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Land and Ocean Floor Measurements

Approximately 180 magnetic observatories send digital data to World Data Centers ( Figure 4-1) in support of the geomagnetic studies described in this report. At present, 13 observatories are operated by the United States. Although their actual number is significant, they are unevenly distributed; most are located in the Northern Hemisphere, particularly in Europe. There are no observatories on the ocean floor; consequently, vast areas of the globe—the ocean basins—are not sampled. In addition to standard observatories, there are temporary or semi-permanent variometer stations, which do not record absolute values, as well as repeat stations for recording long-term baseline fluctuations (typically measured at intervals of a year or longer). In the past, arrays of many tens of simultaneously recording variometers have been temporarily deployed to detect electrical conductivity anomalies in the crust and upper mantle or to record activity in the ionosphere and magnetosphere, but at present there are no arrays of high-frequency instruments available to the scientific community in the United States.

The uneven distribution of magnetic observatories, which is the result of historical circumstances, provides incomplete knowledge of the field behavior and biases many global studies, including the model of the IGRF and the derivation of magnetic activity indices such as the auroral electrojet magnetic activity index (AE) and the disturbance storm time equatorial magnetospheric activity index Dst.¹ The IGRF is a spherical harmonic description of the magnetic potential to degree and order 10.

¹ The much-used Kp index (planetary K-index) as traditionally constructed, while purportedly a “global” index, is an indicator of magnetic activity at midlatitudes and does not rely on a regional or global distribution of observatories as do the AE and Dst indices, respectively; thus, the Kp index is not “biased” in the same way that the high-latitude AE index and the low-latitude Dst index are.

Front Matter (R1-R16)

Executive Summary (1-10)

Scientific Framework (11-17)

Scientific Issues and Research Opportunities (18-50)

Observational Needs and Facilities (51-60)

Data Management (61-67)

Communication and Coordination (68-73)

Appendix A: Topical Working Group Reports (74-74)

A1: The Magnetosphere, Ionosphere, and Atmosphere (75-99)

A2: Understanding the Nature and Evolution of the Lithosphere from Magnetic Anomolies (100-118)

A3: Electromagnetic Induction Studies in the Earth and Oceans (119-133)

A4: Main Field and Core Processes (134-154)

B1: Operational Platforms (155-189)

B2: Data Management Systems (190-207)

B3: Interagency Communication and Coordination (208-218)

Appendix C: Workshop Organization (219-240)

Appendix D: Acronyms, Abbreviations, and Special Names (241-246)