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Science, Volume 385, Issue 6711, Page 814-815, August 2024.

Science, Volume 385, Issue 6711, Page 816-816, August 2024.

Science, Volume 385, Issue 6711, Page 810-811, August 2024.

Science, Volume 385, Issue 6711, Page 809-809, August 2024.

Science, Volume 385, Issue 6711, Page 831-833, August 2024.

Science, Volume 385, Issue 6711, Page 838-840, August 2024.

Abstract

We survey crossings of Jupiter's dawn magnetopause during the Juno prime mission to identify and characterize Jupiter's magnetopause boundary layer. Using plasma and magnetic field observations from Jovian Auroral Distributions Experiment and Juno Magnetic Field investigation, we identify 53 boundary layer events from the 62 magnetopause crossings studied here. We find that the boundary layer generally exhibits mixed properties of magnetosheath and magnetosphere electron distributions, including lower characteristic electron energies and denser ion populations than in the magnetosphere, but higher characteristic electron energies and less dense ion populations than in the magnetosheath. Boundary layer proton speeds are on average slower than both the magnetosheath and magnetosphere. Other proton parameters in the boundary layer have intermediate values between the magnetosheath and magnetosphere. Through ion composition analysis in regions adjacent to the magnetopause, we find evidence of solar wind and magnetospheric plasma in the boundary layer that suggests plasma is transported across the magnetopause in both directions. This mass and energy transport may be the result of solar wind interactions such as magnetic reconnection and Kelvin-Helmholtz instabilities. However, many boundary layer events do not exhibit local signatures of these solar wind interactions and plasma may be transported by a non-local process or diffusively transported.

Abstract

We present a new technique for the upcoming tri-static incoherent scatter radar system EISCAT 3D (E3D) to perform a volumetric reconstruction of the 3D ionospheric electric current density vector field, focusing on the feasibility of the E3D system. The input to our volumetric reconstruction technique are estimates of the 3D current density perpendicular to the main magnetic field, j ⊥, and its covariance, to be obtained from E3D observations based on two main assumptions: (a) Ions fully magnetized above the E region, set to 200 km here. (b) Electrons fully magnetized above the base of our domain, set to 90 km. In this way, j ⊥ estimates are obtained without assumptions about the neutral wind field, allowing it to be subsequently determined. The volumetric reconstruction of the full 3D current density is implemented as vertically coupled horizontal layers represented by Spherical Elementary Current Systems with a built-in current continuity constraint. We demonstrate that our technique is able to retrieve the three dimensional nature of the currents in our idealized setup, taken from a simulation of an active auroral ionosphere using the Geospace Environment Model of Ion-Neutral Interactions (GEMINI). The vertical current is typically less constrained than the horizontal, but we outline strategies for improvement by utilizing additional data sources in the inversion. The ability to reconstruct the neutral wind field perpendicular to the magnetic field in the E region is demonstrated to mostly be within ±50 m/s in a limited region above the radar system in our setup.

Abstract

We use the full NASA Van Allen Probes mission (2012–2019) to extract the electron plasma density from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) and Electric Field and Waves (EFW) instruments and discuss the evolution of the plasmasphere. We generate new statistics including mean and standard deviations of the plasma density with respect to L-shell, magnetic local time (MLT), and various geomagnetic indices. These statistics are generated to be applied in radiation belt physics and space weather codes (with fits provided). The mean plasmasphere is circular around Earth with respect to MLT for Kp < 1. The mean 100 cm−3 level line is above L = 5 and mean 10 cm−3 level expands above the Van Allen Probes apogee for Kp < 1. The outer electron belt lies within the plasmasphere for 60% of all times. As activity increases (Kp > 2), a gradual MLT asymmetry forms with higher mean density in the afternoon sector due to plumes expanding outward. Conversely, the mean density decreases on the dawn and night sectors. The mean density is between ∼500 and ∼50 cm−3 between L ∼ 4 and L ∼ 6 during quiet and moderately active times (Kp < 3), representing ∼80% of all times. Statistics in regions of high density below L = 2 are underdefined for intense activity. The highest standard deviation of density represents a factor 2.5 to 3 times the mean above L = 5 and for active times. We find the percent difference between the EFW and EMFISIS densities is bounded by ±20% for quiet and moderate activity (Kp < 5) and goes up to ±100% for extreme activity.

Abstract

Weather features, such as extratropical cyclones, atmospheric rivers (ARs), and fronts, contribute to substantial amounts of precipitation globally and are associated with different precipitation characteristics. However, future changes in these characteristics, as well as their representation in climate models, remain uncertain. We attribute 6-hourly accumulated precipitation to cyclones, moisture transport axes (AR-like features), fronts, and cold air outbreaks, and the combinations thereof in 10 ensemble members of the CESM2-LE between 1960 and 2100 under the SSP3-7.0 scenario. We find that, despite some biases in both precipitation and weather features, CESM2-LE adeptly represents the precipitation characteristics associated with the different combinations of weather features. The combinations of weather features that contribute most to precipitation in the present climate also contribute the most to future changes, both due to changes in intensity as well as frequency. While the increase in precipitation intensity dominates the overall response for total precipitation in the storm track regions, the precipitation intensity for the individual weather features does not necessarily change significantly. Instead, approximately half of the increase in precipitation intensity in the storm track regions can be attributed to a higher occurrence of the more intensely precipitating combinations of weather features, such as the co-occurrence of extratropical cyclones, fronts, and moisture transport axes.

