Thermospheric wind measurements with EISCAT

Thermospheric wind measurements with the EISCAT UHF radar around the evening Harang discontinuity are presented both in the E- and F-layers. Within the E-layer auroral oval the Lorentz and Coriolis force are shown to be more or less in balance. The neutral velocity is a factor of the order of two smaller than the ion velocity and is on average advanced 90° in a clockwise direction compared to the ion velocity. In the low electron density region just before the Harang discontinuity and outside the auroral oval a large (~250 m s⁻¹), thermally dominated neutral wind is closely followed by the ion wind in the antisolar direction. There is also a large downward flow present just before the Harang discontinuity. In the F-layer the neutral wind approximately follows the ion convection pattern, except for a couple of hours after the sudden change in the ion convection just after the passage of the evening Harang discontinuity. The close resemblance between the equilibrium ion and neutral flow when the neutral-ion collision frequency is close to twice the Earth's angular velocity may be connected to back pressures created by Joule heating in the case of an appreciable ion-neutral velocity difference.     

Neutral wind measurements over Waltair using meteor wind radar

A coherent pulse Doppler Radar System at Waltair (17°43′N, 83°18′E) has been used to measure neutral winds in the altitude range 80–110 km. Preliminary results obtained during July and August 1979 are presented. The diurnal component is found to be the dominant tidal mode for most of the time. The results are compared with meteor wind observations at other stations.     

Summertime stratospheric wind measurements above the South Pole

Observations of the mean wind flow and wave motions in the stratosphere at the South Pole are presented. The atmospheric motions are determined from the tracking of a high altitude, zero-pressure balloon launched from Amundsen-Scott Station during the austral summer of 1985–1986. The balloon position was precisely monitored by an optical theodolite for a large portion of the flight so that small scale motions could be resolved. The mean flow above the pole was approximately 3ms⁻¹. Atmospheric motions characteristic of internal gravity waves were observed with an intrinsic period of approximately 4.5 h and vertical and horizontal wavelengths of approximately 2.5km and 125km, respectively. The horizontal perturbation velocity of the observed waves was large compared to the mean horizontal flow velocity. The implication is that wave motions play a dominant role in the transport of stratospheric constituents in regions where the mean winds are light, such as over the South Pole during austral summer.     

Vertical neutral wind in the equatorial F-region deduced from electric field and ion density measurements

DC electric field and ion density measurements near density depletion regions (that is, equatorial plasma bubbles) are used to estimate the vertical neutral wind speed. The measured zonal electric field in a series of density depletions crossed by the San Marco D satellite at 01.47-01.52 UT on 25 October 1988, can be explained if a downward neutral wind of 15–30 m s⁻¹ exists. Simultaneously, the F-region plasma was moving downward at a speed of 30–50 m s⁻¹ These events appear in the local time sector of 23.002̄23.15 in which strong downward neutral winds may occur. Indeed, airglow measurements suggest that downward neutral velocities of 25–50 m s⁻¹ are possible at times near midnight in the equatorial F-region.     

Ionospheric modification experiments in northern Scandinavia

The heating facility at Ramfjordmoen near Tromsø, Norway, is briefly described, and a survey is given of the experiments performed with this facility until now. These experiments comprise D-region modification, polar electrojet modulation at VLF, ELF and ULF, HF absorption and backscatter due to short-scale field-aligned irregularities, stimulated radio wave emission of the modified ionospheric plasma, short-time scale HF absorption due to the parametric decay instability, airglow modification, excitation of large-scale irregularities, and F-region cross modulation.     

