[1] The Sun's Bastille Day flare on July 14, 2000 produced a variety of geoeffective events. This solar eruption consisted of an X-class flare followed by a coronal mass ejection that produced a major geomagnetic storm. We have undertaken a study of this event beginning with an analysis of the effects of the radiative phase of the flare on the dayglow and the ionosphere. The key new enabling work is a novel method of evaluating the X-ray and extreme ultraviolet (EUV) solar spectral irradiance changes associated with the flare. We find that the solar radiative output enhancements modeled during the flare are consistent with measurements of both solar EUV irradiance and far UV Earth thermospheric dayglow. We use the SAMI2 model to predict global ionospheric changes along a magnetic meridian that show significantly different northern and southern effects, suggesting that flares can be used to study ionospheric dynamics.

Abstract. We present a technique for using the measured variations of ultraviolet emissions produced by radiative recombination at 911 and 1356 • to determine the nighttime altitude distribution of F region O + ions and electrons. The algorithm uses an iterative scheme based on discrete inverse theory to determine the best fit to the data. We present the results of simulations that demonstrate the convergence properties of the algorithm and the fidelity with which it reproduces the input ionosphere. The algorithm was tested against more realistic simulated "data" generated using the international reference ionosphere (IRI-90) [Bilitza, 1990]. The algorithm accurately retrieved the nighttime F region electron density at midlatitudes (_+25ø-65øN) over a wide range of solar and geomagnetic activity and local time.

Abstract. A series of campaigns has been carried out in the Caribbean over a one-year period to study intense midlatitude spreaA-F events using a cluster of diversified instrumentation. These events are relatively rare but a number of them have now been captured and will be discussed in this and several companion papers. This paper focuses on 630 nm airglow images obtained by the Cornell All-Sky Imager for two of the more spectacular cases that began on February 17, 1998 and February 17, 1999. In the latter case, and for the first time, a poleward surge of depletion/enhancement airglow zones was captured by radar as well as an airglow imager. In the former case structures grew in place overhead and produced strong VHF F-region backscatter as observed by the CUPRI and University of Illinois radars; the other event, exactly one year later, did not result in detectable 3-m backscatter. The two data sets show quantitatively that the low airglow region is elevated in height and depleted in plasma density and Pedersen conductivity. We suggest an enhanced eastward electric field inside the low conductivity zone may be responsible for the surge. The data also suggest small scale turbulence can only be observed in developing structures.

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[1] We present our observations of the global ionospheric response to the X-class solar flare that started the Bastille Day storm on 14 June 2000. The observations were made using the Low-Resolution Airglow and Aurora Spectrograph (LORAAS) instrument on the Advanced Research and Global Observation Satellite (ARGOS). The ARGOS is in a Sun-synchronous orbit at 0230/1430 LT at approximately 840 km altitude. During the daytime the LORAAS observes the 911-Å emission; this emission is produced by radiative recombination of F region O + and electrons. We simultaneously invert approximately one-half of an orbit of 911-Å limb scans (approximately 30-45 min of observing) using a tomographic inversion technique to produce dayside electron density maps in the orbit plane. We compare our observations of orbits immediately before and after the flare to the orbit in which the flare occurred. We observed a 41% increase in the average 911-Å brightness during the flare orbit compared to the orbits before and after the flare. This corresponds to an overall increase of electron density by $20%. This density enhancement has largely decayed by the next orbit. At altitudes near the F region peak, 250-450 km, the density enhancement has decayed to the preflare value. An enhancement of the electron densities at approximately À50°geomagnetic latitude has moved northward in the flare orbit, which may be indicative of enhanced meridional transport postflare. We compared our results to output from the SAMI-2 model, which was run for the flare study presents in the work of Meier et al. [2002].