[1] The EISCAT radar in Tromsø (67 cgmLat) has been used to estimate statistics of electromagnetic (EM) energy transfer rates by utilizing calculated electric fields, conductivities and E-region neutral winds. It was found that the magnetospheric EM energy input is slightly larger in the evening than morning sector, but due to winds, the Joule heating rate has the largest values in the morning sector. The duskside subauroral region contains large northward electric fields and is a site of significant magnetospheric EM energy input and Joule heating. For quiet conditions (Kp: 0-2 + ), the neutral wind is the major source for Joule heating at all MLT except at the evening maximum of magnetospheric EM input. For medium (Kp: 3 À -4 + ) and high (Kp ≥ 5 À ) activity levels, winds increase Joule heating rates in the morning, but decrease them in the evening. The positive contribution of winds during the morning maximum is 30% and 20% for medium and high activity levels, respectively. The region where winds are a net load for the magnetospheric EM energy input is 17-20 MLT for medium and 13-18 MLT for high activity conditions. The median EM energy transfer to mechanical work made on winds is 20% at maximum. An event with a long-lasting high electric field showed that the ion drag acting on neutrals can decrease the Joule (ion-neutral collisional) heating by more than 50%.Citation: Aikio, A. T., L. Cai, and T. Nygrén (2012), Statistical distribution of height-integrated energy exchange rates in the ionosphere,

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[1] The statistical properties of the altitude profiles of the different energy transfer rates in the auroral ionosphere are studied by using the European Incoherent Scatter radar measurements in Tromsø (67 ı cgmLat). Aikio et al. (2012) found that during active conditions, winds reduce the height-integrated Joule heating rates in the evening but enhance them in the morning. Here we show that the reduction in the evening takes place close to and above the peak altitude of Joule heating, so that the Joule heating peak descends from the Pedersen conductivity maximum at 120 km down to about 115 km. Values close to the peak are reduced also in the morning, but the positive effect by winds above the peak makes the net effect positive. The altitude range where the electromagnetic energy of magnetospheric origin is converted to the mechanical energy of the neutrals is only 20-35 km wide in the E region and shows a clear magnetic local time variation. Model calculations are made to study the effect of the angle between the wind and electric field directions on the energy transfer rates and to explain the observed features.

[1] A new method utilizing stochastic inversion in determining the electric field and neutral wind from monostatic beam swing incoherent scatter measurements is described. The method consists of two stages. In the first stage, beam-aligned ion velocities from a chosen F region height interval and a set of subsequent beam directions are taken as measurements. The unknowns are the two electric field components and the field-aligned ion velocity profile. The solution gives the most probable values of the unknowns with error estimates. In the second stage, the measurements consist of beam-aligned ion velocities from the E region, and the electric fields given by the first inversion problem are also used as measurements. The number of applied beam directions may be greater than in the first inversion problem. This is a feasible approach since the neutral wind usually changes more slowly than the electric field. The solution of the second inversion problem gives the most probable values of the three neutral wind components. Results of the method are shown for 11 September 2005, when the European Incoherent Scatter (EISCAT) UHF radar was running in the CP2 experiment mode, which is a four-position 6 min monostatic cycle. In addition, from each beam direction a tristatic measurement at one F region range gate was made using two additional receivers. That allowed comparison between the monostatic and tristatic electric field results, which were in excellent agreement. The calculated neutral wind components were in good accordance with previous measurements during disturbed conditions from the same site.Citation: Nygrén, T., A. T. Aikio, R. Kuula, and M. Voiculescu (2011), Electric fields and neutral winds from monostatic incoherent scatter measurements by means of stochastic inversion,

Abstract. The present standard EISCAT incoherent scatter experiments are based on alternating codes that are decoded in power domain by simple summation and subtraction operations. The signal is first digitised and then different lagged products are calculated and decoded in real time. Only the decoded lagged products are saved for further analysis so that both the original data samples and the undecoded lagged products are lost. A fit of plasma parameters can be later performed using the recorded lagged products. In this paper we describe a different analysis method, which makes use of statistical inversion in removing range ambiguities from the lag profiles. An analysis program carrying out both the lag profile inversion and the fit of the plasma parameters has been constructed. Because recording the received signal itself instead of the lagged products allows very flexible data analysis, the program is constructed to use raw data, i.e. IQsampled signal recorded from an IF stage of the radar. The program is now capable of analysing standard alternatingcoded EISCAT experiments as well as experiments with any other kind of radar modulation if raw data is available. The program calculates the ambiguous lag profiles and is capable of inverting them as such but, for analysis in real time, time integration is needed before inversion. We demonstrate the method using alternating code experiments in the EISCAT UHF radar and specific hardware connected to the second IF stage of the receiver. This method produces a data stream of complex samples, which are stored for later processing. The raw data is analysed with lag profile inversion and the results are compared to those given by the standard method.

