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Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) have long been a subject of interest in ionospheric research. However, their spatiotemporal variability across regions, local times, seasons, and solar cycles is very complicated and remains not well established. Using Total Electron Content (TEC) data from global GNSS receiver networks processed at MIT Haystack Observatory, we perform a detailed statistical analysis of MSTIDs over the Continental US (CONUS). Differential TEC data every day from 2012 to 2023 are processed using a keogram-based image processing technique to identify MSTID wave properties, including the occurrence, propagation direction, phase speed, wavelength, and period. Focusing on eastern US midlatitudes (80 degrees W, 40 degrees N), we extend comparisons longitudinally and latitudinally across CONUS. Our results reveal significant variability in MSTID occurrence rates and propagation directions, notably linked to solar terminators. MSTID occurrence peaks after summer sunrise (with minor maxima near winter daytime), around summer sunset, and after summer midnight. Occurrence generally correlates positively with solar activity in summer but can become negative after winter midnight. In winter, MSTIDs propagate southeastward in the morning and rotate clockwise to west-northwestward after midnight; in summer, propagation is more variable. Comparisons across the CONUS highlight strong regional differences. Our findings reflect complex drivers behind MSTIDs, including gravity waves, electrodynamic processes, and solar terminators. Their relative influences vary with local time, season, and location. This long-term analysis provides critical insights into MSTID climatology and forms a basis for in-depth investigations of MSTID generation mechanisms.
We investigate the impacts of increased CO2 concentration on migrating diurnal tide (DW1). A future climate simulation is conducted using a WACCM-X model, with surface CO2 levels increasing according to the RCP8.5 scenario. The DW1 (1,1) mode, a propagating tide peaking near the equator, exhibits a statistically significant positive trend in a range of 20-70 km, and a significant negative trend in a range of 90-110 km. The positive trend is likely driven by a reduction in atmospheric density in the mesosphere and enhanced equatorial convective activity, while the negative trend appears in the mesosphere, which overwhelms the positive trend. Two potential mechanisms may explain the negative trend. First, increasing CO2 enhances mesospheric stability, reducing tidal vertical wavelengths. In our simulation, equatorial temperatures around similar to 50-70 km become cooler than those in similar to 70-90 km. This strong cooling could be linked to CO2 mixing and transport, as well as the contraction of the mesospheric ozone layer due to atmospheric descent induced by CO2-driven cooling. Second, stronger convective activity intensifies gravity wave generation, increasing gravity wave diffusion in the mesosphere. This strong convective activity also likely intensifies the tide below similar to 70 km. While our positive DW1 trend is consistent with McLandress and Fomichev (2006), the negative trend in the lower thermosphere contrasts with their results. This discrepancy might arise because their model used a time-independent diffusion coefficient, whereas WACCM-X accounts for CO2-driven changes in gravity wave diffusion. The negative trend is confirmed in SABER observation for the last two decades, while the positive trend is not verified.
Barrier layer (BL), by reinforcing ocean stratification, can maintain sea surface waters warming and limit nutrients supply into the euphotic layer, which is important to marine life. This study investigates the influence of stratospheric aerosol geoengineering (SAG) on the seasonal variability of the BL in the northeastern Gulf of Guinea (NEGG) and its causes based on data from the Geoengineering Large Ensemble project simulated under a high anthropogenic emission scenario and on observations. Results show that the model reproduces well the BL pattern according to observations in the northern Gulf of Guinea. BL is thicker in the NEGG, especially during boreal autumn, with barrier layer thickness (BLT) reaching a maximum value of 19 m in October. Under global warming compared to the current climate, the BLT increases slightly at the beginning of the year and strongly in boreal autumn by 14
Landfills are an important component of the environment, serving as major sources of methane (CH4) and reactive trace gases that contribute to radiative forcing and modify atmospheric chemistry, making them a critical target for mitigation. This study employs modeling to investigate the immediate air quality and indirect radiative effects of mitigating landfill CH4 emissions. The analysis is motivated by the potential of a novel, fuel-flexible combustion technology capable of converting all CH4 emissions to carbon dioxide. Three scenarios are assessed: (BASE) a control simulation with unchanged landfill CH4 emissions; (LCC_NAT) a hypothetical national implementation of the combustion system over a summer month; and (LCC_REG) a regional application over Texas. One-month simulations show that, compared to BASE, LCC_NAT yields clear concentration reductions in surface and column-averaged CH4 (XCH4) of -3.03 and -1.60 ppb across the contiguous United States, while LCC_REG shows declines of -2.38 and -1.42 ppb over Texas. CH4 reductions coincide with increases in hydroxyl radical (OH) concentrations under both LCC_NAT and LCC_REG scenarios, indicating an enhanced atmospheric self-cleaning capacity. At the national scale, CH4 reductions in the LCC_NAT scenario also result in improved air quality, with surface concentrations of carbon monoxide (CO), ozone (O3), and fine particulate matter (PM2.5) decreasing by 32.7 ppb, 0.27 ppb, and 0.01 μg m-3, respectively. Atmospheric cooling is induced within the atmosphere, driven primarily by negative longwave radiative forcing under clear-sky conditions in both LCC_REG (-0.38 W m-2) and LCC_NAT (-0.04 W m-2) scenarios. These cooling effects are stronger under all-sky conditions due to cloud radiative effects, as clouds may absorb efficiently thermal radiation emitted from the surface. Furthermore, net radiative forcing under all-sky conditions leads to surface cooling in LCC_NAT but regional warming in LCC_REG, highlighting the spatial variability of climate responses.
The electron density of the solar corona is a fundamental parameter in many areas of solar physics. Traditionally, routine estimates of coronal density have relied exclusively on white-light observations. However, these density estimates, obtained by inverting the white-light data, require simplifying assumptions, which may affect the robustness of the measurements. Hence, to improve the reliability of coronal density measurements, it is highly desirable to explore other complementary methods. In this study, we estimate the coronal electron densities in the middle corona, between approximately 1.7 and 3.5 R circle dot, using low-frequency radio observations from the recently commissioned Long Wavelength Array at the Owens Valley Radio Observatory (OVRO-LWA). The results demonstrate consistency with those derived from white-light coronagraph data and predictions from theoretical models. We also derive a density model valid between 1.7 and 3.5 r circle dot, given by rho(r ')=1.27r '-2+29.02r '-4+71.18r '-6 , where r '=r/R circle dot , with r the heliocentric distance. OVRO-LWA is a solar-dedicated radio interferometer that provides science-ready images with low latency, making it well suited for generating regular and independent estimates of coronal densities to complement existing white-light techniques.
