Studying travelling ionospheric disturbances from near-vertical ionosphere sounding with high temporal resolution
In this study, we analyze the near-vertical ionospheric sounding data obtained with a multipurpose digital chirp ionosonde. The ionosonde was recording ionograms once each minute. We analyzed the results of processing the datasets over three observational years from 2010 to 2012. Obtaining ionograms with a high temporal resolution allowed us to trace the dynamics and evolution of additional traces referred to as “cusps”, and also to combine ionograms with such traces into sequences. The percentage of ionograms containing cusps proved to be more than 10% of the overall number of ionograms. Thus, during daytime, the rate surpasses 30%, whereas, during nighttime, such ionograms are practically absent. The typical cusp lifetime proved to be 4-15 min, therefore, disturbed ionograms are much more rarely detected with standard vertical sounding ionosondes. The presence of such traces unambiguously evidences significant electron density horizontal gradients caused by travelling ionospheric disturbances (TIDs) with scales up to 50 km.
Observations of traveling ionospheric disturbances on the basis of vertical and near-vertical sounding data
We have conducted a morphological analysis of vertical and near — vertical sounding ionograms. The reported experimental results were produced by vertical incidence ionosonde located in Tory settlement (52°53 N, 103° 16 E) and by near-vertical ionospheric sounding from the town of Usolie (51°48 N, 103°50 E) to Tory (ground range of 120km). The observations were carried out from 2011 till 2016 years continuously. Apart from themain trace, some ionograms feature an additional trace (called “cusp”). Cusp-shaped traces on ionograms have been associated with off-angle reflections from tilted surfaces of constant ionization density caused by the passage of traveling ionospheric disturbances (TID). Simulation revealed typical scales and amplitudes of TIDs that had caused cusps. Conventional cusps (so-called U-shaped cusps) have been considered to reveal their occurrence rate, average duration dependent on the time of the day. The ionosonde records were taken once each minute over a period of six years, which allowed us to trace the dynamics and evolution of cusps as well as seasonal characteristics of TID occurrence. Normally, cusps in the ionograms were found to move from the region of high frequencies and large group delays toward the region of lower frequencies and smaller group delays (downward and from right to left along the main trace of the ionogram). There were also cases when cusps moved in the opposite direction or changed their direction, but such cases were quite rare. We also studied dependence of the average cusp occurrence and duration of cusps onthe time of the day, seasons of year and geomagnetic activity.
New Sweet-Tasting C21-Pregnane Glycosides from Pericarps of Myriopteron extensum.
Ten novel C21 pregnane glycosides, extensumside C-L (1-10), were isolated as highly sweet-tasting substances from the edible pericarps of Myriopteron extensum (Wight) K. Schum by sensory-guided fractionation and purification. Their structures were determined through 1D and 2D NMR, such as HSQC, HMBC, 1H-1H COSY, HSQC-TOCSY, and ROESY, as well as other spectroscopic analysis combined with chemical evidence. These compounds shared the same aglycone, 3β,16α-dihydroxy-pregn-5-en-20-one, and contained the deoxysugar chain and the glucose chain which were linked to C-3 and C-16 of the aglycone, respectively. The sweetness potency was evaluated by a human sensory panel test and preliminary structure-taste relationship was discussed. The sweetness intensities of these compounds are between 50 and 400 times greater than that of sucrose. Furthermore, quantitation analyses of compounds 1, 3, 4, and 6 in different parts of M. extensum indicated that the concentrations of these sweet components in the pericarps are obviously higher than those in stems and roots.