Ring Current Composition During Sawtooth Storms

Recent IMAGE observations have shown that the gradual development of the hydrogen ring current during sawtooth storms is accompanied by a bursty occurrence of oxygen. The observed oxygen energetic neutral atom (ENA) fluxes are as high, if not sometimes higher, than oxygen fluxes associated with non-sawtooth storms. They appear predominantly during individual sawtooth injections. Once a sawtooth injection has occurred, oxygen ENA fluxes quickly abate due to a combination of precipitation, drift loss and charge exchange. We use ENA inversion techniques to estimate the amount of hydrogen and oxygen plasma in the inner magnetosphere during sawtooth events. Due to the orbit of IMAGE we can monitor the plasma content for 70-80 percent of the time, split into uninterrupted stretches of up to 10 hours apiece. This coverage allows us not only to study the time development of the ring current and the oxygen content during a storm, but to also study several consecutive "teeth" without interruption. We present results from several sawtooth storms that occurred since the fall of 2001. We show the time development of the ring current during those storms, and contrast it with the time history of observed oxygen. For comparison, we will also show data from non-sawtooth storms since 2001.