Some F2-layer effects during the January06-11,1997 cedar storm period as observed with theMillstoneHill incoherent scatter facility

Abstract

An observed daytime negative storm effect on 10 January and strongpost-midnight N m F 2 increases on 7 and 8 January followed by a steep T e decrease down to T n are analyzed. Daytime neutral composition and T n(h) were inferred from incoherent scatter (IS) radar observations using aself-consistent approach to F 2 -layer modelling. Observed daytime T e , T i , N e profiles were corrected for the disturbed day using the calculated ioncomposition. The main reason for the observed N m F 2 negative storm effectis the O/(N 2 O 2 ) ratio decrease in the thermosphere. The calculated O/N 2 ratio at hm F 2 is less by a factor of 3.7 than MSIS prediction for 10January and is close to MSIS for quiet days. Strong Nm F 2 night-time increase by afactor of 3 is due to a plasma compression mechanism under the action of observed EB drift(westward E-field) moving plasma from higher L shells to lower ones and squeezing it into the F 2 -region. Moderate (1-2)10 8 cm -2 s -1 O fluxes in agreement with IS observations were shown to be sufficient to account for the night-timeN m F 2 increase. This elevation in the F 2 -region electron densityis shown to be the main reason for the observed steep Te post-midnight decrease. 1999 ElsevierScience Ltd. All rights reserved.