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Precursor techniques, in particular those using geomagnetic indices, often are used in the prediction of the maximum amplitude
for a sunspot cycle. Here, the year 2008 is taken as being the sunspot minimum year for cycle 24. Based on the average aa index value for the year of the sunspot minimum and the preceding four years, we estimate the expected annual maximum amplitude
for cycle 24 to be about 92.8±19.6 (1-sigma accuracy), indicating a somewhat weaker cycle 24 as compared to cycles 21 – 23.
Presuming a smoothed monthly mean sunspot number minimum in August 2008, a smoothed monthly mean sunspot number maximum is
expected about October 2012±4 months (1-sigma accuracy). 相似文献
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Ahmed Nasir Bodrud-Doza Md. Islam S. M. Didar-Ul Choudhry Manzoor Ahmad Muhib Md. Iftakharul Zahid Anwar Hossain Shahadat Moniruzzaman Md. Deb Nipa Bhuiyan Md. Abdul Quaiyum 《中国地球化学学报》2019,38(3):440-455
Acta Geochimica - To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and... 相似文献
3.
A few prediction methods have been developed based on the precursor technique which is found to be successful for forecasting
the solar activity. Considering the geomagnetic activity aa indices during the descending phase of the preceding solar cycle as the precursor, we predict the maximum amplitude of annual
mean sunspot number in cycle 24 to be 111 ± 21. This suggests that the maximum amplitude of the upcoming cycle 24 will be
less than cycles 21–22. Further, we have estimated the annual mean geomagnetic activity aa index for the solar maximum year in cycle 24 to be 20.6 ± 4.7 and the average of the annual mean sunspot number during the
descending phase of cycle 24 is estimated to be 48 ± 16.8. 相似文献
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Rajmal Jain Vishal Joshi Yoichiro Hanaoka T. Sakurai Nipa Upadhyay 《Journal of Astrophysics and Astronomy》2006,27(2-3):339-346
We present a study of 10 microflares observed in 4–30 keV by SOXS mission simultaneously with Hα observations made at NAOJ,
Japan during the interval between February and August 2004. The X-ray and Hα light curves showed that the lifetime of microflares
varies between 4 and 25 min. We found that the X-ray emission in all microflares under study in the dynamic energy range of
4–30 keV can be fitted by thermal plus non-thermal components. The thermal spectrum appeared to start from almost 4 keV, low
level discriminator (LLD) of both Si and CZT detectors, however it ends below 8 keV. We also observed the Fe line complex
features at 6.7 keV in some microflares and attempted to fit this line by isothermal temperature assumption. The temperature
of isothermal plasma of microflares varies in the range between 8.6 and 10.1 MK while emission measure between 0.5 and 2x1049 cm-3. Non-thermal (NT) emission appeared in the energy range 7–15 keV with exponent -6.8 ≤γ≤-4.8. Our study of microflares that had occurred on 25 February 2004 showed that sometimes a given active region produces
recurrent microflare activity of a similar nature. We concluded from X-ray and simultaneous Hα observations that the microflares
are perhaps the result of the interaction of low lying loops. It appears that the electrons that accelerated during reconnection
heat the ambient coronal plasma as well as interact with material while moving down along the loops and thereby produce Hα
bright kernels. 相似文献
5.
Nasir Ahmed Md.Bodrud-Doza S.M.Didar-Ul Islam Manzoor Ahmad Choudhry Md.Iftakharul Muhib Anwar Zahid Shahadat Hossain Md.Moniruzzaman Nipa Deb Md.Abdul Quaiyum Bhuiyan 《Acta Geochimica》2019,(3):440-455
To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and analyzed for temperature, pH, Eh, EC,DO, DOC, Na^+, K^+, Ca2+, Mg2+, Cl^-, SO_42-, NO_3^-,HCO_3^-, SiO_2^-, Fe, Mn and As. Besides, 12 surface water samples from Surma and Kushiyara Rivers were also collected and analyzed to understand the influence into aquifers. Results revealed that, most of the groundwater samples are acidic in nature, and Na–HCO_3 is the dominant groundwater type. The mean value of temperature, EC,Na^+, K^+, Ca2+, Mg2+, Cl^-, NO_3^- and SO_42- were found within the range of permissible limits, while most of the samples exceeds the allowable limits of Fe, Mn and As concentrations. However, relatively higher concentration of Fe and Mn were found in deep water samples and reverse trend was found in case of As. The mean concentrations of As in shallow, intermediate and deep wells were 39.3, 25.3and 21.4 lg/L respectively, which varied from 0.03 to148 lg/L. From spatial distribution, it was found that Fe,Mn and As concentrations are high but patchy in northern,north-western, and south-western part of Sylhet region. The most influential geochemical process in study area were identified as silicate weathering, characterized by active cation exchange process and carbonate weathering, which thereby can enhance the elemental concentrations in groundwater. Pearson's correlation matrix, principal component analysis and cluster analysis were also employed to evaluate the controlling factors, and it was found that, both natural and anthropogenic sources were influencing the groundwater chemistry of the aquifers. However, surface water has no significant role to contaminate the aquifers,rather geogenic factors affecting the trace elemental contamination. Thus it is expected that, outcomes of this study will provide useful insights for future groundwater monitoring and management of the study area. 相似文献
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