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1.
Evidence is presented to show that during epochs of high sunspot activity, the duration of manifestation of equatorial spread-F (ESF) irregularities in the Earth's equatorial ionosphere undergoes a systematic modulation around the times of crossing of the heliospheric current sheet by the Earth. The modulation which is assessed as an indirect and geomagnetic activity-associated effect, is characterised by an enhancement in the duration of ESF conditions prior to the current sheet crossing and a reduction thereafter. It is suggested that the observed response of the equatorial ionosphere to the current sheet passage is primarily a manifestation of the geomagnetic activity related modifications in the equatorial east-west electric field in the post-sunset period. 相似文献
2.
A field experiment was conducted on wheat at New Delhi with five treatments of Nitrogen (N) fertilizer application (0, 30,
60, 90 and 120 kgha-1). Relationship has been established between observed leaf area index (LAI) and remotely sensed vegetation indices. These
relationships are inverted and used for predicting LAI from vegetation indices on different days after sowing. The “re-initialization”
strategy is implemented in model WTGROWS in which initial conditions of model are changed so that the model simulated LAI
match remote sensing predicted LAI. The model performance with re-initialization has been evaluated by comparing the simulated
grain yield and total above-ground dry matter (TDM) values with the actual observations. The results show that in-season re-initialization
is effective in model course correction by improving the simulated results of yield and TDM for different N treatments even
though the model was run with no N stress condition. Model re-initialization at different days shows that the closer is the
day of re-initialization to crop anthesis the more effective is model course correction. Also, the treatment showing maximum
error in yield simulation without re-initialization shows maximum reduction in error by re-initialization. The approach shows
that the remote sensing inputs can substitute for some of the inputs or errors in inputs required by crop models for yield
prediction. 相似文献
3.
P.S.R. Reddy D.K. Sengupta S.R.S. Sastri K.S. Narasimhan 《International Journal of Mineral Processing》1984,13(4):259-269
A technique to arrive at conditions congenial to maintaining a stable suspension of fine particles has been described. The technique involves continuous monitoring of apparent loss of weight of a body suspended in settling slurries. Such a technique is useful in fixing the best conditions for gravity separation of fine particles involving Bartles-Mozley concentrators or hydrocyclones. 相似文献
4.
Measurements of the changes in phase path of F-region reflections at normal incidence at Kodaikanal (77° 28′E, 10° 14′N, dip 3°N) from February 1991 to February 1993 are used to determine the variation of the equatorial evening F-region vertical drifts (Vz) with season, solar and magnetic activity. It is found that on average, at Kodaikanal, the post-sunset peak in Vz(Vzp) is higher in equinox and local winter months than in local summer. The day-to-day variability in Vzp is highest in summer and lowest in winter. This seasonal trend persists even on magnetically quiet days (Ap\leq14). Vzp is found to increase with 10.7 cm solar flux in all three seasons but tends to saturate for large flux values (>230 units) during local summer and winter months. Magnetic activity [represented by Ap as well as the time-weighted accumulations of ap and ap ()] does not seem to have any statistically significant effect on Vzp, except during equinoctial months of moderate solar activity, when Vzp decreases as magnetic activity increases. 相似文献
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6.
Distribution, over the lunar age, of the frequency of occurrence of the afternoon counter-electrojet events at Trivandrum during the period 1959–1978 is examined in each of the calendar months. A strong lunar modulation on the occurrence frequency is seen in January; this may be related to the global enhancement of the lunar tide during January. The modulation is also prominent in April, although 62% of the events in that month occur irrespective of the lunar age. The occurrence frequency at Trivandrum appears to be least influenced by the Moon in the northern summer months. 相似文献
7.
Summary. The contributions from the oceanic and ionospheric dynamos, Lo and LI respectively, to the geomagnetic lunar daily variation, L , at Alibag, a coastal station in the Indian equatorial region, are calculated from the L harmonics derived from a 41–yr long series of observations. The analysis in the calendar months shows a steady and significant ocean dynamo contribution in the vertical component, Z, in all the months except April. Examination, by an analysis of the data year by year, of the association of Lo and LI with varying solar and magnetic activities reveals, surprisingly, a stable correlation between the magnetic activity index A P and the oceanic part in the horizontal and vertical components but not in declination, which probably indicates the influence of induced currents, along the latitudes, on L o . 相似文献
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9.
J. Hanumath Sastri H. Luhr H. Tachihara T.-I. Kitamura J. V. S. V. Rao 《Annales Geophysicae》2000,18(2):252-256
Measurements with a HF Doppler sounder at Kodaikanal (10.2°N, 77.5°E, geomagnetic latitude 0.8°N) showed conspicuous quasi-periodic fluctuations (period 25/35 min) in F region vertical plasma drift, Vz in the interval 0047/0210 IST on the night of 23/24 December, 1991 (Ap = 14, Kp < 4–). The fluctuations in F region vertical drift are found to be coherent with variations in Bz (north-south) component of interplanetary magnetic field (IMF), in geomagnetic H/X components at high-mid latitude locations both in the sunlit and dark hemispheres and near the dayside dip equator, suggestive of DP2 origin. But the polarity of the electric field fluctuations at the midnight dip equator (eastward) is the same as the dayside equator inferred from magnetic variations, contrary to what is expected of equatorial DP2. The origin of the coherent occurrence of equatorial electric field fluctuations in the DP2 range of the same sign in the day and night hemispheres is unclear and merits further investigations. 相似文献
10.
J. Hanumath Sastri 《Solar physics》1986,105(1):191-196
As a sequel to our recent identification of the high-speed stream as the candidate structure in the solar wind at 1 AU, that is primarily responsible for the geomagnetic disturbances occasionally noticed after disparition brusques (DBs) of solar filaments (Sastri et al., 1985), we report here that the streams, inferred to be recurrent in our earlier study, were consistently preceded by a stream interface, as expected of corotating streams. This observation substantiates the role of corotating streams of coronal hole origin in the apparent link between DBs and geomagnetic activity, and strengthens the view that DBs are not a unique source of geomagnetic activity. 相似文献