Impact of sudden stratospheric warmings on the neutral density, temperature and wind in the MLT region

In this study, the neutral density and horizontal wind observed by the four meteor radars, as well as the temperature measured by the Microwave Limb Sounder (MLS) onboard the Aura satellite are used to examine the response of neutral density, wind, and temperature in the MLT region to the stratospheric sudden warmings (SSWs) during 2005 to 2021 in the Northern Hemisphere. The four meteor radars include the Svalbard (78.3°N, 16°E) and Tromsø (69.6°N, 19.2°E) meteor radars at high latitudes and the Mohe (53.5°N, 122.3°E) and Beijing (40.3°N, 116.2°E) meteor radars at middle latitudes. The superposed epoch analysis results indicate that: 1) the neutral density over Svalbard and Tromsø at high latitude increased at the beginning of SSWs and decreased after the zonal mean stratospheric temperature reached the maximum. However, the neutral density over Mohe at midlatitudes decreased in neutral density at the beginning of SSW and increase after the zonal mean stratospheric temperature reached the maximum. 2) The zonal wind at high latitudes show a westward enhancement at the beginning of SSWs and then shows an eastward enhancement after the stratospheric temperature reaches maximum. However, the zonal wind at midlatitudes shows an opposite variation to at high latitudes, with an eastward enhancement at the onset and changing to westward enhancements after the stratospheric temperature maximum. The meridional winds at high and midlatitudes show a southward enhancement after the onset of SSW and then show a northward enhancement after the stratospheric temperature maximum. 3) In general, the temperature in the MLT region decreased throughout SSWs. However, as the latitudes decrease, the temperature cooling appears to lag a few days to the higher latitudes, and the degree of cooling will decrease relatively

Impact of sudden stratospheric warmings on the neutral density, temperature and wind in the MLT region

In this study, the neutral density and horizontal wind observed by the four meteor radars, as well as the temperature measured by the Microwave Limb Sounder (MLS) onboard the Aura satellite are used to examine the response of neutral density, wind, and temperature in the MLT region to the stratospheric sudden warmings (SSWs) during 2005 to 2021 in the Northern Hemisphere. The four meteor radars include the Svalbard (78.3°N, 16°E) and Tromsø (69.6°N, 19.2°E) meteor radars at high latitudes and the Mohe (53.5°N, 122.3°E) and Beijing (40.3°N, 116.2°E) meteor radars at middle latitudes. The superposed epoch analysis results indicate that: 1) the neutral density over Svalbard and Tromsø at high latitude increased at the beginning of SSWs and decreased after the zonal mean stratospheric temperature reached the maximum. However, the neutral density over Mohe at midlatitudes decreased in neutral density at the beginning of SSW and increase after the zonal mean stratospheric temperature reached the maximum. 2) The zonal wind at high latitudes show a westward enhancement at the beginning of SSWs and then shows an eastward enhancement after the stratospheric temperature reaches maximum. However, the zonal wind at midlatitudes shows an opposite variation to at high latitudes, with an eastward enhancement at the onset and changing to westward enhancements after the stratospheric temperature maximum. The meridional winds at high and midlatitudes show a southward enhancement after the onset of SSW and then show a northward enhancement after the stratospheric temperature maximum. 3) In general, the temperature in the MLT region decreased throughout SSWs. However, as the latitudes decrease, the temperature cooling appears to lag a few days to the higher latitudes, and the degree of cooling will decrease relatively

Rhodamine 6G/Transition Metal Dichalcogenide Hybrid Nanoscrolls for Enhanced Optoelectronic Performance

The low light absorption efficiency has seriously hindered the application of two-dimensional transition metal dichalcogenide (TMDC) nanosheets in the field of optoelectronic devices. Various approaches have been used to improve the performance of TMDC nanosheets. Preparation of one-dimensional TMDC nanoscrolls in combination with photoactive materials has been a promising method to improve their properties recently. In this work, we report a facile method to enhance the optoelectronic performance of TMDC nanoscrolls by wrapping the photoactive organic dye rhodamine (R6G) into them. After R6G molecules were deposited on monolayer TMDC nanosheets by the solution method, the R6G/MoS2 nanoscrolls with lengths up to hundreds of microns were prepared in a short time by dropping a mixture of ammonia and ethanol solution on the R6G/MoS2 nanosheets. The as-obtained R6G/MoS2 nanoscrolls were well characterized by optical microscopy, atomic force microscopy, Raman spectroscopy, and transmission electron microscopy to prove the encapsulation of R6G. There are multiple type II heterojunction interfaces in the R6G/MoS2 nanoscrolls, which can promote the generation of photo-induced carriers and the following electron–hole separation. The separated electrons were transported rapidly along the axial direction of the R6G/MoS2 nanoscrolls, which greatly improves the efficiency of light absorption and photoresponse. Under the irradiation of an incident 405 nm laser, the photoresponsivity, carrier mobility, external quantum efficiency, and detectivity of R6G/MoS2 nanoscrolls were enhanced to 66.07 A/W, 132.93 cm2V−1s−1, 20,261%, and 1.25 × 1012 cm·Hz1/2W−1, which are four orders of magnitude higher than those of monolayer MoS2 nanosheets. Our work indicates that the R6G/TMDC hybrid nanoscrolls could be promising materials for high-performance optoelectronic devices

