ or $pB$ images, this ratio changes from feature to feature. Understanding how to best interpret or decode information like this from PUNCH observations is a key science goal of the mission (read more about PUNCH science here).

Lastly, one important aspect to appreciate is how inherently dynamic a data-driven, time-evolving coronal model appears to be. To initiate the heliospheric part of the solution, we relaxed the initial heliospheric domain to a steady-state using the snapshot of the coronal model on July 21st, 00:00 UT. Then, when the official prediction calculation begins, this time-stationary heliospheric solution is progressively blown out by the continuous dynamics of the corona below. This behavior is visible in the first several days of the above animations, which begin on July 21st. A “steady” heliosphere is not seen again.