Despite decades of academic research, space science remains a field full of unanswered questions. Ionospheric research, as a portion of space science, has its fair share of unanswered questions that have important implications for short-wave radio wave propagation. While average behavior of ionosphere is reasonably well understood and is reflected in empirical models, surprisingly large day-to-day variability in ionospheric parameters remains a topic of active research. Ionospheric disturbances can exist on a variety of temporal scales, from several minutes to multi-day, and cover vastly varying geographic regions, from several degrees in latitude/longitude to the entire hemisphere.  This presentation will discuss several types of ionospheric disturbances related to  geomagnetic storms, including positive and negative storm effects, SED (Storm Enhanced Density), and LSTIDs (Large-Scale Travelling Ionospheric Disturbances). It will also discuss ionospheric disturbances related to influences from lower atmosphere, including gravity waves and associated MSTIDs (Medium-Scale Travelling ionospheric Disturbances), thunderstorms, tides, and sudden stratospheric warmings. In addition to a variety of natural phenomena, ionospheric electron density and, consequently, radio wave propagation can be affected by human activity, for example by rocket or missile launches. As ionospheric system remains strongly undersampled by traditional observation methods, networks developed by amateur radio operators can provide critical information with a potential to advance physical understanding of near-Earth space environment.