Variation with lunar phase of midday critical frequencies and heights of the F2 layer over Ahmedabad and other low latitude stations

The paper contains an analysis of the variation of the midday values of foF2, h'F2 and hpF2 with lunar phase at Ahmedabad during the years 1954 and 1955 and of foF2 alone at Bombay, Madras and Tiruchirapalli during 1954. It is found that while the semidiurnal lunar tidal variations at Ahmedabad and Bombay agree in phase with those observed at middle latitudes, the phase reverses in direction between Bombay and Madras. The results are compared with those relating to Huancayo and Singapore

Expression of expanded FMR1-CGG repeats alters mitochondrial miRNAs and modulates mitochondrial functions and cell death in cellular model of FXTAS

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disorder caused by an expansion of 55 to 200 CGG repeats located within 5′UTR of FMR1.These CGG repeats are transcribed into RNAs, which sequester several RNA binding proteins and alter the processing of miRNAs. CGG repeats are also translated into a toxic polyglycine-containing protein, FMRpolyG, that affects mitochondrial and nuclear functions reported in cell and animal models and patient studies. Nuclear-encoded small non-coding RNAs, including miRNAs, are transported to mitochondria; however, the role of mitochondrial miRNAs in FXTAS pathogenesis is not understood. Here, we analyzed mitochondrial miRNAs from HEK293 cells expressing expanded CGG repeats and their implication in the regulation of mitochondrial functions. The analysis of next generation sequencing (NGS) data of small RNAs from HEK293 cells expressing CGG premutation showed decreased level of cellular miRNAs and an altered pattern of association of miRNAs with mitochondria (mito-miRs). Among such mito-miRs, miR-320a was highly enriched in mitoplast and RNA immunoprecipitation of Ago2 (Argonaute-2) followed by Droplet digital PCR (ddPCR)suggested that miR-320a may form a complex with Ago2 and mitotranscripts. Finally, transfection of miR-320a mimic in cells expressing CGG permutation recovers mitochondrial functions and rescues cell death. Overall, this work reveals an altered translocation of miRNAs to mitochondria and the role of miR-320a in FXTAS pathology

Ionospheric Absorption on 2.5 MHz at Ahmedabad

110-113A study is made of diurnal and day-to-day variations of ionospheric absorption on 2·5 MHz measured by Al method at Ahmedabad (23 oN, 72·6 °E; magnetic dip 34 °N) for the year 1973. It is shown that the diurnal variation of absorption follows a law L=L0 cosn where L0 is absorption when the sun is at zenith. The value of the index n is found to vary from 0·4 to 1·05 during the course of a year, its yearly mean value turning out to be 0·70. The maximum of absorption occurs a little later than noon, the delay being about 45 min in winter and about 12 min in summer. Among the day-to-day variations, the increases in absorption are related to the increases in 1-8 Å solar X -ray flux and the decreases to the occurrences of a reflecting low-type sporadic-E layer. The results are discussed in the context of the roles played by the D- and E- layer ionizations and the atmospheric composition

Some Anomalous Features of the Ionospheric F2-Layer at Low Latitude Conjugate Places

22-25The diurnal variation of the F2-layer critical frequency (f0F2) is compared with the diurnal variations of the horizontal component H of the earth's magnetic field and of the declination D at a pair of low latitude conjugate stations in the Pacific and the Atlantic zones for a medium-low solar activity period. It is shown that the day-time bite-out in f0F2 and its seasonal anomaly are dependent on the characteristic daily variation of the H-field. There is also an indication of the effect of E-W declination on the diurnal variation of f0F2 at places near magnetic dip 45_50° as explained by H. Kohl, J. W. King & D. Eccles [J. atmos. terr. Phys., 31 (1969), 1011]; such effect is not observed at low latitudes. The day-time depression in f0F2 seems to be more pronounced at Port Stanley in summer than at its northern conjugate Puerto Rico, perhaps because of the additional effect of the neutral wind-associated vertical drift of ionization, for which the situation of Port Stanley (mean magnetic dip= 46.3') is very favourable

