Paul T.M. Loto’aniu 1,2 and H.J. Singer 1 NOAA Space Environment Center 1

1. Space Weather Products from the GOES-R Magnetometer Paul T.M. Loto’aniu1,2 and H.J. Singer1 NOAA Space Environment Center1 CIRES, University of Colorado2 Abstract Since their inception in the 1970's, the GOES satellites have monitored Earth's highly variable magnetic field using magnetometers. The GOES-R magnetometer requirements are similar to the tri-axial fluxgates that have previously flown. GOES-R requires measurements of three components of the geomagnetic field with a resolution of least 0.016 nT and sampling at a 2 Hz threshold with goal of 8 Hz. This instrument will provide measurements of the space environment magnetic field that controls charged particle dynamics in the outer region of the magnetosphere. These particles can be dangerous to spacecraft and human spaceflight. The geomagnetic field measurements are important for providing alerts and warnings to many customers, including satellite operators and the power utilities. GOES magnetometer data are also important in research, being among the most widely used spacecraft data by the national and international research community. The GOES-R magnetometer products will be an integral part of the NOAA space weather operations providing, for example, information on the general level of geomagnetic activity and permitting detection of magnetopause crossings and storm sudden commencements. In addition measurements will be used to validate large-scale space environment models that are used in operations. In this presentation, in addition to briefly describing the instrument requirements and its uses, we will also describe some of the products under development through the Algorithm Working Group activities. Coordinate transformations GOES-R products include converting magnetometer data to alternative coordinate systems. The need for use of more than one coordinate system arises because different physical phenomena in space physics can best be understood or described in different coordinate systems. For GOES-R, data will be converted to VDH, GEI, GSM and GSE. The VDH system is similar to MAG. GEI and GSE are inertial non-magnetic coordinates systems fixed to the stars and Sun, respectively. VDH and GSM are magnetic coordinate systems defined relate to the magnetic dipole axis. Solar wind shock Impact and magnetopause crossings at geosynchronous orbit Solar wind sudden impact or shock arrival at the magnetosphere can lead to enhanced geomagnetic activity and compress the magnetosphere within geosynchronous orbit. The enhanced activity can lead to dangerous levels of energetic particles, while during magnetopause crossings spacecraft encounter magnetic fields that can be directed opposite to what is normally expected. These conditions can have undesirable effects on spacecraft that use torquer currents as part of their attitude control and momentum management. • Magnetometer requirements • Measurement range: +/- 512 nT axis • Measurement precision: 0.016 nT/axis • Measurement accuracy: 1.0 nT/axis • Orthogonality: +/- 0.5o, 3 axes • Orientation stability: +/- 0.25o • Orientation knowledge: Threshold: +/- 1o, Goal: +/- 0.5o • Refresh rate (per axis): Threshold: 2Hz, Goal: 8 Hz • Data Latency: Real time (5 sec) 1-minute magnetic field averages Instrument requirements include 0.5 sec sample rate with a goal of 0.125 sec. However, large-scale changes in the geomagnetic field in space often occur over scales longer then one minute. Hence, 1-minute averages provide general features of the magnetic field at geosynchronous orbit. The average data are used in operations and by the scientific community. The basic principle of a fluxgate magnetometer consists of a magnetic core which is periodically hard saturated by the first coil, while a second coil senses the resulting electromagnetic field. An external field (geomagnetic) will cause an in balance in the toroid’s hysteresis which results in a net field that is detected by the sense coil. The GOES-R space weather products will provide auto-detection of sudden impulses and magnetopause crossing. Comparison to magnetic field models Products for magnetometer • MAG.07: Convert data to alternate coordinate systems. • MAG.08: 1-minute averages. • MAG.09: Comparison to quiet fields. • MAG.10: Auto-detection of Magnetopause crossings. • MAG.12: Auto-detection of Magnetic Sudden Impulses. The GOES-R magnetometer data will be used to verify operational global magnetic field models. The current GOES data are widely used by the scientific community to verify non-operational magnetospheric models. Utility of magnetometer data A 3-D global model example is shown on the left. An example comparison of GOES magnetic data to field models are shown in the bottom left. The GOES-R space weather products will include the ability to compare measurements to a quiet magnetic field model. The chosen model is Olson-Piftzer 1977 (OP77), which requires no external data. High resolution magnetic data • Assessing the level of geomagnetic activity • Detecting magnetopause crossings • Alerting customers to solar wind shocks or sudden impulses • Distinguishing among different sources of energetic particle events • Validating global magnetospheric models used in operations • Developing techniques for new operational applications • Providing data to NGDC for archives and the scientific community • Real-time data to the US Air Force Weather Agency • Supporting rocket launch decisions and other real-time activities • Conducting research for understanding the space environment The higher resolution GOES magnetic data are often used to study plasma waves in near-Earth space. Some of these waves are thought to contribute to the acceleration and loss of relativistic electrons that are hazardous to spacecraft and human’s in space. U. Of Michigan (Gombosi et al.) M. Kessel et al. CISM: Huang et al. CWS Ziesolleck et al. (1996)