Abstract

The Atacama Desert is amongst the driest places on Earth yet large dust outbreaks seem rare. We present the first quantitative assessment of dust events in the Atacama for 1950–2021 based on station observations. A total of 1920 dust days were recorded with less than 10% being classified as dust storms. We calculated the wind speeds at 5%, 25% and 50% of the dust-event frequency distribution. The mean wind speed for the threshold of 5% is 10.9 ± 1.6 ms−1 which is twice as large as the values in the Taklamakan, Western Sahel, and Sudan, and consistent with the perceptually infrequent dust activity despite the exceptional aridity. We see no overall long-term trend but increased dust activity for 1970–1978, 1984–1988 and 2013–2017. A combination of changes in the wind speed statistics and soil conditions, possibly including anthropogenic land-use changes have led to the variability in dust activity.

Abstract

Religious burning (RB) has been identified as a major source of atmospheric aerosols on the Qinghai-Tibet Plateau. However, there is limited understanding of the detailed chemical composition, size distribution, and optical properties of RB aerosols in this region. To characterize these important aerosol properties, ambient PM2.5 and size resolved aerosols from RB emissions in Lhasa were collected during summer 2019. Organic functional group (OFG) and inorganic ion composition was measured using Fourier transform infrared spectroscopy and ion chromatography, respectively. The ambient PM2.5 was dominated by organic components, with the OFG concentrations significantly higher during religious events, reflecting the substantial impact of RB emissions on local air quality. The RB aerosols were characterized by high fractions of alkane (34%), hydroxyl (29%), and carboxylic acid (13%) groups, with peak mass in the accumulation mode (0.56–1.00 μm). The high abundance of hydroxyl group and the size distribution pattern suggested that the RB aerosols were formed from volatilization of fuel materials followed by unaltered condensation, a process that may be unique to the low-temperature, low-oxygen burning in the scattered burners at the temples. The absorption coefficient of RB aerosols showed similar size distribution to the mass size distribution, but the absorption Ångström exponent displayed the lowest value in the 0.56–1.00 μm size mode. This specific size distribution aligned with the mass fraction of carboxylic acids and mirrored the mass proportion of alkanes, suggesting that smaller and larger particles were enriched with substances that have higher light-absorbing capabilities.

Abstract

We investigate the synoptic and mesoscale dynamics of two wet and two dry cold surges in January 2021 using a combination of observations, reanalysis, and convective-scale model forecasts from the Met Office Unified Model (MetUM). We focus on the wet surges, and particularly the wettest days which are locally extreme over Singapore and the surrounding region (i.e., the daily mean and area-averaged rainfall over 20 years exceeds the 99th percentile). On the large scale, the wet surges are characterized by an anomalously strong anticyclone over Siberia prior to their onset. The anticyclone and resultant surge winds are stronger than those of the dry surges. There is also a relatively moist (dry) environment prior to the onset of the wet (dry) surges, with the Madden-Julian Oscillation (MJO) being in Phase 3 (Phase 6). On the mesoscale, the combination of the cold surge and a local tropical low produce strong, moist north-easterly winds and convection over the Singapore region. The equatorward advection of positive anomalies of equivalent potential temperature resembles a weak gravity-current-like structure at its head, although the spatial scale is much too large for a gravity current. There is a moist bias in the model forecasts, although the precipitation is underestimated regionally during the wet surges and particularly on the extreme rainfall days. Overall, the model forecasts perform well synoptically but not in the details of mesoscale convection.

Abstract

Over the past 30 years, the Arctic Dipole Anomaly (DA) has repeatedly led to record lows in summer sea ice extent, with cloud radiative effects (CRE) playing a crucial regulatory role. Here, we reveal the CRE variations between positive and negative DA events and elucidate the slowing impacts of CRE on sea ice thickness (SIT) changes. The DA triggers robust meridional winds and transpolar drift, markedly reducing SIT in the Beaufort Sea (BeS), Chukchi Sea (CS), and East Siberian Sea (ESS), while increasing it in the Greenland Sea (GS). CRE significantly slow SIT changes, contributing +14.4, +4.4, +16.4, and −26.7 cm to changes from June to August, against total changes of −55.9, −29.4, −39.8, and +42.8 cm in September over BeS, CS, ESS, and GS, respectively. This study underscores the key impacts of CRE on sea ice variation, emphasizing their significance in the polar climate system.

