Lower ionosphere,lower atmosphere and IMF sector structure in winter

There are two basic types of IMF sector boundary crossing effect. One is observed in the IMF magnitude, geomagnetic activity, the nighttime lower ionosphere in high mid-latitudes and in an inverse form in cosmic rays and is reasonably well explained. The other is observed in the noon lower ionosphere in high mid-latitudes and in the troposphere; its interpretation remains open.     

The impact of gravity waves on nitric oxide in the lower thermosphere

Observations of nitric oxide (NO) by the Solar Mesosphere Explorer (SME) during equinox indicate a lower-thermosphere equatorial minimum which is at variance with theoretical predictions. To address this discrepancy a zonally averaged model of the thermosphere and upper mesosphere is used to evaluate the influence of a latitude variation in turbulence. Five numerical simulations were performed with different latitude structures of eddy diffusion (K_T), ranging from uniform in latitude, peaks at low, mid-, or high-latitude, to a hemispherically asymmetric distribution. A local increase in eddy diffusion causes the lower thermosphere to cool and induces a latitude pressure gradient that drives horizontal and vertical winds. The circulation, turbulent transport and temperature dependent chemistry act to change the distribution of species. Comparison of the model predictions of NO with SME data, and simulated wind and temperature structure with empirical climatology, indicates a preference for a midlatitude peak in K_T.     

Effect of severe auroral disturbances on the equatorial ionosphere

It is now an established fact that during extremely strong magnetic storms a sudden anomalous decrease in the F-layer critical frequency foF2 is sometimes noticed at the equator around noon-time and the duration of this effect is known to be anywhere between some tens of minutes to several hours. As an extension of earlier work by Turunen and Rao, 1980, seven severe auroral storm events based on AE index have been selected during the period July 1958–June 1960 and their effects on the equatorial ionosphere have been investigated utilizing the published ionospheric data for the chain of Indian stations starting from equatorial latitudes and extending up to the mid-latitudes. From this study, it is noted that at the equator around noontime the foF2 values decrease and the noon bite-out phenomena are enhanced. However, as one goes towards mid-latitudes this trend is reversed. Because of this, the Appleton anomaly is also enhanced during disturbed days. Besides, the fF_s values at the magnetic equator show an increase during disturbed days indicating thereby that the eastward equatorial electrojet current is enhanced on disturbed days. This suggests that the auroral electrojet current is coupled to the equatorial electrojet current possibly via the magnetosphere.     

VLF transmissions observed at anomalously high latitude above the ionosphere in the conjugate hemisphere

Ariel 3 and 4 satellite observations of the GBR 16 kHz and NAA 17.8 kHz transmissions above the ionosphere in the conjugate hemisphere show that their wave-fields generally show a rapid reduction in signal strength for geomagnetic latitudes greater than 55°–60°. Sometimes, however, the signal strength has been observed to be high in the invariant latitude range > 60°. At certain times during these observations, the signal showed clear evidence of amplification, whilst at other times the pattern of signal strength was displaced to higher latitude with the signal strength integrated over latitude being unchanged from that normally observed.It is shown that the plasmapause can guide both the NAA and GBR signals but that the efficiency of this guiding depends on the plasmapause position. The important condition is found that the plasmapause must be situated sufficiently equatorwards that half the equatorial electron gyrofrequency at the plasmapause position is greater than (or approximately equal to) the transmitter signal frequency. Ray-tracing calculations in a realistic magnetosphere model indicate that for the 16 kHz GBR signal, the efficiency of guiding falls off for L_pp, (the L-value of the plasmapause) > 3.0 and guiding effectively ceases for L_pp > 3.5.Guidance by the plasmapause results in a wave-field at higher latitude than for non-guided propagation. This will only occur when, following geomagnetic storms, the plasmapause position is at a sufficiently low L-value. This is in agreement with the experimental observations of anomalously high latitude signal reception following strong magnetic storms (K_p ≥ 4+).     

Acceleration of electrons in the ionosphere under the action of intense radio-waves near electron cyclotron harmonics

The effect of electron acceleration by intense ionospheric plasma turbulence induced by a high-power radio wave is studied theoretically, under conditions when the turbulence frequency is nearly equal to harmonics of the electron-cyclotron frequency. The turbulence located in a thin layer at the region of the pump-wave upper-hybrid resonance gives rise to the formation of an intense electron distribution function tail at high energies. Given the resonantly absorbed fraction of the pump-wave energy and the typical plasma turbulence scale, one can estimate the turbulence energy density and calculate the modified electron distribution function.     