Ionospheric plasma convection in the southern hemisphere

The first ionospheric plasma convection maps ordered by the y- and z-components of the IMF using only data from the southern hemisphere are presented. These patterns are determined from line-of-sight velocity measurements of the Polar Anglo-American Conjugate Experiment (PACE) located at Halley, Antarctica, with the majority of the observations coming from 65°–75° magnetic latitude. For IMF Bz positive and negative conditions, the observed plasma motions are consistent with a standard two cell pattern. For the periods from dusk through midnight to dawn, flow speeds are at least twice as large for Bz negative component compared with Bz positive. The observations about noon are significantly different from each other. For Bz positive, little ordered plasma motion is observed. For Bz negative, there are large anti-sunward flows the orientation of which is ordered by IMF By. These By orientated flows are consistent with theoretical predictions, and are anti-symmetric to those reported from the northern hemisphere. The two most significant differences from previous observations are that the convection reversal in the late morning sector for By negative conditions occurs at about a 4° lower latitude than the Heppner and Maynard (1987) model. This may be due to a seasonal bias in the PACE dataset. Also, the separatrix between eastward and westward flow near midnight has a very different shape dependent upon the orientation of IMF By. For positive By conditions, the separatrix is observed at progressively lower latitudes at later local times, but for By negative conditions, the separatrix appears at increasingly higher latitudes at later times.     

Ionospheric changes in response to IMF variations

This paper attempts to summarize the results of investigations of IMF effects on the ionosphere, published mostly in Russian, and to place them in context in up-to-date knowledge of IMF/magnetosphere/ionosphere relationships. Effects of the IMF sector structure and of the IMF B_z component turnings on the ionospheric F-layer are considered, including variations of position of the main ionospheric trough (MIT). The paper includes results of both theoretical calculations and observational data obtained mostly by the Cosmos-900, Intercosmos-19 and Cosmos-1809 satellites at subauroral, middle and low latitudes. The MIT position dependence on longitude has been derived as a background for further study. It has been shown that the nightside winter trough position at the storm growth phase correlates best with K_P index taken with a time delay τ, which is proportional to a disturbance growth rate ΔK_p/Δt. The MIT position dependence on D_st, B_z and B_y is also shown. Two troughs have been found to be formed usually in the storm recovery phase at postmidnight hours: these are the MIT (main ionospheric trough) and RIT (ring ionospheric trough) associated with the DR-current. In general the MIT position's response to B_z southward turnings corresponds well to changes of the amoral diffuse precipitation equatorial edge. For B_z southward turnings the height of the equatorial night-time F-layer lowers, and at equatorial latitudes f_oF2 decreases sharply, the latter effect being most pronounced at 03 LT. Large-scale internal gravity waves arriving at equatorial latitudes from the auroral oval cause intensification of the equatorial anomaly, both in daytime and night-time. A schematic pattern of a global ionospheric response to a magnetic disturbance is constructed using as an example the strong storm on 3–4 April 1979.     

Some aspects of Doppler radar measurements of the mean and fluctuating components of the wind field in the upper middle atmosphere

The basic assumptions made when a Doppler radar is used to measure the mean and fluctuating components of the wind field in the middle atmosphere with various beam configurations are examined. Particular reference is made to the measurement of the various components of the Reynolds stress tensor associated with short period internal gravity waves. It is shown that it is not generally possible to measure the upward flux of horizontal momentum with the conventional Doppler radar beam configuration in the upper middle atmosphere and that an optimum beam configuration is that in which beams are directed at +θ,0 and − θ to the zenith in both the zonal and meridional planes. This allows five of the six components of the Reynolds stress tensor (all those except the horizontal transport of momentum) to be obtained directly from the mean square radial velocities. In addition, the mean wind components and, in principle, the horizontal divergence and stretching deformations may be obtained. The power spectrum of the horizontal velocity may also be calculated using only the assumption that the statistics of the motions are horizontally homogeneous.     

Ionospheric F2-kegion storms at midlatitudes starting in the daytime and the night-time

Disturbances in the F2-region during geomagnetic storms have been studied statistically, using foF2 data for two midlatitude stations in Japan. It is found

• 1.(i) that during the initial stage of the storm foF2 increases on the average for storms starting in the daytime and decreases for storms starting in the night-time, in all seasons,
• 2.(ii) foF2 decreases in summer and at the equinoxes and increases in winter irrespective of the local time of the storm onset.
• 3.(iii) disturbances of foF2 in winter for storms starting in the night-time are larger than those for storms starting in the daytime. Greater positive disturbances occur on the average for strong geomagnetic storms.

