[2] The longitudinal variations in the height of the midlatitudinal ionospheric F2 layer in both hemispheres for summer midnight conditions were revealed and studied in detail using the data of the topside sounding onboard the Intercosmos 19 satellite [Deminov and Karpachev, 1988; Karpachev and Gasilov, 1998]. Using theoretical models of the ionosphere [Ben'kova et al., 1986; Buonsanto et al., 1989; Miller et al., 1997; Rishbeth, 1967; Rishbeth et al., 1978], the variations in the plasma vertical drift velocity, W, induced by the neutral wind were derived from the longitudinal variations in hmF2. Then, applying the empirical model of the thermosphere Mass Spectrometer Incoherent Scatter (MSIS), the contributions of the neutral wind, composition and temperature into the longitudinal effect (LE) were estimated [Karpachev and Gasilov, 1998]. Since the reliability of the repeatedly tested ionospheric models and MSIS model is beyond any doubt [see Titheridge, 1995], one can believe in reliability of the estimates of the contributions obtained on the basis of these models. Further, the problem of a determination of the contributions of both components of the neutral wind (zonal and meridional) was formulated [Karpachev and Gasilov, 2000, 2001]. It turned out that for the classical solution of this problem, the availability of hmF2 measurements in the both coordinate systems (geomagnetic and geographic) and some additional physical assumptions are required. To overcome these difficulties, the Tikhonov regularization method [Tikhonov and Arsenin, 1986] was used. The approach developed on the basis of this method makes it possible to determine fairly accurately the meridional component of the neutral wind and much less reliably to determine the zonal component. In this paper we try to apply the developed approach to the analysis and evaluation of the contribution of various factors into the longitudinal and latitudinal variations in the height of the summer nighttime F2 layer in a broad belt of latitudes from middle to auroral ones. To estimate the contribution of the zonal component and to compare with the calculations, the neutral wind model Horizontal Wind Model (HWM) [Hedin et al., 1991] is used.
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