Abstract. We present here the results of a statistical study of the ionospheric trough observed in 2003 by means of satellite tomography. We focus on the seasonal morphology of the trough occurrence and investigate the trough latitude, width and the horizontal gradients at the edges, at different magnetic local times, as well as their relations to geomagnetic activity and the interplanetary magnetic field. A seasonal effect is noticed in the diurnal variation of the trough latitude, indicating that summer clearly differs from the other seasons. In winter the troughs seem to follow the solar terminator. The width of the trough has a diurnal variation and it depends on the season, as well. The broadest troughs are observed in winter and the narrowest ones in summer. A discontinuity in the diurnal variation of the trough latitude is observed before noon. It is suggested that this is an indication of a difference between the generation mechanisms of morningside and eveningside troughs. The density gradients at the edges have a complex dependence on the latitude of the trough and on geomagnetic activity. The photoionization and the auroral precipitation are competing in the formation of the trough walls at different magnetic local times. An important finding is that the interplanetary magnetic field plays a role in the occurrence of the trough at different levels of geomagnetic activity. This is probably associated with the topology of the polar cap convection pattern, which depends on the directions of the IMF components B y and B z .

We describe the electrodynamics of a postmidnight, high‐latitude ionospheric trough, observed with the European Incoherent Scatter radar in northern Scandinavia on 24–25 June 2003 around 22:00–02:30 UT during quiet conditions. The UHF radar made meridian scans with a 30 min cadence resulting in nine cross sections of ionospheric parameters. The F region electric field was also determined with the tristatic system. Ionospheric equivalent currents, calculated from ground magnetometer data, mostly show an electrojet‐like current that is reasonably uniform in the longitudinal direction. Combined analysis of the conductances and equivalent current with a local Kamide‐Richmond‐Matsushita (KRM) method yields the ionospheric electric field and field‐aligned current (FAC) in a 2‐D (latitude‐longitude) area around the radar. We conclude that the most likely scenario is one where the trough is initially created poleward of the auroral oval by downward FAC that evacuates the F region, but as the trough moves to lower latitudes during the early morning hours, it becomes colocated with the westward electrojet. There the electron density further decreases due to increased recombination caused by enhanced ion temperature, which in turn is brought about by a larger convection speed. Later in the morning the convection speed decreases and the trough is filled by increasing photoionization.

Abstract. This paper presents binary phase codes and corresponding decoding filters which are optimal in the sense that they produce no sidelobes and they maximise the signal-tonoise ratio (SNR henceforth). The search is made by investigating all possible binary phase codes with a given length. After selecting the code, the first step is to find a filter which produces no sidelobes. This is possible for all codes with no zeros in the frequency domain, and it turns out that most codes satisfy this requirement. An example of a code which cannot be decoded in this way is a code with a single phase, i.e. a long pulse. The second step is to investigate the SNR performance of the codes. Then the optimal code of a given length is the one with the highest SNR at the filter output. All codes with lengths of 3-25 bits were studied, which means investigating 33 554 428 binary phase codes. It turns out that all Barker codes except the 11-bit code are optimal in the above sense. It is well known that the performance of matched-filter decoding of Barker codes is better than decoding without sidelobes. In the case of the 7-bit Barker code, it is shown here that the SNR given by sidelobe-free decoding is nearly 30% worse than that of standard decoding, but for the 13-bit code sidelobe-free decoding is only about 5% worse. The deterioration of SNR should be evaluated against the benefits gained in disposing of the sidelobes, which, even for the 13-bit code, contribute by 7.1% to the total signal power from a homogeneous target. Thus, regions of weak scattering can be contaminated by the sidelobes from neighbouring layers of strong scattering, causing broadening of thin spatial structures and giving a lower spatial resolution than implied by the bit length. A practical example is shown where sidelobes mask a weak signal when the standard matched filter is used in the analysis. An improvement is achieved when sidelobe-free filtering is carried out.