This paper investigates the small scale plasma structures observed by ROCSAT‐1 in the equatorial F region through the newly developed Hilbert‐Huang transform (HHT) method in the time (space) domain under the frozen‐in approximation. The new method allows us to decompose the non‐stationary, nonlinear data into a finite number of intrinsic scale modes. In this report the structures of vertical ion velocity and horizontal density gradient inside a plasma bubble are analyzed mode by mode anatomically without making the usual linearization assumption. We found that the intrinsic modes for velocity and density gradient of the selected event have identical wave form for structures with scales between 300 m and 50 m. This implies that the vertical velocity fluctuations induced from the electric field follows the exact Boltzmann relation in the limited regime of scale length between 300 m and 50 m. A spectral break at 50 m is clearly seen in the velocity HHT spectrum. The spectral form of velocity differs greatly from that of density gradient at scale lengths shorter than 50 m.

Wind fluctuations observed by the MST radar technique often show complicated temporal behavior. Waves with different periods may occur at different times. Conventional fast Fourier transform (FFT) analysis will not be able to follow the temporal evolution of the wave spectrum. Multiscale, multiresolution wavelet analysis proposed in this paper is quite useful to study this transient behavior of the waves. A complex Gabor wavelet with a few cycles of monochromatic waves is chosen as the wavelet base, and this choice leads to successful results for gravity‐wave like wind disturbances observed by MST radar in the troposphere. Possible interpretations in terms of nonlinear wave‐wave or wave‐mean flow interactions are proposed.