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Abstract

This study investigates the escape of Mercury's sodium-group ions (Na+-group, including ions with m/q from 21 to 30 amu/e) and their dependence on true anomaly angle (TAA), that is, Mercury's orbital phase around the Sun, using measurements from MESSENGER. The measurements are categorized into solar wind, magnetosheath, and magnetosphere, and further divided into four TAA intervals. Na+-group ions form escape plumes in the solar wind and magnetosheath, with higher fluxes along the solar wind's motional electric field. The total escape rates vary from 0.2 to 1 × 1025 atoms/s with the magnetosheath being the main escaping region. These rates exhibit a TAA dependence, peaking near the perihelion and similar during Mercury's remaining orbit. Despite Mercury's tenuous exosphere, Na+-group ions escape rate is comparable to other inner planets. This can be attributed to several processes, including that Na+-group ions may include several ion species, efficient photoionization frequency for elements within Na-group, etc.

Abstract

In this study, we investigate the role of cold pools in modulating convective organization throughout the Madden-Julian Oscillation (MJO) life cycle using a modeling approach that combines Eulerian and Lagrangian techniques. First, we conduct a simulation using the soundings and forcing of the DYNAMO/AMIE campaign. The simulation shows a lag of several days between the precipitation rate peak time associated with MJO and the highest convective organization time. Second, to analyze the role of cold pools, we consider a series of 2-day simulations conducted at different stages of the MJO. The simulation results suggest that cold pools are larger and last longer during the mature stages of the MJO, possibly because of decreased environmental surface latent heat fluxes and stronger downdrafts. These lead to the formation of moist rings at the leading edges of cold pools, facilitating the formation of more convective cores and increasing the degree of convective organization.

Abstract

Antarctic Bottom Water has been warming in recent decades throughout most of the oceans and freshening in regions close to its Indian and Pacific sector sources. We assess warming rates on isobars in the eastern Pacific sector of the Southern Ocean using CTD data collected from shipboard surveys from the early 1990s through the late 2010s together with CTD data collected from Deep Argo floats deployed in the region in January 2023. We show cooling and freshening in the temperature-salinity relation for water colder than ∼0.4°C. We further find a recent acceleration in the regional bottom water warming rate vertically averaged for pressures exceeding 3,700 dbar, with the 2017/18 to 2023/24 trend of 7.5 (±0.9) m°C yr−1 nearly triple the 1992/95 to 2023/24 trend of 2.8 (±0.2) m°C yr−1. The 0.2°C isotherm descent rate for these same time periods nearly quadruples from 7.8 to 28 m yr−1.

Abstract

During February 2023, the quasi-4-day wave (Q4DW) with westward zonal wavenumber 2 (W2) reached its largest amplitude of ∼400 m in the Southern Hemisphere (SH) geopotential height observations since 2004, which occurred simultaneously with an Arctic major sudden stratospheric warming (SSW) with an elevated stratopause (ES). However, the Q4DW-W2 perturbations in the Northern Hemisphere (NH) were unexpectedly suppressed despite the unstable Arctic stratosphere and mesosphere during the 2023 ES-SSW. Diagnostic analysis shows that the westward winds at ∼54°N–70°N in the upper stratosphere of ∼-79 m/s during the 2023 ES-SSW were the strongest during boreal winters over the past two decades, which benefited from the onset of a preceding minor SSW at the end of January. The strongest westward wind generated a wave geometry configuration of full reflection for Q4DW-W2 in the NH, while the Q4DW-W2 enhancement in the SH was induced by the in-situ amplification of the surviving seeding perturbations.

