| CUSP Sounding Rocket |
CUSP Sounding Rocket - SIIBelow are some first-cut scientific results from the CUSP SII instrument. All the plots are courtesy of Johnathan Burchill.
The two colours on the floating potential (or "sensor bias") plot represent an estimate of the upper and lower bounds on the SII floating potential. Having the sensor negatively charged had the effect of attracting the positive ions we wanted to measure. As an aside, the payload ground was slightly positive with respect to the plasma in proximity to SII and so was repelling the ions from it. The next three plots show velocities of ions as measured by SII thoughout the flight. The major assumption used in generating these figures is that the predominant ion species is singly ionized atomic hydrogen (H+), otherwise known as protons. This assumption gives about the right magnitudes for the flows except where noted below.
This first plot is of the components of measured ion bulk flow relative to the rocket (solid curve) and of the rocket velocity relative to the Earth (dashed curve) along the direction parallel to the Earth's magnetic field.
This plot is of the same ion velocity data, but with the rocket's velocity subtracted from it. Thus we get a plot of the direction of ion flow relative to only the Earth. The velocity values at the beginning and end of the flight should probably not be trusted, as perhaps other species contributed to the ion density. However, CUSP did fly from within the cusp region of the magnetosphere and out of it in a generally southerly direction, so perhaps the measured outflow (positive velocity) at the beginning of the flight is real, and is associated with the polar cap or cusp region where ion outflows are know to exist. We are almost 100% sure that the downflow of ions at the end of the flight is not 'geophysical'. Notice the downflow around 600 seconds into the flight. We are not yet sure if it is real, because there was a change in the SII floating potential near that event. More careful analysis is required. A look at the wave spectra from the electric field measurement instrument onboard may help. If there were parallel velocity shear driven waves at the edges of this downflow then it is more likely that the downflow is geophysical instead of an artifact due to the change in the floating potential.
The final plot shows the ion flows perdendicular to the Earth's magnetic field. SII only measured one component of the ion flow in the direction perpendicular to Earth's magnetic field, so the measured flows contain modulation due to the spin of the rocket as it moves through the plasma at a speed of 1 to 2 km/s. Information can be obtained about these "ionized winds" by comparing the SII flows with electric and magnetic field measurements made by other instruments onboard the same rocket. |