An ionospheric bubble is first modeled based on in situ data measured on board a satellite. The effect such a bubble may have on radio signals propagating through it is next simulated by solving numerically a parabolic equation. Considerable pulse distortion is found. When the computational technique is applied to a frozen but moving bubble, these results imply that the pulse excess arrival time, the pulse width, and its skewness will fluctuate with time, leading to the pulse jitter problem often observed experimentally.