In this paper we discuss the e ects of several signal preprocessing methods for enhancing the Medium Scale Traveling Ionospheric Dis- turbances (MSTIDs) signal. The MSTIDs signal are the ionospheric signatures of waves with a typical scale variation from 50 to 300 m/s, which can be detected and modeled from variation of the ionospheric Vertical Total Electron Content (VTEC) with dual-frequency mea- surements of Global Navigation Satellite Systems (GNSS). In order to enhance the useful information of the signal, and also reduce the noise, we purpose the use of di erent numerical methods for preprocessing the MSTIDs signal. A rst approach to preprocessing the signal is a simple high-pass ltering or Slant Total Electron Content (STEC) detrending of the ionospheric carrier phase LI [see Hernndez-Pajares et al. 2006, Hernndez-Pajares et al. 2012]. In this work, we propose the following signal processing steps in order to enhance the signal: (1) Parabolic subtraction adopted in eliminating the typical geometric length variation within the ionosphere carrier phase LI, (2) decima- tion techniques used to instead of classic STEC detrending method, (3) low pass ltering adapted to the properties of the desired signal. From the results by testing the observing data on the day 1, 2011 obtained from the small area GNSS network in California, it's shown that the MSTIDs signal after preprocessing techniques are more clear, smooth and robust.