C. Nick Arge

Air Force Data Assimilative Photospheric Flux Transport (ADAPT) Model

As the primary input to coronal and solar wind models, global estimates of the solar photospheric magnetic field distribution are critical to space weather forecasting. These global magnetic maps are essential for accurate modeling of the corona and solar wind, which is vital for gaining the basic understanding necessary to improve forecasting models needed for Air Force operations. In this paper, we describe our efforts and progress toward developing the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model. ADAPT incorporates the various data assimilation techniques, including an ensemble Kalman filter, with a photospheric magnetic flux transport model. The flux transport model evolves the magnetic flux on the Sun using relatively well understood transport processes when observations are not available and then updates the modeled flux with new observations using data assimilation. The data assimilation rigorously takes into account model and observational uncertainties, as well as accoun...

Data Assimilation in the ADAPT Photospheric Flux Transport Model

Global maps of the solar photospheric magnetic flux are fundamental drivers for simulations of the corona and solar wind and therefore are important predictors of geoeffective events. However, observations of the solar photosphere are only made intermittently over approximately half of the solar surface. The Air Force Data Assimilative Photospheric Flux Transport (ADAPT) model uses localized ensemble Kalman filtering techniques to adjust a set of photospheric simulations to agree with the available observations. At the same time, this information is propagated to areas of the simulation that have not been observed. ADAPT implements a local ensemble transform Kalman filter (LETKF) to accomplish data assimilation, allowing the covariance structure of the flux-transport model to influence assimilation of photosphere observations while eliminating spurious correlations between ensemble members arising from a limited ensemble size. We give a detailed account of the implementation of the LETKF into ADAPT. Advantages of the LETKF scheme over previously implemented assimilation methods are highlighted.

Modeling the corona and solar wind using ADAPT maps that include far-side observations

As the primary input to nearly all coronal and solar wind models, global estimates of the solar photospheric magnetic field distribution are critical for reliable modeling of the corona and heliosphere. Over the last several years the Air Force Research Laboratory (AFRL), in collaboration with Los Alamos National Laboratory (LANL) and the National Solar Observatory (NSO), has developed a model that produces more realistic estimates of the instantaneous global photospheric magnetic field distribution than those provided by traditional photospheric field synoptic maps. The Air Force Data Assimilative Photospheric flux Transport (ADAPT) model is a photospheric flux transport model, originally developed at NSO, that makes use of data assimilation methodologies developed at LANL. The flux transport model evolves the observed solar magnetic flux using relatively well understood transport processes when measurements are not available and then updates the modeled flux with new observations using data assimilation methods that rigorously take into account model and observational uncertainties. ADAPT originally only made use of Earth-side magnetograms, but the code has now been modified to assimilate helioseismic far-side active region data such as those available from the Global Oscillation Network Group. As a preliminary test, a helioseismically detected active region that first emerged on the far-side of the Sun in early July 2010 is incorporated into maps produced by ADAPT and then used in the Wang-Sheeley-Arge (WSA) model to simulate the corona and solar wind. The WSA model results, with and without far-side data included in the ADAPT global maps, are compared here with coronal EUV and in situ solar wind observations available from STEREO. We find that the observed and modeled values are in better agreement when including the far-side detection.

Earthward directed CMEs seen in large-scale coronal magnetic field changes, SOHO LASCO coronagraph and solar wind

One picture of coronal mass ejection (CME) initiation relates these events to the expansion into space of previously closed coronal magnetic fields, often part of the helmet streamer belt. The work described here makes use of the potential field source surface model based on updated synoptic photospheric field maps to study the large-scale coronal field changes. We isolate those field lines that change from closed to open configurations (newly opening field lines) by comparing potential field source surface models from adjacent magnetograph observations, wherein the same starting foot points on the photosphere are used. If there are some newly opening field lines between the times of two maps, we assume there was a possibility for CME occurrence(s) between these times. In particular, if there are newly opening field lines near the solar disk center, an earthward directed CME may have been generated. Monitoring the coronal magnetic field behavior can in principle reinforce (or not) days in advance predictions of magnetic storms based on Solar and Heliospheric Observatory (SOHO) Large-Angle Spectrometric Coronagraph (LASCO) halo CMEs. Moreover, the coronal field over the visible hemisphere contains information about the possible geoeffectiveness of a particular CME because it shows the approximate orientation and location of the active arcades. By comparing halo CMEs with the newly opening field lines, the solar wind measurements from Wind and ACE spacecraft and the Dst index, we show that, like soft X-ray sigmoids, disappearing filaments, and Extreme ultraviolet Imaging Telescope (EIT) waves on the disk of the Sun, magnetograph observation-based coronal field models may provide additional information on the likelihood of CME effects at the Earth.

Laboratory-generated Coronal Mass Ejections

We have begun a series of laboratory experiments focused on understanding how coronal mass ejections (CME) interact and evolve in the solar wind. The experiments make use of the Helicon-Cathode (HelCat) plasma facility, and the Plasma Bubble eXperiment (PBeX). PBeX can generate CME-like structures (sphereomak geometry) that propagate into the high-density, magnetized background plasma of the HelCat device. The goal of the current research is to compare CME evolution under conditions where there is sheared flow in the background plasma, versus without flow; observations suggest that CME evolution is strongly influenced by such sheared flow regions. Results of these studies will be used to validate numerical simulations of CME evolution, in particular the 3D BATS-R-US MHD code of the University of Michigan. Initial studies have characterized the plasma bubble as it evolves into the background field with and without plasma (no shear).