The winter nighttime ionosphere at L=4 reveals frequent increases in F region peak density (Nmax) accompanied by a constant or declining total electron content (TEC). This effect is examined statistically by using two winter periods of simultaneous TEC and Nmax data and 24 years of December f0F2 observations. The month of December 1971 was chosen for a detailed analysis. Two nights, December 9 and 15, were used in simulation attempts to identify the conditions needed to account for the increasing Nmax-constant TEC effect. For each case study, Isis 2 topside sounder Ne(h) interpolated data and Ne(h) profiles from ground-based ionosondes were combined with simultaneous TEC measurements to form a semiempirical computer model for Ne(h) versus latitude from h=0 to geostationary satellite height. The results indicate that vertical distortions of the Ne(h) profile over a wide latitude range are needed to reproduce the increasing Nmax-constant TEC effect. The mechanism causing these distortions is still poorly understood. It is suggested that substorm-enhanced westward electric fields induce a lowering of the F layer during which air drag effcts may permit a buildup of plasma at hmax before enhanced loss processes take over.