Drought is a slow-onset, creeping natural hazard and a recurrent phenomenon in the arid and semi-arid regions of Gujarat (India). In Asia, the standardized precipitation index (SPI) has gained wider acceptance in the detection and the estimation of the intensity, magnitude and spatial extent of droughts. The main advantage of the SPI, in comparison with other indices, is that the SPI enables both determination of drought conditions at different time scales and monitoring of different drought types. This index captures the accumulated deficit (SPI < 0) or surplus (SPI > 0) of precipitation over a specified period, and provides a normalized measure (i.e. spatially invariant Z score) of relative precipitation anomalies at multiple time scales. In the present study, monthly time series of rainfall data ) from 160 stations were used to derive SPI, particularly at 3-month time scales. This 3-month SPI was interpolated to depict spatial patterns of meteorological drought and its severity during typical drought and wet years. Correlation analysis was also done to evaluate usefulness of SPI to quantify effects of drought on food grain productivity. Further, time series of SPI were exploited to assess the drought risk in Gujarat.
The growth in altitude/latitude of equatorial plasma bubbles was monitored, using simultaneous recordings of VHF scintillations at five locations situated between 3° and 23°N magnetic latitudes along a common meridian (84°E) during February 1980. The onsets of postsunset scintillation were mostly abrupt in character, and their occurrence at higher latitudes was conditional on their prior appearance at lower latitudes, indicating a causal link to irregularities associated with rising equatorial plasma bubbles. The day‐to‐day occurrence and the latitudinal, and effectively altitudinal, growths are examined in relation to the prereversal enhancement in h′F during sunset hours and its rate of rise, the onset of a postsunset secondary maximum (PSSM) in ionospheric electron content (IEC), and equatorial electrojet strength (EEJ) variations. It is observed that the bubble and associated irregularities, after its onset over the magnetic equator, reached the highest altitudes/latitudes only on those days when a prior PSSM in IEC is observed there in addition to high values of h′F, dh′F/dt and bubble rise velocity; otherwise it will be confined to near equatorial latitudes only. Also, the equatorial h′F, dh′F/dt, magnitude of PSSM and intensity of 4 GHz scintillations at low latitude are all showing positive correlation with daytime EEJ strength variations. It is concluded that, after the initial development of a bubble, the ExB drift and the PSSM play an important role in the subsequent growth and evolution, and EEJ is a useful parameter for the prediction of the development.
Based on cycles 17 -23, linear correlations are obtained between 12-month moving averages of the number of disturbed days when Ap is greater than or equal to 25, called the Disturbance Index (DI), at thirteen selected times (called variate blocks 1, 2, . . . , each of six-month duration) during the declining portion of the ongoing sunspot cycle and the maximum amplitude of the following sunspot cycle. In particular, variate block 9, which occurs just prior to subsequent cycle minimum, gives the best correlation (0.94) with a minimum standard error of estimation of ± 13, and hindcasting shows agreement between predicted and observed maximum amplitudes to about 10%. As applied to cycle 24, the modified precursor technique yields maximum amplitude of about 124 ± 23 occurring about 45 ± 4 months after its minimum amplitude occurrence, probably in mid to late 2011.
Abstract. The observations on the ionospheric electron and ion temperatures (T e and T i ) measured by the RPA payload aboard the SROSS-C2 satellite have been used to study the effect of solar flares on ionospheric heating. The data on solar flare has been obtained from the National Geophysical Data Center (NGDC) Boulder, Colorado (USA). It has been found that the electron and ion temperatures have a consistent enhancement during the solar flares on the dayside Earth's ionosphere. The estimated enhancement for the average electron temperature is from 1.3 to 1.9 times whereas for ion temperature it is from 1.2 to 1.4 times to the normal days average temperature. The enhancement of ionospheric temperatures due to solar flares is correlated with the diurnal variation of normal days' ionospheric temperatures. The solar flare does not have any significant effect on the nightside ionosphere. A comparison with the temperature obtained from the IRI-95 model also shows a similar enhancement.
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