New results of the measurements of the atmospheric temperature and density at heights of about 100 km in the summer seasons of 1999-2002 near Nizhny Novgorod (φ = 56.15oN, λ = 44.3oE) are presented. The measurements on 10-12 August 1999 include the period of a solar eclipse. In summer of 2000 and 2001 the measurements were conducted during the sunrises and sunsets. The measurements were conducted by the method of Bragg backscattering at artificial periodical irregularities of the ionospheric plasma. In the sunrise and sunset periods a propagation of internal gravity waves with periods of 15-60 min, and temperature and density amplitudes of 0.04-0.14 and ~0.12, respectively, was detected. The variations in the temperature vertical profile in the absence of wave perturbations confirm the existence of a temperature minimum near 100 km.