Analysis of GPS phase fluctuations in conjunction with regional total electron content (TEC) maps, in situ measurements of subauroral polarization streams (SAPS) and auroral convection from several Defense Meteorological Satellite Program spacecraft, and dynasonde measurements at the Bear Lake Observatory obtained during the intense magnetic storm of 7–8 November 2004 have indicated the serious impact of large ionospheric velocities on GPS‐based navigation systems within the midlatitude region in the North American sector. The major difference between this superstorm and the others observed during the earlier October‐November 2003 events is the absence of appreciable storm‐enhanced density gradients, with the midlatitude region being enveloped by either the auroral oval or the ionospheric trough within which the SAPS were confined during the local dusk to nighttime hours. This shows that it is possible to disable GPS‐based navigation systems for many hours even in the absence of appreciable TEC gradients, provided an intense flow channel is present in the ionosphere during nighttime hours. The competing effects of irregularity amplitude ΔN/N, the background F region density, and the magnitude of SAPS or auroral convection are discussed in establishing the extent of the region of impact on such systems.

A description, history and the capabilities of an ionospheric sounder in the auroral zone near Tromsø, Norway are presented, together with some scientific applications. The sounder, which is of the dynasonde type, has provided a data set which has improved dramatically in quantity, quality and information content. A similar sounder is planned to be installed in the polar cap near Longyearbyen on Spitsbergen.

The problem of electron density inversion of digital ionograms is reconsidered from the viewpoints of new possibilities and of modern requirements. The data processing system of an advanced ionosonde (the dynasonde) provides accurate measurements not only of echo group range but also of direction of arrival, among other physical parameters, thus yielding the three‐dimensional distribution of apparent echolocations in each ionogram recording. An iterative ray‐tracing approach is described here to recover the parameters of a quite sophisticated three‐dimensional (so‐called wedge‐stratified ionosphere) model of the local electron density distribution, characterizing its actual vertical Ne(h) profile together with horizontal gradients and general tilts. The power of a contemporary PC is sufficient to accomplish this analysis quickly. This approach is implemented in the algorithm introduced here, is named “NeXtYZ,” and is pronounced “next wise.”

We consider VHF amplitude scintillations, GPS phase fluctuations, ionosonde measurements, maps of GPS total electron content (TEC), observations of daytime aurora and TIMED GUVI images during the large magnetic storms of October 29–31, 2003, and find two distinct classes of plasma processes that produce midlatitude ionospheric irregularities. One is associated with auroral plasma processes; the other, with storm enhanced density (SED) gradients, a part of which occur in close proximity to sub‐auroral polarization stream (SAPS) electric fields as discussed by J. C. Foster et al. (2002). We analyze in detail the storm event of October 30, 2003. The SAPS‐associated plasma structures may occur by an ion temperature gradient convective instability (M. J. Keskinen et al., 2004), but structuring by auroral processes requires elucidation.

Because the ionospheric plasma drifts, radio sounding signals encounter different irregularities of electron density, even at only slightly different times, causing temporal phase variations; these may be characterized conveniently by the structure function. We have proposed in several recent publications a new irregularity diagnostic method based on this effect, and it is now useful to consider the range of irregularity scales affecting the observed phase fluctuations. We show, in particular, that for the two‐dimensional irregularity power spectrum index 2 < ν < 3 (quite typical for the ionosphere) the phase structure function value at the smallest available lag (0.01 s) is sensitive to irregularities in a broad range of scales, between several meters and several kilometers.

Properties of radio wave reflection from an optically thick, plane monotonic layer of ionospheric plasma with random density irregularities are considered by investigating numerically the influence of multiple scattering on the angular distribution and the integral intensity of the reflected signal. We use an improved solution of the radiative transfer equation in the approximation of small‐angle scattering in invariant ray coordinates (“SASIRC”). The case of midlatitude ionosphere conditions is treated in most detail, but some conclusions about latitudinal dependence are also obtained, for both vertical and slightly oblique sounding cases. Conclusions from earlier versions of the theory showing a strong anomalous‐attenuation effect are confirmed, with adjustments of the quantitative results. We describe a special amplitude calibration procedure for estimation of anomalous attenuation in practical experiments using dynasonde techniques, and discuss the application of our results to an explanation of ionogram spread F.

