Nonmigrating thermal tides, which do not move in synchrony with the Sun, are detected in the analyses of the First GARP Global Experiment (FGGE) Level IIIb data during the special observation period (SOP-1) of January 10, to February 9, 1979. The first is the westward moving diurnal mode, with the zonal wave number (m) 5 (f=-1, m=5), and the second is an eastward moving diurnal mode, with the zonal wave number 3 (f=1, m=3), where f is the frequency in day-1. These modes are closely related to wave number 4 of the topography at low latitudes and have clear peaks in the space-time power spectra in the sea level pressure field. A maximum value of 0.2 mbar is the same with both modes, as expected from theory, while maximum values of the background diurnal (f=-1, m=1) and semidiurnal (f=-2, m=2) migrating modes are 0.6 and 1.2 mbar, respectively. These nonmigrating modes are essentially the same ones that Tokioka and Yagai <1987> reported in their analysis of general circulation model (GCM) simulation in January. By comparing FGGE IIIb data analysis and the Meterological Research Institute (MRI) GCM-I simulation, diurnal (f=-1, m=1) and semidiurnal (f=-1, m=2) modes are simulated well in the sea level pressure field and relatively well at the lower troposphere in the geopotential field. The simulated nonmigrating modes have horizontal structures similar to those observed in the sea level pressure field, which are the most reliable data and are based on a large enough number of observations to detect these modes. In the geopotential field, horizontal structure of the nonmigrating modes is identified in the troposphere at low latitudes by simulation and observation. The wind data is also analyzed, but the correspondence between the simulation and observation is found only at the lowest level of the (f=-1, m=5) mode. ¿ American Geophysical Union 1989