Temperature Tides Across the Mid-Latitude Summer Turbopause Measured by a Sodium Lidar and MIGHTI/ICON

Local full diurnal coverage of temperature variations across the turbopause (∼90–115 km altitude) is achieved by combining the nocturnal observations of a Sodium (Na) Doppler lidar on the Utah State University (USU) campus (41.7°N, 248.2°E) and NASA Michelson interferometer for global high-resolution thermospheric imaging (MIGHTI)/Ionospheric connection explorer (ICON) daytime observations made in the same vicinity. In this study, utilizing this hybrid data set during summer 2020 between June 12th and July 15th, we retrieve the temperature signatures of diurnal and semidiurnal tides in this region. The tidal amplitudes of both components have similar vertical variation with increasing altitude: less than 5 K below ∼98 km but increase considerably above, up to 19 K near 104 km. Both experience significant dissipation near turbopause altitudes, down to ∼12 K up to 113 km for the diurnal tide and ∼13 K for the semidiurnal tide near 110 km. In addition, while the semidiurnal tidal behavior is consistent with the theoretical predictions, the diurnal amplitude is considerably larger than what is expected in the turbopause region. The tidal phase profile shows a dominance of tidal components with a long vertical wavelength (longer than 40 km) for the semidiurnal tide. On the other hand, the diurnal tide demonstrates close to an evanescent wave behavior in the turbopause region, which is absent in the model results and Thermosphere ionosphere mesosphere energetics and dynamics (TIMED)/Sounding of the atmosphere using broadband radiometry (SABER) observations

Yersinia pestis strains from Latvia show depletion of the pla virulence gene at the end of the second plague pandemic

Ancient genomic studies have identified Yersinia pestis (Y. pestis) as the causative agent of the second plague pandemic (fourteenth-eighteenth century) that started with the Black Death (1,347-1,353). Most of the Y. pestis strains investigated from this pandemic have been isolated from western Europe, and not much is known about the diversity and microevolution of this bacterium in eastern European countries. In this study, we investigated human remains excavated from two cemeteries in Riga (Latvia). Historical evidence suggests that the burials were a consequence of plague outbreaks during the seventeenth century. DNA was extracted from teeth of 16 individuals and subjected to shotgun sequencing. Analysis of the metagenomic data revealed the presence of Y. pestis sequences in four remains, confirming that the buried individuals were victims of plague. In two samples, Y. pestis DNA coverage was sufficient for genome reconstruction. Subsequent phylogenetic analysis showed that the Riga strains fell within the diversity of the already known post-Black Death genomes. Interestingly, the two Latvian isolates did not cluster together. Moreover, we detected a drop in coverage of the pPCP1 plasmid region containing the pla gene. Further analysis indicated the presence of two pPCP1 plasmids, one with and one without the pla gene region, and only one bacterial chromosome, indicating that the same bacterium carried two distinct pPCP1 plasmids. In addition, we found the same pattern in the majority of previously published post-Black Death strains, but not in the Black Death strains. The pla gene is an important virulence factor for the infection of and transmission in humans. Thus, the spread of pla-depleted strains may, among other causes, have contributed to the disappearance of the second plague pandemic in eighteenth century Europe