The normalized variance and power spectrum of the atmospheric scintillation has been measured above the Observatorio de Teide (Canary Islands), at 2400-m altitude, in the NIR atmospheric windows, J, H, K and L, using a 50-cm-aperture telescope. Observations were made between zenith distances 9 and 81 deg. The dependence on wavelength and air mass obtained agrees with the theoretical predictions of Tatarski (1961) and Reiger (1963). A possible distribution of the refractive index structure coefficient with height has been obtained, using a modified expression of Fried's (1967) exponential model that accounts for the contribution of the tropopause. This theoretical turbulence distribution and the experimental wind velocity data make it possible to predict correctly the observed stellar power spectrum. The bandwidth of the temporal frequency spectra has been also studied. The time scales were measured from the temporal autocorrelation functions, and their values range between 10 and 20 ms.