The Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) has observed small- and meso-scale temperature fluctuations during a special limb-tracking operation. Analysis of late-December 1994 data shows that there exist significant radiance fluctuations with horizontal scales of 10's--100's km associated with upper tropospheric convection and the stratospheric polar vortex. Phase coherence and amplitude growth with height are observed, showing the presence of vertically propagating waves. Variance maps generated for the limb-tracking days further show that the MLS instrument can measure horizontal temperature variations at scales less than 100 km in both limb-scanning and limb-tracking observation modes. ¿ American Geophysical Union 1996