Abstract

Ozone (O3) pollution is a severe air quality issue in China, posing a threat to human health and ecosystems. The climate change will affect O3 levels by directly changing physical and chemical processes of O3 and indirectly changing natural emissions of O3 precursors. In this study, near-surface O3 concentrations in China in 2030 and 2060 are predicted using the process-based interpretable Extreme Gradient Boosting (XGBoost) model integrated with multi-source data. The results show that the climate-driven O3 levels over eastern China are projected to decrease by more than 0.4 ppb in 2060 under the carbon neutral scenario (SSP1-1.9) compared with the high emission scenario (SSP5-8.5). Among this reduction, 80% is attributed to the changes in physical and chemical processes of O3 related to a cooler climate, while the remaining 20% is attributed to the reduced biogenic isoprene emissions.

Abstract

The quantitative relationship between Mesoscale Convective Systems (MCSs) and floods over East Asia has not been established. In this study, MCSs are clustered into four types with Self-Organizing Map approach. Floods in June-August of 2000–2021 are linked with different types of MCS by automated algorithms we constructed. We find that among the major floods (potential flood peak periods), 91% (87%) are related to MCS, 65% (78%) are dominated by MCS, and 38% (20%) are dominated by multi-types of MCS. Types 1 and 2 MCS have higher flood-inducing efficiencies than common MCS (Type-4). Type-1 MCS, characterized by the least number (2% of the total number), the largest precipitation volume, longest lifetime, slowest moving, strongest precipitation, can most efficiently produce floods. Type-2 MCS, characterized by the second largest precipitation volume, more numerous than Type-1 particularly over land, can induce floods not only relatively efficiently but also more frequently than Type-1.

Abstract

An area of ocean centered on 179°E, 46°S has warmed to full depth since 2006, with surface warming around 5 times the global rate. This Subtropical Front area is associated with a confluence of warm, salty, subtropical water from the north carried in a western boundary current and cold, fresh, subantarctic water from the south carried in the northernmost branch of the Antarctic Circumpolar Current. Temperature and salinity changes observed from Argo floats indicate that the Subtropical Frontal Zone has moved west ∼120 km, creating this area of strong warming analogous to changes in extension regions of other western boundary currents. The warming is a result of changes in the local flows of subantarctic water, evident in satellite altimeter data and 1,000 m Argo trajectories, which in turn likely result from changes in meridional ocean heat content and winds. The warming has placed this biologically-significant region in almost perpetual marine heatwave conditions.

Abstract

We evaluate average wave intensities at frequencies up to 10 kHz measured by two ground stations in Canada and two others in Finland at auroral and subauroral latitudes over a full year, as well as by the low-altitude DEMETER spacecraft during the years 2004–2010. Lightning location and energy data obtained by the World Wide Lightning Location Network, along with geomagnetic activity characterized by the Kp index, are further used. Latitudinal, diurnal, and annual variations are analyzed, and the global intensities measured on the ground and by the spacecraft are systematically compared for the first time. We show that lightning-generated waves often dominate the measured wave intensities, particularly during the night, in summer, and at higher frequencies. DEMETER observations, supported by ray-tracing analysis, reveal a significant role of nonducted lightning-generated whistler propagation between the hemispheres. Finally, the wave intensity response to geomagnetic activity variations is quite different on the ground compared to in space. While spacecraft-measured wave intensities are considerably larger during periods of enhanced geomagnetic activity, the ground-based intensities are only sporadically enhanced during geomagnetically active periods.

Abstract

We present broadband ionospheric scintillation observations of highly defined symmetric quasi-periodic scintillations (QPS: Maruyama, 1991, https://doi.org/10.1029/91rs00357) caused by plasma structures in the mid-latitude ionosphere using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013, https://doi.org/10.1051/0004-6361/201220873). Two case studies are shown, one from 15 December 2016, and one from 30 January 2018, in which well-defined main signal fades are observed to be bounded by secondary diffraction fringing. The ionospheric plasma structures effectively behave as a Fresnel obstacle, in which steep plasma gradients at the periphery result in a series of decreasing intensity interference fringes, while the center of the structures largely block the incoming radio signal altogether. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behavior in the QPSs which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delay-Doppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPSs ranging from 50 to 00 m s−1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5 and 20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, co-temporal ionosonde data, suggest the propagation of the plasma structures causing the QPSs are in the E-region. Each of the two events is accurately reproduced using a thin screen phase model. Individual signal fades and enhancements were modeled using small variations in total electron content (TEC) amplitudes of order 1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modeling of QPSs in the literature.

