Verification of Low Latitude Ionosphere Effects on WAAS During October 2003 Geomagnetic Storm

摘要

The Federal Aviation Administration's Wide Area Augmentation System (WAAS) provides high integrity GPS-based precision navigation service to users in the conterminous United States. In October 2003, only four months after WAAS was commissioned, a series of coronal mass ejections from the sun triggered one of the strongest geomagnetic and ionospheric storms of the solar cycle. WAAS user integrity was maintained during this entire time by reducing precision navigation service availability. Toward the end of this storm period a localized region of enhanced TEC that persisted for several hours was observed over Florida. GPS measurements of TEC made from the WAAS sites near the Gulf of Mexico indicate that the high density region was as much as 60 TECU (about 10 m delay at L1) higher than the surrounding ionosphere. The feature was observed in the Florida region from local evening on October 30, 2003, through midnight on the 31st. It is conjectured that this feature is not in reality so localized as to have the spatial area of roughly Florida, but may be part of a larger ionospheric structure in that longitude sector, spanning many degrees of latitude south of the sampling area of the WAAS GPS reference network. It is also thought to be the case that this larger structure may exist due to the effects of the geomagnetic storm in the South Atlantic Anomaly.