     

Ionospheric absorption and Pc1-type micropulsations following enhanced geomagnetic activity

Data of Pc 1-type micropulsations and ionospheric absorption derived from measurements at mid-latitudes were analysed during and after geomagnetically disturbed periods. In comparison to the normal Pc 1 activity, a rather reduced one has been found during disturbed conditions. A distinct increase of Pc 1 activity occurred, however, after selected key days in the investigated interval between days ‘+2’ and ‘+7’. A clear after-effect could also be shown for ionospheric absorption, measured at three frequencies in Kühlungsborn (φ∼55°N) and a quite moderate one at somewhat lower geographic latitudes (φ ∼ 48°–49°N). In Kühlungsborn the ionospheric after-effect is particularly prominent at all investigated frequencies in case of a simultaneous after-effect in Pc 1 pulsations. It is restrained in the LF-range and missing in the MF-range when the after-effect is lacking in Pc 1 pulsations.     

Ionospheric modelling in support of single station location of long range transmitters

Position estimates derived from a large data base of bearing and elevation angles of signals from distant HF transmitters have been analysed, with a view to comparing the validity of available ionospheric models and to examining ionospheric limitations to the accuracy of single station location of such transmitters. In general, the accuracy of the position estimates is almost entirely controlled by a limited ability to model in sufficiently accurate detail the ionospheric effects on the signal propagation. Median miss distances for those cases with a reliable identification of the propagation mode were about 7% for both E and F2 propagation for all models considered. Difficulties were encountered with the International Reference Ionosphere, which failed to support the observed propagation in half the F2 propagation cases. Standard deviations of the bearing errors were about 0.5° for E modes and 0.7° for F2 modes and were largely attributable to the effects of the ionosphere and not to instrumental errors     

Ionospheric trends in mid-latitudes as a possible indicator of the atmospheric greenhouse effect

Using long-term ionosonde measurements in mid-latitudes (Juliusruh: 54.6°N, 13.4°E; 1957–1990), the first experimental hints of a decrease of the peak height of the ionospheric F2-layer were found. In contrast to that the long-term variations of the peak electron densities in the F2-layer, as well as the E-layer, are small. These results qualitatively agree with the predictions of Rishbeth [(1990) Planet. Space Sci.38, 945] who expected a lowering of the E- and F2-layer caused by a global cooling of the strato, meso- and thermosphere due to the increasing greenhouse effect.     

Ionospheric conductivity dependence of the cross-polar cap potential difference and global Joule heating rate

We examine the extent to which the cross-polar cap potential difference ϕ and the global Joule heating rate, U, both determined by the magnetogram-inversion method (Kamideet al., 1981, J. geophys. Res. 86, 801), depend upon the assumed conductance models. For this purpose two statistically-determined conductance models developed by Siroet al. (1982, J. geophys. Res. 87, 8215) and ahn et al. (1983b, Planet. Space Sci. 31, 641), and a realistic conductance distribution estimated from bremsstrahlung X-ray image data (Ahnet al., 1989, J. geophys. Res. 94, 2565) have been used. As expected from earlier studies, U is less affected by the choice of conductance models than is ϕ. This is because U is a globally integrated quantity, and thus the local structures of the electric potential pattern do not affect it appreciably, whereas they are crucial in determining ϕ, which is defined as the difference between the maximum and minimum potential values usually found in the dawn and dusk sectors, respectively. A comparison between Uand ϕ based on the statistical conductance models and U and ϕ based on a realistic conductance distribution shows that there are considerable similarities, thus enabling us to use statistical conductance models as a first approximation in deriving such global quantities as the cross-polar cap potential difference and the global Joule heating rate in the study of solar wind-magnetosphere coupling. Several suggestions are made for improving the present available conductance models and some limitations (possibly intrinsic ones) are also discussed.     