Geomagnetic Storms & Associated Ionospheric Effects

15-19Some typical cases of ionospheric disturbances associated with geomagnetic storms in different seasons are studied for dip-conjugate low and middle latitude places located along nearly the same longitude. The results show initial changes in NmF2 similar to those in the magnetic field at all places, but later, the changes in the F2-ionization seem to be governed by the heating of the upper atmosphere and the accompanied changes in the neutral wind pattern and the gas composition. The anomalous increase of F2 electron density in winter at midlatitude during the main phase and after, of the storm is traced to the change in the meridional wind system and to the neutral wind transport from the summer hemisphere to the winter hemisphere. Satellite observations of the day-to-day and disturbed F-region also confirm changes in the gas composition in good correlation with the changes in NmF2 or total electron content. As against the instantaneous effects of the storm in the F2-ionization, there is an after-effect of the storm in the D-region at midlatitudes but practically no such storm-effects in the low-latitude D-region. It is believed that the post-storm low energy electrons precipitate into the lower ionosphere from the magnetospheric slot and cause the delayed increase in the D-region ionization at midlatitudes. The D-region effects are inferred from the absorption of hf radio waves

Diurnal & Seasonal Variation of Frequency Dependence of Ionospheric Absorption at a Tropical Latitude

119-124Multifrequency ionospheric AI-absorption data obtained at Ahmedabad (23°N, 72.6°E, mag. dip 34°N) are analyzed to study the frequency dependence of absorption for low and high solar activity epochs, and also for low and moderately high solar activity years (1976 and 1978).The exponent m in the inverse frequency dependence of measured absorption is determined for practical purposes. The diurnal variation of the index m for different months and its seasonal variation at a fixed solar zenith angle (SZA) are studied for total absorption (Ltotal) as well as for its non-deviative (Lnd) part. It is found that (Ltotal) does not obey the inverse frequency square law. During sunspot minimum, m is found to vary with time of the day showing maximum (annual average =0.71) around noon and falling towards morning and evening hours, whereas for sunspot number Rz = 100, it shows the opposite trend showing minimum (average value =0.60) around noon and increasing towards morning and evening hours. In the case of non-deviative (Lnd) absorption. the index m in 1976 and 1978behaves in a manner similar to that of Ltotal for Rz =00 and 100, but m for Lnd has higher values and range of variation, the values being clustered around the theoretical value 2 near noon, in the spring months of 1976and for most part of the day in August 1978. These results suggest that the higher value of m on the average for Ltotal during increased solar activity is due to major contribution of non-deviative absorption and only small contribution of deviative absorption to the total absorption during high solar activity. It is also verified that the value of the proportionality constant A in the assumed frequency dependence law of total absorption changes with the or SZA corresponding to the changes in the value of m

Differences in Seasonal Variation of Noon F2-ionization at Dip-conjugate Places

231-234A study is made of noon foF2over a period of one solar cycle (1958-69) at some pairs of magnetically near-conjugate places in the eastern and central zones with dips (I) 0-60°, Seasonal dependence of the sensitivity of foF2 on solar activity is studied and the differences in the seasonal variation of foF2 are shown for low and high solar activity epochs, It is found that the seasonal variation of noon foF2 at dip-conjugates are significantly different, and the change-over seems to occur at the geographic equator, The midlatitude winter anomaly of foF2 found in north is not observed at the southern dip-conjugate till near the peak of the sunspot cycle, The results are discussed specially with reference to the neutral wind and the associated changes in the gas composition

A Comparative Study of Some Aspects of Low & Middle Latitude Ionospheric Absorption

232-235Results of a study of AI method ionospheric absorption on 2.3 MHz at a midlatitude station, De Bilt (52.1°N, 5.2°E), for the years 1975-80 to find the seasonal and solar cycle variations of the index n of co sχ for diurnal variation of absorption (Ldb), delay time () in its daily maximum, and absorption at constant solar zenith angle (SZA, χ)are presented. These are compared with the results of such variations obtained at a low latitude station, Ahmedabad (23°N, 72.6°E), which is well outside the winter anomaly zone. It is found that there is, in general, an agreement in the seasonal variation of n at the two places, but not so in the case of . The time-delay at Ahmedabad is generally larger in winter than in summer varying almost in opposition to n while it has a sharp peak in winter and a shallow trough in summer at De Bilt, thus having no definite relation with n. But reasonably good anticorrelation between n and at midlatitude is also obtained if the values of these parameters for winter months are not taken into account. The range of seasonal changes in n and seems to decrease with increase in solar activity and the yearly smoothed values of rather than n also indicate a fall at the midlatitude. The absorption at constant SZA taken together for all months varies according to a linear relation with solar activity at Ahmedabad and at De Bilt; however, the linearity at the latter place is masked by the anomalous increase of absorption in winter. A curious feature noticed was that the absorption during Apr-Oct 1979 fell below that observed during the same months in 1978 although the solar activity in 1979 continued to rise. The above results have been discussed at appropriate contexts in the light of the ionizing radiations, changes in gas composition and the loss rate of ionization