[1] As the number of ground-based and space-based receivers tracking the Global Positioning System (GPS) satellites steadily increases, it is becoming possible to monitor changes in the ionosphere continuously and on a global scale with unprecedented accuracy and reliability. As of August 2005, there are more than 1000 globally distributed dual-frequency GPS receivers available using publicly accessible networks including, for example, the International GPS Service and the continuously operating reference stations. To take advantage of the vast amount of GPS data, researchers use a number of techniques to estimate satellite and receiver interfrequency biases and the total electron content (TEC) of the ionosphere. Most techniques estimate vertical ionospheric structure and, simultaneously, hardware-related biases treated as nuisance parameters. These methods often are limited to 200 GPS receivers and use a sequential least squares or Kalman filter approach. The biases are later removed from the measurements to obtain unbiased TEC. In our approach to calibrating GPS receiver and transmitter interfrequency biases we take advantage of all available GPS receivers using a new processing algorithm based on the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This new capability is designed to estimate receiver biases for all stations. We solve for the instrumental biases by modeling the ionospheric delay and removing it from the observation equation using precomputed GIM maps. The precomputed GIM maps rely on 200 globally distributed GPS receivers to establish the ''background'' used to model the ionosphere at the remaining 800 GPS sites.Citation: Komjathy, A., L. Sparks, B. D. Wilson, and A. J. Mannucci (2005), Automated daily processing of more than 1000 ground-based GPS receivers for studying intense ionospheric storms, Radio Sci., 40, RS6006,

Solar radio bursts during December 2006 were sufficiently intense to be measurable with GPS receivers. The strongest event occurred on 6 December 2006 and affected the operation of many GPS receivers. This event exceeded 1,000,000 solar flux unit and was about 10 times larger than any previously reported event. The strength of the event was especially surprising since the solar radio bursts occurred near solar minimum. The strongest periods of solar radio burst activity lasted a few minutes to a few tens of minutes and, in some cases, exhibited large intensity differences between L1 (1575.42 MHz) and L2 (1227.60 MHz). Civilian dual frequency GPS receivers were the most severely affected, and these events suggest that continuous, precise positioning services should account for solar radio bursts in their operational plans. This investigation raises the possibility of even more intense solar radio bursts during the next solar maximum that will significantly impact the operation of GPS receivers.

Ionospheric total electron content (TEC) data derived from dual‐frequency Global Positioning System (GPS) signals from 30 globally distributed network sites are fit to a simple ionospheric shell model, yielding a map of the ionosphere in the northern hemisphere every 12 hours during the January 1–15, 1993 period, as well as values for the satellite and receiver instrumental biases. Root‐mean‐square (RMS) residuals of 2–3 TEC units are observed over the 20°–80° latitude band. Various systematic errors affecting the TEC estimates are discussed. The capability of using these global maps to produce ionospheric calibrations for sites at which no GPS data are available is also investigated.

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AB STRACTThe four-di men sional Global Assimilative Ion o spheric Model (GAIM) is ap plied to a study of ion o spheric dis tur bances. The in ves ti ga tion is fo cused on dis tur bance fea tures, par tic u larly in the al ti tude and lat i tude di men sions, at low lat i tudes dur ing a geo mag netic storm on 7 Au gust 2006, un der so lar min i mum con di tions. The mod el ing of storm-time ion o spheric state (elec tron den sity) is con ducted by as sim i lat ing an un prec e dented vol ume of line-of-sight TEC data col lected by the Global Po si tion ing Sys tem (GPS) occultation re ceiv ers on board six FORMOSAT-3/COS MIC sat el lites and geo detic-qual ity GPS re ceiv ers at two hun dred glob ally-dis trib uted ground track ing sta tions. With a band-lim ited Kalman fil ter tech nique to up date the ion o spheric state, the assimilative mod el ing re veals a pro nounced en hance ment in the equa to rial anom aly in the East Asia sec tor dur ing dusk and eve ning hours. The dis tur bance char ac ter is tics, ob tained by com par ing with the quiet con di tions prior to the storm also mod eled in this study through data as sim i la tion, in clude lifted F layer and re duced elec tron den sity in the equa to rial re gion, en hanced den sity at the mag net i cally con ju gate anom aly lat i tudes, and tilted fea ture of den sity in crease to wards higher al ti tudes at lower lat i tudes. The char ac ter is tics are at trib uted to the en hanced plasma foun tain ef fect driven by an en hanced east ward zonal elec tric field. These re sults en able us to dis tin guish the storm-time elec tric field per tur ba tions clearly from other sources dur ing the storm. The pos si ble origins of electric field perturbations are also discussed, including penetration of the magnetospheric electric field and wind dynamo disturbances. Ocean. Sci., 20, 273-285, doi: 10.3319/TAO.2008.01.04.01(F3C) IN TRO DUC TIONThe re cent de vel op ment of assimilative ion o spheric mod els marks a tran si tion from first-prin ci ples or for ward mod el ing to a new ca pa bil ity for spec i fy ing the Earth's ion ospheric weather. A fun da men tal dif fi culty of the for ward mod el ing ap proach is the spec i fi ca tions of the weather condi tions of re quired model driv ers, in clud ing the so lar EUV ra di a tion spec trum, elec tric field in the up per at mo sphere that drives plasma con vec tion, thermospheric com po si tion and wind, and charged par ti cle pre cip i ta tion. In tra di tional mod el ing prac tice these driv ers are pro vided ei ther by es timates ob tained from em pir i cal mod els that char ac ter ize statis ti cal pat terns, or from the first prin ci ples phys ics-based mod els. The re sults of such mod el ing ap proaches of ten deviate from the weather con di tions due to the sig nif i cant variabil ity of the driv ers. Assimilative mod els in cor po rate the first-prin ci ples mod els and op ti mi za tion mod ules, al low ing as sim i la tion of mea sure ments into the for ward mod els and help ing to bring the m...