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Diurnal changes in F2 ionization distribution as measured during June and July 1966 over the Tamanrasset meridian reveal two types of asymmetric phenomena distorting the crest-and-trough system (formerly known as the equatorial F2 ionization anomaly). The first type corresponds to a general time variation of the latitude asymmetry. Our observations yield four independent parameters of this asymmetry; for 80% of the time, the variation can be attributed to ion drag due to a time-varying meridian air wind. Magnetic activity is correlated with the amplitude of this wind, and the low-altitude thermospheric circulation is discussed. Day-to-day fluctuations of the diurnal evolution pattern suggest a possible long-term control of the equatorial electric field by the general dynamo current system. A second type of asymmetry shows more intense, local, and short-lived phases superimposed on the fountain and neutral wind fluctuations. It has the character of a transitory forced-diffusion process. We believe that the factor responsible is electron temperature gradients produced by conjugate photoelectron heating.