Electron temperature and electron density in the F-region of the ionosphere. I. Observed relationship

Ionospheric data from three incoherent scatter stations over the height range 225–450 km were studied for all daylight hours over a wide range of solar conditions. The relationship between electron temperature T_e, electron density Nand solar flux at 10.7 cm wavelength S_10.7 was expressed as T_e = A−B·(N−5 × 10¹¹) + C·(S_10.7−750), where N is in units of m⁻³ and S_10.7 in kJy.This provided a very satisfactory expression for all data taken at Malvern and St. Santin between 0800 and 1600 LT. For data taken at Arecibo, however, the linearity broke down at low electron densities. The data from all three stations were therefore divided into two sets according to electron density and reexamined.ForN < 5 × 10¹¹ m⁻³ B increased steadily with height and decreased steadily with latitude.For N > 5 × 10¹¹ m⁻³ B did not appear to vary with height, with season or with latitude. C was approximately constant for all sets of data.The different mechanisms involved in the heat balance of the electron population are discussed and a qualitative explanation for the relationship is proposed.     

Role of chemical effects in the formation of electron concentration depletions during HF heating of the ionosphere

A chemical mechanism which reduces the electron concentration in the upper ionosphere during HF heating is presented. It is based on the excitation of nitrogen vibrational levels by fast electrons which have appeared as a result of absorption of a radio wave. The vibrational excitation of nitrogen leads to an increase in ion-molecular exchange, followed by a depletion of the electron concentration because the positive molecular ions are very effective in electron -ion recombination. Two different models arc discussed. In the equilibrium model, the vibrational temperature has been established in the region disturbed by the radio wave. In the nonequilibrium model, the fast electrons are moving inside a thin duct where the time of vibrational-vibrational relaxation is greater than the time required by the excited molecules to leave the channel due to diffusion, so that the vibrational temperature cannot be established.     

The lower paleolithic of the Near East

The Near East forms the geographic crossroads between Africa, Asia and Europe and was certainly a main route for the dispersal of Homo erectusinto Eurasia. The study of Lower Paleolithic sites in this region and in the neighboring Caucasus area sheds some light on several potential colonization events. Sites such as Ubeidiya (Jordan Valley) and Dmanisi (Georgia) suggest the early sorties took place around 1.4-1.0 Ma. Despite the lack of radiometric dates, sequences of raised beaches, marine deposits, river terraces, and paleolake formations have enabled various investigators to identify several series of major aggradation and erosion periods within the Pleistocene. Lithic assemblages derived from a few systematic excavations and collections from stratigraphically dated outcrops led to a threefold subdivision of the Acheulian sequence into the Lower, Middle, and Upper Acheulian. The study of nonbiface assemblages, however, has not resolved the question of whether these assemblages deserve inclusion as separate entities or should be viewed as sites within the Acheulian settlement pattern. While the typotechnological definitions of each major phase can be compared to what is known from other regions of the Old World, the Acheulo-Yabrudian (or the Mugharan Tradition) is seen as a local entity. Rare human remains and scarce data concerning subsistence activities do not warrant a comparative discussion with what is known from African and some European sites.     

Some aspects of ULF electromagnetic wave relations in a stratified ionosphere by the method of boundary value problem

Formulation and boundary conditions are developed to solve for the electromagnetic waves in a stratified ionosphere and atmosphere as a two-point boundary value problem. In the general case there are up-going and down-going Alfvén modes, up-going and down-going fast modes. It is shown that while large horizontal structure of the perturbation can be attributed to both the fast wave and the Alfvén mode, small horizontal structure can only be attributed to the Alfvén mode. The ratios of the electric field to magnetic field are given for various altitudes, frequencies and horizontal scale sizes. The results show that the magnetic field leads the electric field for the Alfvén mode and the electric field leads the magnetic field for the fast mode. The results also show that the ratio of the electric field to the magnetic field is varied and is not the Alfvén speed of the local medium. Analytical solutions are presented as tests against the numerical ones.     

Inorganic bromine in the lower stratosphere

Inorganic bromine content in the lower stratosphere was determined from a series of three balloon flights conducted in 1981 and 1982 from Holloman AFB, New Mexico (33°N). A Direct Flow Sampler (DFS) sampled large quantities of stratospheric air through a 35 cm diameter filter mounted upstream of a blower. Filters were prepared with an inert organic oil and a strong organic base in order to capture both acidic and particulate species. Following flight, the filters underwent an extraction process. Then, aliquots of the solution were subjected to neutron activation analysis. The methodology involved a radiochemical procedure which was developed and tested to measure, simultaneously, both chlorine and bromine content. High-resolution gamma spectrometry was used and bromine content was determined by counting ⁸⁰Br activity. The resulting values for volume mixing ratios of bromine increased from a low of 2.6 pptv at 15 km to a high of 15.6 pptv for the 25–30 km band. The results are shown to be in agreement with earlier measurements by Sedlacek et al. (1984) and with one-dimensional photochemical model predictions by yung et al. (1980).