AGU Advances最新文献

The radiant energy budget (REB) is a fundamental physical parameter for planetary bodies, though studies constraining the REB for bodies beyond Earth are relatively limited. We generate the first meridional profiles of Mars' REB at seasonal and annual timescales through measurements based on long term multi-instrument observations from spacecraft orbiting Mars. Then, we compare our findings to Earth's REB using contemporary satellite data sets. Each planet exhibits remarkably distinct seasonal REB distributions due to differences in their orbital, atmospheric, and surface properties. Annually, Earth's REB exhibits a tropical energy surplus and a deficit at the poles. In contrast, Mars' annual REB displays an inverted meridional distribution with significant hemispheric asymmetry. Additionally, global dust storms significantly modify the Martian REB. Our observations are employable in future studies to improve models on Mars' general circulation, meteorology, and polar ice cap evolution.

I investigate the detectability of magma reservoirs in the vertical gravity gradient (VGG) anomalies calculated from satellite altimetry data. First, I calculate a suite of synthetic seamount models to show the expected VGG anomaly characteristic wavelength and amplitude for a simplified magmatic system, hydrothermal system, and a caldera infill, varying their dimensions for a given depth and density contrast. I find that most magmatic and hydrothermal systems create VGG anomalies with a characteristic wavelength and amplitude greater than the data uncertainty and are therefore detectable. The proposed approach consists in three main steps: (a) calculate the VGG from the two components of the deflection of the vertical, (b) calculate and remove the gravity contribution of the bathymetry interface using an independent bathymetry data set (e.g., acquired by multibeam echosounders) to obtain a VGG Bouguer gravity anomaly, (c) invert the Bouguer VGG anomaly to obtain a 3D density model. I image a 6-by-8-km low density body between 3 and 9 km depth under Brothers volcano in the Kermadec arc. I hypothesize that it represents the main magmatic system, possibly with a minor fraction of hydrothermal fluids at the shallower depths. There are about 225 submarine volcanoes globally that could be studied with satellite altimetry-derived gravity data to potentially image their magmatic system. Future altimetry data will increase the gravity data resolution and allow us to image smaller features. This is thus an invaluable data set for the study of underexplored submarine volcanoes and can help improve our volcano hazards assessment.

Human activity influence Earth's environment, including the space environment hundreds to thousands of kilometers above the Earth. One direct evidence is that the 19.8 kHz electromagnetic signals launched by the North West Cape (NWC) transmitter station in Australia produce a wisp-like energy distribution of precipitating energetic electrons in Earth's inner radiation belt, observed by many Low Earth Orbiting satellites. Typically, satellites observe a single wisp with energy that decreases with increasing L (approximately the radial distance in the equatorial plane), which is produced by a first-order cyclotron resonance of transmitter signals with energetic electrons. Here we report, for the first time, multiple wisps observed by the Relativistic Electron and Proton Telescope integrated little experiment-2 (REPTile-2) on board the recently launched Colorado Inner Radiation Belt Experiment (CIRBE) CubeSat. Based on simulation results, we demonstrate that harmonic cyclotron resonances including the 1, −1, and 2 orders by highly oblique NWC transmitter signals produce these multiple wisps. The discovery of multiple-order cyclotron resonances simultaneously occurring in space sheds new light on wave-particle interactions in near-Earth space. It also has implications for developing artificial radiation belt remediation techniques and understanding the propagation and scattering of plasma waves in planetary magnetospheres.

Reanalysis data show a significant weakening of summertime circulation in the Northern Hemisphere (NH) midlatitudes in the satellite era with implications for surface weather extremes. Recent work showed the weakening is not significantly affected by changes in the Arctic, but did not examine the role of different anthropogenic forcings such as aerosols. Here we use the Detection and Attribution Model Intercomparison Project (DAMIP) simulations to quantify the impact of anthropogenic aerosol and greenhouse gas forcing. The DAMIP simulations show aerosols and greenhouse gases contribute equally to zonal-mean circulation weakening. Regionally, aerosol dominates the Pacific storm track weakening whereas greenhouse gas dominates in the Atlantic. Using a regional energetic framework, we show why the impact of aerosol is the largest in the Pacific. Reduced sulfate aerosol emissions over Eurasia and North America increase (clear-sky) surface shortwave radiation and turbulent fluxes. This enhances land-to-ocean energy contrast and energy transport via stationary circulations to the ocean. Consequently, energy converges poleward of oceanic storm tracks, demanding weaker poleward energy transport storm tracks, and the storm tracks weaken. The impact is larger over the Pacific following the larger emission decrease over Eurasia than North America. Similar yet opposite, increased aerosol emissions over South and East Asia decrease shortwave radiation and weaken land-to-ocean energy transport. This diverges energy equatorward of the Pacific storm track, further weakening it. Our results show aerosols are a dominant driver of regional circulation weakening during the NH summertime in the satellite era and a regional energetic framework explaining the underlying processes.

In this paper we demonstrate that several ubiquitous hyporheic exchange mechanisms can be represented simply as a one-dimensional diffusion process, where the diffusivity decays exponentially with depth into the streambed. Based on a meta-analysis of 106 previously published laboratory measurements of hyporheic exchange (capturing a range of bed morphologies, hydraulic conditions, streambed properties, and experimental approaches) we find that the reference diffusivity and mixing length-scale are functions of the permeability Reynolds Number and Schmidt Number. These dimensionless numbers, in turn, can be estimated for a particular stream from the median grain size of the streambed and the stream's depth, slope, and temperature. Application of these results to a seminal study of nitrate removal in 72 headwater streams across the United States, reveals: (a) streams draining urban and agricultural landscapes have a diminished capacity for in-stream and in-bed mixing along with smaller subsurface storage zones compared to streams draining reference landscapes; (b) under steady-state conditions nitrate uptake in the streambed is primarily biologically controlled; and (c) median reaction timescales for nitrate removal in the hyporheic zone are $��\approx �$0.5 and 20 hr for uptake by assimilation and denitrification, respectively. While further research is needed, the simplicity and extensibility of the framework described here should facilitate cross-disciplinary discussions and inform reach-scale studies of pollutant fate and transport and their scale-up to watersheds and beyond.

The circulation response to climate change shapes regional climate and extremes. Over the last decade an increasing number of atmospheric circulation signals have been documented, with some attributed to human activities. The circulation signals represent an exciting opportunity for improving our understanding of dynamical mechanisms, testing our theories and reducing uncertainties. The signals have also presented puzzles that represent an opportunity for better understanding the circulation response to climate change, its contribution to climate extremes, interactions with moisture, and connection to thermodynamic discrepancies. The next decade is likely to be a golden age for dynamics with many advances possible.