HR: 16:50h
AN: SH54B-03 INVITED     [Abstracts]
TI: A Continuous Long-Term Record of Magnetic-Storm Occurrence and Intensity
AU: * Love, J J
EM: jlove@usgs.gov
AF: USGS Geomagnetism Program, Box 25046 MS 966 DFC, Denver, CO 80225, United States
AB: Hourly magnetometer data have been produced by ground-based magnetic observatories for over a century. These data are used for a wide variety of applications, including many for space physics. In particular, hourly data from a longitudinal necklace of mid-latitude observatories can be used to construct a time series recording the storm-time disturbance index Dst, one of the most useful scalar summaries of magnetic storm intensity which is generally interpreted in terms of an equivalent equatorial magnetospheric ring current. Dst has been routinely calculated in a temporally piece-wise fashion since the IGY using a subset of the available observatories: four or five stations, typically including Honolulu (HON), San Juan (SJG), Kakioka Japan (KAK), Hermanus South Africa (HER), and Alibag India (ABG). In this presentation we discuss a single continuous Dst time series made using a denser and more uniform distribution of observatories than that which is standard: including, additionally, Watheroo Australia (WAT), Apia Samoa (API), and Vassouras Brazil (VSS). Starting first with the data from each individual observatory, we subtract the geomagnetic secular variation, caused primarily by the core dynamo, and the solar-quiet (Sq) variation, caused primarily by the ionospheric dynamo. The latter requires careful spectral analysis, and those intermediate results are, themselves, of scientific interest. Following this, we combine the disturbance residuals from each station to form the continuous Dst time series. Statistics deduced from this model allow us to quantify the likelihood of storm occurrence and intensity, both of which are modulated in time by the solar cycle. This analysis is accomplished using a 50 year Dst time series. The prospects for constructing a longer continuous Dst time series are discussed.
DE: 1530 Rapid time variations
DE: 2778 Ring current
DE: 2788 Magnetic storms and substorms (7954)
DE: 7536 Solar activity cycle (2162)
DE: 7924 Forecasting (2722)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Joint Assembly