Some F-2-layer effects during the January 06-11, 1997 CEDAR storm period as observed with the Millstone Hill incoherent scatter facility

An observed daytime negative storm effect on 10 January and strong post-mid night NmF2 increases on 7 and 8 January followed by a steep T-e decrease do wn to T-n are analyzed. Daytime neutral composition and T-n(h) were inferre d from incoherent scatter (IS) radar observations using a self-consistent a pproach to F-2-layer modelling. Observed daytime T-e, T-i, N-e profiles wer e corrected for the disturbed day using the calculated ion composition. The main reason for the observed NmF2 negative storm effect is the O/(N-2 + O- 2) ratio decrease in the thermosphere. The calculated O/N-2 ratio at h(m)F( 2) is less by a factor of 3.7 than MSIS prediction for 10 January and is cl ose to MSIS for quiet days. Strong NmF2 night-time increase by a factor of 3 is due to a plasma compression mechanism under the action of observed E x B drift (westward E-field) moving plasma from higher L shells to lower one s and squeezing it into the F-2-region. Moderate (1-2) x 10(8) cm(-2)s(-1) O+ fluxes in agreement with IS observations were shown to be sufficient to account for the night-time NmF2 increase. This elevation in the F-2-region electron density is shown to be the main reason for the observed steep T-e post-midnight decrease. (C) 1999 Elsevier Science Ltd. All rights reserved.