Solar thermal tides are dominant global-scale oscillations in temperature, density, and winds whose periods are integral fractions of a solar day in the middle and upper atmosphere. They can be excited by the absorption of solar radiation from tropospheric water vapor and stratospheric ozone, latent heat release of deep convective system, as well as nonlinear interactions between tides and planetary waves. Tides generated from the lower atmosphere can propagate upwards and deposit their energy and momentum in the upper atmosphere during dissipation process and induce profound effects on the ionosphere and thermosphere. Present estimates are that atmospheric waves (including tides, planetary and gravity waves) from the lower atmosphere contribute on average roughly the same amount of energy to the upper atmosphere as forcing from above does during geomagnetic quiet conditions and medium solar conditions. Accurate forecasting of space weather requires a better understanding of the temporal and spatial variability of these waves. This talk reviews the complex picture of atmospheric tides in our atmosphere, their inter-annual, seasonal, day-to-day variability and how they affect the ionosphere and thermosphere.