Summary The theory of multiple scattering of MF/HF radio waves by intermediate-scale (0.1-2 km) ionospheric irregularities in the course of near-normal incidence reflection, as developed earlier by the authors [1,2], predicts significant reduction of the integral intensity of a signal reflected from the ionosphere in the vicinity of a ground-based transmitter (several tens of kilometers), followed by an enhancement at a greater distance. This effect is measurable using pulsed radar signals and a mobile setup comprising a digital receiver, a controlling laptop computer, and a GPS receiver. We report the first results of the experiment and of a related theoretical development. References 1. Zabotin N.A., A.G. Bronin, and G.A. Zhbankov, “The Radiation Transfer at a Layer of Magnetized Plasma With Random Irregularities,” Waves in Random Media , 8 , 1998, p. 421-436. (http://stacks.iop.org/WRM/8/421). 2. Zabotin N.A., J.W. Wright, and E.S. Kovalenko, “Multiple scattering effects in ionospheric radio sounding,”

We address the need for an easily observable indicator of thermospheric state, and particularly one sensitive to the neutral concentration ratio, [O]/[N2]. Accepting foF2 as the observable of choice, several options for a derived thermospheric daily index are considered; these include midday and nighttime mean values of foF22, and others based on the rate of change of foF22 during sunrise, which might serve as indicators of [O]/[N2]. We show the global morphology of a promising sunrise index over more than three solar cycles, derived from data in the National Geophysical Data Center Ionospheric Digital Database (NGDC/IDD) and similar databases. There are well‐defined dependencies on solar activity, season, geography, and storm‐disturbance level. We compare the indices to ESRO4 satellite global observations of [O]/[N2] and find correlation coefficients as low as 0.3 (southern winter) and as high as 0.8 (close passes, all data), depending upon hemisphere and season, satellite/ground‐site proximity, satellite altitude, etc. Using median foF22 to compare our sunrise index to the Mass Spectrometer‐Incoherent Scatter (MSIS‐90) model atmosphere at a constant pressure level, we find similar latitude variations in three longitude sectors and two solar cycle extremes. A successful index of [O]/[N2], available daily from monitoring ionosondes (and perhaps from Global Positioning System. Total Electron Content (GPS/TEC) monitors, derived similarly), would have important applications in aeronomy, space weather, and telecommunications forecasting.

We show that ubiquitous small conducting particles of meteoric origin in the mesosphere and stratosphere may explain some features of sprite occurrence and fine structure. The main processes involved are: electrostatic field amplification by microspires on the dust surface, “cathode‐like instability” in their vicinity, autoemission and explosive emission of electrons. Additional observations, theoretical development and perhaps laboratory experiments are warranted.

We present a new approach to investigating ionospheric irregularities, using the temporal structure function of totally reflected radio echo phase variations. Modern digital ionosondes (e.g., the dynasonde) measure the echo phase with very high resolution and precision, at closely spaced antennas, frequencies, and times. A “stringing” procedure gives continuous and unambiguous phase variation data for time intervals of any desired length. Quasi‐periods of tens of seconds up through several minutes are caused by large‐scale movements of the ionospheric plasma, while shorter‐period phase variations result from the interaction of the sounding signal with small‐scale irregularities. The relevant irregularity spatial domain extends from decameter radio wavelengths to the first Fresnel scale, a few kilometers. We obtain a theoretical relation between structure functions of the temporal phase variations and spatial irregularities with a simple model of frozen horizontal drift. The relation permits solutions of both the direct and inverse problems. Although long‐period phase measurements are practicable and essential to exploring larger irregularity scales, they require observing modes dedicated to multiple fixed‐frequency time series, and this undesirably limits the number of altitudes that can be monitored simultaneously. An alternative “rudimentary structure function” is obtainable from standard dynasonde “B‐mode” ionograms; it offers good altitude and time resolution for irregularity studies while permitting other established diagnostics (electron density profiles, vector velocities, critical frequencies, etc.) with the same data. We show some example analyses by these methods as applied to auroral and magnetic‐equatorial dynasonde observations. We find irregularity amplitudes in the range 0.001 < ΔN/N < 0.1 (for a nominal scale of 1 km) and spectral indices in the range 2 < v < 4, with evidence of diurnal variation in both quantities at both locations.

Modern ionosondes make almost simultaneous measurements of the time rate of change of phase path in different directions and at different heights. By combining these ‘Doppler’ measurements and angles of arrival of many such radar echoes it is possible to derive reliable estimates of plasma drift velocity for a defined scattering volume. Results from both multifrequency and kinesonde-mode soundings at 3-min resolution show that the Dynasonde-derived F-region drift velocity is in good agreement with EISCAT, despite data loss during intervals of ‘blanketing’ by intense E-region ionisation. It is clear that the Tromsø Dynasonde, employing standard operating modes, gives a reliable indication of overall convection patterns during quiet to moderately active conditions.

The arithmetic mean, and sample variance, are the most common summary statistics of a data set. There are circumstances (within computational loops, and in real-time data analysis, for examples) where it is desirable to maintain a current estimate of the mean and variance. The ''lossy'' (sometimes called the ''running'') mean and variance are frequently useful also. We present an algorithm for these applications, and show the provisions necessary for use with cyclical (e.g. phase-angle) data.

