[1] Hourly averaged interplanetary magnetic field (IMF) and plasma data from the Advanced Composition Explorer (ACE) and Wind spacecraft, generated from 1 to 4 min resolution data time-shifted to Earth have been analyzed for systematic and random differences. ACE moments-based proton densities are larger than Wind/Solar Wind Experiment (SWE) fits-based densities by up to 18%, depending on solar wind speed. ACE temperatures are less than Wind/SWE temperatures by up to $25%. ACE densities and temperatures were normalized to equivalent Wind values in National Space Science Data Center's creation of the OMNI 2 data set that contains 1963-2004 solar wind field and plasma data and other data. For times of ACE-Wind transverse separations <60 R E , random differences between Wind values and normalized ACE values are $0.2 nT for jBj, $0.45 nT for IMF Cartesian components, $5 km/s for flow speed, and $15 and $30% for proton densities and temperatures. These differences grow as a function of transverse separation more rapidly for IMF parameters than for plasma parameters. Autocorrelation analyses show that spatial scales become progressively shorter for the parameter sequence: flow speed, IMF magnitude, plasma density and temperature, IMF X and Y components, and IMF Z component. IMF variations have shorter scales at solar quiet times than at solar active times, while plasma variations show no equivalent solar cycle dependence.Citation: King, J. H., and N. E. Papitashvili (2005), Solar wind spatial scales in and comparisons of hourly Wind and ACE plasma and magnetic field data,
Abstract.NSSDC's OMNI dataset, which now spans 1963-1999, contains a collection of hourly means of interplanetary magnetic field (IMF) and solar wind (SW) plasma parameters measured near the Earth's orbit, as well as some auxiliary data. We report a study of solar cycle effects in planetary geomagnetic activity in which 27-day averages of several OMNI parameters are compared with equivalent Kp and Dst averages. Some established trends in these parameters over solar cycles are confirmed; for example, it is concluded that changes in the magnitude (rather than in direction) constitute the primary solar cycle variation in the IMF. However, this study also reveals that long-term changes in planetary geomagnetic activity are driven more actively by solar wind-magnetosphere coupling of an electrodynamic nature rather than by plasma transport into the magnetosphere. This suggests that ambient (background) interplanetary "electric" environment (in which the Earth's magnetosphere is immersed over the solar cycles) may play a more significant role in causing changes in the frequency of geomagnetic storms and substorms than previously realized.
The K indices are to be hand-scaled from analogue magnetograms following morphological criteria expressed in the so-called Mayaud rules. All observatories used to follow these rules in the routine hand-scaling of K indices from analogue magnetograms. As a result of digitalization and automation of observatories, however, observers in charge who are experienced in K scaling from analogue magnetograms are becoming increasingly rare. Therefore the organizations running observatories were forced to find compensating machine methods for the production of K indices. The basic features of the K indices and the Mayaud rules are first reviewed, and then the methods developed for computer derivation of K indices are discussed.In order to decide which of the proposed algorithms was suitable, a comparison among them was organized by the IAGA Working Group on geomagnetic indices. The comparison was made with a common data set, using the same statistical tests. The results are summarized and discussed. Further comparisons between the K indices produced by computer with the different methods are presented in this paper. Four methods were acknowledged by the Working Group during the Vienna IUGG general Assembly in 1991. The results confirm that these methods provide acceptable results in comparison to the average quality of hand-scaled indices.A comparison between computer-produced K indices and reference K indices handscaled following the Bartels-Mayaud rules is also presented. It appears that only two acknowledged methods provide computer-produced K in good agreement with handscaled K. The best computer method (the FMI method) is found to be good enough to allow the continuation of the long tradition of producing K indices without any serious jump in the statistics.
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