Ionospheric plasma modification in the vicinity of a spacecraft by powerful radio pulses in topside sounding

A mechanism of strong turbulence is proposed for interpretation of the resonances observed by a wide-band receiver during topside sounding. The turbulence is created in the vicinity of the spacecraft due to the striction modulation instability. Experimental results obtained with the aid of a wide-band receiver on board the Intercosmos-19 satellite are discussed in terms of strong wave-wave and/or wave-particle interaction, namely electron acceleration in Langmuir cavitons and non-linear generation of the electron Langmuir plasma waves and Tonks-Dattner resonances.     

Ionospheric mechanism for the two maxima in the spatial distribution of Pc3 geomagnetic pulsations

A modelling of the spatial distribution of Pc3 geomagnetic pulsations on the Earth's surface is carried out. We propose that the main contribution to the PC3 amplitude is due to ionospheric currents fluctuating because of conductivity variations associated with the modulation of electron precipitations which occurs in the field of compressional waves coming, probably, from the solar wind. A coincidence of the two dayside maxima in Pc3 geomagnetic pulsation amplitude (at latitudes ~ 70° and 55–60°) with two maxima in electron precipitations is in favour of such a proposition.     

Permanent monitoring of the upper mesosphere and lower thermosphere wind fields (prevailing and semidiurnal tidal components) obtained from LF D1 measurements in 1991 at the Collm Geophysical Observatory

The wind field of the upper mesosphere and lower thermosphere region (85–105 km) over Central Europe (52°N, 15°E) has been continually and reliably recorded by regular daily D1 radio wind measurements in the LF range (177, 225 and 270 kHz) using commercial radio transmitters. These measurements show the prevailing winds, the tidal wind components and the effects of internal gravity waves, as well as the seasonal and irregular variations of these parameters. The height of the wind measurements is determined by measuring the travel time differences between corresponding modulation bursts in the sky wave and in the ground wave. Using a quasi-online calculation procedure, the results are available immediately. Therefore they are useful for monitoring the upper atmospheric circulation with regard to upper atmosphere meteorology in the future. Vertical profiles of the wind field parameters can be derived with the aid of the combined wind and height measurements. Height-time cross-sections of the monthly mean prevailing winds and semidiurnal wind components have been calculated almost continuously for the last 10 years. The present paper deals with recent results for the year 1991.     

Municipal history and activities

The emergence of synthetic alkali production in Britain during the early nineteenth century was associated with pronounced regional growth. Three areas in particular developed an incipient soda industry: south‐west Lancashire, Tyneside and especially the central valley of Scotland. This paper sets out to evaluate the importance of raw materials and market structures as locational factors at a time when knowledge of this new technology was in the hands of the few and its diffusion was strongly channelled by an emerging chemical fraternity. In doing so some understanding of an industrial legacy which has proved difficult to change and impossible to obliterate is provided.     

MST radar studies of wind and turbulence in the middle atmosphere

A survey is presented of recent developments in the observation of wind and turbulence in the stratosphere and mesosphere using MST radars. One of the highlights of these developments is the growing recognition that the MST/ST radar is a valuable tool for routine monitoring of the atmospheric wind field. Furthermore, preliminary observations have shown the feasibility of monitoring atmospheric turbulence as well. Recent observations of mesospheric turbulence support theoretical models that emphasize the role of propagating waves in coupling the lower and middle atmospheres. Scientific groups in several countries are now planning or constructing MST radars so that within a few years observations should be available from diverse geographical locations spanning the globe.     

Long term periodicities in lower thermospheric wind variations

An analysis of long term meteor radar wind measurements for three temperature latitude stations shows that significant solar cycle oscillations with periods of 22 years and 11 years can be detected in the data.     

Law enforcement activities in Italy

This article examines the organization and function of Italy’s police forces. In contrast with other countries there have been very few recent studies on policing in Italy. This article starts from the origins of the modern police in Italy and tracks changes over time. Police activities that relate specifically to surveillance of territory and individuals, maintaining public order, controlling immigration and the coordination of police operations are reconstructed and documented, with a specific focus on crime prevention. The article attempts to assess to what extent this has been achieved in recent decades, and to what extent the efficiency of crime prevention has increased or decreased over the last thirty years. The article also examines the relations between the size of the police force and crime statistics to discover whether the increase in the former is directly linked to a decline in the latter.