This derived product set consists of Global Navigation Satellite System a Ionosphere Vertical Total Electron Content (VTEC) fluctuation measurement product (daily files) from the NASA Crustal Dynamics Data Information System (CDDIS). GNSS provide autonomous geo-spatial positioning with global coverage. GNSS data sets from ground receivers at the CDDIS consist primarily of the data from the U.S. Global Positioning System (GPS) and the Russian GLObal NAvigation Satellite System (GLONASS). Since 2011, the CDDIS GNSS archive includes data from other GNSS (Europe’s Galileo, China’s Beidou, Japan’s Quasi-Zenith Satellite System/QZSS, the Indian Regional Navigation Satellite System/IRNSS, and worldwide Satellite Based Augmentation Systems/SBASs), which are similar to the U.S. GPS in terms of the satellite constellation, orbits, and signal structure. GNSS observations from a global network can be utilized for atmospheric measurements. Analysis Centers (ACs) of the International GNSS Service (IGS) retrieve GNSS data on regular schedules to produce independently computed VTEC maps. These fluctuations in TEC consists of a rate of TEC change index (ROTI) maps which are constructed with the grid of 2 degrees by 2 degrees resolution as a function of the magnetic local time and corrected magnetic latitude. GNSS data are used to determine ROTI maps, the standard deviation of rate of TEC change over a specified time span; ROTI can be used to describe irregularities in the ionosphere.