Measurements of metastable helium in Earth’s atmosphere by resonance lidar

Monitoring and predicting space weather activity is increasingly important given society’s growing reliance on space-based infrastructure but is hampered by a lack of observational data. Airglow at 1083 nm from metastable helium He(23S) in the thermosphere has long been a target for remote-sensing instruments seeking to fill that gap; however, passive measurements of He(23S) fluorescence are limited by low brightness, and interpretation of these observations is complicated by the > 500 km depth of the He(23S) layer. Here, we demonstrate a lidar instrument that is able to stimulate and detect He(23S) fluorescence, and we present measured profiles of He(23S) density. These measurements provide crucial validation to space weather models, support predictions of peak number density ( ~ 1 cm−3) and the dependence of density on altitude, solar zenith angle, and season, and extend by a factor of 4 the maximum probed altitude range by an atmospheric profiling lidar. These measurements open the door for the development of more sophisticated lidars: by applying well-established spectroscopic lidar techniques, one can measure the Doppler shift and broadening of the He(23S) line, thereby retrieving profiles of neutral wind speed and temperature, opening a window for studying space weather phenomena

Pathogenic Fungi Regulate Immunity by Inducing Neutrophilic Myeloid-Derived Suppressor Cells

Peer reviewedPublisher PD

U-Pb zircon and monazite age constraints on granulite-facies metamorphism and deformation in the Strangways Metamorphic Complex (central Australia)

The age of Proterozoic granulite facies metamorphism and deformation in the Strangways Metamorphic Complex (SMC) of central Australia is determined on zircon grown in syn-metamorphic and syn-deformational orthopyroxene-bearing, enderbitic, veins. SHRIMP zircon studies suggest that M1-M2 and the correlated periods of intense deformation (D1-D2) are part of a single tectonothermal event between 1,717 ± 2 and 1,732 ± 7 Ma. It is considered unlikely that the two metamorphic phases (M1, M2) suggested by earlier work represent separate events occurring within 10-25 Ma of each other. Previous higher estimates for the age of M1 granulite metamorphism in the SMC (Early Strangways event at ca. 1,770 Ma) based on U-Pb zircon dating of granitic, intrusive rocks, are not believed to relate to the metamorphism, but to represent pre-metamorphic intrusion ages. Conventional multigrain U-Pb monazite analyses on high-grade metasediments from three widely spaced localities in the western SMC yield 207Pb/235U ages between 1,728 ± 11 and 1,712 ± 2 Ma. The age range of the monazites corresponds to the SHRIMP zircon ages in the granulitic veins and is interpreted to record monazite growth (prograde in the metasedimentary rocks). The data imply a maximum time-span of 30 Ma for high-grade metamorphism and deformation in the SMC. There is, thus, no evidence for an extremely long period of continuous high-temperature conditions from 1,770 to ca. 1,720 Ma as previously proposed. The results firmly establish that the SMC has a very different high-grade metamorphic history than the neighbouring Harts Range, where upper amphibolite facies metamorphism in the Palaeozoic caused widespread growth or recrystallization of monazite

Development of a Helium Resonance Lidar for the Upper Thermosphere

Resonance lidars targeting fluorescence lines of metallic layers in the mesosphere and lower thermosphere have long been used to measure profiles of wind and temperature [1], most recently achieving a maximum altitude of 300 km [2], but the rapidly decreasing densities of these metallic species prevents measurements at higher altitudes. An alternative, first proposed in 1997 [3], is an extension of this technique to metastable helium, which would increase the possible range of resonance lidar measurements to 1000 km or higher. Last year, for the first time, a helium resonance lidar system was realized at the German Aerospace Center (DLR) in southern Germany [4]. The initial measurements by this instrument, made last year between January and March, captured the first profiles of metastable helium density, extending to an altitude of 700 km. We present an overview of this lidar system; we report an update on its status, including the results of the second measurement campaign; and we discuss the potential for wind and temperature measurements given anticipated improvements to system performance. [1] Fricke, K. & von Zahn, U. (1985) Mesopause temperatures derived from probing the hyperfine structure of the D2 resonance line of sodium by lidar. J. Atmos. Terrestrial Phys. 47, 499–512. [2] Jiao, J., Chu, X., Jin, H., Wang, Z., Xun, Y., Du, L., et al. (2022). First lidar profiling of meteoric Ca+ ion transport from 80 to 300 km in the midlatitude nighttime ionosphere. Geophysical Research Letters, 49, e2022GL100537. https://doi.org/10.1029/2022GL100537 [3] Gerrard, A. J., Kane, T. J., Meisel, D. D., Thayer, J. P. & Kerr, R. B. (1997) Investigation of a resonance lidar for measurement of thermospheric metastable helium. J. Atmos. Sol. Terrestrial Phys. 59, 2023–2035 [4] Kaifler, B., Geach, C., Büdenbender, H.C. et al. (2022) Measurements of metastable helium in Earth’s atmosphere by resonance lidar. Nat Commun 13, 6042 https://doi.org/10.1038/s41467-022-33751-