The time structure and spectra of X ray and extreme ultraviolet (EUV) bursts during solar flares are described from the viewpoint of evaluating their ionospheric effects. The impulsive flare component is strong in emissions from solar source regions with temperatures in the range 104°K–106°K, which are strong in the 90‐ to 1027‐Å range. The strength of the impulsive EUV emissions incident on the ionosphere depends on the location of the flare on the sun. The impulsive EUV emission produces short‐lived large absolute enhancements of photo‐ionization rates above the bottom of the preflare E layer and in the F region. The slow components are very strong in emissions from solar sources with temperatures in the range 1–30 × 106°K and are particularly strong at soft X ray wavelengths (1–90 Å). The slow 1‐ to 8‐Å burst causes the large percentage increase in ionization production below the bottom of the preflare E layer and in the D region. The large absolute flare emission in the 8‐ to 90‐Å emission and the K shell absorption edge of N2 near 31 Å causes the large slow enhancement of photo‐ionization in the 100‐ to 130‐km altitude range.
This case study describes an effective method to ameliorate the cognitive load caused by new terminology and concepts in lectures. Ten online pre‐lecture resources whose design was underpinned by the principles of cognitive load theory were provided to a class of 49 first year university level chemistry students. Each resource introduced a number of key concepts to the forthcoming lecture and included a quiz for students to test understandings and identify misconceptions. The evaluation of the implementation of resources was measured by considering the difference in exam marks for in‐semester test and end of module exam. These showed that the marks for students who had no prior knowledge of chemistry before coming to college significantly improved to the point that there was no difference between students with and without prior knowledge. A key outcome of this work is that providing students with resources to prepare for lectures can help in reducing their cognitive load. Practitioner Notes What is already known about this topic Prior knowledge (eg, from school level) is a strong predictor factor for future performance (eg, at college level). Cognitive load theory describes how the working memory has a limited capacity to process new information. E‐resources can be designed so as to minimise the difficulty of extracting new information from the resources. What this paper adds Designing e‐resources to introduce some core concepts for a lecture can help students identify these in a lecture with a lot of new terminology. These e‐resources can be easily embedded into the virtual learning environment so that students can access resources, complete quiz and receive feedback and a grade with little extra work for the lecturer. These e‐resources can provide a basis for in‐lecture discussion between students and between lecturer and students to further discuss content using core terminology. Implications for practice/policy Embedding of the resources into the module design is important to attribute them value. The lecture should build on the material introduced in the e‐resource. Feedback should be as rich as possible, correcting wrong ideas for novices to the discipline and misconceptions for those with prior knowledge. Identifying core concepts in a structured way before each lecture and providing feedback on students' understanding of these gives students an opportunity to take control of their own learning both before and after a lecture.
Periodicity in the 13-14 day range for full-disk UV fluxes comes mainly from episodes of solar activity with two peaks per rotation, produced by the solar rotational modulation from two groups of active regions roughly 180 ~ apart in solar longitude. Thirteen-day periodicity is quite strong relative to the 27-day periodicity for the solar UV flux at most wavelengths in the 1750-2900 A, range, because the rapid decrease in UV plage emission on average with increasing solar central angle shapes the UV variations for two peaks per rotation into nearly a 13-day sinusoid, with deep minima when the main groups of active regions are near the limb. Chromospheric EUV lines and ground-based chromospheric indices have moderate 13-day periodicity, where the slightly greater emission of regions near the limbs causes a lower strength relative to the 27-day variations than in the above UV case. The lack of 13-day periodicity in the solar 10.7 cm flux is caused by its broad central angle dependence that averages out the 13-day variations and produces nearly sinusoidal 27-day variations. Optically thin full-disk soft X-rays can have 13-day periodicity out of phase with that of the UV flux because the X-ray emission peaks when both groups of active regions are within view, one group at each limb, when the optically thick UV flux is at a rotational minimum. The lack of 13-day periodicity in the strong coronal lines of Fexv at 284 A, and FexvI at 335 A during episodes of 13-day periodicity in UV and soft X-ray fluxes shows that the active region emission in these strong lines is not optically thin; resonant scattering is suggested to cause an effective optical depth near unity in these hot coronal lines for active regions near the limb.
The temporal characteristics of the full-disk chromospheric EUV fluxes agree well with those of the ground-based'measurements of the chromospheric He I absorption line at 10,830 A and differ systematically from those of the coronal EUV and 10.7-cm flux. The ratio of the flux increase during the rise of solar cycle 21 to that during solar rotation variations is uniformly high for the chromospheric EUV and corroborating 10,830-/!/fluxes, highest for the transition region and'"cool" coronal EUV fluxes (T < 2 x 106 øK), and lowest for the "hot" coronal EUV and 10.7-em flux. The rise and decay rates of episodes of major activity progress from those for the hot coronal EUV lines and the 10.7-cm flux to slower values for the chromospheric H Lyman alpha line, 10,830-A line, and photospheric 2050-/!• UV flux. We suggest that active region remnants contribute significantly to the solar cycle increase and during the decay of episodes of major activity. The ratio of power in 13-day periodicity to that for 27 days is high (1/3) for the photospheric UV flux, medium (1/6) for the chromospheric EUV and 10,830-A fluxes, and small to negligible for the hot coronal EUV fluxes. These ratios are used to estimate the dependence of active region emission on the solar central meridian distance for chromospheric and coronal EUV fluxes. SOLAR UV AND EUV RADIATION The solar UV full-disk flux at 2050 A, measured by the NIMBUS 7 satellite, was shown by Donnelly et al. [1985] to vary in close agreement with ground-based measurements of the He I absorption line at 10,830/•. These variations included the following three time scales: (1) short-term variations with quasi-periodicity of about 13.5 or 27.5 days that are caused by solar rotation of active region plages, (2) intermediate-term enhancements of several months caused by episodes of major activity, and (3) long-term solar cycle variations. These UV variations were also shown to differ from those of the 10.7-cm solar radio flux (F10) during episodes of major activity and when the 13.5-day periodicity was strong in the UV flux [Donnelly et al., 1983]. This paper extends the research of UV and 10,830-• temporal characteristics by including comparisons with the solar extreme ultraviolet (EUV) flux measurements from the AE-E satellite. The remainder of this section introduces the data studied and our general knowledge of solar UV and EUV radiations, including their terrestrial importance, spectral differences, magnitudes of variations, and solar source regions. The next section describes the AE-E data studied. Then the temporal characteristics and comparisons of the EUV, UV, and 10,830-/• measurements for short-, intermediate-, and long-term variations are presented. Next, the implications of the 13-day periodicity on the dependence of active region radiation on the region's central meridian distance (CMD) are discussed for chromospheric and coronal EUV lines. Finally, the relation of our results to the temporal characteristics of ground-based measures of solar This paper is not subject to U.S...
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