Abstract

The impact of the boreal summer intraseasonal oscillation (BSISO) on rainfall anomalies in the Yangtze–Huaihe River Basin (YHRB) was found to be modulated by the stratospheric quasi-biennial oscillation (QBO), which is reasonable for the close associations between the QBO and summer extreme precipitation in the YHRB. It was found that the extreme precipitation preferentially occurred in the YHRB during the easterly phase of the QBO (EQBO) compared to the westerly phase of the QBO (WQBO). This was primarily because the BSISO was more prone to cause rainfall extremes in the YHRB during the EQBO summers than during the WQBO summers. The EQBO can induce the background stratospheric easterly wind to arch downward into the troposphere, which enhanced the BSISO-associated moisture transport and moisture convergence and thus resulted in stronger rainfall extremes in the YHRB.

Abstract

The interplay between seismic activity and fluid flow is essential during the evolution of hydrothermal systems. Although earthquakes can trigger transient fluid flow and phase changes in dilational jogs, the temporal scale and the geologic conditions that enhance such process are poorly quantified. Here, we use numerical simulations of deformation and fluid flow to constrain the conditions that maximize adiabatic boiling—referred to as flashing—and estimate the extent and duration of such process. We show that there is an optimal geometry for a dilational jog that maximizes co-seismic flashing within the jog. Fluid flow simulations indicate that the duration, intensity, and propagation of the flashing front are limited and highly dependent on the magnitude of the co-seismic slip and the initial pressure-enthalpy conditions. Our results are valuable to better understand the implications of pressure fluctuations during the seismogenic cycle, as well the mineralization processes in the Earth's crust.

Abstract

The overflow of cold water through the Faroe Bank Channel (FBC) is the densest water crossing the Greenland-Scotland Ridge and the densest source for the Atlantic Meridional Overturning Circulation (AMOC). Here, we show that the overflow volume transport remained stable from 1996 to 2022, but that the bottom water warmed at an average rate of 0.1°C per decade, mainly caused by warming of deep waters upstream. The salinity of the overflow water has increased as a lagged and reduced response to the salinity increase seen in the upper-layer source waters. Therefore, the potential density of the bottom water over the FBC sill shows no statistically significant trend. After entrainment of warmer ambient waters downstream of the FBC, the nonlinear density dependence upon temperature implies, however, that the overflow contributed water of reduced density to the local overturning and the deep limb of the AMOC.

Abstract

Observational and modeling studies have elucidated the influential role played by the southern and northern extratropical Pacific (SEP and NEP) forcing in shaping dynamics of tropical Pacific climate variability. However, the relative importance of the NEP and SEP and the timescale on which they impact the tropics remain unclear. Using a linear inverse model (LIM) that selectively incorporates or excludes tropical-extratropical coupling, we find a reduction in tropical interannual variability (∼40%) and low-frequency (sub-decadal to decadal) variability in the southeastern tropical Pacific region (∼70%) in the absence of SEP. Conversely, the absence of NEP yields no significant impact on tropical interannual variability but markedly diminishes low-frequency variability in the central tropical Pacific region (∼70%). LIM and statistic diagnostics on CMIP6 models show the low-frequency to total variability ratio in the tropical Pacific depending on their NEP and SEP representation. Models with more (less) low-frequency power tend to show stronger NEP (SEP) dynamics.

Abstract

We evaluate the skill and sources of skill in initialized seasonal climate forecasts of monthly global mean temperature from the North American Multi-Model Ensemble (NMME) during the period 1991–2024. The forecasts demonstrate skill in addition to that from the long-term trend, and that skill is primarily attributable to ENSO. However, the skill varies seasonally, with skill being lowest for target periods during Northern Hemisphere summer. Single model ensembles show underdispersion at short leads, while the multi-model ensemble is overdispersed, suggesting initial condition errors and highlighting the importance of model initialization for quantification of forecast uncertainty. Lead-time dependent errors in global mean temperature trends appear related to Pacific trend errors. The multi-model mean captured the overall trend but underestimated the record-breaking temperatures of 2023. Forecasts for the remainder of 2024 indicate cooling by the end of the year.

Abstract

We present the first global geospace simulation to reproduce auroral giant undulations (GUs). To identify their magnetospheric drivers, we employ the MAGE (Multiscale Atmosphere-Geospace Environment) model in a case study of a geomagnetic storm for which there were spacecraft- and ground-based observations of GUs. The model reproduces the spatial and temporal scales of the GUs as well as the presence of duskside subauroral polarization streams (SAPS) and plasmapause undulations. Based on our modeling, we are able to identify the magnetospheric drivers of GUs as mesoscale ring current injections which, after drifting westward, create inverted regions of flux-tube entropy (FTE) and subsequent interchange instability. Outward-protruding interchange fingers disrupt shielding of the inner magnetosphere, creating longitudinally localized ripples in magnetospheric convection equatorward of the magnetospheric instability, which structure the plasmapause and duskside diffuse precipitation. While not causal, SAPS and plasmapause undulations are a consequence of the unstable magnetospheric configuration.