Incoherent-scatter radar and ionospheric sounding are powerful and complementary techniques in the study of the Earth's ionosphere. The work presented here involves the use of the Tromsø Dynasonde as a correlative diagnostic with the EISCAT incoherent-scatter radar. A comparison of electron-density profiles shows how a Dynasonde can be used to calibrate an incoherent-scatter radar and to monitor changes in the system. Skymaps of the direction of Dynasonde echoes are compared with EISCAT-derived density profiles to illustrate how a Dynasonde can be used to measure the drift velocity of auroral features. Vector velocities fitted to Dynasonde echoes are compared with EISCAT-derived plasma velocities. The results show good agreement when the data are taken during quiet to moderately active conditions and averaged over time scales of 30 min or more.

Oestrogen replacement therapy has been shown to protect postmenopausal women from ischaemic heart disease, strokes and hypertension. The mechanism of protection conferred by oestrogen, although partly attributable to changes in serum lipoproteins, is not fully understood. The present study was undertaken to assess the effect of hormone replacement therapy on the composition of platelet membrane fatty acids in postmenopausal women. These were analysed by gas-liquid chromatography before and six weeks after continuous conjugated equine oestrogen therapy (0.625 mg daily) combined with cyclical therapy with 75 micrograms L-norgestrel from day 17 to 28 of a 28-day cycle. Each subject acted as her own control. The principal findings of the study were that, following treatment, there was a 16.2% reduction in platelet membrane polyunsaturated fatty acids (P < 0.001), an increase of 9.1 and 7.1% in saturated fatty acids and monounsaturated fatty acids respectively (P < 0.001) and a 17.8% reduction in arachidonic acid (P < 0.003). There was no correlation between changes in membrane fatty acids and serum lipoproteins. This suggests that the changes in membrane composition noted in this study may be a primary effect of hormone replacement therapy, especially oestrogen.

The use of a 35 mm or similar camera set up over a theodolite is described for surveying mountain and polar glaciers where conditions do not allow for extensive detailed surveying or the use of heavy phototheodolites. Though used initially by Spender and Wright in the 1930s on Mount Everest and in Greenland and Arctic Canada, but apparently not by others since then, it was again tried out by Wright in Iceland in 1992. Modern analytical techniques have shown that heights accurate to within 2 m can be obtained from these photographs at distances up to 5 km. In addition, five times as many points can be identified and intersected in the laboratory from the photographs as was possible using sketches in difficult field conditions. Some reasons are suggested for the lack of use of this technique by others. The potential of existing survey photographs taken in Arctic Canada for large scale surveys of high polar glaciers in 1938 is described, with the hope that glaciologists and photogrammetrists might undertake their analysis.

Esq echo intensities recorded by a dynasonde system operated at Huancayo, Peru, are used to estimate the scattering cross section of equatorial electrojet plasma irregularities in the 3 to 7 MHz frequency band. The scattering radar cross section of vertically propagating ∼20‐m scale electrojet irregularities is estimated as ∼3×10−7 m−1 over a period exhibiting ƒ0E values of 2.7 to 2.9 MHz. The cross‐section variation with Bragg wavenumber k is found to be characterized with a power law index of approximately −3 over the HF band.

Apart from spread F and some forms of sporadic E, little attention is usually paid to the variable occurrence of ''chaotic'' or disordered ''scatter'' in ionosonde measurements. In contrast to the echoes of broad radio bandwidth and high amplitude from the plane-stratified ionosphere, for which total internal reflection is unmistakably applicable, the processes responsible for occasional scattering are not obvious. With the multiparameter information of a digital ionosonde it should be possible to develop criteria by which the echoing processes can be decided, if not on an echo-by-echo basis, at least for groups of echoes that bear similar properties. The distinction is important since these chaotic echoes may be identified with significant physical processes, whereupon the ionosonde becomes one of their more powerful diagnostics. Three examples illustrate these points; they arise in consequence of (1) the (magnetic) equatorial electrojet; (2) some suggested neutral-atmosphere interactions near sporadic E at mid latitudes; and (3) the auroral electrojet, respectively.

The accuracy and efficiency with which radio echo parameters may be estimated by a programmable ionosonde of high resolution depend upon software‐designed strategies of pulse set design and receiving antenna layout. All of the echo parameters, except amplitude and time of arrival (thus three components of echolocation, Doppler, polarization rotation, and an average phase angle) are determined by phase angle differences. The solution is conveniently expressed as a least squares estimation, provided that more than six independent phase measurements are available. Since the observed phases are necessarily obtained modulo 360°, from 12‐bit complex amplitude data, each parameter is subject to aliasing ambiguities which must be anticipated in each strategy, and minimized.