The principal objective of the Flare Genesis Experiment (FGE) is to understand the origins of solar activity. Flares, Ellerman bombs, and coronal heating are caused by dissipation of energy associated with current-carrying magnetic flux ropes. This assertion is based on the close association between magnetic fields and these phenomena and on the paucity of viable alternative explanations for solar activity. But advancement beyond this level of insight has been extremely difficult. The consensus among solar physicists is that greatly improved magnetic field observations are needed. Higher resolution, greater stability during observations, and longer runs without interruptions are needed to reveal key features of magnetic energy buildup and release.

The FGE is a unique and versatile solar observatory. It can measure the surface magnetic fields and motions with a unique balloon-borne 80-cm (aperture) telescope. By observing continuously from the Antarctic stratosphere, above 99.7% of the atmosphere, the FGE overcomes the principal problems that have hindered magnetic field observations from the ground.

Our principal aim is to understand how fibrous and twisted magnetic fields emerge at the solar surface and how they coalesce, unravel and erupt. It is important because magnetic fields are the root cause of flares, coronal mass ejections (CMEs), and most other solar activity. This effort may lead to reliable forecasts of solar activity and of the arrival of shocks and atomic particles at Earth.

Recent models of eruptions have focused on the slow evolution of pre-event, closed magnetic structures. The conceptual basis for these models is a gradual build up and storage of energy in a pre-eruption structure, such as a swollen helmet streamer. Possible drivers of the build-up include the emergence of new magnetic flux, the shear of field lines across a magnetic neutral line, or helicity charging.

Explosive energy release probably occurs by the development of an instability in twisted magnetic fields. The unstable fields erupt; then electric current sheets form, generating heat and mass motion. The FGE concentrates on magnetic flux developments, including the build-up of twist (magnetic helicity), in the emerged fields.

Measurements of electric current helicity, which is proportional to magnetic helicity, can be obtained with the FGE over a wide range of spatial scales. We plan to investigate the spectrum of helicity to determine if, for example, most helicity in active regions is concentrated in elementary flux ropes or in large-scale patterns.

While the evolution of active regions is closely connected to the basic processes leading to flares and CMEs, there are questions related directly to the evolution of an active region per se: How do the surface manifestations of convection change just prior to new flux emergence? Can we quantify the changes observed in granulation near active regions? Where does the magnetic field emerge relative to the various scales of convection (granules, mesogranules and supergranules)? What are the properties of the velocity and magnetic field at emergence? Are the flux tubes vertical or horizontal?

Basic properties of magnetic elements need to be studied and the following questions addressed: How do plage, network, and inner-network magnetic fields differ? How stable are flux tubes and what is their average lifetime? Does the helicity in the field account for the formation of filaments and other nonpotential magnetic structures? What is the connection between facular features and magnetic flux tubes? How do magnetic elements coalesce into larger features? What causes these features to decay? What are the dynamical process that cause magnetic flux to disappear? How does this disappearance relate to features on the Sun such as prominences and spots?

High resolution observations are crucial to understanding the formation of prominences, which apparently depends strongly on emergence or canceling of underlying magnetic fields. Many MHD models of prominences assume that hot coronal material condenses into magnetic field lines or that chromospheric plasma is injected into a dip formed by the magnetic field lines. But these theories do not explain how prominences are connected to the low atmosphere. When we observe prominences at the limb, we clearly see legs of prominences anchored in the photosphere; on the disk they look like fibrils, perhaps going to the boundaries of supergranules or perhaps into the middle of them. Reconnection and cancellation of magnetic flux may favor the creation of long threads and lift up the treads to prominence altitude. The FGE can detect the small magnetic flux elements in filament channels and follow their evolution along with the evolution of Ha features.

There will be X-ray and UV telescopes aboard the YOHKOH, SOHO and TRACE missions and on the NOAA GOES satellites during our balloon flights. By comparing our images with pictures of the Sun in X-rays and UV, it should be possible to determine precisely how the coronal and transition zone features relate to the underlying vector magnetic field structures.

FGE can address the following key scientific issues:

• The basic physical processes leading to solar flares.
• The basic physical processes leading to coronal mass ejections.
• The evolution of active region magnetic fields.
• The evolution of magnetic helicity in active regions.
• The photospheric drivers of chromospheric and coronal heating.
• The properties of small-scale magnetic elements and their contribution to solar luminosity variations and coronal heating.
• The structure of magnetic fields in sunspots and filaments.