Abstract

Despite more than half a century of Collisionless shock (CS) research, our understanding of the processes of the shock energy dissipation into the charge particle heating and acceleration remains incomplete. To help to address the problem of the rate of the data analysis on CSs being well below of the rate of the data acquisition, an open-source high-level database of shocks and a centralized source of advanced tools for the purpose of analyzing shock structure and dynamics have been developed. The database is called SHARP shock database by the name of the project SHARP (Shocks: structure, AcceleRation, dissiPation) funded by the European Union's Horizon 2020 program. The SHARP shock database contains shock crossings and corresponding parameters obtained from Cluster and MMS (Magnetospheric Multiscale) missions for terrestrial bow shocks, THEMIS (Time History of Events and Macroscale Interactions during Substorms)/ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun) missions for interplanetary shocks, and MAVEN (Mars Atmosphere and Volatile EvolutioN) and VEX (Venus Express) missions for shocks at non-magnetized planets. The SHARP shock database can be accessed via https://sharp.fmi.fi/shock-database/.

Abstract

The OI 630.0 nm airglow emission variability provides salient information on the dynamical changes taking place in the upper atmosphere at around 250 km. The emission rates vary with the changes in the ambient electron densities and the neutral constituents that are associated with these emissions. On several occasions, enhancements in these emissions are observed during post-sunset hours, around 21 local time (LT), as measured from Mt. Abu (24.6°N, 72.7°E, 19°N Mag), a low-latitude location at Indian longitudes. These enhancements occur following the typical monotonic decrease in emission intensity after sunset. The presence of poleward meridional wind preceded by cessation and reversal of equatorward wind at the post-sunset hours was shown to be the cause for such observed emission enhancements in an earlier study. In this study, the cause of such reversal in meridional winds during post-sunset hours has been investigated using the variation in electron densities and meridional winds simulated by the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X), which also shows enhancements in electron densities similar to those observed in the post-sunset OI 630.0 nm nightglow emissions, and simultaneous reversal in meridional winds as well. The amplitudes and phases of different components of tides obtained from WACCM-X meridional winds reveal a significant contribution of higher-order tides, especially, quarter-diurnal tides, to the observed reversal in the meridional winds during post-sunset hours.

Abstract

The strong noise of satellite-based Time-Variable Gravity (TVG) field is often suppressed by applying the averaging filters. However, how to appropriately compromise the data blurring and de-noising remains as a challenge. In our hypothesis, the optimum spatial averaging filter expects to contain averaging kernels that capture the same amount of orbital samples everywhere, to avoid introducing excessive data blurring. To achieve the goal, we take advantages of the spherical convolution and introduce extra spatial constraints into a Gaussian kernel: (1) its half-width radius adapts to the global inhomogeneity of satellite orbit, and (2) the kernel is reshaped as an ellipsoid to adapt to the regional anisotropy. In this way, we designed optimal filters that contain a spatially-Varying non-isotropic Gaussian-based Convolution (VGC) kernel. The VGC-based filter is compared against three most popular filters through real TVG fields and another closed-loop simulation. In both scenarios, VGC-based filters retain more realistic secular trend and seasonal characteristics, in particular at high latitudes. The spatial correlation between the VGC estimates and the simulated ground truth is found to be 0.95 and 0.86 over Greenland and Antarctica, which is found to be 10% better than other tested filters. Temporal correlations with the ground truth are also found to be considerably better than the other filters over 90% of the globally distributed river basin. Besides, the VGC-based filters provide tolerable efficiency (3.5 s per month) and sufficient accuracy (integral error less than 3%). The method can be extended to the next generation gravity mission as well.

