There are at least five spacecraft currently operating that make frequent measurements of the solar wind in the interplanetary medium near Earth. Those measurements are far from redundant since the spacecraft are in different locations, and the fundamental spatial and temporal structure of the wind can make significant differences in the measurements. In addition, there are effects due to spacecraft's proximity to Earth's bow shock and foreshock regions. Differences in the observations are worthy of study in themselves, because they can reveal the basic structure of the wind as well as provide important information relevant to magnetospheric and space weather studies for which the solar wind is a basic input parameter.
But before any detailed science can be done, it is crucial that the observations from different spacecraft be intercalibrated by comparing measurements taken when the spacecraft are near one another. Wind is an ideal choice for a "standard" of comparison because its orbit was near the L1 Lagrangian point (approximately 240 Earth radii towards the Sun) during first months of ACE observations near L1. Such a calibration will also assure the space science community that there will be continuity of usefully-comparable data from the spacecraft involved. Thus we propose a two-phase program: intercalibration of data from the SWE experiment on Wind and the SWEPAM experiment on ACE followed by cross-correlation studies between those and other spacecraft.
Overall, the addition of ACE to the fleet of spacecraft in the
interplanetary wind gives us a great opportunity to compare measurements of
intrinsic variations in the wind and to do so in a period of rising solar
activity.
Our Email Address: asc@srl.caltech.edu