Multimode tunable terahertz absorber based on a quarter graphene disk structure

In this research work, in order to solve the unadjustability of traditional noble metal absorbers to meet the complex application requirements in the actual electromagnetic environment, we designed a simple tunable absorber based on graphene with tunable Fermi level. The performance of the proposed absorber is theoretically simulated by the finite difference time domain (FDTD) method. The proposed absorber has two perfect absorption peaks with high efficiency of 99.51% and 99.548% in its working band (90–155 μm). We have performed an in-depth analysis of the causes of perfect absorption and focused on the tunability of the absorber. The absorption frequency can be adjusted by controlling the relaxation time and Fermi level of graphene, and the same purpose can be achieved by changing the refractive index (relative dielectric constant) of the medium. In addition, we also explored the influence of the change of the top structure parameters on the absorption performance. The proposed absorber has the ability to adapt to different electromagnetic environments. In general, it can be flexibly regulated in practical applications, which will provide new possibilities for the development of many fields such as detection and communication

Mesopause temperatures and relative densities at midlatitudes observed by the Mengcheng meteor radar

The atmospheric temperatures and densities in the mesosphere and lower thermosphere (MLT) region are essential for studying the dynamics and climate of the middle and upper atmosphere. In this study, we present more than 9 years of mesopause temperatures and relative densities estimated by using ambipolar diffusion coefficient measurements observed by the Mengcheng meteor radar (33.4°N, 116.5°E). The intercomparison between the meteor radar and Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere by Broadband Emission Radiometry (TIMED/SABER) and Earth Observing System (EOS) Aura/Microwave Limb Sounder (MLS) observations indicates that the meteor radar temperatures and densities agree well with the simultaneous satellite measurements. Annual variations dominate the mesopause temperatures, with the maximum during winter and the minimum during summer. The mesopause relative densities also show annual variations, with strong maxima near the spring equinox and weak maxima before the winter solstice, and with a minimum during summer. In addition, the mesopause density exhibits a structure similar to that of the zonal wind: as the zonal wind flows eastward (westward), the mesopause density decreases (increases). At the same time, the meridional wind shows a structure similar to that of the mesopause temperature: as the meridional wind shows northward (southward) enhancements, the mesopause temperature increases (decreases). Simultaneous horizontal wind, temperature, and density observations provide multiple mesospheric parameters for investigating mesospheric dynamics and thermodynamic processes and have the potential to improve widely used empirical atmospheric models

Significant methane undersaturation during austral summer in the Ross Sea (Southern Ocean)

Methane (CH4) is a climate-relevant trace gas that is emitted from the open and coastal oceans in considerable amounts. However, its distribution in remote oceanic areas is largely unknown. To fill this knowledge gap, dissolved CH4 was measured at nine stations at 75°S in the Ross Sea during austral summer in January 2020. CH4 undersaturation (mean: 82 ± 20%) was found throughout the water column. In subsurface waters, the distribution of CH4 mainly resulted from mixing of water masses and in situ consumption, whereas the CH4 concentrations in the surface mixed layer were mainly driven by air–sea exchange and diapycnal diffusion between the surface and subsurface layers, as well as consumption of CH4. With a mean air–sea CH4 flux density of −0.44 ± 0.34 μmol m−2 d−1, the Ross Sea was a substantial sink for atmospheric CH4 during austral summer, which is in contrast with most oceanic regions, which are known sources

Significant methane undersaturation during austral summer in the Ross Sea (Southern Ocean)

Abstract Methane (CH4) is a climate‐relevant trace gas that is emitted from the open and coastal oceans in considerable amounts. However, its distribution in remote oceanic areas is largely unknown. To fill this knowledge gap, dissolved CH4 was measured at nine stations at 75°S in the Ross Sea during austral summer in January 2020. CH4 undersaturation (mean: 82 ± 20%) was found throughout the water column. In subsurface waters, the distribution of CH4 mainly resulted from mixing of water masses and in situ consumption, whereas the CH4 concentrations in the surface mixed layer were mainly driven by air–sea exchange and diapycnal diffusion between the surface and subsurface layers, as well as consumption of CH4. With a mean air–sea CH4 flux density of −0.44 ± 0.34 μmol m−2 d−1, the Ross Sea was a substantial sink for atmospheric CH4 during austral summer, which is in contrast with most oceanic regions, which are known sources