Plain Language Summary

Time-Variable Gravity (TVG) fields of the Gravity Recovery and Climate Experiment (GRACE) and its Follow-On mission (GRACE-FO) need proper filtering to suppress the noise before being applied for intended geophysical studies. Existing filters are generally designed in the spectral domain. Though they are numerically efficient, they can hardly treat the noise in fairness, globally. As a result, the TVG fields may get over-smoothed after applying those filters, particularly in regions with high-latitudes. However, it would be mathematically simple to design a filter by applying a spherical convolution, whose kernels can be easily constrained and tuned in the spatial domain. This study introduces filters with spatially-Varying non-isotropic Gaussian-based Convolution kernel (VGC) that is enforced to comply with the spatial distribution of the TVG noise. The proposed filter is found to preserve a finer spatial resolution of TVG fields, and at the same time, to be able to de-noise them at a comparable level as the existing techniques. Geophysical applications that use GRACE-like TVG fields might have benefits from this practical filtering technique.

Abstract

To address the lack of publicly available inter-frequency clock bias (IFCB) products and the impact of IFCB on real-time or near-real-time multi-frequency precision positioning, a MATLAB-based software for multi-GNSS IFCB estimation and forecast (M_IFCB) was produced for multi-frequency users. This software can estimate the IFCB of GPS, BDS-2, Galileo and BDS-3 satellites and provide three alternative forecast models for GPS satellites with large IFCB amplitude variations. To verify the availability of M_IFCB, 194 and 41 globally evenly distributed MGEX continuous tracking stations were used for IFCB estimation and GPS triple-frequency uncombined precise point positioning (PPP) performance evaluation, respectively. The results show that the precision of the static solutions of the triple-frequency uncombined PPP increased by about 20.4% in the horizontal direction and 18.5% in the vertical direction, respectively. Incorporating the predicted IFCB correction, the precision of the static solutions increased by about 19.9% in the horizontal direction and 17.6% in the vertical direction, respectively.

Н.Н. Колачевский

Publication date: Available online 26 June 2024

Source: Advances in Space Research

Author(s): David J. Fitzpatrick, Scott E. Palo

Publication date: Available online 25 June 2024

Source: Advances in Space Research

Author(s): Luke T. Cornwell, Mark J. Burchell, Penelope J. Wozniakiewicz

Publication date: Available online 25 June 2024

Source: Advances in Space Research

Author(s): Ershen Wang, Yilin He, Tengli Yu, Liang Liu, Song Xu, Pingping Qu, Tao Pang

Publication date: Available online 25 June 2024

Source: Advances in Space Research

Author(s): Donghwa Kang, Andreas Haungs

Quantitative Sub-Ice and Marine Tracing of Antarctic Sediment Provenance (TASP v1.0)
Jim Marschalek, Edward Gasson, Tina van de Flierdt, Claus-Dieter Hillenbrand, Martin Siegert, and Liam Holder
Geosci. Model Dev. Discuss., https//doi.org/10.5194/gmd-2024-104,2024
Preprint under review for GMD (discussion: open, 0 comments)
Ice sheet models can help predict how Antarctica's ice sheets respond to environmental change, and such models benefit from comparison to geological data. Here, we use an ice sheet model output, plus other data, to predict the erosion of debris and trace its transport to where it is deposited on the ocean floor. This allows the results of ice sheet modelling to be directly and quantitively compared to real-world data, helping to reduce uncertainty regarding Antarctic sea level contribution.

Wind comparisons between meteor radar and Doppler shifts in airglow emissions using field-widened Michelson interferometers
Samuel K. Kristoffersen, William E. Ward, and Chris E. Meek
Atmos. Meas. Tech., 17, 3995–4014, https://doi.org/10.5194/amt-17-3995-2024, 2024
In this paper, the relationship between observations from two instruments, a meteor radar and a field-widened Michelson interferometer (ERWIN) which provide complementary information on this region, is investigated. On average the ratio of ERWIN winds to meteor radar winds is ∼ 0.7. Differences between the wind observations may be caused by variations in the airglow brightness associated with dissipating gravity waves.